An impinging shock wave/turbulent boundary layer interaction over a compliant panel was experimentally examined in a Mach 4 Ludwieg Tube through simultaneous measurements of both the fluid and structure response. Synchronized measurements were obtained using colinear focused laser differential interferometry and high-speed schlieren together with single-camera stereo-photogrammetry. The static and dynamic behavior of the compliant panel itself was also characterized through response to pressurization, roving hammer, and panel flutter experiments.
\r\n\r\nWhen the compliant panel was subjected to shock impingement at the mid-chord and leading-edge locations, the initial panel response was dominated by oscillations at the fundamental vibration mode and was primarily governed by one-way uncoupled fluid-structure behavior. However, under leading-edge impingement, oscillations at the fundamental vibration mode eventually dampened, and a transition to a two-way coupled fluid-structure response was observed. Under two-way coupling, the interaction was characterized by a reduction in oscillation amplitudes and an increase in relative strength of high-order vibration modes.
\r\n\r\nPhase analysis at the fundamental vibration mode between the separation and reattachment shock motion revealed that the one-way uncoupled mid-chord impingement case exhibited a repeatable phase alignment, where the phase of the separation shock tended to lead that of the reattachment shock by approximately one quarter of a panel oscillation. However, consistent with the behavior in rigid wall shock wave/boundary layer interactions, the instantaneous reattachment motion was anti-correlated and led that of the separation shock in all compliant cases. The transition to a two-way coupled response strengthened the synchronization between the separation shock and panel motion compared to that of the one-way uncoupled response.
\r\n\r\nSpectral analysis of the mid- and high-frequency content of density fluctuations in the separation bubble and boundary layer showed that the spectral distributions were not significantly modified due to surface compliance. Instead, the magnitude of the density fluctuations inside the separation bubble were attenuated under mid-chord impingement compared to that of leading edge impingement. Moreover, in all compliant cases, surface compliance amplified the spectral energy in the boundary layer downstream of flow reattachment by over a factor two compared to that of the rigid case.
" }, { "name": "Anuszczyk, Simon R.", "degree": "PhD", "year": "2026", "title": "Robotically Controlled Jellyfish Swimming Dynamics and Energetics for Ocean Exploration", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282026-191205274", "creators": [ { "name": { "family": "Anuszczyk", "given": "Simon R." }, "id": "Anuszczyk-Simon-R", "orcid": "0009-0000-9840-9442", "display_name": "Anuszczyk, Simon R." } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "orcid": "0000-0002-3904-0195", "role": "member", "display_name": "Goentoro, Lea A." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/e5mq-6k14", "abstract": "Robotic platforms inspired or enabled by aquatic organisms have the potential to augment conventional technologies for ocean exploration, enabling a more thorough understanding of the impacts of climate change. We present a biohybrid robotic jellyfish that leverages direct stimulation of live Aurelia aurita jellyfish muscle tissue via implanted microelectronics. We conduct swimming experiments using a 3D-printed passive mechanical attachment to streamline the jellyfish shape and enhance payload capacity. A six-meter-tall, 13,600-liter saltwater facility was constructed to enable testing of the vertical swimming capabilities of the biohybrid robotic jellyfish. We found that the combination of external swimming control and the addition of the mechanical forebody resulted in an increase in swimming speeds to 4.5 times natural jellyfish locomotion while carrying a payload volume of up to 105% of the jellyfish body volume. In order to measure the energy consumption of free-swimming jellyfish in this facility, we developed a physiological method based on laser-scanned, 3D morphological reconstructions of the animal. Computer vision-based feedback control was used to enable continuous swimming against a flow current for 50 hours without encountering the vertical limits of the tank. Changes in animal volume, measured with reconstructions, were converted to energy consumption using the body chemical composition. Free-swimming, electrically stimulated animals were found to consume 2.5 times more energy than similarly stimulated animals in a constrained environment. Simplified drag models could not fully account for the increased energy consumption. Swimmer biomechanics and energetics cannot be fully understood independently of the surrounding flow field. We experimentally investigated the increased energy consumption using three-dimensional, full velocity field Particle Image Velocimetry to simultaneously study wake energy, momentum, and animal biomechanics. We found electrical stimulation increased posterior wake energy loss by a factor of 2.9 compared to unstimulated jellyfish, primarily due to heightened pulse rates. Stimulation was also found to modify swimming biomechanics by reducing total bell margin movement and relaxation duration. Together, these results demonstrate that biohybrid robotic jellyfish can achieve substantial performance enhancements while revealing the hydrodynamic and energetic tradeoffs associated with electrically controlled swimming. This platform offers a scalable and efficient tool for ocean exploration and provides new insight into the fluid dynamics and energetics of jellyfish locomotion." }, { "name": "Bollt, Scott Alexander", "degree": "PhD", "year": "2026", "title": "Vortex Dynamics of Unsteady Plate Motions", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012026-040254289", "creators": [ { "name": { "family": "Bollt", "given": "Scott Alexander" }, "id": "Bollt-Scott-Alexander", "orcid": "0000-0003-4795-4496", "display_name": "Bollt, Scott Alexander" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/s04q-7j86", "abstract": "The vortex dynamics which result from unsteady motions of perforated and solid plates is studied from complementary experimental and theoretical perspectives. The flow that results from starting a perforated plate from rest is studied, and the effect of changing the plate's open area fraction is investigated. Contributions culminating in successfully holding a vortex above the leading edge of a plate while it is in motion, using real-time PIV to provide controlled feedback of the plate's motion, are also presented. These contributions include RapidPIV, a method and software which enables fluid flows to be visualized in real time at over 1000 frames per second, and a steady thin airfoil theory which makes qualitatively useful predictions about the nature of plates and thin airfoils interacting with leading-edge vortices." }, { "name": "Carmi, Meital Oshrit", "degree": "PhD", "year": "2026", "title": "Buckling of Open Cross-Section Deployable Composite Thin Shells with Manufacturing Imperfections", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272026-045028254", "creators": [ { "name": { "family": "Carmi", "given": "Meital Oshrit" }, "id": "Carmi-Meital-Oshrit", "orcid": "0009-0000-7837-2910", "display_name": "Carmi, Meital Oshrit" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Shaikeea", "given": "Angkur" }, "id": "Shaikeea-Angkur-J", "orcid": "0000-0002-6706-0492", "role": "member", "display_name": "Shaikeea, Angkur" } ], "option_major": [ "space" ], "doi": "10.7907/ffpp-gr08", "abstract": "Thin composite shells are increasingly being used to support large area space systems due to their high strength to mass ratio and ability to withstand tight packaging for launch and then deploy once in space. This thesis specifically focuses on long, slender composite shells (longerons) with an open cross-section consisting of two circular arc flanges bonded along one edge. They are useful components of lightweight space structures, including the Caltech Space Solar Power Project spacecraft. The flanges of the longerons are less than 100 \u00b5m thick, and these extremely thin composite shells are prone to manufacturing imperfections and local buckling. Therefore, the primary objective of this thesis is to better understand the buckling behavior of open cross-section, ultra-thin composite shells that contain manufacturing imperfections, with the goal of informing the design of future space structures that are more resistant to buckling.
\r\n\r\nThe first step towards understanding a structure\u2019s imperfection sensitivity is to measure its imperfections. Thus, the thesis begins by characterizing the geometric imperfections present in experimental composite longerons. A method to measure and quantify the parameters of both local and global imperfections in thin shells is developed and applied. Results show that the longerons contain local imperfections as large as five to ten times the shell thickness, which can have serious implications for local buckling.
\r\n\r\nOnce the imperfections were measured, both numerical and experimental studies are performed to study the effects of these imperfections on the buckling behavior and knockdown factor of longerons loaded in pure bending. In the numerical study, a finite element analysis is used to characterize the effect of a single imperfection, created using a simplified model based on the shape of the experimentally measured imperfections, with a wide range of geometric parameters. Then, experiments are performed to measure the buckling behavior of actual longerons, whose random manufacturing imperfections were characterized. The results of these studies show that imperfections, especially ones with large amplitudes, significantly reduce the longeron\u2019s critical buckling load and bending stiffness. Good agreement between the experimental and numerical results was achieved, particularly for higher quality longerons with a single, dominant imperfection.
\r\n\r\nMotivated by the imperfections and their detrimental effects found in the earlier parts of the thesis, key parameters of the longeron's cross-section are varied with the goal of increasing its stability. The subtended angle of the longeron's flanges is varied in both experiments and numerical simulations of longerons loaded in bending. The results show good agreement between the experiments and simulations, with both showing a trend of increasing critical buckling load and bending stiffness with increasing flange subtended angle. Then, based on these promising results, the radius at the edge of the flange is decreased, which is shown to significant improve the longeron's stability and imperfection sensitivity without increasing its mass.
\r\n\r\nFinally, the effect of length on the buckling behavior of longerons loaded in bending is studied numerically with the goal of extending the current work to longer longerons. For lengths varying from 0.5 m to 5 m, both perfect and imperfect longerons with realistic geometric imperfections are studied. It is shown that for longer longerons, the critical buckling moment and imperfection sensitivity remain almost constant with increasing length, which is promising for future large space structures.
" }, { "name": "Davis, Branson William", "degree": "PhD", "year": "2026", "title": "Autoignition Modeling and a Generalized Hot Surface Ignition Criterion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262025-221106238", "creators": [ { "name": { "family": "Davis", "given": "Branson William" }, "id": "Davis-Branson-William", "orcid": "0000-0002-5288-7913", "display_name": "Davis, Branson William" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/meyv-1317", "abstract": "This work investigates the fundamental physics and predictive modeling of thermal ignition in heated volumes and near hot surfaces. Three-dimensional simulations of the ASTM-E659 apparatus revealed how natural convection and fuel stratification influence ignition timing and location, highlighting key limitations in standardized AIT testing. A one-dimensional analog further demonstrated the impact of radial temperature gradients on ignition behavior.
\r\n\r\nTo isolate the core mechanisms of thermal runaway, a canonical hot surface ignition problem was analyzed, showing that inclusion of low-temperature chemistry induces two-stage ignition and lowers critical surface temperatures. Building on insights from classical theory, a novel ignition model was developed based on chemical and thermal length scales. The model collapses ignition data across a wide range of configurations and defines a critical Damk\u00f6hler number. Despite some limitations for NTC fuels and catalytic effects, this unified framework represents a major advance over existing models.
" }, { "name": "Devey, Sean Patrick", "degree": "PhD", "year": "2026", "title": "Part I: A Novel Compact Water Tunnel. Part II: Evolution of Delta Wing Surface Contour from Flat Plates to Boxfish at Low Reynolds Numbers", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:09012025-210751150", "creators": [ { "name": { "family": "Devey", "given": "Sean Patrick" }, "id": "Devey-Sean-Patrick", "orcid": "0000-0002-8937-939X", "display_name": "Devey, Sean Patrick" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T-E", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rv8x-jm07", "abstract": "This thesis is presented in two parts.
\r\n\r\nPart I (Chapters 1\u20132) addresses a common challenge for experimentalists: the scarcity of laboratory space. Inspired by recent advances in fan-array wind tunnels, a novel, ultra-compact water tunnel was developed that uses an array of submerged thrusters to drive flow within a rectangular tank. Prioritizing space efficiency over power efficiency, the design achieves flow quality comparable to traditional facilities while occupying just 8% of the typical footprint. Flow characterization using particle image velocimetry (PIV), hot-film anemometry, and laser Doppler velocimetry (LDV) demonstrates the tunnel\u2019s effectiveness and suitability for fluid dynamic research.
\r\n\r\nPart II (Chapters 3\u20135) uses this new facility to investigate the aerodynamics of delta wings with extreme leeward surface contours in low Reynolds number subsonic flow. While the canonical delta wing flow field is dominated by a pair of counter-rotating leading-edge vortices (LEVs), similar vortex structures have been observed over a range of geometries\u2014including biological forms such as boxfish. However, the influence of non-uniform thickness and large leeward surface deformations on LEV behavior remains poorly understood.
\r\n\r\nTo address this, a family of 70\u00b0 sweep delta wing shapes was defined using B\u00e9zier splines, spanning a continuum from flat plates to forms approaching bluff bodies. Eight 3D-printed wing models were fabricated, with systematic variation in cross-sectional curvature and thickness, including a conical apex section with a thickness-to-span ratio of 0.5. Dye visualization, stereoscopic PIV (SPIV), and load cell measurements were used to examine LEV strength, position, and wing performance across multiple angles of attack. Results show that increasing the leeward surface height, effectively confining the LEV, leads to substantial reductions in vortex strength and shifts in vortex position. Experimental evidence of a dual primary vortex structure over thick delta wings is reported for the first time. Tomographic dye reconstructions reveal complex three-dimensional vortex behavior in the aft section of the wings, including flow separation patterns reminiscent of those seen in hatchbacks and Ahmed bodies. Force measurements reflect the observed flow field, with highly non-linear force evolution with angle of attack depending on model cross-sectional and longitudinal profiles. These findings provide new insight into the interplay between surface shape and vortex structure, and further demonstrate the capabilities of the compact flow facility.
" }, { "name": "Luo, Ying", "degree": "PhD", "year": "2026", "title": "Near-Wake Structure and Dynamics of a Cylinder in Hypervelocity Flows", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03122026-190459583", "creators": [ { "name": { "family": "Luo", "given": "Ying" }, "id": "Luo-Ying", "orcid": "0009-0004-2832-7715", "display_name": "Luo, Ying" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/v935-3c96", "abstract": "The near-wake of a circular cylinder at hypersonic conditions was investigated experimentally to assess the influence of high stagnation enthalpy thermochemical effects on mean wake structure and near-wake dynamics. Experiments were conducted in the T5 Free-Piston Reflected Shock Tunnel and the Caltech Ludwieg Tube using high-speed schlieren and simultaneous focused laser differential interferometry and high-speed schlieren.
\r\n\r\nMean flow quantities, including the separation point, separation region size, shock angles, and neck width, were extracted from schlieren data. Relative to perfect-gas conditions, high stagnation enthalpy flow exhibited a downstream shift of the separation point and a reduction in the separation region size. These features retained a strong dependence on Reynolds number at high stagnation enthalpy. The recompression shock angle was found to be largely insensitive to key flow parameters, remaining approximately constant within experimental uncertainty, while the neck width decreased with increasing stagnation enthalpy and followed a Re-1/2 scaling consistent with laminar perfect gas behavior.
\r\n\r\nNear-wake dynamics were examined using power spectral density (PSD) analysis and Spectral Proper Orthogonal Decomposition (SPOD). A dominant shear layer frequency and a secondary frequency were identified in both facilities, with both remaining approximately constant along the shear layer. Although this frequency in high stagnation enthalpy flow was higher than that observed in perfect-gas experiments at similar Reynolds numbers, scaling by the shear layer length collapsed the data onto a Strouhal number consistent with previous studies.
\r\n \r\nPSD contours and SPOD modes at the dominant frequency revealed standing wave structures in the separation region and banded structures between the shear layer and the separation shock. SPOD, correlation analysis, and direct schlieren visualization revealed downstream-propagating disturbances consistent with the Kelvin Helmholtz instability, accompanied by waves indicative of Mach wave radiation; upstream-propagating waves between the shear layer and the separation shock, originating near the neck and hypothesized to be associated with upstream-traveling acoustic disturbances within the recirculation region; and stationary standing wave structures. These observations are consistent with a resonant aeroacoustic feedback mechanism in which downstream-propagating instabilities generate acoustic waves that travel upstream through the recirculation region and perturb the shear layer at separation. The physical origin of the secondary frequency remains uncertain; the data are analyzed in the context of existing theories to evaluate their consistency with current observations, although further data are required for conclusive identification.
" }, { "name": "Mandralis, Ioannis M.", "degree": "PhD", "year": "2026", "title": "Leveraging Aerial Transformation for Enhanced Air\u2013Ground Robotic Mobility", "advisor": "Gharib, Morteza; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11032025-192332480", "creators": [ { "name": { "family": "Mandralis", "given": "Ioannis M." }, "id": "Mandralis-Ioannis-M", "orcid": "0000-0001-5270-0672", "display_name": "Mandralis, Ioannis M." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/srg8-sx98", "abstract": "Ground-aerial robots can extend endurance, versatility, and robustness by combining wheeled motion with flight, yet many flying-rolling robot designs add actuators that increase weight and reduce efficiency. Morphobots mitigate this by using multi-purpose actuators and body shape change to switch modes on the ground, but unpredictable vehicle-ground interactions can be an obstacle to robust operation. This dissertation develops the Aerially Transforming Morphobot (ATMO), a quadcopter that reconfigures in flight to land on wheels, enabling reliable air-ground transitions, mode switching without the hindrances of ground-morphing, and improved agility. We present ATMO\u2019s design and performance characterization, analyze its dynamics\u2013revealing transformation-induced couplings incompatible with standard quadcopter control\u2013and introduce a model-predictive control framework that stabilizes ATMO through aerial transformation to execute dynamic transitions. We then compare this approach with a learning-based controller that uses deep reinforcement learning for end-to-end morpho-transition, validating both experimentally. Finally, we revisit ATMO\u2019s design using aerodynamic principles to expand morphing flight through wake vectoring, showing that passive structures in the rotor wake substantially increase available thrust authority. Overall, we demonstrate that aerial shape change improves agility and reliability, highlighting a new direction for research in ground-aerial robotics." }, { "name": "Mendoza, Sean A.", "degree": "PhD", "year": "2026", "title": "Toroidal Plasmoid Generation via Extreme Hydrodynamic Shear: Optical and Magnetic Studies", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012026-203030942", "creators": [ { "name": { "family": "Mendoza", "given": "Sean A." }, "id": "Mendoza-Sean-A", "orcid": "0009-0004-9945-0200", "display_name": "Mendoza, Sean A." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "orcid": "0000-0002-5203-3635", "role": "chair", "display_name": "Hutzler, Nicholas R." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7meb-df80", "abstract": "Water is a ubiquitous molecule that mediates our interactions with the world and the dynamics of the universe on scales from astrophysical to biomolecular. Controlling its behavior is an essential step in semiconductor manufacturing and water purification. While commonly viewed as a conductive medium, pure water is in fact quite a good insulator, with a resistivity of \u03c1 \u2248 18 M\u03a9 cm. Such purity is typically short-lived; however, water of sufficient purity allows for unique interactions with solid media as a result of its strong polarization and high dielectric strength (\u03b5 \u2248 80, dipole moment \u03c1 \u2248 3 D). In contact with normal glass, this leads to electric double layer buildup, where the substrate's superficial atoms -oxygen, typically- preferentially adsorb the polarized hydrogen atoms of the water molecules, resulting in the generation of an electrical potential known as contact electrification. If the fluid is further accelerated against the glass, this effect is amplified via a charge-ripping process whose exact nature is still debated.
\r\n\r\nIn this work, we examine a specific result of this contact electrification and triboelectrification process via the impingement of a high-speed jet of pure water, normal to dielectric substrates - mainly quartz glass and lithium niobate - with velocities up to 250 m s-1. We observe a velocity-dependent electric field which, at a critical threshold of approximately 120 m s-1, exceeds the breakdown threshold for electrical discharge in air (\u2248 3 MV m-1), resulting in the formation of a toroidal plasma. We show that the condition of the water, e.g. its resistivity, is essential for this phenomenon, and that the intense shear resulting from this impingement is the primary driver of electrification. By changing the ambient gas to helium or argon, a near-complete shift in the optical spectrum is observed, demonstrating that this is mainly a gas-phase phenomenon.
\r\n\r\nWe further investigate the case of argon, which shows an anomalous pale blue luminescence, and determine that the majority of the visible luminescence in the case of argon is a result of bremsstrahlung radiation, i.e. the deceleration of electrons on impact with argon neutrals, and that a symmetric toroidal core near the jet annulus - functionally a cathode - corresponds to a region of elevated electron temperature within a roughly 10 \u00b5m radial extent of the jet surface. The near-perfect symmetry of this interior core, along with the elevated electron energy, suggests that the energy and the symmetry may be related.
\r\n\r\nGiven the non-thermal nature of this plasma, we estimate that a magnetic field of up to approximately 290 mT would be required to balance the nitrogen electron pressure (nekBTe \u2248 10-68 kPa). To determine whether this is phenomenologically feasible, we develop an approach for magnetic field measurement at extreme proximity via remote sensing, in which the sensing elements are directly embedded into the dielectric target. A lab-grown diamond with a thin 5 \u00b5m layer of nitrogen-vacancy (NV-) centers allows magnetometry within approximately 75 \u00b5m of the plasma core while requiring no modification to the flow or plasma field. We are able to remotely perform a vector measurement which demonstrates a magnetic field structure consistent with a negatively charged stream of distilled water, and we measure a field strength of up to \u00b11 \u00b5T at a measurement standoff distance of z = -75 \u00b5m, which drops rapidly to about 0.25 \u00b5T after the onset of plasma. Based on the extensive averaging times of this embodiment, we conjecture that this drop is a consequence of the pulsatile behavior of the discharge, with a signal outside of the dynamic range of our detector.
\r\n\r\nWe then develop a simple electrostatic and magnetostatic picture of the electric field and currents. An electric field model is built from the measurements and the proposed charge distribution. Treating the system as a single closed current circuit, the azimuthal magnetic field follows directly from the enclosed current by Amp\u00e8re's law, B\u03b8 = \u00b50 I / (2\u03c0r), with no field where no net current is enclosed.
\r\n\r\nWe consider two currents within this circuit. A weak fluid charging current, O(10 mA) advected with the jet, accounts for the pre-onset field; because our sensor sits outside the enclosed current - where an axisymmetric current produces no field - the \u00b11 \u00b5T we measure reflects the non-axisymmetric part of the distribution. During breakdown a much larger, highly uncertain discharge current (instantaneous peak O(50 A), pulsed at a duty cycle O(10-4), so its time-average matches the charging current) gives a surface field O(100 mT) at the nominal core radius r \u2248 100 \u00b5m, whose magnetic pressure B\u03b82/2\u00b50 (~a few kPa) acts outward, tending to expand the current loop. This magnetic pressure is of the same order as the computed electron pressures (10-68 kPa)- likely weaker, but not negligible - and both act outward, so a self-consistent model of the observed structure must account for both. While a real azimuthal magnetic field accompanies the flow, the stark symmetry of the plasma core is more plausibly set by the impinging-jet stagnation hydrodynamics and triboelectric charging than by the magnetic self-field.
" }, { "name": "Popov, George Arthur", "degree": "PhD", "year": "2026", "title": "Stable Method of Attaching Thin Films to Torsionally Compliant Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042026-211328312", "creators": [ { "name": { "family": "Popov", "given": "George Arthur" }, "id": "Popov-George-Arthur", "orcid": "0000-0001-5938-0528", "display_name": "Popov, George Arthur" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Shaikeea", "given": "Angkur" }, "id": "Shaikeea-Angkur-J", "orcid": "0000-0002-6706-0492", "role": "member", "display_name": "Shaikeea, Angkur" } ], "option_major": [ "aerospace", "space" ], "doi": "10.7907/0n4d-3v80", "abstract": "Ultralight space structures utilize composite structural elements supporting active thin films in order to achieve deployed configurations with lower areal densities. However, as these space structures get larger, they get increasingly less stiff, leaving them susceptible to adverse effects, such as torsional buckling. Simultaneously, this conflicts with the requirements that more ambitious space missions impose on the surface accuracy to make technologies like large phased arrays viable.
\r\n\r\nThis thesis presents a novel method of continuously attaching thin films to deployable thin shell structures, allowing for materials with widely different coefficients of thermal expansion. It proposes a double s-spring border that exhibits a local post-buckling behavior and provides a tunable continuous edge attachment method that can maintain constant preload under large thermal strains. The mechanical behavior of the double s-spring under different mechanical loading conditions is studied both numerically and experimentally. Additionally, a reduced order model that greatly reduces the computational cost of optimizing double s-springs for various applications is presented.
\r\n\r\nIn parallel, the torsional buckling of elastic composite frames is studied to understand the fundamental limits of attaching thin films without incurring torsional buckling. This study analytically calculates the critical prestress of torsionally soft square frames supporting an internal thin film. The study highlights the role of the attachment scheme, which has a very significant impact on the critical prestress. It is shown that the average of the compression load on a frame caused by a prestress is an invariant buckling load. The analytical calculation is verified via numerical finite element analyses and an experiment, which characterizes the post-buckling behavior of the torsionally soft frames as well. It is concluded that distributed edge attachments, such as the double s-spring, significantly increase the stability of space structures against torsional buckling. The findings for the torsionally soft square frames are validated against a high fidelity orthotropic material model in order to justify the assumptions made in the analytical study.
\r\n\r\nIn the final section of the thesis, it is shown that the double s-spring continuous attachment scheme enables consistent deployment and compact packaging. The scheme is also shown to be versatile for additional applications, enabling novel deployment and folding schemes, such as a doubly-curved composite foldable toroid.
" }, { "name": "Soni, Divesh", "degree": "PhD", "year": "2026", "title": "Agile Slew Maneuvers of Ultralight Space Structures with Momentum Actuators", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012026-192750566", "creators": [ { "name": { "family": "Soni", "given": "Divesh" }, "id": "Soni-Divesh", "orcid": "0000-0002-5239-756X", "display_name": "Soni, Divesh" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "orcid": "0000-0001-7524-4833", "role": "chair", "display_name": "Watkins, Michael M." }, { "name": { "family": "Manchester", "given": "Zachary" }, "id": "Manchester-Zachary", "orcid": "0000-0002-3071-7091", "role": "member", "display_name": "Manchester, Zachary" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/4f89-0w03", "abstract": "Ultralight deployable spacecraft structures are at least an order of magnitude lighter and more volume efficient for launch than state-of-the art spacecraft structures of the same size, thanks to advancements in thin lightweight composites and new packaging schemes. As a result, they are suitable for a wide range of applications requiring extremely large apertures. For example, one of the application that we are currently interested is in-space computer servers. These ultralight spacecraft could not only support photovoltaics that generate large amounts of power, but at the same time act as extremely large radiators for dissipating heat. Similarly, for space-based solar power missions, they can hold functional layers of photovoltaics and phased array antennas to provide uninterrupted energy transmission to any location on Earth.
\r\n\r\nHowever, this improvement in mass/volume efficiency comes at a price. Ultralight spacecraft exhibit high structural compliance posing new challenges in spacecraft attitude control, which includes residual vibrations in the flexible structure and decreased pointing accuracy, leading to new requirements in structure/control design and testing of these architectures. The present work demonstrates new maneuver techniques and testing methodologies for Caltech\u2019s Space Solar Power Project (SSPP) architecture.
\r\n\r\nReal-world structures are imperfect and require ground tests to characterize their in-space behavior. We present an experimental methodology to perform slew maneuvers to help study the simultaneous behavior of the actuator, control scheme, and the flexible structure response. We present the design of a momentum device prototype and a small-scale, lightweight, flexible structure built for performing slew maneuvers. The flexible structure is designed to be highly compliant along the maneuver direction, allowing the study of its elastic deformation. Smooth polynomial maneuvers are performed with the actuator-structure system mounted on an air bearing; the central hub orientation and flexible structure response is measured. Assuming deformations to be comprised of a single dominant mode, input shaping is applied to the smooth polynomial maneuver, using Zero Velocity (ZV) shaper to suppress vibrations post maneuver. Input-shaping experiments show a remarkable reduction in structural vibrations for high-agility rotations, which directly contributes to an increased power transmission capability in full-scale spacecraft.
\r\n\r\nAlthough small-scale prototypes are useful for demonstrating control techniques and system-level performance, its quite complex to predict results for full-sized space structures given the lack of detailed similitude models for a combination of actuator-structure behavior and real-world defects. Moreover, full-scale structures are difficult to test on the ground in their deployed configuration, due to limitations in the current gravity compensation techniques. With increases in computational capability, data-centric system identification is the solution to robust modeling of real-world structures. These techniques are powerful not only in decomposing spatial-temporal variations but also in finding complex nonlinear behaviors. In the present work, reduced-order models are created from actuator-flexible structure experiments with equation-based nonlinear extensions to existing data-driven techniques. These models are then used to explore vibration-optimal agile maneuvers without making any assumptions about structural properties. These maneuvers, when tested in the experiments, result in fast rotations with a significant reduction of residual vibrations. This work directly contributes to improving the robustness of existing control schemes, enabling scalability to larger spacecraft and decreasing sensitivity to variations in the deployed structure over time.
\r\n\r\nTogether, these results demonstrate that large ultralight spacecraft can be designed and robustly controlled while addressing unwanted effects due to their low stiffness. This development enables their application to next-generation space missions such as space-based solar power, in-space servers, solar sail demonstrations, and much more.
" }, { "name": "Stramenga, Michael John", "degree": "PhD", "year": "2026", "title": "Experimental Investigation of Hypervelocity Shock Wave\u2013Boundary-Layer Interactions on a Deflected Control Surface", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292026-180459768", "creators": [ { "name": { "family": "Stramenga", "given": "Michael John" }, "id": "Stramenga-Michael-John", "orcid": "0000-0002-1554-7389", "display_name": "Stramenga, Michael John" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "space" ], "doi": "10.7907/jsrn-an22", "abstract": "Three-dimensional shock wave\u2013boundary-layer interactions generated by a cone-slice-ramp geometry were experimentally investigated in the T5 Free-Piston Reflected Shock Tunnel. Four air test conditions were examined, spanning Re_edge = 2 \u00d7 10\u2076 to 6 \u00d7 10\u2076 m\u207b\u00b9 at nominal h\u2080 = 8 MJ kg\u207b\u00b9, with one higher enthalpy condition at h\u2080 = 14 MJ kg\u207b\u00b9 and Re_edge = 3 \u00d7 10\u2076 m\u207b\u00b9. Surface heat flux measurements, high-speed schlieren imaging, focused laser differential interferometry, and surface dynamic pressure measurements were used to characterize the mean interaction, surface heating, and separated shear layer unsteadiness.
\r\n\r\nThe test conditions produced both laminar and transitional incoming boundary layers, with separated shear layers that either remained laminar or transitioned within the separation region. Increasing unit Reynolds number at h\u2080 = 8 MJ kg\u207b\u00b9 promoted earlier transition within the separated shear layer, reducing the separation extent and altering both the streamwise and spanwise heating distributions on the ramp. For all test cases, the reattached flow transitioned to turbulence on the ramp surface, and peak streamwise heating was measured in this turbulent region downstream of reattachment. Increasing stagnation enthalpy at constant unit Reynolds number delayed transition onset, causing the separated shear layer to remain laminar and increasing the separation extent.
\r\n\r\nA separated shear layer instability was observed whose dominant frequency decreased and whose amplitude increased downstream. These disturbances appeared above the separated shear layer as Mach radiation and inside the separation bubble as coherent wave-like density gradient structures. The instability frequencies were not collapsed by either Rossiter-type scaling based on the separated shear layer length or Kelvin-Helmholtz scaling based on the separated shear layer thickness. In contrast, wall-normal acoustic scaling based on the shear layer height above the wall collapsed the dominant frequencies upstream of the ramp, suggesting acoustic communication between the separated shear layer and the model surface. Downstream of the ramp leading edge, this scaling breaks down and the phase relationship between structures inside and above the separation bubble changes, indicating that a different, presently unresolved mechanism influences the downstream shear layer instability.
" }, { "name": "Aller, Brayden Gieschen", "degree": "PhD", "year": "2025", "title": "Strain Sensing in Thin Composite Laminates with Embedded Fiber Bragg Grating Sensors", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012025-194857973", "creators": [ { "name": { "family": "Aller", "given": "Brayden Gieschen" }, "id": "Aller-Brayden-Gieschen", "orcid": "0000-0002-5258-4154", "display_name": "Aller, Brayden Gieschen" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/zj2k-h305", "abstract": "Deployable structures are popular for space applications as they enable large, complex spacecraft structures to overcome the size constraints of launch vehicle fairings. Such structures are increasingly manufactured out of thin (< 200 \u03bcm thick) composite laminates as they have a high stiffness-to-weight ratio, the ability to withstand high curvatures during stowage, and the potential for self-deployment using stored strain energy. To ensure the reliability of these thin composite spacecraft structures in operation, it is of interest to be able to continuously monitor their internal strain state to detect potential changes or damage that may compromise their integrity.
\r\n \r\nAlthough there are a number of potential sensors that could be used for this, fiber Bragg grating (FBG) sensors are especially well suited for this task and have a track record of successfully monitoring both composite materials and large aerospace structures. However standard size FBG sensors, which have a cladding diameter of 125 \u03bcm, are too large to be integrated into the thin composite structures of interest. To overcome this, we worked with several suppliers to develop and manufacture ultra-thin FBG sensors (< 30 \u03bcm cladding diameter) for this work that are able to be successfully embedded into thin composite laminates.
\r\n\r\nThe primary objective of this thesis was to investigate the suitability of ultra-thin FBG sensors for the monitoring of strain changes in thin composite spacecraft structures. To this end, the work in this thesis first investigated how to best embed ultra-thin FBG sensors to be able to measure the internal strain changes of interest while minimizing their disruptions to the surrounding laminates. Second, mechanical testing was performed to assess the effect that the embedded ultra-thin FBG sensors have on the mechanical properties of thin laminates. Third, the ability of these sensors to detect and monitor for strain changes in thin composite laminates was assessed through further mechanical testing. Finally, the effects of temperature on ultra-thin FBG sensors were studied experimentally.
\r\n\r\nThrough this work, which was done at the coupon level, we sought to demonstrate the ability of these ultra-thin FBG sensors to monitor for strain changes in thin composite laminates and their potential for the health monitoring of thin composite spacecraft structures. It is our hope that our findings in this thesis help lay the groundwork for the future implementation of these sensors in not only thin composite spacecraft structures, but to many other composite materials and aerospace structures as well.
" }, { "name": "Arun, Rahul", "degree": "PhD", "year": "2025", "title": "Beyond Symmetry: Normality-Based Analysis of Velocity Gradients in Turbulent Flows", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-232647443", "creators": [ { "name": { "family": "Arun", "given": "Rahul" }, "id": "Arun-Rahul", "orcid": "0000-0002-5942-169X", "display_name": "Arun, Rahul" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Lozano-Dur\u00e1n", "given": "Adri\u00e1n" }, "id": "Lozano-Duran-A", "orcid": "0000-0001-9306-0261", "role": "chair", "display_name": "Lozano-Dur\u00e1n, Adri\u00e1n" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3py1-wj85", "abstract": "Small-scale turbulence is a hallmark of countless natural and engineered flows. Its features are often described and modeled using the velocity gradient tensor (VGT), which is conventionally decomposed into the (symmetric) strain-rate tensor and the (antisymmetric) vorticity tensor. Although this symmetry-based decomposition has found use in areas such as vortex identification and closure modeling, it provides limited insight into local flow structure. A more refined description can be obtained by further distinguishing the normal and non-normal parts of the VGT. The resulting normality-based decomposition identifies contributions associated with normal straining (symmetric/normal), rigid rotation (antisymmetric/normal), and pure shearing (non-normal). We use this decomposition to identify flow features that are obscured by symmetry-based analyses yet have significant implications for efforts to understand and model turbulent flows.
\r\n\r\nWe first demonstrate that partitioning the strength of velocity gradients using our normality-based approach can distinguish between different regimes in various turbulent flows. In wall-bounded flows, the near-wall partitioning is dominated by shearing whereas the partitioning far from the wall collapses onto the partitioning associated with isotropic turbulence. In an unbounded vortex ring collision, our analysis distinguishes the initial vortex rings, which have a strong imprint from rigid rotation, from the decaying turbulent cloud produced by their collision, for which the partitioning is similar to that of isotropic turbulence. It also identifies enhanced shear\u2013rotation correlations as a distinctive fingerprint of the elliptic instability during transition, which can be interpreted using relevant geometric features of local streamlines. By deriving algebraic expressions for the partitioning constituents in terms of the invariants of the VGT and an additional parameter, which represents the alignment of shear vorticity with the local rotation axis, we identify a key facet of our analysis that goes beyond previous analyses of the VGT.
\r\n\r\nWe then apply our normality-based framework to filtered velocity gradients in direct and large-eddy simulations of isotropic turbulence. Our analysis enables shear layers, which are associated with shear vorticity, to be distinguished from vortex cores, which are associated with rigid rotation, in a multiscale setting. It reveals that filtering mitigates the relative contribution of shear layers in the subinertial range of the energy cascade. Moreover, it identifies crucial (yet perhaps overlooked) contributions from shear layers to fundamental energy transfer mechanisms, including strain self-amplification, vortex stretching, and backscatter associated with strain\u2013vorticity covariance. The dominant role of shear layers in the backscatter mechanism suggests that they contribute significantly to the bottleneck effect in the subinertial range of the cascade. Our analysis of large-eddy simulation data shows that they also amplify the artificial bottleneck effect produced by an eddy viscosity model in the inertial range. This reflects that the eddy viscosity model mimics an unfiltered direct numerical simulation at a lower Reynolds number. A mixed model can be used to mitigate the artificial bottleneck effect since it more accurately mimics a filtered direct numerical simulation.
" }, { "name": "Chan, Miles J.", "degree": "PhD", "year": "2025", "title": "Reduced Order Modeling of Near-Wall and Roughness Sublayer Turbulence Using Resolvent Analysis", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-012553215", "creators": [ { "name": { "family": "Chan", "given": "Miles J." }, "id": "Chan-Miles-J", "orcid": "0009-0007-7898-3739", "display_name": "Chan, Miles J." } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Piomelli", "given": "Ugo" }, "id": "Piomelli-Ugo", "orcid": "0000-0002-7834-7894", "role": "member", "display_name": "Piomelli, Ugo" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5ycd-9x89", "abstract": "Modeling near-wall and roughness sublayer turbulence using physics-based methods remains a topic of paramount importance, since most engineering-relevant flows are turbulent and most surfaces are not smooth. While today there exists a wide range of empirical, data-driven modeling approaches for turbulence, these methods are limited because fully resolved turbulence data remains expensive to generate and burdensome to store and analyze. Therefore, the ability to predict out-of-sample is important, and since data-driven methods struggle to extrapolate, developing physics-based approximations that give useful, inexpensive predictions remains necessary. Yet the complexity of near-wall turbulence makes developing theoretical models difficult. This thesis tackles two main challenges. First, methods for reduced order modeling of the sensitivity of turbulence to multiscale, engineering-relevant roughness geometries are developed. In particular, a physics-based method for incorporating a drag-scaled, Reynolds-decomposed volume penalization into resolvent analysis yields a linear reduced order model that gives computationally inexpensive estimates for roughness sublayer fluctuations and dispersive stresses given a surface geometry and the mean flow profile in a rough wall channel flow. Then, an iterative method is developed to predict the mean flow profile, equivalent sand grain roughness, and Hama roughness function that utilizes the discovered relationship between the fluctuations and the mean flow. That model yields a closed-loop system for predicting roughness sublayer turbulence and the mean response given only a scan of the roughness geometry and a bulk Reynolds number in a rough wall channel flow. Second, a methodology for generating spatiotemporal representations of near-wall turbulence with very few degrees of freedom is developed. It utilizes a coarse-graining approach to reduce the number of modes required to describe a turbulent flow, selection criteria for picking descriptive modes, and Reynolds number scaling to provide predictions for an out-of-sample, higher Reynolds number flow. A spatiotemporal representation is generated, and results from Piomelli et al. that incorporate the modal representation into the wall layer of a wall modeled large eddy simulation are presented. Overall, this thesis contributes new reduced order modeling approaches that make use of physics-based insights to tackle outstanding problems in the prediction of near-wall and roughness sublayer turbulence." }, { "name": "Dassanayake, D. M. Sahangi Pulsarani", "degree": "PhD", "year": "2025", "title": "Space Legos: A Concept for In-Space Assembly of Large Structures with a Stationary Robot", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072024-033128289", "creators": [ { "name": { "family": "Dassanayake", "given": "D. M. Sahangi Pulsarani" }, "id": "Dassanayake-D-M-Sahangi-Pulsarani", "orcid": "0000-0002-1363-5764", "display_name": "Dassanayake, D. M. Sahangi Pulsarani" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/0pn5-3w42", "abstract": "Human nature is inherently driven by the desire to build; advancing from primitive shelters to skyscrapers, and extending this relentless pursuit of progress to space through technological innovations. As space missions require larger and more complex structures, traditional deployable systems face challenges due to constraints on launch mass, volume, and complex deployment mechanisms. In-space assembly (ISA) offers a promising solution for constructing large structures, such as telescopes and satellites, directly in space.
\r\n\r\nThis thesis introduces a novel ISA concept with a centralized `truss builder' for autonomous assembly of polygonal-ring structures, using simple, repetitive operations and focusing on scalable mesh reflectors for communication and imaging. Utilizing the standard AstroMesh architecture, a rapid generalized design method is developed. Through the analysis of reflector geometry, optimized cable prestress, structural design, and a high-fidelity finite element model, analytical scaling laws are derived for mass, stowed envelope, and natural frequency based on aperture diameter. A semi-analytical homogenization model is introduced to efficiently predict fundamental natural frequencies. Stowed volume is a key limitation for large deployable reflectors, approaching current and future launch capacity limits, while the proposed ISA reflectors face no such constraints for apertures up to 200 meters.
\r\n\r\nA two-dimensional finite element model simulates the assembly kinematics of large ring-like structures with the proposed ISA concept, enhancing understanding of the process and evaluating key design aspects of a stationary robot assembling scalable ring-like trusses. The model provides insights for optimizing autonomous assembly systems and underscores the need for advanced numerical simulations to ensure smooth assembly and stability during ISA, especially as structures scale.
\r\n\r\nLab-scale prototype testing validates the ISA concept, with results aligning qualitatively with simulations. Both experiments and simulations reveal a range of viable solutions, demonstrating flexibility for future mission designs. This research offers crucial insights into the design and scaling of mesh reflectors, setting the stage for comparing ISA with traditional deployable systems. The proposed ISA concept presents a practical solution for building high-precision, large-scale structures in space, advancing the field of space construction and supporting future extended space missions.
" }, { "name": "Harms, Tanner David", "degree": "PhD", "year": "2025", "title": "Chasing After the Wind: Flow Structure Detection Strategies for Autonomous Mobile Flow Field Measurements", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09142024-001942971", "creators": [ { "name": { "family": "Harms", "given": "Tanner David" }, "id": "Harms-Tanner-David", "orcid": "0009-0003-2913-7414", "display_name": "Harms, Tanner David" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Brunton", "given": "Steven L." }, "id": "Brunton-S-L", "orcid": "0000-0002-6565-5118", "role": "member", "display_name": "Brunton, Steven L." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aerospace" ], "doi": "10.7907/vjvv-vb21", "abstract": "Modern flow measurement technology enables studies of fluid motion that, half a century ago, would have seemed unfathomable. However, despite staggering capabilities, measuring many natural flows in the field remains challenging. In particular, resolving coherent flow structures within physical scales ranging from meters to kilometers is not readily achieved. This dissertation proposes autonomous mobile flow field measurements (AMFM) as a paradigm for expanding flow field measurement capabilities into this range of scales. In the AMFM framework, a mobile platform such as a drone would identify critical flow structures and follow them autonomously as they evolve; the device would be taught, in a sense, to chase after the wind for the sake of measuring it. The greatest theoretical challenge to AMFM is that of flow structure detection: what, after all, should be identified in the flow? How is it to be measured? Answering these questions is the overarching motivation of this dissertation. In response, two principal contributions are developed. The first is a theoretical approach to gradient estimation labeled Lagrangian gradient regression (LGR), which enables instantaneous and finite-time flow gradients to be approximated from sparse flow observations. The second is a semantic approach to flow measurement, which provides the ability to discern fluid motion from complex natural images using arbitrarily defined flow tracers. Together, these tools enable a range of studies which would be difficult to conduct otherwise. To demonstrate their combined ability, two experiments are performed. The first examines the motion of imperfect surface tracers measured by the proposed methods relative to sub-surface flows measured by conventional techniques. The second experiment analyzes flow features in the Caltech turtle ponds using only tracers naturally occurring on its surface. While it is demonstrated that the methods and results obtained in this work are meritorious in their own right, they also provide a framework from which future AMFM technologies can be built." }, { "name": "Heidt, Liam Frank Raven", "degree": "PhD", "year": "2025", "title": "Modal Analysis of Harmonically Forced Turbulent Flows with Application to Jets", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:08072024-203148023", "creators": [ { "name": { "family": "Heidt", "given": "Liam Frank Raven" }, "id": "Heidt-Liam-Frank-Raven", "orcid": "0000-0003-1967-6847", "display_name": "Heidt, Liam Frank Raven" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/e6fe-kz94", "abstract": "Many turbulent flows exhibit time-periodic statistics. These include flows in turbomachinery, the wakes of bluff bodies, and flows exposed to harmonic actuation. However, many existing techniques for identifying and modeling coherent structures, most notably spectral proper orthogonal decomposition (SPOD) and resolvent analysis, assume statistical stationarity. In this thesis, we develop extensions to study turbulent flows with periodic statistics. We focus on the application of turbulent jets and jet noise reduction through harmonic actuation, which is of interest for both commercial and military aviation due to its success in reducing noise by up to 5dB.
\r\n\r\nTo analyze the coherent structures in harmonically forced flows, we develop the cyclostationary spectral proper orthogonal decomposition (CS-SPOD). We examine the resulting properties of CS-SPOD and develop a theoretical connection between CS-SPOD and harmonic resolvent analysis (HRA), thereby providing the theoretical basis for HRA to be used as a model for coherent structures of cyclostationary flows. We develop and validate a computationally efficient algorithm and then illustrate its efficacy using the linearized (complex) Ginzburg-Landau equation.
\r\n\r\nWe next employ cyclostationary analysis to investigate the impact of an axisymmetric acoustic harmonic forcing on the mean, turbulence, and coherent structures of a round turbulent jet with a Mach number of 0.4 and a Reynolds number of 450000. We perform large-eddy simulations for four cases at two forcing frequencies and amplitudes. Both low-frequency (Strouhal number of 0.3) and high-frequency (Strouhal number of 1.5) forcing is found to generate an energetic, nonlinear, tonal response consisting of the rollup of vortices via the Kelvin-Helmholtz mechanism. However, the impact of forcing on the broadband turbulence and coherent structures is limited, particularly at the low forcing amplitude associated with jet-noise-reduction devices. Additionally, the dominant coherent structures for the forced jets are similar in their energy, structure, and mechanism. At high forcing amplitudes, phase-dependent features arise in the dominant coherent structures and are associated with coupling to the high-velocity/shear regions of the mean. Overall, our results support the existing hypotheses that jet noise reduction can be associated with the deformation of the mean flow field rather than through direct interaction between the forcing and the turbulence. Lastly, we find that HRA predicts the dominant coherent structures well. This shows that HRA can be used to develop models of forced jets in a similar manner to how resolvent is employed for natural jets, which may be useful to guide future sound-source models of jets subjected to active control.
" }, { "name": "Hooper, Meredith Leigh", "degree": "PhD", "year": "2025", "title": "Machine-Learned Propulsion Strategies: From Adaptive Damage Compensation to Advanced Aeromobility", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042025-002343274", "creators": [ { "name": { "family": "Hooper", "given": "Meredith Leigh" }, "id": "Hooper-Meredith-Leigh", "orcid": "0009-0004-4819-9941", "display_name": "Hooper, Meredith Leigh" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/79aa-ja50", "abstract": "Autonomous vehicles are regularly sent into \"dull, dirty, and dangerous\" environments where the risk of damage is high. Avoidance or mitigation of such damage is therefore paramount to maintain effective autonomy. In this thesis, we use machine learning to investigate two different propulsive strategies that may be used by autonomous vehicles. The first, flapping propulsion, shows remarkable ability in nature to recover from damage simply by altering stroke kinematics. Using machine learning, we ask whether and how such mitigation of damage would be possible for a robotic autonomous vehicle. The second propulsive strategy we investigate is single-rotor propulsion, most commonly seen in helicopters. With this system, we seek to avoid damage before it occurs by improving mobility and control authority via thrust vectoring.
\r\n\r\nIn Part I, we use an evolutionary strategy (CMA-ES) with hardware-in-the-loop to explore optimal machine-learned adaptations to propulsor damage. Experimental function evaluations are performed by a flexible propulsor actuated by a spherical parallel manipulator (SPM). The machine-learned forces and trajectory parameters are compared to in vivo observations in order to determine whether bio-inspired strategies to adapt to significant propulsor damage are the most efficient, or whether they may be affected by irrelevant evolutionary pressures. With amputation of approximately 50% of the propulsor, we find that a complete recovery in thrust production and fitness is made. Some characteristics of the recovered trajectory are similar to natural swimmers, while others differ. Recovery when producing side-force is even more complex. Not all trials are able to recover force production and fitness, and no clear strategy to modify amplitude or frequency is seen. We conclude Part I by using PIV measurements to detail the effect of compensatory strategies on hydrodynamics. Both amputated and intact trajectories clearly show utilization of a drag-based paddling strategy, but the hydrodynamics of the intact and amputated fins differ significantly. This suggests that the machine-learned trajectories are not simply reestablishing the same wake as the intact fin to achieve the same thrust and fitness.
\r\n\r\nGiven the success in applying machine learning in-the-loop to a complex propulsive system where fluid-structure interactions are significant, we utilize the same strategy in Part II to begin to explore helicopter aeromechanics. We built an independent blade control (IBC) system that interfaces with the CMA-ES algorithm to explore optimal blade pitch trajectories. Using this platform, we explore two preliminary optimizations designed to vector thrust; the first, for sustained thrust vectoring that might be utilized upon takeoff or landing, and the second, for short-time thrust vectoring that could be used for enhanced maneuverability. We present some preliminary results from these optimizations and lay out a foundation for future applications of this experimental system.
" }, { "name": "Lupu, Elena Sorina", "degree": "PhD", "year": "2025", "title": "Perception-Driven Autonomy and Learning Control for Ground Vehicles", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092025-020707222", "creators": [ { "name": { "family": "Lupu", "given": "Elena Sorina" }, "id": "Lupu-Elena-Sorina", "orcid": "0000-0002-3968-2630", "display_name": "Lupu, Elena Sorina" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/79tk-eg16", "abstract": "Autonomous robots are widely recognized as highly valuable and are expected to become increasingly prevalent. They will play a critical role across a wide range of terrestrial applications in complex, unstructured environments, as well as in space, supporting infrastructure and exploration on various bodies throughout the solar system and beyond. Looking ahead, autonomous robots will play a crucial role in the search for extraterrestrial life by enabling exploration of remote and extreme environments beyond Earth.\r\nAs robots need to approach more complex tasks, the ability to rapidly perceive, understand, make real-time decisions, and operate at speed requires advances in perception-driven controls, improved predictability, and robustness to disturbances. \r\nTo enable these capabilities, the first part of this thesis proposes an innovative approach to enhancing ground vehicle mobility by integrating a vision-based control algorithm that adapts to changes in real-time. \r\nOur approach improves the vehicle's ability to assess and respond to complex terrains in real-time by leveraging visual information through visual foundation models and meta-learning.\r\nOur controller has provable guarantees of exponential stability and was validated on board two ground vehicles.\r\nNext, an extension of the previously mentioned method applied to detecting objects in space using a visual foundation model is presented. Our method was successfully demonstrated in space in early 2025 aboard the EdgeNode Lite spacecraft.\r\nEfficient operation comes from the synergy of suitable autonomy and control with a suitable robot body.\r\nFollowing this consideration, the second part of the thesis presents the design and control of multi-degrees of freedom robots designed for mobility in complex environments.\r\nIt presents a nonlinear tracking controller with adaptation to improve the walking performance of walking-flying robots. This is illustrated by our implementation on Leonardo, the first robot to combine walking with flying to create a new type of locomotion, which we showcase in complex acrobatic movements such as slacklining and skateboarding.\r\nIn a second case study, we aim to further understand and improve biped walking by introducing a bipedal robot designed to be lightweight, easily manufactured, and easily repaired, serving as a platform for testing learning-based controllers.\r\nWe introduce and demonstrate the performance of two controllers: a model-based and a learning-based control.\r\nThis work highlights the importance of tightly integrated perception, control, and electromechanical design in achieving robust autonomy: on Earth, in orbit, and beyond." }, { "name": "Mohebbi, Nina", "degree": "PhD", "year": "2025", "title": "Flow Induced by Collective Vertical Migration: Impact of Swimmer Distribution, Buoyancy, and Wake Interactions", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082025-223940273", "creators": [ { "name": { "family": "Mohebbi", "given": "Nina" }, "id": "Mohebbi-Nina", "orcid": "0000-0003-4014-6111", "display_name": "Mohebbi, Nina" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Lozano-Duran", "given": "Adrian" }, "id": "Lozano-Duran-A", "orcid": "0000-0001-9306-0261", "role": "member", "display_name": "Lozano-Duran, Adrian" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hz5j-g795", "abstract": "Various animal species exhibit collective motion, characterized by coordinated movement within groups of organisms. A prominent oceanic example is diel vertical migration (DVM), wherein zooplankton migrate vertically from deeper waters during the day to shallower regions at night, often covering distances of approximately 1 kilometer. Despite numerous field measurements, laboratory observations, and theoretical studies of biogenic mixing resulting from collective swimming, the scale of fluid mixing induced by DVM remains unresolved. A key challenge is linking the behavior and flows created by large numbers of individual organisms to collective-scale fluid dynamics. Since most swimmers involved in DVM operate at intermediate Reynolds numbers, the dynamics of these systems are nonlinear and span a wide range of spatial and temporal scales.
\r\n\r\nThis thesis investigates flow scaling generated by vertical migration of brine shrimp (Artemia salina) aggregates, using laboratory measurements complemented by semi-analytical modeling. A volumetric laser scanning system first measured swimmer behaviors and flow interactions during laboratory-induced vertical migrations. Swimmers consistently maintained vertical swimming velocities under varying environmental conditions, showed a Gaussian horizontal distribution within the tank cross-section, and exhibited a pronounced tendency toward the tank center, where illumination was brightest. A scaling relationship between swimmer buoyancy, ascent speeds, and resulting flow velocities was developed to contextualize these results.
\r\n\r\nA semi-analytical model was then developed to estimate the flow generated by wakes of multiple swimmers in proximity. Individual swimmer behaviors were informed by empirical observations and combined through an iterative approach that conserves mass and momentum, providing an aggregation-scale flow solution. Numerical results indicated that induced upstream flows within the aggregation were relatively insensitive to downstream swimmer presence, that average flow speeds approached a plateau beyond a critical aggregation length, and that closer swimmer spacing significantly enhanced induced flow velocities.
" }, { "name": "Pederson, John Monroe Jr.", "degree": "PhD", "year": "2025", "title": "Thermoelastic Deflections of Thin-Shell Composite Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12172024-163805389", "creators": [ { "name": { "family": "Pederson", "given": "John Monroe Jr." }, "id": "Pederson-John-Monroe-Jr", "orcid": "0009-0002-8500-2285", "display_name": "Pederson, John Monroe Jr." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xyry-w852", "abstract": "As space structures become larger, lighter, and deployable, thermal deflections induced by sunlight become a significant source of structural inaccuracy and even spacecraft vibration. Studying these deflections is notoriously difficult: analytical solutions rapidly become intractable, experiments under vacuum and cooling are low-visibility and expensive, and multiphysics finite-element simulations are computationally demanding and usually don\u2019t account for coupled thermo-structural analyses and/or changing radiation view factors.
\r\n\r\nThis work demonstrates key improvements in experimental methods and thermo-structural simulation of these thermal deflections. First, simultaneous full-field measurements of structural temperatures and deflections are achieved by constructing and using a custom vacuum chamber and heating setup; significant thermal gradients and repeatable thermal deformations are measured and analyzed, forming a ground truth for succeeding simulations. Second, multiphysics models of the experimental chamber are created in COMSOL Multiphysics and characterized, even accounting for residual convection, and used to inform prototype improvements and more advanced simulations. Third, based off such predictions, the unit structure prototype composite is improved by adding a layer of graphitized polymer film, with further experimentation showing a dramatic reduction in deflections.
\r\n\r\nFinally, the accumulated knowledge is used to simulate a satellite slew maneuver with realistic orbital heating; a custom technique to couple thermal (Thermal Desktop) and structural (Abaqus) finite-element software via a MATLAB script allows for the recalculation of radiation view factors during simulations, a feat necessary for accurate heating calculations on deployable structures. These results have immediate applicability in predicting structural temperatures and deflections during the satellite maneuvers proposed for the Caltech Space Solar Power Project, as well as suggesting critical improvements to ensure reliability and mission success.
" }, { "name": "Schoeffler, Donner Thomas", "degree": "PhD", "year": "2025", "title": "Measurement and Modeling of Detonation-Driven Shock Tube Flows", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272025-230901725", "creators": [ { "name": { "family": "Schoeffler", "given": "Donner Thomas" }, "id": "Schoeffler-Donner-Thomas", "orcid": "0000-0002-1932-5986", "display_name": "Schoeffler, Donner Thomas" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T-E", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/vedz-t661", "abstract": "The detonation driver is a device for generating the strong shock waves used in high-enthalpy hypersonic flow research facilities. The dynamic production of high-pressure and high-temperature driver gas has several advantages for shock-tube performance, however the unsteady gas dynamics of detonation waves also introduces several challenges. These are investigated here analytically and experimentally.
\r\n\r\nFor forward-mode operation, where the detonation propagates into the shock-tube diaphragm, the detonation Taylor wave attenuates the driven shock, and a model is needed to predict the resulting shock dynamics. This is accomplished by first analyzing the problem of plane shock decay generally. A new approximate solution is formulated for the classic piston start-stop problem and shown to be a significant advancement over predecessors. This result is applied to the shock decay from a detonation driver, and a two-parameter model is fit to simulation data, yielding a method for predicting shock trajectories from shock-tube initial conditions.
\r\n\r\nA small-scale shock tube is designed and constructed using a detonation driver that is operable in both the forward and reverse mode. A transparent driven section is used with large field-of-view shadowgraphy to perform novel time-resolved shock speed measurements. These are used to calibrate the decay model for a forward-mode driver and enable unique observations of shock-speed oscillations, resulting from diaphragm rupture and detonation initiation processes. Results are also obtained for shock tube operation with a conventional high-pressure helium driver.
\r\n\r\nThe gradients and fluctuations in post-shock flows are characterized using a heterodyne focused laser interferometer, a new instrument with advanced capabilities for measuring large phase changes with high resolution. As a development upon the FLDI, spatial filtering characteristics are preserved, and both differential and absolute phase data are acquired simultaneously, enabling a new technique for measurement of gas densities. The instrument is developed, experimentally validated, and then used to probe detonation-driven shock tube flows, achieving phase measurements of over 100 radians with milliradian resolution in a 10 MHz bandwidth. Results from forward-mode operation find that a hydrogen-oxygen driver produces remarkably disturbance-free flows. For reverse-mode operation, the amplitude of flow oscillations is found to be positively correlated with the contact-surface sound-speed ratio, and frequencies are consistent with first-order lateral acoustic waves.
" }, { "name": "Tawney, Jacqueline Rose", "degree": "PhD", "year": "2025", "title": "Aqueous Metallo-Megasupramolecules: From Stability to Extensional Flow Properties", "advisor": "Kornfield, Julia A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-131020183", "creators": [ { "name": { "family": "Tawney", "given": "Jacqueline Rose" }, "id": "Tawney-Jacqueline-Rose", "orcid": "0000-0002-4276-0652", "display_name": "Tawney, Jacqueline Rose" } ], "advisors": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "advisor", "display_name": "Kornfield, Julia A." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Nelson", "given": "Chris W." }, "id": "Nelson-Chris-W", "role": "member", "display_name": "Nelson, Chris W." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "aerospace" ], "doi": "10.7907/98fw-fx90", "abstract": "The addition of long, flexible polymers (> 1 Mg/mol) to a fluid is known to reduce turbulent drag and control droplet behavior, which has the potential to significantly enhance the efficiency of engineering flows across various industries, from agriculture to aviation. However, hydrodynamic forces can break the polymers and diminish their effectiveness, which is presently a major roadblock to their practical utilization in both applications and research. To address this challenge, the Kornfield group developed end-associative, self-healing polymers for use in fuel and, more recently, for use in water\u2014aqueous terpyridine-ended polyacrylamide (TPAM) supramolecules. This thesis examines the relationships between the molecular structure of TPAM, the amount of metal provided to link pairs of chain ends, and kinetic processes of the resulting supramolecules and the rheological properties and performance they provide. The most useful polymers for reducing turbulent drag, controlling mist, and tailoring droplet impact behavior combine high efficacy at low concentration (< 0.1 wt%), minimal impact on shear viscosity (< 2x), and long extensional relaxation time (> 1 ms), enabling them to stretch and resist elongational flow in turbulent eddies or fluid filaments. This thesis explores the fundamental nature of TPAM supramolecules and their potential utility as a rheological modifier, using measurements of molecular weight distributions and extensional relaxation times to illuminate the relationship between supramolecular structure and flow behavior.
\r\n\r\nFirst, we examine chemical degradation (desirable in the environment, but not during use), revealing that its rate can be controlled by limiting air exposure, avoiding an excess of metal ions relative to ligands, and storing samples in refrigerated conditions (4℃). Next, we assess how changes in metal-to-ligand ratios (M:L) and unimer lengths influence TPAM\u2019s megasupramolecular size, equilibration, and decay dynamics, showing that the presence of supramolecules comprising over 10 unimers gives rise to a relaxation time around 2 ms at 0.04 wt%\u2014long and dilute enough to cause drag reduction. In pursuit of even longer supramolecules (and thus longer relaxation times) with the same amount of TPAM, we modified the solution preparation protocol by introducing metal ions to a more concentrated TPAM solution prior to dilution. This exposed new and intriguing topologies with molecular weights extending beyond our measurable limit (10 Mg/mol), expanding the envelope of the longest accessible relaxation times (from ~2 to ~6 ms with M:L = 1:2 for Ni(II):terpyridine). We evaluated their potential as chain scission-resistant, turbulent drag-reducing agents. Initially, they reduce drag while maintaining backbone integrity; however, their supramolecular structure and extended relaxation time are not retained after multiple passes through contraction, turbulent, and expansion flows. The preservation of backbone integrity, along with the broad range of relaxation times achieved using more conventional linear topologies (up to ~3 ms), suggests that TPAM is a promising and robust rheological modifier worthy of continued investigation. Our findings enhance understanding of TPAM\u2019s structural and rheological properties under a range of conditions and lay the groundwork for further study of aqueous megasupramolecule dynamics and applications.
" }, { "name": "Gomez De La Cruz, Salvador Rey", "degree": "PhD", "year": "2024", "title": "Linear Amplification in Nonequilibrium Turbulent Boundary Layers", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312023-005517217", "creators": [ { "name": { "family": "Gomez De La Cruz", "given": "Salvador Rey" }, "id": "Gomez-De-La-Cruz-Salvador-Rey", "orcid": "0000-0002-7568-721X", "display_name": "Gomez De La Cruz, Salvador Rey" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Di Renzo", "given": "Mario" }, "id": "Di Renzo-Mario", "orcid": "0000-0003-0468-3606", "role": "member", "display_name": "Di Renzo, Mario" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hn98-c285", "abstract": "Resolvent analysis is applied to nonequilibrium incompressible adverse pressure gradient (APG) turbulent boundary layers (TBL) and hypersonic boundary layers with high temperature real gas effects, including chemical nonequilibrium. Resolvent analysis is an equation-based, scale-dependent decomposition of the Navier Stokes equations, linearized about a known mean flow field. The decomposition identifies the optimal response and forcing modes, ranked by their linear amplification. To treat the nonequilibrium APG TBL, a biglobal resolvent analysis approach is used to account for the streamwise and wall-normal inhomogeneities in the streamwise developing flow. For the hypersonic boundary layer in chemical nonequilibrium, the resolvent analysis is constructed using a parallel flow assumption, incorporating N\u2082, O\u2082, NO, N, and O as a mixture of chemically reacting gases.
\r\n \r\nBiglobal resolvent analysis is first applied to the zero pressure gradient (ZPG) TBL. Scaling relationships are determined for the spanwise wavenumber and temporal frequency that admit self-similar resolvent modes in the inner layer, mesolayer, and outer layer regions of the ZPG TBL. The APG effects on the inner scaling of the biglobal modes are shown to diminish as their self-similarity improves with increased Reynolds number. An increase in APG strength is shown to increase the linear amplification of the large-scale biglobal modes in the outer region, similar to the energization of large scale modes observed in simulation. The linear amplification of these modes grows linearly with the APG history, measured as the streamwise averaged APG strength, and relates to a novel pressure-based velocity scale.
\r\n \r\nResolvent analysis is then used to identify the length scales most affected by the high-temperature gas effects in hypersonic TBLs. It is shown that the high-temperature gas effects primarily affect modes localized near the peak mean temperature. Due to the chemical nonequilibrium effects, the modes can be linearly amplified through changes in chemical concentration, which have non-negligible effects on the higher order modes. Correlations in the components of the small-scale resolvent modes agree qualitatively with similar correlations in simulation data.
\r\n\r\nFinally, efficient strategies for resolvent analysis are presented. These include an algorithm to autonomously sample the large amplification regions using a Bayesian Optimization-like approach and a projection-based method to approximate resolvent analysis through a reduced eigenvalue problem, derived from calculus of variations.
" }, { "name": "Graebener, Josefine Berta Marie", "degree": "PhD", "year": "2024", "title": "Formal Methods for Test and Evaluation: Reasoning over Tests, Automated Test Synthesis, and System Diagnostics", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312024-094443866", "creators": [ { "name": { "family": "Graebener", "given": "Josefine Berta Marie" }, "id": "Graebener-Josefine-Berta-Marie", "orcid": "0000-0002-1376-0741", "display_name": "Graebener, Josefine Berta Marie" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/4xdc-b988", "abstract": "With the integration of autonomous systems into our everyday lives edging closer to reality, ensuring the safety of these systems is paramount. Part of the safety verification process is a rigorous testing procedure, which currently does not exist for autonomous vehicles. In this thesis, we aim to provide approaches using formal methods to increase the efficiency of testing campaigns.\r\nFirst, we provide a framework based on assume-guarantee contracts to specify tests in the form of a test structure. Using these test structures, we then show how to combine, split, and compare tests. Additionally, we characterize when tests can be combined and when the resulting test requires temporal constraints. Next, we demonstrate the approach on examples and find a strategy for a test agent using winning sets and Monte Carlo tree search.
\r\n\r\nSecond, we present a framework to automatically synthesize a test environment, consisting of static and reactive obstacles, and dynamic test agents. We characterize the desired test behavior in a system and a test objective in the form of a linear temporal logic specification, consisting of sub-tasks commonly used for robotic missions. This test environment must ensure that the test is not impossible (i.e. a correct system can pass the test), but also that every test execution that satisfies the system objective also satisfies the test objective. We use tools from automata theory to construct the virtual product graph that represents all possible test executions, and the virtual system graph, which corresponds to the system's perspective.\r\nWe formulate this routing problem as a network flow optimization on the virtual product graph in the form of a mixed integer linear program for different test environments. We show that this routing problem is NP-hard. We propose a counterexample-guided search using GR(1) synthesis to find a strategy for a test agent. This framework is demonstrated in several examples in simulation and hardware.
\r\n\r\nLastly, we present a framework to diagnose a system-level fault by identifying the component responsible for the failure. We make use of assume-guarantee contracts and Pacti, a tool for compositional system analysis and design, to construct a diagnostics map, which allows us to trace a system-level guarantee to possible causes. We show that this framework can reduce the number of statements that need to be checked in the diagnostics process. We illustrate this framework on several abstract examples and two examples inspired by a real-world autonomous system.
" }, { "name": "Gunnarson, Peter John", "degree": "PhD", "year": "2024", "title": "Autonomous Flow-Based Navigation in Unsteady Underwater Environments", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052024-052757779", "creators": [ { "name": { "family": "Gunnarson", "given": "Peter John" }, "id": "Gunnarson-Peter-John", "orcid": "0000-0002-4437-5379", "display_name": "Gunnarson, Peter John" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/vnh6-3t44", "abstract": "Autonomous ocean-exploring robots promise to significantly enhance the rate at which we can explore ocean environments. However, the limited range and speed of existing autonomous underwater vehicles (AUVs) are barriers to comprehensive ocean exploration. To address these limitations, the work in this thesis investigates strategies for improving the capabilities of existing AUVs, such as targeted sampling and efficient navigation through background flows. Inspired by the ability of aquatic animals to navigate via flow sensing, hydrodynamic cues are investigated as a sensory input for accomplishing these feats of autonomous navigation using only onboard sensors. First, reinforcement learning (RL) is investigated as an algorithm for accomplishing efficient point-to-point navigation in simulated cylinder flow. The algorithm entails inputting point measurements of flow quantities such as velocity and vorticity into a deep neural network, which then determines a swimmer's actions. Using point velocity as the sensory input, the RL algorithm achieved a near 100 percent success rate in reaching the target locations while approaching the time-efficiency of optimal navigation trajectories. To test RL and flow-based navigation in a physical setting, we next developed the Caltech autonomous reinforcement learning robot (CARL), a palm-sized underwater robotic platform. As proof-of-concept analogy for tracking hydrothermal vent plumes in the ocean, the robot was tasked with locating the center of turbulent jet flows in a 13,000-liter water tank using data from onboard pressure sensors. Using a navigation policy trained with RL in a simulated flow environment, CARL successfully located the turbulent plumes at more than twice the rate of random searching by detecting mean flow gradients with the onboard pressure sensors. Lastly, combing both flow sensing and efficient navigation, the accelerometer onboard CARL was used to sense and exploit the flow from a passing vortex ring for energy-efficient propulsion. Body acceleration and rotation were shown to be effective methods of indirect flow sensing, which enabled the energy-efficient vortex ring surfing strategy. Throughout this work, efforts are made to understand the governing physics behind the discovered navigation strategies to generalize the results beyond a specific navigation problem, sensor type, or robotic implementation." }, { "name": "Rivi\u00e8re, Benjamin Pierre", "degree": "PhD", "year": "2024", "title": "Do Robots Dream of Random Trees? Monte Carlo Tree Search for Dynamical, Partially Observable, and Multi-Agent Systems", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-152357240", "creators": [ { "name": { "family": "Rivi\u00e8re", "given": "Benjamin Pierre" }, "id": "Rivi\u00e8re-Benjamin-Pierre", "orcid": "0000-0002-0597-5400", "display_name": "Rivi\u00e8re, Benjamin Pierre" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/dbwa-we50", "abstract": "Autonomous robots are poised to transform various aspects of society, spanning transportation, labor, and scientific space exploration. A critical component to enable their capabilities is the algorithm that interprets sensor data to generate intelligent planned behavior. Although reinforcement learning methods that train parameterized policies offline from data have shown recent success, they are inherently limited when robots inevitably encounter situations outside their training domain. In contrast, optimal control techniques, which compute trajectories in real-time using numerical optimization, typically yield only locally optimal solutions.
\r\n\r\nThis research endeavors to bridge the gap by developing algorithms that compute trajectories in real-time while converging towards globally optimal solutions. Building upon the Monte Carlo Tree Search (MCTS) framework\u2014a stochastic tree search method that simulates future trajectories while balancing exploration and exploitation\u2014the research focus is twofold: (i) constructing an efficient discrete representation of continuous systems in a decision trees, and (ii) searching on the resulting tree while balancing exploration and exploitation to achieve global optimality.
\r\n\r\nThe study spans theoretical analysis, algorithmic design, and hardware demonstrations across dynamical, partially observable, and multi-agent systems. By addressing these critical questions, this research aims to advance the field of autonomous robotics, enabling the deployment of intelligent robots in complex and diverse environments.
" }, { "name": "Wen, Alexander Huai-Cheng", "degree": "PhD", "year": "2024", "title": "Vibration Damping of Coiled Structures Through Frictional Slip", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132023-225911259", "creators": [ { "name": { "family": "Wen", "given": "Alexander Huai-Cheng" }, "id": "Wen-Alexander-Huai-Cheng", "orcid": "0009-0008-9038-3039", "display_name": "Wen, Alexander Huai-Cheng" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/gvps-8x65", "abstract": "Vibration management is important for the survivability of structures. The response of a structure under vibration is dependent upon interaction between the excitation environment and the properties of the structure. If the input excitation cannot be adjusted, then the structure must be engineered to survive. One approach to engineering structures to reduce vibration response is through damping, which is achieved by adding damping devices or materials to covert kinetic energy into heat, where removing energy from the system reduces the amplitude of response. There are a variety of existing vibration damping concepts and techniques, however, conventional methods of these approaches are subject to limitations such as compromising stiffness for increased damping and performance that is excitation profile dependent.
\r\n\r\nThis research proposes a novel, passive vibration damping concept which is motivated by recent deployable structures for space that use coiling as a packaging architecture. The proposed concept, referred to as \"wound roll damping\", is a friction-based damping scheme for coiled structures, where the structure is wound around a mandrel with tension that allows interlayer slip during vibration. The friction between slipping layers provides an energy dissipation mechanism, which reduces the overall level of response. The concept was developed with the challenges of mitigating spacecraft launch vibration and the limitations of conventional damping techniques in mind.
\r\n\r\nUnderstanding of the working principle and performance of this damping concept is achieved using a combination of experiments, analysis, and FEA. A method for determining the locations of slip within a wound roll under vibration is presented. This consists of modeling the interlayer friction forces, using analytical expressions for the stress fields that arise during tension winding of wound rolls, and comparing these values against loading estimates obtained from analysis and FEA. The locations of slip for wound rolls supported by a cantilevered mandrel with bending vibration modes are towards the root of the wound roll structure, near the inner layers.
\r\n\r\nExperimental studies that demonstrate the performance and properties of this damping concept are presented in this work. A wound roll test sample is subjected to a range of excitation profiles including: sine sweep, sine dwell, random, and shock with varying levels of sample winding tension and excitation amplitude. Using these experiments, this concept is demonstrated to not be subject to the limitations of conventional damping schemes. This scheme is observed to be capable of significantly increasing the overall stiffness while providing elevated damping levels, with a performance that is tunable with winding tension, independent of excitation profile, and scales with excitation amplitude. The locations of slip are observed to be consistent with predictions from FEA and analysis.
\r\n\r\nTwo approaches to simulate and model the wound roll damper are developed to both better understand the physical mechanism of this concept and provide analysis tools. The first method is an FEA model, consisting of the base vibration of concentric shells and solids that have frictional contact interactions. The second method is a 2-DoF reduced order model that simulates the frictional contact between two mass-spring-damper systems. Both methods are demonstrated to have good correlation with experimental measurements.\r\n
\r\n\r\nA majority of this work demonstrates the performance of this concept, using both experiments and simulation at lab scales. This work also presents simulation studies that demonstrate the viability of this concept at realistic scales. Using simulations scaled to recent coilable space structures, both implemented and proposed, the wound roll damping concept is demonstrated to provide significant stiffness and damping.
" }, { "name": "Yu, Wesley Minlai", "degree": "PhD", "year": "2024", "title": "Experiments on Separation Shear Layer Instabilities in Hypervelocity Flows", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202024-181545768", "creators": [ { "name": { "family": "Yu", "given": "Wesley Minlai" }, "id": "Yu-Wesley-Minlai", "orcid": "0000-0002-1133-3199", "display_name": "Yu, Wesley Minlai" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1m4t-5n55", "abstract": "Shock-boundary layer interactions (SBLI) are complex fluid dynamic phenomena that occur when shocks are generated near corners and irregular geometries on vehicles flying near or above supersonic speeds, causing external flow distortion and possible boundary layer separation. Accurate prediction of the mean and unsteady SBLI surface interaction is imperative to avoid failure from highly localized aerodynamic and heating loads, and loss of authority near a control surface. For hypersonic flight-enthalpy matched conditions, current SBLI simulations tend to under-predict thermal loads and have significant disagreements with ground-based experiments in separation location, and location and magnitude of peak heating. These discrepancies are potentially largely due to uncertainties in the modeling and recreation of the coupled real-gas (thermochemical) molecular and gas dynamic processes. To address this issue, efforts have been placed on developing and validating thermochemical gas models, which presents a need for off-surface experimental data. The disagreement between simulations and high-enthalpy ground test experiments have also highlighted the need to better characterize the freestream thermodynamic, velocity, and noise conditions.
\r\n\r\nExtensive freestream characterization of the T5 Free-Piston Reflected Shock Tunnel was performed over the course of numerous experimental campaigns using high-speed shadowgraph/schlieren imaging, static and pitot pressure probes, tunable diode laser absorption spectroscopy (TDLAS), and focused laser differential interferometry (FLDI). Accurate time-resolved static pressure measurements are key to characterizing the operation and freestream thermodynamic state in hypervelocity reflected shock tunnels, through both direct measurement and for interpretation of TDLAS signals. A series of three static pressure probes were built for use in T5 at a range of conditions from 8-16 MJ/kg stagnation enthalpies, and measurements agreed well with TDLAS-inferred pressure and numerical simulations of the static probe response. At higher enthalpy conditions, TDLAS measurements showed a substantial decrease in freestream temperature (~1000 K) while velocity was constant. This finding motivated the need for a method to characterize the arrival time and degree of driver gas contamination in T5. An opposing-wedge detector was designed to leverage the sensitivity of the canonical Mach stem flow to the freestream \u03b3, such that the flow would choke at a prescribed increase in \u03b3 corresponding to the arrival of a specific mole fraction of monatomic driver gas. With high-speed schlieren/shadowgraph imaging, driver gas arrival times and mole fractions were obtained for the 8 MJ/kg test condition.
\r\n\r\nInformed by these freestream characterization experiments, near-surface FLDI measurements of instabilities in a separation shear layer on a 25\u00b0-55\u00b0 double-cone model were performed with simultaneous static pressure and freestream tunnel noise measurements in hypervelocity conditions. Three main frequency regimes were considered: i) low-frequency content associated with Kelvin-Helmholtz instabilities and streamwise acoustic disturbances along the shear layer, ii) a strong medium-frequency (peak ~370-450 kHz) signal associated with shear layer instabilities communicating with the model surface, and iii) high-frequency features associated with Mack (second-mode) disturbances. Length scaling arguments are discussed for each case, informed by axisymmetric simulations of the mean flow over the double-cone. A ray-tracing model was used to simulate the FLDI response to certain disturbances. The low-frequency Kelvin-Helmholtz and streamwise acoustic disturbance frequencies did not vary beyond uncertainty bounds along the shear layer. The medium-frequency content had a clear dependence on the local separation height, with the mean frequency decreasing with streamwise position. The high-frequency Mack mode disturbances were only observed in some experiments, suggesting the disturbance is limited only to within the shear layer, making detection difficult if any bulk shear layer motion occurs relative to the FLDI beam positions. This study provides the first known FLDI data on shear layers in hypervelocity flows, together with simultaneous freestream characterization, with the aim to inform future experiments in hypervelocity ground testing facilities and high-resolution numerical simulations.
" }, { "name": "Canales Escobedo, Fabricio Gianfranco", "degree": "PhD", "year": "2023", "title": "Numerical Analysis of Folding and Deployment Dynamics of Thin Shell Structures with Localized Folds", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-233806562", "creators": [ { "name": { "family": "Canales Escobedo", "given": "Fabricio Gianfranco" }, "id": "Canales-Escobedo-Fabricio-Gianfranco", "orcid": "0000-0001-9071-3263", "display_name": "Canales Escobedo, Fabricio Gianfranco" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/gt81-0s18", "abstract": "This thesis focuses on the analysis of tape springs folded in the opposite sense and their dynamic deployment, and aims to use methods to reduce the computational cost of the analysis. The tape spring is a thin shell deployable structure that has features in common with other deployable structures. The deployment process of such structures can be difficult to predict, and the use of numerical models can be a more cost-effective alternative to experimental testing. Approaches to reduce the computational cost of the analysis of tape springs are investigated such as adaptive meshing and reduced order models. The thesis also presents an accurate analysis of tape spring deployment and a detailed study of the energies and the physics of the deployment. This is used to investigate the energy leak observed in previous tape spring deployment work. Overall, this thesis contributes to improving the efficiency and accuracy of the analysis of deployable structures, particularly tape springs, which can have significant applications in spacecraft technology." }, { "name": "Gandhi, Vatsa Bhupeshkumar", "degree": "PhD", "year": "2023", "title": "Shock Compression of Body-Centered Cubic Metals from the Atomistic to Continuum Scale: Iron and Molybdenum", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05052023-185856720", "creators": [ { "name": { "family": "Gandhi", "given": "Vatsa Bhupeshkumar" }, "id": "Gandhi-Vatsa-Bhupeshkumar", "orcid": "0000-0002-6752-113X", "display_name": "Gandhi, Vatsa Bhupeshkumar" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/kwf1-7y79", "abstract": "Fundamental understanding of material behavior under extreme conditions is crucial for designing high strength, light weight, and high temperature resistance materials, and for modeling planetary physics problems such as behavior of the core and impact phenomena. Under extreme conditions, materials not only exhibit a different mechanical, thermal, and failure response but can also undergo structural changes, such as phase transformations, which significantly alters their material properties. This motivates studying their dynamic response and developing constitutive models for applications such as hypersonics, high speed manufacturing, impact and blast of structures, aircraft and spacecraft shielding, meteorite impact, and collision of planets. Despite the importance, experimental investigations of shock induced phase transitions, inelastic material behavior, and elastic-plastic anisotropy under multi-axial stress states and at microscopic length scales of metals still remains largely unexplored. Thus, the focus of this thesis is on the shock compression behavior of body-centered cubic (BCC) metals, specifically iron and molybdenum, under compression-shear loading and at the atomistic-continuum spatial scales. In particular, the role of solid-solid phase transformation of body-centered cubic (BCC) iron on material strength and the orientation dependence of single crystal molybdenum on its elastic-plastic transition is investigated.
\r\n\t \r\nIron in its high pressure hexagonal close-packed (HCP) \u03f5-phase is critical in geological and planetary applications such as inner cores of rocky planets and hypervelocity impacts of asteroids, and meteorites. Thus, understanding plasticity behavior of iron under these condensed matter states is important to develop more accurate models for such applications and to understand deformation mechanisms of inner planetary cores. Because the \u03f5-phase is unstable, iron reverts to its ambient \u03b1-phase (BCC) upon release making it difficult to probe the strength behavior using conventional methods. Additionally, solid-solid phase transformations provide a unique opportunity to study material strength as they are crucial for expanding the design space for various load-bearing applications. In the first part of the thesis, the pressure dependent dynamic strength behavior of both the ambient BCC \u03b1-phase and high-pressure HCP \u03f5-phase of iron at strain rates on the order of 1 X 10\u2075 s\u207b\u00b9 and pressures up to 42 GPa is investigated. Pressure shear plate impact experiments are conducted using a sandwich configuration to decouple the effect of pressure and shear thereby allowing to probe shear strength once the sample reaches an equilibrated state of pressure but prior to release. The strength of the \u03f5-phase is observed to be more than double the strength of \u03b1-phase possibly due to microstructural evolution during phase transformation. Additionally, the evolution of yield properties with pressure, temperature, and strain is presented for the first time, enabling more accurate modeling of extreme deformation phenomena associated with iron-rich celestial bodies such as planetary collisions.
\r\n\t\r\nMolybdenum, its alloys, and other body-centered cubic (BCC) refractory metals are critical in geological and planetary applications such as structural properties of terrestrial planetary composition, formation of the earth-moon system, and hypervelocity impacts of rocky planets. Additionally, the high temperature specific strength, creep resistance, and ductility of BCC refractory metals make them ideal for aerospace and armor/anti-armor applications. Under high strain-rate inelastic loadings, the macroscopic response of these metals is often influenced by the atomistic mechanisms including dislocation motion and deformation twinning. Current material models rely on investigations that involve continuum measurements followed by postmortem microstructural analysis of recovered samples. However, these may not reflect the material behavior during the passage of the shock wave and, thus, requires real-time in-situ atomistic characterization to link the microstructure to macroscopic response. In the second part of the thesis, plate impact experiments coupled with both laser interferometry continuum measurements and in-situ dynamic Laue x-ray diffraction (XRD), at the Advanced Photon Source (APS), are conducted on single crystal molybdenum. Here, the role of crystal orientation, either [100] or [111], on deformation mechanisms during the elastic-plastic transition and the steady state response is explored at pressures ranging from 9-19 GPa. Complementary simulation methodology is developed to analyze the evolution of the Laue diffraction spots captured during impact. By extracting the lattice strain and stresses from XRD images, dislocation slip along [110]\u2329111\u232a and [112]\u2329111\u232a is found to be the probable deformation mechanism during compression with negligible anisotropy observed at the Hugoniot state. For the first time, real-time evidence of molybdenum undergoing deformation twinning along [112\u0305]\u2329111\u232a during shock release beyond a critical pressure of 16 GPa irrespective of the loading orientation is presented.
" }, { "name": "Martin, Conor Daniel", "degree": "PhD", "year": "2023", "title": "Experiments in Thermal Ignition: Influence of Natural Convection on Properties of Gaseous Explosions", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-192522565", "creators": [ { "name": { "family": "Martin", "given": "Conor Daniel" }, "id": "Martin-Conor-Daniel", "orcid": "0000-0003-2332-7383", "display_name": "Martin, Conor Daniel" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/twcf-m219", "abstract": "Explosion hazards exist in many industrial sectors including chemical processing, mining, nuclear power, and aviation. Thermal ignition is the name given to the particular case where the initiation energy is supplied via thermal heating of a gas. The critical conditions leading to thermal ignition are in general highly configuration dependent and require a broad set of experimentation to investigate the influence of wide ranging physical processes on ignition. To aid this effort the present work comprises three main experiments covering a range of thermal ignition hazards. First, a heated atmosphere test with fuel injection (ASTM-E659) was implemented to enable the study of heavy hydrocarbon fuels such as Jet A and multicomponent surrogates. This approach showed the existence of cool flame ignition modes near the ignition thresholds for most fuels. The autoignition temperature (AIT) of commodity Jet A was found to be reasonably reproducible by most alkane fuels including n-hexane. Multicomponent surrogates were also able to match the cool flame ignition regimes reasonably well.
\r\n\r\nNext, ignition using a vertical heated surface in a cold reactive atmosphere was studied in the laminar flow regime. The effects of dilution with nitrogen and reduced pressure were explored for n-hexane/oxygen/nitrogen mixtures. Results found a modest dependence of minimum ignition temperatures on pressure and nitrogen fraction however, with a significant reduction in explosion severity as measured by the maximum overpressure and transient duration. At sufficiently reduced oxygen concentrations, localized weakly propagating flames were found to form in the thermal layer near the surface and produce sustained puffing flame instabilities. One-dimensional flame simulations with detailed kinetics were conducted to supplement and aid in interpretation of the experimental measurements for diluted mixtures. Correlation of ignition thresholds were found to be possible using simplified flame properties and laminar natural convection boundary layer theory.
\r\n\r\nFinally, a novel experiment was designed to explore the effects of turbulent transition and confinement of large heated surfaces on ignition thresholds. Modeling of the energy balance for resistive heating showed that cylinders up to 36 in. long could be heated using modest power supplies. Six cylinder sizes of varying length were chosen based on this analysis to explore laminar, transitional, and turbulent flow regimes. A large scale flow visualization system was created to study these flow regimes and found that turbulent transition occurred for cylinders as small as 10 in. long for wall temperatures of 1000 K. A study of the transitional dependence on temperatures for large temperature difference (T = 555--1140 K), highly non-Boussinesq conditions found that the transitional Rayleigh number decreased by two orders of magnitude in this regime. The thermal layer thickness at the transition height was estimated in order to obtain a relevant length scale to the boundary layer transition problem. Using this a more consistent transition criteria was obtained (Ra using the thermal thickness length scale) and found to vary by only a factor of two in the high temperature cases studied.
\r\n\r\nThe implementation of these cylinders in ignition testing revealed that there was a strong influence of heating rate due to confinement. The use of absorption spectroscopy showed that for low heating rates the fuel was mostly consumed in low temperature reactions prior to or in place of rapid ignition. This resulted in larger ignition temperatures and weak flames which propagate only in the thermal boundary layer. This effect was explained as a consequence of reduced flow recirculation times due to confinement. A strong influence of turbulence was also found for ignition thresholds when compared with other data for ignition by vertical hot surfaces in the laminar regime. Turbulence was also found to strongly influence the explosion properties due to turbulent flame acceleration. This resulted in larger explosion pressures, shorter transients, and faster flames.
" }, { "name": "Oshima, Emile Kazuo", "degree": "PhD", "year": "2023", "title": "Experimental Studies of Flow Control Techniques for Future Aircraft", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02042023-015312785", "creators": [ { "name": { "family": "Oshima", "given": "Emile Kazuo" }, "id": "Oshima-Emile-Kazuo", "orcid": "0000-0002-1689-3726", "display_name": "Oshima, Emile Kazuo" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Wygnanski", "given": "Israel J." }, "id": "Wygnanski-I-J", "orcid": "0009-0001-5711-7029", "role": "member", "display_name": "Wygnanski, Israel J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fpcj-w268", "abstract": "From the signing of the Paris Agreement to the COVID-19 outbreak, the past decade has truly challenged the aviation industry to adapt. New technologies need to be developed constantly to meet the increasing commercial and defense demands for more efficient, quiet, safe, and agile aircraft. To keep up with these rapidly changing times, an approach that marries a fundamental understanding of aerodynamics with systems design and optimization is necessary. This thesis explores two promising concepts for controlling flow over next-generation aircraft: active control on a swept wing for airplane applications, and passive control on a rotating blade for drone applications. In each, force measurements are combined with advanced flow visualization techniques to create a research framework that is both data-driven and physics-informed.
\r\n\r\nIn Part I, a comprehensive wind tunnel campaign is carried out on a swept wing model of modular geometry equipped with an array of sweeping jet actuators, which have demonstrated tremendous promise for flow control authority in both laboratory settings and full-scale flight tests. The flow physics and performance of the wing is investigated first without actuation, revealing separation behaviors at both the leading and trailing edges that are crucial to consider when flow control is applied. This paves the way for an optimization study in a newly proposed framework that relies on fluid power coefficients rather than the momentum coefficient that has been the accepted parameter of choice for characterizing blowing systems over the past seven decades of active flow control research.
\r\n\r\nPart II explores the feasibility of a \"prop-shroud\" concept for small-scale aerial vehicles, in which the shroud is directly attached to the blade tips and thus co-rotates with the propeller. Such a configuration has the potential to provide the various aerodynamic and engineering benefits of a shrouded propeller without the associated costs and complexities of its installation. The hover efficiency of a prop-shroud is shown to be comparable to commercially available drone propellers, even without a rigorous optimization of its geometry. The effect of the co-rotating shroud is then analyzed in detail on the time-averaged, phase-averaged, and unsteady features of the flow field. A model based on vortex formation time is developed, laying out a foundation for future research and understanding.
" }, { "name": "Palmer, Emily Hope", "degree": "PhD", "year": "2023", "title": "Locomotory Control Algorithms and Their Neuronal Implementation in Drosophila melanogaster", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192023-015643241", "creators": [ { "name": { "family": "Palmer", "given": "Emily Hope" }, "id": "Palmer-Emily-Hope", "orcid": "0009-0006-8370-4709", "display_name": "Palmer, Emily Hope" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yyjd-a554", "abstract": "Scientists and engineers alike have long looked to animals in their pursuit of understanding the natural world and how best to interact with it. While researchers have looked across diverse classes, insects have been extensively studied for their rich diversity of life histories and abilities to perform at spatial and temporal scales difficult for engineered systems. Within insects, the fruit fly, Drosophila melanogaster, is a particularly well-studied organism because of its experimental tractability and status as a genetic model organism, providing both detailed descriptions of a broad suite of behaviors and access to and control over specific sets of tissue. In this work, we make use of these tools to study two behaviors in Drosophila, local search, the behavior in which walking flies will search the area around a food site in search of other food sources nearby, and the optomotor response, wherein they will stabilize in response to visual motion during flight. In these studies, we will use modern techniques from both biology and engineering, to exhaustively characterize and describe the observed behaviors and attempt to untangle the underlying algorithms and their neuronal implementation.
\r\n\r\nFirst, we explore the algorithmic structure of local search in fruit flies. When flies encounter a piece of food, they will often perform walking searches nearby; as food tends to be patchy in natural settings, searches may allow flies to locate other food sites in the area. We induce local search using optogenetic stimulation of sugar-sensing neurons and constrain the flies to a dark, annular arena. These experimental details result in a simplified behavior, as the fly has access to a limited sensory environment, so that the search can be interpreted as an example of idiothetic path integration, and the search itself is one-dimensionalized and therefore more easily analyzed. Our experiments, in tandem with complementary modeling using a state transition diagram formalization of the behaviors, generate two principle findings. First, flies can integrate their location in two dimensions--after the optogenetic activation is disabled and the flies can no longer receive the food stimulus, they will continue to search over the former food site even after completing a full revolution of the annular arena. Second, when multiple food sites are present, they search over a center of the food sites, rather than over one distinct food site. These results both provide insights into the algorithmic structure of local search and an experimental and descriptive paradigm for further inquiries into the behavior.
\r\n\r\nSecond, we investigate the role of a population of neurons, the DNg02s, in the optomotor response. In response to visual patterns of wide-field motion, such that the entire world is moving in the fly-centric reference frame, the animal will attempt to steer to cancel the visual motion, as the most parsimonious explanation of the motion is that the fly itself is moving in the global reference frame. We demonstrate that the DNg02 neurons are a required component in the neural circuitry underlying the optomotor response, but that they are insufficient to induce steering behaviors. We conclude with a set of models that fully recapitulate the collected dataset. With current techniques, distinguishing between the two possible models of the downstream connectivity from the DNg02s to the motor neurons associated with wing motor output is not possible. However, as new datasets become available, particularly complete connectomes of the Drosophila nervous system, the neuronal pathways from the DNg02s to the motor systems may be elucidated.
" }, { "name": "Reddy, Narravula Harshavardhan", "degree": "PhD", "year": "2023", "title": "Folding and Dynamic Deployment of Ultralight Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292023-160132013", "creators": [ { "name": { "family": "Reddy", "given": "Narravula Harshavardhan" }, "id": "Reddy-Narravula-Harshavardhan", "orcid": "0000-0003-3897-8162", "display_name": "Reddy, Narravula Harshavardhan" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/m7rd-6s86", "abstract": "Thin-shell structures are becoming increasingly popular for space missions due to their high stiffness-to-mass ratio, easy folding and coiling, and self-deployment using stored strain energy. Broadly, two deployment strategies exist: 1) controlled or deterministic, and 2) unconstrained. Controlled deployment involves carefully orchestrated events using control or guidance systems, while in unconstrained deployment, the structure is simply allowed to self-deploy with minimal guidance. Unconstrained deployment offers lighter deployment mechanisms and better packaging efficiency but the unpredictability of this process has been a significant obstacle to its adoption.
\r\n\r\nThis study focuses on demonstrating the predictability of unconstrained dynamic deployment of thin-shell structures, using the Caltech Space Solar Power Project (SSPP) structures as a case study. The Caltech SSPP uses composite triangular rollable and coilable longerons as the primary building blocks to create large bending-stiff structures. The specific objective is to improve the predictability and robustness of the unconstrained dynamic deployment of the Caltech SSPP structures. Deployment is influenced by the initial conditions and the interaction between the structure and the mechanism during the deployment. To understand these effects, high-fidelity numerical simulations are developed and validated against experiments. The study also examines the sensitivity of deployment characteristics to various design parameters and external influences to ensure the robustness of deployment.
\r\n\r\nThis research demonstrates that the interaction between the structure and the deployment mechanism must be minimal to ensure the predictability of deployment, as thin-shell structures can self-deploy using stored strain energy. This study's sensitivity analysis will inform the design of future SSPP deployment mechanisms and structures. Additionally, the numerical simulation techniques developed have broader applicability beyond this specific case study to any deployable thin-shell structure.
\r\n\r\nDue to the large aspect ratios of thin-shell structures, a very fine finite element mesh is required to model them accurately. A dense finite element mesh is also required to model the contact interactions between the structure and the rigid components of the deployment mechanism. As large spacecraft structures become increasingly complex, full-scale numerical modeling becomes impractical, necessitating the search for more computationally efficient finite element methods. In this study, NURBS-based isogeometric analysis is explored, and it is shown that it is not yet worth switching to NURBS-based elements for the analysis of thin-shell deployable structures. In addition, h-adaptive meshing for quadrilateral shell elements is investigated, and more efficient refinement indicators and solution mapping techniques for nonlinear analyses are proposed and their superior performance is demonstrated using a test case of quasi-static folding of a tape spring.
\r\n\r\nThis thesis fills a gap in the literature on unconstrained dynamic deployment of space structures, providing crucial insights and numerical modeling tools for further research. It establishes a knowledge and resource foundation to advance space structure design and promote more frequent use of unconstrained deployment, marking a pivotal contribution to the field and enabling safe and efficient space structure deployment. Furthermore, the study provides insights into more computationally efficient finite element methods, such as h-adaptive meshing. These insights are broadly applicable and can inform the design of future deployable structures beyond the tested cases.
" }, { "name": "Renn, Peter Ian James", "degree": "PhD", "year": "2023", "title": "Applied Machine Learning for Prediction and Control of Fluid Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02272023-230531120", "creators": [ { "name": { "family": "Renn", "given": "Peter Ian James" }, "id": "Renn-Peter-Ian-James", "orcid": "0000-0002-5735-3873", "display_name": "Renn, Peter Ian James" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/smnv-tz73", "abstract": "Modern aerodynamic technologies such as unmanned aerial systems and horizontal axis wind turbines must regularly contend with forces from highly stochastic and turbulent atmospheric gusts. Conventional methods for modeling and controlling fluid flows are limited in their ability to mitigate these aerodynamic forces in real-time. By applying modern machine learning techniques in an experimental setting, this thesis demonstrates the utility of machine learning in addressing these important problems. We follow two complementary approaches towards this goal.
\r\n\r\nFirst, we find an end-to-end solution for control in a gusty environment with model-free reinforcement learning. We deploy state-of-the-art reinforcement learning algorithms on a generalized aerodynamic test-bed consisting of an airfoil with motorized trailing edge flaps. The system features embedded flow sensors, enabling the inclusion of flow measurements in state observations. We place this system in a highly irregular wake behind a bluff-body, dynamically mounted on elastic bands and therefore free to oscillate, and train reinforcement learning agents to minimize the net lifting force on the system by controlling the position of the trailing edge flaps. We find that model-free reinforcement learning agents can outperform basic linear controllers in this gusty, turbulent environment. We also show that augmenting state observations with flow measurements can lead to more consistent learning of the system dynamics.
\r\n\r\nNext, we explore Fourier neural operators (FNOs) as a method for forecasting the time evolution of turbulent fluid flows. FNOs are capable of learning underlying operator solutions to families of partial differential equations and can be evaluated in just milliseconds. We specifically focus on training FNOs with experimentally measured velocity fields of bluff body wakes in the subcritical regime. To the best of our knowledge, this is the first application of operator learning for fluid mechanics that features experimental measurements. We find that FNOs can accurately predict the evolution of these turbulent wakes even when trained with imperfect measurements. We then show that FNOs can quickly adapt to unseen conditions with minimal data and training through transfer learning. Finally, we consider the performance of FNOs over longer prediction horizons. This approach could enable real-time gust prediction capabilities and monitoring for applied aerodynamic systems.
" }, { "name": "Tsukamoto, Hiroyasu", "degree": "PhD", "year": "2023", "title": "Contraction Theory for Robust Learning-Based Control: Toward Aerospace and Robotic Autonomy", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262023-141116640", "creators": [ { "name": { "family": "Tsukamoto", "given": "Hiroyasu" }, "id": "Tsukamoto-Hiroyasu", "orcid": "0000-0002-6337-266", "display_name": "Tsukamoto, Hiroyasu" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/rznp-g568", "abstract": "Machine learning and AI have been used for achieving autonomy in various aerospace and robotic systems. In next-generation research tasks, which could involve highly nonlinear, complicated, and large-scale decision-making problems in safety-critical situations, however, the existing performance guarantees of black-box AI approaches may not be sufficiently powerful. This thesis gives a mathematical overview of contraction theory, with some practical examples drawn from joint projects with NASA JPL, for enjoying formal guarantees of nonlinear control theory even with the use of machine learning-based and data-driven methods. This is not to argue that these methods are always better than conventional approaches, but to provide formal tools to investigate their performance for further discussion, so we can design and operate truly autonomous aerospace and robotic systems safely, robustly, adaptively, and intelligently in real-time.
\r\n\r\nContraction theory is an analytical tool to study differential dynamics of a non-autonomous (i.e., time-varying) nonlinear system under a contraction metric defined with a uniformly positive definite matrix, the existence of which results in a necessary and sufficient characterization of incremental exponential stability of multiple solution trajectories with respect to each other. Its nonlinear stability analysis boils down to finding a suitable contraction metric that satisfies a stability condition expressed as a linear matrix inequality, resulting in many parallels drawn between linear systems theory and contraction theory for nonlinear systems. This yields much-needed safety and stability guarantees for neural network-based control and estimation schemes, without resorting to a more involved method of using uniform asymptotic stability for input-to-state stability. Such distinctive features permit the systematic construction of a contraction metric via convex optimization, thereby obtaining an explicit exponential bound on the distance between a time-varying target trajectory and solution trajectories perturbed externally due to disturbances and learning errors. The first two parts of this thesis are about a theoretical overview of contraction theory and its advantages, with an emphasis on deriving formal robustness and stability guarantees for deep learning-based 1) feedback control, 2) state estimation, 3) motion planning, 4) multi-agent collision avoidance and robust tracking augmentation, 5) adaptive control, 6) neural net-based system identification and control, for nonlinear systems perturbed externally by deterministic and stochastic disturbances. In particular, we provide a detailed review of techniques for finding contraction metrics and associated control and estimation laws using deep neural networks.
\r\n\r\nIn the third part of the thesis, we present several numerical simulations and empirical validation of our proposed approaches to assess the impact of our findings on realizing aerospace and robotic autonomy. We mainly focus on the two joint projects with NASA JPL: 1) Science-Infused Spacecraft Autonomy for Interstellar Object Exploration and 2) Constellation Autonomous Space Technology Demonstration of Orbital Reconfiguration (CASTOR), where we also perform hardware demonstrations of our methods using our thruster-based spacecraft simulators (M-STAR) and in high-conflict, distributed, intelligent UAV swarm reconfiguration with up to 20 UAVs (crazyflies).
" }, { "name": "Ubamanyu, Kanthasamy (Uba)", "degree": "PhD", "year": "2023", "title": "Time-Dependent Failure of Thin-Ply Composite Laminates", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312023-210300139", "creators": [ { "name": { "family": "Ubamanyu", "given": "Kanthasamy (Uba)" }, "id": "Ubamanyu-Kanthasamy-Uba", "orcid": "0000-0002-3679-6173", "display_name": "Ubamanyu, Kanthasamy (Uba)" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/x286-g488", "abstract": "The demand for larger and lighter structures for next-generation space designs necessitates the use of deployable structures. Among the materials that hold promise for such applications, thin-laminate fiber composites with thicknesses less than 200 μm stand out due to their strength-to-weight ratio, packaging efficiency, and ability to deploy using stored strain energy. However, designing deployable structures with thin-laminate composites is challenging as they need to be stiff enough to withstand loads during deployment while also having a small volume in the packaged configuration. Complicating matters further, stress relaxation of the polymer matrix within the composite during long-term stowage in response to an imposed curvature can drastically impact both the deployment process and the performance of the structure in its deployed state, even leading to catastrophic failure in the stowed configuration.
\r\n\r\nThis thesis presents a comprehensive study of the time-dependent failure behavior of thin-laminate fiber composites under bending, with a focus on a fundamental material-level understanding. The work is divided into three main parts. First, a novel test method called Flattening to Rupture (FTR) test was developed to effectively load composite coupons under long-term bending, enabling the measurement of time-dependent rupture and identification of the underlying failure mechanisms. Second, numerical simulations using the Abaqus/Standard finite element software were developed to understand the sequence of rupture events and the influence of several parameters that affect time-dependent rupture. Finally, a statistical approach was proposed to model the stochastic nature of the failure of thin composite laminates.
\r\n\r\nThe contributions of this thesis extend the understanding of the microscale failure mechanisms involved in the time-dependent failure of fiber composites. These new insights pave the way for the efficient design of tightly and safely packaged deployable structures under long-term loading. The findings of this research can be utilized to optimize the design and performance of deployable space structures made of fiber composites, leading to new technologies that can advance space exploration.
" }, { "name": "Wei, Nathaniel James", "degree": "PhD", "year": "2023", "title": "Dynamics and Performance of Wind-Energy Systems in Unsteady Flow Conditions", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-233342281", "creators": [ { "name": { "family": "Wei", "given": "Nathaniel James" }, "id": "Wei-Nathaniel-James", "orcid": "0000-0001-5846-6485", "display_name": "Wei, Nathaniel James" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/d9wh-pj98", "abstract": "Wind energy is poised to play a considerable role in the global transition to clean-energy technologies within the next few decades. Modern wind turbines, like aircraft and other aerodynamic structures, are typically designed with the assumption that the flows they encounter will be uniform and steady. However, atmospheric flows are highly unsteady, and systems operating within them must contend with gust disturbances that can lead to performance losses and structural damage. Therefore, the next generation of wind-energy systems requires physics-informed design principles that effectively account for and even leverage these unsteady flow phenomena for enhanced power generation, robustness, and operational longevity. Accordingly, this work details experimental and analytical efforts to characterize unsteady aerodynamics in wind-turbine contexts. First, the effects of unsteady streamwise motion on turbine performance are studied, as recent work has suggested that these dynamics may enable time-averaged efficiencies that exceed the steady-flow Betz limit on turbine efficiency. The power production of and flow around a periodically surging wind turbine are thus investigated using wind-tunnel experiments, which suggest that turbines in these flow conditions could leverage unsteady surge motions for power-extraction gains of up to 6.4% over the stationary case. Linearized and nonlinear dynamical models of the response of the turbine to these time-varying flows are derived and validated against the experimental data. These models are also coupled with a potential-flow model of the upstream induction zone of the turbine in order to predict temporal variations in the flow velocities and pressures in this region. Unsteady contributions to the time-averaged efficiency are also considered through theoretical potential-flow derivations. Additionally, a novel three-dimensional particle-tracking velocimetry approach using artificial snow as seeding particles is deployed to obtain volumetric flow measurements in the wakes of full-scale vertical-axis wind turbines in field conditions. These measurements yield insights into the effects of unsteady vortex dynamics on the structure of the near wake, with implications for the performance of turbines in wind-farm arrays. These investigations provide the analytical and experimental foundations for future studies of unsteady atmospheric flows, and will lead to the development of principles and techniques for wind-farm siting, control, and optimization." }, { "name": "Dorn, Charles Jacob", "degree": "PhD", "year": "2022", "title": "Geometry Synthesis and Multi-Configuration Rigidity of Reconfigurable Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:09182021-045958776", "creators": [ { "name": { "family": "Dorn", "given": "Charles Jacob" }, "id": "Dorn-Charles-Jacob", "orcid": "0000-0001-6516-2586", "display_name": "Dorn, Charles Jacob" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/ph2w-9a34", "abstract": "Reconfigurable structures are structures that can change their shapes to change their functionalities. Origami-inspired folding offers a path to achieving shape changes that enables multi-functional structures in electronics, robotics, architecture and beyond. Folding structures with many kinematic degrees of freedom are appealing because they are capable of achieving drastic shape changes, but are consequently highly flexible and therefore challenging to implement as load-bearing engineering structures. This thesis presents two contributions with the aim of enabling folding structures with many degrees of freedom to be load-bearing engineering structures.
\r\n\r\nThe first contribution is the synthesis of kirigami patterns capable of achieving multiple target surfaces. The inverse design problem of generating origami or kirigami patterns to achieve a single target shape has been extensively studied. However, the problem of designing a single fold pattern capable of achieving multiple target surfaces has received little attention. In this work, a constrained optimization framework is presented to generate kirigami fold patterns that can transform between several target surfaces with varying Gaussian curvature. The resulting fold patterns have many kinematic degrees of freedom to achieve these drastic geometric changes, complicating their use in the design of practical load-bearing structures.
\r\n\r\nTo address this challenge, the second part of this thesis introduces the concept of multi-configuration rigidity as a means of achieving load-bearing capabilities in structures with multiple degrees of freedom. By embedding springs and unilateral constraints, multiple configurations are rigidly held due to the prestress between the springs and unilateral constraints. This results in a structure capable of rigidly supporting finite loads in multiple configurations so long as the loads do not exceed some threshold magnitude. A theoretical framework for rigidity due to embedded springs and unilateral constraints is developed, followed by a systematic method for designing springs to maximize the load-bearing capacity in a set of target configurations. An experimental study then validates theoretical predictions for a linkage structure. Together, the application of geometry synthesis and multi-configuration rigidity constitute a path towards engineering reconfigurable load-bearing structures.
" }, { "name": "Dougherty, Christopher John", "degree": "PhD", "year": "2022", "title": "On the Experimental Simulation of Atmospheric-Like Disturbances Near the Surface", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-085410375", "creators": [ { "name": { "family": "Dougherty", "given": "Christopher John" }, "id": "Dougherty-Christopher-John", "orcid": "0000-0002-0974-5696", "display_name": "Dougherty, Christopher John" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Brown", "given": "Garry L." }, "id": "Brown-Garry-L", "role": "member", "display_name": "Brown, Garry L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/293w-ev66", "abstract": "Any and every 'decision-maker'\u2019 gravity-bound to the planetary surface (or very nearly so) must contend with the frictional complexities confined to its relatively small surface layer. From the perspective of the near-surface bound small autonomous flyer, it is the microclimatic local set of atmospheric conditions (i.e. the weather), characterized by moisture, temperature, and the parameters describing wind, that determines the baseline flowfields within which these flyers must navigate and negotiate. Unlike their human-on-board counterparts, mission parameters relegate small (nearly) massless autonomous flyers to the lower regions of the atmospheric boundary layer, where they may not be fortuned enough to soar above the effects of friction or wait for clearer skies. Relatively little focus has been placed on the experimental strategies of how these machines might learn to function in challenging scenarios well-before encountering them in the real-world. To address such shortcomings, this work focuses on the experimental simulation of flight-relevant environments through the development of multi-source wind generating apparatuses (i.e. fan arrays) that can initialize velocity distributions discretely-individually or in-concert to produce appropriate mean and fluctuating velocities through an ample open-air test envelope that enables full-scale conventional statically-mounted aerodynamic-characterizations up through free-flight autonomous vehicle testing. Though outside the scope of current experimental work, as full of an environmental description (i.e. moisture, temperature, and wind) is given as possible, prior to ultimately reducing the scope to a neutrally stable atmosphere devoid of any major weather events other than a reasonably strong prevailing wind. Nearly always set amongst the backdrop of a high Reynolds number turbulent flowfield, two primary prototypical flowfields (continuous-gust and discrete-gust) are identified as meriting consideration for mainstay experimental simulation. The core features within the spectral overlap of these windy disturbance environments with the response characteristics of flyers of interest ensure that the turbulence of consideration is nearly always of the mechanical-type. Unlike air motions far above local effects in the inertial sublayer (ISL), the dominant flow mechanism within regions of interest near canopied surfaces is augmented by the presence of coherent structures due to the prevalence of locally initiated mixing layers and wakes such that the task becomes one of simulation of suitable forcing spectra in the physical domain for the regions of interest during anticipated times-of-flight.
\r\n\r\nLikely to prove challenging to the small autonomous flyer are encounters of a change in wind state that occur upon piercing the dividing streamline of air masses of two different velocities. From the view of the flyer navigating the built-up environment, intermittent free shear layers due to wind-interactions with surface roughness elements are unavoidable and are experienced discretely when the flyer and shear layer dynamics are decoupled. Fan array techniques for the generation of mixing layers, the basic building block of any such free shear layer, is explored as a candidate flowfield for the experimental simulation of a discrete gust forcing input for the flyer near the surface. Both initialized dual-stream and triple-stream mixing layers at flight-relevant freestream velocity differences are explored and found to principally behave like the mixing layers developed in a more conventional splitterplate experiment. The Reynolds number Reδω based on the velocity difference ΔU and vorticity thickness δω (both outer scale parameters) is shown to linearly increase with downstream development as the vorticity thickness increases commensurately. The spectral analysis along the centerline confirms local isotropy for every tested case.
\r\n\r\nThe continuous-gust flowfield (simply referred to as 'turbulence) is prevalent throughout the atmospheric boundary layer as are quasi-coherent flowfields of superimposed wakes within canopied environments. Because velocity fluctuations manifest as (predominantly) random deviations at any given instant, these flowfields are good candidates for statistical analysis. Generation techniques to produce such turbulent flowfields are introduced and compared against the uniform flow modality (i.e. all fan units set to produce nominally the same initial velocity condition to develop a well-mixed turbulent flowfield beyond x/L \u223c 0.5 with ReλT = 135). The random-phase (R-P) perturbation technique proves useful in increasing ReλT upwards of nearly sevenfold with only a slight further-loss-of-uniformity (to within 3.7% of the mean). The uniform flow modality with the (R-P) perturbation activated is shown, through the presence of a -5/3 slope power law region, to be locally isotropic at relevant freestream velocities. Significant increases in ReλT are made through a static-reconfiguring of the discrete source fan units into a so called quasi-grid (Q-G) configuration. The highest recorded Taylor microscale Reynolds number was found to be ReλT = 2700, likely accompanied by a non-negligible loss of uniformity at the fixed measurement location, though traverses were not undertaken during this campaign so no direct statement of homogeneity is put forth.
\r\n\r\nFor all the flow modalities presented (i.e uniform, pseudo-random, quasi-coherent, and mixing layer), the high-Re number criteria (Reδω \u2248 104 , ReλT \u2248 102) has been met. This serves, then, as a necessary minimum benchmark in the development of multi-source wind tunnels with intended use as environmental simulators for flyers near the surface and also provides the basis for a spectral framework of comparison to enable systematic development of flowfields in future work. Characteristics of the evolving flowfields can further be tuned through the introduction of perturbation techniques applied as initial conditions to both increase the standard deviation of the fluctuating velocities about a desired mean as well as to initiate, evolve, and combine flowfields in representative ways. A preliminary example of one such combination of flow modalities (pseudo-random and mixing layer) indicates significant alteration of flow development compared to a nominal mixing layer case.
" }, { "name": "Hooper, Morgan Louise", "degree": "PhD", "year": "2022", "title": "Characterization and Optimization of a Fully Passive Flapping Foil in an Unsteady Environment for Power Production and Propulsion", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312022-024822211", "creators": [ { "name": { "family": "Hooper", "given": "Morgan Louise" }, "id": "Hooper-Morgan-Louise", "display_name": "Hooper, Morgan Louise" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Brunton", "given": "Steven L." }, "id": "Brunton-S-L", "role": "member", "display_name": "Brunton, Steven L." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tymc-1985", "abstract": "This thesis provides an experimental window into the duality between thrust production and energy harvesting by a flapping foil subject to unsteadiness in an oncoming flow. In particular, an airfoil is placed downstream of a circular cylinder, and allowed to interact with the vorticity shed in its wake to produce motions in both the transverse and streamwise directions. It is confirmed that under the right conditions, passive fluid-structure interactions arising from such a configuration give rise to simultaneous extraction of energy from the flow, coupled with net thrust larger than net drag experienced by the airfoil.
\r\n\r\nMeasurements of forces acting on the airfoil and the motion that arises are presented, for cases where the flapping motion is both active (the foil is driven through a pre-planned trajectory) and fully passive (the foil is allowed to react to the fluid forcing it experiences). These are coupled with simultaneous Particle Image Velocimetry (PIV) measurements of the flow field in the region of the airfoil. These measurements allow for direct observation of fluid-structure interactions which give rise to both thrust production and power extraction potential, illuminating the mechanisms driving each. The dynamics of a fully passive flapping foil are largely determined by the mounting system used to facilitate its motion. It is shown that by leveraging Cyber-Physical Fluid Dynamics (CPFD) capabilities to tune these mounting parameters, the behaviour of a fully passive flapping foil can be made similar to that of a representative driven system. A framework based on a simplified linear model for mounting system dynamics is presented, to allow for the optimization of such a system for power extraction potential subject to relevant engineering constraints. The effects of nonlinearity on airfoil behaviour, particularly those due to friction in the mechanism(s) permitting passive flapping, are also explored. Finally, two-dimensional motion of a fully passive flapping foil is demonstrated, allowing for the foil to travel upstream against the oncoming flow solely due to forces induced by interactions with oncoming unsteadiness.
" }, { "name": "Song, Yichuan", "degree": "PhD", "year": "2022", "title": "Rheological Measurements in Moderate Reynolds Number Liquid-Solid Flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-033735914", "creators": [ { "name": { "family": "Song", "given": "Yichuan" }, "id": "Yichuan-Song", "orcid": "0000-0001-7276-2029", "display_name": "Song, Yichuan" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5ey8-v324", "abstract": "Liquid-solid flows with inertial and viscous effects are critical for many engineering and geophysical applications, such as the processing of biomass slurry and the control of debris flows. However, modeling the rheological behaviors of these complex flows remains a challenge. Prior investigations on the liquid-solid flows typically cover suspensions in which the particle Reynolds numbers (Re) based on the particle diameter and shear rate are less than 1. Limited prior study at Caltech focuses on particle Reynolds numbers above 10. This thesis focuses on rheological experiments for the moderate Reynolds number regime where both inertial and viscous effects are important, with particle Reynolds numbers from 0.5 to 800. The rheological experiments include torque measurements of mm scale-sized polystyrene and SAN particles with a range of solid fractions from 10% to 50%, considering both neutrally-buoyant and settling suspensions with density ratios of 1 and 1.05. This thesis discusses rheological measurements of three different fields: pure fluids, neutrally-buoyant suspensions, and non-neutrally-buoyant suspensions.
\r\n\r\nThe pure fluids measurements determine the flow starts to transition to turbulent flow for gap Reynolds numbers above 6500 in the Caltech Couette flow device. For suspensions with matched particle and fluid densities and solid fractions less than 40%, we find that the effective viscosity only depends on the particle solid fraction until we observe the shear-thickening behaviors for Re of approximately 10. For the intermediate Re from 10 to 100 and lower solid fractions, the effective viscosity not only depends on the particle solid fraction, but also shows increased dependence on Re. For Re greater than 100, the liquid-solid flows transition to the turbulent regime, similar to what we see for the pure fluids. At the maximum solid fraction of 50%, the magnitude of the effective viscosity has increased by a factor of 20 as compared to the results of the 10% solid fraction, but the effective viscosity is nearly independent of Re. A particle Reynolds number (Re') based on the maximum shear flow velocity and the particle diameter is introduced to examine the effective viscosity of the suspensions. Since the present studies use particles with different sizes, Re' is found to be a better way to correlate the effective viscosity than the traditional Re. For the analysis of liquid-solid flows with a density ratio of 1.05, the effective viscosity of the particulate flow increases with the Stokes number for loading fractions of 10% and 20%, while the dependence is reversed for higher solid fractions.
" }, { "name": "Jones, Silken Michelle", "degree": "PhD", "year": "2021", "title": "Thermal Ignition by Vertical Cylinders", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182020-055522985", "creators": [ { "name": { "family": "Jones", "given": "Silken Michelle" }, "id": "Jones-Silken-Michelle", "orcid": "0000-0003-3496-7191", "display_name": "Jones, Silken Michelle" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverly J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverly J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9g5j-2b97", "abstract": "Accidental thermal ignition events present a significant hazard to the aviation industry. There is scarcity of experimental data on ignition by external natural convection flows for surface areas larger than 10 cm\u00b2. In this work, thermal ignition of external natural convection flows by vertical cylinders is investigated. The effect of geometry is studied by resistively heating stainless steel cylinders of various sizes in a stoichiometric n-hexane and air mixture at 298 K and 1 bar. Cylinder lengths range from 12.7 to 25.4 cm, and cylinder surface areas vary from 25 to 200 cm\u00b2. Logistic regression is used to provide statistical information about the ignition threshold (50% probability of ignition). The maximum ignition threshold found is 1117 K for a cylinder 12.7 cm long and 50 cm\u00b2 in surface area. The minimum ignition threshold found is 1019 K for a cylinder 25.4 cm long and 200 cm\u00b2 in surface area. The maximum uncertainty on these ignition thresholds is \u00b129 K, which comes from the maximum uncertainty on the pyrometer measurement used to record cylinder surface temperatures. \r\nThe dependence of ignition threshold on both surface area and length of a cylinder is found to be minor. High speed visualizations of ignition indicated that ignition occurs near the top edge of all cylinders.
\r\n \r\nThe entire experimental setup is heated to allow for ignition tests with multi-component, heavy-hydrocarbon fuels including Jet A and two surrogate fuels, Aachen and JI. The cylinder used for all testing of heavier fuels is 25.4 cm long and 200 cm\u00b2 in surface area. Hexane is also tested with the heated vessel to investigate the effect of ambient temperature on ignition. At an ambient temperature of 393 K, the ignition threshold of hexane is 933 K. Aachen has an ignition threshold of 947 K at an ambient temperature of 373 K. JI has an ignition temperature of 984 K at an ambient temperature of 393 K. Jet A has an ignition temperature of 971 K at an ambient temperature of 333 K. The maximum uncertainty on these thresholds is \u00b129 K. JI is found to be the most appropriate surrogate for Jet A.
\r\n \r\nFrom the experiments, two main conclusions are reached. Ignition threshold temperatures in external natural convection flows are very weakly correlated with surface area. The observed ignition thresholds do not show the drastic transition of ignition temperature with surface area that is observed in internal natural convection situations. Observed ignition thresholds for comparable surface areas (100 to 200 cm\u00b2) are 500 to 600 K higher for external natural convection than internal natural convection. Hexane was found to be a reasonable surrogate for Jet A (38 K difference in ignition threshold) in external natural convection ignition testing. The more complex multi-component JI surrogate, while having an ignition threshold more comparable to Jet A (13 K difference in ignition threshold), requires heating the experimental apparatus and associated difficulties of fuel handling as well as the soot generation by combustion.
\r\n \r\nTwo simplified models of ignition are explored. The first is an investigation of ignition chemistry using a zero-dimensional reactor and a detailed kinetic mechanism for hexane. The temperature history of the reactor is prescribed by an artificial streamline whose rate of temperature increase is parametrically varied. The results from the zero-dimensional reactor computation reveal that a gradually heated streamline exhibits two-stage ignition behavior, while a rapidly heated streamline only experiences one ignition event. The second model of ignition is a one-dimensional simulation of ignition adjacent to a cylinder at a prescribed temperature. The formulation included diffusion of species and thermal energy as well as chemical reaction and employed Lagrangian coordinates. The chemistry is modeled with a reaction mechanism for hydrogen to reduce numerical demand. Heat flux and energy balance are analysed to gain insight into the ignition dynamics. Initially, heat transfer is from the wall into the gas, and a mostly nonreactive thermal boundary layer develops around the cylinder. As reaction in the gas near the surface begins to release energy, the heat transfer decreases, and, near the critical temperature for ignition, the direction of heat flux reverses and is from the gas into the wall. In a case where ignition takes place, there is rapid rise in temperature in the gas within the thermal layer, and a propagating flame is observed to emerge into surrounding cold gas. The heat transfer from the hot combustion products results in a continuous heat flux from the gas into the wall. In a case where ignition does not take place, no flame is observed and the heat flux at the wall is slightly positive. For the critical condition just below the ignition threshold, a balance between energy release and diffusion in the adjacent gas results in a small temperature rise in the thermal layer, but a propagating flame is not created. The Van't Hoff ignition criterion of vanishing heat flux at the ignition threshold is approximately but not exactly satisfied. Contrasting the two modeling ideas, we observe that modeling adiabatic flows along computed nonreactive streamlines is useful in examining the role of detailed chemistry but lacks important diffusion effects. Including mass and thermal transport provides more insight into important ignition dynamics but comes at the expense of increased computational complexity.
" }, { "name": "Lawson, Joel Michael", "degree": "PhD", "year": "2021", "title": "Focused Laser Differential Interferometry", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132021-180953405", "creators": [ { "name": { "family": "Lawson", "given": "Joel Michael" }, "id": "Lawson-Joel-Michael", "orcid": "0000-0002-3042-0909", "display_name": "Lawson, Joel Michael" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5thh-f652", "abstract": "The focused laser differential interferometer (FLDI) is a non-imaging optical diagnostic that is sensitive to density disturbances. A distinguishing feature is reduced sensitivity away from the focal plane of its beams. The spatial resolution is sub-mm, and the temporal resolution is restricted only by photodetector bandwidth, typically >10 MHz. These traits make FLDI particularly suited to measurements in hypervelocity ground-testing facilities, where the low densities, short time-scales, and harsh environments preclude the use of intrusive diagnostics. Line of sight integration issues associated with other optical techniques are therefore minimized, a distinct advantage for measurements in impulse facilities, where the core flow of interest is often surrounded by highly-turbulent shear layers.
\r\n\r\nThe systematic design principles for single and double FLDI systems are discussed, based on ray transfer matrix analysis combined with Gaussian optics. A detailed guide is presented for the practicalities of aligning, calibrating, and operating an FLDI.
\r\n\r\nA modular numerical implementation of Schmidt and Shepherd's FLDI ray-tracing model is developed, capable of accepting arbitrary flow-fields defined via analytical expressions, simulation coupling, or experimental datasets. This numerical implementation is used to perform the first comprehensive experimental validation of the model, using known static and dynamic phase objects. Quantitatively-accurate predictions of the response of real FLDI systems are obtained. Importantly, the spatial sensitivity of the instrument is found to be dependent on disturbance wavelength, with scaling matching that predicted analytically from the model. Propagating shock waves are used as another highly-dynamic test phase object, and it is shown that FLDI maintains its theoretical performance at sub-μs time-scales.
\r\n\r\nThe validated ray-tracing model is used to develop analytical expressions for the response of FLDI to propagating plane waves, extending on the results of Schmidt and Shepherd, and Settles and Fulghum. For the first time, the inverse problem is solved for this class of flow-field, allowing the density fluctuation spectrum to be recovered quantitatively from FLDI phase shift data. This approach is validated using synthetic flow-fields with the numerical ray-tracing scheme, and is also compared with the approximate approach introduced by Parziale et al.
\r\n\r\nFLDI is used to make freestream density fluctuation measurements on two facilities: a conventional blowdown tunnel, and an expansion tube. On the conventional tunnel, a comparison is made between pitot-probe and FLDI measurements after converting both to freestream pressure fluctuation spectra. A modification of Stainback and Wagner's theory, incorporating recent numerical results from Chaudhry et al., is used to interpret the pitot data, while the new inversion algorithm is applied to the FLDI data. Close agreement is found between the two sets of spectra, showing that accurate quantitative data can be obtained with FLDI, and used to extend spectra beyond the pitot bandwidth.
\r\n\r\nOn the expansion tube, the theory of Paull and Stalker for freestream noise originating in the driver gas is investigated. Their proposed relationship between freestream density fluctuations and the primary interface sound speed ratio is not observed. Spectral banding is also absent, however this is expected due to the relatively low secondary expansion strengths. The envelope of accessible conditions is somewhat restricted due to the low mean freestream densities that lead to signal-to-noise issues.
\r\n\r\nSignificant performance improvements can still be made to FLDI, in terms of its noise and bandwidth limitations, and to the spatial localization of its sensitive region; suggestions are given for possible approaches. With the ray-tracing model now validated, it can be used to optimize FLDI, or even to suggest derivative instruments based on similar principles.
" }, { "name": "Nakka, Yashwanth Kumar", "degree": "PhD", "year": "2021", "title": "Spacecraft Motion Planning and Control under Probabilistic Uncertainty for Coordinated Inspection and Safe Learning", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142021-163257155", "creators": [ { "name": { "family": "Nakka", "given": "Yashwanth Kumar" }, "id": "Nakka-Yashwanth-Kumar", "orcid": "0000-0001-7897-3644", "display_name": "Nakka, Yashwanth Kumar" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/6329-sf68", "abstract": "During a spacecraft mission design process, engineers often balance the following three criteria: science return, optimality in performance, and safety. Given a science criterion, engineers design the orbit parameters with predefined performance and safety. Often in this approach, the spacecraft has no understanding of the expected outcome or the knowledge of the mission safety criteria. Autonomous science-driven orbit (or goal) selection and planning for safety under uncertainty enable efficient and adaptable missions. To this end, we propose an architecture for information-based guidance and control for coordinated inspection, motion planning and control algorithms for safe and optimal guidance under uncertainty, and architecture for safe exploration.
\r\n\r\nIn the first part of this thesis, we present an architecture for inspection or mapping of a target spacecraft in a low Earth orbit using multiple observer spacecraft. We use an information gain approach to directly consider the trade-off between gathered data and fuel/energy cost. The estimated information gain is a crucial input to the motion planner, which computes orbits and reconfiguration strategies for each of the observers to maximize the information gain from distributed observations of the target spacecraft. The resulting motion trajectories jointly consider observational coverage of the target spacecraft and fuel/energy cost. We validate our architecture in a mission simulation to visually inspect the target spacecraft and on the three degree-of-freedom robotic spacecraft dynamics simulator testbed.
\r\n\r\nIn the second part of the thesis, we present gPC-SCP, Generalized Polynomial Chaos-based Sequential Convex Programming method, to compute a sub-optimal solution for a continuous-time chance-constrained stochastic nonlinear optimal control (SNOC) problem. The approach enables motion planning and control of robotic systems under uncertainty. The proposed method involves two steps. The first step is to derive a deterministic nonlinear optimal control problem (DNOC) with convex constraints that are surrogate to the SNOC by using gPC expansion and the distributionally-robust convex subset of the chance constraints. The second step is to solve the DNOC problem using sequential convex programming (SCP) for trajectory generation and control. We prove that in the unconstrained case, the optimal value of the DNOC converges to that of SNOC asymptotically and that any feasible solution of the constrained DNOC is a feasible solution of the chance-constrained SNOC. We derive a stable stochastic model predictive controller using the gPC-SCP for tracking a potentially unsafe trajectory in the presence of uncertainty. We empirically demonstrate the efficacy of the gPC-SCP method for the following three test cases: 1) collision checking under uncertainty in actuation, 2) collision checking with stochastic obstacles, and 3) safe trajectory tracking under uncertainty in the dynamics and obstacle location by using a receding horizon control approach. We validate the effectiveness of the gPC-SCP method on the robotic spacecraft testbed.
\r\n\r\n\r\nIn the third part of this thesis, we present a new approach for optimal motion planning for safe exploration that integrates the chance-constrained stochastic optimal control with dynamics learning and feedback control. We derive an iterative convex optimization algorithm that solves an Information-cost Stochastic Nonlinear Optimal Control problem (Info-SNOC). The optimization objective encodes control cost for performance and exploration cost for learning, and the safety is incorporated as distributionally robust chance constraints. The dynamics are predicted from a robust regression model that is learned from data. The Info-SNOC algorithm is used to compute a sub-optimal pool of safe motion plans that aid in exploration for learning unknown residual dynamics under safety constraints. A stable feedback controller is used to execute the motion plan and collect data for model learning. We prove the safety of rollout from our exploration method and reduction in uncertainty over epochs, thereby guaranteeing the consistency of our learning method. We validate the effectiveness of Info-SNOC by designing and implementing a pool of safe trajectories for a planar robot. We demonstrate that our approach has a higher success rate in ensuring safety when compared to a deterministic trajectory optimization approach.
" }, { "name": "Pastor, Daniel", "degree": "PhD", "year": "2021", "title": "Towards Learning Robotic Dynamics: Application to Multirotor Takeoff and Landing", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152021-082447788", "creators": [ { "name": { "family": "Pastor", "given": "Daniel" }, "id": "Pastor-Daniel", "orcid": "0000-0003-3452-0605", "display_name": "Pastor, Daniel" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "chair", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "space" ], "doi": "10.7907/199j-dk87", "abstract": "Multirotors have become widespread but their usage is still limited. Ensuring safety during take-off and landing is still an open problem. Towards this goal this thesis proposes two different solutions to address this problem. The two approaches complement each other and they are tested on hardware.
\r\n \r\nThe first approach is to design a vehicle that is stable during take-off, despite hardware failures or unsteady take-off platforms. A solution is to use a ballistic launch to impose a deterministic path, preventing collisions with its environment. Following this approach led to the development of several SQUID (Streamlined Quick Unfolding Investigation Drone) vehicles. The main challenges are the ballistic initial flight, large accelerations during launch, and limited volume. A first prototype was developed, which is able to transition mid-flight from stable ballistic flight to a fully controllable multirotor. The system has been fabricated and field tested from a moving vehicle up to 50mph to successfully demonstrate the feasibility of the concept and experimentally validate the design's aerodynamic stability and deployment reliability. A second prototype expanded the first one's capabilities incorporating fully-autonomous vision-based navigation, while keeping the ballistic passive stability and stable transition abilities. The new design includes a more reliable plate-based structure and more effective folding fins.
\r\n \r\nThe second approach focuses on designing controllers that are safe regardless of the platform. For that purpose, a Model Predictive Control (MPC) is used to ensure state and input constraints. Given the highly non-linear dynamics platforms and fast dynamics that require a quick controller evaluation, the work in this thesis is built using Koopman Operator theory, which allows tools from linear analysis to be applied to systems with inherently non-linear dynamics. One of the main contributions is a novel method to find Koopman Eigenfunctions directly from data. Another key contribution is an episodic approach to model non-linear actuation dynamics. The proposed method is first tested on simulation and it outperforms comparable approaches. The method is also demonstrated on-board a multirotor for a fast landing application, where the nonlinear ground effect is learned and used to improve landing speed and quality. An additional extension considers model uncertainty in the MPC architecture, where an Ensemble Kalman Sampler is used to learn the uncertainty distribution.
" }, { "name": "Pedivellano, Antonio", "degree": "PhD", "year": "2021", "title": "Deployment Dynamics of Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012021-002457442", "creators": [ { "name": { "family": "Pedivellano", "given": "Antonio" }, "id": "Pedivellano-Antonio", "orcid": "0000-0003-2321-7301", "display_name": "Pedivellano, Antonio" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/4zbq-g037", "abstract": "Thin-shell structures provide a lightweight solution for deployable structure applications. Despite being only few tens of microns thick, these structures provide excellent bending stiffness, thanks to their curved cross-section. Their thinness also allows them to be elastically packaged into small volumes to fit into a launch vehicle; once in space, they can be self-deployed by releasing their stored elastic energy.
\r\n\r\nMost space applications use thin-shell structures to deploy and tension thin membranes, such as solar sails, drag sails, and solar arrays. Recently, a novel space solar power architecture has been developed at Caltech, and it relies on distributed thin-shell components, connected in a space frame, to create large-area deployable structures. Thanks to the unique properties of thin shells, these structure provide superior stiffness-to-mass ratio and self-deployment capabilities. However, to demonstrate their reliability and enable their use on space missions, their deployment dynamics must be understood and predicted.
\r\n\r\nGround testing is the established approach to verify a structure throughout its design and qualification process. However, replicating the space environment in a laboratory setting is generally not possible, especially for lightweight structures, which are very sensitive to the effects of gravity and air. Numerical models are therefore the only tool to predict the behavior of a structure in space. However, validation with ground experiments is necessary to build confidence in the models, which must be able to capture the complexity of the interaction with air, gravity, and the suspension system that supports the weight of the structure.
\r\n\r\nThe goal of this thesis is to develop high-fidelity models for large space structures, where multiple thin-shell components are folded together and deploy by releasing their strain energy. This overall objective is achieved in 3 steps. First, a ladder-type rectangular strip is introduced, as a building block for more complex architectures. The strip is composed by two thin-shell longerons, symmetrically folded at two locations. The deployment dynamics of this structure is investigated through experiments on 1 m-scale prototypes, both in air and in vacuum. A detailed analysis of its elastic folds is performed using full-field displacement measurements from Digital Image Correlation. A finite element model of this strip is presented, and it is shown to accurately capture the dynamics of the strip for all tested conditions. Then, the implementation of the packaging and deployment scheme of a space solar power spacecraft, composed of multiple strips, is discussed. A kinematic model of the structure is proposed as a design tool to achieve systematic folding. A novel concept of a deployment mechanism to coil the structure in a robust and reliable way is proposed. Also, a staged deployment scheme is demonstrated, to reduce the uncertainty of strain-energy deployment for large space structures. Finally, the deployment dynamics of a 2 m-scale space structural prototype, based on the space solar power architecture, is investigated. A full-scale finite element model of the structure is implemented to replicate its complex folding scheme and capture the deployment process, including the interaction with the deployment mechanism and the suspension system. The simulations predict well the behavior of the structure observed in experiments through motion capture techniques.
\r\n\r\nThe work presented in this thesis advances previous studies on the deployment dynamics of simple thin-shell components, and demonstrates that even complex thin-shell architectures can be packaged and deployed in a controlled and predictable way. The solutions proposed in this thesis have guided the packaging process and the design of the deployment mechanism for DOLCE, an upcoming flight demonstration of the space solar power architecture described in this work. However, this research has much broader implications, as the experimental and numerical framework presented herein can be generalized to different shell-based architectures, and contributes to enabling a new generation of lightweight deployable structures for future space applications.
" }, { "name": "Royer, Fabien A.", "degree": "PhD", "year": "2021", "title": "Probing the Buckling of Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312021-185024653", "creators": [ { "name": { "family": "Royer", "given": "Fabien A." }, "id": "Royer-Fabien-A", "orcid": "0000-0003-2452-2893", "display_name": "Royer, Fabien A." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/ksn2-t598", "abstract": "The overarching goal of the research presented in this dissertation is to apply and extend a newly developed methodology to understand the buckling of complex thin shell structures. This methodology enables the determination of tighter buckling criteria and paves the way to the development of more efficient structures, used closer than ever to their buckling load and even beyond. It would result in dramatically lighter structures to be built and has the potential to enable new applications, such as extremely large aperture satellites.
\r\n\r\nWe first analyze the stability of open section thin shell structures under a pure bending moment, through simulations. These structures are composed of longitudinal thin-shell elements connected transversely by thin rods, and inspired by real spacecraft structures. The present study applies and extends recent work on the stability of cylindrical and spherical shells. The role of localization in the buckling of these structures is investigated and early transitions into the post-buckling regime are unveiled using a probe that locally displaces the structure. The probing method enables the computation of the energy input needed to transition early into a post-buckling state, which is central to determining the critical buckling mechanism for the structure. We show that the structure follows stability landscapes also found in cylindrical and spherical shell buckling problems. This initial computational study is the basis for the first ever probing experiment on a complex structure.
\r\n\r\nIn order to test these new structures under bending, a new bending apparatus is designed and implemented. The boundary conditions are chosen such that the apparatus is statically determinate (isostatic), and no state of self stress can develop in the sample during its mounting and testing. This feature is especially desirable in the study of thin shell structures and their elastic instabilities, for which imperfection sensitivity plays a crucial role in the buckling transition and the post-buckling regime. The accuracy of the isostatic bending machine is first assessed through the testing of rods, and its imperfection insensitive behavior is then highlighted in experiments on tape springs, and through numerical studies of the same structures.
\r\n\r\nThe new bending machine is complemented by a probing apparatus, and the stability of the open section thin-shell structures subjected to a pure bending moment is studied experimentally. The experiment confirms that localization of deformations plays a paramount role in the structure's nonlinear post-buckling regime and is extremely sensitive to imperfections. This characteristic is investigated through probing experiments. The range of moments for which the early buckling of the structure can be triggered using this probe perturbation is determined, as well as the energy barrier separating the pre-buckling and post-buckling states. The stability of the local buckling mode is then illustrated by an experimental stability landscape of shell buckling, and probing is then extended to the entire structure to reveal alternate buckling modes disconnected from the structure's fundamental path. These results can be used to elaborate efficient buckling criteria for this type of structures, through the use of transition diagrams determined experimentally.
\r\n\r\nFinally, the buckling and post-buckling behavior of ultralight ladder-type coilable structures is investigated. These specific structures are used in the Space Solar Power Project at Caltech and are referred to as strips. Similarly to the previous studies, the stability of strip structures loaded by normal pressure is computationally studied by applying controlled perturbations through localized probing. The probing technique is generalized to higher-order bifurcations along the post-buckling path, and low-energy escape paths into buckling that cannot be predicted by a classical eigenvalue formulation are identified. It is shown that the stability landscape for a pressure-loaded strip is similar to the landscape for classical shells, and the open section thin shell structure studied initially in this thesis. While classical shell structures buckle catastrophically, strip structures feature a large stable post-buckling range. Probing enables the full characterization of the structure's unstable behavior, which paves the way to extend its operation closer than ever to the buckling load, and even in the post-buckling regime. It would enable the design of more efficient structures by dramatically reducing their mass, therefore enabling new large spacecraft to be built.
" }, { "name": "Shamai, Maysam", "degree": "PhD", "year": "2021", "title": "Complexity Reduction of Fluid-Structure Systems at Low Forcing Frequencies", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-215050622", "creators": [ { "name": { "family": "Shamai", "given": "Maysam" }, "id": "Shamai-Maysam", "orcid": "0000-0002-1099-1456", "display_name": "Shamai, Maysam" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Plesniak", "given": "Michael W." }, "id": "Plesniak-M-W", "orcid": "0000-0001-6575-5074", "role": "member", "display_name": "Plesniak, Michael W." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rhs5-yq49", "abstract": "This thesis addresses complexity reduction in periodic fluid-structure systems at low forcing frequencies. A novel quasi-steady time scaling framework is developed to relate the dynamics of a forced system to a corresponding unforced system.
\r\n\r\nParticle Image Velocimetry and dye flow visualization are used to study the streamwise-oscillating cylinder's wake at a mean Reynolds number of 900. Forcing frequencies both one and two orders of magnitude below the stationary shedding frequency are considered. Forcing amplitudes are such that the instantaneous Reynolds number remains above the critical value at all times. It is shown that this forcing regime is synonymous with the development of both frequency and amplitude modulation in the wake. While frequency modulation is linked to vortex shedding, amplitude modulation arises due to symmetric reorganization of the wake at certain phases in the forcing cycle. Furthermore, Dynamic Mode Decomposition is used to extract underlying flow structures and quasi-steady time scaling is employed to relate dynamics to the corresponding unforced system. Specifically, forcing regimes where quasi-steady shedding can develop are identified and time is scaled to transform the system to resemble the stationary cylinder at the same mean Reynolds number.
\r\n\r\nExperimental flowfields are also used to analyze the wake of a surface mounted hemisphere subject to a highly pulsatile freestream, characterized by a forcing amplitude equal to the mean. Although this flow sees regular shedding of hairpin vortices in the unforced case, pulsatile forcing leads to significant deviations. For a nominal mean Reynolds number of 1000, analysis of the wake shows that forcing at a frequency much smaller than that associated with hairpin shedding can lead to frequency modulated shedding. Consequently, time scaling is employed to reduce system complexity associated with hairpin shedding and to relate wake dynamics to the analogous unforced system.
" }, { "name": "Shen, Naijian", "degree": "PhD", "year": "2021", "title": "Part I: The Equations of Plasma Physics and the Richtmyer-Meshkov Instability in Magnetohydrodynamics. Part II: Evolution of Perturbed Planar Shockwaves.", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:10042020-174941725", "creators": [ { "name": { "family": "Shen", "given": "Naijian" }, "id": "Shen-Naijian", "orcid": "0000-0002-0533-8081", "display_name": "Shen, Naijian" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/e9b8-y318", "abstract": "Part I: Mitigating the Richtmyer-Meshkov instability (RMI) is critical for energy production in inertial confinement fusion. Suitable plasma models are required to study the hydrodynamic and electromagnetic interactions associated with the RMI in a conducting medium. First, a sequence of asymptotic expansions in several small parameters, as formal limits of the non-dissipative and non-resistive two-fluid plasma equations, leads to five simplified plasma/magnetohydrodynamics (MHD) systems. Each system is characterized by its own physical range of validity and dispersion relations, and includes the widely used magnetohydrodynamic (MHD) and Hall-MHD equations. Next we focus on the RMI in MHD. Using ideal MHD, it has been shown that the RMI is suppressed by the presence of an external magnetic field. We utilize the incompressible, Hall-MHD model to investigate the stabilization mechanism when the plasma ion skin depth and Larmor radius are nonzero. The evolution of an impulsively accelerated, sinusoidally perturbed density interface between two conducting fluids is solved as a linearized initial-value problem. An initially uniform background magnetic field of arbitrary orientation is applied. The incipient RMI is found suppressed through oscillatory motions of the interface due to the ion cyclotron effect. This suppression is most effective for near tangential magnetic fields but becomes less effective with increasing plasma length scales. The vorticity dynamics that facilitates the stabilization is discussed.
\r\n\r\nPart II: We consider the evolution of a planar gas-dynamic shock wave subject to smooth initial perturbations in both Mach number and shock shape profile. A complex variable formulation for the general shock motion is developed based on an expansion of the Euler equations proposed by Best [Shock Waves, {1}: 251-273, (1991)]. The zeroth-order truncation of Best's system is related to the well-known geometrical shock dynamics (GSD) equations while higher-order corrections provide a hierarchy of closed systems, as detailed initial flow conditions immediately behind the shock are prescribed. Solutions to Best's generalized GSD system for the evolution of two-dimensional perturbations are explored numerically up to second order in the weak and strong shock limits. Two specific problems are investigated: a shock generated by an impulsively accelerated piston with a corrugated surface, and a shock traversing a density gradient. For the piston-driven flow, it is shown that this approach allows full determination of derivative jump conditions across the shock required to specify initial conditions for the retained, higher-order correction equations. In both cases, spontaneous development of curvature singularity in the shock shape is detected. The critical time at which a singularity occurs follows a scaling inversely proportional to the initial perturbation size. This result agrees with the weakly nonlinear GSD analysis of Mostert et al. [J. Fluid Mech., {846}: 536-562, (2018)].
" }, { "name": "Shi, Xichen", "degree": "PhD", "year": "2021", "title": "Intelligent Control for Fixed-Wing eVTOL Aircraft", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182021-040721884", "creators": [ { "name": { "family": "Shi", "given": "Xichen" }, "id": "Shi-Xichen", "orcid": "0000-0002-5366-9256", "display_name": "Shi, Xichen" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "space" ], "doi": "10.7907/51c6-aa57", "abstract": "Urban Air Mobility (UAM) holds promise for personal air transportation by deploying \"flying cars\" over cities. As such, fixed-wing electric vertical take-off and landing (eVTOL) aircraft has gained popularity as they can swiftly traverse cluttered areas, while also efficiently covering longer distances. These modes of operation call for an enhanced level of precision, safety, and intelligence for flight control. The hybrid nature of these aircraft poses a unique challenge that stems from complex aerodynamic interactions between wings, rotors, and the environment. Thus accurate estimation of external forces is indispensable for a high performance flight. However, traditional methods that stitch together different control schemes often fall short during hybrid flight modes. On the other hand, learning-based approaches circumvent modeling complexities, but they often lack theoretical guarantees for stability.
\r\n\r\nIn the first part of this thesis, we study the theoretical benefits of these fixed-wing eVTOL aircraft, followed by the derivation of a novel unified control framework. It consists of nonlinear position and attitude controllers using forces and moments as inputs; and control allocation modules that determine desired attitudes and thruster signals. Next, we present a composite adaptation scheme for linear-in-parameter (LiP) dynamics models, which provides accurate realtime estimation for wing and rotor forces based on measurements from a three-dimensional airflow sensor. Then, we introduce a design method to optimize multirotor configuration that ensures a property of robustness against rotor failures.
\r\n\r\nIn the second part of the thesis, we use deep neural networks (DNN) to learn part of unmodeled dynamics of the flight vehicles. Spectral normalization that regulates the Lipschitz constants of the neural network is applied for better generalization outside the training domain. The resultant network is utilized in a nonlinear feedback controller with a contraction mapping update, solving the nonaffine-in-control issue that arises. Next, we formulate general methods for designing and training DNN-based dynamics, controller, and observer. The general framework can theoretically handle any nonlinear dynamics with prior knowledge of its structure. Finally, we establish a delay compensation technique that transforms nominal controllers for an undelayed system into a sample-based predictive controller with numerical integration. The proposed method handles both first-order and transport delays in actuators and balances between numerical accuracy and computational efficiency to guarantee stability under strict hardware limitations.
" }, { "name": "Toedtli, Simon Silvio", "degree": "PhD", "year": "2021", "title": "Control of Wall-Bounded Turbulence Through Closed-Loop Wall Transpiration", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272021-055610816", "creators": [ { "name": { "family": "Toedtli", "given": "Simon Silvio" }, "id": "Toedtli-Simon-Silvio", "orcid": "0000-0001-9371-9572", "display_name": "Toedtli, Simon Silvio" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Hutchins", "given": "Nicholas" }, "id": "Hutchins-Nicholas", "role": "member", "display_name": "Hutchins, Nicholas" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/me3y-te05", "abstract": "Many wall-bounded flows of practical relevance are turbulent, including the flows past airplanes and ships. The turbulent motions enhance momentum mixing and, as a result, the drag force on the engineering surface increases, for transportation vessels typically by at least a factor of two compared to laminar flow. Turbulent flow control aimed at drag reduction therefore has the potential to deliver enormous energetic and economic savings, but many challenges remain despite active research for well over a century. The present thesis aims to contribute towards two open questions of the field: first, what are suitable controller design tools for high Reynolds number flows? And second, how does actuation through closed-loop wall transpiration change the flow physics? We investigate aspects of these questions through direct numerical simulation (DNS) and modal analyses of an example control scheme, which is applied to a low Reynolds number turbulent channel flow. The controller is a generalization of the opposition control scheme, and introduces a phase shift between the Fourier transformed sensor measurement and actuator response.
\r\n\r\nThe first part of the thesis demonstrates that a low-order model based on the resolvent framework is able to approximate the drag reduction results of DNS over the entire parameter space considered. The model is about two orders of magnitude cheaper to evaluate than DNS at low Reynolds numbers, and we present a strategy based on subsampling of the wave number space and analytical scaling laws that enables model-based flow control design at technologically relevant Reynolds numbers. The second part of the thesis shows that the physics of the controlled flow can be understood from two distinct families of spatial scales, termed streamwise-elongated and spanwise-elongated scales, respectively. Wall transpiration with streamwise-elongated scales attenuates or amplifies the near-wall cycle and therefore leads to drag reduction or increase, depending on the phase shift. In contrast, wall transpiration with spanwise-elongated scales only leads to drag increase, which occurs at positive phase shifts and is due to the appearance of spanwise rollers which largely enhance momentum mixing. Both patterns are robust features of flows with closed-loop wall transpiration, and the present study offers a simple explanation of their origin in terms of phase relations at distinct spatial scales. The findings of this study may set the stage for a unifying framework for various forms of wall transpiration, and implications for future flow control design are discussed.
" }, { "name": "Ferraro, Serena", "degree": "PhD", "year": "2020", "title": "Topology Optimization and Failure Analysis of Deployable Thin Shells with Cutouts", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:02032020-164711057", "creators": [ { "name": { "family": "Ferraro", "given": "Serena" }, "id": "Ferraro-Serena", "orcid": "0000-0002-6038-7863", "display_name": "Ferraro, Serena" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/9VZ4-3E71", "abstract": "Shell structures with cutouts are widely used in architectural and engineering applications. For thin, lightweight, and deployable space structures, cutouts are cleverly positioned to fold and store the structure in a small volume. To maintain shape accuracy, these structures must fold without becoming damaged and must be stiff in their deployed configurations. Intuitive designs often fail to satisfy these two requirements. This research proposes solutions to the topology optimization of composite, thin shell structures with cutouts.
\r\n\r\nA novel optimization algorithm was developed that makes no assumptions on the initial number, shape, and location of cutouts on deployable thin shells. The algorithm uses a density-based approach, which distributes the material within the structure by assigning a density parameter to discretized locations. This parametrization of the design domain allows for the finding of new features and the connectivity of the domain, thus providing a completely general formulation to the optimization problem. The goal is to study the effects of volume and stress constraints imposed in a deformed configuration of thin shell structures. While classical topology optimization studies focus on finding solutions to linear problems, this method is applicable to geometrically nonlinear problems and implements stress constraints in the deformed, and hence most stressed, configuration of these shells. A mathematical formulation of the optimization problem and interpolation schemes for stiffness tensor, volume, and stress are presented. A sensitivity analysis of objective function, volume, and stress constraints is provided. Finally, solutions for a thin plate and a tape spring are proposed.
\r\n\r\nDensity-based methods are computationally expensive when applied to large structures and complex shapes because of the large number of design variables. To address these challenges, two optimization methods that provide more specific solutions to the problem of composite, deployable shells are proposed. The first method uses level sets to parametrize the cutouts, thereby restricting the design space and simultaneously limiting the number of design variables. This greatly reduces the computational cost. Using this approach, successful solutions are found for stiff, composite, thin shells with complex shapes that can fold without becoming damaged. The second method uses a spline representation of the contour of a single cutout on the shell, thus performing fine tuning of the shape of the cutout. Modeling techniques that simulate localized strain and experimental methods for studying the quasi-static folding of these composite shells are developed. A laminate failure criterion suitable for thin, plain-weave composites is used in simulations to predict the onset of failure in folded shells. Numerical results are validated with folding experiments that demonstrated good agreement with numerical solutions.
\r\n\r\nLastly, it was discovered that many of the best performing solutions have multiple closely spaced cutouts, as opposed to current designs for deployable space structures that have fewer large cutouts. This leads to the formation of small strips of material between cutouts. Hence, the behavior of thin, plain-weave composite material was characterized and the first study on size-scaling effects at small length scales (\u2264 15 mm) in this type of material was performed. Size-scaling effects on stiffness and strength shown in this study were introduced in numerical simulations of deployable thin shells. The study demonstrates that the prediction of the onset of failure in folded shells strongly depends on these size effects. Numerical predictions are corroborated by an experimental investigation of localized damage in thin strips of material forming between cutouts. Deployable shells resulting from the optimization studies are built and tested and localized damage is measured via digital volume correlation techniques.
" }, { "name": "Figueroa-Schibber, Erika", "degree": "PhD", "year": "2020", "title": "High-Cycle Dynamic Cell Fatigue with Applications on Oncotripsy", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:01202020-210729635", "creators": [ { "name": { "family": "Figueroa-Schibber", "given": "Erika" }, "id": "Figueroa-Schibber-Erika", "orcid": "0000-00002-6629-297X", "display_name": "Figueroa-Schibber, Erika" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "space" ], "doi": "10.7907/0425-SN62", "abstract": "The method of oncotripsy (from Greek, onco- meaning \"tumor\" and \u2013tripsy \"to break\") exploits aberrations in the material properties and morphology of cancerous cells to target them selectively using tuned low-intensity pulsed ultrasound. Compared to other noninvasive ultrasound treatments that ablate malignant tissue, oncotripsy has the capability of targeting unhealthy tissue with minimal damage to healthy cells in the ablation process.
\r\n\r\nWe propose a model of oncotripsy that follows as an application of cell dynamics, statistical mechanical theory of network elasticity and 'birth-death' kinetics to describe processes of damage and repair of the cytoskeleton. We also develop a reduced dynamical model that approximates the three-dimensional dynamics of the cell and facilitates parameter studies, including sensitivity analysis and process optimization.
\r\n\r\nThe dynamical system encompasses the relative motion of the nucleus to the cell membrane and a state variable measuring the extent of damage to the cytoskeleton. The dynamical system evolves in time as a result of structural dynamics and kinetics of cytoskeletal damage and repair. The resulting dynamics are complex and exhibits behavior on multiple time scales, including the period of vibration and attenuation, the characteristic time of cytoskeletal healing, the pulsing period and the time of exposure to the ultrasound. Damage on the cells develops in the order of millions of ultrasound cycles, and the failure mechanism is explained as a fatigue process. We also account for cell variability and estimate the attendant variance of the time-to-death of a cell population. We show that the dynamical model predicts \u2014 and provides a conceptual basis for understanding \u2014 the oncotripsy effect and other trends observed in experiments.
" }, { "name": "Garc\u00eda Su\u00e1rez, Antonio Joaqu\u00edn", "degree": "PhD", "year": "2020", "title": "Application of Path-Independent Integrals to Soil-Structure Interaction", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:11212019-100323260", "creators": [ { "name": { "family": "Garc\u00eda Su\u00e1rez", "given": "Antonio Joaqu\u00edn" }, "id": "Garc\u00eda-Su\u00e1rez-Antonio-Joaqu\u00edn", "orcid": "0000-0001-8830-4348", "display_name": "Garc\u00eda Su\u00e1rez, Antonio Joaqu\u00edn" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MMWW-B046", "abstract": "Assessing seismic pressure increment on buried structures is a critical step in the design of infrastructure in earthquake-prone areas. Due to intrinsic complexities derived from the need to match the solution in the far-field to the localized solution around the structure, the near-field, researchers have aimed at finding simplified models focused on engineering variables as the seismic earth thrust. One such model is the so-called Younan-Veletsos model, which pivots on a stringent assumption on the stress tensor.
\r\n\r\nAt the same time, the might of the path-independent integrals of solid mechanics to deal with problems in Geotechnical Engineering at large, and Soil-Structure Interaction in particular, has remained unexplored, despite of a rich landscape of potential applications. The unbridled success of these path-independent integrals in Fracture Mechanics, a discipline which cannot be understood without them currently, may be mirrored in problems in Geotechnical Engineering, since the two fields, despite appearing very detached from each other at first glance, share deep traits: in both cases, the system under consideration can be conceptualized as a domain with simple, easy-to-assess regions (the areas where remote loading is applied and the far-field, respectively) and also with other complex, hard-to-understand regions (the crack tip, the near-field).
\r\n\r\nWe present the first derivation of the exact solution of the Younan-Veletsos problem, which is later analyzed to reveal phenomena not captured by previous approximate solutions. Then, we introduce a novel model which relies on the path-independent Rice\u2019s J-integral, a customary tool in Fracture Mechanics, which is applied here in the Soil-structure Interaction context for the first time. This novel model captures those features of the exact solution that were missed by prior approximations. The capabilities of the J-integral to, first, find an upper bound of the force induced by earthquakes over the walls of underground structures, under some conditions, and, second, to understand the soil-structure kinematic interaction phenomenon are also assessed.
\r\n\r\nAdditionally, the intermediate step of analyzing of the far-field yielded some results concerning Site Response Analysis which are also included in the text.
" }, { "name": "Leclerc, Christophe", "degree": "PhD", "year": "2020", "title": "Mechanics of Ultra-Thin Composite Coilable Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:01232020-134850757", "creators": [ { "name": { "family": "Leclerc", "given": "Christophe" }, "id": "Leclerc-Christophe", "orcid": "0000-0003-1999-4757", "display_name": "Leclerc, Christophe" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/X60S-BR30", "abstract": "Coilable structures are thin-shell structures that can be coiled around a hub by flattening their cross-section. They are attractive for multiple space applications as they allow efficient packaging and deployment of large planar structures. Reducing the shell thickness enables smaller coiling radius and more efficient packaging.
\r\n\r\nThis thesis investigates TRAC structures, a type of coilable structure, made of ultra-thin composite materials. A design using a laminate made of glass fiber plainweave fabric and carbon fiber unidirectional tape is proposed, leading to a shell thickness of 0.08 mm. An in-autoclave, two-cure manufacturing process is presented, and a shape measurement method is used to mitigate post-cure shape changes due to residual stresses.
\r\n\r\nA study of the structure behavior in its deployed configuration is performed. First, the behavior when subjected to pure bending is investigated experimentally for structures with a length of 575 mm. Two regimes are observed, with a pre-buckling phase transitioning to a stable post-buckling phase after an initial buckling event. The ultimate buckling moment following the stable post-buckling regime can be as high as four times the initial buckling moment. A finite element model is developed and is able to reproduce all the features observed experimentally, except the ultimate buckling. This simulation model is used to study the effect of varying the structure length from 300 mm to 5000 mm on the initial buckling moment. Results show that nonlinearities in the pre-buckling deformations of the flanges under compression lead to a constant wavelength lateral-torsional buckling mode for which the critical moment is mostly constant across the range of length. The torsional behavior of the TRAC structure is also investigated. Good agreement is obtained between experiments and numerical simulations, and initial twist in the structure is shown to have little effect on the overall behavior due to the small torsional stiffness in the underformed configuration.
\r\n\r\nAn analytical method to predict the buckling load of a TRAC structure under pure bending is presented. It is achieved by considering only one flange of the structure and solving the problem of a cylindrical shell panel with a longitudinal free edge under non-uniform axial compression. Partially uncoupled stability equations for a balanced laminate are derived and are used in conjunction with the Rayleigh-Ritz method to approximate the buckling load. This method overestimates the buckling load by 44% in the case of a 500 mm TRAC structure made with ultra-thin composite materials.
\r\n\r\nA study of the coiling behavior is also presented. High localized curvature in the transition region between the coiled and deployed regions is observed in experiments, leading to material failure for a structure made only of carbon fiber unidirectional tape. A numerical framework is developed and reproduces the localized curvature observed in experiments, predicting stress concentration at this location. The study shows that changing the laminate to a a single ply of carbon fiber unidirectional tape sandwiched between plies of glass fiber plainweave fabrics reduces significantly the maximum stress in the transition region, to the extent that the highest stress is now in the fully coiled region and can be accurately predicted using simple equations based on the change of curvatures due to the coiling process.
" }, { "name": "Leibowitz, Matthew Gregory", "degree": "PhD", "year": "2020", "title": "Hypervelocity Shock Tunnel Studies of Blunt Body Aerothermodynamics in Carbon Dioxide for Mars Entry", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272020-173051776", "creators": [ { "name": { "family": "Leibowitz", "given": "Matthew Gregory" }, "id": "Leibowitz-Matthew-Gregory", "orcid": "0000-0002-7297-2592", "display_name": "Leibowitz, Matthew Gregory" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/chyn-ea06", "abstract": "A low mass and reliable thermal protection system for Martian atmospheric entry requires an accurate prediction of the aerothermal environment encountered by the spacecraft. In order to move forward with predictive models for larger vehicles needed for manned and sample return missions, anomalous data needs to be resolved.\r\nThis work aims to address two critical problems relevant for Mars missions.
\r\n\r\nI) We investigate significant discrepancies between experimental and simulated blunt body bow shock standoff distance in ground test facilities. Experiments using high-speed and high-resolution schlieren imaging are conducted in the T5 reflected shock tunnel and the Hypervelocity Expansion Tube (HET) to examine facility\r\nindependence of the measurements. A recently-developed model for sphere and sphere-cone behavior is in good agreement with experiments, and with predictions from Navier-Stokes simulations with thermal and chemical nonequilibrium. The need to account for the divergence of the streamlines in conical nozzles is highlighted.\r\nThe contributions of vibrational and chemical nonequilibrium to the stagnation-line density profile are quantified using the simulation results in order to compare different reaction rate models.
\r\n\r\nII) We measure and characterize carbon dioxide mid-wave infrared radiation in hypervelocity flow. Initially assumed negligible in the design of the Mars Science Laboratory (MSL) mission heat shield, this mechanism of heating must be considered for accurate predictions of the heating environment. Specifically, carbon dioxide radiation can be a dominant source of heating in the afterbody, particularly later in the trajectory at lower velocities. Presented are spectral measurements of the 4.3 \u03bcm fundamental band of carbon dioxide radiation measured using fiber optics embedded on the surface of an MSL scaled heat shield model. When comparing experiments and simulations, good agreement is found when running the HET in shock tube mode where the shock layer is optically thick, while discrepancies are observed in expansion tube mode where the shock layer is optically thin. A thorough analysis of flow features in the line-of-sight including freestream uncertainties is performed to explore possible reasons for this discrepancy. After developing the spectroscopic calibration technique and obtaining forebody measurements in the expansion tube, an experimental campaign is completed in the T5 Reflected Shock Tunnel to measure spectral radiation in the forebody and afterbody. The accompanying T5 simulations needed for radiation predictions are being carried out by NASA Ames.
" }, { "name": "McMullen, Ryan Michael", "degree": "PhD", "year": "2020", "title": "Aspects of Reduced-Order Modeling of Turbulent Channel Flows: From Linear Mechanisms to Data-Driven Approaches", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282020-161209039", "creators": [ { "name": { "family": "McMullen", "given": "Ryan Michael" }, "id": "McMullen-Ryan-Michael", "orcid": "0000-0003-1371-7150", "display_name": "McMullen, Ryan Michael" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Graham", "given": "Michael D." }, "id": "Graham-Michael-D", "role": "member", "display_name": "Graham, Michael D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wayx-eh75", "abstract": "This thesis concerns three key aspects of reduced-order modeling for turbulent shear flows. They are linear mechanisms, nonlinear interactions, and data-driven techniques. Each aspect is explored by way of example through analysis of three different problems relevant to the broad area of turbulent channel flow.
\r\n\r\nFirst, linear analyses are used to both describe and better understand the dominant flow structures in elastoinertial turbulence of dilute polymer solutions. It is demonstrated that the most-amplified mode predicted by resolvent analysis (McKeon and Sharma, 2010) strongly resembles these features. Then, the origin of these\r\nstructures is investigated, and it is shown that they are likely linked to the classical Tollmien-Schichting waves.
\r\n\r\nSecond, resolvent analysis is again utilized to investigate nonlinear interactions in Newtonian turbulence. An alternative decomposition of the resolvent operator into Orr-Sommerfeld and Squire families (Rosenberg and McKeon, 2019b) enables a highly accurate low-order representation of the second-order turbulence statistics. The reason for its excellent performance is argued to result from the fact that the decomposition enables a competition mechanism between the Orr-Sommerfeld and Squire vorticity responses. This insight is then leveraged to make predictions about how resolvent mode weights belonging to several special classes scale with increasing Reynolds number.
\r\n\r\nThe final application concerns special solutions of the Navier-Stokes equations known as exact coherent states. Specifically, we detail a proof of concept for a data-driven method centered around a neural network to generate good initial guesses for upper-branch equilibria in Couette flow. It is demonstrated that the neural network is capable of producing upper-branch solution predictions that successfully converge to numerical solutions of the governing equations over a limited range of Reynolds numbers. These converged solutions are then analyzed, with a particular emphasis on symmetries. Interestingly, they do not share any symmetries with the known equilibria used to train the network. The implications of this finding, as well as broader outlook for the scope of the proposed method, are discussed.
" }, { "name": "Pajunen, Kirsti Mari", "degree": "PhD", "year": "2020", "title": "Dynamics of Lightweight Tensegrity-Inspired Metamaterials Fabricated with 3D-Printing", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-003455628", "creators": [ { "name": { "family": "Pajunen", "given": "Kirsti Mari" }, "id": "Pajunen-Kirsti-Mari", "orcid": "0000-0002-5366-1190", "display_name": "Pajunen, Kirsti Mari" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "member", "display_name": "Hofmann, Douglas C." } ], "option_major": [ "space" ], "doi": "10.7907/wm2f-4013", "abstract": "Tensegrity structures and lattices have been of interest in engineering applications for decades, with their dynamics becoming a thriving field of study. Tensegrities consist of structural members under purely axial loading, either tension or compression, and obtain their stability from prestress. They possess unique characteristics such as high strength-to-weight ratio, nonlinear behavior, and elastic response under severe deformation. Tensegrity lattices (or metamaterials) have been shown to exhibit appealing dynamic attributes such as continuous tunability with prestress, impact mitigation, energy trapping and lensing, and nonlinear wave propagation, to name a few. However, their pin-jointed and prestressed nature presents significant manufacturing limitations, especially in the formation of lattices with large numbers of tessellated unit cells. Therefore, experimental validation of the dynamics of tensegrity metamaterials has remained elusive. For lattices with tensegrity-like characteristics to be manifested for real-world applications, a method for producing tensegrity-like metamaterials at multiple length scales is needed.
\r\n\r\nIn this thesis, we present a design for a 3D-printable tensegrity-inspired structure with the equivalent strain energy capacity and stress-strain response as a pin-jointed tensegrity. Using this structure as a building block for multidimensional lattices, we subject them to a range of dynamic loading conditions to study their response. First, we perform experiments and simulations to obtain the dispersion relations for 1D and 3D lattices. We demonstrate the lattices\u2019 ability to continuously tune the dispersion characteristics (e.g., band gap and wave speed) under precompression. This trait shows potential for acoustic lensing and dispersive wave propagation. In 3D, we show that the lattice shows the same type of unique properties, such as faster shear speed than longitudinal speed, as pin-jointed tensegrity lattices. Next, we study the lattices under impact loading. Long-duration impact experiments on baseline unit cells and 1D lattices show their resilience to repeated deformation, elasticity, and load limitation behaviors. Short-duration impulse experiments and simulations exhibit a wealth of desirable properties, such as high force transmission reduction, highly dispersive wave propagation, tunable wave speeds, energy trapping, and redirection of energy. We demonstrate that these tensegrity-inspired metamaterials not only exhibit and experimentally demonstrate tensegrity-like characteristics, but open a new range of lightweight metamaterials with unprecedented dynamic properties.
" }, { "name": "Talon, Thibaud", "degree": "PhD", "year": "2020", "title": "Surface Reconstruction from Distributed Angle Measurements", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:02282020-192725947", "creators": [ { "name": { "family": "Talon", "given": "Thibaud" }, "id": "Talon-Thibaud", "orcid": "0000-0002-8240-1101", "display_name": "Talon, Thibaud" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/ZG2D-2K77", "abstract": "This thesis presents an innovative solution to the shape measurement of large structures for space applications. The current state-of-the-art heavily relies on optical solutions such as cameras or lasers to recover the shape of a surface. Because of the impracticality of placing a system in front of a large structure flying in space, new solutions need to be developed. The proposed solution is to embed angular sensors (such as sun sensors) directly on the surface. The sensors provide a collection of distributed measurements that form a discrete map of the angular orientation of the structure. An integration scheme can then estimate the 3D shape of the surface.
\r\n\r\nA mathematical model to perform the integration from angle measurements to the shape of a 3D surface is presented first. This model is purely geometric and serves as a basis for similar concepts. The surface is known in a reference configuration and is assumed to have deformed inextensibly to its current shape. Inextensibility conditions are enforced through a discretization of the metric tensor generating a finite number of constraints. This model parameterizes the shape of the surface using a small number of unknowns, and thus requires a small number of sensors. We study the singularities of the equations and derive necessary conditions for the problem to be well-posed. The limitations of the algorithm are highlighted. Simulations are performed on developable surfaces to analyze the performance of the method and to show the influence of the parameters used in the algorithm. Optimal schemes which lower the RMS error between the reconstructed shape and the actual one are presented.
\r\n\r\nAn experimental validation of the proposed solution and algorithm is performed on a 1.3 x 0.25 m structure with 14 embedded sun sensors. The sensors measure the two local angles of the surface from a light source placed in front of the surface. A small, lightweight and expandable design of the sensors is shown in this thesis. A calibration procedure accurately correlates the output of the sensor with a 0.5\u00b0 precision. The procedure also highlights the limitations of the design. The structure was deformed in bending and torsion with amplitudes of a few centimeters, and its shape was reconstructed to an accuracy on the order of a millimeter.
\r\n\r\nThe accuracy of the initial algorithm is found to be limited by local shape deformations caused by the mechanical response of the structure. A new algorithm, replacing the discrete inextensibility conditions with the equilibrium equations derived from a finite-element model, is shown. This new algorithm is tested on the experimental structure and the accuracy of the reconstruction is increased by a factor of 2. The RMS error is under a millimeter on average over the different applied shapes and goes as low as 0.3 mm.
\r\n\r\nTo understand how this solution can apply to large space structures, simulations are performed on a model of a large planar spacecraft. A 25 x 25 m structure representing the current concept for the Caltech Space Solar Power Project satellite is used as an example. Sensors with similar noise properties as the ones built for the experiment are placed on the spacecraft. A finite-element model combining the vibration of the spacecraft with large rigid body rotations is presented. This model is used in a Kalman filter that estimates the shape of the structure by iterative prediction from the dynamic finite-element model and correction from the angle measurements. Simulations are performed around the thruster actuation applied at the corner of the structure to follow a specific guidance scheme that is optimal for space solar power satellites. The actuation creates both vibrations of the structure with amplitudes of few centimeters and large rotations of the spacecraft. The designed Kalman filter can accurately estimate both effects and it is shown that millimeter accuracy is achievable. The relationship between the number of sensors, the reconstructed shape error, as well as potential stiffness deviations in the FE model is studied. The results provide first order estimates of the performance of this measurement system, in order to enable the design of future space missions.
" }, { "name": "Yanes, Nelson Javier", "degree": "PhD", "year": "2020", "title": "Ultraviolet Radiation of Hypervelocity Stagnation Flows and Shock/Boundary-Layer Interactions", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02112020-170613058", "creators": [ { "name": { "family": "Yanes", "given": "Nelson Javier" }, "id": "Yanes-Nelson-Javier", "orcid": "0000-0001-8423-6958", "display_name": "Yanes, Nelson Javier" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WYHM-1218", "abstract": "Shock/boundary-layer interactions can induce flow distortion, create flow separation with loss of control authority, and result in high thermal loads. Correct prediction of the flow structure and heating loads is vital for vehicle survival. However, a recent NATO workshop revealed severe underprediction of thermal loads and discrepancies in the location of separation by simulations of high enthalpy air flows. Due to the coupling between thermochemistry and fluid mechanics, a substantial effort has been placed on the development and validation of thermochemical models. As a result, there is a need for experimental data that are more than mean flow surface measurements.
\r\n\r\nSpatially resolved emission spectra are collected in the post-shock regime of hypervelocity flow over a circular cylinder and a 30-55 degree double wedge. The Hypervelocity Expansion Tube (HET) is used to generate high Mach number, high enthalpy flow (Mach numbers 5 - 7, h\u2080 = 4 - 8 MJ/kg) with minimal freestream dissociation. The NO \u03b3 band (A\u00b2\u03a3\u207a - X\u00b2\u03a0) emission is measured in the ultraviolet range of 210-250 nm at downstream locations behind shock waves. Excitation temperatures are extracted from the NO \u03b3 emission from spectrum fitting. The result is a temperature relaxation profile that quantifies the state thermal non-equilibrium. Profiles of vibrational band intensity as a function of streamwise distance are used as direct measurements of chemical non-equilibrium in the flow.
\r\n\r\nCylinder experiments are performed with varying freestream total enthalpy, Mach number, and test gas O\u2082 mole fraction to examine changes in relaxation profile. Schlieren images are used to accurately measure standoff distance. Temperature measurements are compared against a zero-dimensional state-to-state model. Strategies for spectrum fitting are presented for cases where the gas is not optically thin and for radiation containing multiple electronic states. For freestream mixtures with reduced oxygen mole fraction, an electronic excitation temperature is required to describe the radiation of the NO \u03b3, \u03b2 (B\u00b2\u03a0 - X\u00b2\u03a0), and \u03b4 (C\u00b2\u03a0 - X\u00b2\u03a0) transitions. The creation of electronically excited NO is discussed in the context of measured vibrational band intensities and computed NO(A) number density profiles using a two-temperature reactive Landau-Teller model.
\r\n\r\nEmission spectra are collected in the post bow shock and reattachment shock region of hypervelocity flow over a double wedge. High speed schlieren imaging is performed to investigate facility startup effects and for tracking features in a shock/boundary-layer interaction. Detector exposures occur at select times throughout the flow development process to study temporal changes in thermal and chemical non-equilibrium. Time evolution of temperatures at strategic locations of the flow is obtained from spectrum fitting. Two-temperature calculations of the oblique shock system are compared against the emission results. Radiation data are discussed in the context of recent simulation efforts.
" }, { "name": "Bilgi, Pavaman", "degree": "PhD", "year": "2019", "title": "Optimization of CCD Charge Transfer for Ground and Space-Based Astronomy", "advisor": "Kulkarni, Shrinivas R.; Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-172558320", "creators": [ { "name": { "family": "Bilgi", "given": "Pavaman" }, "id": "Bilgi-Pavaman", "orcid": "0000-0002-2642-8553", "display_name": "Bilgi, Pavaman" } ], "advisors": [ { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "role": "advisor", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "co-advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Smith", "given": "Roger M." }, "id": "Smith-Roger-M", "role": "member", "display_name": "Smith, Roger M." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CNKG-8Y84", "abstract": "This thesis will be of particular interest to anyone integrating Charge-Coupled Devices (CCDs) into any precision scientific imaging instrument, especially so in space. The first part of the thesis concerns optimization of a CCD camera as a whole. CCDs for the WaSP imager at the Hale telescope are characterized using a minimal amount of data using just a flat-field illumination source. By measuring performance over the entire parameter space of (clock and bias) inputs and analyzing the multidimensional output (linearity, dynamic range, read noise etc), optimal operating conditions can be selected quickly (and possibly automatically). With ever growing sizes of detector arrays such as the recently launched Gaia mission, the upcoming Euclid mission and ground-based cameras such as the LSST (189 CCDs), the task of streamlining detector optimization will be increasingly important. In the second (larger) part, the optimization of Charge Transfer Efficiency (CTE) is explored in particular. In modern CCDs, CTE is caused by lattice defects in the bulk silicon and is significantly worsened by radiation exposure, which is unavoidable in space. As shown in the literature, just a year of exposure to high energy solar proton radiation at low earth orbit can result in CTE reducing to 0.9999 for a signal level of 10,000e- \u2014 problematic for most precision astronomical measurements. Here, CTE degrading traps are fully explored in an undamaged CCD to new levels of accuracy. Several unique species are identified, and their population statistics are analyzed by both wafer and sub-pixel location. Subsequently, easily applied CTE measurement techniques are presented, yielding results with new levels of accuracy, concluding in the presentation of a new trap mitigating readout clocking scheme. This scheme can be readily applied to any CCD employing a parallel transfer gate without readout speed penalty. It is proposed that the results herein may be used to construct a simple model to predict CTE given a temperature, readout timing and signal level. This model could then be used to automatically optimize CTE for any CCD, given only its trap parameter statistics.
" }, { "name": "Deffo Nde, Arnold Durel", "degree": "PhD", "year": "2019", "title": "A Line-Free Method of Monopoles for 3D Dislocation Dynamics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042018-083338014", "creators": [ { "name": { "family": "Deffo Nde", "given": "Arnold Durel" }, "id": "Deffo-Nde-Arnold-Durel", "orcid": "0000-0001-9077-8315", "display_name": "Deffo Nde, Arnold Durel" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ariza", "given": "Pilar" }, "id": "Ariza-Pilar", "role": "member", "display_name": "Ariza, Pilar" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/23YV-3312", "abstract": "Despite the emergence of architected materials for various applications, metals still play a key role in engineering in general and aeronautics in particular. Turbine blades in jets engines for instance are made from single-crystal Nickel superalloys. As a result, studying the failure mechanism of these crystalline materials would help understand the limits of their applications. At the core of this mechanism are line defects called dislocations. Indeed, the plastic deformation of metals is governed by the motion of dislocation ensembles inside the crystal. In this thesis, we propose a novel approach to dislocation dynamics through the method of monopoles. In this approach, we discretize the dislocation line as a collection of points (or monopoles), each of which carries a Burgers \"charge\" and an element of line. The fundamental difference between our method and current methods for dislocation dynamics lies in the fact that the latter discretize the dislocation as a collection of line segments from which spans a need to keep track of the connectivity of the nodes. In our approach, we propose a \"line-free\" discretization where a linear connectivity or sequence between monopoles need not be defined. This attribute of the formulation offers significant computational advantages in terms of simplicity and efficiency. Through verification examples, we show that our method is consistent with existing results for simple configurations. We then build on this success to investigate increasingly complex examples, this with the ultimate goal of simulating the plastic deformation of a BCC grain in an elastic matrix.
" }, { "name": "Dhandapani, Chandru", "degree": "PhD", "year": "2019", "title": "Using the Force: Applications and Implications of Turbulence Forcing Terms in Direct Numerical Simulations", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102019-185605511", "creators": [ { "name": { "family": "Dhandapani", "given": "Chandru" }, "id": "Dhandapani-Chandru", "orcid": "0000-0002-7319-557X", "display_name": "Dhandapani, Chandru" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FH31-4468", "abstract": "Most energy requirements of modern life can be fulfilled by renewable energy sources, but it is impossible in the near future to provide an alternative energy source to combustion for airplanes. That being said, combustion in aviation can be made more sustainable by using alternative jet fuels, which are made from renewable sources like agricultural wastes, solid wastes, oils, and sugars. These alternative fuels can be used in commercial flights only after a long certification process by the Federal Aviation Agency (FAA) and ASTM International. Unfortunately, in over 50 years of fuel research, only five fuels have been certified.\r\nThis research project aims to speed up the certification process with quicker testing of alternative fuels. Engine testing and even laboratory testing require large amounts of time and fuel. Simulations can make the process much more efficient, but accurately simulating highly turbulent flames in such complex geometries would need large amounts of computational resources. The goal of this thesis is to create an efficient computational framework, that can replicate different engine-like turbulent flow conditions in simple geometries with numerical tractability.
\r\n\r\nThe central idea is to decompose the flow field into ensemble mean and fluctuating quantities. The simulations then resolve only the fluctuations using simple computational domains, while emulating the effect of the mean flow using \"forcing\" terms. These forcing terms are calculated first for incompressible turbulence, and this method is later extended to turbulent reacting flows. In incompressible turbulence, Direct Numerical Simulations (DNS) performed on simple triply periodic cubic domains reasonably capture the statistically stationary shear turbulence, that is observed in free shear flows. The simulations are also performed in cuboidal domains, that are longer in one direction and with an inflow/outflow along it. Both changes are observed to not have a significant impact on the turbulence statistics. Finally, shear convection is applied to the turbulence simulations with inflow/outflow, which has a significant impact on the turbulence. These simulations accurately capture the turbulence anisotropy in free-shear flows.
\r\n\r\nThe study is extended to DNS of highly turbulent n-heptane-air flames performed under different flow conditions. Turbulent flames involve two-way coupling between fluid mechanics and combustion. The effects of the flame on the turbulence and the impact of the turbulent flow conditions on the flame behavior are analyzed. The focus is placed on the effects of turbulence production, shear convection, and pressure gradients. The anisotropy produced in the turbulence due to the different flow conditions and the flame are also compared and contrasted. While the global behavior and flow anisotropy were affected by these conditions, the local chemistry effects were unaffected, and depend only on the laminar flame properties and turbulence intensity. These findings can help predict turbulent flame behavior, and can expedite the search and testing of sustainable alternatives to conventional jet fuels.
" }, { "name": "Guerrero Vela, Pedro Pablo", "degree": "PhD", "year": "2019", "title": "Plasma Surface Interactions in LaB\u2086 Hollow Cathodes with Internal Xe Gas Discharge", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032019-100503451", "creators": [ { "name": { "family": "Guerrero Vela", "given": "Pedro Pablo" }, "id": "Guerrero-Vela-Pedro-Pablo", "orcid": "0000-0001-5766-2038", "display_name": "Guerrero Vela, Pedro Pablo" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "space" ], "doi": "10.7907/4CW7-2K35", "abstract": "The ultimate goals of space vehicles are to move faster, further, and more reliably in the space environment. Electric propulsion (EP) has proven to be a necessary technology in the exploration of our solar system ever since its working principle was empirically tested in space in 1964. Thanks to the high exhaust velocities of ionized propellant gases, EP enables efficient utilization of the limited supply of propellant aboard spacecrafts. This technology has opened the possibility of long distance autonomous space missions.
\r\n\r\nEP devices require electron sources to ionize the propellant gas and to neutralize charges that are leaving the spacecraft. In modern EP thrusters, this is achieved by the use of hollow cathodes -- complex devices that employ low work function materials to emit electrons. Hollow cathodes using polycrystalline LaB6 inserts are attractive candidates for long duration EP based space missions. However, the physics behind LaB6 hollow cathode operation has not been studied in detail, which limits the possibility of their optimization. This work presents an integrated experimental and computational approach to investigate LaB6 hollow cathode thermal behaviour and the interplay between LaB6 insert surface chemistry and xenon plasma.
\r\n\r\nOur investigation of the thermal behaviour of LaB6 cathodes led to the unexpected discovery of a thermal transient when a new insert is first used. Specifically, we observed that the cathode temperature decreases by approximately 300 degrees over 50 hours before reaching steady state. This finding suggests a beneficial dynamic evolution of the cathode's chemical state when it interacts with its own plasma. This evolution is intrinsic to cathode operation and can only be precisely understood when the multiphysic nature of the cathode is self-consistently simulated. Thus, we built a numerical platform capable of combining the plasma, thermal and chemical behavior of a discharging hollow cathode. Simulations incorporating different neutralization models, inelastic ion-surface interaction and heterogeneous chemical evolution led to two major conclusions. First, simulations predicted a significant reduction of the LaB6 work function (0.42~eV) compared to previously reported baseline values, which is of paramount importance for EP thruster efficiency and operational lifetimes. Second, simulations suggested that the interaction between xenon low energy ions (<\t50 eV) and the LaB6 surface occurs following a two step neutralization mechanism. The predicted work function reduction was experimentally confirmed by photoemission spectroscopy. Furthermore, using a combination of crystallographic analysis, scanning electron microscopy and profilometry, we demonstrated that work function reduction is caused by the creation of a crystallographic texture at the LaB6 surface upon interaction with Xe plasma. In addition, we postulated the existence of a work function enhancing mechanism of secondary importance, which can be explained by forced cationic termination of plasma exposed crystals.
\r\n\r\nOur results revealed the unexpected phenomenon of work function reduction upon plasma exposure of LaB6. These findings suggest that LaB6 hollow cathodes may outperform current technologies and become the component of choice in EP thrusters for future space missions.
" }, { "name": "Huertas-Cerdeira, Cecilia", "degree": "PhD", "year": "2019", "title": "On the Dynamics of Flat Plates in a Fluid Environment: A Study of Inverted Flag Flapping and Caudal Fin Maneuvering", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-103225366", "creators": [ { "name": { "family": "Huertas-Cerdeira", "given": "Cecilia" }, "id": "Huertas-Cerdeira-Cecilia", "orcid": "0000-0003-4553-0470", "display_name": "Huertas-Cerdeira, Cecilia" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/326X-M576", "abstract": "Despite serving analogous functions, the mechanical designs conceived by human engineering and those that result from natural evolution often possess fundamentally differing properties. This thesis explores the use of principles that stem from natural evolution to improve the performance of engineered mechanisms, focusing on systems whose role is to interact with a fluid environment. Two different principles are considered: the use of compliance, abundant in nature's structures, and the use of flapping propulsion, prevalent among nature's swimmers.
\r\n\r\nThe first part of this thesis is dedicated to investigating the physics that govern the behavior of an inverted-flag energy harvester; an unactuated flexible cantilever plate that is clamped at its trailing edge and submerged in a flow. The resonance between solid motion and fluid forcing generates large-amplitude unsteady deformations of the structure that may be used for energy harvesting purposes. The effect of the flag's aspect ratio on its stability is first evaluated. Flags of very small aspect ratio are demonstrated to undergo a saddle-node bifurcation instead of a divergence instability. The angle of attack of the flag is then modified to reveal the existence of dynamical regimes additional to those present at zero angle of attack. A side-by-side flag configuration is finally explored, highlighting the presence of an energetically favorable symmetric flapping mode among other coupled dynamics.
\r\n\r\nThe second part of this thesis delves into the analysis of underwater flapping propellers and the optimization of their three-dimensional motion to generate desired maneuvering forces, with the objective of obtaining an appendage for use in autonomous underwater vehicles that can perform both fast maneuvering and efficient propulsion. An experimental optimization procedure is employed to obtain the most efficient trajectory that generates a specified side force. The effect of increasing the fin's aspect ratio is examined, and a highly efficient trajectory, that makes use of high three-dimensionality and rotation angles, is obtained for a fin of AR=4. The use of a flexible fin is then analyzed and shown to be detrimental to the maneuvering efficiency of the system.
" }, { "name": "Huynh, David Pham", "degree": "PhD", "year": "2019", "title": "Spatio-Temporal Response of a Compliant-Wall, Turbulent Boundary Layer System to Dynamic Roughness Forcing", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04232019-162807004", "creators": [ { "name": { "family": "Huynh", "given": "David Pham" }, "id": "Huynh-David-Pham", "orcid": "0000-0002-8430-6255", "display_name": "Huynh, David Pham" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A5PS-GT54", "abstract": "This thesis investigates the interaction between an elastic compliant surface and a turbulent boundary layer exposed to dynamic roughness forcing. The goals are to explore a unique perspective of this fluid-structural problem through narrow-band forcing, and to further develop the understanding of dynamic roughness. Water tunnel experiments are designed with flow and surface measurements, both phase-locked to the roughness actuation. This enables a phase-averaged analysis, which leverages the deterministic input to isolate the temporally correlated components of the flow and surface response. Identifying the directly interacting velocity and deformation modes allows the complex, fluid-structural system to be studied in a more tractable, input-output manner.
\r\n\r\nThe first experiment is conducted with a smooth-wall turbulent boundary layer forced by dynamic roughness, and contributes to the knowledge of this type of forcing through structure-resolved particle image velocimetry. This allows for the streamwise-spatial nature and the wall-normal velocity component (v) of the roughness-forced flow to be explored, which had not been previously studied. A spatial amplitude modulation is observed in the synthetic structure and investigated directly through the spatial spectra. Through a parametric study and an empirical fit, the forcing frequency may now be selected to target a particular streamwise length scale.
\r\n\r\nThe second experiment implements a gelatin sample subject to an unforced turbulent boundary layer. The surface response is characterized and serves as a base case with which to identify the roughness-forced component of the deformations. This naturally leads to the third experiment, where the full compliant-wall, dynamic-roughness-forced turbulent boundary layer system is considered. The surface response to the synthetic flow structure is confirmed, which sets the stage for a comparison between the smooth-wall and compliant-wall data to study the effect of the compliant surface.
\r\n\r\nThe smooth/compliant comparison is guided by a resolvent analysis, which predicts a virtual wall feature in the v velocity mode for the elastic material under consideration. Using this prediction to inform a conditional average, the virtual wall is revealed in the experimental data. Thus, the action of the elastic surface is interpreted as opposing the v velocity near the wall, in a manner similar to wall-jet opposition control.\r\nPrevious experimental studies of viscoelastic compliant surfaces have demonstrated the potential for turbulent drag reduction, though either indirectly via the turbulence intensities or with relatively high skin friction measurement error. A common observation in these studies was the importance of the interaction between the surface and the coherent structures in the flow. To that end, this study has isolated and modeled the behavior of the fluid-structural system with a single spatio-temporal scale generated by dynamic roughness forcing. The results provide a physical interpretation of the effect of an elastic surface on turbulent boundary layer flow structures and informs the ongoing development of a reduced-order modeling tool in the resolvent analysis.
" }, { "name": "Kettenbeil, Christian", "degree": "PhD", "year": "2019", "title": "Dynamic Strength of Silica Glasses at High Pressures and Strain Rates", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202019-104738145", "creators": [ { "name": { "family": "Kettenbeil", "given": "Christian" }, "id": "Kettenbeil-Christian", "orcid": "0000-0003-0301-3678", "display_name": "Kettenbeil, Christian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Clifton", "given": "Rodney J." }, "id": "Clifton-Rodney-J", "role": "member", "display_name": "Clifton, Rodney J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/RZJW-MX30", "abstract": "Understanding the behavior of silica glasses at high pressures and strain rates is of great importance for geological processes and highly relevant to many technological applications including high-powered laser-matter interactions in optical elements and impact/blast damage in defense systems. Materials typically experience large inelastic deformations at high pressures, which are strongly affected by strength-related phenomena such as work hardening, damage and thermal softening. The pressure-shear plate impact experiment (PSPI) provides detailed information on the pressure and strain rate dependent strength properties of materials subjected to uniaxial compression. However, its range of attainable pressures has so far been limited and the assumptions required for its analysis become invalid at pressures beyond the Hugoniot elastic limit of the anvil materials. In this dissertation, a high-pressure PSPI (HP-PSPI) technique is developed that greatly extends the range of attainable experimental conditions by achieving higher terminal projectile velocities in a powder gun setup. A novel fiber-optic heterodyne transverse velocimeter (HTV) is developed to enable the use of robust frequency-based data reduction techniques, which reduce the effect of signal noise and light coupling losses. A forward analysis method, based on finite element simulations, is employed to match the experimentally observed material response during HP-PSPI experiments on soda-lime glass samples while considering the inelastic deformation of the utilized tungsten carbide anvils. Symmetric HP-PSPI experiments on tungsten carbide revealed a loss of strength at normal stresses exceeding 25 GPa, which hint at active damage or softening mechanisms under nominally uniaxial strain compression. A pressure-dependent strain softening model transitions soda-lime glass from an intact strength of 2.8 GPa, below strains of 10-30%, to a failed granular state following extensive inelastic shear deformation, which accurately predicts the measured response over a wide range of stresses (9-21 GPa) and strain rates (3\u2022105-2\u2022107s-1). Extending the range of previously attainable pressures and strain rates in PSPI experiments, combined with more robust diagnostics and analysis tools, will greatly benefit our understanding of material strength in extreme environments and enables the investigation of material behavior in a currently unexplored range of pressures and strain rates.
" }, { "name": "Kumar, Siddhant", "degree": "PhD", "year": "2019", "title": "An Enhanced Maximum-Entropy Based Meshfree Method: Theory and Applications", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062019-043913897", "creators": [ { "name": { "family": "Kumar", "given": "Siddhant" }, "id": "Kumar-Siddhant", "orcid": "0000-0003-1602-8641", "display_name": "Kumar, Siddhant" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Danas", "given": "Konstantinos" }, "id": "Danas-Konstantinos", "role": "member", "display_name": "Danas, Konstantinos" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0AP6-5F94", "abstract": "This thesis develops an enhanced meshfree method based on the local maximum-entropy (max-ent) approximation and explores its applications. The proposed method offers an adaptive approximation that addresses the tensile instability which arises in updated-Lagrangian meshfree methods during severe, finite deformations. The proposed method achieves robust stability in the updated-Lagrangian setting and fully realizes the potential of meshfree methods in simulating large-deformation mechanics, as shown for benchmark problems of severe elastic and elastoplastic deformations. The improved local maximum-entropy approximation method is of a general construct and has a wide variety of applications. This thesis presents an extensive study of two applications - the modeling of equal-channel angular extrusion (ECAE) based on high-fidelity plasticity models, and the numerical relaxation of nonconvex energy potentials. In ECAE, the aforementioned enhanced maximum-entropy scheme allows the stable simulation of large deformations at the macroscale. This scheme is especially suitable for ECAE as the latter falls into the category of severe plastic deformation processes where simulations using mesh-based methods (e.g. the finite element method (FEM)) are limited due to severe mesh distortions. In the second application, the aforementioned max-ent meshfree method outperforms FEM and FFT-based schemes in numerical relaxation of nonconvex energy potentials, which is essential in discovering the effective response and associated energy-minimizing microstructures and patterns. The results from both of these applications show that the proposed method brings new possibilities to the subject of computational solid mechanics that are not within the reach of traditional mesh-based and meshfree methods.
\r\n" }, { "name": "Morgan, Jonathan Philip", "degree": "PhD", "year": "2019", "title": "Linear and Non-linear Interactions in a Rough-Wall Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112019-234812867", "creators": [ { "name": { "family": "Morgan", "given": "Jonathan Philip" }, "id": "Morgan-Jonathan-Philip", "orcid": "0000-0003-2898-4868", "display_name": "Morgan, Jonathan Philip" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7RSR-3277", "abstract": "This thesis explores the linear and non-linear interactions which take place in a rough-wall turbulent boundary through experiments and modeling. In order to derive physics-based models for the relation between roughness geometry and flow physics, two very simple periodic roughnesses were 3D printed and placed in a boundary layer wind tunnel for separate experiments. Hot-wire measurements were taken at a grid of points within a single period of the roughness in order to map the spatial variation of important flow statistics in way that allows correlation back to the roughness geometry. Time averaged streamwise velocity and the power spectrum of instantaneous streamwise velocity were both found to vary coherently with the roughness. The spatial variation of the time averaged velocity was identified as the linear result of the roughness, as it has identical wavenumber and frequency to the static roughness geometry. Modeling the time-averaged velocity field as a response mode of the linear resolvent operator was found to be reasonable for certain wavenumbers. The spatial distribution of the power spectrum was shown to be a non-linear effect of the roughness; the power spectrum only measures the energy of convecting modes, which necessarily have non-zero frequency and cannot correlate linearly to the static roughness. The spatial modulation of the power spectrum was found to be indicative of non-linear triadic interactions between the static velocity Fourier modes and pairs of convecting modes, as allowed by the Navier-Stokes equations. A low-order model for these interactions, and their effect on the power spectrum, was constructed using resolvent response modes to represent all velocity Fourier modes. The model was found to qualitatively predict the modulation of the power spectrum for several sets of wavenumbers. The success of such a simple model suggests that it presents a useful low-order understanding of non-linear forcing between scales in rough-wall boundary layers.
" }, { "name": "Phlipot, Gregory Paul", "degree": "PhD", "year": "2019", "title": "A Fully-Nonlocal Quasicontinuum Method to Model the Nonlinear Response of Periodic Truss Lattices", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242019-115317802", "creators": [ { "name": { "family": "Phlipot", "given": "Gregory Paul" }, "id": "Phlipot-Gregory-Paul", "orcid": "0000-0003-2721-8678", "display_name": "Phlipot, Gregory Paul" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "space" ], "doi": "10.7907/3MPP-Q119", "abstract": "We present a framework for the efficient, yet accurate description of general periodic truss networks based on concepts of the quasicontinuum (QC) method. Previous research in coarse-grained truss models has focused either on simple bar trusses or on two-dimensional beam lattices undergoing small deformations. Here, we extend the truss QC methodology to nonlinear deformations, general periodic beam lattices, and three dimensions. We introduce geometric nonlinearity into the model by using a corotational beam description at the level of individual truss members. Coarse-graining is achieved by the introduction of representative unit cells and a polynomial interpolation analogous to traditional QC. General periodic lattices defined by the periodic assembly of a single unit cell are modeled by retaining all unique degrees of freedom of the unit cell (identified by a lattice decomposition into simple Bravais lattices) at each macroscopic point in the simulation, and interpolating each degree of freedom individually. We show that this interpolation scheme accurately captures the homogenized properties of periodic truss lattices for uniform deformations. In order to showcase the efficiency and accuracy of the method, we compare coarse-grained simulations to fully-resolved simulations for various test problems, including: brittle fracture toughness prediction, static and dynamic indentation with geometric and material nonlinearities, and uniaxial tension of a truss lattice plate with a cylindrical hole. We also discover the notion of stretch locking --- a phenomenon where certain lattice topologies are over-constrained, resulting in artificially stiff behavior similar to volumetric locking in finite elements --- and show that using higher-order interpolation instead of affine interpolation significantly reduces the error in the presence of stretch locking in 2D and 3D. Overall, the new technique shows convincing agreement with exact, discrete results for a wide variety of lattice architectures, and offers opportunities to reduce computational expenses in structural lattice simulations and thus to efficiently extract the effective mechanical performance of discrete networks." }, { "name": "Ratnaswamy, Vishagan", "degree": "PhD", "year": "2019", "title": "Constraining the Mantle's Rheology Using Methods in Uncertainty Quantification", "advisor": "Gurnis, Michael C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132019-143045769", "creators": [ { "name": { "family": "Ratnaswamy", "given": "Vishagan" }, "id": "Ratnaswamy-Vishagan", "orcid": "0000-0002-2371-807X", "display_name": "Ratnaswamy, Vishagan" } ], "advisors": [ { "name": { "family": "Gurnis", "given": "Michael C." }, "id": "Gurnis-M-C", "role": "advisor", "display_name": "Gurnis, Michael C." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Simons", "given": "Mark" }, "id": "Simons-M", "role": "member", "display_name": "Simons, Mark" }, { "name": { "family": "Gurnis", "given": "Michael C." }, "id": "Gurnis-M-C", "role": "member", "display_name": "Gurnis, Michael C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F6FW-T648", "abstract": "An accurate estimation of the large-scale forces in the mantle has been difficult to obtain as numerical models either do not use an accurate rheology nor reproduce surface observations. While much work has been done in developing high-fidelity forward models that capture the salient physics of shear-thinning and dynamic weakening, they fail to reproduce observations such as plate motions and topography. In this thesis, we develop an optimization methodology that minimizes the misfit in surface observations such as plate motions and average effective viscosity for certain regions of the mantle. We utilize adjoints to calculate the gradient, while using second-order adjoints to construct the Hessian so as to infer the rheological parameters of the mantle's rheology. Furthermore, we build on this optimization scheme by constructing the Gaussian approximation of the posterior distribution for the inferred rheological parameters using the Hessian and establish the trade-offs between each parameter through their conditional distributions. We further extend this Gaussian approximation to infer extrinsic quantities such as the stresses in the fault zones and the average effective viscosity in the hinge zones to not only quantify the uncertainty, but also to see partitioning of the coupling of each subduction zone. " }, { "name": "Sridhar, Akshay", "degree": "PhD", "year": "2019", "title": "Large-Eddy Simulation of Turbulent Boundary Layers with Spatially Varying Roughness", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:09082018-212920204", "creators": [ { "name": { "family": "Sridhar", "given": "Akshay" }, "id": "Sridhar-Akshay", "orcid": "0000-0002-2642-8246", "display_name": "Sridhar, Akshay" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Callies", "given": "Joern" }, "id": "Callies-J", "orcid": "0000-0002-6815-1230", "role": "member", "display_name": "Callies, Joern" } ], "option_major": [ "space" ], "doi": "10.7907/8YWS-B862", "abstract": "This dissertation addresses high Reynolds number turbulent boundary layers flows with different inhomogeneous surface roughness distributions using large eddy simulations. The stretched vortex subgrid scale model for the outer flow LES is coupled with a virtual-wall model for the friction velocity with a correction accounting for local roughness effects.
\r\n\r\nA semi-empirical model that describes a fully developed rough-walled turbulent boundary layer with sand-grain roughness length-scale ks = \u03b1x that varies linearly with streamwise distance is first developed, with \u03b1 a dimensionless constant. For large Rex and a free-stream velocity U\u221e ~ xm, a simple log-wake model of the local turbulent mean-velocity profile is used that contains a standard mean-velocity correction for the asymptotic, fully rough regime. A two parameter (\u03b1; m) family of solutions is obtained for which U\u221e+ (or equivalently Cf) and boundary-layer measures can be calculated. These correspond to perfectly self-similar boundary-layer growth in the streamwise direction with similarity variable z/ks where z is the wall-normal co-ordinate. Results over a range of \u03b1 are discussed for cases including the zero-pressure gradient (m = 0) and sink-flow (m = -1) boundary layers. Model trends are supported by high Re wall-modeled LES. Linear streamwise growth of boundary layer measures is confirmed, while for each \u03b1, mean-velocity profiles and streamwise turbulent stresses are shown to collapse against z/(\u03b1x). Inner scaled velocity defects are shown to collapse against z/\u0394, where \u0394 is the Rotta-Clauser parameter. The present results suggest that these flows may be interpreted as the fully-rough limit for boundary layers in the presence of small-scale, linear roughness.
\r\n\r\nNext, an LES study of a flat-plate turbulent boundary layer at high Re under nonequilibrium flow conditions due to the presence of abrupt changes in surface roughness is presented. Two specific cases, smooth-rough (SR) and rough-smooth (RS) transition are examined in detail. Streamwise developing velocity and turbulent stress profiles are considered and sharp departures from equilibrium flow properties with subsequent relaxation are shown downstream. Relaxation trends are studied using integral parameters and higher-order mean flow statistics with emphasis on Re\u03c4 and ks+ dependence. Results are compared with RS experiments at matched Re\u03c4, and show good agreement in terms of recovery rates.
\r\n\r\nFinally, the case of static, impulsive wall-roughness in flows at high Re is addressed using the same LES framework. The initial perturbation from smooth-to-rough appears to dominate the flow behaviour with the length of the impulsive patch showing little effect on recovery rates at matched Re\u03c4 and ks+. The resulting trends show good agreement with low Re experiments and support the wall-modeled LES framework as a suitable method for analysing high Re flows in practical applications.
" }, { "name": "Tutcuoglu, Abbas Davud", "degree": "PhD", "year": "2019", "title": "Stochastic Multiscale Modeling of Dynamic Recrystallization", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242019-144233476", "creators": [ { "name": { "family": "Tutcuoglu", "given": "Abbas Davud" }, "id": "Tutcuoglu-Abbas-Davud", "orcid": "0000-0003-2360-706X", "display_name": "Tutcuoglu, Abbas Davud" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "space" ], "doi": "10.7907/1VVP-T060", "abstract": "Materials by design is a core driver in enhancing sustainability and improving efficiency in a broad spectrum of industries. To this end, thermo-mechanical processes and many of the underlying phenomena were studied extensively in the context of specific cases. The goal of this thesis is threefold: First, we aim to establish a novel numerical model on the micro- and mesoscale that captures dynamic recrystallization in a generalized framework. Based on the inheritance of the idea of state switches, we term this scheme Field-Monte-Carlo Potts method. We employ a finite deformation framework in conjunction with a continuum-scale crystal plasticity formulation and extend the idea of state switches to cover both grain migration and nucleation. We introduce physically-motivated state-switch rules, based on which we achieve a natural marriage between the deterministic nature of crystal plasticity and the stochastic nature of dynamic recrystallization. Using a novel approach to undertake the states-switches in a transient manner, the new scheme benefits from enhanced stability and can, therefore, handle arbitrary levels of anisotropy. We demonstrate this functionality at the example of pure Mg at room temperature, which experiences strong anisotropy through the different hardening behavior on the \u2329c+a\u232a-pyramidal and prismatic slip systems as opposed to the basal slip systems as well as through the presence of twinning as an alternative strain accommodating mechanisms. Building on this generalized approach, we demonstrate spatial convergence of the scheme along with the ability to capture the transformation from single- to multi-peak stress-strain behavior.
\r\n\r\nSecond, motivated by the lack of transparency concerning the benefits of high-fidelity approaches in the modeling of dynamic recrystallization, we present two derivative models of the Field-Monte-Carlo Potts method, both of which afford reduced computational expense. One model preserves the spatial interpretation of grains, but imposes a Taylor assumption regarding the distribution of strain; the other reduces the spatial notion of a grain to a volume fraction in the idea of a Taylor model. In order to concentrate on the differences in accuracy between the various approaches, we fit all three schemes to experimental data for pure copper, which allows us to employ a well-understood crystal plasticity-based constitutive model and to simultaneously provide sufficient data for the analysis of the texture, stress and grain-size evolution. Owing to the large strains attained in these simulations, using the FFT-based scheme, we achieve capturing a precursor of continuous dynamic recrystallization. For low temperatures, the Taylor model fails to replicate the nucleation-dominated recrystallization process, whereas, at high temperatures, it shows compelling agreement with experiments and the two higher-fidelity models both in terms of the homogenized stress-evolution and the microstructural evolution.
\r\n\r\nFinally, we present a novel multiscale analysis of thermo-mechanical processes through coupling of the computationally efficient Taylor model for modeling dynamic recrystallization on the mesoscale to a max-ent based meshfree approach on the macroscale in the idea of vertical homogenization. We analyze the severe plastic deformation-based process of equal channel angular extrusion, which is intriguing from a numerical perspective due to the heavily localized zone of extensive shear deformation. By employing novel tools on the microscale regarding the stable update of internal variables as well as a careful interpretation of macroscale boundary conditions, we present the first multiscale analysis of a severe plastic deformation process informing simultaneously about the evolution of stress, texture and grain refinement. We attain convincing qualitative agreements for the evolution of the plunger force and texture. As an outlook on future investigations, we analyze multiple passes of the same billet in the form of route C with emphasis on the texture evolution after the second pass.
" }, { "name": "Veilleux, Jean-Christophe", "degree": "PhD", "year": "2019", "title": "Pressure and Stress Transients in Autoinjector Devices", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02172019-174051312", "creators": [ { "name": { "family": "Veilleux", "given": "Jean-Christophe" }, "id": "Veilleux-Jean-Christophe", "orcid": "0000-0002-5420-9411", "display_name": "Veilleux, Jean-Christophe" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VJSH-TF65", "abstract": "The viscosity of drug solutions delivered parenterally has been increasing over the years. Injecting viscous drug solutions using spring-actuated autoinjector devices is challenging due to a number of technical and human factor constraints. Some of the related challenges are investigated in this thesis.
\r\n\r\nActuation of autoinjector devices powered using stiff springs can create deleterious pressure and stress transients which are not needed to achieve the normal functions of the device. Experimental measurements have shown that peak pressures and stresses substantially larger than what is needed to achieve the normal device function can occur during the actuation phase, creating unnecessary potential for device failure.
\r\n\r\nThe acceleration of the syringe during actuation can be very large, often creating transient cavitation in the cone region. The occurrence or absence of cavitation is determined by the relative timing of syringe pressurization and syringe acceleration, which is affected by several factors such as the presence, location, and size of an air gap inside the syringe, and the friction between the plunger-stopper and the syringe.
\r\n\r\nExperiments and numerical simulations have shown that sharp pressure waves traveling inside the syringe can be amplified within the cone terminating the syringe. Despite the potential for shock focusing, the impulsive pressurization and the rapid deceleration of pre-filled syringes create a potential for failure which is localized in the syringe shoulder and at the junction between the flange and the barrel, not inside the cone. The cavitation events, on the other hand, create a potential for failure which is limited to a region in close proximity of the bubble upon collapse. The collapse of cavitation bubbles located within the syringe cone can be enhanced due to geometrical effects, and the resulting stresses can be large enough to cause syringe failure.
\r\n\r\nThis thesis demonstrates that static and quasi-static analyses do not provide accurate estimates of the peak pressures and stresses occurring within the device. The pressure and stresses created by the highly dynamic events occurring during actuation need to be accounted for during device design in order to improve device reliability, the user's experience, and patient's adherence to prescribed treatments. The findings discussed in this work provide insights and guidance as to how the transient events can be mitigated.
" }, { "name": "Vidyasagar, A.", "degree": "PhD", "year": "2019", "title": "Predicting Microstructural Pattern Formation Using Stabilized Spectral Homogenization", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272019-170619076", "creators": [ { "name": { "family": "Vidyasagar", "given": "A." }, "id": "Vidyasagar-A", "orcid": "0000-0003-0262-5429", "display_name": "Vidyasagar, A." } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F1VN-1X80", "abstract": "Instability-induced patterns are ubiquitous in nature, from phase transformations and ferroelectric switching to spinodal decomposition and cellular organization. While the mathematical basis for pattern formation has been well-established, autonomous numerical prediction of complex pattern formation has remained an open challenge. This work aims to simulate realistic pattern evolution in material systems exhibiting non-(quasi)convex energy landscapes. These simulations are performed using fast Fourier spectral techniques, developed for high-resolution numerical homogenization. In a departure from previous efforts, compositions of standard FFT-based spectral techniques with finite-difference schemes are used to overcome ringing artifacts while adding grid-dependent implicit regularization.
\r\n\r\nThe resulting spectral homogenization strategies are first validated using benchmark energy minimization examples involving non-convex energy landscapes. The first investigation involves the St. Venant-Kirchhoff model, and is followed by a novel phase transformation model and finally a finite-strain single-slip crystal plasticity model. In all these examples, numerical approximations of energy envelopes, computed through homogenization, are compared to laminate constructions and, where available, analytical quasiconvex hulls.
\r\n\r\nSubsequently, as an extension of single-slip plasticity, a finite-strain viscoplastic formulation for hexagonal-closed-packed magnesium is presented. Microscale intragranular inelastic behavior is captured through high-fidelity simulations, providing insight into the micromechanical deformation and failure mechanisms in magnesium. Studies of numerical homogenization in polycrystals, with varying numbers of grains and textures, are also performed to quantify convergence statistics for the macroscopic viscoplastic response.
\r\n\r\nIn order to simulate the kinetics of pattern evolution, stabilized spectral techniques are utilized to solve phase-field equations. As an example of conservative gradient-flow kinetics, phase separation by anisotropic spinodal decomposition is shown to result in cellular structures with tunable elastic properties and promise for metamaterial design. Finally, as an example of nonconservative kinetics, the study of domain wall motion in polycrystalline ferroelectric ceramics predicts electromechanical hysteresis behavior under large bias fields. A first-principles approach using DFT-informed model constants is outlined for lead zirconate titanate, producing results showing convincing qualitative agreement with in-house experiments. Overall, these examples demonstrate the promise of the stabilized spectral scheme in predicting pattern evolution as well as effective homogenized response in systems with non-quasiconvex energy landscapes.
" }, { "name": "Wang, Cong", "degree": "PhD", "year": "2019", "title": "On the Manipulation of a Turbulent Boundary Layer by Unsteady Boundary Conditions", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-114300433", "creators": [ { "name": { "family": "Wang", "given": "Cong" }, "id": "Wang-Cong", "orcid": "0000-0002-8271-5637", "display_name": "Wang, Cong" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Brown", "given": "Garry L." }, "id": "Brown-Garry-L", "role": "member", "display_name": "Brown, Garry L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FT8M-PM75", "abstract": "Reducing the frictional drag generated by a turbulent boundary layer (TBL) is critical for many engineering applications. Motivated by existing turbulent drag reduction methods, this study explores the possibility of sustaining wall-attached air-films and manipulating the near-wall turbulence in hydrodynamic TBL. An innovative air-retaining system is designed to sustain and dynamically modulate the wall-attached air-films in TBL. In still water, the oscillating air-films induce vortical motions in the near-region of air-films. In TBL, phenomena such as Stokes-type oscillatory motion, zero- shear-stress layer, 'inactive' turbulence and reduced viscous shear stress are observed in the vicinity region of air-films. The analysis shows that TBL momentum transfer toward the wall is suppressed and a turbulence re-laminarization mechanism is induced in the near-wall region. One potential physical mechanism points to the process of vorticity generation in the near-region of oscillating air-films, which 'pushes' the TBL near-wall vortical structures away from the wall. With this viewpoint, the phenomena mentioned above can be explained. The modified momentum transfer mechanism and turbulence re-laminarization process are shown to be the potential cause of suppressed viscous shear stress in the near-wall region. Estimated using the Clauser chart method, the turbulent wall-skin friction shows a noticeable decrease in the presence of air-films.
" }, { "name": "Wei, Yuchen", "degree": "PhD", "year": "2019", "title": "Deployable Piezoelectric Thin Shell Structures: Concepts, Characterization and Vibration Control", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-114129662", "creators": [ { "name": { "family": "Wei", "given": "Yuchen" }, "id": "Wei-Yuchen", "orcid": "0000-0002-7669-020X", "display_name": "Wei, Yuchen" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/4DRX-2X87", "abstract": "The thesis presents three interconnected technology paths to the design and realization of novel deployable active thin shell structures. The baseline concept envisioned is built upon a deployable ultra-thin piezoelectric active thin shell architecture, with segmented tessellations. This vision is motivated by the need to deploy and control large, curved and precise surfaces for a variety of applications including future space telescopes, and is made possible by recent progress in ultra-thin high-performance composites and active material technologies. The thesis uses a combination of heuristic design, theoretical analysis, numerical modeling and novel experimental techniques to construct and validate proposed concepts for deployable piezoelectric thin shells.
\r\n\r\nSpecifically, the thesis answers the following questions: i) How to design and manufacture precise, foldable and curved piezoelectric shells. ii) How to deploy these shells reliably and maintain shape correctability in the deployed state. iii) How to synthesize large, curved deployable surfaces with the aforementioned advantages. iv) How to characterize and predict the nonlinear behavior of piezoelectric materials and thin structures under high electric field actuation and large bending deformations. v) How to improve the shape stability of piezoelectric active thin shells under dynamic disturbances without introducing external sensors.
\r\n\r\nFirst, the thesis proposes new methodologies and design criteria to synthesize deployable, modular edge-supported thin shells based on a combination of origami-inspired folding patterns and spatial mechanisms. In contrast to traditional deployable surface designs, which attach rigid shells to deployable trusses, the proposed methodology enables concurrent folding of flat or curved shells along with the support structures. Starting from a basic module, a variety of deployable surface concepts are proposed through tessellations of the module.
\r\n\r\nA piezoelectric material unimorph architecture is further introduced, providing global curvature and shape correction capabilities. All components of the basic concept are validated through model prototyping and material folding tests, and it is discovered that both the ultra thin carbon fiber composites and piezoelectric ceramic materials can achieve a small folding radius without failure. A composite, doubly-curved foldable shell is also designed and manufactured while still maintaining low shape error. These efforts have led to a new family of deployable piezoelectric thin shell structures that integrate low areal density, high shape accuracy, and structural foldability to an unprecedented degree.
\r\n\r\nThe thesis then tackles the challenge of estimating the actuation response and residual structural deformation of unimorph active thin shells under high electric field and large bending motion. A rate-independent, full field phenomenological constitutive model for a polycrystalline piezoelectric material is characterized experimentally. It successfully captures both the observed ferroelectric and ferroelastic domain switching effects. To overcome the difficulty of testing ultra thin piezoelectric plates, a set of novel characterization techniques is developed and implemented to measure the dielectric and mechanical responses of this material. The characterized material constitutive relation is implemented in an efficient model for estimating the structural response of unimorph thin shells under general electric and mechanical loading. The complete set of governing equations is integrated with a Backward-Euler algorithm, reproducing the measured responses of both the material and the structure under complex loading sequences.
\r\n\r\nActive vibration damping based on self-sensing piezoelectric thin shells is then analyzed and demonstrated on testbed. The self-sensing architecture removes redundant external sensors by making dual use of the piezoelectric layer of the active shell. An adaptive identification method with the associated hardware to track the evolution of field dependent piezoelectric capacitance is implemented, and a new identification strategy is proposed. Closed loop damping with in-situ capacitance adaptation is conducted in bench tests on self-sensing cantilever beams and achieves -12~dB attenuation at the resonance frequency. A highly efficient modeling technique for general self-sensing piezoelectric thin shell structures is proposed which is able to construct closed loop dynamic models based on the vibration eigenmodes and actuation responses obtained from commercial finite element software. These validated modeling techniques are extended to a multi-electrode doubly curved thin shell, where the improvements of shape stability under closed loop damping are evaluated through simulations. It is discovered that the electrode pattern of the self-sensing piezoelectric layer determines the damping performance under the specific boundary conditions of the shell.
" }, { "name": "Braun, Noah Oakley", "degree": "PhD", "year": "2018", "title": "An LES and RANS Study of the Canonical Shock-Turbulence Interaction", "advisor": "Pullin, Dale Ian; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212018-165403115", "creators": [ { "name": { "family": "Braun", "given": "Noah Oakley" }, "id": "Braun-Noah-Oakley", "orcid": "0000-0002-9710-0686", "display_name": "Braun, Noah Oakley" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "co-advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gore", "given": "Robert A." }, "id": "Gore-Robert-A", "role": "member", "display_name": "Gore, Robert A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BGX1-C128", "abstract": "The canonical problem of a nearly stationary, nearly planar shockwave passing through isotropic turbulence is investigated within high Reynolds number regimes. The subject flow contains a wide range of turbulent scales and is addressed in Large Eddy Simulation (LES) to relax the otherwise prohibitive computational cost of simulating these flows. Aliasing errors in the LES of the upstream isotropic turbulence are shown to interact with the mean compression of the shock in a problematic matter, and may result in nonphysical behavior such as a reduction in the dissipation rate as the flow crosses the shock. A method for the regularization of LES of shock-turbulence interactions is presented which is constructed to enforce that the energy content in the highest resolved wavenumbers decays as k-5/3, and is computed locally in physical space at low computational cost. The application of the regularization to an existing subgrid scale model is shown to remove high wavenumber errors while maintaining agreement with DNS of forced and decaying isotropic turbulence. Comparisons to analytical models suggest that the regularization significantly improves the ability of the LES to predict amplifications in subgrid terms over the modeled shockwave.
\r\n\r\nThe regularization method is then employed in high resolution LES intended to illustrate the physical behavior of the shocked, turbulent flow. Turbulent statistics downstream of the interaction are provided for a range of weakly compressible upstream turbulent Mach numbers Mt = 0.03 - 0.18, shock Mach numbers Ms = 1.2 - 3.0, and Taylor-based Reynolds numbers Re\u03bb = 20 - 2500. The LES displays minimal Reynolds number effects once an inertial range has developed for Re\u03bb > 100. The inertial range scales of the turbulence are shown to quickly return to isotropy, and downstream of sufficiently strong shocks this process generates a net transfer of energy from transverse into streamwise velocity fluctuations. The streamwise shock displacements are shown to approximately follow a k-11/3 decay with wavenumber as predicted by linear analysis. In conjunction with other statistics this suggests that the instantaneous interaction of the shock with the upstream turbulence proceeds in an approximately linear manner, but nonlinear effects immediately downstream of the shock significantly modify the flow even at the lowest considered turbulent Mach numbers.
\r\n\r\nLES allows consideration of high Re\u03bb flows, but remains expensive to compute relative to lower cost modeling approaches such as Reynolds-Averaged Navier Stokes (RANS). Conventional RANS models are often not well suited for simulations containing discontinuous features such as shocks and, in an effort to improve the performance of RANS, models for averaged shock corrugation effects and the impact of turbulent entropy or acoustic modes on the energy equation are presented. Unlike previous RANS work that has focused on the modification of turbulent statistics by the shock, the proposed models are introduced to capture the effects of the turbulence on the profiles of primitive variables --- mean density, velocity, and pressure. By producing accurate profiles for the primitive variables, it is shown that the proposed models improve numerical convergence behavior with mesh refinement about a shock, and introduce the physical effects of shock asphericity in a converging shock geometry. These effects are achieved by local closures to turbulent statistics in the averaged Navier-Stokes equations, and can be applied in conjunction with existing Reynolds stress closures that have been constructed for broader applications beyond shock-turbulence interactions.
" }, { "name": "Fragoso, Anthony Thomas", "degree": "PhD", "year": "2018", "title": "Egospace Motion Planning Representations for Micro Air Vehicles", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10242017-193520989", "creators": [ { "name": { "family": "Fragoso", "given": "Anthony Thomas" }, "id": "Fragoso-Anthony-Thomas", "orcid": "0000-0002-5805-9668", "display_name": "Fragoso, Anthony Thomas" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Matthies", "given": "Larry H." }, "id": "Matthies-L-H", "role": "member", "display_name": "Matthies, Larry H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9GX48RJ", "abstract": "Navigation of micro air vehicles (MAVs) in unknown environments is a complex sensing and trajectory generation task, particularly at high velocities. In this work, we introduce an efficient sense-and-avoid pipeline that compactly represents range measurements from multiple sensors, trajectory generation, and motion planning in a 2.5\u2013dimensional projective data structure called an egospace representation. Egospace coordinates generalize depth image obstacle representations and are a particularly convenient choice for configuration flat mobile robots, which are differentially flat in their configuration variables and include a number of commonly used MAV plant models. After characterizing egospace obstacle avoidance for robots with trivial dynamics and establishing limits on applicability and performance, we generalize to motion planning over full configuration flat dynamics using motion primitives expressed directly in egospace coordinates. In comparison to approaches based on world coordinates, egospace uses the natural sensor geometry to combine the benefits of a multi-resolution and multi-sensor representation architecture into a single simple and efficient layer.\r\nWe also present an experimental implementation, based on perception with stereo vision and an egocylinder obstacle representation, that demonstrates the specialization of our theoretical results to particular mission scenarios. The natural pixel parameterization of the egocylinder is used to quickly identify dynamically feasible maneuvers onto radial paths, expressed directly in egocylinder coordinates, that enable finely detailed planning at extreme ranges within milliseconds. We have implemented our obstacle avoidance pipeline with an Asctec Pelican quadcopter, and demonstrate the efficiency of our approach experimentally with a set of challenging field scenarios. The scalability potential of our system is discussed in terms of sensor horizon, actuation, and computational limitations and the speed limits that each imposes, and its generality to more challenging environments with multiple moving obstacles is developed as an immediate extension to the static framework." }, { "name": "Gat, Ilana Batya", "degree": "PhD", "year": "2018", "title": "Investigations of Incompressible Variable-Density Turbulence in an External Acceleration Field", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052017-154614667", "creators": [ { "name": { "family": "Gat", "given": "Ilana Batya" }, "id": "Gat-Ilana-Batya", "orcid": "0000-0003-0223-0507", "display_name": "Gat, Ilana Batya" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Matheou", "given": "Georgios" }, "id": "Matheou-Georgios", "role": "member", "display_name": "Matheou, Georgios" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9JM27V7", "abstract": "Of interest to turbulence modeling is the behavior of variable-density flow at high Reynolds numbers - a flow difficult to model. This thesis provides insight into variable-density flow behavior by examining the dynamics and mixing of variable-density turbulence subject to an externally imposed acceleration field. The flow is studied in the zero-Mach-number limit with a series of direct numerical simulations. The flow configuration consists of alternating slabs of high- and low-density fluid in a triply periodic domain. Density ratios in the range of 1.005 to 10 are investigated. The flow produces temporally evolving shear layers.
\r\n\r\nA perpendicular mean density\u2013pressure gradient is maintained as the flow evolves, with multi-scale baroclinic torques generated in the turbulent flow that ensues. For all density ratios studied, the simulations attain Reynolds numbers at the beginning of the fully developed turbulence regime.
\r\n\r\nAn empirical relation for the convection velocity predicts the observed entrainment-ratio and dominant mixed-fluid composition statistics. Two mixing-layer temporal evolution regimes are identified: an initial diffusion-dominated regime with a growth rate with the square-root of time followed by a turbulence-dominated regime with a cubic growth rate in time. In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted ('non-marching') hump, corresponding to the most probable mole fraction. The shear layers preferentially entrain low-density fluid by volume at all density ratios, which is reflected in the mixed-fluid composition.
\r\n\r\nThe mixed-fluid orientations of vorticity, baroclinic torques, density gradients, and pressure gradients are presented. Baroclinic torques, the cross product of the density and pressure gradients, tend to be aligned with positive or negative vorticity direction, with vorticity preferentially aligning with the intermediate eigenvector of the local strain-rate tensor, with some variance.
" }, { "name": "Gori, Marcello", "degree": "PhD", "year": "2018", "title": "Laboratory Investigation of Shear Ruptures: Supersonic Propagation and Nucleation by Fluid Injection", "advisor": "Rosakis, Ares J.; Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-150338327", "creators": [ { "name": { "family": "Gori", "given": "Marcello" }, "id": "Gori-Marcello", "orcid": "0000-0002-7380-3723", "display_name": "Gori, Marcello" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "co-advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AH9X-V905", "abstract": "Shear rupture nucleation and dynamic propagation is a challenging, non- linear, highly interactive process with important practical implications. Here we focus on two aspects of this problem: propagation speeds and shock front radiation from the dynamic crack tip as well as nucleation of dynamic rupture due to fluid injection.
\r\n\r\nSpontaneously propagating cracks in solids emit pressure and shear waves and are, in part, driven by energy transfer due to them. When a shear crack propagates faster than the shear wave speed of the material, the coalescence of the shear wavelets emitted by the near-crack-tip region forms a shock front that significantly concentrates particle motion. The equivalent scenario involving a pressure shock front should not be possible, since cracks should not be able to exceed the pressure wave speed, at least in an isotropic linear-elastic solid. Here we present full-field experimental evidence of dynamic shear cracks in viscoelastic polymers that result in the formation of a pressure shock front, in addition to the shear one. In that sense, the crack appears to be supersonic. The apparent violation of classic theories is explained by the strain-rate-dependent material behavior of polymers: the increased wave speeds within the highly- strained region around the crack tip allow for supersonic crack propagation with respect to the (lower) wave speeds at short distances away from the interface, resulting in the formation of the pressure shock front. The crack speed remains below the pressure wave speed prevailing locally, about its tip, in agreement with basic physics and energy considerations of linear-elastic theories.
\r\n\r\nWe find that the shock fronts emitted by the shear cracks in the viscoelastic materials are curved and propose a novel method to quantify the viscoelastic wave speeds of the solids in the dynamic range of strain rates based on the curvature. Only kinematic relationships are used in the method, without the need for the constitutive relationship of the material. Measuring or inferring the material properties at elevated strain rates in viscoelastic solids is a difficult task, because of practical limitations of obtaining accurate measurements in that regime. Under the quasi-elastic solid approximation, in which the strain-rate history is neglected, we use the pressure-wave speed measurements to infer the associated value of the Young\u2019s modulus, estimated by assuming a constant value of the Poisson\u2019s ratio. We complement these results with the characterization of the Young\u2019s modulus at lower strain rates via canonical compressive tests. Our results not only confirm previous findings that the Young\u2019s modulus dependence on the strain rate in PMMA is significant but also demonstrate that its variation is more pronounced in the dynamic strain-rate range, with important consequences for the design of structures employing viscoelastic materials that are required to withstand elevated strain rates.
\r\n\r\nThe second part of the study concentrates on the nucleation of shear dynamic rupture due to fluid injection or, more broadly, on the interaction of frictional faulting with fluids. Fluid overpressure is recognized to play a fundamental role in promoting fault motion. A large number of observations has shed light on the interplay between fluids and faulting, both in natural events and in earth-quakes induced by human activities, such as wastewater disposal associated with oil and gas extraction. Fluids can induce a variety of earthquake source behaviors ranging from unstable, dynamic motions to stable, quasi-static ones, which a number of field studies suggests that can coexist on the same fault areas at different times, depending on the local conditions. In fact, a higher pore pres-sure plays the dual role of reducing the frictional strength of the fault and of increasing the nucleation size, e.g., the critical length for a shear crack to transition from quasi-static to dynamic motions. However, due to the complexity of the frictional problem at the fault interface, the understanding of which of these two effects prevails remains elusive. The assumption of a critical nucleation length represents a powerful, yet simplified concept, which currently does not include the dependence on the rate of the pore pressure increase.
\r\n\r\nHere, we explore the effect of the rate of the pore pressure increase on the rupture nucleation. We find that elevated injection rates induce triggering of the rupture at lower pressure values and minimal volumes of the injected fluid, if compared to slow injection rates. For the slow injection rates, we experimentally observe a much larger portion of interface wetted by the fluid and a phase of accelerated slip prior to the dynamic event (quasi-dynamic nucleation process). In some cases, we record much smaller foreshock-like events at the injection site. These findings suggest the presence of a prominent quasi-static nucleation process over the interface. In cases of rapid pore pressure increase, the nucleation process is much shorter in time and much more compact in space, being highly concentrated around the injection location. The dynamic events, once initiated, are qualitatively similar across different injection rates, but quantitatively different, with the slow-injection ones experiencing higher stress drops and higher slips, perhaps due to the effect of fluids on the friction properties.\r\nThese findings suggest the need to develop nucleation size estimates that include the rate of the pore pressure increase and motivate further investigation of how friction properties depend on the presence of fluids. The details of the obtained experimental findings, once analyzed through numerical modeling, will place important constrains on the forms of the acceptable friction laws, including the effects of pore fluid pressure and its rate of change.
" }, { "name": "Grivel, Morgane Anne Marie", "degree": "PhD", "year": "2018", "title": "On the Effect of Large-Scale Patterned Wettability on Contact Line Hydrodynamics", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182017-103752052", "creators": [ { "name": { "family": "Grivel", "given": "Morgane Anne Marie" }, "id": "Grivel-Morgane-Anne-Marie", "orcid": "0000-0002-4391-799X", "display_name": "Grivel, Morgane Anne Marie" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9736P2V", "abstract": "Numerous studies have investigated how liquid water behaves on solid surfaces with uniformly hydrophilic or uniformly hydrophobic wetting properties. In particular, uniformly hydrophobic surfaces have been widely studied for modifying flow behavior of rivulets and drops at smaller scales, as well as for drag reduction on ships or other free-surface-piercing bodies at larger scales. Despite the extensive body of work on surfaces with uniform wetting properties, minimal work has been done to investigate how combining hydrophilic and hydrophobic regions onto a single surface to create macroscopic non-uniform wetting properties affects flows. Research in this vein has predominantly focused on low Reynolds number flows, such as in microfluidic channels or droplet impacts.
\r\n\r\nThis thesis expands on the current literature by investigating contact line dynamics and global flow behavior on surfaces with larger-scale non-uniform wetting properties. Experiments were first carried out to study thin sheet flow down an inclined plate at Re ~ 50 - 1200. The plate's wetting condition was changed by introducing alternating hydrophilic and hydrophobic bands 2-25 mm wide oriented at different angles with respect to the flow direction. Results show that the contact line of such flows is heavily modified compared to the uniform cases. At low Reynolds numbers, large-scale wettability heterogeneities are observed to tune the fingering instability wavelength if the bands are parallel to the flow direction and to dampen finger oscillations if the bands are perpendicular to the flow direction. At higher Reynolds numbers, roller structures are introduced at every hydrophilic-to-hydrophobic junction, modifying the global flow morphology. Entrained air bubbles are also captured and observed to coalesce if the bands are perpendicular to the flow direction.
\r\n\r\nThese experiments were then extended to a surface-piercing hydrofoil coated with alternating hydrophilic and hydrophobic bands. Experiments were run in Caltech's Free Surface Laboratory water tunnel for Re on the order of 104 to 105. The experiments demonstrate that the contact line is modulated in this context, alternating from concave to convex over the different wettability regions. The modulation of the contact line propagates to the rest of the water free-surface via the generation of standing waves and further modifies the free-surface separation point's location and steadiness. In addition, changes in wettability are observed to generate side force, which is of interest for vessel maneuvers in naval applications.
" }, { "name": "Kirchdoerfer, Trenton Thomas", "degree": "PhD", "year": "2018", "title": "Data Driven Computing", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:09122017-092017294", "creators": [ { "name": { "family": "Kirchdoerfer", "given": "Trenton Thomas" }, "id": "Kirchdoerfer-Trenton-Thomas", "orcid": "0000-0003-2290-1857", "display_name": "Kirchdoerfer, Trenton Thomas" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Z899MV", "abstract": "Data Driven Computing is a new field of computational analysis which uses provided data to directly produce predictive outcomes. This thesis first establishes definitions of Data-Driven solvers and working examples of static mechanics problems to demonstrate efficacy. Significant extensions are then explored to both accommodate noisy data sets and apply the deveoloped methods to dynamic problems within mechanics. Possible method improvements discuss incorporation of data quality metrics and adaptive data sampling, while new applications focus on multi-scale analysis and the need for public databases to support constitutive data collaboration.\r\n" }, { "name": "Maggi, Alessandro", "degree": "PhD", "year": "2018", "title": "Three-Dimensional Nano-Architected Materials as Platforms for Designing Effective Bone Implants", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12242017-060345135", "creators": [ { "name": { "family": "Maggi", "given": "Alessandro" }, "id": "Maggi-Alessandro", "display_name": "Maggi, Alessandro" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/Z947482K", "abstract": "The growing world population coupled with longer human life expectancy warrants the need for better medical implant development. Recent advances in lithographic techniques have opened the door to a variety of approaches to tackle the aforementioned issue. However, several scientific hurdles must be overcome before patients can use fully synthetic and effective implants.
\r\n\r\nIdentifying the optimal material, porosity, and mechanical properties of the scaffold to induce cell functionality are key obstacles. Limitations in established fabrication techniques have hindered the ability to fully understand cell behavior on 3D substrates. 3D printing is limited to feature sizes that are at least one order of magnitude larger than a single cell (~10\u03bcm); electrospinning is able to yield features that are on the same scale as cells, but its stochastic nature leads to scaffolds with poor mechanical properties; salt leeching doesn\u2019t allow for control of pore size and distribution which have detrimental effects on nutrient diffusion and cell ingrowth, thereby thwarting the formation of functional tissue.
\r\n\r\nMuch effort has been made to create a suitable platform for regenerating a relatively less complex organ, such as bone, yet the inability to fully understand cell mechanics on 3D scaffolds has curbed the fabrication of effective bone implants.
\r\n\r\nThe first part of this thesis focuses on the suitability of nanoarchitected materials as 3D platforms for bone-tissue growth. We employed two-photon lithography to create polymeric and hydroxyapatite-coated 3D nanolattices to explore scaffold biocompatibility and material effects on osteoblast attachment and growth. Our experiments showed that the unit cell geometry, tetrakaidekahedron, and size, 25\u03bcm, were adequate for cell attachment and infiltration, which are hallmark signs of biocompatibility. Our study also corroborated previous findings that mammalian cells respond differently to different materials that they come in contact with. To isolate structural effects, we fabricated nanolattices coated with a uniform 20nm-thick outermost layer of TiO2. These nanolattices, which had fixed porosity and unit cell size (25\u03bcm) while they varied in structural stiffness (~2-9MPa) were used to explore the influence of scaffold properties on the viability of osteoblasts in a microenvironment similar to that of natural bone. Upon growing osteogenic cells on the nanolattices, significant cell attachment and presence of various calcium phosphate species, which are commonly found in natural bone, were observed. These findings suggest that 3-dimensional nano-architected materials can be used as effective scaffolds for bone cell growth and proliferation.
\r\n\r\nThe second part of the thesis investigates the effects of nanolattice structural stiffness and loading conditions on osteoblast behavior. We fabricated nanolattices with stiffness ranging from ~0.7MPa to 100MPa. Experiments done by seeding osteoblast-like cells on these nanolattices revealed that both stress fiber concentration and bioapatite deposition were higher on the most compliant nanolattice, (0.7 MPa) by ~20% and ~40% respectively. These results provide insights into cell behavior in 3D microenvironments which can lead to a better understanding of stress shielding at the cellular level. Preventing stress shielding by creating scaffolds with structural stiffness and porosity that enhances osteoblasts activity could lead to the creation of effective implants with improved mechanical stability which ultimately improves osteointegration.
\r\n\r\nIn addition to investigating static cell-scaffold interactions we took advantage of the nanolattices tunability to study the effects of dynamic loading on cell behavior. Bone adaptation is driven by dynamic, rather than static loading, however there is still wide controversy on whether stress, strain or loading frequency plays the most significant role in bone remodeling, which drives bone healing.
\r\n\r\nIn order to understand cell sensitivity to varying loads, displacements and frequencies, we fabricated hollow TiO2 nanolattices with stiffness ranging from ~0.7-35MPa which were populated with osteoblast-like cells and subjected to cyclic compression to either a constant stress or strain. After seeding SAOS-2 cells on the nanolattices for 12 days different dynamic loading conditions were tested: (1) cyclic uniaxial compressions to strains ranging from ~0.3-2% strain were carried out to investigate the effects of strain magnitude on cell behavior. (2) Cyclic uniaxial compressions to stresses spanning from ~0.02-1MPa were performed to explore the role of stress magnitude on the cells\u2019 stress fibers formation. (3) The nanolattices were cyclically loaded at different frequencies, ~0.1-3Hz, while maintaining stress and strain constant, which provided insights into how loading frequency affects osteoblasts behavior.
\r\n\r\nCell activity, which was measured by monitoring f-actin and vinculin fluorescence intensity, revealed increased fluorescence in those cells that were mechanically stimulated as opposed to those that were statically grown on the nanolattices regardless of loading condition. Cell response was most drastically affected by varying the loading frequency. A ~30% increase in f-actin fluorescence was observed in the cells grown on the nanolattices that were loaded at ~3Hz compared to those that were grown on the nanolattices that were cyclically compressed at ~0.1Hz.
\r\n\r\nThe last part of this thesis is focused on developing a three-dimensional architected capacitor that could be used as a strain gauge to further our understanding of cell mechanics in 3D. We took advantage of the mechanical tunability of the nanolattices to fabricate a 3D parallel-plate capacitor with a basal capacitance of ~280fF and able to sense forces as low as ~30\u03bcN. This work points to nano-architected materials as promising candidates for ideal platforms to investigate more realistic cellular conditions which can immensely benefit the field of tissue engineering.
" }, { "name": "Martin, Nathan Koon-Hung", "degree": "PhD", "year": "2018", "title": "Analysis of Flapping Propulsion: Comparison, Characterization, and Optimization", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-133402239", "creators": [ { "name": { "family": "Martin", "given": "Nathan Koon-Hung" }, "id": "Martin-Nathan-Koon-Hung", "orcid": "0000-0001-6038-6177", "display_name": "Martin, Nathan Koon-Hung" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q6CG-QY57", "abstract": "In recent decades, the development of autonomous underwater vehicles (AUVs) has rapidly increased and inspiration for novel designs has recently come from nature, primarily based on the fast, efficient, and maneuverable flapping motion of fish. Due to its potential, flapping propulsion is investigated through three studies.
\r\n\r\nThe first study involves the comparison between swimming by flapping and by periodic contractions. A direct comparison is made between the two propulsion mechanisms by simplifying the motions, utilizing a machine that can operate in either mode of propulsion, and evaluating the average thrust generated and the average input power required per cycle between the two mechanisms when the overall kinematics are identical. The two propulsion mechanisms are tested using a variety of overall kinematics, flexible plates, and modified duty cycles, all of which suggest that flapping propulsion is the more efficient; however, periodic contractions with a modified duty cycle are shown to generate more thrust per cycle.
\r\n\r\nThe second study involves the characterization of the impact of chord-wise curvature on the hydrodynamic forces and torques, motivated by the dorso-ventral bending of a fish's caudal fin during locomotion. The impact of curvature is shown to depend on the planform area of the flapping plate. Plates with a smaller or an identical planform area compared with a baseline rigid flat rectangular plate either decrease or increase the generated thrust, respectively. These phenomena are utilized to develop an actuated plate for velocity modulation and a snap-buckling plate to provide a greater thrust and efficiency compared with a rigid plate propulsor.
\r\n\r\nThe third study involves the development and demonstration of a method to experimentally optimize an arbitrary three-dimensional trajectory for a flapping propulsor. The trajectory is parameterized by variables inspired by birds and fish, executed by a mechanism that can actuate an arbitrary motion in a hemisphere, and optimized using an adaptive evolutionary strategy. The trajectories are scored based upon their difference from a desired force set-point and their efficiency. All trajectory searches demonstrate good convergence properties and match the desired force set-point almost immediately. Additional generations primarily improve the efficiency. This novel approach finds optimal trajectories for generating side-forces, similar to how a fish's pectoral fin or a bird's wing functions, and for generating thrust, similar to how a fish's caudal fin operates.
" }, { "name": "Mateos Arrieta, Arturo Jos\u00e9", "degree": "PhD", "year": "2018", "title": "Tensile Failure and Fracture of Three-Dimensional Brittle Nanolattices", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122018-094549478", "creators": [ { "name": { "family": "Mateos Arrieta", "given": "Arturo Jos\u00e9" }, "id": "Mateos-Arrieta-Arturo-Jos\u00e9", "orcid": "0000-0002-9306-3531", "display_name": "Mateos Arrieta, Arturo Jos\u00e9" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AZXG-NB17", "abstract": "The emergence of a new class of cellular solids, i.e., nano- and micro-architected materials, poses the question of whether they can be characterized as a continuum solid. Extensive research has shown that these ultralight and strong structural metamaterials are particularly attractive for mechanically-demanding applications; yet their susceptibility to flaws, fracture behavior, and discrete-continuum duality remains relatively unexplored. In the course of this work, we report the fabrication and tensile-to-failure response of three-dimensional ceramic nanolattices, comprised of 50nm-thick alumina tubes that are arranged into periodic 5um-wide octet-truss unit cells, with and without pre-fabricated through-thickness center notches oriented at different angles to the loading direction. In-situ uniaxial tensile experiments revealed that for all notch orientations, failure always initiated at the notch root, as would be in a monolithic material, with the tube walls at nodal junctions fracturing first, followed by instantaneous crack propagation through the discrete lattice architecture along nodal planes orthogonal to the loading direction. Measured tensile strength of 27.4 MPa was highest for the unnotched samples and decreased systematically with the increase of notch orientation to its minimum of 7.2 MPa in the orthogonally-notched samples. We found the specific tensile strength of hollow-tube octet alumina nanolattices to be 4 times higher than what has been reported for architected and bulk materials at similar low densities. Three-dimensional finite element simulations closely reproduce the observed failure mechanism and trends in failure strength. A direct comparison is made between the experimental measurements, finite element simulations, and predictions of linear elastic fracture mechanics for a self-similar monolithic tensile samples made out of an ideally-brittle solid. Results are in good agreement with the scaling of failure strengths from classical mode I fracture criteria and suggest that trajectory of crack propagation can be adequately explained by considering the connectivity of the lattice architecture. These findings imply that the continuum nature of nano-architected materials offers predictability of failure stresses, which helps enable the development of advanced materials through informed architectural design." }, { "name": "Newman, Matthew Gregory", "degree": "PhD", "year": "2018", "title": "On the Kinetics of Materials of Geophysical Interest", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282017-105838669", "creators": [ { "name": { "family": "Newman", "given": "Matthew Gregory" }, "id": "Newman-Matthew-Gregory", "orcid": "0000-0003-2752-0121", "display_name": "Newman, Matthew Gregory" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kraus", "given": "Richard" }, "id": "Kraus-Richard", "role": "member", "display_name": "Kraus, Richard" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9319T35", "abstract": "Knowledge of the equation of state and phase diagram of magnesium silicates and light iron alloys is important for understanding the thermal evolution and interior structure of terrestrial planets. Dynamic compression techniques are the primary viable methods to create the temperature and pressure conditions that are relevant to Earth and super-Earth (1-10 Earth mass) sized planets. However, due to the kinetic constraints imposed by the timescale of dynamic compression experiments, the nature of the state within the dynamically compressed sample (whether equilibrium or metastable) is uncertain. Here, we present the results of a series of dynamic compression experiments performed on both laser driven compression and plate impact facilities to study the nanosecond to microsecond response of forsterite and iron silicide. In situ x-ray diffraction measurements are used to probe the crystal structure of solid phases and test for the presence of melt, from which we investigate the decomposition of forsterite and iron silicide into compositionally distinct phases at high pressure. For forsterite, we do not observe chemical segregation in the solid phase, however the presence of melt speeds up the kinetics and allows chemical segregation to occur on nanosecond timescales. For iron silicide, our results show a textured solid phase upon shock compression to pressures ranging from 166(14) to 282(24) GPa consistent with cubic and hcp structures in coexistence. Above 313(29) GPa, the intense and textured solid diffraction peaks give way to a diffuse scattering feature and loss of texture, consistent with melting along the Hugoniot." }, { "name": "Rosenberg, Kevin Thomas", "degree": "PhD", "year": "2018", "title": "Resolvent-Based Modeling of Flows in a Channel", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-114927289", "creators": [ { "name": { "family": "Rosenberg", "given": "Kevin Thomas" }, "id": "Rosenberg-Kevin-Thomas", "orcid": "0000-0001-6101-3823", "display_name": "Rosenberg, Kevin Thomas" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PHDW-Z389", "abstract": "This thesis concerns the continued development of the resolvent framework (McKeon and Sharma, 2010) to model wall-bounded turbulent flows. Herein, we introduce novel modifications and extensions of the framework to improve the compact representation of flows in a channel. In particular, inspired by ideas rooted in classical linear stability theory, we introduce a decomposition of the velocity field into Orr-Sommerfeld (OS) and Squire (SQ) modes in a nonlinear context via the resolvent operator. We demonstrate through the analysis of a number of exact coherent states (ECS) of the Navier-Stokes equations (NSE) in Couette and Poiseuille flow that this decomposition offers a significant improvement in the low-dimensional representation of these flows. With this efficient basis, we are able to develop through the notion of interaction coefficients a method to compute accurate, self-consistent solutions of the NSE with knowledge of only the mean velocity profile. We also highlight the role of the solenoidal component of the nonlinear forcing in the solution process. In addition, the resolvent framework is extended to the analysis of 2D/3C flows. This approach, again applied to ECS, sheds light on the underlying scale interactions which sustain these solutions. Notably, it reveals that lower branch ECS can be effectively described in their entirety with a single resolvent response mode. This discovery is leveraged to construct a method to compute accurate approximations of ECS starting from a laminar profile using a single parameter model. This thesis also utilizes a constant time-step DNS of a turbulent channel to perform a direct characterization of the nonlinear forcing terms. We compute power spectra and confirm that the nonlinear forcing has a non-trivial signature in the wavenumber-frequency domain. We also compute and analyze spectra for the OS/SQ vorticity and discuss the potential benefit of this decomposition technique to the study of fully turbulent flows as well.
" }, { "name": "Sakovsky, Maria", "degree": "PhD", "year": "2018", "title": "Design and Characterization of Dual-Matrix Composite Deployable Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-165415595", "creators": [ { "name": { "family": "Sakovsky", "given": "Maria" }, "id": "Sakovsky-Maria", "orcid": "0000-0002-3683-8505", "display_name": "Sakovsky, Maria" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/CNPY-A883", "abstract": "Dual-matrix composites are a promising approach to deployable high performance antennas for small satellites. Several techniques exist for packaging large antenna apertures. Assemblies of rigid bars and hinges obtain high deployed precision but are heavy and mechanically complex. Thin shell structures deployed using stored strain energy are a lightweight alternative offering efficient packaging but reduced surface precision. Moreover, elastomer composites shells attain even smaller fold radii upon packaging but are limited by the deployed structure's stiffness. Dual-matrix composites combine the advantages of several of these approaches to enable larger antenna apertures. They consist of a continuous woven fiber reinforcement with an elastomer matrix embedded in localized hinge regions and a stiff epoxy resin elsewhere. Such structures can achieve small fold radii, are strain energy deployable, and promise high deployed stiffness.
\r\n\r\nThis research demonstrates the capabilities of the proposed dual-matrix structures through direct comparison to existing antenna designs. Analytic scaling relations between structural and electromagnetic performance of various deployable antenna designs are developed. These are used to rapidly predict achievable antenna performance as a function of a common set of antenna geometric parameters. Plotting of this data on a coordinated set of 2D design plots enables the direct comparison of antenna concepts and the selection of specific designs meeting all requirements. This methodology was used to design a deployable dual-matrix composite conical log spiral (CLS) antenna for use on CubeSats which outperformed existing off-the-shelf designs through higher gain, higher bandwidth, and more efficient packaging.
\r\n\r\nStarting from this initial design, the antenna is tuned to maximize performance and an assembly including the CubeSat, dual-matrix antenna, dual-matrix hinge for antenna deployment, and a flexible feeding network is developed. All portions of the assembly are prototyped and tested. The antenna electromagnetic performance is predicted using ANSYS HFSS and verified by testing in an anaechoic chamber with antenna gains predicted within 4% of measured values. Structural stiffness is characterized through the antenna's fundamental frequency with simulated performance in the Abaqus finite element software within 6% of measured values. Comparison of antenna performance before and after packaging and deployment shows the structural frequency, antenna gain, and antenna bandwidth are unaffected by folding, demonstrating that dual-matrix composites are appropriate for use as deployable structures.
\r\n\r\nTechniques for the quasi-static deployment of dual-matrix composites are presented. An analytic minimum energy method, which accounts for fiber microbuckling in regions of high curvature, is used to predict the folded shape and deployment moments of a dual-matrix hinge. The model shows excellent agreement with LS-Dyna finite element simulations for a variety of material properties. Comparison with experimental characterization demonstrates the capability of the models to predict folded radii and deployment moment of a prototype hinge withing 5% of measured values. The developed analysis tool-set enables a design of deployment restraints and mechanisms.
\r\n\r\nThe woven elastomer composites forming the fold regions in dual-matrix composites have been the subject of very few studies. Existing methods for predicting the stiffness of woven epoxy composites are applied to elastomer composites here and show poor agreement with measurements. A novel approach is presented for the prediction of tow stiffness in elastomer composites using a semi-empirical approach. The reinforcing efficiency parameter in the well-established Halpin-Tsai model for tow homogenization is estimated using experimental measurements of stiffnesses of several laminates. It is shown that for elastomer composites, the parameter values are orders of magnitude higher than the heuristic values used for epoxy composites. The method is used to predict the stiffness of woven epoxy and elastomer composites making up the dual-matrix structures studied in this work showing agreement withing 15% of experimental measurements for arbitrary layups. The method is extended to the prediction of viscoelastic behavior of dual-matrix structures to enable investigation of deployment reliability after long storage times.
" }, { "name": "Schlup, Jason Robert", "degree": "PhD", "year": "2018", "title": "Numerical Investigations of Transport and Chemistry Modeling for Lean Premixed Hydrogen Combustion", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-170312588", "creators": [ { "name": { "family": "Schlup", "given": "Jason Robert" }, "id": "Schlup-Jason-Robert", "orcid": "0000-0002-3121-3477", "display_name": "Schlup, Jason Robert" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KFN6-7K54", "abstract": "The use of hydrogen as a fuel for power generation applications has been suggested as an additive to, or replacement of, hydrocarbon fuels. The safety of hydrogen combustion has also received recent attention due to nuclear power plant disasters and the rise of hydrogen refuelling stations. In these uses and scenarios, lean hydrogen--air flames are prone to thermo-diffusive instabilities which can be dangerous to equipment and personnel. These instabilities are heavily influenced by two mechanisms: transport properties (e.g., diffusion) and chemical species production rates. This thesis investigates lean premixed hydrogen combustion using direct numerical simulations. A wide range of flame configurations are considered, spanning one-dimensional steady configurations to three-dimensional unsteady laminar and turbulent flames with high curvature. In particular, the two controlling mechanisms of thermo-diffusive instabilities are carefully investigated.
\r\n\t\r\nThe effects of transport properties, in particular the importance of thermal diffusion in these mixtures, are quantified through global and local evaluations. Thermal diffusion is found to change flame speeds in one-dimensional flat flames, and also modify species profiles due to the increased diffusivity of light reactants. The impact of thermal diffusion is greatly enhanced in the presence of flame curvature, resulting in higher flame speeds (20% to 30% for two- and three-dimensional laminar and turbulent flames), fuel consumption, and flame surface area relative to simulations neglecting thermal diffusion. The mixture-averaged thermal diffusion model proposed by Chapman and Cowling (1970) is found to accurately reproduce global and local flame statistics (including enhanced burning and local extinction) computed using multicomponent transport at significantly reduced costs. Further cost reductions of the mixture-averaged thermal diffusion method are undertaken, and a new model is developed with constant computational requirements for large (~100 species) chemical models. The resulting reduced thermal diffusion model additionally improves upon the accuracy of the mixture-averaged thermal diffusion technique.
\r\n\t\r\nThe effects of fluctuating chemical source terms on flame instabilities are then investigated using tabulated chemistry. One-dimensional unstretched flames including non-equal diffusion and thermal diffusion are incorporated into a chemistry table. This table successfully captures the interaction of differential diffusion and flame curvature. The chemistry tabulation approach is applied to a similar set of flame configurations, and accurate predictions of global and local statistics are found. The tabulated chemistry method reproduces flame curvature, local enhanced burning, and local extinction of unstable flames using one-dimensional, flat, burning flames in its construction. The proposed reduced-order thermal diffusion and chemistry tabulation models significantly reduce computational costs while simultaneously including physical properties necessary to predict lean premixed hydrogen--air flame instabilities.
" }, { "name": "Symon, Sean Pearson", "degree": "PhD", "year": "2018", "title": "Reconstruction and Estimation of Flows Using Resolvent Analysis and Data-Assimilation", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-181049042", "creators": [ { "name": { "family": "Symon", "given": "Sean Pearson" }, "id": "Symon-Sean-Pearson", "orcid": "0000-0001-9085-0778", "display_name": "Symon, Sean Pearson" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B4K7-K876", "abstract": "A flow reconstruction methodology is presented for incompressible, statistically stationary flows using resolvent analysis and data-assimilation. The only inputs necessary for the procedure are a rough approximation of the mean profile and a single time-resolved measurement. The objective is to estimate both the mean and fluctuating states of experimental flows with limited measurements which do not include pressure. The input data may be incomplete, in the sense that measurements near a body are difficult to obtain with techniques such as particle image velocimetry (PIV), or contaminated by noise. The tools developed in this thesis are capable of filling in missing data and reducing the amount of measurement noise by leveraging the governing equations. The reconstructed flow is capable of estimating fluctuations where time-resolved data are not available and solving the flow on larger domains where the mean profile is not known.
\r\n\r\nThe first part of the thesis focuses on how resolvent analysis of the mean flow selects amplification mechanisms. Eigenspectra and pseudospectra of the mean linear Navier-Stokes (LNS) operator are used to characterize amplification mechanisms in flows where linear mechanisms are important. The real parts of the eigenvalues are responsible for resonant amplification and the resolvent operator is low-rank when the eigenvalues are sufficiently separated in the spectrum. Two test cases are studied: low Reynolds number cylinder flow and turbulent channel flow. The latter is studied by considering well-known turbulent structures while the former contains a marginally stable eigenvalue which drowns out the effect of other eigenvalues over a large range of temporal frequencies. There is a geometric manifestation of this dominant mode in the mean profile, suggesting that it leaves a significant footprint on the time-averaged flow that the resolvent can identify. The resolvent does not provide an efficient basis at temporal frequencies where there is no separation of singular values. It can still be leveraged, nevertheless, to identify coherent structures in the flow by approximating the nonlinear forcing from the interaction of highly amplified coherent structures.
\r\n\r\nThe second part of the thesis extends the framework of Foures et al. (2014), who data-assimilated the mean cylinder wake at very low Reynolds numbers. The contributions presented here are to assess the minimum domain for successfully reconstructing Reynolds stress gradients, modifying the algorithm to assimilate mean pressure, determining whether weighting input measurements contributes to improved performance, and adapting the method to experimental data at higher Reynolds numbers. The results from data-assimilating the mean cylinder wake at low Reynolds numbers suggest that the measurement domain needs to coincide with the spatial support of the Reynolds stress gradients while point weighting has a minimal impact on the performance. Finally, a smoothing procedure adapted from Foures et al. (2014) is proposed to cope with data-assimilating an experimental mean profile obtained from PIV data. The data-assimilated mean profiles for an idealized airfoil and NACA 0018 airfoil are solved on a large domain making the mean profile suitable for global resolvent analysis. Data-assimilation is also able to fill in missing or unreliable vectors near the airfoil surface.
\r\n\r\nThe final piece of the thesis is to synthesize the knowledge and techniques developed in the first two parts to reconstruct the experimental flow around a NACA 0018 airfoil. Preliminary results are presented for the case where \u03b1 = 0\u00b0 and Re = 10250. The mean profile is data-assimilated and used as an input to resolvent analysis to educe coherent structures in the flow. The resolvent operator for non- amplified temporal frequencies is forced by an approximated nonlinear forcing. The amplitude and phase of the modes are obtained from the discrete Fourier-transform of a time-resolved probe point measurement. The final reconstruction contains less measurement noise compared to the PIV snapshots and obeys the incompressible Navier-Stokes equations (NSE). The thesis concludes with a discussion of how elements of this methodology can be incorporated into the development of estimators for turbulent flows at high Reynolds numbers.
" }, { "name": "Delapierre, M\u00e9lanie", "degree": "PhD", "year": "2017", "title": "Dynamics and Stability of Spinning Membranes", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222017-093718571", "creators": [ { "name": { "family": "Delapierre", "given": "M\u00e9lanie" }, "id": "Delapierre-M\u00e9lanie", "display_name": "Delapierre, M\u00e9lanie" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z9HT2MC8", "abstract": "Many future space missions require large structures subject to stringent shape accuracy requirements. Spinning membrane-like structures are a cost effective solution for these applications. However, any small deflection of a spinning structure, due to maneuvers or solar radiation pressure, leads to geometrically nonlinear effects on its stability and dynamics. Accurate experiments, simulation tools, and models are required to ensure that buckling and vibrations will not affect mission objectives.
\r\n \r\nWe first focus on the influence of transverse uniform loads on the dynamics and stability of spinning isotropic uniform membranes. A transverse uniform load models the effect of a transverse light beam on flat membranes with small deflections. We present experimental measurements of the angular velocities at which various membranes become wrinkled, and of the wrinkling mode transitions that occur upon spin down. A theoretical formulation to predict the critical angular velocities and critical transverse loads is also presented. The transition between bending dominated and in-plane dominated behavior is identified, and the wrinkling modes are obtained. Next, deflected, non-buckled membranes are further analyzed. Axisymmetric nonlinear oscillations are studied analytically, and a reduced-order model is presented. This model predicts that the deflection of the membrane introduces a hardening behavior at low angular velocities and a softening behavior at high angular velocities. This model is validated through experiments and FEM simulations.
\r\n \r\nThen, we relax the assumption of uniform membranes loaded by transverse light beams. We present an Abaqus model of foldable membranes and show that for particular types of hinges and at high angular velocities, these structures behave like uniform membranes. Finally, we derive an FEM model for solar radiation pressure for quadrilateral surface elements and 3D problems and present its implementation in Abaqus. We show that this follower load introduces an unsymmetric stiffness matrix and that instabilities known as solarelastic flutter can develop. This new FEM capability enables equilibrium and frequency-based stability analyses for a wide range of spacecraft.
" }, { "name": "Hirsch, Damian George", "degree": "PhD", "year": "2017", "title": "An Experimental and Theoretical Study of Active Flow Control", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092017-112408552", "creators": [ { "name": { "family": "Hirsch", "given": "Damian George" }, "id": "Hirsch-Damian-George", "display_name": "Hirsch, Damian George" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Wygnanski", "given": "Israel J." }, "id": "Wygnanski-I-J", "orcid": "0009-0001-5711-7029", "role": "member", "display_name": "Wygnanski, Israel J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9N014KR", "abstract": "The accelerating growth of environmental awareness has not stopped at the aerospace industry. The need for greener and more efficient airplanes threatens to outpace the flow of new technology. This has ignited development in several fields, one of which is active flow control (AFC). Active flow control has quickly proven its tremendous potential for real applications. Even though the roots of this technology date back a century, we still lack fundamental understanding. This thesis combines both modern and traditional approaches to lay out a new foundation for future research.
\r\n\r\nThe thesis first focuses on the rising stars of active flow control: the so-called fluidic oscillators or sweeping jet actuators. These devices consist of simple, rigid internal geometries that create a sweeping output jet motion. The fluid dynamic interactions with the internal geometry are studied in detail using high-speed Schlieren imaging. Additionally, the influence of adjacent sweeping jets is investigated. It is revealed that the internal driving mechanism is far stronger than the fluid dynamic interactions at the outlet, resulting in a completely independent jet behavior.
\r\n\r\nNext, a high-lift airfoil design is combined with active flow control, and an extensive wind tunnel study is carried out. It is shown that for the given wing design active flow control leads to much higher lift benefits when applied to the trailing edge. Applied to the leading edge active flow control disrupts the vortex lift of the high-lift airfoil, resulting in a deleterious lift effect; however, it shows potential for pitch moment control. This project also underlines the advantages of jet-like active flow control over steady blowing actuation at limited available mass flow rates.
\r\n\r\nThe momentum input coefficient as an important parameter in active flow control is discussed in detail, identifying common misconceptions and difficulties that hinder its proper calculation. An innovative, much simpler approach is introduced. This allows a detailed study of the underlying physics, unveiling unknown limitations of active flow control. The approach is then used as a model to derive the novel concept of thermal active flow control. Experimental studies, including a wind tunnel test campaign, are performed to confirm the viability of the concept for practical applications.
\r\n\r\nThe new calculation method of the input momentum coefficient emphasizes its weakness as a similarity parameter in active flow control studies. The extended mass flow coefficient is introduced as a new parameter. It is shown that it can overcome the deficiencies of the input momentum coefficient without suffering other disadvantages. Its further investigation leads to a deeper understanding of active flow control, which is supported by PIV experiments. The main findings of this investigation divide active flow control into three different \"states\": boundary layer thickening, separation control, and supercirculation.
" }, { "name": "Hogstrom, Kristina", "degree": "PhD", "year": "2017", "title": "Robotically Assembled Space Telescopes with Deployable Modules: Concepts and Design Methodologies", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182016-100030713", "creators": [ { "name": { "family": "Hogstrom", "given": "Kristina" }, "id": "Hogstrom-Kristina", "display_name": "Hogstrom, Kristina" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "space" ], "doi": "10.7907/Z9T151NT", "abstract": "This thesis first presents a novel architecture for robotically assembled optical telescopes with apertures between 20 m and 100 m, that utilizes only currently available technology. In this architecture, the primary mirror consists of two layers: a reflective layer and a truss backplane layer. The reflective layer is divided into mirror modules, or groups of mirror segments and actuators. The truss backplane layer is divided into truss modules that fold compactly for launch and are deployed in space by the robot. In this thesis, the design methodology of the mirror modules and truss modules is detailed. The ability of the designed truss layer to maintain precision requirements in the presence of typical space environment loads is demonstrated.
\r\n \r\nThis architecture requires the deployment of many truss modules, and thus the deployment must be reliable despite errors introduced during manufacturing. In this thesis, a new simulation-based toolkit for estimating deployment reliability is described, including the experimental validation of the deployment simulation and the Monte Carlo-style method for repeating deployment simulations with different distributions of random fabrication errors to statistically estimate reliability. Using the toolkit, a set of reliability trade studies are then presented, revealing how different types of errors and design parameters affect reliability. Finally, the manufacturing tolerances and design modifications required to ensure high reliability are proposed.
\r\n \r\nEven if all modules deploy successfully, fabrication errors will still be present and may affect the assembly process. In this thesis, a new simulation method is presented that can model the step-by-step assembly of flexible modules with errors. The method is used to reveal that overall shape errors grow with the number of connections, resulting in significantly decreased surface precision and large-scale deformations from the nominal backplane shape as the size of the backplane increases. The misalignment at each individual connection does not increase as the backplane increases, but can still be much larger than the applied manufacturing tolerances simply due to random combinations. A simple design for the interconnects between modules is then tested, with simulation results demonstrating that it is unlikely to fully engage when the expected errors are present. With this information, a requirement on the complexity of the interconnect design is inferred, and potential modifications that may increase its efficacy are suggested.
" }, { "name": "Hufstedler, Esteban Antonio Lemus", "degree": "PhD", "year": "2017", "title": "Experimental Generation and Modeling of Vortical Gusts and Their Interactions with an Airfoil", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232017-111820349", "creators": [ { "name": { "family": "Hufstedler", "given": "Esteban Antonio Lemus" }, "id": "Hufstedler-Esteban-Antonio-Lemus", "orcid": "0000-0001-7162-920X", "display_name": "Hufstedler, Esteban Antonio Lemus" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Q52MN5", "abstract": "This thesis examines two methods of vortical gust generation and the interaction between these gusts and an airfoil. These flows were studied with both experiments at a Reynolds number of 20,000 and with potential-flow based simulations.
\r\n\r\nThe standard method of generating a vortical gust has been to rapidly pitch an airfoil. A novel approach is presented: heaving a plate across the tunnel, and changing direction rapidly to release a vortex. This method is motivated by the desire to limit a test article's exposure to the wake of the gust generator by moving it to the side of the tunnel.
\r\n\r\nA series of potential flow models were used to examine these flows: steady and unsteady thin airfoil theory, an extension of Tchieu and Leonard's unsteady airfoil model, and an unsteady vortex panel method.
\r\n\r\nExperiments characterized the generated gusts and verified that the strength of the shed vortices approximately matched the theoretical predictions. The inviscid simulations were unable to predict viscous effects like the wakes of the generators. The pitching airfoil resulted in a persistent wake in the test section, whereas the wake of the heaving plate only temporarily disturbed the flow.
\r\n\r\nThe vortex-wing interaction was examined using both mechanisms. When the wake of the generator was far from the wing, the unsteady simulations provided reasonable estimates for the early variation in lift. This demonstrated that the initial lift peak is due to inviscid effects. Each of the potential flow methods with wake models provided reasonable estimates of this lift. The simplicity of the unsteady thin airfoil theory model recommends its use for examining early vortex-wing interactions.
\r\n\r\nWith the test article mounted at the midline of the tunnel, the wakes had substantial effects when the pitching generator was near the midline of the tunnel, or when the heaving plate passed the midline. The simulations were not able to capture the effects of the wakes or predict the effects of the airfoil's angle of attack. This had the largest effect on the timescale of the post-gust approach to the final forces. With the airfoil at \u03b1=0\u00b0, this was 5-10 convective time units, which is characteristic of attached flows. The airfoil at \u03b1=10\u00b0 needed double the time to approach its final state after perturbations due to its separated flow. The heaving plate's withdrawal allowed for measurement of the resumption of vortex shedding, which was impossible with the pitching airfoil's persistent wake.
" }, { "name": "Nadkarni, Neel P.", "degree": "PhD", "year": "2017", "title": "Nonlinear Dynamics of Transition Waves in Multi-Stable Discrete and Continuous Media", "advisor": "Kochmann, Dennis M.; Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132017-035026894", "creators": [ { "name": { "family": "Nadkarni", "given": "Neel P." }, "id": "Nadkarni-Neel-P", "orcid": "0000-0002-4311-2817", "display_name": "Nadkarni, Neel P." } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Abeyaratne", "given": "Rohan" }, "id": "Abeyaratne-R", "role": "member", "display_name": "Abeyaratne, Rohan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9DR2SG2", "abstract": "The concept of phase transitions, i.e., switching between two or more different equilibrium states of a system, is commonly encountered in many physical, chemical and biological phenomena. The exact mechanism of this switching is a highly nonlinear dynamical process that is accommodated by the propagation of a localized wave. The characteristics of the nonlinear wave such as its profile, velocity, energy, and width of transition are governed by the type and specifics of the system that it is propagating through which may be conservative, dissipative, or diffusive in nature. The goal of this thesis is to develop a fundamental understanding of the dynamics of such processes in general nonlinear systems capable of undergoing phase transitions and the application of new theories to elucidate the kinetic and energetic properties of transition waves in different scenarios. In conservative systems, we show that there are three different modes of stable wave propagation that we analytically solve for and validate computationally. In contrast, dissipative and diffusive systems allow the stable propagation of only the strongly nonlinear kink mode whose kinetic energy and propagation velocity are linked through a linear relation. We further validate our results in dissipative systems experimentally by fabricating and testing a strongly nonlinear lattice and show that transition waves are unidirectional in nature, as predicted by theory. Finally, as an application, we devise a strategy of using the physics of dissipative phase transitions to propagate stable mechanical signals in highly dissipative media such as soft polymers which effectively damp out small-amplitude linear waves." }, { "name": "Palm, Steven Leslie", "degree": "PhD", "year": "2017", "title": "Thermo-Acoustic Coupling and Dynamic Response of a Premixed Methane-Air Flame", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302017-214955280", "creators": [ { "name": { "family": "Palm", "given": "Steven Leslie" }, "id": "Palm-Steven-Leslie", "orcid": "0000-0003-3095-0368", "display_name": "Palm, Steven Leslie" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Yang", "given": "Vigor" }, "id": "Yang-Vigor", "role": "member", "display_name": "Yang, Vigor" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9V12309", "abstract": "The work herein generally applies to the problem of combustion instability. Combustion instabilities first arose in engineering practice in the 1940s when they were experienced during the development of solid and liquid propellant rocket engines. Later, similar problems arose in gas turbine combustors and afterburners. However, the earliest technical case of the phenomenon dates back to Rijke in 1859 with his \"singing\" tube.
\r\n\r\nThe presented work focuses on the study of a simple, stagnation plane stabilized, laminar, flat-flame burner. In particular the dynamic response of the burner is examined under excitation by a driven acoustic field. After characterization of the burner\u2019s operational range, the response of the system is measured from 20 Hz to nearly 2000 Hz over the span of operating parameters using an optically filtered PMT and lens combination. A library of the collected and reduced data is generated.
\r\n\r\nA deeper investigation of the burner dynamics at a given reference operating condition is performed using phase-resolved PLIF. Fluctuations in the spatial distributions of the LIF signals for several target species (OH, CH, CH2O) under acoustic forcing are measured. In addition, visualization of the unsteady reactant flow using precision acetone seeding and PLIF at 277 nm is performed. Subsequent cinematographic sequences are produced along with spatially resolved plots of the combustion response function and the forced Rayleigh index for numerous drive frequencies. A library of the collected and reduced data is assembled.
\r\n\r\nAnalysis of the collected data reveals two principal mechanisms contributing to the unsteady response of the flame. Structure development in (and subsequent convention along) the unsteady shear layer of the laminar jet dominates the response at the outer reaches of the flame. The inner region of the flame is driven largely by the Helmholtz response of the burner nozzle cavity. These two operations mutually contribute to produce the general shape of the combustion response curve. Ultimately, the data is used to construct a simplified model for the combustion response function. The model is enhanced with two additional revisions guided by the improved understanding of the mechanisms involved.
\r\n\r\nThe document ends with numerous appendices describing, in detail, the equipment used, much of which was fabricated specifically for this work. These appendices, in combination with information presented in the chapters, provide substantial detail regarding the experimental configuration and operating conditions. Great effort was made to provide the necessary information to allow replication of the experiments as well as to support future modeling endeavors as a validation dataset.
\r\n" }, { "name": "Roh, Chris", "degree": "PhD", "year": "2017", "title": "Hydrodynamics of Insects. Part 1. Jetting of the Dragonfly Larvae. Part 2. Honeybee at the Air-water Interface: Surfing with the Capillary Wave", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-183218154", "creators": [ { "name": { "family": "Roh", "given": "Chris" }, "id": "Roh-Chris", "orcid": "0000-0002-5681-0040", "display_name": "Roh, Chris" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "chair", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z97P8WFW", "abstract": "This thesis presents the study on the hydrodynamics of two insects commonly known for their aerial adaptation: the dragonfly and the honeybee.
\r\n\r\nPart 1: Anisopteran dragonflies live underwater in their larval stages. The key factor for their aquatic adaptation is the modified hindgut chamber that is used as a pump. The two main functions of this biological pump are jet propulsion and respiration. Both functions involve jetting and refilling of the chamber through an orifice guard by a tri-leaflet anal valve. Despite it being a unique machinery among insects, associated hydrodynamic studies are limited thus far. In the first part of this thesis, various aspects of the hydrodynamics of the dragonfly larvae\u2019s ventilatory flow are studied. The flow visualization showed that the respiratory flow is laminar but the propulsion flow is turbulent. The hydrodynamic force analysis showed that jetting and refilling phase forces are dominated by quasi-steady momentum flux and unsteady acceleration, respectively. Finally, simultaneous measurement of the anal valve kinematics and jet flow showed that the larvae could influence the direction and magnitude of the jet by controlling the anal valve leaflets.
\r\n\r\nPart 2: Water-collecting honeybees often fall onto water surfaces. However, bees trapped by the \u201cstickiness\u201d of the water can propel by vibrating their wings, often making it to shore. In the second part of this thesis, the honeybee\u2019s propulsion mechanisms at the air\u2013water interface is studied. The result shows that the bees can achieve three body-lengths per second propulsion speed. High-speed video of their wing motion shows that honeybee\u2019s propulsion involves pulling blobs of water with the underside of the wing, while pushing on a surface wave with its trailing edge. This propulsion mechanism resembles surfing on a self-generated capillary wave. Moreover, their wing vibration generates complicated surface waves and flows, below which the deeper water flow shows a single jet stream. From the wave and flow field measurements, the average force imparted to the surrounding fluid is estimated and compared to the average force calculated from the bee\u2019s body motion. The resulting average forces are of the same order of magnitude, which means that generating wave and flow are both important for the bee\u2019s propulsion.
" }, { "name": "Sternberger, Zachary Martin Murphy", "degree": "PhD", "year": "2017", "title": "Determining Strength of Materials Under Dynamic Loading Conditions Using Hydrodynamic Instabilities", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182017-095600418", "creators": [ { "name": { "family": "Sternberger", "given": "Zachary Martin Murphy" }, "id": "Sternberger-Zachary-Martin-Murphy", "orcid": "0000-0002-7612-673X", "display_name": "Sternberger, Zachary Martin Murphy" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9N877T5", "abstract": "Hydrodynamic instability experiments allow access to material properties at extreme conditions where the pressure exceeds 100 GPa and the strain rate exceeds 106 1/s. Laser ablation dynamically loads a sample, causing a manufactured initial perturbation to grow due to hydrodynamic instability. The instability growth rate depends on the strength of the sample. Material strength can then be inferred from a measurement of the instability growth. Past experiments relied on in-flight diagnostics to measure the amplitude growth, which are not available at all facilities.
\r\n\r\nRecovery instability experiments, where the initial and final amplitude of the instability are measured before and after the sample is dynamically loaded, obviate the need for in-flight diagnostics. Recovery targets containing copper and tantalum samples coined with 2D (hill and valley) and 3D (eggcrate) initial perturbations were dynamically loaded using the Janus laser at the Jupiter Laser Facility, Lawrence Livermore National Laboratory. The energy of the laser pulse was varied to cover a range of conditions in the dynamically compressed sample with pressures in the range 10 GPa to 150 GPa and strain rates in the range 105 1/s to 108 1/s.
\r\n\r\nThe coupling of laser energy into a loading wave was studied with a combination of laser-matter interaction simulations (Hyades) and velocity interferometry data (VISAR). Laser ablation of the recovery targets generated a blast wave, loading the coined initial perturbations with a shock wave followed by a release wave. Different ablator materials and variations in the amount of laser energy deposited in the ablator lead to variations in the loading wave and consequently variations in instability growth.
\r\n\r\nThe growth of the initial perturbation amplitude from initial to final conditions was studied with hydrocode simulations (CTH). During dynamic loading of the sample, the shock wave caused amplitude growth due to hydrodynamic instability. The release wave accelerated the perturbed interface and slowed amplitude growth, in some cases reversing growth.
\r\n\r\nThe sensitivity of the instability growth to coarse changes in the strength model was demonstrated. However, uncertainty in modeling the laser ablation loading prevented a definitive comparison between simulation and experiment.
" }, { "name": "Summy, Dustin Phillip", "degree": "PhD", "year": "2017", "title": "Maximum Entropy Reconstruction for Gas Dynamics", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262017-215132894", "creators": [ { "name": { "family": "Summy", "given": "Dustin Phillip" }, "id": "Summy-Dustin-Phillip", "orcid": "0000-0002-6383-0621", "display_name": "Summy, Dustin Phillip" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9GT5K7W", "abstract": "We present a method for selecting a unique and natural probability distribution function (PDF) which satisfies a given number of known moments and apply it for use in the closure of moment-based schemes for approximately solving the Boltzmann equation in gas dynamics.
\r\n\r\nThe method used for determining the PDF is the Maximum Entropy Reconstruction (MER) procedure, which determines the PDF with maximum entropy which satisfies a given set of constraining moments. For the five-moment truncated Hamburger moment problem in one dimension, the MER takes the form of the exponential of a quartic polynomial. This implies a bimodal structure which gives rise to a small-amplitude packet of PDF-density sitting quite far from the mean. This is referred to as the Itinerant Moment Packet (IMP). It is shown by asymptotic analysis that the IMP gives rise to a solution that, in the space of constraining moments, is singular along a line emanating from, but not including, the point representing thermodynamic equilibrium. We use this analysis of the IMP to develop a numerical regularization of the MER, creating a procedure we call the Hybrid MER (HMER). Compared with the MER, the HMER is a significant improvement in terms of robustness and efficiency while preserving accuracy in its prediction of other important distribution features, such as higher order moments.
\r\n\r\nWe apply the one-dimensional HMER to close a fourth order moment system derived from the Boltzmann equation by using a specific set of moment constraints which allow the full, three-dimensional velocity PDF to be treated as a product of three independent, one-dimensional PDFs. From this system, we extract solutions to the problem of spatially homogeneous relaxation and find excellent agreement with a standard method of solution. We further apply this method to the problem of computing the profile within a normal shock wave, and find that solutions exist only within a finite shock Mach number interval. We examine the structure of this solution and find that it has interesting behavior connected to the singularity of the MER and the IMP. Comparison is made to standard solution methods. It is determined that the use of the MER in gas dynamics remains uncertain and possible avenues for further progress are discussed.
" }, { "name": "Wilson, Lee L.", "degree": "PhD", "year": "2017", "title": "Analysis of Packaging and Deployment of Ultralight Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242017-230338904", "creators": [ { "name": { "family": "Wilson", "given": "Lee L." }, "id": "Wilson-Lee-L", "orcid": "0000-0002-5865-9903", "display_name": "Wilson, Lee L." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "space" ], "doi": "10.7907/Z9B27S96", "abstract": "This thesis presents a new approach to modeling in finite element analysis (FEA) creased thin-film sheets such as those used for drag sails, as well as modeling the packaging behavior of coilable deployable booms. This is highly advantageous because these deployable space structures are challenging to test on the ground due to their lightweight nature and the effects of gravity and air resistance. Such structures are utilized in the space industry due to their low mass and ability to be packaged into a small volume during their launch into space.
\r\n\r\nIt is shown that removing the crease bending stiffness in creased sheets still allows the deployment behavior of a benchmark problem to be captured, including deployment forces and equilibrium configurations. In addition, folding creased sheets from a flat state into a packaged configuration can result in crease crumpling and excessive wrinkling. To avoid this the Momentless Crease Force Folding (MCFF) technique is developed.
\r\n\r\nFurther presented is the behavior of tape springs and Tubular Rollable and Coilable (TRAC) booms when coiled to radii greater than their natural bend radius. Under these conditions the booms can form multiple localized folds which may jam during boom deployment. Understanding this behavior is important for extending the use of these booms to large scale space structures such as orbital solar power stations.
\r\n\r\nA useful analytical model is developed determining when the localized folds in a tape spring will bifurcate and is verified against simulation results. Additionally, a numerical model of the wrapping an isotropic tape spring around a hub with a radius greater than the localized fold radii is validated against physical experiments. This model is used to predict trends in the force required to fully wrap a tape spring around a given hub radii.
\r\n\r\nFinally, when examining the coiling and uncoiling behavior of TRAC booms it was found that the tension force required to keep a TRAC boom tightly coiled is significantly less than the force required to initially coil the boom.
" }, { "name": "Araya, Daniel Borsodi", "degree": "PhD", "year": "2016", "title": "Aerodynamics of Vertical-Axis Wind Turbines in Full-Scale and Laboratory-Scale Experiments", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022015-023535926", "creators": [ { "name": { "family": "Araya", "given": "Daniel Borsodi" }, "id": "Araya-Daniel-Borsodi", "display_name": "Araya, Daniel Borsodi" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9VD6WC2 ", "abstract": "Within a wind farm, multiple turbine wakes can interact and have a substantial effect on the overall power production. This makes an understanding of the wake recovery process critically important to optimizing wind farm efficiency. Vertical-axis wind turbines (VAWTs) exhibit features that are amenable to dramatically improving this efficiency. However, the physics of the flow around VAWTs is not well understood, especially as it pertains to wake interactions, and it is the goal of this thesis to partially fill this void. This objective is approached from two broadly different perspectives: a low-order view of wind farm aerodynamics, and a detailed experimental analysis of the VAWT wake.
\r\n\r\nOne of the contributions of this thesis is the development of a semi-empirical model of wind farm aerodynamics, known as the LRB model, that is able to predict turbine array configurations to leading order accuracy. Another contribution is the characterization of the VAWT wake as a function of turbine solidity. It was found that three distinct regions of flow exist in the VAWT wake: (1) the near wake, where periodic blade shedding of vorticity dominates; (2) a transition region, where growth of a shear-layer instability occurs; (3) the far wake, where bluff-body oscillations dominate. The wake transition can be predicted using a new parameter, the dynamic solidity, which establishes a quantitative connection between the wake of a VAWT and that of a circular cylinder. The results provide insight into the mechanism of the VAWT wake recovery and the potential means to control it.
" }, { "name": "Arya, Manan", "degree": "PhD", "year": "2016", "title": "Packaging and Deployment of Large Planar Spacecraft Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-115519723", "creators": [ { "name": { "family": "Arya", "given": "Manan" }, "id": "Arya-Manan", "orcid": "0000-0003-3522-6010", "display_name": "Arya, Manan" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z9Z60M0D", "abstract": "This thesis presents a set of novel methods to biaxially package planar structures by folding and wrapping. The structure is divided into strips connected by folds that can slip during wrapping to accommodate material thickness. These packaging schemes are highly efficient, with theoretical packaging efficiencies approaching 100%. Packaging tests on meter-scale physical models have demonstrated packaging efficiencies of up to 83%. These methods avoid permanent deformation of the structure, allowing an initially flat structure to be deployed to a flat state.
\r\n\r\nAlso presented are structural architectures and deployment schemes that are compatible with these packaging methods. These structural architectures use either in-plane pretension -- suitable for membrane structures -- or out-of-plane bending stiffness to resist loading. Physical models are constructed to realize these structural architectures. The deployment of these types of structures is shown to be controllable and repeatable by conducting experiments on lab-scale models.
\r\n\r\nThese packaging methods, structural architectures, and deployment schemes are applicable to a variety of spacecraft structures such as solar power arrays, solar sails, antenna arrays, and drag sails; they have the potential to enable larger variants of these structures while reducing the packaging volume required. In this thesis, these methods are applied to the preliminary structural design of a space solar power satellite. This deployable spacecraft, measuring 60 m x 60 m, can be packaged into a cylinder measuring 1.5 m in height and 1 m in diameter. It can be deployed to a flat configuration, where it acts as a stiff lightweight support framework for multifunctional tiles that collect sunlight, generate electric power, and transmit it to a ground station on Earth.
" }, { "name": "Burgoyne, Hayden Andrew", "degree": "PhD", "year": "2016", "title": "Dynamics of Granular Crystals with Elastic-Plastic Contacts", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182016-164150213", "creators": [ { "name": { "family": "Burgoyne", "given": "Hayden Andrew" }, "id": "Burgoyne-Hayden-Andrew", "orcid": "0000-0003-0891-6411", "display_name": "Burgoyne, Hayden Andrew" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Newman", "given": "John A." }, "id": "Newman-J-A", "role": "member", "display_name": "Newman, John A." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "space" ], "doi": "10.7907/Z9J38QG6", "abstract": "We study the behavior of granular crystals subjected to impact loading that creates plastic deformation at the contacts between constituent particles. Granular crystals are highly periodic arrangements of spherical particles, arranged into densely packed structures resembling crystals. This special class of granular materials has been shown to have unique dynamics with suggested applications in impact protection. However, previous work has focused on very low amplitude impacts where every contact point can be described using the Hertzian contact law, valid only for purely elastic deformation. In this thesis, we extend previous investigation of the dynamics of granular crystals to significantly higher impact energies more suitable for the majority of applications. Additionally, we demonstrate new properties specific to elastic-plastic granular crystals and discuss their potential applications as well. We first develop a new contact law to describe the interaction between particles for large amplitude compression of elastic-plastic spherical particles including a formulation for strain-rate dependent plasticity. We numerically and experimentally demonstrate the applicability of this contact law to a variety of materials typically used in granular crystals. We then extend our investigation to one-dimensional chains of elastic-plastic particles, including chains of alternating dissimilar materials. We show that, using the new elastic-plastic contact law, we can predict the speed at which impact waves with plastic dissipation propagate based on the material properties of the constituent particles. Finally, we experimentally and numerically investigate the dynamics of two-dimensional and three-dimensional granular crystals with elastic-plastic contacts. We first show that the predicted wave speeds for 1D granular crystals can be extended to 2D and 3D materials. We then investigate the behavior of waves propagating across oblique interfaces of dissimilar particles. We show that the character of the refracted wave can be predicted using an analog to Snell's law for elastic-plastic granular crystals and ultimately show how it can be used to design impact guiding \"lenses\" for mitigation applications." }, { "name": "Coronel, Stephanie Alexandra", "degree": "PhD", "year": "2016", "title": "Thermal Ignition Using Moving Hot Particles", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-210051818", "creators": [ { "name": { "family": "Coronel", "given": "Stephanie Alexandra" }, "id": "Coronel-Stephanie-Alexandra", "orcid": "0000-0002-7088-7976", "display_name": "Coronel, Stephanie Alexandra" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9W37T9X", "abstract": "In this work, ignition of n-hexane-air mixtures was investigated using moving hot spheres of various diameters and surface temperatures. Alumina spheres of 1.8-6 mm diameter were heated using a high power CO2 laser and injected with an average velocity of 2.4 m/s into a premixed n-hexane-air mixture at a nominal initial temperature and pressure of 298 K and 100 kPa, respectively. The 90% probability of ignition using a 6 mm diameter sphere was 1224 K. High-speed experimental visualizations using interferometry indicated that ignition occurred in the vicinity of the separation point in the boundary layer of the sphere when the sphere surface temperature was near the ignition threshold. Additionally, the ignition threshold was found to be insensitive to the mixture composition and showed little variation with sphere diameter.
\r\n\r\nNumerical simulations of a transient one-dimensional boundary layer using detailed chemistry in a gas a layer adjacent to a hot wall indicated that ignition takes place away from the hot surface; the igniting gas that is a distance away from the surface can overcome diffusive heat losses back to the wall when there is heat release due to chemical activity. Finally, a simple approximation of the thermal and momentum boundary layer profiles indicated that the residence time within a boundary layer varies drastically, for example, a fluid parcel originating at very close to the wall has a residence time that is 65x longer than the residence time of a fluid parcel traveling along the edge of the momentum boundary layer.
\r\n\r\nA non-linear methodology was developed for the extraction of laminar flame properties from synthetic spherically expanding flames. The results indicated that for accurate measurements of the flame speed and Markstein length, a minimum of 50 points is needed in the data set (flame radius vs. time) and a minimum range of 48 mm in the flame radius. The non-linear methodology was applied to experimental n-hexane-air spherically expanding flames. The measured flame speed was insensitive to the mixture initial pressure from 50 to 100 kPa and increased with increasing mixture initial temperature. One-dimensional freely-propagating flame calculations showed excellent agreement with the experimental flame speeds using the JetSurF and CaltechMech chemical mechanisms.
" }, { "name": "Cymbalist, Niccolo", "degree": "PhD", "year": "2016", "title": "Mixing, Chemical Reactions, and Combustion in Supersonic Flows", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242016-143905617", "creators": [ { "name": { "family": "Cymbalist", "given": "Niccolo" }, "id": "Cymbalist-Niccolo", "display_name": "Cymbalist, Niccolo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9G73BNR", "abstract": "Experiments were conducted at the GALCIT supersonic shear-layer facility to investigate\r\naspects of reacting transverse jets in supersonic crossflow using chemiluminescence and schlieren\r\nimage-correlation velocimetry. In particular, experiments were designed to examine mixing-delay\r\nlength dependencies on jet-fluid molar mass, jet diameter, and jet inclination.
\r\n\r\nThe experimental results show that mixing-delay length depends on jet Reynolds number, when\r\nappropriately normalized, up to a jet Reynolds number of 500,000. Jet inclination increases the\r\nmixing-delay length, but causes less disturbance to the crossflow when compared to normal jet\r\ninjection. This can be explained, in part, in terms of a control-volume analysis that relates jet\r\ninclination to flow conditions downstream of injection.
\r\n\r\nIn the second part of this thesis, a combustion-modeling framework is proposed and developed\r\nthat is tailored to large-eddy simulations of turbulent combustion in high-speed flows. Scaling arguments place supersonic hydrocarbon combustion in a regime of autoignition-dominated distributed\r\nreaction zones (DRZ). The proposed evolution-variable manifold (EVM) framework incorporates an\r\nignition-delay data-driven induction model with a post-ignition manifold that uses a Lagrangian\r\nconvected 'balloon' reactor model for chemistry tabulation. A large-eddy simulation incorporating\r\nthe EVM framework captures several important reacting-flow features of a transverse hydrogen jet\r\nin heated-air crossflow experiment.
" }, { "name": "Duvvuri, Subrahmanyam", "degree": "PhD", "year": "2016", "title": "Non-Linear Scale Interactions in a Forced Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02292016-143116051", "creators": [ { "name": { "family": "Duvvuri", "given": "Subrahmanyam" }, "id": "Duvvuri-Subrahmanyam", "display_name": "Duvvuri, Subrahmanyam" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Z31WKP ", "abstract": "This thesis explores the dynamics of scale interactions in a turbulent boundary layer through a forcing-response type experimental study. An emphasis is placed on the analysis of triadic wavenumber interactions since the governing Navier-Stokes equations for the flow necessitate a direct coupling between triadically consist scales. Two sets of experiments were performed in which deterministic disturbances were introduced into the flow using a spatially-impulsive dynamic wall perturbation. Hotwire anemometry was employed to measure the downstream turbulent velocity and study the flow response to the external forcing. In the first set of experiments, which were based on a recent investigation of dynamic forcing effects in a turbulent boundary layer, a 2D (spanwise constant) spatio-temporal normal mode was excited in the flow; the streamwise length and time scales of the synthetic mode roughly correspond to the very-large-scale-motions (VLSM) found naturally in canonical flows. Correlation studies between the large- and small-scale velocity signals reveal an alteration of the natural phase relations between scales by the synthetic mode. In particular, a strong phase-locking or organizing effect is seen on directly coupled small-scales through triadic interactions. Having characterized the bulk influence of a single energetic mode on the flow dynamics, a second set of experiments aimed at isolating specific triadic interactions was performed. Two distinct 2D large-scale normal modes were excited in the flow, and the response at the corresponding sum and difference wavenumbers was isolated from the turbulent signals. Results from this experiment serve as an unique demonstration of direct non-linear interactions in a fully turbulent wall-bounded flow, and allow for examination of phase relationships involving specific interacting scales. A direct connection is also made to the Navier-Stokes resolvent operator framework developed in recent literature. Results and analysis from the present work offer insights into the dynamical structure of wall turbulence, and have interesting implications for design of practical turbulence manipulation or control strategies." }, { "name": "Lapointe, Simon", "degree": "PhD", "year": "2016", "title": "Simulation of Premixed Hydrocarbon Flames at High Turbulence Intensities", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-105842881", "creators": [ { "name": { "family": "Lapointe", "given": "Simon" }, "id": "Lapointe-Simon", "display_name": "Lapointe, Simon" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z90V89SW", "abstract": "Turbulent premixed hydrocarbon flames in the thin and distributed reaction zones regimes are simulated using both Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). A series of DNS is performed to study the transition from the thin reaction zones regime to the distributed reaction zones regime. Differential diffusion effects, distributed burning, and local extinctions are quantified. Different fuels, chemical mechanisms, and equivalence ratios are considered. The fuel Lewis number significantly influences the chemical source terms and turbulent flame speeds. More precisely, simulations with differential diffusion effects exhibit lower mean fuel consumption and heat release rates than their unity Lewis number counterparts. However, the differences are reduced as the reaction zone Karlovitz number is increased. The turbulent reaction zone surface areas increase with the turbulence intensity but aren't strongly affected by fuel, equivalence ratio, chemical mechanism, or differential diffusion. Unsurprisingly, changes in the integral length at a fixed Karlovitz number do not affect the chemical source terms but lead to an increase in flame surface area. Assumptions behind closure models for the filtered source term are then studied a priori using the DNS results. Using the concept of optimal estimators, it is shown that a tabulation approach using a progress variable and its variance can predict accurately the filtered progress variable source term. The filtered source terms are compared to predictions from two common presumed sub-filter Probability Density Functions (PDF) models. Both models show deviations from the filtered DNS source terms but predict accurately the mean turbulent flame speed. Finally, LES of experimentally-studied piloted premixed jet flames are performed using tabulated chemistry. Velocity and flame height measurements from simulations and experiments are compared. The LES are in good agreement with the experimental results for the four different hydrocarbon fuels and three different Reynolds numbers simulated. This corroborates that fuel and chemistry effects in turbulent flames are limited to effects present in laminar flames." }, { "name": "Liska, Sebastian", "degree": "PhD", "year": "2016", "title": "Fast Lattice Green's Function Methods for Viscous Incompressible Flows on Unbounded Domains", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:04062016-223108239", "creators": [ { "name": { "family": "Liska", "given": "Sebastian" }, "id": "Liska-Sebastian", "orcid": "0000-0003-4139-9364", "display_name": "Liska, Sebastian" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9ZC80TG", "abstract": "In this thesis, a collection of novel numerical techniques culminating in a fast, parallel method for the direct numerical simulation of incompressible viscous flows around surfaces immersed in unbounded fluid domains is presented. At the core of all these techniques is the use of the fundamental solutions, or lattice Green\u2019s functions, of discrete operators to solve inhomogeneous elliptic difference equations arising in the discretization of the three-dimensional incompressible Navier-Stokes equations on unbounded regular grids. In addition to automatically enforcing the natural free-space boundary conditions, these new lattice Green\u2019s function techniques facilitate the implementation of robust staggered-Cartesian-grid flow solvers with efficient nodal distributions and fast multipole methods. The provable conservation and stability properties of the appropriately combined discretization and solution techniques ensure robust numerical solutions. Numerical experiments on thin vortex rings, low-aspect-ratio flat plates, and spheres are used verify the accuracy, physical fidelity, and computational efficiency of the present formulations." }, { "name": "Meng, Jomela Chen-Chen", "degree": "PhD", "year": "2016", "title": "Numerical Simulations of Droplet Aerobreakup", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-092840941", "creators": [ { "name": { "family": "Meng", "given": "Jomela Chen-Chen" }, "id": "Meng-Jomela-Chen-Chen", "display_name": "Meng, Jomela Chen-Chen" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9KW5D09", "abstract": "The work presented in this thesis aims to bridge an existing gap in the state of droplet aerobreakup knowledge associated with the fundamental flow physics that govern the experimentally observable droplet morphologies. Using direct numerical simulations of the aerobreakup of water cylinders and droplets in the flow behind shock waves in air, we investigate the behavior of the surrounding gas flow to gain insight into the droplet\u2019s deformation and evolution in the stripping breakup regime. The compressible multicomponent Navier-Stokes equations are solved using the Multicomponent Flow Code \u2014 a high-order accurate structured finite-volume flow solver with shock- and interface-capturing. Following qualitative descriptions of the aerobreakup process, comparisons are made with available experimental data. In 2D, accurate measurements of the cylinder\u2019s center-of-mass acceleration across a range of incident shock Mach numbers allow characterization of the unsteady drag coefficient. Additionally, mass loss measurements from viscous simulations refute a well-known boundary layer stripping theory. The results of a 3D nonaxisymmetric aerobreakup simulation are presented with an emphasis on describing the intricate flow phenomena observable in the wake region. Subsequent analyses of the surface instabilities and a Fourier decomposition of the flow field reveal asymmetrical azimuthal modulations and broadband instability growth that result in the devolution of the wake region into chaotic flow." }, { "name": "Mitchell, Stephanie Jane", "degree": "PhD", "year": "2016", "title": "Metaconcrete: Engineered Aggregates for Enhanced Dynamic Performance", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:07072015-124133131", "creators": [ { "name": { "family": "Mitchell", "given": "Stephanie Jane" }, "id": "Mitchell-Stephanie-Jane", "orcid": "0000-0002-7303-8216", "display_name": "Mitchell, Stephanie Jane" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" } ], "option_major": [ "space" ], "doi": "10.7907/Z9H12ZXN", "abstract": "This work presents the development and investigation of a new type of concrete for the attenuation of waves induced by dynamic excitation. Recent progress in the field of metamaterials science has led to a range of novel composites which display unusual properties when interacting with electromagnetic, acoustic, and elastic waves. A new structural metamaterial with enhanced properties for dynamic loading applications is presented, which is named metaconcrete. In this new composite material the standard stone and gravel aggregates of regular concrete are replaced with spherical engineered inclusions. Each metaconcrete aggregate has a layered structure, consisting of a heavy core and a thin compliant outer coating. This structure allows for resonance at or near the eigenfrequencies of the inclusions, and the aggregates can be tuned so that resonant oscillations will be activated by particular frequencies of an applied dynamic loading. The activation of resonance within the aggregates causes the overall system to exhibit negative effective mass, which leads to attenuation of the applied wave motion. To investigate the behavior of metaconcrete slabs under a variety of different loading conditions a finite element slab model containing a periodic array of aggregates is utilized. The frequency dependent nature of metaconcrete is investigated by considering the transmission of wave energy through a slab, which indicates the presence of large attenuation bands near the resonant frequencies of the aggregates. Applying a blast wave loading to both an elastic slab and a slab model that incorporates the fracture characteristics of the mortar matrix reveals that a significant portion of the supplied energy can be absorbed by aggregates which are activated by the chosen blast wave profile. The transfer of energy from the mortar matrix to the metaconcrete aggregates leads to a significant reduction in the maximum longitudinal stress, greatly improving the ability of the material to resist damage induced by a propagating shock wave. The various analyses presented in this work provide the theoretical and numerical background necessary for the informed design and development of metaconcrete aggregates for dynamic loading applications, such as blast shielding, impact protection, and seismic mitigation." }, { "name": "Montemayor, Lauren Christine", "degree": "PhD", "year": "2016", "title": "Fabrication, Characterization, And Deformation of 3D Structural Meta-Materials ", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07132015-150843708", "creators": [ { "name": { "family": "Montemayor", "given": "Lauren Christine" }, "id": "Montemayor-Lauren-Christine", "display_name": "Montemayor, Lauren Christine" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "space" ], "doi": "10.7907/Z9D21VH2", "abstract": "Current technological advances in fabrication methods have provided pathways to creating architected structural meta-materials similar to those found in natural organisms that are structurally robust and lightweight, such as diatoms. Structural meta-materials are materials with mechanical properties that are determined by material properties at various length scales, which range from the material microstructure (nm) to the macro-scale architecture (\u03bcm \u2013 mm). It is now possible to exploit material size effect, which emerge at the nanometer length scale, as well as structural effects to tune the material properties and failure mechanisms of small-scale cellular solids, such as nanolattices. \r\nThis work demonstrates the fabrication and mechanical properties of 3-dimensional hollow nanolattices in both tension and compression. Hollow gold nanolattices loaded in uniaxial compression demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. Structural effects were explored by increasing the unit cell angle from 30\u00b0 to 60\u00b0 while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200nm to 635nm, at a constant relative density and grain size. In-situ uniaxial compression experiments reveal an order-of-magnitude increase in yield stress and modulus in nanolattices with greater lattice angles, and a 150% increase in the yield strength without a concomitant change in modulus in thicker-walled nanolattices for fixed lattice angles. These results imply that independent control of structural and material size effects enables tunability of mechanical properties of 3-dimensional architected meta-materials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics. \r\nThis work also explores the flaw tolerance of 3D hollow-tube alumina kagome nanolattices with and without pre-fabricated notches, both in experiment and simulation. Experiments demonstrate that the hollow kagome nanolattices in uniaxial tension always fail at the same load when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. For notches with (a/w) > 1/3, the samples fail at lower peak loads and this is attributed to the increased compliance as fewer unit cells span the un-notched region. Finite element simulations of the kagome tension samples show that the failure is governed by tensile loading for (a/w) < 1/3 but as (a/w) increases, bending begins to play a significant role in the failure. This work explores the flaw sensitivity of hollow alumina kagome nanolattices in tension, using experiments and simulations, and demonstrates that the discrete-continuum duality of architected structural meta-materials gives rise to their flaw insensitivity even when made entirely of intrinsically brittle materials.\r\n" }, { "name": "Schmidt, Bryan Eric", "degree": "PhD", "year": "2016", "title": "On the Stability of Supersonic Boundary Layers with Injection", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-141702166", "creators": [ { "name": { "family": "Schmidt", "given": "Bryan Eric" }, "id": "Schmidt-Bryan-Eric", "orcid": "0000-0001-9193-7760", "display_name": "Schmidt, Bryan Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z93X84M6", "abstract": "The problem of supersonic flow over a 5 degree half-angle cone with injection of gas through a porous section on the body into the boundary layer is studied experimentally. Three injected gases are used: helium, nitrogen, and RC318 (octafluorocyclobutane). Experiments are performed in a Mach 4 Ludwieg tube with nitrogen as the free stream gas. Shaping of the injector section relative to the rest of the body is found to admit a \"tuned\" injection rate which minimizes the strength of shock waves formed by injection. A high-speed schlieren imaging system with a framing rate of 290 kHz is used to study the instability in the region of flow downstream of\r\ninjection, referred to as the injection layer. This work provides the first experimental data on the wavelength, convective speed, and frequency of the instability in such a flow. The stability characteristics of the injection layer are found to be very similar to those of a free shear layer. The findings of this work present a new paradigm for future stability analyses of supersonic flow with injection." }, { "name": "Bitter, Neal Phillip", "degree": "PhD", "year": "2015", "title": "Stability of Hypervelocity Boundary Layers", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-111128842", "creators": [ { "name": { "family": "Bitter", "given": "Neal Phillip" }, "id": "Bitter-Neal-Phillip", "display_name": "Bitter, Neal Phillip" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Q23X5Z", "abstract": "The early stage of laminar-turbulent transition in a hypervelocity boundary layer is studied using a combination of modal linear stability analysis, transient growth analysis, and direct numerical simulation. Modal stability analysis is used to clarify the behavior of first and second mode instabilities on flat plates and sharp cones for a wide range of high enthalpy flow conditions relevant to experiments in impulse facilities. Vibrational nonequilibrium is included in this analysis, its influence on the stability properties is investigated, and simple models for predicting when it is important are described.
\r\n\r\nTransient growth analysis is used to determine the optimal initial conditions that lead to the largest possible energy amplification within the flow. Such analysis is performed for both spatially and temporally evolving disturbances. The analysis again targets flows that have large stagnation enthalpy, such as those found in shock tunnels, expansion tubes, and atmospheric flight at high Mach numbers, and clarifies the effects of Mach number and wall temperature on the amplification achieved. Direct comparisons between modal and non-modal growth are made to determine the relative importance of these mechanisms under different flow regimes.
\r\n\r\nConventional stability analysis employs the assumption that disturbances evolve with either a fixed frequency (spatial analysis) or a fixed wavenumber (temporal analysis). Direct numerical simulations are employed to relax these assumptions and investigate the downstream propagation of wave packets that are localized in space and time, and hence contain a distribution of frequencies and wavenumbers. Such wave packets are commonly observed in experiments and hence their amplification is highly relevant to boundary layer transition prediction. It is demonstrated that such localized wave packets experience much less growth than is predicted by spatial stability analysis, and therefore it is essential that the bandwidth of localized noise sources that excite the instability be taken into account in making transition estimates. A simple model based on linear stability theory is also developed which yields comparable results with an enormous reduction in computational expense. This enables the amplification of finite-width wave packets to be taken into account in transition prediction.
" }, { "name": "Gabuchian, Vahe", "degree": "PhD", "year": "2015", "title": "Experimental Investigation of Thrust Fault Rupture Mechanics", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222014-195027916", "creators": [ { "name": { "family": "Gabuchian", "given": "Vahe" }, "id": "Gabuchian-Vahe", "orcid": "0000-0001-7457-5921", "display_name": "Gabuchian, Vahe" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhat", "given": "Harsha S." }, "id": "Bhat-H-S", "role": "member", "display_name": "Bhat, Harsha S." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9J96497", "abstract": "Thrust fault earthquakes are investigated in the laboratory by generating dynamic shear ruptures along pre-existing frictional faults in rectangular plates. A considerable body of evidence suggests that dip-slip earthquakes exhibit enhanced ground motions in the acute hanging wall wedge as an outcome of broken symmetry between hanging and foot wall plates with respect to the earth surface. To understand the physical behavior of thrust fault earthquakes, particularly ground motions near the earth surface, ruptures are nucleated in analog laboratory experiments and guided up-dip towards the simulated earth surface. The transient slip event and emitted radiation mimic a natural thrust earthquake. High-speed photography and laser velocimeters capture the rupture evolution, outputting a full-field view of photo-elastic fringe contours proportional to maximum shearing stresses as well as continuous ground motion velocity records at discrete points on the specimen. Earth surface-normal measurements validate selective enhancement of hanging wall ground motions for both sub-Rayleigh and super-shear rupture speeds. The earth surface breaks upon rupture tip arrival to the fault trace, generating prominent Rayleigh surface waves. A rupture wave is sensed in the hanging wall but is, however, absent from the foot wall plate: a direct consequence of proximity from fault to seismometer. Signatures in earth surface-normal records attenuate with distance from the fault trace. Super-shear earthquakes feature greater amplitudes of ground shaking profiles, as expected from the increased tectonic pressures required to induce super-shear transition. Paired stations measure fault parallel and fault normal ground motions at various depths, which yield slip and opening rates through direct subtraction of like components. Peak fault slip and opening rates associated with the rupture tip increase with proximity to the fault trace, a result of selective ground motion amplification in the hanging wall. Fault opening rates indicate that the hanging and foot walls detach near the earth surface, a phenomenon promoted by a decrease in magnitude of far-field tectonic loads. Subsequent shutting of the fault sends an opening pulse back down-dip. In case of a sub-Rayleigh earthquake, feedback from the reflected S wave re-ruptures the locked fault at super-shear speeds, providing another mechanism of super-shear transition." }, { "name": "Mbengue, Cheikh Oumar", "degree": "PhD", "year": "2015", "title": "Storm Track Response to Perturbations in Climate", "advisor": "Schneider, Tapio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112015-075223217", "creators": [ { "name": { "family": "Mbengue", "given": "Cheikh Oumar" }, "id": "Mbengue-Cheikh-Oumar", "display_name": "Mbengue, Cheikh Oumar" } ], "advisors": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "advisor", "display_name": "Schneider, Tapio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Teixeira", "given": "Joao" }, "id": "Teixeira-Joao", "role": "member", "display_name": "Teixeira, Joao" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9FT8J05", "abstract": "This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it.
\r\n\r\nWe demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation.
\r\n\r\nWe develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks.
\r\n\r\nThe simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.
" }, { "name": "Ning, Xin", "degree": "PhD", "year": "2015", "title": "Imperfection Insensitive Thin Shells", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212015-174045815", "creators": [ { "name": { "family": "Ning", "given": "Xin" }, "id": "Ning-Xin", "display_name": "Ning, Xin" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "space" ], "doi": "10.7907/Z91J97P9", "abstract": "The buckling of axially compressed cylindrical shells and externally pressurized spherical shells is extremely sensitive to even very small geometric imperfections. In practice this issue is addressed by either using overly conservative knockdown factors, while keeping perfect axial or spherical symmetry, or adding closely and equally spaced stiffeners on shell surface. The influence of imperfection-sensitivity is mitigated, but the shells designed from these approaches are either too heavy or very expensive and are still sensitive to imperfections. Despite their drawbacks, these approaches have been used for more than half a century.
\r\n\r\nThis thesis proposes a novel method to design imperfection-insensitive cylindrical shells subject to axial compression. Instead of following the classical paths, focused on axially symmetric or high-order rotationally symmetric cross-sections, the method in this thesis adopts optimal symmetry-breaking wavy cross-sections (wavy shells). The avoidance of imperfection sensitivity is achieved by searching with an evolutionary algorithm for smooth cross-sectional shapes that maximize the minimum among the buckling loads of geometrically perfect and imperfect wavy shells. It is found that the shells designed through this approach can achieve higher critical stresses and knockdown factors than any previously known monocoque cylindrical shells. It is also found that these shells have superior mass efficiency to almost all previously reported stiffened shells.
\r\n\r\nExperimental studies on a design of composite wavy shell obtained through the proposed method are presented in this thesis. A method of making composite wavy shells and a photogrametry technique of measuring full-field geometric imperfections have been developed. Numerical predictions based on the measured geometric imperfections match remarkably well with the experiments. Experimental results confirm that the wavy shells are not sensitive to imperfections and can carry axial compression with superior mass efficiency.
\r\n\r\nAn efficient computational method for the buckling analysis of corrugated and stiffened cylindrical shells subject to axial compression has been developed in this thesis. This method modifies the traditional Bloch wave method based on the stiffness matrix method of rotationally periodic structures. A highly efficient algorithm has been developed to implement the modified Bloch wave method. This method is applied in buckling analyses of a series of corrugated composite cylindrical shells and a large-scale orthogonally stiffened aluminum cylindrical shell. Numerical examples show that the modified Bloch wave method can achieve very high accuracy and require much less computational time than linear and nonlinear analyses of detailed full finite element models.
\r\n\r\nThis thesis presents parametric studies on a series of externally pressurized pseudo-spherical shells, i.e., polyhedral shells, including icosahedron, geodesic shells, and triambic icosahedra. Several optimization methods have been developed to further improve the performance of pseudo-spherical shells under external pressure. It has been shown that the buckling pressures of the shell designs obtained from the optimizations are much higher than the spherical shells and not sensitive to imperfections.
\r\n" }, { "name": "Savard, Bruno", "degree": "PhD", "year": "2015", "title": "Characterization and Modeling of Premixed Turbulent n-Heptane Flames in the Thin Reaction Zone Regime", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-154709861", "creators": [ { "name": { "family": "Savard", "given": "Bruno" }, "id": "Savard-Bruno", "display_name": "Savard, Bruno" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "space" ], "doi": "10.7907/Z9GM858F", "abstract": "n-heptane/air premixed turbulent flames in the high-Karlovitz portion of the thin reaction zone regime are characterized and modeled in this thesis using Direct Numerical Simulations (DNS) with detailed chemistry. In order to perform these simulations, a time-integration scheme that can efficiently handle the stiffness of the equations solved is developed first. A first simulation with unity Lewis number is considered in order to assess the effect of turbulence on the flame in the absence of differential diffusion. A second simulation with non-unity Lewis numbers is considered to study how turbulence affects differential diffusion. In the absence of differential diffusion, minimal departure from the 1D unstretched flame structure (species vs. temperature profiles) is observed. In the non-unity Lewis number case, the flame structure lies between that of 1D unstretched flames with \"laminar\" non-unity Lewis numbers and unity Lewis number. This is attributed to effective Lewis numbers resulting from intense turbulent mixing and a first model is proposed. The reaction zone is shown to be thin for both flames, yet large chemical source term fluctuations are observed. The fuel consumption rate is found to be only weakly correlated with stretch, although local extinctions in the non-unity Lewis number case are well correlated with high curvature. These results explain the apparent turbulent flame speeds. Other variables that better correlate with this fuel burning rate are identified through a coordinate transformation. It is shown that the unity Lewis number turbulent flames can be accurately described by a set of 1D (in progress variable space) flamelet equations parameterized by the dissipation rate of the progress variable. In the non-unity Lewis number flames, the flamelet equations suggest a dependence on a second parameter, the diffusion of the progress variable. A new tabulation approach is proposed for the simulation of such flames with these dimensionally-reduced manifolds." }, { "name": "Steeves, John Bradley", "degree": "PhD", "year": "2015", "title": "Multilayer Active Shell Mirrors", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-145339959", "creators": [ { "name": { "family": "Steeves", "given": "John Bradley" }, "id": "Steeves-John-Bradley", "display_name": "Steeves, John Bradley" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z99W0CFB", "abstract": "This thesis presents a novel active mirror technology based on carbon fiber composites and replication manufacturing processes. Multiple additional layers are implemented into the structure in order to provide the reflective layer, actuation capabilities and electrode routing. The mirror is thin, lightweight, and has large actuation capabilities. These features, along with the associated manufacturing processes, represent a significant change in design compared to traditional optics. Structural redundancy in the form of added material or support structures is replaced by thin, unsupported lightweight substrates with large actuation capabilities.
\r\n\r\nSeveral studies motivated by the desire to improve as-manufactured figure quality are performed. Firstly, imperfections in thin CFRP laminates and their effect on post-cure shape errors are studied. Numerical models are developed and compared to experimental measurements on flat laminates. Techniques to mitigate figure errors for thicker laminates are also identified. A method of properly integrating the reflective facesheet onto the front surface of the CFRP substrate is also presented. Finally, the effect of bonding multiple initially flat active plates to the backside of a curved CFRP substrate is studied. Figure deformations along with local surface defects are predicted and characterized experimentally. By understanding the mechanics behind these processes, significant improvements to the overall figure quality have been made.
\r\n\r\nStudies related to the actuation response of the mirror are also performed. The active properties of two materials are characterized and compared. Optimal active layer thicknesses for thin surface-parallel schemes are determined. Finite element simulations are used to make predictions on shape correction capabilities, demonstrating high correctabiliity and stroke over low-order modes. The effect of actuator saturation is studied and shown to significantly degrade shape correction performance.
\r\n\r\nThe initial figure as well as actuation capabilities of a fully-integrated active mirror prototype are characterized experimentally using a Projected Hartmann test. A description of the test apparatus is presented along with two verification measurements. The apparatus is shown to accurately capture both high-amplitude low spatial-frequency figure errors as well as those at lower amplitudes but higher spatial frequencies. A closed-loop figure correction is performed, reducing figure errors by 94%.
" }, { "name": "Wojnar, Charles Stanley", "degree": "PhD", "year": "2015", "title": "Exploring the Kinetics of Domain Switching in Ferroelectrics for Structural Applications", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302015-221358386", "creators": [ { "name": { "family": "Wojnar", "given": "Charles Stanley" }, "id": "Wojnar-Charles-Stanley", "display_name": "Wojnar, Charles Stanley" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9HD7SM7", "abstract": "The complex domain structure in ferroelectrics gives rise to electromechanical coupling, and its evolution (via domain switching) results in a time-dependent (i.e. viscoelastic) response. Although ferroelectrics are used in many technological applications, most do not attempt to exploit the viscoelastic response of ferroelectrics, mainly due to a lack of understanding and accurate models for their description and prediction. Thus, the aim of this thesis research is to gain better understanding of the influence of domain evolution in ferroelectrics on their dynamic mechanical response.\r\n\r\nThere have been few studies on the viscoelastic properties of ferroelectrics, mainly due to a lack of experimental methods. Therefore, an apparatus and method called Broadband Electromechanical Spectroscopy (BES) was designed and built. BES allows for the simultaneous application of dynamic mechanical and electrical loading in a vacuum environment. Using BES, the dynamic stiffness and loss tangent in bending and torsion of a particular ferroelectric, viz. lead zirconate titanate (PZT), was characterized for different combinations of electrical and mechanical loading frequencies throughout the entire electric displacement hysteresis. Experimental results showed significant increases in loss tangent (by nearly an order of magnitude) and compliance during domain switching, which shows promise as a new approach to structural damping.\r\n\r\nA continuum model of the viscoelasticity of ferroelectrics was developed, which incorporates microstructural evolution via internal variables and associated kinetic relations. For the first time, through a new linearization process, the incremental dynamic stiffness and loss tangent of materials were computed throughout the entire electric displacement hysteresis for different combinations of mechanical and electrical loading frequencies. The model accurately captured experimental results.\r\n\r\nUsing the understanding gained from the characterization and modeling of PZT, two applications of domain switching kinetics were explored by using Micro Fiber Composites (MFCs). Proofs of concept of set-and-hold actuation and structural damping using MFCs were demonstrated." }, { "name": "Coss\u00e9, Julia Theresa", "degree": "PhD", "year": "2014", "title": "On the Behavior of Pliable Plate Dynamics in Wind: Application to Vertical Axis Wind Turbines", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272014-160129404", "creators": [ { "name": { "family": "Coss\u00e9", "given": "Julia Theresa" }, "id": "Coss\u00e9-Julia-Theresa", "display_name": "Coss\u00e9, Julia Theresa" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X7S3-CS74", "abstract": "Numerous studies have shown that flexible materials improve resilience and durability of a structure. Several studies have investigated the behavior of elastic plates under the influence of a free stream, such as studies of the fluttering flag and others of shape reconfiguration, due to a free stream.
\r\n\r\nThe principle engineering contribution of this thesis is the design and development of a vertical axis wind turbine that features pliable blades which undergo various modes of behavior, ultimately leading to rotational propulsion of the turbine. The wind turbine design was tested in a wind tunnel and at the Caltech Laboratory for Optimized Wind Energy. Ultimately, the flexible blade vertical axis wind turbine proved to be an effective way of harnessing the power of the wind.
\r\n\r\nIn addition, this body of work builds on the current knowledge of elastic cantilever plates in a free stream flow by investigating the inverted flag. While previous studies have focused on the fluid structure interaction of a free stream on elastic cantilever plates, none had studied the plate configuration where the trailing edge was clamped, leaving the leading edge free to move. Furthermore, the studies presented in this thesis establish the geometric boundaries of where the large-amplitude flapping occurs.
" }, { "name": "Fokoua Djodom, Landry", "degree": "PhD", "year": "2014", "title": "Optimal Scaling in Ductile Fracture", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162013-221817628", "creators": [ { "name": { "family": "Fokoua Djodom", "given": "Landry" }, "id": "Fokoua-Djodom-Landry", "display_name": "Fokoua Djodom, Landry" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Weinberg", "given": "Kerstin" }, "id": "Weinberg-K", "role": "member", "display_name": "Weinberg, Kerstin" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B1TW-2D81", "abstract": "This work is concerned with the derivation of optimal scaling laws, in the sense of matching lower and upper bounds on the energy, for a solid undergoing ductile fracture. The specific problem considered concerns a material sample in the form of an infinite slab of finite thickness subjected to prescribed opening displacements on its two surfaces. The solid is assumed to obey deformation-theory of plasticity and, in order to further simplify the analysis, we assume isotropic rigid-plastic deformations with zero plastic spin. When hardening exponents are given values consistent with observation, the energy is found to exhibit sublinear growth. We regularize the energy through the addition of nonlocal energy terms of the strain-gradient plasticity type. This nonlocal regularization has the effect of introducing an intrinsic length scale into the energy. We also put forth a physical argument that identifies the intrinsic length and suggests a linear growth of the nonlocal energy. Under these assumptions, ductile fracture emerges as the net result of two competing effects: whereas the sublinear growth of the local energy promotes localization of deformation to failure planes, the nonlocal regularization stabilizes this process, thus resulting in an orderly progression towards failure and a well-defined specific fracture energy. The optimal scaling laws derived here show that ductile fracture results from localization of deformations to void sheets, and that it requires a well-defined energy per unit fracture area. In particular, fractal modes of fracture are ruled out under the assumptions of the analysis. The optimal scaling laws additionally show that ductile fracture is cohesive in nature, i.e., it obeys a well-defined relation between tractions and opening displacements. Finally, the scaling laws supply a link between micromechanical properties and macroscopic fracture properties. In particular, they reveal the relative roles that surface energy and microplasticity play as contributors to the specific fracture energy of the material. Next, we present an experimental assessment of the optimal scaling laws. We show that when the specific fracture energy is renormalized in a manner suggested by the optimal scaling laws, the data falls within the bounds predicted by the analysis and, moreover, they ostensibly collapse---with allowances made for experimental scatter---on a master curve dependent on the hardening exponent, but otherwise material independent." }, { "name": "Jewell, Joseph Stephen", "degree": "PhD", "year": "2014", "title": "Boundary-Layer Transition on a Slender Cone in Hypervelocity Flow with Real Gas Effects", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-220110640", "creators": [ { "name": { "family": "Jewell", "given": "Joseph Stephen" }, "id": "Jewell-Joseph-Stephen", "orcid": "0000-0002-4047-9998", "display_name": "Jewell, Joseph Stephen" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leyva", "given": "Ivett A." }, "id": "Leyva-I-A", "role": "member", "display_name": "Leyva, Ivett A." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9H9935V", "abstract": "The laminar to turbulent transition process in boundary layer flows in thermochemical nonequilibrium at high enthalpy is measured and characterized. Experiments are performed in the T5 Hypervelocity Reflected Shock Tunnel at Caltech, using a 1 m length 5-degree half angle axisymmetric cone instrumented with 80 fast-response annular thermocouples, complemented by boundary layer stability computations using the STABL software suite. A new mixing tank is added to the shock tube fill apparatus for premixed freestream gas experiments, and a new cleaning procedure results in more consistent transition measurements. Transition location is nondimensionalized using a scaling with the boundary layer thickness, which is correlated with the acoustic properties of the boundary layer, and compared with parabolized stability equation (PSE) analysis. In these nondimensionalized terms, transition delay with increasing CO2 concentration is observed: tests in 100% and 50% CO2, by mass, transition up to 25% and 15% later, respectively, than air experiments. These results are consistent with previous work indicating that CO2 molecules at elevated temperatures absorb acoustic instabilities in the MHz range, which is the expected frequency of the Mack second-mode instability at these conditions, and also consistent with predictions from PSE analysis. A strong unit Reynolds number effect is observed, which is believed to arise from tunnel noise. NTr for air from 5.4 to 13.2 is computed, substantially higher than previously reported for noisy facilities. Time- and spatially-resolved heat transfer traces are used to track the propagation of turbulent spots, and convection rates at 90%, 76%, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, centroid, and trailing edge of the spots. A model constructed with these spot propagation parameters is used to infer spot generation rates from measured transition onset to completion distance. Finally, a novel method to control transition location with boundary layer gas injection is investigated. An appropriate porous-metal injector section for the cone is designed and fabricated, and the efficacy of injected CO2 for delaying transition is gauged at various mass flow rates, and compared with both no injection and chemically inert argon injection cases. While CO2 injection seems to delay transition, and argon injection seems to promote it, the experimental results are inconclusive and matching computations do not predict a reduction in N factor from any CO2 injection condition computed.
" }, { "name": "John, Kristen Kathleen", "degree": "PhD", "year": "2014", "title": "Strength of Tantalum at High Pressures through Richtmyer-Meshkov Laser Compression Experiments and Simulations", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08092014-195153430", "creators": [ { "name": { "family": "John", "given": "Kristen Kathleen" }, "id": "John-Kristen-Kathleen", "display_name": "John, Kristen Kathleen" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NE7Y-CK04", "abstract": "Strength at extreme pressures (>1 Mbar or 100 GPa) and high strain rates (106-108 s-1) of materials is not well characterized. The goal of the research outlined in this thesis is to study the strength of tantalum (Ta) at these conditions. The Omega Laser in the Laboratory for Laser Energetics in Rochester, New York is used to create such extreme conditions. Targets are designed with ripples or waves on the surface, and these samples are subjected to high pressures using Omega\u2019s high energy laser beams. In these experiments, the observational parameter is the Richtmyer-Meshkov (RM) instability in the form of ripple growth on single-mode ripples. The experimental platform used for these experiments is the \u201cride-along\u201d laser compression recovery experiments, which provide a way to recover the specimens having been subjected to high pressures. Six different experiments are performed on the Omega laser using single-mode tantalum targets at different laser energies. The energy indicates the amount of laser energy that impinges the target. For each target, values for growth factor are obtained by comparing the profile of ripples before and after the experiment. With increasing energy, the growth factor increased.
\r\n \r\nEngineering simulations are used to interpret and correlate the measurements of growth factor to a measure of strength. In order to validate the engineering constitutive model for tantalum, a series of simulations are performed using the code Eureka, based on the Optimal Transportation Meshfree (OTM) method. Two different configurations are studied in the simulations: RM instabilities in single and multimode ripples. Six different simulations are performed for the single ripple configuration of the RM instability experiment, with drives corresponding to laser energies used in the experiments. Each successive simulation is performed at higher drive energy, and it is observed that with increasing energy, the growth factor increases. Overall, there is favorable agreement between the data from the simulations and the experiments. The peak growth factors from the simulations and the experiments are within 10% agreement. For the multimode simulations, the goal is to assist in the design of the laser driven experiments using the Omega laser. A series of three-mode and four-mode patterns are simulated at various energies and the resulting growth of the RM instability is computed. Based on the results of the simulations, a configuration is selected for the multimode experiments. These simulations also serve as validation for the constitutive model and the material parameters for tantalum that are used in the simulations.
\r\n\r\nBy designing samples with initial perturbations in the form of single-mode and multimode ripples and subjecting these samples to high pressures, the Richtmyer-Meshkov instability is investigated in both laser compression experiments and simulations. By correlating the growth of these ripples to measures of strength, a better understanding of the strength of tantalum at high pressures is achieved.
\r\n" }, { "name": "Lyon, Bradley Joseph", "degree": "PhD", "year": "2014", "title": "A Multi-Scale Approach to Shaping Carbon Nanotube Structures for Hollow Microneedles", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-012121120", "creators": [ { "name": { "family": "Lyon", "given": "Bradley Joseph" }, "id": "Lyon-Bradley-Joseph", "display_name": "Lyon, Bradley Joseph" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJGT-TB74", "abstract": "The concept of a carbon nanotube microneedle array is explored in this thesis from multiple perspectives including microneedle fabrication, physical aspects of transdermal delivery, and in vivo transdermal drug delivery experiments. Starting with standard techniques in carbon nanotube (CNT) fabrication, including catalyst patterning and chemical vapor deposition, vertically-aligned carbon nanotubes are utilized as a scaffold to define the shape of the hollow microneedle. Passive, scalable techniques based on capillary action and unique photolithographic methods are utilized to produce a CNT-polymer composite microneedle. Specific examples of CNT-polyimide and CNT-epoxy microneedles are investigated. Further analysis of the transport properties of polymer resins reveals general requirements for applying arbitrary polymers to the fabrication process.
\r\n\r\nThe bottom-up fabrication approach embodied by vertically-aligned carbon nanotubes allows for more direct construction of complex high-aspect ratio features than standard top-down fabrication approaches, making microneedles an ideal application for CNTs. However, current vertically-aligned CNT fabrication techniques only allow for the production of extruded geometries with a constant cross-sectional area, such as cylinders. To rectify this limitation, isotropic oxygen etching is introduced as a novel fabrication technique to create true 3D CNT geometry. Oxygen etching is utilized to create a conical geometry from a cylindrical CNT structure as well as create complex shape transformations in other CNT geometries.
\r\n\r\nCNT-polymer composite microneedles are anchored onto a common polymer base less than 50 \u00b5m thick, which allows for the microneedles to be incorporated into multiple drug delivery platforms, including modified hypodermic syringes and silicone skin patches. Cylindrical microneedles are fabricated with 100 \u00b5m outer diameter and height of 200-250 \u00b5m with a central cavity, or lumen, diameter of 30 \u00b5m to facilitate liquid drug flow. In vitro delivery experiments in swine skin demonstrate the ability of the microneedles to successfully penetrate the skin and deliver aqueous solutions.
\r\n\r\nAn in vivo study was performed to assess the ability of the CNT-polymer microneedles to deliver drugs transdermally. CNT-polymer microneedles are attached to a hand actuated silicone skin patch that holds a liquid reservoir of drugs. Fentanyl, a potent analgesic, was administered to New Zealand White Rabbits through 3 routes of delivery: topical patch, CNT-polymer microneedles, and subcutaneous hypodermic injection. Results demonstrate that the CNT-polymer microneedles have a similar onset of action as the topical patch. CNT-polymer microneedles were also vetted as a painless delivery approach compared to hypodermic injection. Comparative analysis with contemporary microneedle designs demonstrates that the delivery achieved through CNT-polymer microneedles is akin to current hollow microneedle architectures. The inherent advantage of applying a bottom-up fabrication approach alongside similar delivery performance to contemporary microneedle designs demonstrates that the CNT-polymer composite microneedle is a viable architecture in the emerging field of painless transdermal delivery.
\r\n" }, { "name": "Maqueda Jim\u00e9nez, Ignacio", "degree": "PhD", "year": "2014", "title": "High Strain Composites and Dual-Matrix Composite Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-191924394", "creators": [ { "name": { "family": "Maqueda Jim\u00e9nez", "given": "Ignacio" }, "id": "Maqueda-Jim\u00e9nez-Ignacio", "display_name": "Maqueda Jim\u00e9nez, Ignacio" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Murphey", "given": "Thomas" }, "id": "Murphey-T", "role": "member", "display_name": "Murphey, Thomas" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z34C-NY82", "abstract": "Most space applications require deployable structures due to the limiting size of current launch vehicles. Specifically, payloads in nanosatellites such as CubeSats require very high compaction ratios due to the very limited space available in this typo of platform. Strain-energy-storing deployable structures can be suitable for these applications, but the curvature to which these structures can be folded is limited to the elastic range. Thanks to fiber microbuckling, high-strain composite materials can be folded into much higher curvatures without showing significant damage, which makes them suitable for very high compaction deployable structure applications. However, in applications that require carrying loads in compression, fiber microbuckling also dominates the strength of the material. A good understanding of the strength in compression of high-strain composites is then needed to determine how suitable they are for this type of application.
\r\n\r\nThe goal of this thesis is to investigate, experimentally and numerically, the microbuckling in compression of high-strain composites. Particularly, the behavior in compression of unidirectional carbon fiber reinforced silicone rods (CFRS) is studied. Experimental testing of the compression failure of CFRS rods showed a higher strength in compression than the strength estimated by analytical models, which is unusual in standard polymer composites. This effect, first discovered in the present research, was attributed to the variation in random carbon fiber angles respect to the nominal direction. This is an important effect, as it implies that microbuckling strength might be increased by controlling the fiber angles. With a higher microbuckling strength, high-strain materials could carry loads in compression without reaching microbuckling and therefore be suitable for several space applications.
\r\n\r\nA finite element model was developed to predict the homogenized stiffness of the CFRS, and the homogenization results were used in another finite element model that simulated a homogenized rod under axial compression. A statistical representation of the fiber angles was implemented in the model. The presence of fiber angles increased the longitudinal shear stiffness of the material, resulting in a higher strength in compression. The simulations showed a large increase of the strength in compression for lower values of the standard deviation of the fiber angle, and a slight decrease of strength in compression for lower values of the mean fiber angle. The strength observed in the experiments was achieved with the minimum local angle standard deviation observed in the CFRS rods, whereas the shear stiffness measured in torsion tests was achieved with the overall fiber angle distribution observed in the CFRS rods.
\r\n\r\nHigh strain composites exhibit good bending capabilities, but they tend to be soft out-of-plane. To achieve a higher out-of-plane stiffness, the concept of dual-matrix composites is introduced. Dual-matrix composites are foldable composites which are soft in the crease regions and stiff elsewhere. Previous attempts to fabricate continuous dual-matrix fiber composite shells had limited performance due to excessive resin flow and matrix mixing. An alternative method, presented in this thesis uses UV-cure silicone and fiberglass to avoid these problems. Preliminary experiments on the effect of folding on the out-of-plane stiffness are presented. An application to a conical log-periodic antenna for CubeSats is proposed, using origami-inspired stowing schemes, that allow a conical dual-matrix composite shell to reach very high compaction ratios.
" }, { "name": "Mohan, Nisha", "degree": "PhD", "year": "2014", "title": "Extracting Material Response from Simple Mechanical Tests on Hardening-Softening-Hardening Viscoplastic Solids", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142014-151151819", "creators": [ { "name": { "family": "Mohan", "given": "Nisha" }, "id": "Mohan-Nisha", "display_name": "Mohan, Nisha" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "space" ], "doi": "10.7907/MMTW-FF91", "abstract": "Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches.
\r\n\r\nA fundamental question that motivates the modeling of foams is \u2018how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?\u2019 A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,\u201cAnalysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,\u201d J. Mech.Phys. Solids, 59, pp. 2227\u20132237, Erratum 60, 1753\u20131756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like
\r\n1) The initial linear elastic response.
\r\n2) One or more nonlinear instabilities, yielding, and hardening.
The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.
" }, { "name": "Patterson, Keith D.", "degree": "PhD", "year": "2014", "title": "Lightweight Deformable Mirrors for Future Space Telescopes", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182013-094108778", "creators": [ { "name": { "family": "Patterson", "given": "Keith D." }, "id": "Patterson-Keith-D", "display_name": "Patterson, Keith D." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S7JS-A837", "abstract": "This thesis presents a concept for ultra-lightweight deformable mirrors based on a thin substrate of optical surface quality coated with continuous active piezopolymer layers that provide modes of actuation and shape correction. This concept eliminates any kind of stiff backing structure for the mirror surface and exploits micro-fabrication technologies to provide a tight integration of the active materials into the mirror structure, to avoid actuator print-through effects. Proof-of-concept, 10-cm-diameter mirrors with a low areal density of about 0.5 kg/m² have been designed, built and tested to measure their shape-correction performance and verify the models used for design. The low cost manufacturing scheme uses replication techniques, and strives for minimizing residual stresses that deviate the optical figure from the master mandrel. It does not require precision tolerancing, is lightweight, and is therefore potentially scalable to larger diameters for use in large, modular space telescopes. Other potential applications for such a laminate could include ground-based mirrors for solar energy collection, adaptive optics for atmospheric turbulence, laser communications, and other shape control applications.
\r\n\r\nThe immediate application for these mirrors is for the Autonomous Assembly and Reconfiguration of a Space Telescope (AAReST) mission, which is a university mission under development by Caltech, the University of Surrey, and JPL. The design concept, fabrication methodology, material behaviors and measurements, mirror modeling, mounting and control electronics design, shape control experiments, predictive performance analysis, and remaining challenges are presented herein. The experiments have validated numerical models of the mirror, and the mirror models have been used within a model of the telescope in order to predict the optical performance. A demonstration of this mirror concept, along with other new telescope technologies, is planned to take place during the AAReST mission.
\r\n\r\n" }, { "name": "Rabinovitch, Jason", "degree": "PhD", "year": "2014", "title": "Advancing EDL Technologies for Future Space Missions: From Ground Testing Facilities to Ablative Heatshields", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-140011538", "creators": [ { "name": { "family": "Rabinovitch", "given": "Jason" }, "id": "Rabinovitch-Jason", "orcid": "0000-0002-1914-7964", "display_name": "Rabinovitch, Jason" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XKM7-7368", "abstract": "Motivated by recent MSL results where the ablation rate of the PICA heatshield was over-predicted, and staying true to the objectives outlined in the NASA Space Technology Roadmaps and Priorities report, this work focuses on advancing EDL technologies for future space missions.
\r\n\r\nDue to the difficulties in performing flight tests in the hypervelocity regime, a new ground testing facility called the vertical expansion tunnel is proposed. The adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. If some sacrifice of the reservoir conditions can be made, the VET can be utilized in hypervelocity ground testing, without the problems associated with secondary diaphragm rupture.
\r\n\r\nThe performance of different constraints for the Rate-Controlled Constrained-Equilibrium (RCCE) method is investigated in the context of modeling reacting flows characteristic to ground testing facilities, and re-entry conditions. The effectiveness of different constraints are isolated, and new constraints previously unmentioned in the literature are introduced. Three main benefits from the RCCE method were determined: 1) the reduction in number of equations that need to be solved to model a reacting flow; 2) the reduction in stiffness of the system of equations needed to be solved; and 3) the ability to tabulate chemical properties as a function of a constraint once, prior to running a simulation, along with the ability to use the same table for multiple simulations.
\r\n\r\nFinally, published physical properties of PICA are compiled, and the composition of the pyrolysis gases that form at high temperatures internal to a heatshield is investigated. A necessary link between the composition of the solid resin, and the composition of the pyrolysis gases created is provided. This link, combined with a detailed investigation into a reacting pyrolysis gas mixture, allows a much needed consistent, and thorough description of many of the physical phenomena occurring in a PICA heatshield, and their implications, to be presented.
\r\n\r\nThrough the use of computational fluid mechanics and computational chemistry methods, significant contributions have been made to advancing ground testing facilities, computational methods for reacting flows, and ablation modeling.
" }, { "name": "Richmond, Victoria Stolyar", "degree": "PhD", "year": "2014", "title": "Techniques for Strength Measurement at High Pressures and Strain-Rates using Transverse Waves", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152014-115401299", "creators": [ { "name": { "family": "Richmond", "given": "Victoria Stolyar" }, "id": "Richmond-Victoria-Stolyar", "display_name": "Richmond, Victoria Stolyar" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/SH60-5659", "abstract": "The study of the strength of a material is relevant to a variety of applications including automobile collisions, armor penetration and inertial confinement fusion. Although dynamic behavior of materials at high pressures and strain-rates has been studied extensively using plate impact experiments, the results provide measurements in one direction only. Material behavior that is dependent on strength is unaccounted for. The research in this study proposes two novel configurations to mitigate this problem.
\r\n\r\nThe first configuration introduced is the oblique wedge experiment, which is comprised of a driver material, an angled target of interest and a backing material used to measure in-situ velocities. Upon impact, a shock wave is generated in the driver material. As the shock encounters the angled target, it is reflected back into the driver and transmitted into the target. Due to the angle of obliquity of the incident wave, a transverse wave is generated that allows the target to be subjected to shear while being compressed by the initial longitudinal shock such that the material does not slip. Using numerical simulations, this study shows that a variety of oblique wedge configurations can be used to study the shear response of materials and this can be extended to strength measurement as well. Experiments were performed on an oblique wedge setup with a copper impactor, polymethylmethacrylate driver, aluminum 6061-t6 target, and a lithium fluoride window. Particle velocities were measured using laser interferometry and results agree well with the simulations.
\r\n\r\nThe second novel configuration is the y-cut quartz sandwich design, which uses the anisotropic properties of y-cut quartz to generate a shear wave that is transmitted into a thin sample. By using an anvil material to back the thin sample, particle velocities measured at the rear surface of the backing plate can be implemented to calculate the shear stress in the material and subsequently the strength. Numerical simulations were conducted to show that this configuration has the ability to measure the strength for a variety of materials.
\r\n" }, { "name": "Saito, Namiko", "degree": "PhD", "year": "2014", "title": "Large-Eddy Simulations of Fully Developed Turbulent Channel and Pipe Flows with Smooth and Rough Walls", "advisor": "Pullin, Dale I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02142014-112419793", "creators": [ { "name": { "family": "Saito", "given": "Namiko" }, "id": "Saito-Namiko", "display_name": "Saito, Namiko" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale I." }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WKNJ-ET18", "abstract": "Studies in turbulence often focus on two flow conditions, both of which occur frequently in real-world flows and are sought-after for their value in advancing turbulence theory. These are the high Reynolds number regime and the effect of wall surface roughness. In this dissertation, a Large-Eddy Simulation (LES) recreates both conditions over a wide range of Reynolds numbers Reτ = O(102)-O(108) and accounts for roughness by locally modeling the statistical effects of near-wall anisotropic fine scales in a thin layer immediately above the rough surface. A subgrid, roughness-corrected wall model is introduced to dynamically transmit this modeled information from the wall to the outer LES, which uses a stretched-vortex subgrid-scale model operating in the bulk of the flow. Of primary interest is the Reynolds number and roughness dependence of these flows in terms of first and second order statistics. The LES is first applied to a fully turbulent uniformly-smooth/rough channel flow to capture the flow dynamics over smooth, transitionally rough and fully rough regimes. Results include a Moody-like diagram for the wall averaged friction factor, believed to be the first of its kind obtained from LES. Confirmation is found for experimentally observed logarithmic behavior in the normalized stream-wise turbulent intensities. Tight logarithmic collapse, scaled on the wall friction velocity, is found for smooth-wall flows when Reτ ≥ O(106) and in fully rough cases. Since the wall model operates locally and dynamically, the framework is used to investigate non-uniform roughness distribution cases in a channel, where the flow adjustments to sudden surface changes are investigated. Recovery of mean quantities and turbulent statistics after transitions are discussed qualitatively and quantitatively at various roughness and Reynolds number levels. The internal boundary layer, which is defined as the border between the flow affected by the new surface condition and the unaffected part, is computed, and a collapse of the profiles on a length scale containing the logarithm of friction Reynolds number is presented. Finally, we turn to the possibility of expanding the present framework to accommodate more general geometries. As a first step, the whole LES framework is modified for use in the curvilinear geometry of a fully-developed turbulent pipe flow, with implementation carried out in a spectral element solver capable of handling complex wall profiles. The friction factors have shown favorable agreement with the superpipe data, and the LES estimates of the Karman constant and additive constant of the log-law closely match values obtained from experiment." }, { "name": "Verma, Siddhartha", "degree": "PhD", "year": "2014", "title": "Velocity Resolved - Scalar Modeled Simulations of High Schmidt Number Turbulent Transport", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042014-163735743", "creators": [ { "name": { "family": "Verma", "given": "Siddhartha" }, "id": "Verma-Siddhartha", "display_name": "Verma, Siddhartha" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PTD9-W004", "abstract": "The objective of this thesis is to develop a framework to conduct velocity resolved - scalar modeled (VR-SM) simulations, which will enable accurate simulations at higher Reynolds and Schmidt (Sc) numbers than are currently feasible. The framework established will serve as a first step to enable future simulation studies for practical applications. To achieve this goal, in-depth analyses of the physical, numerical, and modeling aspects related to Sc>>1 are presented, specifically when modeling in the viscous-convective subrange. Transport characteristics are scrutinized by examining scalar-velocity Fourier mode interactions in Direct Numerical Simulation (DNS) datasets and suggest that scalar modes in the viscous-convective subrange do not directly affect large-scale transport for high Sc. Further observations confirm that discretization errors inherent in numerical schemes can be sufficiently large to wipe out any meaningful contribution from subfilter models. This provides strong incentive to develop more effective numerical schemes to support high Sc simulations. To lower numerical dissipation while maintaining physically and mathematically appropriate scalar bounds during the convection step, a novel method of enforcing bounds is formulated, specifically for use with cubic Hermite polynomials. Boundedness of the scalar being transported is effected by applying derivative limiting techniques, and physically plausible single sub-cell extrema are allowed to exist to help minimize numerical dissipation. The proposed bounding algorithm results in significant performance gain in DNS of turbulent mixing layers and of homogeneous isotropic turbulence. Next, the combined physical/mathematical behavior of the subfilter scalar-flux vector is analyzed in homogeneous isotropic turbulence, by examining vector orientation in the strain-rate eigenframe. The results indicate no discernible dependence on the modeled scalar field, and lead to the identification of the tensor-diffusivity model as a good representation of the subfilter flux. Velocity resolved - scalar modeled simulations of homogeneous isotropic turbulence are conducted to confirm the behavior theorized in these a priori analyses, and suggest that the tensor-diffusivity model is ideal for use in the viscous-convective subrange. Simulations of a turbulent mixing layer are also discussed, with the partial objective of analyzing Schmidt number dependence of a variety of scalar statistics. Large-scale statistics are confirmed to be relatively independent of the Schmidt number for Sc>>1, which is explained by the dominance of subfilter dissipation over resolved molecular dissipation in the simulations. Overall, the VR-SM framework presented is quite effective in predicting large-scale transport characteristics of high Schmidt number scalars, however, it is determined that prediction of subfilter quantities would entail additional modeling intended specifically for this purpose. The VR-SM simulations presented in this thesis provide us with the opportunity to overlap with experimental studies, while at the same time creating an assortment of baseline datasets for future validation of LES models, thereby satisfying the objectives outlined for this work." }, { "name": "Xuan, Yuan", "degree": "PhD", "year": "2014", "title": "Progress in Numerical Modeling of Non-Premixed Combustion", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-112456783", "creators": [ { "name": { "family": "Xuan", "given": "Yuan" }, "id": "Xuan-Yuan", "orcid": "0000-0001-9326-2197", "display_name": "Xuan, Yuan" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZED4-A872", "abstract": "Progress is made on the numerical modeling of both laminar and turbulent non-premixed flames. Instead of solving the transport equations for the numerous species involved in the combustion process, the present study proposes reduced-order combustion models based on local flame structures.
\r\n\r\nFor laminar non-premixed flames, curvature and multi-dimensional diffusion effects are found critical for the accurate prediction of sooting tendencies. A new numerical model based on modified flamelet equations is proposed. Sooting tendencies are calculated numerically using the proposed model for a wide range of species. These first numerically-computed sooting tendencies are in good agreement with experimental data. To further quantify curvature and multi-dimensional effects, a general flamelet formulation is derived mathematically. A budget analysis of the general flamelet equations is performed on an axisymmetric laminar diffusion flame. A new chemistry tabulation method based on the general flamelet formulation is proposed. This new tabulation method is applied to the same flame and demonstrates significant improvement compared to previous techniques.
\r\n\r\nFor turbulent non-premixed flames, a new model to account for chemistry-turbulence interactions is proposed. %It is found that these interactions are not important for radicals and small species, but substantial for aromatic species. The validity of various existing flamelet-based chemistry tabulation methods is examined, and a new linear relaxation model is proposed for aromatic species. The proposed relaxation model is validated against full chemistry calculations. To further quantify the importance of aromatic chemistry-turbulence interactions, Large-Eddy Simulations (LES) have been performed on a turbulent sooting jet flame. %The aforementioned relaxation model is used to provide closure for the chemical source terms of transported aromatic species. The effects of turbulent unsteadiness on soot are highlighted by comparing the LES results with a separate LES using fully-tabulated chemistry. It is shown that turbulent unsteady effects are of critical importance for the accurate prediction of not only the inception locations, but also the magnitude and fluctuations of soot.
" }, { "name": "Aria, Adrianus Indrat", "degree": "PhD", "year": "2013", "title": "Control of Wettability of Carbon Nanotube Array by Reversible Dry Oxidation for Superhydrophobic Coating and Supercapacitor Applications", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012013-192515668", "creators": [ { "name": { "family": "Aria", "given": "Adrianus Indrat" }, "id": "Aria-Adrianus-Indrat", "display_name": "Aria, Adrianus Indrat" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "member", "display_name": "Heath, James R." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B6MF-FX89", "abstract": "In this thesis, dry chemical modification methods involving UV/ozone, oxygen plasma, and vacuum annealing treatments are explored to precisely control the wettability of CNT arrays. By varying the exposure time of these treatments the surface concentration of oxygenated groups adsorbed on the CNT arrays can be controlled. CNT arrays with very low amount of oxygenated groups exhibit a superhydrophobic behavior. In addition to their extremely high static contact angle, they cannot be dispersed in DI water and their impedance in aqueous electrolytes is extremely high. These arrays have an extreme water repellency capability such that a water droplet will bounce off of their surface upon impact and a thin film of air is formed on their surface as they are immersed in a deep pool of water. In contrast, CNT arrays with very high surface concentration of oxygenated functional groups exhibit an extreme hydrophilic behavior. In addition to their extremely low static contact angle, they can be dispersed easily in DI water and their impedance in aqueous electrolytes is tremendously low. Since the bulk structure of the CNT arrays are preserved during the UV/ozone, oxygen plasma, and vacuum annealing treatments, all CNT arrays can be repeatedly switched between superhydrophilic and superhydrophobic, as long as their O/C ratio is kept below 18%.
\r\n\r\nThe effect of oxidation using UV/ozone and oxygen plasma treatments is highly reversible as long as the O/C ratio of the CNT arrays is kept below 18%. At O/C ratios higher than 18%, the effect of oxidation is no longer reversible. This irreversible oxidation is caused by irreversible changes to the CNT atomic structure during the oxidation process. During the oxidation process, CNT arrays undergo three different processes. For CNT arrays with O/C ratios lower than 40%, the oxidation process results in the functionalization of CNT outer walls by oxygenated groups. Although this functionalization process introduces defects, vacancies and micropores opening, the graphitic structure of the CNT is still largely intact. For CNT arrays with O/C ratios between 40% and 45%, the oxidation process results in the etching of CNT outer walls. This etching process introduces large scale defects and holes that can be obviously seen under TEM at high magnification. Most of these holes are found to be several layers deep and, in some cases, a large portion of the CNT side walls are cut open. For CNT arrays with O/C ratios higher than 45%, the oxidation process results in the exfoliation of the CNT walls and amorphization of the remaining CNT structure. This amorphization process can be implied from the disappearance of C-C sp2 peak in the XPS spectra associated with the pi-bond network.
\r\n\r\nThe impact behavior of water droplet impinging on superhydrophobic CNT arrays in a low viscosity regime is investigated for the first time. Here, the experimental data are presented in the form of several important impact behavior characteristics including critical Weber number, volume ratio, restitution coefficient, and maximum spreading diameter. As observed experimentally, three different impact regimes are identified while another impact regime is proposed. These regimes are partitioned by three critical Weber numbers, two of which are experimentally observed. The volume ratio between the primary and the secondary droplets is found to decrease with the increase of Weber number in all impact regimes other than the first one. In the first impact regime, this is found to be independent of Weber number since the droplet remains intact during and subsequent to the impingement. Experimental data show that the coefficient of restitution decreases with the increase of Weber number in all impact regimes. The rate of decrease of the coefficient of restitution in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Experimental data also show that the maximum spreading factor increases with the increase of Weber number in all impact regimes. The rate of increase of the maximum spreading factor in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Phenomenological approximations and interpretations of the experimental data, as well as brief comparisons to the previously proposed scaling laws, are shown here.
\r\n\r\nDry oxidation methods are used for the first time to characterize the influence of oxidation on the capacitive behavior of CNT array EDLCs. The capacitive behavior of CNT array EDLCs can be tailored by varying their oxygen content, represented by their O/C ratio. The specific capacitance of these CNT arrays increases with the increase of their oxygen content in both KOH and Et4NBF4/PC electrolytes. As a result, their gravimetric energy density increases with the increase of their oxygen content. However, their gravimetric power density decreases with the increase of their oxygen content. The optimally oxidized CNT arrays are able to withstand more than 35,000 charge/discharge cycles in Et4NBF4/PC at a current density of 5 A/g while only losing 10% of their original capacitance.
" }, { "name": "Bourguignon, Jean-Loup", "degree": "PhD", "year": "2013", "title": "Models of Turbulent Pipe Flow", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11272012-130849053", "creators": [ { "name": { "family": "Bourguignon", "given": "Jean-Loup" }, "id": "Bourguignon-Jean-Loup", "display_name": "Bourguignon, Jean-Loup" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BPEZ-VM28", "abstract": "The physics of turbulent pipe flow was investigated via the use of two models based on simplified versions of the Navier-Stokes equations. The first model was a streamwise-constant projection of these equations, and was used to study the change in mean flow that occurs during transition to turbulence. The second model was based on the analysis of the turbulent pipe flow resolvent, and provided a radial basis for the modal decomposition of turbulent pipe flow. The two models were tested numerically and validated against experimental and numerical data.
\r\n\r\nAnalysis of the streamwise-constant model showed that both non-normal and nonlinear effects are required to capture the blunting of the velocity profile, which occurs during pipe flow transition. The model generated flow fields characterized by the presence of high- and low-speed streaks, whose distribution over the cross-section of the pipe was remarkably similar to the one observed in the velocity field near the trailing edge of the puff structures present in pipe flow transition.
\r\n\r\nA modal decomposition of turbulent pipe flow, in the three spatial directions and in time, was performed, and made possible by the significant reduction in data requirements achieved via the use of compressive sampling and model-based radial basis functions. The application and efficiency of compressive sampling in wall-bounded turbulence was demonstrated.
\r\n\r\nApproximately sparse representations of turbulent pipe flow by propagating waves with model-based radial basis functions, were derived. The basis functions, obtained by singular value decomposition of the resolvent, captured the wall-normal coherence of the flow; and provided a link between the propagating waves and the governing equations, allowing for the identification of the dominant mechanims sustaining the waves, as a function of their streamwise wavenumber.
\r\n\r\nAnalysis of the resolvent showed that the long streamwise waves are amplified mainly via non-normality effects, and are also constrained to be tall in the wall-normal direction, which decreases the influence of viscous dissipation. The short streamwise waves were shown to be localized near the critical-layer (defined as the wall-normal location where the convection velocity of the wave equals the local mean velocity), and thus exhibit amplification with a large contribution from criticality. The work in this thesis allows the reconciliation of the well-known results concerning optimal disturbance amplification due to non-normal effects with recent resolvent analyses, which highlighted the importance of criticality effects.
\r\n" }, { "name": "Damazo, Jason Scott", "degree": "PhD", "year": "2013", "title": "Planar Reflection of Gaseous Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112013-153305610", "creators": [ { "name": { "family": "Damazo", "given": "Jason Scott" }, "id": "Damazo-Jason-Scott", "orcid": "0000-0002-4155-7177", "display_name": "Damazo, Jason Scott" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4QW7-TK55", "abstract": "Pipes containing flammable gaseous mixtures may be subjected to internal detonation. When the detonation normally impinges on a closed end, a reflected shock wave is created to bring the flow back to rest. This study built on the work of Karnesky (2010) and examined deformation of thin-walled stainless steel tubes subjected to internal reflected gaseous detonations. A ripple pattern was observed in the tube wall for certain fill pressures, and a criterion was developed that predicted when the ripple pattern would form. A two-dimensional finite element analysis was performed using Johnson-Cook material properties; the pressure loading created by reflected gaseous detonations was accounted for with a previously developed pressure model. The residual plastic strain between experiments and computations was in good agreement.
\r\n\r\nDuring the examination of detonation-driven deformation, discrepancies were discovered in our understanding of reflected gaseous detonation behavior. Previous models did not accurately describe the nature of the reflected shock wave, which motivated further experiments in a detonation tube with optical access. Pressure sensors and schlieren images were used to examine reflected shock behavior, and it was determined that the discrepancies were related to the reaction zone thickness extant behind the detonation front. During these experiments reflected shock bifurcation did not appear to occur, but the unfocused visualization system made certainty impossible. This prompted construction of a focused schlieren system that investigated possible shock wave-boundary layer interaction, and heat-flux gauges analyzed the boundary layer behind the detonation front. Using these data with an analytical boundary layer solution, it was determined that the strong thermal boundary layer present behind the detonation front inhibits the development of reflected shock wave bifurcation.
" }, { "name": "Gdoutos, Eleftherios E.", "degree": "PhD", "year": "2013", "title": "Thin Metastructures with Engineered Thermal Expansion", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292013-162505920", "creators": [ { "name": { "family": "Gdoutos", "given": "Eleftherios E." }, "id": "Gdoutos-Eleftherios-E", "display_name": "Gdoutos, Eleftherios E." } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "member", "display_name": "Shapiro, Andrew A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M69R-3A76", "abstract": "The geometry and constituent materials of metastructures can be used to engineer the thermal expansion coefficient. In this thesis, we design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and three-dimensional finite element method modeling is used to drive the design and inform experiments, and predict the response of these metastructures. We demonstrate computationally the significance of out-of-plane effects in the metastructure response. We develop an experimental setup using digital image correlation and an infrared camera to experimentally measure full displacement and temperature fields during testing and accurately measure the metastructures\u2019 CTE. We experimentally demonstrate high aspect ratio metastructures of Ti/Al and Kovar/Al which exhibit near-zero and negative CTE, respectively. We demonstrate robust fabrication procedures for thermally stable samples with high aspect ratios in thin foil and thin film scales. We investigate the lattice structure and mechanical properties of thin films comprising a near-zero CTE metastructure. The mechanics developed in this work can be used to engineer metastructures of arbitrary CTE and can be extended to three dimensions." }, { "name": "Jacobi, Ian", "degree": "PhD", "year": "2013", "title": "Structure of the Turbulent Boundary Layer under Static and Dynamic Impulsive Roughness Perturbation", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102012-152431583", "creators": [ { "name": { "family": "Jacobi", "given": "Ian" }, "id": "Jacobi-Ian", "display_name": "Jacobi, Ian" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H5WJ-RK31", "abstract": "The zero-pressure gradient turbulent boundary layer at Reynolds numbers (based on momentum thickness) ranging from 2700--4100 was perturbed using an impulsively short patch of two-dimensional, spanwise roughness elements. A spatial perturbation was considered in which the roughness patch was held statically on the flat-plate, and the flow downstream of the perturbation was measured by hotwire and particle-image velocimetry. A dynamic perturbation, in which the roughness patch was actuated periodically in time, was also studied, and additional measurements were taken by phase-locking to the dynamic actuation itself.
\r\n\r\nThe static perturbation distorted the boundary layer through the generation of a `stress bore' which modified the mean streamwise velocity gradient. The effect of this stress bore was observed in a modification of statistical and spectral measures of the turbulence, as well as a redistribution of coherent structures in the boundary layer. The characterization of the statically perturbed boundary layer provided a base flow from which to consider the dynamically perturbed flow. The dynamically perturbed flow manifested both effects analogous to the static perturbation, as well as a coherent, periodic, large-scale velocity fluctuation. The extent to which these two features could be treated as linearly independent was studied by a variety of statistical and spectral means. Moreover, the very large scale motion synthesized by the dynamic perturbation was isolated by phase-locked measurement, and its behavior was predicted with reasonable success by employing a resolvent operator approach to a forced version of the Orr-Sommerfeld equation.
\r\n\r\nThe relationship between large-scale motions and an envelope of small-scale motions in the turbulent boundary layer was studied in both the unperturbed and perturbed flows. A variety of correlation techniques were used to interpret the interaction between the different scale motions in the context of a phase-relationship between large and small scales. This phase relationship was shown to provide a physically-grounded perspective on the relationship between the synthetic very large scale motion produced by the dynamic perturbation and the smaller scales in the flow, and was able to provide a foundation for thinking about new approaches to controlling turbulence through large-scale forcing.
" }, { "name": "Johnson, Gwendolyn Brook", "degree": "PhD", "year": "2013", "title": "Modeling, Simulation, and Design of Self-Assembling Space Systems: Accurate Collision Detection, Robust Time Integration, and Optimal Control", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132012-125328533", "creators": [ { "name": { "family": "Johnson", "given": "Gwendolyn Brook" }, "id": "Johnson-G-B", "display_name": "Johnson, Gwendolyn Brook" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Leyendecker", "given": "Sigrid" }, "id": "Leyendecker-S", "role": "member", "display_name": "Leyendecker, Sigrid" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73S0-Y593", "abstract": "Motivated by issues inherent in modeling and designing self-assembling systems (e.g. multiple collisions, collisions between non-smooth bodies, clumping and jamming behaviors, etc.), the goal of this thesis is to develop robust numerical tools that enable ecient and accurate direct simulation of self assembling systems and the application of optimal control methods to this type of system. The systems will be alternately modeled using linear nite elements, rigid bodies, or chains of rigid bodies. To this end, this work begins with development of a linear programming based collision detection algorithm for general convex polyhedral bodies. The resulting linear program has several features which render it extremely useful in determining the force system at the time of contact in numerical collision integrators. With robust collision detection in hand, three related numerical integration methods for dynamics with collisions are treated; a direct potential-based approach, and exact collision integrator in a discrete variational setting, and a decomposition-based algorithm, again in the discrete variational setting. Finally, several control problems are treated in the Discrete Mechanics and Optimal Control{Constrained (DMOCC) framework in which collisions between non-smooth bodies either need to be avoided or explicitly included in the optimal control problem. A globally stable feedback controller and a family of trajectories for spacecraft docking are also developed and tested with an accurate representation of an optimized CubeSat docking system." }, { "name": "Kwok, Kawai", "degree": "PhD", "year": "2013", "title": "Mechanics of Viscoelastic Thin-Walled Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122012-184825377", "creators": [ { "name": { "family": "Kwok", "given": "Kawai" }, "id": "Kwok-Kawai", "orcid": "0000-0001-6876-4267", "display_name": "Kwok, Kawai" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RSSF-1C35", "abstract": "Thin-walled structures made of polymers and reinforced polymer composites are prominent candidates for constructing large lightweight structures. A major challenge in designing polymer-based thin-walled structures is their time and temperature dependent behavior originating from material viscoelasticity and its interaction with the highly geometrically nonlinear response due to thinness of the walls. Although polymer viscoelasticity and geometric nonlinearity have been extensively studied, the mechanics of structures exhibiting both phenomena are not well understood.
\r\n\r\nThis thesis presents a combination of experimental, numerical, and analytical investigations of the behavior of viscoelastic thin-walled structures. The first goal of this research is to establish general methods of analysis for two types of structural components, namely composite shells and polymer membranes, that will serve as the basis for full-scale structural analysis. The second goal is to demonstrate the capability of the developed methods by analyzing time and temperature dependent behavior of deployable structures and balloon structures.
\r\n\r\nIn the study of deployable structures, the deployment and shape recovery processes after stowage are investigated. Fundamental features of viscoelastic deployable structures are studied first with homogeneous polymer beams and shells. A simple closed-form solution describing the shape evolution of a beam after stowage is proposed. The effects of rate and temperature on the bending instability of shells are revealed. Building on the understanding gained from the analysis of homogeneous structures, modeling techniques are developed for polymer composite structures. A micromechanical viscoelastic model for carbon fiber reinforced polymer thin shells is established through finite element homogenization and applied to evaluate the effects of long-term stowage in a representative composite deployable structure.
\r\n\r\nIn the study of balloon structures, a membrane model is developed to study polymer balloon films with stress concentrations due to thickness variation. A nonlinear viscoelastic constitutive model is first formulated for the film material. The wrinkling instability behavior is incorporated into the model through correction of stress and strain states in the presence of wrinkling. Stress concentration factors in balloon films are predicted and measured with the membrane model and full-field displacement measurement techniques, respectively.
" }, { "name": "Lopez Ortega, Alejandro", "degree": "PhD", "year": "2013", "title": "Simulation of Richtmyer-Meshkov Flows for Elastic-Plastic Solids in Planar and Converging Geometries Using an Eulerian Framework", "advisor": "Pullin, Dale Ian; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202013-185004693", "creators": [ { "name": { "family": "Lopez Ortega", "given": "Alejandro" }, "id": "Lopez-Ortega-Alejandro", "display_name": "Lopez Ortega, Alejandro" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WJ6-D795", "abstract": "This thesis presents a numerical and analytical study of two problems of interest involving shock waves propagating through elastic-plastic media: the motion of converging (imploding) shocks and the Richtmyer-Meshkov (RM) instability. Since the stress conditions encountered in these cases normally produce large deformations in the materials, an Eulerian description, in which the spatial coordinates are fixed, is employed. This formulation enables a direct comparison of similarities and differences between the present study of phenomena driven by shock-loading in elastic-plastic solids, and in fluids, where they have been studied extensively. In the first application, Whitham's shock dynamics (WSD) theory is employed for obtaining an approximate description of the motion of an elastic-plastic material processed by a cylindrically/spherically converging shock. Comparison with numerical simulations of the full set of equations of motion reveal that WSD is an accurate tool for characterizing the evolution of converging shocks at all stages. The study of the Richtmyer-Meshkov flow (i.e., interaction between the interface separating two materials of different density and a shock wave incoming at an angle) in solids is performed by means of analytical models for purely elastic solids and numerical simulations when plasticity is included in the material model. To this effect, an updated version of a previously developed multi-material, level-set-based, Eulerian framework for solid mechanics is employed. The revised code includes the use of a multi-material HLLD Riemann problem for imposing material boundary conditions, and a new formulation of the equations of motion that makes use of the stretch tensor while avoiding the degeneracy of the stress tensor under rotation. Results reveal that the interface separating two elastic solids always behaves in a stable oscillatory or decaying oscillatory manner due to the existence of shear waves, which are able to transport the initial vorticity away from the interface. In the case of elastic-plastic materials, the interface behaves at first in an unstable manner similar to a fluid. Ejecta formation is appreciated under certain initial conditions while in other conditions, after an initial period of growth, the interface displays a quasi-stationary long-term behavior due to stress relaxation. The effect of secondary shock-interface interactions (re-shocks) in converging geometries is also studied. A turbulent mixing zone, similar to what is observed in gas--gas interfaces, is created, especially when materials with low strength driven by moderate to strong shocks are considered." }, { "name": "Mehrotra, Prakhar", "degree": "Engineering Degree", "year": "2013", "title": "Sustainable Energy Solutions for Irrigation and Harvesting in Developing Countries", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112013-114509037", "creators": [ { "name": { "family": "Mehrotra", "given": "Prakhar" }, "id": "Mehrotra-Prakhar", "display_name": "Mehrotra, Prakhar" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KV5Y-4960", "abstract": "One of the critical problems currently being faced by agriculture industry in developing nations is the alarming rate of groundwater depletion. Irrigation accounts for over 70% of the total groundwater withdrawn everyday. Compounding this issue is the use of polluting diesel generators to pump groundwater for irrigation. This has made irrigation not only the biggest consumer of groundwater but also one of the major contributors to green house gases. The aim of this thesis is to present a solution to the energy-water nexus. To make agriculture less dependent on fossil fuels, the use of a solar-powered Stirling engine as the power generator for on-farm energy needs is discussed. The Stirling cycle is revisited and practical and ideal Stirling cycles are compared. Based on agricultural needs and financial constraints faced by farmers in developing countries, the use of a Fresnel lens as a solar-concentrator and a Beta-type Stirling engine unit is suggested for sustainable power generation on the farms. To reduce the groundwater consumption and to make irrigation more sustainable, the conceptual idea of using a Stirling engine in drip irrigation is presented. To tackle the shortage of over 37 million tonnes of cold-storage in India, the idea of cost-effective solar-powered on-farm cold storage unit is discussed." }, { "name": "Mihaly, Jonathan Michael", "degree": "PhD", "year": "2013", "title": "Investigation of Hypervelocity Impact Phenomena Using Real-time Concurrent Diagnostics", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-143355354", "creators": [ { "name": { "family": "Mihaly", "given": "Jonathan Michael" }, "id": "Mihaly-Jonathan-Michael", "display_name": "Mihaly, Jonathan Michael" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V3A7-7686", "abstract": "Hypervelocity impact of meteoroids and orbital debris poses a serious and growing threat to spacecraft. To study hypervelocity impact phenomena, a comprehensive ensemble of real-time concurrently operated diagnostics has been developed and implemented in the Small Particle Hypervelocity Impact Range (SPHIR) facility. This suite of simultaneously operated instrumentation provides multiple complementary measurements that facilitate the characterization of many impact phenomena in a single experiment. The investigation of hypervelocity impact phenomena described in this work focuses on normal impacts of 1.8 mm nylon 6/6 cylinder projectiles and variable thickness aluminum targets. The SPHIR facility two-stage light-gas gun is capable of routinely launching 5.5 mg nylon impactors to speeds of 5 to 7 km/s. Refinement of legacy SPHIR operation procedures and the investigation of first-stage pressure have improved the velocity performance of the facility, resulting in an increase in average impact velocity of at least 0.57 km/s. Results for the perforation area indicate the considered range of target thicknesses represent multiple regimes describing the non-monotonic scaling of target perforation with decreasing target thickness. The laser side-lighting (LSL) system has been developed to provide ultra-high-speed shadowgraph images of the impact event. This novel optical technique is demonstrated to characterize the propagation velocity and two-dimensional optical density of impact-generated debris clouds. Additionally, a debris capture system is located behind the target during every experiment to provide complementary information regarding the trajectory distribution and penetration depth of individual debris particles. The utilization of a coherent, collimated illumination source in the LSL system facilitates the simultaneous measurement of impact phenomena with near-IR and UV-vis spectrograph systems. Comparison of LSL images to concurrent IR results indicates two distinctly different phenomena. A high-speed, pressure-dependent IR-emitting cloud is observed in experiments to expand at velocities much higher than the debris and ejecta phenomena observed using the LSL system. In double-plate target configurations, this phenomena is observed to interact with the rear-wall several micro-seconds before the subsequent arrival of the debris cloud. Additionally, dimensional analysis presented by Whitham for blast waves is shown to describe the pressure-dependent radial expansion of the observed IR-emitting phenomena. Although this work focuses on a single hypervelocity impact configuration, the diagnostic capabilities and techniques described can be used with a wide variety of impactors, materials, and geometries to investigate any number of engineering and scientific problems." }, { "name": "O'Farrell, Clara", "degree": "PhD", "year": "2013", "title": "A Dynamical Systems Analysis of Vortex Pinch-Off", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032013-161632237", "creators": [ { "name": { "family": "O'Farrell", "given": "Clara" }, "id": "O'Farrell-Clara", "display_name": "O'Farrell, Clara" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/AFAA-KF43", "abstract": "Vortex rings constitute the main structure in the wakes of a wide class of swimming and flying animals, as well as in cardiac flows and in the jets generated by some moss and fungi. However, there is a physical limit, determined by an energy maximization principle called the Kelvin-Benjamin principle, to the size that axisymmetric vortex rings can achieve. The existence of this limit is known to lead to the separation of a growing vortex ring from the shear layer feeding it, a process known as `vortex pinch-off', and characterized by the dimensionless vortex formation number. The goal of this thesis is to improve our understanding of vortex pinch-off as it relates to biological propulsion, and to provide future researchers with tools to assist in identifying and predicting pinch-off in biological flows.
\r\n\r\nTo this end, we introduce a method for identifying pinch-off in starting jets using the Lagrangian coherent structures in the flow, and apply this criterion to an experimentally generated starting jet. Since most naturally occurring vortex rings are not circular, we extend the definition of the vortex formation number to include non-axisymmetric vortex rings, and find that the formation number for moderately non-axisymmetric vortices is similar to that of circular vortex rings. This suggests that naturally occurring vortex rings may be modeled as axisymmetric vortex rings. Therefore, we consider the perturbation response of the Norbury family of axisymmetric vortex rings. This family is chosen to model vortex rings of increasing thickness and circulation, and their response to prolate shape perturbations is simulated using contour dynamics. Finally, the response of more realistic models for vortex rings, constructed from experimental data using nested contours, to perturbations which resemble those encountered by forming vortices more closely, is simulated using contour dynamics. In both families of models, a change in response analogous to pinch-off is found as members of the family with progressively thicker cores are considered. We posit that this analogy may be exploited to understand and predict pinch-off in complex biological flows, where current methods are not applicable in practice, and criteria based on the properties of vortex rings alone are necessary.
" }, { "name": "Parziale, Nicholaus J.", "degree": "PhD", "year": "2013", "title": "Slender-Body Hypervelocity Boundary-Layer Instability", "advisor": "Shepherd, Joseph E.; Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-164534236", "creators": [ { "name": { "family": "Parziale", "given": "Nicholaus J." }, "id": "Parziale-Nicholaus-J", "orcid": "0000-0001-9880-1727", "display_name": "Parziale, Nicholaus J." } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "co-advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZJ1-Y009", "abstract": "With novel application of optical techniques, the slender-body hypervelocity boundary-layer instability is characterized in the previously unexplored regime where thermo-chemical effects are important. Narrowband disturbances (500-3000 kHz) are measured in boundary layers with edge velocities of up to 5~km/s at two points along the generator of a 5 degree half angle cone. Experimental amplification factor spectra are presented. Linear stability and PSE analysis is performed, with fair prediction of the frequency content of the disturbances; however, the analysis over-predicts the amplification of disturbances. The results of this work have two key implications: 1) the acoustic instability is present and may be studied in a large-scale hypervelocity reflected-shock tunnel, and 2) the new data set provides a new basis on which the instability can be studied.
" }, { "name": "Rought, Rebecca Lynn", "degree": "Engineering Degree", "year": "2013", "title": "Identification of Thermally-Tagged Coherent Structures in the Zero Pressure Gradient Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06172013-144232973", "creators": [ { "name": { "family": "Rought", "given": "Rebecca Lynn" }, "id": "Rought-Rebecca-Lynn", "display_name": "Rought, Rebecca Lynn" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z2V0-9V82", "abstract": "A zero pressure gradient boundary layer over a flat plate is subjected to step changes in thermal condition at the wall, causing the formation of internal, heated layers. The resulting temperature fluctuations and their corresponding density variations are associated with turbulent coherent structures. Aero-optical distortion occurs when light passes through the boundary layer, encountering the changing index of refraction resulting from the density variations. Instantaneous measurements of streamwise velocity, temperature and the optical deflection angle experienced by a laser traversing the boundary layer are made using hot and cold wires and a Malley probe, respectively. Correlations of the deflection angle with the temperature and velocity records suggest that the dominant contribution to the deflection angle comes from thermally-tagged structures in the outer boundary layer with a convective velocity of approximately 0.8U\u221e. An examination of instantaneous temperature and velocity and their temporal gradients conditionally averaged around significant optical deflections shows behavior consistent with the passage of a heated vortex. Strong deflections are associated with strong negative temperature gradients, and strong positive velocity gradients where the sign of the streamwise velocity fluctuation changes. The power density spectrum of the optical deflections reveals associated structure size to be on the order of the boundary layer thickness. A comparison to the temperature and velocity spectra suggests that the responsible structures are smaller vortices in the outer boundary layer as opposed to larger scale motions. Notable differences between the power density spectra of the optical deflections and the temperature remain unresolved due to the low frequency response of the cold wire." }, { "name": "Szelengowicz, Ivan Michel Nicolas", "degree": "PhD", "year": "2013", "title": "Analysis and Optimization of Stress Wave Propagation in Two-Dimensional Granular Crystals with Defects", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082013-161911202", "creators": [ { "name": { "family": "Szelengowicz", "given": "Ivan Michel Nicolas" }, "id": "Szelengowicz-Ivan-Michel-Nicolas", "display_name": "Szelengowicz, Ivan Michel Nicolas" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TE86-1A15", "abstract": "Granular crystals are compact periodic assemblies of elastic particles in Hertzian contact whose dynamic response can be tuned from strongly nonlinear to linear by the addition of a static precompression force. This unique feature allows for a wide range of studies that include the investigation of new fundamental nonlinear phenomena in discrete systems such as solitary waves, shock waves, discrete breathers and other defect modes. In the absence of precompression, a particularly interesting property of these systems is their ability to support the formation and propagation of spatially localized soliton-like waves with highly tunable properties. The wealth of parameters one can modify (particle size, geometry and material properties, periodicity of the crystal, presence of a static force, type of excitation, etc.) makes them ideal candidates for the design of new materials for practical applications. This thesis describes several ways to optimally control and tailor the propagation of stress waves in granular crystals through the use of heterogeneities (interstitial defect particles and material heterogeneities) in otherwise perfectly ordered systems. We focus on uncompressed two-dimensional granular crystals with interstitial spherical intruders and composite hexagonal packings and study their dynamic response using a combination of experimental, numerical and analytical techniques. We first investigate the interaction of defect particles with a solitary wave and utilize this fundamental knowledge in the optimal design of novel composite wave guides, shock or vibration absorbers obtained using gradient-based optimization methods." }, { "name": "Whittlesey, Robert Wells", "degree": "PhD", "year": "2013", "title": "Dynamics and Scaling of Self-Excited Passive Vortex Generators for Underwater Propulsion", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282013-114822808", "creators": [ { "name": { "family": "Whittlesey", "given": "Robert Wells" }, "id": "Whittlesey-Robert-Wells", "display_name": "Whittlesey, Robert Wells" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SC4M-8896", "abstract": "A series of experiments was conducted on the use of a device to passively generate vortex rings, henceforth a passive vortex generator (PVG). The device is intended as a means of propulsion for underwater vehicles, as the use of vortex rings has been shown to decrease the fuel consumption of a vehicle by up to 40% Ruiz (2010).
\r\n\r\nThe PVG was constructed out of a collapsible tube encased in a rigid, airtight box. By adjusting the pressure within the airtight box while fluid was flowing through the tube, it was possible to create a pulsed jet with vortex rings via self-excited oscillations of the collapsible tube.
\r\n\r\nA study of PVG integration into an existing autonomous underwater vehicle (AUV) system was conducted. A small AUV was used to retrofit a PVG with limited alterations to the original vehicle. The PVG-integrated AUV was used for self-propelled testing to measure the hydrodynamic (Froude) efficiency of the system. The results show that the PVG-integrated AUV had a 22% increase in the Froude efficiency using a pulsed jet over a steady jet. The maximum increase in the Froude efficiency was realized when the formation time of the pulsed jet, a nondimensional time to characterize vortex ring formation, was coincident with vortex ring pinch-off. This is consistent with previous studies that indicate that the maximization of efficiency for a pulsed jet vehicle is realized when the formation of vortex rings maximizes the vortex ring energy and size.
\r\n\r\nThe other study was a parameter study of the physical dimensions of a PVG. This study was conducted to determine the effect of the tube diameter and length on the oscillation characteristics such as the frequency. By changing the tube diameter and length by factors of 3, the frequency of self-excited oscillations was found to scale as f~D_0^{-1/2} L_0^0, where D_0 is the tube diameter and L_0 the tube length. The mechanism of operation is suggested to rely on traveling waves between the tube throat and the end of the tube. A model based on this mechanism yields oscillation frequencies that are within the range observed by the experiment.
" }, { "name": "Boettcher, Philipp Andreas", "degree": "PhD", "year": "2012", "title": "Thermal Ignition", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162012-131336010", "creators": [ { "name": { "family": "Boettcher", "given": "Philipp Andreas" }, "id": "Boettcher-Philipp-Andreas", "display_name": "Boettcher, Philipp Andreas" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H2W9-ZK95", "abstract": "Accidental ignition of flammable gases is a critical safety concern in many industrial applications. Particularly in the aviation industry, the main areas of concern on an aircraft are the fuel tank and adjoining regions, where spilled fuel has a high likelihood of creating a flammable mixture. To this end, a fundamental understanding of the ignition phenomenon is necessary in order to develop more accurate test methods and standards as a means of designing safer air vehicles. The focus of this work is thermal ignition, particularly auto-ignition with emphasis on the effect of heating rate, hot surface ignition and flame propagation, and puffing flames.
\r\n\r\nCombustion of hydrocarbon fuels is traditionally separated into slow reaction, cool flame, and ignition regimes based on pressure and temperature. Standard tests, such as the ASTM E659, are used to determine the lowest temperature required to ignite a specific fuel mixed with air at atmospheric pressure. It is expected that the initial pressure and the rate at which the mixture is heated also influences the limiting temperature and the type of combustion. This study investigates the effect of heating rate, between 4 and 15 K/min, and initial pressure, in the range of 25 to 100 kPa, on ignition of n-hexane air mixtures. Mixtures with equivalence ratio ranging from 0.6 to = 1.2 were investigated. The problem is also modeled computationally using an extension of Semenov's classical auto-ignition theory with a detailed chemical mechanism. Experiments and simulations both show that in the same reactor either a slow reaction or an ignition event can take place depending on the heating rate. Analysis of the detailed chemistry demonstrates that a mixture which approaches the ignition region slowly undergoes a significant modification of its composition. This change in composition induces a progressive shift of the explosion limit until the mixture is no longer flammable. A mixture that approaches the ignition region sufficiently rapidly undergoes only a moderate amount of thermal decomposition and explodes quite violently. This behavior can also be captured and analyzed using a one-step reaction model, where the heat release is in competition with the depletion of reactants.
\r\n\r\nHot surface ignition is examined using a glow plug or heated nickel element in a series of premixed n-hexane air mixtures. High-speed schlieren photography, a thermocouple, and a fast response pressure transducer are used to record flame characteristics such as ignition temperature, flame speed, pressure rises, and combustion mode. The ignition event is captured by considering the dominant balance of diffusion and chemical reaction that occurs near a hot surface. Experiments and models show a dependence of ignition temperature on mixture composition, initial pressure, and hot surface size. The mixtures exhibit the known lower flammability limit where the maximum temperature of the hot surface was insufficient at igniting the mixture. Away from the lower flammability limit, the ignition temperature drops to an almost constant value over a wide range of equivalence ratios (0.7 to 2.8) with large variations as the upper flammability limit is approached. Variations in the initial pressure and equivalence ratio also give rise to different modes of combustion: single flame, re-ignition, and puffing flames. These results are successfully compared to computational results obtained using a flamelet model and a detailed chemical mechanism for n-heptane. These different regimes can be delineated by considering the competition between inertia, i.e., flame propagation, and buoyancy, which can be expressed in the Richardson number.
\r\n\r\nIn experiments of hot surface ignition and subsequent flame propagation a 10 Hz puffing flame instability is visible in mixtures that are stagnant and premixed prior to the ignition sequence. By varying the size of the hot surface, power input, and combustion vessel volume, we determined that the instability is a function of the interaction of the flame with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed a competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puffing is proportional to the gravitational acceleration and inversely proportional to the flame speed. We propose a relation describing the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for lean and rich n-hexane-air as well as lean hydrogen-air flames.
" }, { "name": "Capece, Angela Maria", "degree": "PhD", "year": "2012", "title": "Plasma-Surface Interactions in Hollow Cathode Discharges for Electric Propulsion\r ", "advisor": "Shepherd, Joseph E.; Polk, James E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-113856351", "creators": [ { "name": { "family": "Capece", "given": "Angela Maria" }, "id": "Capece-Angela-Maria", "orcid": "0000-0003-4147-7174", "display_name": "Capece, Angela Maria" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "co-advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "co-advisor", "display_name": "Polk, James E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Goebel", "given": "Dan M." }, "id": "Goebel-D-M", "role": "member", "display_name": "Goebel, Dan M." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7TDQ-DR81", "abstract": "Electric thrusters generate high exhaust velocities and can achieve specific impulses in excess of 1000 s. The low thrust generation and high specific impulse make electric propulsion ideal for interplanetary missions, spacecraft station keeping, and orbit raising maneuvers. Consequently, these devices have been used on a variety of space missions including Deep Space 1, Dawn, and hundreds of commercial spacecraft in Earth orbit. In order to provide the required total impulses, thruster burn time can often exceed 10,000 hours, making thruster lifetime essential.
\r\n\r\nOne of the main life-limiting components on ion engines is the hollow cathode, which serves as the electron source for ionization of the xenon propellant gas. Reactive contaminants such as oxygen can modify the cathode surface morphology and degrade the electron emission properties. Hollow cathodes that operate with reactive impurities in the propellant will experience higher operating temperatures, which increase evaporation of the emission materials and reduce cathode life. A deeper understanding of the mechanisms initiating cathode failure will improve thruster operation, increase lifetime, and ultimately reduce cost.
\r\n \r\nA significant amount of work has been done previously to understand the effects of oxygen poisoning on vacuum cathodes; however, the xenon plasma adds complexity, and its role during cathode poisoning is not completely understood. The work presented here represents the first attempt at understanding how oxygen impurities in the xenon discharge plasma alter the emitter surface and affect operation of a 4:1:1 BaO-CaO-Al2O3 hollow cathode.
\r\n \r\nA combination of experimentation and modeling was used to investigate how oxygen impurities in the discharge plasma alter the emitter surface and reduce the electron emission capability. The experimental effort involved operating a 4:1:1 hollow cathode at various conditions with oxygen impurities in the xenon flow. Since direct measurements of the emitter surface state cannot be obtained because of the cathode geometry and high particles fluxes, measurements of the emitter temperature using a two-color pyrometer were used to determine the oxygen surface coverage and characterize the rate processes that occur during poisoning.
\r\n \r\nA model describing the material transport in the plasma discharge was developed and is used to predict the barium and oxygen fluxes to the emitter surface during cathode operation by solving the species continuity and momentum equations. The dominant ionization process for molecular oxygen in the plasma gas is resonant charge exchange with xenon ions. Barium is effectively recycled in the plasma; however, BaO and O2 are not. The model shows that the oxygen flux to the surface is not diffusion limited.
\r\n\r\nExperimental results indicate that the oxygen poisoning rate is slow and that the oxygen poisoning coverage on the emitter surface is less than 3%. A time-dependent model of the reaction kinetics of oxygen and barium at the tungsten surface was developed using the experimental results.
\r\n \r\nThe experiments and kinetics model indicate that the dominant processes at the emitter surface are dissociative adsorption of O2, sputtering of the O2 precursor, and desorption of O. Ion sputtering of the weakly bound O2 precursor state limits the poisoning rate and yields low oxygen coverage. Removal of chemisorbed atomic oxygen is dominated by thermal processes. Based on the low oxygen coverage and long poisoning transients, plasma cathodes appear to be able to withstand higher oxygen concentrations than vacuum cathodes.
" }, { "name": "Deng, Xiaowei", "degree": "PhD", "year": "2012", "title": "Clefted Equilibrium Shapes of Superpressure Balloon Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062012-202646378", "creators": [ { "name": { "family": "Deng", "given": "Xiaowei" }, "id": "Deng-Xiaowei", "display_name": "Deng, Xiaowei" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YYTP-2005", "abstract": "This thesis presents a numerical and analytical study of the clefted equilibrium shape of superpressure balloon structures. Lobed superpressure balloons have shown a tendency to deploy into unexpected asymmetric shapes, hence their design has to strike a balance between the lower stresses achieved by increasing lobing and the risk of incomplete deployment. Extensive clefting is a regular feature of balloons that are incompletely inflated, and is regularly seen during launch and ascent. Our particular interest in the research is in clefts that remain once a balloon has reached its float altitude and is fully pressurized.
\r\n\r\nA simplified simulation technique for orthotropic viscoelastic membranes is presented in the thesis. Wrinkling is detected by a combined stress-strain criterion and an iterative scheme searches for the wrinkle angle using a pseudoelastic material stiffness matrix based on a nonlinear viscoelastic constitutive model. This simplified model has been implemented in ABAQUS/Explicit and is able to compute the behavior of a membrane structure by superposition of a small number of response increments. The model has been tested against a published solution for a time-independent isotropic membrane under simple shear and also against experimental results on StratoFilm 420 under simple shear.
\r\n\r\n\r\nA fully three-dimensional finite element model of balloon structures incorporating wrinkling and frictionless contact, able to simulate the shapes taken up by lobed superpressure balloons during the final stages of their ascent has been established. Two different methods have been considered to predict the clefts: (i) deflation and\r\ninflation method and (ii) constraint shift method. In method (i), the starting configuration is obtained by deflating an initially symmetric balloon subject to uniform pressure. The deflation simulation is continued until the differential pressure at the bottom of the balloon has become negative, at which point the balloon is extensively clefted. The balloon is then inflated by increasing the bottom pressure while maintaining a uniform vertical ressure gradient, and the evolution of the shape and stress distribution of the balloon is studied. Two different designs of uperpressure balloons are investigated: a flat facet balloon and a ighly lobed balloon. It is found that the flat facet balloon follows essentially the same path during deflation and inflation, and hence will deploy into a unique, symmetric shape. For the lobed balloon it is found that it follows different paths during deflation and inflation, and deploys into an alternate, clefted equilibrium shape.
\r\n\r\nCompared to method (i), method (ii) is computationally a more efficient clefting test. The test consists in setting up the balloon in its symmetrically inflated configuration, then breaking the symmetry of this shape by artificially introducing a clefting imperfection, and finally determining the equilibrium shape of the balloon. The clefting imperfection is computed by shifting the constraint at the bottom of the balloon and removing the pressure in the bottom region, below the shifted constraint. The clefting test is applied successfully to three 27~m diameter superpressure balloons that have been tested indoors by NASA, of which one had remained clefted when it was inflated and the other two had deployed completely.
\r\n\r\nIn addition to numerical simulations, formulation of a new cleft factor, employed as an indicator of tendency to S-cleft for superpressure balloons based on constant-stress design has been established through dimensional analysis. The cleft factor, defined as the ratio of clefted volume to cyclically symmetrical volume, is expressed in the form of power law relation of the dimensionless groups. An example illustrates how to calculate the coefficients of the analytical formula and analyze sensitivity of design parameters to clefting.
" }, { "name": "Inoue, Michio", "degree": "PhD", "year": "2012", "title": "Large-Eddy Simulation of the Flat-Plate Turbulent Boundary Layer at High Reynolds Numbers", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222012-183141047", "creators": [ { "name": { "family": "Inoue", "given": "Michio" }, "id": "Inoue-Michio", "display_name": "Inoue, Michio" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PXTM-W616", "abstract": "The near-wall, subgrid-scale (SGS) model [Chung and Pullin, \"Large-eddy simulation and wall-modeling of turbulent channel flow\", J. Fluid Mech. 631, 281--309 (2009)] is used to perform large-eddy simulations (LES) of the incompressible developing, smooth-wall, flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. This is then used to study several aspects of zero- and adverse-pressure gradient turbulent boundary layers.
\r\n\r\nFirst, LES of the zero-pressure gradient turbulent boundary layer are performed at Reynolds numbers Re\u03b8 based on the free-stream velocity and the momentum thickness in the range Re\u03b8 = 103 - 1012. Results include the inverse skin friction coefficient, \u221a2/Cf, velocity profiles, the shape factor H, the Karman \"constant\", and the Coles wake factor as functions of Re\u03b8. Comparisons with some direct numerical simulation (DNS) and experiment are made, including turbulent intensity data from atmospheric-layer measurements at Re\u03b8 = O(106. At extremely large Re\u03b8, the empirical Coles-Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot of itself probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that the LES is suggestive of the asymptotic, infinite Reynolds-number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum Re\u03b8 of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger Re\u03b8 could be achieved with quad- or higher-precision arithmetic.
\r\n\r\nSecond, the time series velocity signals obtained from LES within the logarithmic region of the zero-pressure gradient turbulent boundary layer are used in combination with an empirical, predictive inner--outer wall model [Marusic et al., \"Predictive model for wall-bounded turbulent flow\", Science 329, 193 (2010)] to calculate the statistics of the fluctuating streamwise velocity in the inner region of the zero-pressure gradient turbulent boundary layer. Results, including spectra and moments up to fourth order, are compared with equivalent predictions using experimental time series, as well as with direct experimental measurements at Reynolds numbers Re\u03c4 based on the friction velocity and the boundary layer thickness, Re\u03c4 =7,300, 13,600 and 19,000. LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers Re\u03c4 =62,000, 100,000 and 200,000 that lie within a gap in log(Re\u03c4) space between laboratory measurements and surface-layer, atmospheric experiments. The present results support a log-like increase in the near-wall peak of the streamwise turbulence intensities with Re\u03c4 and also provide a means of extending LES results at large Reynolds numbers to the near-wall region of wall-bounded turbulent flows.
\r\n\r\nFinally, we apply the wall model to LES of a turbulent boundary layer subject to an adverse pressure gradient. Computed statistics are found to be consistent with recent experiments and some Reynolds number similarity is observed over a range of two orders of magnitude.
" }, { "name": "Karol, Robert Frederick", "degree": "Senior Minor", "year": "2012", "title": "Peak-Seeking Controller for Real-Time Mobile Satellite Tracking", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082012-142445518", "creators": [ { "name": { "family": "Karol", "given": "Robert Frederick" }, "id": "Karol-Robert-Frederick", "display_name": "Karol, Robert Frederick" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "mecheng" ], "doi": "10.7907/CCW3-V522", "abstract": "Increasingly tightened restrictions on antenna beam-width force the use of higher performance hardware in gimbaled satellite communication transceivers. The need for more precise hardware is forcing the price of gimbal-mounted satellites antennas higher. In addition to the increased cost, as more satellites are launched every year, the demand for antenna systems which can receive data from the new satellites grows. Although algorithms capable of tracking a satellite with a mobile antenna have been developed and characterized in detail, instabilities in the system and cross-axis eects degrade the performance. Since an increase in tracking capability would be most benecial if it did not require extensive hardware changes, this project focuses on improvements to the conical scanning algorithm. An algorithm which is one of the oldest, and most common mobile satellite tracking system implementations. Initial work was done on developing and characterizing a new estimator which could be used while continuing to scan the antenna with as few software modications as possible. After successful development, work was done to eliminate the induced scanning motion and gain observability in the system using nothing but the noise inherent in the system." }, { "name": "Khatri, Devvrath", "degree": "PhD", "year": "2012", "title": "Non-Destructive Evaluation of Material System Using Highly Nonlinear Acoustic Waves", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102012-091402754", "creators": [ { "name": { "family": "Khatri", "given": "Devvrath" }, "id": "Khatri-Devvrath", "display_name": "Khatri, Devvrath" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Yang", "given": "Jinkyu" }, "id": "Yang-Jinkyu", "role": "member", "display_name": "Yang, Jinkyu" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P3VR-Q582", "abstract": "A chain of granular particles is one of the most studied examples of highly nonlinear systems deriving its response from the nonlinear Hertzian contact interaction between particles. Interest in these systems derives from their tunable dynamic response, encompassing linear, weakly nonlinear, and strongly nonlinear regimes, controlled by varying the static and dynamic load applied. In chains with a very weak (or zero) static precompression, the system supports the formation and propagation of highly nonlinear solitary waves (HNSWs). The dual-nonlinear interaction between particles (i.e., a power-law type contact potential in compression, and zero strength in tension) combined with discreteness of the system, makes the granular system highly tunable. The propagation properties of these waves, such as traveling pulse width, wave speed, number of separated pulses (single or train of pulses), etc., can be controlled by modifying one or many of the parameters, like the particle's dimension, material properties, static and dynamic force amplitude, the type and duration of the initial excitation applied to the system, and/or the periodicity of the chain. The ability to control the wave properties in such chains has been proposed for several different practical engineering applications.
\r\n\r\nThe dynamic properties of these granular chains have been conventionally studied using discrete particle models (DPMs) which consider the particles in the chains as point masses connected by nonlinear Hertzian springs with the neighboring particles. Although, this is a good approximation under proper circumstances, it does not capture many features of the three dimensional elastic particles such as the elastic wave propagation within the particles, the local deformation of the particles in the vicinity of the contact point, the corresponding changes in the contact area, and the collective vibrations of the particles among others. This thesis focuses on the development of a nite element model (FEM)using the commercially available software Abaqus, which takes into account many of these characteristic features. The nite element model discretizes particles by considering them as three-dimensional deformable bodies of revolution and describes the nonlinear dynamic response of one-dimensional granular chains composed of particles with various geometries and orientations. We showed that particles' geometries and orientations provide additional design parameters for controlling the dynamic response of the system, compared to chains composed of spherical particles. We also showed that the tunable and compact nature of these waves can be used to tailor the properties of HNSWs for specfic application, such as information carriers for actuation and sensing of mechanical properties and boundary effects of adjoining media in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Using experiments and numerics, we characterized interface dynamics between granular media and adjoining linear elastic media, and found that the coupling produced temporary localization of the incident waves at the boundaries between the two media and their decomposition into reflected waves. We monitored the formation of reflected solitary waves propagating back from the interface and found that their properties are sensitive to the geometric and material properties of the adjoining media. The work done in this research enhances our understanding of the basic physics and tunability of nonlinear granular media, and further establishes a theoretical and numerical foundation\r\nin the applications of HNSWs as information carriers.
" }, { "name": "LeHew, Jeffrey Allen", "degree": "PhD", "year": "2012", "title": "Spatio-Temporal Analysis of the Turbulent Boundary Layer and An Investigation of the Effects of Periodic Disturbances", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232012-142127799", "creators": [ { "name": { "family": "LeHew", "given": "Jeffrey Allen" }, "id": "LeHew-Jeffrey-Allen", "display_name": "LeHew, Jeffrey Allen" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/20CM-EV70", "abstract": "The purpose of this study was to investigate the turbulent boundary layer to learn more about the dynamics of the flow and how it might be controlled through the input of spatially and/or temporally periodic disturbances. The first part of this work studies the structure of a zero-pressure-gradient turbulent boundary layer using time-resolved particle image velocimetry in both wall-normal and wall-parallel planes. Using data from wall-parallel measurements, a 3D spectrum over streamwise, spanwise, and temporal wavelengths was constructed for the first time, a major focus of this work. Among several uses, this spectrum allows the calculation of a scale-based convection velocity, that is, a convection velocity for each streamwise-spanwise scale pair present in the flow. This data set also provided a method for investigating the temporal evolution of coherent structures in the flow, of which, swirling coherent structures (SCS), indicative of vortices, and low-momentum regions were investigated thoroughly. The convection velocity and lifetime of the SCS were measured; using histograms of the SCS convection velocity in multiple wall-parallel planes, it was possible to statistically infer different SCS structures that could be categorized as ``attached'' or ``detached'' from the wall.
\r\n\t\r\nA study was also performed on the response of the turbulent boundary layer to a stationary periodic roughness inspired by the scale pattern on the sailfish. The roughness was relatively sparse with element spacing on the order of the boundary layer thickness allowing the measurement of turbulent statistics at different points along the roughness as well as below the crests of the roughness elements, a region not commonly accessible in rough-wall boundary layer studies. The streamwise turbulent statistics were studied using hotwire anemometry from which it was found that while the outer part of the flow remained similar, the near-wall region was perturbed by structures of size similar to the roughness spacing.
" }, { "name": "Mello, Michael", "degree": "PhD", "year": "2012", "title": "Identifying the Unique Ground Motion Signatures of Supershear Earthquakes: Theory and Experiments", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072012-032023169", "creators": [ { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "display_name": "Mello, Michael" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DJDD-2487", "abstract": "The near-field ground motion signatures associated with sub-Rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by Rosakis and co-workers (Xia et al., 2004, 2005a; Lu et al., 2007; Rosakis et al., 2007). Heterodyne laser interferometers enable continuous, high-bandwidth measurements of fault-normal (FN), fault-parallel (FP), and vertical (V) particle velocity ``ground motion\" records at discrete locations on the surface of a Homalite-100 test specimen as a sub-Rayleigh or a supershear rupture sweeps along the frictional fault. Photoelastic interference fringes, acquired using high-speed digital photography, provide a synchronized, spatially resolved, whole field view of the advancing rupture tip and surrounding maximum shear stress field.
\r\n\r\nThe first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures. Experimental results demonstrate that a shear Mach front produced by a stable supershear rupture is characterized by a dominant FP velocity component. The situation is shown to reverse in the sub-Rayleigh rupture speed regime whereby the FN particle velocity component dominates the ground motion record. Additional distinguishing particle velocity signatures, consistent with theoretical and numerical predictions, and repeatedly observed in experimental records are, (1) a pronounced peak in the FP velocity record induced by the leading dilatational field, which sweeps the measurement station in advance of the shear Mach front, and (2) a pronounced velocity swing in the FN record associated with the arrival of a trailing Rayleigh sub-Rayleigh (secondary) rupture, which follows the arrival of the shear Mach front. Analysis of the particle velocity records also confirms 2D steady-state theoretical predictions pertaining to the separation, attenuation, and radiation partitioning of the shear and dilatational portions of the rupture velocity field components.
\r\n\r\nThe second phase of our experimental investigations re-examine the 2002, Mw7.9, Denali fault earthquake and the remarkable set of near-source ground motion records obtained at (PS10), located approximately 85 km east of the epicenter and just 3 km north of the fault along the Alaska pipeline. Motivated by the analysis and interpretation of these records by (Ellsworth et al., 2004; Dunham and Archuleta, 2004, 2005), we attempt to mimic the Denali strike-slip rupture scenario and replicate the PS10 ground motion signatures using a laboratory earthquake experiment. The experiments feature a left-to-right (west-to-east) propagating right lateral rupture within a Homalite-100 test specimen with particle velocity data collected at a near-field station situated just above (north of) the fault. Both sub-Rayleigh and supershear laboratory earthquake experiments are conducted using the Denali PS10 configuration in order to compare and contrast the resulting particle velocity signatures. Supershear laboratory records capture all of the prominent features displayed within the PS10 ground motion records. Noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence. Scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time, to match the scale of the PS10 ground motion records. The strong correlation between the scaled experimental records and the actual PS10 ground motion records support the hypothesis that the Denali strike-slip fault exhibited a supershear burst.
\r\n\r\nFinally, we present a 2D steady state, stress-velocity formulation that relates the FP and FN particle velocity records measured close to the fault, to the evolution of the stress tensor at the same location. A locally steady-state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses, \u03c3xx(t) and \u03c4(t), at the near-fault station. Dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration. Experimental findings are presented, which capture the temporal and spatial distributions of \u03c3xx and \u03c4, evolution of the dynamic friction coefficient, and velocity weakening behavior of a supershear slip-pulse.
" }, { "name": "Ziegler, John Lewis (Jack)", "degree": "PhD", "year": "2012", "title": "Simulations of Compressible, Diffusive, Reactive Flows with Detailed Chemistry Using a High-Order Hybrid WENO-CD Scheme", "advisor": "Pullin, Dale Ian; Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12302011-185742249", "creators": [ { "name": { "family": "Ziegler", "given": "John Lewis (Jack)" }, "id": "Ziegler-John-Lewis-Jack", "orcid": "0000-0001-6127-5567", "display_name": "Ziegler, John Lewis (Jack)" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "co-advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "co-advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZKW8-ES97", "abstract": "A hybrid weighted essentially non-oscillatory (WENO)/centered-difference (CD) numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR), has been developed for the direct numerical simulation (DNS) of the multicomponent, compressive, reactive Navier-Stokes equations. The method enables accurate resolution of diffusive processes within reaction zones. This numerical method is verified with a series of one- and two-dimensional test problems, including a convergence test of a two-dimensional unsteady reactive double Mach reflection problem. Validation of the method is conducted with experimental comparisons of three applications all of which model multi-dimensional, unsteady reactive flow: an irregular propane detonation, shock and detonation bifurcations, and spark ignition deflagrations.
\r\n\r\nThe numerical approach combines time-split reactive source terms with a high-order, shock-capturing scheme specifically designed for diffusive flows. A description of the order-optimized, symmetric, finite difference, flux-based, hybrid WENO / centered-difference scheme is given, along with its implementation in a high-order SAMR framework. The implementation of new techniques for discontinuity flagging, scheme-switching, and high-order prolongation and restriction is described. In particular, the refined methodology does not require upwinded WENO at grid refinement interfaces for stability, allowing high-order prolongation and thereby eliminating a significant source of numerical diffusion within the overall code performance.
\r\n\r\nA minimally reduced irregular detonation mixture mechanism (22 species and 53 reversible reactions) is developed and combined with the WENO-CD numerical method to accurately model two-dimensional hydrocarbon (propane) detonations with detailed chemistry and transport. First of its kind, resolved double Mach reflection (DMR) detonation simulations with a large hyrdocarbon mixture are presented. Detailed discussions and comparisons of the influence of grid resolution, lower-order numerical methods, and inviscid approximations are made in addition to the detailed presentation of fluid dynamics found in an unsteady, highly unstable, reactive DMR simulation. Also conducted are direct experimental comparisons to soot foils and schlieren images with an unresolved large-scale propane detonation channel simulation.
\r\n\r\nThe numerical method is also applied to the DNS of two other problems, detonation/shock bifurcations and spark ignited deflagrations. Through the resolution of viscous/diffusive scales, new insights into how a bifurcated foot develops after a detonation end wall reflection, and how geometry can influence the development of a flame kernel after spark ignition are found.
\r\n" }, { "name": "Boechler, Nicholas Sebastian", "degree": "PhD", "year": "2011", "title": "Granular Crystals: Controlling Mechanical Energy with Nonlinearity and Discreteness", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162011-131929134", "creators": [ { "name": { "family": "Boechler", "given": "Nicholas Sebastian" }, "id": "Boechler-Nicholas-Sebastian", "orcid": "0000-0001-9639-1533", "display_name": "Boechler, Nicholas Sebastian" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Davis", "given": "Gregory L." }, "id": "Davis-G-L", "role": "member", "display_name": "Davis, Gregory L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BAHK-WD44", "abstract": "The presence of structural discreteness and periodicity can affect the propagation of phonons, sound, and other mechanical waves. A fundamental property of many of the periodic structures and materials designed for this purpose is the presence of complete band gaps in their dispersion relation. Waves with frequencies in the band gap cannot propagate and are reflected by the material. Like the concept of a band gap, the functionality of these periodic structures has historically been based on concepts from linear dynamics. Nonlinear systems can offer increased flexibility over linear systems including new ways to localize energy, convert energy between frequencies, and tune the response of the system. Granular crystals are arrays of elastic particles that interact nonlinearly via Hertzian contact, and are a type of nonlinear periodic structure whose response to dynamic excitations can be tuned to encompass linear, weakly nonlinear, and strongly nonlinear regimes. Drawing on ideas from condensed matter physics and nonlinear science, this thesis focuses on how the nonlinearity and structural discreteness of granular crystals can be used to control mechanical energy. The dynamic response of one-dimensional granular crystals composed of compressed elastic spheres (or cylinders) is studied using a combination of experimental, numerical, and analytical techniques. The discovery of fundamental physical phenomena occurring in the linear and weakly nonlinear regimes is described, along with how such phenomena can be used to create new ways to control the propagation of mechanical wave energy. The specific mechanisms investigated include tunable frequency band gaps, discrete breathers, nonlinear localized defect modes, and bifurcations. These mechanisms are utilized to create novel devices for tunable vibration filtering, energy harvesting and conversion, and tunable acoustic rectification." }, { "name": "Gonzalez, Marcial", "degree": "PhD", "year": "2011", "title": "Energy and Force Stepping Integrators in Lagrangian Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-230939247", "creators": [ { "name": { "family": "Gonzalez", "given": "Marcial" }, "id": "Gonzalez-Marcial", "display_name": "Gonzalez, Marcial" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SP10-A207", "abstract": "The overarching goal of this thesis is to develop new numerical time integration schemes for Lagrangian mechanics that better cope with the challenges of understanding the dynamic behavior of materials. We specifically address the formulation of convergent time integration schemes that exhibit good long-term behavior---such as conferred by symplecticity and exact conservation properties---and that have the ability to automatically and asynchronously modulate the time step in different regions of the domain. We achieve these properties in a progression of three developments: (i) energy-stepping, (ii) force-stepping, and (iii) asynchronous energy-stepping integrators. These developments are based on a new method of approximation for Lagrangian mechanics, proposed in this thesis, that consists of replacing the Lagrangian of the system by a sequence of approximate Lagrangians that can be solved exactly. Then, energy-stepping integrators result from replacing the potential energy by a piecewise constant approximation, force-stepping integrators result from replacing the potential energy by a piecewise affine approximation, and asynchronous energy-stepping integrators result from replacing localized potential energies by piecewise constant approximations. Throughout the dissertation, the properties of these time integrators are theoretically predicted and born out by a number of selected examples of application. Furthermore, we address the challenges of understanding the propagation of solitary waves in granular crystals at low impact velocity conditions by investigating the role of energy-trapping effects with the numerical time integration schemes developed in this work.\r\n" }, { "name": "Lopez Jimenez, Francisco", "degree": "PhD", "year": "2011", "title": "Mechanics of Thin Carbon Fiber Composites with a Silicone Matrix", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152011-154253229", "creators": [ { "name": { "family": "Lopez Jimenez", "given": "Francisco" }, "id": "Lopez-Jimenez-Francisco", "display_name": "Lopez Jimenez, Francisco" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A773-KF92", "abstract": "This thesis presents an experimental, numerical and analytical study of the behavior of thin fiber composites with a silicone matrix. The main difference with respect to traditional composites with epoxy matrix is the fact that the soft matrix allows the fibers to microbuckle without breaking. This process acts as a stress relief mechanism during folding, and allows the material to reach very high curvatures, which makes them particularly interesting as components of space deployable structures. The goal of this study is to characterize the behavior and understand the mechanics of this type of composite.
\r\n\r\nExperimental testing of the bending behavior of unidirectional composites with a silicone matrix shows a highly non-linear moment vs. curvature relationship, as well as strain softening under cyclic loading. These effects are not usually observed in composites with an epoxy matrix. In the case of tension in the direction transverse to the fibers, the behavior shows again non-linearity and strain softening, as well as an initial stiffness much higher than what would be expected based on the traditional estimates for fiber composites.
\r\n\r\nThe micro mechanics of the material have been studied with a finite element model. It uses solid elements and a random fiber arrangement produced with a reconstruction process based on micrographs of the material cross section. The simulations capture the macroscopic non-linear response, as well as the fiber microbuckling, and show how microbuckling reduces the strain in the fibers. The model shows good agreement for the bending stiffness of specimens with low fiber volume fraction, but it overestimates the effect of the matrix for more densely packed fibers. This is due to the high matrix strain that derives from the assumption of perfect bonding between fiber and matrix. In the case of tension transverse to the fibers, the model shows a much better agreement with experiments than traditional composite theory, and shows that the reason for the observed high stiffness is the incompressibility of the matrix. In order to capture the strain softening due to fiber debonding, cohesive elements have been introduced between the fibers and the matrix. This allows the model to capture quantitatively the non-linear behavior in the case of loading transverse to the fibers, and the damage due to cyclic loading. A single set of parameters for the cohesive elements produce good agreement with the experimental results for very different values of the fiber volume fraction, and could also be used in the analysis of more complicated loading cases, such as bending or biaxial tension.
\r\n\r\nIn addition to the simulations, a homogenized analytical model has also been created. It extends previous analysis of composites with a soft matrix to the case of very thin composites. It provides a good qualitative description of the material behavior, and it helps understand the mechanics that take place within the material, such as the equilibrium of energy terms leading to a finite wave length, as opposed to microbuckling under compression.
" }, { "name": "Reina Romo, Celia", "degree": "PhD", "year": "2011", "title": "Multiscale Modeling and Simulation of Damage by Void Nucleation and Growth", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11022010-080434454", "creators": [ { "name": { "family": "Reina Romo", "given": "Celia" }, "id": "Reina-Romo-Celua", "display_name": "Reina Romo, Celia" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Marian", "given": "Jaime" }, "id": "Marian-J", "role": "member", "display_name": "Marian, Jaime" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WFYW-AS22", "abstract": "Voids are observed to be generated under sufficient loading in many materials, ranging from polymers and metals to biological tissues. The presence of these voids can have drastic implications at the macroscopic level including strong material softening and more incipient fracture. Developing tools to appropriately account for these effects is therefore very desirable.
\r\n\r\nThis thesis is concerned with both, the appearance of voids (nucleation process) and the modeling and simulation of materials in the presence of voids. A particular nucleation mechanism based on vacancy aggregation in high purity metallic single crystals is analyzed. A multiscale model is developed in order to obtain an approximate value of the time required for vacancies to form sufficiently large clusters for further growth by plastic deformation. It is based on quantum mechanical results, kinetic Monte Carlo methods and continuum mechanics estimates calibrated with quasi-continuum results. The ultimate goal of these simulations is to determine the feasibility of this nucleation mechanism under shock loading conditions, where the temperature and tensions are high and vacancy diffusion is promoted.
\r\n\r\nOn the other hand, the effective behavior of materials with pre-existent voids is analyzed within the general framework of continuum mechanics and is therefore applicable to any material. The overall properties of the heterogeneous material are obtained through a two-level characterization: a representative volume element consisting of a hollow sphere is used to describe the \"microscopic\" fields, and an equivalent homogeneous material is used for the \"macroscopic\" behavior. A variational formulation of this two-scale model is presented. It provides a consistent definition of the macro-variables under general loading conditions, extending the well-known static averaging results so as to include microdynamic effects under finite deformations. This variational framework also provides a suitable starting point for time discretization and consistent definitions within discrete time. The spatial boundary value problem resulting from this multiscale model is solved with a particular spherical shell element specially developed for this problem. The approximation space is based on spherical harmonics, which respects the symmetries of the porous material and allows the representation of the fields on the sphere with very few degrees of freedom. Numerical tools, such as the exact representation of the boundary conditions and an exact quadrature rule, are also provided. The resulting numerical model is verified extensively, demonstrating good convergence results, and its applicability is shown through several material point calculations and a full two-scale finite element implementation.
" }, { "name": "Silva, Michael Lee", "degree": "PhD", "year": "2011", "title": "Damage Evolution in Composite Materials and Sandwich Structures Under Impulse Loading", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122011-154526450", "creators": [ { "name": { "family": "Silva", "given": "Michael Lee" }, "id": "Silva-Michael-Lee", "display_name": "Silva, Michael Lee" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Shukla", "given": "Arun" }, "id": "Shukla-A", "role": "member", "display_name": "Shukla, Arun" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CRX1-7D43", "abstract": "Damage evolution in composite materials is a rather complex phenomenon. There are numerous failure modes in composite materials stemming from the interaction of the various constituent materials and the particular loading conditions. This thesis is concerned with investigating damage evolution in sandwich structures under repeated transient loading conditions associated with impulse loading due to hull slamming of high-speed marine craft. To fully understand the complex stress interactions, a full field technique to reveal stress or strain is required. Several full field techniques exist but are limited to materials with particular optical properties. A full field technique applicable to most materials is known as thermoelastic stress analysis (TSA) and reveals the variation in sum of principal stresses of a cyclically loaded sample by correlating the stresses to a small temperature change occurring at the loading frequency. Digital image correlation (DIC) is another noncontact full field technique that reveals the deformation field by tracking the motion of subsets of a random speckle pattern during the loading cycles.
\r\n\r\nA novel experimental technique to aid in the study of damage progression that combines TSA and DIC simultaneously utilizing a single infrared camera is presented in this thesis. A technique to reliably perform DIC with an infrared (IR) camera is developed utilizing variable emissivity paint. The thermal data can then be corrected for rigid-body motion and deformation such that each pixel represents the same material point in all frames. TSA is then performed on this corrected data, reducing motion blur and increasing accuracy. This combined method with a single infrared camera has several advantages, including a straightforward experimental setup without the need to correct for geometric effects of two spatially separate cameras. Additionally, there is no need for external lighting in TSA as the measured electromagnetic radiation is emitted by the sample\u2019s thermal fields.
\r\n\r\nThe particular stress resolution of TSA will depend on properties of the material of interest but the noise floor for the temperature variation is universal to the camera utilized. For the camera system in this thesis, the noise floor was found to be fairly frequency independent with a magnitude of 0.01 oC, giving the minimum measurable stress for 2024 aluminum alloy of 3.6 MPa and for Nylon of 0.84 MPa. The average displacement range found during a static DIC test with IR images was 0.1 pixels. The maximum displacement variation at 1 Hz was 0.018 pixels. The average variation in strain at 1 Hz was 25 microstrain comparable to traditional DIC measurements in the visible optical regime.
\r\n\r\nThe combined TSA-DIC method in IR was validated with several benchmark example problems including plate structures with holes, cracks, and bimaterials. The validated technique was applied to foam-core sandwich composite beams under repeated simulated wave slamming loading. There are numerous failure modes in sandwich composite materials and the full field stress and strain from TSA and DIC, respectively, allow for improved failure analysis and prediction. Understanding damage in sandwich structures under impulse loading is a complex open area of research and the combined TSA-DIC method provides further insight into the failure process.
\r\n" }, { "name": "Stohlman, Olive Remington", "degree": "PhD", "year": "2011", "title": "Repeatability of Joint-Dominated Deployable Masts", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242011-022845109", "creators": [ { "name": { "family": "Stohlman", "given": "Olive Remington" }, "id": "Stohlman-Olive-Remington", "display_name": "Stohlman, Olive Remington" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Kim", "given": "Yunjin" }, "id": "Kim-Yunjin", "role": "member", "display_name": "Kim, Yunjin" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D3AR-G573", "abstract": "Deployable masts are a class of structure that can be stowed in a small volume and expanded into long, slender, and stable booms. Their greatest benefit as space structures is their packing ratio: masts can typically be packed to a fraction of their deployed length at a diameter only modestly wider than their deployed width. This thesis is concerned with precision deployable masts, which can be stowed and deployed with repeatability of the tip position of better than 1 mm over 60 m. The methods of investigation are experimental measurements of a sample mast and numerical modeling of the mast with specially attention to hysteretic joints.
\r\n\r\nA test article of an ADAM mast was used for the experimental work. Two categories of experi- ment were pursued: measurements of mast components as inputs to the model, and measurements of full bays as validation cases for the model. Measurements of the longeron ball end joint friction, cable preload, and latch behavior are of particular note, and were evaluated for their variability. Further measurements were made of a bay in torsion and a short two-bay mast in shear, showing that there is residual displacement in this mast after shear loading is applied and released.
\r\n\r\nThe modeling approach is described in detail, with attention to the treatment of the mast latches, which lock the structure in its deployed configuration. A user element subroutine was used within the framework of the Abaqus finite element analysis solver to model the behavior of the latches with high fidelity.
\r\n\r\nValidation cases for the model are presented in comparison with experimental observations of a two-bay mast. These cases show that the model captures a number of important and complex nonlinear effects of the hysteretic mast components. Parametric studies of the impacts of component behaviors and modeling practices are explored, emphasizing the impacts of part variability and the idealization of the mast latching mechanisms.
" }, { "name": "Suryanarayana, Phanish", "degree": "PhD", "year": "2011", "title": "Coarse-Graining Kohn-Sham Density Functional Theory", "advisor": "Bhattacharya, Kaushik; Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292011-200916324", "creators": [ { "name": { "family": "Suryanarayana", "given": "Phanish" }, "id": "Suryanarayana-Phanish", "display_name": "Suryanarayana, Phanish" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "co-advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GCKH-EX20", "abstract": "Defects, though present in relatively minute concentrations, play a significant role in determining macroscopic properties. Even vacancies, the simplest and most common type of defect, are fundamental to phenomena like creep, spall and radiation ageing. This necessitates an accurate characterization of defects at physically relevant concentrations, which is typically in parts per million. This represents a unique challenge since both the electronic structure of the defect core as well as the long range elastic field need to be resolved simultaneously. Unfortunately, accurate ab-initio electronic structure calculations are limited to a few hundred atoms, which is orders of magnitude smaller than that necessary for a complete description. Thus, defects represent a truly challenging multiscale problem.
\r\n\r\nDensity functional theory developed by Hohenberg, Kohn and Sham (DFT) is a widely accepted, reliable ab-initio method for computing a wide range of material properties. We present a real-space, non-periodic, finite-element and max-ent formulation for DFT. We transform the original variational problem into a local saddle-point problem, and show its well-posedness by proving the existence of minimizers. Further, we prove the convergence of finite-element approximations including numerical quadratures. Based on domain decomposition, we develop parallel finite-element and max-ent implementations of this formulation capable of performing both all-electron and pseudopotential calculations. We assess the accuracy of the formulation through selected test cases and demonstrate good agreement with the literature.
\r\n\r\nTraditional implementations of DFT solve for the wavefunctions, a procedure which has cubic-scaling with respect to the number of atoms. This places serious limitations on the size of the system which can be studied. Further, they are not amenable to coarse-graining since the wavefunctions need to be orthonormal, a global constraint. To overcome this, we develop a linear-scaling method for DFT where the key idea is to directly evaluate the electron density without solving for the individual wavefunctions. Based on this linear-scaling method, we develop a numerical scheme to coarse-grain DFT derived solely based on approximation theory, without the introduction of any new equations and resultant spurious physics. This allows us to study defects at a fraction of the original computational cost, without any significant loss of accuracy. We demonstrate the efficiency and efficacy of the proposed methods through examples. This work enables the study of defects like vacancies, dislocations, interfaces and crack tips using DFT to be computationally viable.
" }, { "name": "Tchieu, Andrew Allen", "degree": "PhD", "year": "2011", "title": "The Development of Low-Order Models for the Study of Fluid-Structure Interactions", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-133354529", "creators": [ { "name": { "family": "Tchieu", "given": "Andrew Allen" }, "id": "Tchieu-Andrew-Allen", "display_name": "Tchieu, Andrew Allen" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SYHX-8A77", "abstract": "In this work, several low-order models are derived to describe and simulate fluid-structure interaction problems with rigid bodies at a modest computational cost. The models are based on the inviscid flow assumption such that potential theory can be used with, in some cases, point vortices in the flow. Three general areas of application are considered. First, a thin airfoil undergoing small-scale unsteady motions in the presence of a freestream flow is investigated. The low-order model that is developed has only one ordinary differential equation for the fluid dynamic variables. This model is used to briefly investigate vortex-induced flutter in the attached-flow regime and control of a free-flying airfoil using synthetic jet actuators. Second, the vortex-induced vibrations of an arbitrary bluff body in the presence of vortices, with or without a freestream flow, are considered. Several examples of the canonical mass-spring-damper system for a circular cylinder and a flat plate are given to demonstrate the use of the vortex-based model for these applications. Finally, the two-body problem in a potential flow is addressed. A relatively simple solution specific to the doubly connected domain is determined and its resulting force and moment are coupled to the rigid bodies to investigate the mutual interactions between the two bodies. Aspects of drafting behind a forced body, the role of the fluid in elastic collision, and flapping flight are discussed in this context. Although a few specific examples and applications are given for each chapter, the main purpose of the thesis is to present low-order potential flow methods that are applicable to a variety of situations.\r\n" }, { "name": "Venturini, Gabriela Natalia", "degree": "PhD", "year": "2011", "title": "Topics in Multiscale Modeling of Metals and Metallic Alloys", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11222010-114324484", "creators": [ { "name": { "family": "Venturini", "given": "Gabriela Natalia" }, "id": "Venturini-Gabriela-Natalia", "display_name": "Venturini, Gabriela Natalia" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Marian", "given": "Jaime" }, "id": "Marian-J", "orcid": "0000-0001-9000-3405", "role": "member", "display_name": "Marian, Jaime" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D6YS-B365", "abstract": "In a number of areas of application, the behavior of systems depends sensitively on properties that pertain to the atomistic scale, i. e., the angstrom and femtosecond scales. However, generally the behaviors of interest are macroscopic and are characterized by slow evolution on the scale of meters and years. This broad disparity of length and time scales places extraordinary challenges in computational material science.
\r\n\r\nThe overarching objective of this dissertation is to address the problem of multiple space and time scales in atomistic systems undergoing slow macroscopic evolution while retaining full atomistic detail. Our approach may be summarized as follows:
\r\n\r\n(1) The issue of accounting for finite temperature in coarse grained systems has not been solved entirely. For finite temperature systems at equilibrium, constructing an effective free energy in terms of a reduced set of atomic degrees of freedom is still an open area of research. In particular, the thermal vibrations of the missing degrees of freedom need to be accounted for. This is specially important if the aim of the simulation is to determine the dynamic properties of a system, or to allow the transmission of dynamic information between regions of different spatial discretization. To this end, we introduce a framework to simulate (spatially) coarse dynamic systems using the Quasicontinuum method (QC). The equations of motion are strictly derived from dissipative Lagrangian mechanics, which provides a classical Langevin implementation where the characteristic time is governed by the vibrations of the finest length scale in the computational cell. In order to assess the framework's ability to transmit information across scales, we study the phonon impoverish spectra in coarse regions and the resulting underestimation of thermal equilibrium properties.
\r\n\r\n(2) Atomistic simulations have been employed for the past thirty years to determine structural and thermodynamic (equilibrium) properties of solids and their defects over a wide range of temperatures and pressures. The traditional Monte Carlo (MC) and Molecular Dynamics (MD) methods, while ideally suited to these calculations, require appreciable computational resources in order to calculate the long-time averages from which properties are obtained. In order to permit a reasonably quick, but accurate determination of the equilibrium properties of interest, we present an extension of the \u201cmaximum entropy\u201d method to build effective alloy potentials while avoiding the treatment of all the system's atomic degrees of freedom. We assess the validity of the model by testing its ability to reproduce experimental measurements.
\r\n\r\n(3) Based upon these effective potentials, we present a numerical framework capable of following the time evolution of atomistic systems over time windows currently beyond the scope of traditional atomistic methods such as Molecular Dynamics (MD) or Monte Carlo (MC). This is accomplished while retaining the underlying atomistic description of the material. We formulate a discrete variational setting in which the simulation of time-dependent phenomena is reduced to a sequence of incremental problems, each characterized by a variational principle. In this fashion we are able to study the interplay between deformation and diffusion using time steps or strain rates that are orders of magnitude larger or smaller than their MD|MC counterparts.
\r\n\r\n(4) We formulate a new class of \u201cReplica Time Integrators\u201d (RTIs) that allows for the two-way transmission of thermal phonons across mesh interfaces. This two-way transmission is accomplished by representing the state of the coarse region by a collection of identical copies or \u201creplicas\u201d of itself. Each replica runs at its own slow time step and is out-of-phase with respect to the others by one fast time step. Then, each replica is capable of absorbing from the fine region the elementary signal that is in phase with the replica. Conversely, each replica is capable of supporting --and transmitting to the fine region-- an elementary signal of a certain phase. Since fine and coarse regions evolve asynchronously in time, RTIs permit both spatial and temporal coarse graining of the system of interest. Using a combination of phase-error analysis and numerical testing we find that RTIs are convergent, and allow step waves and thermal phonons to cross mesh interfaces in both directions losslessly.
\r\n" }, { "name": "Ward, Geoffrey M.", "degree": "PhD", "year": "2011", "title": "The Simulation of Shock- and Impact-Driven Flows with Mie-Gr\u00fcneisen Equations of State", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162010-115725941", "creators": [ { "name": { "family": "Ward", "given": "Geoffrey M." }, "id": "Ward-Geoffrey-M", "display_name": "Ward, Geoffrey M." } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8Q2Q-GT29", "abstract": "An investigation of shock- and impact-driven flows with Mie-Gr\u00fcneisen equation of state derived from a linear shock-particle speed Hugoniot relationship is presented. Cartesian mesh methods using structured adaptive refinement are applied to simulate several flows of interest in an Eulerian frame of reference. The flows central to the investigation include planar Richtmyer-Meshkov instability, the impact of a sphere with a plate, and an impact-driven Mach stem.
\r\n\r\nFirst, for multicomponent shock-driven flows, a dimensionally unsplit, spatially high-order, hybrid, center-difference, limiter methodology is developed. Effective switching between center-difference and upwinding schemes is achieved by a set of robust tolerance and Lax-entropy-based criteria [49]. Oscillations that result from such a mixed stencil scheme are minimized by requiring that the upwinding method approaches the center-difference method in smooth regions. To attain this property a blending limiter is introduced based on the norm of the deviation of WENO reconstruction weights from ideal. The scheme is first demonstrated successfully for the linear advection equation in spatially fourth- and sixth-order forms. A spatially fourth-order version of the method that combines a skew-symmetric kinetic-energy preserving center-difference scheme with a Roe-Riemann solver is then developed and implemented in Caltech's Adaptive Mesh Refinement, Object-oriented C++ (AMROC) [16,17] framework for Euler flows.
\r\n\r\nThe solver is then applied to investigate planar Richtmyer-Meshkov instability in the context of an equation of state comparison. Comparisons of simulations with materials modeled by isotropic stress Mie-Gr\u00fcneisen equations of state derived from a linear shock-particle speed Hugoniot relationship [36,52] to those of perfect gases are made with the intention of exposing the role of the equation of state. First, results for single- and triple-mode planar Richtmyer-Meshkov instability between mid-ocean ridge basalt (MORB) and molybdenum modeled by Mie-Gr\u00fcneisen equations of state are presented for the case of a reflected shock. The single-mode case is explored for incident shock Mach numbers of 1.5 and 2.5. For the planar triple-mode case a single incident Mach number of 2.5 is examined with the initial corrugation wave numbers related by k\u2081=k\u2082+k\u2083. A comparison is drawn to Richtmyer-Meshkov instability in fluids with perfect gas equations of state utilizing matching of a nondimensional pressure jump across the incident shock, the post-shock Atwood ratio, post-shock amplitude-to-wavelength ratio, and time nondimensionalized by the Rcithmyer linear-growth rate time constant prediction. Result comparison demonstrates difference in start-up time and growth rate oscillations. Growth rate oscillation frequency is seen to correlate directly to the expected oscillation frequency of the transmitted and reflected shocks. For the single-mode cases, further comparison is given for vorticity distribution and corrugation centerline shortly after shock interaction that demonstrates only minor differences.
\r\n\r\nAdditionally, examined is single-mode Richtmyer-Meshkov instability when a reflected expansion wave is present for incident Mach numbers of 1.5 and 2.5. Comparison to perfect gas solutions in such cases yields a higher degree of similarity in start-up time and growth rate oscillations. Vorticity distribution and corrugation centerline shortly after shock interaction is also examined. The formation of incipient weak shock waves in the heavy fluid driven by waves emanating from the perturbed transmitted shock is observed when an expansion wave is reflected.
\r\n\r\nNext, the ghost fluid method [83] is explored for application to impact-driven flows with Mie-Gr\u00fcneisen equations of state in a vacuum. Free surfaces are defined utilizing a level-set approach. The level-set is reinitialized to the signed distance function periodically by solution to a Hamilton-Jacobi differential equation in artificial time. Flux reconstruction along each Cartesian direction of the domain is performed by subdividing in a way that allows for robust treatment of grid-scale sized voids. Ghost cells in voided regions near the material-vacuum interface are determined from surface-normal Riemann problem solution. The method is then applied to several impact problems of interest. First, a one-dimensional impact problem is examined in Mie-Gr\u00fcneisen aluminum with simple point erosion used to model separation by spallation under high tension. A similar three-dimensional axisymmetric simulation of two rods impacting is then performed without a model for spallation. Further results for three-dimensional axisymmetric simulation of a sphere hitting a plate are then presented.
\r\n\r\nFinally, a brief investigation of the assumptions utilized in modeling solids as isotropic fluids is undertaken. An Eulerian solver approach to handling elastic and elastic-plastic solids is utilized for comparison to the simple fluid model assumption. First, in one dimension an impact problem is examined for elastic, elastic-plastic, and fluid equations of state for aluminum. The results demonstrate that in one dimension the fluid models the plastic shock structure of the flow well. Further investigation is made using a three-dimensional axisymmetric simulation of an impact problem involving a copper cylinder surrounded by aluminum. An aluminum slab impact drives a faster shock in the outer aluminum region yielding a Mach reflection in the copper. The results demonstrate similar plastic shock structures. Several differences are also notable that include a lack of roll-up instability at the material interface and slip-line emanating from the Mach stem's triple point.
" }, { "name": "Yang, Yue", "degree": "PhD", "year": "2011", "title": "Lagrangian and Vortex-Surface Fields in Turbulence", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212011-233246689", "creators": [ { "name": { "family": "Yang", "given": "Yue" }, "id": "Yang-Yue", "display_name": "Yang, Yue" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DF3E-G629", "abstract": "In this thesis, we focus on Lagrangian investigations of isotropic turbulence, wall-bounded turbulence and vortex dynamics. In particular, the evolutionary multi-scale geometry of Lagrangian structures is quantified and analyzed. Additionally, we also study the dynamics of vortex-surface fields for some simple viscous flows with both Taylor--Green and Kida--Pelz initial conditions.
\r\n\r\nFirst, we study the non-local geometry of finite-sized Lagrangian structures in both stationary, evolving homogenous isotropic turbulence and also with a frozen turbulent velocity field. The multi-scale geometric analysis is applied on the evolution of Lagrangian fields, obtained by a particle-backward-tracking method, to extract Lagrangian structures at different length scales and to characterize their non-local geometry in a space of reduced geometrical parameters. Next, we report a geometric study of both evolving Lagrangian, and also instantaneous Eulerian structures in turbulent channel flow at low and moderate Reynolds numbers. A multi-scale and multi-directional analysis, based on the mirror-extended curvelet transform, is developed to quantify flow structure geometry including the averaged inclination and sweep angles of both classes of turbulent structures at multiple scales ranging from the half-height of the channel to several viscous length scales. Results for turbulent channel flow include the geometry of candidate quasi-streamwise vortices in the near-wall region, the structural evolution of near-wall vortices, and evidence for the existence and geometry of structure packets based on statistical inter-scale correlations.
\r\n\r\nIn order to explore the connection and corresponding representations between Lagrangian kinematics and vortex dynamics, we develop a theoretical formulation and numerical methods for computation of the evolution of a vortex-surface field. Iso-surfaces of the vortex-surface field define vortex surfaces. A systematic methodology is developed for constructing smooth vortex-surface fields for initial Taylor--Green and Kida--Pelz velocity fields by using an optimization approach. Equations describing the evolution of vortex-surface fields are then obtained for both inviscid and viscous incompressible flows. Numerical results on the evolution of vortex-surface fields clarify the continuous vortex dynamics in viscous Taylor--Green and Kida--Pelz flows including the vortex reconnection, rolling-up of vortex tubes, vorticity intensification between anti-parallel vortex tubes, and vortex stretching and twisting. This suggests a possible scenario for explaining the transition from a smooth laminar flow to turbulent flow in terms of topology and geometry of vortex surfaces.
\r\n" }, { "name": "Bane, Sally Page Moffett", "degree": "PhD", "year": "2010", "title": "Spark Ignition: Experimental and Numerical Investigation With Application to Aviation Safety", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-173243262", "creators": [ { "name": { "family": "Bane", "given": "Sally Page Moffett" }, "id": "Bane-Sally-Page-Moffett", "orcid": "0000-0002-4764-3228", "display_name": "Bane, Sally Page Moffett" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W1NB-5W06", "abstract": "Determining the risk of accidental ignition of flammable mixtures is a topic of tremendous importance in industry and aviation safety. The concept of minimum ignition energy (MIE) has traditionally formed the basis for studying ignition hazards of fuels. However, in recent years, particularly in the aviation safety industry, the viewpoint has changed to one where ignition is statistical in nature. Approaching ignition as statistical rather than a threshold phenomenon appears to be more consistent with the inherent variability in the engineering test data.
\r\n\r\nIgnition tests were performed in lean hydrogen-based aviation test mixtures and in two hexane-air mixtures using low-energy capacitive spark ignition systems. Tests were carried out using both short, fixed sparks (1 to 2 mm) and variable length sparks up to 10 mm. The results were analyzed using statistical tools to obtain probability distributions for ignition versus spark energy and spark energy density (energy per unit spark length). Results show that a single threshold MIE value does not exist, and that the energy per unit length may be a more appropriate parameter for quantifying the risk of ignition than only the energy. The probability of ignition versus spark charge was also investigated, and the statistical results for the spark charge and spark energy density were compared. It was found that the test results were less variable with respect to the spark charge than the energy density. However, variability was still present due to phenomena such as plasma instabilities and cathode effects that are caused by the electrodynamics.
\r\n\r\nWork was also done to develop a two-dimensional numerical model of spark ignition that accurately simulates all physical scales of the fluid mechanics and chemistry. In this work a two-dimensional model of spark discharge in air and spark ignition was developed using the non-reactive and reactive Navier-Stokes equations. One-step chemistry models were used to allow for highly resolved simulations, and methods for calculating effective one-step parameters were developed using constant pressure explosion theory. The one-step model was tuned to accurately simulate the flame speed, temperature, and straining behavior using one-dimensional flame computations. The simulations were performed with three different electrode geometries to investigate the effect of the geometry on the fluid mechanics of the evolving spark kernel and on flame formation. The computational results were compared with high-speed schlieren visualization of spark and ignition kernels. It was found that the electrode geometry had a significant effect on the fluid motion following spark discharge and hence influences the ignition process.
\r\n" }, { "name": "Choi, Inki", "degree": "Engineering Degree", "year": "2010", "title": "Catalytic Modification of Flammable Atmosphere in Aircraft Fuel Tanks ", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092010-102349721", "creators": [ { "name": { "family": "Choi", "given": "Inki" }, "id": "Choi-Inki", "display_name": "Choi, Inki" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/69YQ-XZ33", "abstract": "A facility for investigating catalytic combustion and measurement of fuel molecule concentration was built to examine catalyst candidates for inerting systems in aircraft. The facility consists of fuel and oxygen supplies, a catalytic-bed reactor, heating system, and laser-based diagnostics. Two supplementary systems consisting of a calibration test cell and a nitrogen-purged glove box were also constructed. The catalyst under investigation was platinum, and it was mixed with silica particles to increase the surface area available to react. The catalyst/silica mixture was placed in a narrow channel section of the reactor and supported from both sides by glass wool. The fuels investigated were n-octane and n-nonane because their vapor pressure is sufficiently high to create ammable gaseous mixtures with atmospheric air at room temperature. Calibration experiments were performed to determine the absorption cross-section of the two fuels as a function of temperature. The cross-section values were then used to determine the fuel concentration before the flow entered the reactor and after exposure to the heated catalyst. An initial set of experiments was performed with the catalytic-bed reactor at two temperatures, 255 and 500\u00b0C, to investigate pyrolysis and oxidation of the fuel. The presence of the catalyst increased the degree of pyrolysis and oxidation at both temperatures. The results show that catalytic modification of ammable atmospheres may yield a viable alternative for inerting aircraft fuel tanks. However, further tests are required to produce oxidation at sufficiently low temperature to comply with aircraft safety regulations.\r\n" }, { "name": "Karnesky, James Alan", "degree": "PhD", "year": "2010", "title": "Detonation Induced Strain in Tubes", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142010-174001426", "creators": [ { "name": { "family": "Karnesky", "given": "James Alan" }, "id": "Karnesky-James-Alan", "display_name": "Karnesky, James Alan" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GTKC-FY91", "abstract": "When a detonation wave propagates through a piping system, it acts as a traveling pressure load to the pipe wall. The detonation wave must be followed by an expansion wave in order to bring the combustion products to zero velocity at the ignition end. When it reaches a closed end-wall, a reflected shock is formed which propagates back into the tube with a decaying pressure. The present study aims to develop predictive models for the stresses and strains produced in such a situation. To this end, two series of experiments are discussed. The first series used strain gauges and a laser vibrometer to measure the elastic response of the tube to the incident detonation in thin aluminum tubes. The second series used strain gauges and high speed video to measure the plastic response of steel tubes to incident detonations and reflected shocks. In these experiments a novel mode of plastic deformation was discovered in which the residual plastic deformation in the tube wall had a periodic sinusoidal pattern.
\r\n\r\nA semi-empirical model of the pressure history was developed for use as a boundary condition in models of the mechanical response of the tube. This model was tested against experiment, and it was found that the pressure and arrival time could not be simultaneously predicted from the simple model. This and the general form of the pressure traces in the experiment seem to suggest an interaction between the reflected shock and the boundary layer behind the detonation resulting in a possible bifurcation in the reflected shock wave.
\r\n\r\nWith these considerations in mind, the model was applied to single degree of freedom and finite element models of the tube wall. The ripples observed in the experiment were present in the 1-D single degree of freedom models, indicating that they are a result of the interaction of the reflected shock wave with the elastic oscillations set in motion by the detonation wave. Strain-rate hardening was found to be an important consideration under detonation loading conditions. With proper consideration of rate hardening, a single material model may be used to arrive at reasonable predictions the plastic strains resulting from detonations and reflections at initial pressures of 2 and 3 bar initial pressures.
" }, { "name": "Kim, Daegyoum", "degree": "PhD", "year": "2010", "title": "Characteristics of Three-dimensional Vortex Formation and Propulsive Performance in Flapping Locomotion", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-114858790", "creators": [ { "name": { "family": "Kim", "given": "Daegyoum" }, "id": "Kim-Daegyoum", "display_name": "Kim, Daegyoum" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8VZJ-7Z78", "abstract": "Three-dimensional vortex formation and propulsive performance were studied experimentally to identify some of the main characteristic mechanisms of flapping locomotion. Mechanical models with thin plates were used to simulate flapping and translating motions of animal propulsors. Three-dimensional flow fields were mapped quantitatively using defocusing digital particle image velocimetry.
\r\n\r\nFirst, vortex structures made by impulsively translating low aspect-ratio plates were studied. The investigation of translating plates with a 90 degree angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flat-rigid, flexible, and curved-rigid thin plastic plates with the same aspect ratio were used to compare their vortex structures and hydrodynamic forces. The interaction of the tip flow and the nearby vortex is a critical flow phenomenon to distinguish vortex patterns among these three cases. In the flexible plate case, slow development of the vortex structure causes a small initial peak in hydrodynamic force during the acceleration phase. However, after the initial peak, the flexible plate generates large force magnitude comparable to that of the flat-rigid plate case.
\r\n \r\nDrag-based paddling propulsion was also studied to explain some of the fundamental differences in vortex formation of lift-based and drag-based propulsions. While the temporal change of the inner area enclosed by the vortex loop is an important factor in thrust generation of lift-based propulsion, the temporal change of the vortex strength becomes more important in drag-based propulsion. Spanwise flow behind the paddling plate plays an important role in tip vortex motion and thrust generation. The distribution of spanwise flow depends on the propulsor shape and the Reynolds number. A delta-shaped propulsor generates strong spanwise flow compared to a rectangular propulsor. For the low Reynolds number case, the spanwise flow is not as strong as that of the high Reynolds number case. The flexible propulsor can smooth out force peaks during impulsive motions without sacrificing total impulse, which is advantageous in avoiding structural failures and stabilizing body motion. The role of the stopping vortex was addressed in optimizing a stroke angle of paddling animals.
\r\n\r\nIn addition, vortex formation of clapping propulsion was investigated by varying aspect ratio and stroke angle. A low aspect-ratio propulsor produces larger total impulse than a high aspect-ratio propulsor. As the aspect ratio increases, circulation of the vortex is strengthened, and the inner area enclosed by the vortex structure tends to enlarge. Moreover, in terms of thrust, the advantage of a single plate over double clapping plates is larger for the lower aspect-ratio case. These results offer information to better understand the benefit of low aspect-ratio wings in force generation under specific locomotion modes. When a pair of plates claps, a vortex loop forms from two counter-rotating tip vortices by a reconnection process. The dynamics of wake structures are dependent on the aspect ratio and the stroke angle.
\r\n\r\nVortex formation and vorticity transport processes of translating and rotating plates with a 45 degree angle of attack were investigated as well. In both translating and rotating cases, the spanwise flow over the plate and the vorticity tilting process inside the leading-edge vortex were observed. The distribution of spanwise flow is a prominent distinction between the vortex structures of these two cases. While spanwise flow is confined inside the leading-edge vortex for the translating case, it is widely present over the plate and the wake region of the rotating case. As the Reynolds number decreases, due to the increase in viscosity, leading-edge and tip vortices tend to spread inside the area swept by the rotating plate, which results in lower lift force generation.
\r\n\r\nLastly, for translating motion, the dynamics of the vortex in corner regions was compared among three different corner shapes. For a large corner angle, the forward movement of the vortex tends to be uniform along the plate edges. However, for a small corner angle, the vortex close to the corner moves forward following the plate while the vortex away from the corner retards its forward movement.
" }, { "name": "Lamberson, Leslie Elise", "degree": "PhD", "year": "2010", "title": "Dynamic Optical Investigations of Hypervelocity Impact Damage", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-183132978", "creators": [ { "name": { "family": "Lamberson", "given": "Leslie Elise" }, "id": "Lamberson-Leslie-Elise", "orcid": "0000-0002-1340-4667", "display_name": "Lamberson, Leslie Elise" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AQJH-3D60", "abstract": "One of the prominent threats in the endeavor to develop next-generation space assets is the risk of space debris impact in earth\u2019s orbit and micrometeoroid impact damage in near-earth orbit and deep space. To date, there is no study available which concentrates on the analysis of dynamic crack growth from hypervelocity impacts on such structures, resulting in their eventual catastrophic degradation. Experiments conducted using a unique two-stage light-gas gun facility have examined the in situ dynamic fracture of brittle polymers subjected to this high-energy-density event. Optical techniques of caustics and photoelasticity, combined with high-speed photography up to 100 million frames per second, analyze crack growth behavior of Mylar and Homalite 100 thin plates after impact by a 1.8 mm diameter nylon 6-6 right cylindrical slug at velocities ranging from 3 to 7 km/s (7000\u201315500 mph). Crack speeds in both polymers averaged between 0.2 and 0.47 cR, the Rayleigh wave speed (450\u20131000 mph). Shadow spots and surrounding caustics reveal time histories of the dynamic stress intensity factor, as well as the energy release rate ahead of the mode-I, or opening, crack tips. Results indicate that even under extreme impact conditions of out of-plane loading, highly localized heating, and energetic impact phenomena involving plasma formation and ejecta, the dynamic fracture process occurs during a deformation regime dominated by in-plane loading. These findings imply that the reliability of impacted, thin-walled, plate and shell space structures, idealized by the experimental configuration investigated, can be predicted by the well defined principles of classical dynamic fracture mechanics." }, { "name": "Norman, Adam Keith", "degree": "PhD", "year": "2010", "title": "Effect of Surface Morphological Changes on Flow Over a Sphere", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212010-124044645", "creators": [ { "name": { "family": "Norman", "given": "Adam Keith" }, "id": "Norman-Adam-Keith", "display_name": "Norman, Adam Keith" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SED1-5250", "abstract": "An experimental investigation was undertaken to examine the effect of a morphing surface on the flow over a sphere in the Reynolds number range of 5x10\u2074 to 5x10\u2075. Here, a morphing surface is defined as a continuous surface that undergoes small amplitude changes in order to excite flow instabilities, rather than utilizing large mechanical changes to the overall shape as with traditional aerodynamic control surfaces. The sphere was chosen as an ideal geometry for testing morphing surfaces, because of the well-known sensitivity of the flow to small asymmetries on the surface. In this study, an approximation of a morphing surface was made by dynamically moving a small isolated roughness element along the sphere, thus producing small amplitude time-dependent changes to the surface shape. An experimental apparatus was designed that produced the actuation with an internal motor, which moved the roughness element via magnetic interaction. A three-component piezoelectric force sensor placed inside the sphere allowed for accurate, instantaneous measurements of the global effect of the actuator on the flow. It was found that the moving roughness could produce an instantaneous lateral force as large as the drag. Simultaneous force and particle image velocimetry measurements in the subcritical regime were used to show that there is a relatively long timescale associated with the instability growth, entrainment of fluid, and local change of the position of separation. This allowed the roughness to trip an extended region of the flow at once. It is shown that the three-dimensionality of the disturbance leads to the production of two helical counter-rotating vortices in the wake. In addition, it is demonstrated that a mean side force can be obtained by oscillating the roughness element about a point, producing a lateral force an order of magnitude larger than the force caused by a stationary roughness element. Finally, the results from the dynamic roughness were used to help interpret the underlying physical mechanisms that govern the forcing on a smooth sphere." }, { "name": "Sullivan, Regina Mariko", "degree": "PhD", "year": "2010", "title": "The Physics of High-Velocity Ions in the Hall Thruster Near-Field", "advisor": "Shepherd, Joseph E.; Johnson, Lee K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022010-134100215", "creators": [ { "name": { "family": "Sullivan", "given": "Regina Mariko" }, "id": "Sullivan-Regina-Mariko", "display_name": "Sullivan, Regina Mariko" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "co-advisor", "display_name": "Johnson, Lee K." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "member", "display_name": "Johnson, Lee K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8F2Y-NM32", "abstract": "A study of the physics underlying high velocity ion trajectories within the near-field region of a Hall thruster plume is presented. In this context, \"high velocity\" ions are ions that have been accelerated through the full potential drop of the thruster (sometimes referred to as \"primary energy\" or \"primary beam energy\" ions). Results from an experimental survey of an SPT-70 thruster plume are shown, along with simulated data from a Hall thruster code and from a plasma sheath model. Two main features are examined: the central jet along the Hall thruster centerline, and the population of high velocity ions at high angles.
\r\n\r\nIn the experimental portion of the investigation, three diagnostic instruments were employed: (1) a Faraday probe for measuring ion current density, (2) an ExB velocity filter for mapping ions with the primary beam energy, and (3) a Retarding Potential Analyzer (RPA) for determining ion energy distributions. In the numerical portion, two codes were employed: (1) a hybrid-PIC Hall thruster code known as HPHall, and (2) a model of the plasma sheath near the exit plane of the thruster, which was developed by the author.
\r\n\r\nA comparison between the measured and simulated data sets is made, to analyze the degree to which different mechanisms are responsible for the evolution of the thruster\r\nplume in the near-field region. This analysis shows that the central jet is both a function of symmetric expansion of the ion beam as well as asymmetry in the internal potential field of the thruster. Additionally, it is suggested that high energy, high angle ions could be generated given a specific internal electric field configuration, while oscillations are ruled out as the cause of these ions. The results from the sheath model show that while the sheath can change trajectory angles by 10 to 20 degrees, it can not fully explain the presence of\r\nhigh angle ions with high energies.
" }, { "name": "Chung, Daniel", "degree": "PhD", "year": "2009", "title": "Numerical Simulation and Subgrid-Scale Modeling of Mixing and Wall-Bounded Turbulent Flows", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-123828", "creators": [ { "name": { "family": "Chung", "given": "Daniel" }, "id": "Chung-Daniel", "orcid": "0000-0003-3732-364X", "display_name": "Chung, Daniel" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NE1Y-M812", "abstract": "We extend the idea of multiscale large-eddy simulation (LES), the underresolved fluid dynamical simulation that is augmented with a physical description of subgrid-scale (SGS) dynamics. Using a vortex-based SGS model, we consider two areas of specialization: active (buoyant) scalar mixing and wall-bounded turbulence.
\r\n\r\nFirst, we develop a novel method to perform direct numerical simulation (DNS) of statistically stationary buoyancy-driven turbulence by using the fringe-region technique within a triply periodic domain, in which a mixing region is sandwiched between two fringes that supply the flow with unmixed fluids---heavy on top of light. Spectra exhibit small-scale universality, as evidenced by collapse in inner scales. A comparison with high-resolution DNS spectra from Rayleigh--Taylor turbulence reveals some similarities.
\r\n\r\nWe perform LES of this flow to show that a passive scalar SGS model can also be used in an unstably stratified environment. LES spectra, including subgrid extensions, show good agreement with DNS data. For stably stratified flows, we develop an active scalar SGS model by performing a perturbation expansion in small Richardson numbers of the passive scalar SGS model to obtain an expression for the SGS scalar flux that contains buoyancy corrections.
\r\n\r\nWe then develop a wall model for LES in which the near-wall region is unresolved. A special near-wall SGS model is constructed by averaging the streamwise momentum equation together with an assumption of local--inner scaling, giving an ordinary differential equation for the local wall shear stress that is coupled with the LES. An extended form of the stretched-vortex SGS model, which incorporates the production of near-wall Reynolds shear stresses due to the winding of streamwise momentum by near-wall attached SGS vortices, then provides a log relation for the off-wall LES boundary conditions. A Karman-like constant is calculated dynamically as part of the LES. With this closure we perform LES of turbulent channel flow for friction-velocity Reynolds numbers $Rey_\tau=2,\textrm{k}$--$20,\textrm{M}$. Results, including SGS-extended spectra, compare favorably with DNS at Rey_\tau=2,\textrm{k}$, and maintain an $O(1)$ grid dependence on $Rey_\tau$.
\r\n\r\nFinally, we apply the wall model to LES of long channels to capture effects of large-scale structures. Computed correlations are found to be consistent with recent experiments.
" }, { "name": "Harish, Ajay Bangalore", "degree": "Engineering Degree", "year": "2009", "title": "Simulation of Dynamic Interface Fracture Using Spectral Boundary Integral Method", "advisor": "Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272009-165712", "creators": [ { "name": { "family": "Harish", "given": "Ajay Bangalore" }, "id": "Harish-Ajay-Bangalore", "display_name": "Harish, Ajay Bangalore" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B6P7-F707", "abstract": "Simulation of three-dimensional dynamic fracture events constitutes one of the most challenging topics in the field of computational mechanics. Spontaneous dynamic fracture along the interface of two elastic solids is of great importance and interest to a number of disciplines in engineering and science. Applications include dynamic fractures in aircraft structures, earthquakes, thermal shocks in nuclear containment vessels and delamination in layered composite materials.
\r\n\r\nThis thesis presents numerical modeling of laboratory experiments on dynamic shear rupture, giving an insight into the experimental nucleation conditions. We describe a methodology of dynamic rupture simulation using spectral boundary integral method, including the theoretical background, numerical implementation and cohesive zone models relevant to the dynamic fracture problem. The developed numerical implementation is validated using the simulation of Lamb's problem of step loading on an elastic half space and mode I crack propagation along a bonded interface. Then the numerical model and its comparison with experimental measurements is used to investigate the initiation procedure of the dynamic rupture experiments. The inferred parameters of the initiation procedure can be used in future studies to model the experimental results on supershear transition and rupture models.
\r\n" }, { "name": "Kramer, Richard Michael Jack", "degree": "PhD", "year": "2009", "title": "Stable High-Order Finite-Difference Interface Schemes with Application to the Richtmyer-Meshkov Instability", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-095507", "creators": [ { "name": { "family": "Kramer", "given": "Richard Michael Jack" }, "id": "Kramer-Richard-Michael-Jack", "display_name": "Kramer, Richard Michael Jack" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HXGM-DC92", "abstract": "High-order adaptive mesh refinement offers the potential for accurate and efficient resolution of problems in fluid dynamics and other fields where a wide range of length scales is present. A critical requirement for the interface closures used with these methods is stability in the context of hyperbolic systems of partial differential equations.
\r\n\r\nIn this study, a class of energy-stable high-order finite-difference interface closures is presented for grids with step resolution changes in one dimension. Asymptotic stability in time for these schemes is achieved by imposing a summation-by-parts condition on the interface closure, which is thus also nondissipative. Interface closures compatible with interior fourth- and sixth-order explicit, and fourth-order implicit centered schemes are presented. Validation tests include linear and nonlinear problems in one and in two dimensions with tensor-product grid refinement.
\r\n\r\nA second class of stable high-order interface closures is presented for two-dimensional cell-centered grids with patch-refinement and step-changes in resolution. For these grids, coarse and fine nodes are not aligned at the mesh interfaces, resulting in hanging nodes. Stability is achieved by again imposing a summation-by-parts condition, resulting in nondissipative closures, at the cost of accuracy at corner interfaces. Interface stencils for an explicit fourth-order finite-difference scheme are presented for each geometry. Validation tests confirm the stability and accuracy of these closures for linear and nonlinear problems.
\r\n\r\nThe Richtmyer-Meshkov instability is investigated using a novel first-order perturbation of the two-dimensional Navier-Stokes equations about a shock-resolved base flow. The computational domain is efficiently resolved using the one-dimensional fourth-order interface scheme. Results are compared to analytic models of the instability, showing agreement with predicted asymptotic growth rates in the inviscid range, while significant discrepancies are noted in the transient growth phase. Viscous effects are found to be poorly predicted by existing models.
\r\n" }, { "name": "Kramer, Sharlotte Lorraine Bolyard", "degree": "PhD", "year": "2009", "title": "Phase-Shifting Full-Field Interferometric Methods for In-Plane Tensorial Stress Determination for Fracture Studies", "advisor": "Ravichandran, Guruswami; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272009-094456", "creators": [ { "name": { "family": "Kramer", "given": "Sharlotte Lorraine Bolyard" }, "id": "Kramer-Sharlotte-Lorraine-Bolyard", "orcid": "0000-0001-6015-8385", "display_name": "Kramer, Sharlotte Lorraine Bolyard" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M9NV-T722", "abstract": "Anisotropic fracture criteria can be established with understanding of full-field stresses near a crack. The anisotropy of the stresses implies that the full in-plane tensorial stress is required, but current experimental optical techniques only give the sum or difference of principal stresses, motivating development of experimental methods that combines two experimental techniques to determine all of the stress components, such as the proposed hybrid experimental method of phase-shifting photoelasticity and transmission Coherent Gradient Sensing (CGS). This thesis establishes this method for stress determination around cracks in photoelastic materials.
\r\n\r\nThis experimental method first requires a new theory for the use of CGS, a wavefront shearing interferometry technique, for photoelastic materials. The first analysis of transmission wavefront shearing interferometry for photoelastic materials is experimentally demonstrated using CGS in full field for a compressed polycarbonate plate with a side V-shaped notch with good agreement with theoretical data. For the hybrid experimental method, a six-step phase-shifting photoelasticity method determines principal stress directions and the difference of principal stresses, and the transmission CGS method utilizes a standard four-step phase-shifting method to measure the x and y first derivatives of the sum of principal stresses, which are numerically integrated for the sum of principal stresses. The full-field principal stresses may then be separated, followed by the Cartesian and polar coordinate stresses using the principal stress directions and the polar angle. The method is first demonstrated for in-plane tensorial stress determination for a compressed polycarbonate plate with a side V-shaped notch with good comparison to theoretical stress fields. The CGS-photoelasticity experimental method is then applied to determine stresses around Mode I-dominant cracks in Homalite-100. The experimental stress fields have excellent agreement with the full-field 2D asymptotic crack solution using the Mode I and Mode II stress intensity factor values calculated from the experimental data. With this foundation of stress determination around cracks in photoelastic materials and with some future analysis, this experimental method can be extended to determine stresses in anisotropic crystals for fracture studies.
\r\n" }, { "name": "Li, Bo", "degree": "PhD", "year": "2009", "title": "The Optimal Transportation Method in Solid Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212009-173044", "creators": [ { "name": { "family": "Li", "given": "Bo" }, "id": "Li-Bo", "orcid": "0000-0002-0127-8210", "display_name": "Li, Bo" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FAT3-0247", "abstract": "This dissertation is concerned with the development of a robust and efficient meshless method, the Optimal Transportation Method (OTM), for general solid flows involving extremely large deformation, fast, transient loading and hydrodynamic phenomena. This method is a Lagrangian particle method through an integration of optimal transportation theory with meshless interpolation and material point integrations. The theoretical framework developed in this thesis generalized the Benamou-Brenier differential formulation of optimal transportation problems and leads to a multi-field variational characterization of solid flows, including elasticity, inelasticity, equation of state, and general geometries and boundary conditions. To this end, the accuracy, robustness and versatility of OTM is assessed and demonstrated with convergence and stability test, Taylor anvil test and a series of full three-dimensional simulations of high/hyper-velocity impact examples with the aid of a novel meshless dynamic contact algorithm presented in this thesis.\r\n" }, { "name": "Lu, Xiao", "degree": "PhD", "year": "2009", "title": "Combined Experimental and Numerical Study of Spontaneous Dynamic Rupture on Frictional Interfaces", "advisor": "Lapusta, Nadia; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242008-070701", "creators": [ { "name": { "family": "Lu", "given": "Xiao" }, "id": "Lu-Xiao", "display_name": "Lu, Xiao" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BGGT-MC04", "abstract": "The process of spontaneous dynamic frictional sliding along the interface of two elastic solids is of great interest to a number of disciplines in engineering and sciences. Applications include frictional rupture processes in earthquakes, delamination of layered composite materials, and sliding between soft membranes in biological systems. The transient nature of rupture dynamics presents an array of fascinating yet challenging questions, including the nucleation process, the mechanism of interface failure, and the speed and mode of rupture propagation.
\r\n\r\nThis thesis presents such a combined experimental and theoretical study aimed at understanding the conditions for selecting pulse-like vs. crack-like rupture modes and subshear vs. supershear rupture speeds. There are two major contributions in this work. The first one is high-resolution experimental study of the rupture modes on a frictional interface. The study presents first experimental observations of spontaneous pulse-like ruptures in a homogeneous linear-elastic setting that mimics crustal earthquakes, reveals how different rupture modes are selected based on the level of fault prestress, demonstrates that both rupture modes can transition to supershear speeds, and advocates, based on comparison with theoretical studies, importance of velocity-weakening friction for earthquake dynamics. The second major contribution is the numerical modeling of the rupture experiments that reveal the importance of the rupture nucleation mechanism and friction formulations. The modeling of sub-Rayleigh to supershear transition has demonstrated the influence of rupture nucleation mechanism on supershear transition distance, as well as on the mechanism of supershear transition. The modeling of pulse-like to crack-like rupture mode transition has confirmed the necessity of velocity weakening friction for producing pulse-like rupture to match the experimental observations.
\r\n" }, { "name": "Poon, Poh Chieh Benny", "degree": "PhD", "year": "2009", "title": "A Critical Appraisal of Nanoindentation with Application to Elastic-Plastic Solids and Soft Materials", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162008-023546", "creators": [ { "name": { "family": "Poon", "given": "Poh Chieh Benny" }, "id": "Poon-Poh-Chieh-Benny", "display_name": "Poon, Poh Chieh Benny" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Rittel", "given": "Daniel" }, "id": "Rittel-D", "role": "member", "display_name": "Rittel, Daniel" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J1WM-BW36", "abstract": "This study examines the accuracy of the extracted elastic properties using nanoindentation. Since the conventional method to extract these properties utilizes Sneddon\u2019s elastic solution, this study first considers indentations of linearly elastic solids for direct comparison. The study proposes a criterion for a converged specimen\u2019s geometry and modifies Sneddon\u2019s equation to account for the finite tip radius and specimen compressibility effects. A composite correction factor is derived to account for the violations of the underlying assumptions behind Sneddon\u2019s derivation. This factor is a function of indentation depth, and a critical depth is derived beyond which the finite tip radius effect will be insignificant. Techniques to identify the radius of curvature of the indenter and to decouple the elastic constants for linear elastic materials are proposed. Experimental results on nanoindentation of natural latex are reported and discussed in light of the proposed modified relation and techniques.
\r\n\r\nThe second part of the study examines the accuracy of the extracted material properties in elastic-plastic nanoindentations. The study establishes that the accurate determination of the projected area of contact, A, is crucial. However, the conventional method to determine A is largely limited to elastic materials, hence a new electrical resistance method is proposed to measure A for elastic-plastic materials. With an accurate A, the error associated with the extracted elastic material properties is reduced by more than 50% in some cases. This error remains to be a function of the material\u2019s Poisson\u2019s ratio, which is identified to influence the amount of residual stresses at the plastic imprint.
\r\n\r\nFinally, this study examines the accuracy of the extracted material properties in the nanoindentation of soft materials using an Atomic Force Microscope (AFM). The effects of cantilever stiffness, preload, and surface interaction forces are observed to influence the measurements. Three set of experiments were performed to decouple these effects. The effect of a preload resembles a shift of nanoindentation load-displacement curve, while the cantilever stiffness is observed to have significant influence on the measurement of the surface forces. Lastly, a novel technique to account for these effects is proposed, in order to accurately extract the material properties of interest.
" }, { "name": "Rimoli, Julian Jose", "degree": "PhD", "year": "2009", "title": "A Computational Model for Intergranular Stress Corrosion Cracking", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142009-135909", "creators": [ { "name": { "family": "Rimoli", "given": "Julian Jose" }, "id": "Rimoli-Julian-Jose", "orcid": "0000-0002-8707-2968", "display_name": "Rimoli, Julian Jose" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K1HJ-DZ56", "abstract": "Stress corrosion cracking (SCC) is a very common failure mechanism characterized by a slow, environmentally induced crack propagation in structural components. Time-to-failure tests and crack-growth-rate tests are widespread practices for studying the response of various materials undergoing SCC. However, due to the large amount of factors affecting the phenomenon and the scattered data, they do not provide enough information for quantifying the effects of main SCC mechanisms. This thesis is concerned with the development of a novel 3-dimensional, multiphysics model for understanding the intergranular SCC of polycrystalline materials under the effect of impurity-enhanced decohesion. This new model is based upon: (i) a robust algorithm capable of generating the geometry of polycrystals for objects of arbitrary shape; (ii) a continuum finite element model of the crystals including crystal plasticity; (iii) a grain boundary diffusion model informed with first-principles computations of diffusion coefficients; and (iv) an intergranular cohesive model described by concentration-dependent constitutive relations also derived from first-principles. Results are validated and compared against crack-growth-rate and initiation time tests.\r\n" }, { "name": "Benezech, Laurent Jean-Michel", "degree": "Engineering Degree", "year": "2008", "title": "Premixed Hydrocarbon Stagnation Flames: Experiments and Simulations to Validate Combustion Chemical-Kinetic Models", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-113043", "creators": [ { "name": { "family": "Benezech", "given": "Laurent Jean-Michel" }, "id": "Benezech-Laurent-Jean-Michel", "display_name": "Benezech, Laurent Jean-Michel" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TVB9-4266", "abstract": "A methodology based on the comparison of flame simulations relying on reacting flow models with experiment is applied to C1\u2013C3 stagnation flames. The work reported targets the assessment and validation of the modeled reactions and reaction rates relevant to (C1\u2013C3)-flame propagation in several detailed combustion kinetic models. A concensus does not, as yet, exist on the modeling of the reasonably well-understood oxidation of C1\u2013C2 flames, and a better knowledge of C3 hydrocarbon combustion chemistry is required before attempting to bridge the gap between the oxidation of C1\u2013C2 hydrocarbons and the more complex chemistry of heavier hydrocarbons in a single kinetic model.
\r\n\r\nSimultaneous measurements of velocity and CH-radical profiles were performed in atmospheric propane(C3H8)- and propylene(C3H6)-air laminar premixed stagnation flames stabilized in a jet-wall configuration. These nearly-flat flames can be modeled by one-dimensional simulations, providing a means to validate kinetic models. Experimental data for these C3 flames and similar experimental data for atmospheric methane(CH4)-, ethane(C2H6)-, and ethylene(C2H4)-air flames are compared to numerical simulations performed with a one-dimensional hydrodynamic model, a multi-component transport formulation including thermal diffusion, and different detailed-chemistry models, in order to assess the adequacy of the models employed. A novel continuation technique between kinetic models was developed and applied successfully to obtain solutions with the less-robust models. The 2005/12 and 2005/10 releases of the San Diego mechanism are found to have the best overall performance in C3H8 and C3H6 flames, and in CH4, C2H6, and C2H4 flames, respectively.
\r\n\r\nFlame position provides a good surrogate for flame speed in stagnation-flow stabilized flames. The logarithmic sensitivities of the simulated flame locations to variations in the kinetic rates are calculated via the \"brute-force\" method for fifteen representative flames covering the five fuels under study and the very lean, stoichiometric, and very rich burning regimes, in order to identify the most-important reactions for each flame investigated. The rates of reactions identified in this manner are compared between the different kinetic models. Several reaction-rate differences are thus identified that are likely responsible for the variance in flame-position (or flame-speed) predictions in C1\u2013C2 flames.
" }, { "name": "Bermejo-Moreno, Ivan", "degree": "PhD", "year": "2008", "title": "On the Non-Local Geometry of Turbulence", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092008-173614", "creators": [ { "name": { "family": "Bermejo-Moreno", "given": "Ivan" }, "id": "Bermejo-Moreno-Ivan", "display_name": "Bermejo-Moreno, Ivan" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DH9W-Y894", "abstract": "A multi-scale methodology for the study of the non-local geometry of eddy structures in turbulence is developed. Starting from a given three-dimensional field, this consists of three main steps: extraction, characterization and classification of structures. The extraction step is done in two stages. First, a multi-scale decomposition based on the curvelet transform is applied to the full three-dimensional field, resulting in a finite set of component fields, one per scale. Second, by iso-contouring each component field at one or more iso-contour levels, a set of closed iso-surfaces is obtained that represents the structures at that scale. For periodic domains, those structures intersecting boundaries are reconnected with their continuation in the opposite boundaries. The characterization stage is based on the joint probability density function (jpdf), in terms of area coverage on each individual iso-surface, of two differential-geometry properties, the shape index and curvedness, plus the stretching parameter, a dimensionless global invariant of the surface. Taken together, this defines the geometrical signature of the iso-surface. The classification step is based on the construction of a finite set of parameters, obtained from algebraic functions of moments of the jpdf of each structure, that specify its location as a point in a multi-dimensional 'feature space'. At each scale the set of points in feature space represents all structures at that scale, for the specified iso-contour value. This allows the application, to the set, of clustering techniques that search for groups of structures with a common geometry.
\r\n\r\nResults are presented of a first application of this technique to a passive scalar field obtained from 512\u00b3 direct numerical simulation of scalar mixing by forced, isotropic turbulence (Re\u03bb=265). These show transition, with decreasing scale, from blob-like structures in the larger scales to blob- and tube-like structures with small or moderate stretching in the inertial range of scales, and then toward tube and, predominantly, sheet-like structures with high level of stretching in the dissipation range of scales. Implications of these results for the dynamical behavior of passive scalar stirring and mixing by turbulence are discussed.
\r\n\r\nWe apply the same methodology to the enstrophy and kinetic energy dissipation rate instantaneous fields of a second numerical database of incompressible homogeneous isotropic turbulence decaying in time obtained by DNS in a periodic box. Three different resolutions are considered: 256\u00b3, 512\u00b3 and 1024\u00b3 grid points, with kmax\u03b7\u0305 approximately 1, 2, and 4, respectively, the same initial conditions and Re\u03bb \u2248 77. This allows a comparison of the geometry of the structures obtained for different resolutions. For the highest resolution, structures of enstrophy and dissipation evolve in a continuous distribution from blob-like and moderately stretched tube-like shapes at the large scales to highly stretched sheet-like structures at the small scales. The intermediate scales show a predominance of tube-like structures for both fields, much more pronounced for the enstrophy field. The dissipation field shows a tendency toward structures with lower curvedness than those of the enstrophy, for intermediate and small scales. The 256\u00b3 grid resolution case (kmax\u03b7\u0305 \u2248 1) was unable to detect the predominance of highly stretched sheet-like structures at the smaller scales.
\r\n\r\nThe same methodology, but without the multi-scale decomposition, is then applied to two scalar fields used by existing local criteria for the eduction of tube- and sheet-like structures in turbulence, Q and [Aij]+ respectively, obtained from invariants of the velocity gradient tensor and alike in the 1024\u00b3 case. This adds the non-local geometrical characterization and classification to those local criteria, assessing their validity in educing particular geometries.
\r\n\r\nFinally we introduce a new methodology for the study of proximity issues among different sets of structures, based also on geometrical and non-local analyses. We apply it to four of the fields previously studied. Tube-like structures of Q are mainly surrounded by sheets of [Aij]+, which appear at close distances. For the enstrophy, tube-like structures at an intermediate scale are primarily surrounded by sheets of smaller scales of the enstrophy and structures of dissipation at the same and smaller scales. A secondary contribution results from tubes of enstrophy at smaller scales appearing at farther distances. Different configurations of composite structures are presented.
\r\n" }, { "name": "Franck, Christian", "degree": "PhD", "year": "2008", "title": "Quantitative Characterization of 3D Deformations of Cell Interactions with Soft Biomaterials", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-163638", "creators": [ { "name": { "family": "Franck", "given": "Christian" }, "id": "Franck-Christian", "display_name": "Franck, Christian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VMN5-SP86", "abstract": "In recent years, the importance of mechanical forces in directing cellular function has been recognized as a significant factor in biological and physiological processes. In fact, these physical forces are now viewed equally as important as biochemical stimuli in controlling cellular response. Not only do these cellular forces, or cell tractions, play an important role in cell migration, they are also significant to many other physiological and pathological processes, both at the tissue and organ level, including wound healing, inflammation, angiogenesis, and embryogenesis. A complete quantification of cell tractions during cell-material interactions can lead to a deeper understanding of the fundamental role these forces play in cell biology. Thus, understanding the function and role of a cell from a mechanical framework can have important implications towards the development of new implant materials and drug treatments.
\r\n\r\nPrevious research has contributed significant descriptions of cell-tissue interactions by quantifying cell tractions in two-dimensional environments; however, most physiological processes are three-dimensional in nature. Recent studies have shown morphological differences in cells cultured on two-dimensional substrates versus three-dimensional matrices, and that the intrinsic extracellular matrix interactions and migration behavior are different in three dimensions versus two dimensions. Hence, measurement techniques are needed to investigate cellular behavior in all three dimensions.
\r\n\r\nThis thesis presents a full-field imaging technique capable of quantitatively measuring cell traction forces in all three spatial dimensions, and hence addresses the need of a three-dimensional quantitative imaging technique to gain insight into the fundamental role of physical forces in biological processes. The technique combines laser scanning confocal microscopy (LSCM) with digital volume correlation (DVC) to track the motion of fluorescent particles during cell-induced or externally applied deformations. This method is validated by comparing experimentally measured non-uniform deformation fields near hard and soft spherical inclusions under uniaxial compression with the corresponding analytical solution. Utilization of a newly developed computationally efficient stretch-correlation and deconvolution algorithm is shown to improve the overall measurement accuracy, in particular under large deformations.
\r\n\r\nUsing this technique, the full three-dimensional substrate displacement fields are experimentally determined during the migration of individual fibroblast cells on polyacrylamide gels. This is the first study to show the highly three-dimensional structure of cell-induced displacement and traction fields. These new findings suggest a three-dimensional push-pull cell motility, which differs from the traditional theories based on two-dimensional data. These results provide new insight into the dynamic cell-matrix force exchange or mechanotransduction of migrating cells, and will aid in the development of new three-dimensional cell motility and adhesion models.
\r\n\r\nAs this study reveals, the mechanical interactions of cells and their extracellular matrix appear to be highly three-dimensional. It also shows that the LSCM-DVC technique is well suited for investigating the mechanics of cell-matrix interactions while providing a platform to access detailed information of the intricate biomechanical coupling for many cellular responses. Thus, this method has the capability to provide direct quantitative experimental data showing how cells interact with their surroundings in three dimensions and might stimulate new avenues of scientific thought in understanding the fundamental role physical forces play in regulating cell behavior.
" }, { "name": "Hines, George Herbert", "degree": "Senior Minor", "year": "2008", "title": "Nonlinear Three-Dimensional Trajectory Following: Simulation and Application", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212010-164605005", "creators": [ { "name": { "family": "Hines", "given": "George Herbert" }, "id": "Hines-George-Herbert", "display_name": "Hines, George Herbert" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YE4Q-FV39", "abstract": "In light of recent military requirements for unmanned and autonomous vehicles, research into methods of designing arbitrary three-dimensional trajectories and controlling aircraft along them has become vital. In this report, we explore two methods of nonlinear control for the purpose of following three-dimensional trajectories and paths. First, prior work on a dynamic feedback linearization exploiting the differential flatness of the ideal airplane is adapted with the intent of implementing it on a physical testbed in MIT\u2019s Realtime indoor Autonomous Vehicle test ENvironment (RAVEN), but poor behavior\u2014both in simulation and in hardware\u2014under moderate levels of joint parameter uncertainty thwarted attempts at implementation. Additionally, the differential flatness technique in its pure form follows trajectories, which are sometimes inferior intuitively and practically to paths. In the context of unmanned air vehicle (UAV) flight in gusty environments, this motivated the extension of prior work on two-dimensional path following to three-dimensions, and simulations are presented in which the fully nonlinear controller derived from differential flatness follows a trajectory that is generated dynamically from a path. The three-dimensional path-following logic is actually implemented in RAVEN, and results are presented that demonstrate good vertical rise time in response to a step input and centimeter accuracy in vertical and lateral tracking. Future directions are proposed." }, { "name": "Lombardini, Manuel", "degree": "PhD", "year": "2008", "title": "Richtmyer-Meshkov Instability in Converging Geometries", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-140331", "creators": [ { "name": { "family": "Lombardini", "given": "Manuel" }, "id": "Lombardini-Manuel", "display_name": "Lombardini, Manuel" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5SNE-4003", "abstract": "We investigate the Richtmyer-Meshkov instability (RMI) in converging geometries analytically and computationally. The linear, or small amplitude, regime is first covered as it is the onset to subsequent non-linear stages of the perturbation growth. While the plane interaction of a shock with a slightly perturbed density interface is classically viewed as a single interface evolving as baroclinic vorticity have been initially deposited on it, we propose a simple but more complete model characterizing the early interaction between the interface and the receding waves produced by the shock-interface interaction, in the case of a reflected shock. A universal time scale representing the time needed by the RMI to reach its asymptotic growth rate is found analytically and confirmed by ideal gas computations for various incident shock Mach numbers MI and Atwood ratios A, and could be useful especially for experimentalists in non-dimensionalizing their data.
\r\n\r\nConsidering again linear perturbations, we then obtain a general analytical model for the asymptotic growth rate reached by the instability during the concentric interaction of an imploding/exploding cylindrical shock with a cylindrical interface containing three-dimensional orthogonal perturbations, in the azimuthal and axial directions. Stable perturbations, typical of the converging geometry, are discovered. Comparisons are made with simulations where the effects of compressibility, wave reverberations, and flow convergence are isolated. Azimuthal and axial perturbation evolution are compared with results obtained for the plane RMI at comparable initial wavelengths.
\r\n\r\nA second interaction occurs when the transmitted shock, produced by the incident converging shock impacting the interface, converges to the axis and reflects to reshock the initially accelerated interface. This leads to highly non-linear perturbation growth. To isolate the complex wave interaction process, the interface is considered initially unperturbed so that the flow is radially symmetric. An accurate visualization procedure is performed to characterize the underlying physics behind the reshock event. We study extensively the cylindrical and spherical geometry, for various MI and for the air \u2192 SF6 (A=0.67) and SF6 \u2192 (A=-0.67) interactions, and draw important differences with the equivalent plane configuration.
\r\n\r\nA hybrid, low-numerical dissipation/shock-capturing method, embedded into an adaptive mesh refinement framework is optimized in order to achieve large-eddy simulations of the self-similar cylindrical converging shock-driven RMI and the turbulent mixing generated by the reshock. Computations are produced for MI=1.3 and 2.0, and for air -> SF6 SF6 -> air interfaces. We develop statistics tools to study extensively the growth of the turbulent mixing zone using cylindrical averages as well as various measures such as probability density functions of the mixing and turbulent power spectra, with the objectives of understanding the turbulent mixing in this particular geometry.
" }, { "name": "Matheou, Georgios", "degree": "PhD", "year": "2008", "title": "Large-Eddy Simulations of Molecular Mixing in a Recirculating Shear Flow", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262008-152803", "creators": [ { "name": { "family": "Matheou", "given": "Georgios" }, "id": "Matheou-Georgios", "orcid": "0000-0003-4024-4571", "display_name": "Matheou, Georgios" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VFKF-SC30", "abstract": "The flow field and mixing in an expansion-ramp geometry is studied using large-eddy simulation (LES) with subgrid scale (SGS) modeling based on the stretched-vortex model. The expansionramp geometry was developed to provide enhanced mixing and flameholding characteristics while maintaining low total-pressure losses, elements that are important in the design and performance of combustors for hypersonic air-breathing propulsion applications. The mixing was studied by tracking a passive scalar without taking into account the effects of chemical reactions and heat release.
\r\n\r\nIn order to verify the solver and the boundary closure implementation, a method utilizing results from linear stability analysis (LSA) theory is developed. LSA can be used to compute unstable perturbations to a flow, subject to certain approximations. The perturbations computed from LSA are used as an inflow condition to the flow computed by the solver been assessed. A projection based metric is constructed that only assumes the shape of the solution and not the growth rate of the perturbations, thus also allowing the latter to be determined as part of the verification. The growth rate of the perturbations for an unbounded (effectively) incompressible shear layer and a confined compressible shear layer is found to be in agreement with the prediction of the LSA.
\r\n\r\nThe flow and mixing predictions of the LES are in good agreement with experimental measurements. Total (resolved and subgrid) probability density functions (PDFs) of the passive scalar are estimated using an assumed beta-distribution model for the subgrid scalar field. The improved mixing characteristics of the expansion-ramp geometry compared to free shear layers are illustrated by the shapes of the PDFs. Moreover, the temperature rise and the probability of mixed fluid profiles are in good agreement with the experimental measurements, indicating that the mixing on a molecular scale is correctly predicted by the LES\u2013SGS model. Finally, the predictions of the LES are shown to be resolution-independent. The mean fields and passive scalar PDFs have essentially converged at the two finer grid-resolutions used.
" }, { "name": "Taira, Kunihiko (Sam)", "degree": "PhD", "year": "2008", "title": "The Immersed Boundary Projection Method and Its Application to Simulation and Control of Flows Around Low-Aspect-Ratio Wings", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232008-124342", "creators": [ { "name": { "family": "Taira", "given": "Kunihiko (Sam)" }, "id": "Taira-Kunihiko-Sam", "orcid": "0000-0002-3762-8075", "display_name": "Taira, Kunihiko (Sam)" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "mecheng" ], "doi": "10.7907/VSDD-P465", "abstract": "First, we present a new formulation of the immersed boundary method that is algebraically identical to the traditional fractional step algorithm. This method, called the immersed boundary projection method, allows for the simulations of incompressible flows over arbitrarily shaped bodies under motion and/or deformation in both two and three dimensions. The no-slip condition along the immersed boundary is enforced simultaneously with the incompressibility constraint through a single projection. The boundary force is determined implicitly without any constitutive relations for the rigid body formulation, which in turn allows the use of high CFL numbers in our simulations compared to past methods.
\r\n\r\nNext, the above immersed boundary projection method is used to analyze three-dimensional separated flows around low-aspect-ratio flat-plate wings. A number of simulations highlighting the unsteady nature of the separated flows are performed for Re = 300 and 500 with various aspect ratios, angles of attack, and planform geometries. The aspect ratio and angle of attack are found to have a large influence on the stability of the wake profile and the force experienced by the low-aspect-ratio wing. At early times, following an impulsive start, topologies of the wake vortices are found to be the same across different aspect ratios and angles of attack. Behind low-aspect-ratio rectangular plates, leading-edge vortices form and eventually separate as hairpin vortices following the start-up. This phenomenon is found to be similar to dynamic stall observed behind pitching plates. The detached structure would then interact with the tip vortices, reducing the downward velocity induced by the tip vortices acting upon the leading-edge vortex. At large time, depending on the aspect ratio and angles of attack, the wakes reach one of the three states: (i) a steady state, (ii) a periodic unsteady state, or (iii) an aperiodic unsteady state. We have observed that the tip effects in three-dimensional flows can stabilize the flow and also exhibit nonlinear interaction with the shedding vortices.
\r\n\r\nAt last, we apply steady blowing to separated flows behind the low-aspect-ratio rectangular wings. The objective of the flow control is to enhance lift at post-stall angles of attack by changing the dynamics of the wake vortices. This controller strengthens the tip vortices by engulfing the trailing-edge vortex sheet to increase the downward thrust and the downward induced velocity onto the leading-edge vortices. The tip vortices that are traditionally considered as an aerodynamic nuisance, have been used favorably to increase lift in post-stall flows for the considered low-aspect-ratio wings.
" }, { "name": "Zhang, Zhonglin Johnny", "degree": "Senior Minor", "year": "2008", "title": "Identification of Lagrangian Coherent Structures Around Swimming Jellyfish from Experimental Time-Series Data", "advisor": "Dabiri, John O.; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechThesis:01112018-113614173", "creators": [ { "name": { "family": "Zhang", "given": "Zhonglin Johnny" }, "id": "Zhang-Zhonglin-Johnny", "display_name": "Zhang, Zhonglin Johnny" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "advisor", "display_name": "Dabiri, John O." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KK45-ZV02", "abstract": "The unique body kinematics of jellyfish embodies the most intriguing form of biological propulsion, which makes jellyfish a promising resource for developing new locomotion systems. Instead of the conventional Eulerian method, we take an unprecedented Lagrangian approach by tracking individual fluid particles around a swimming jellyfish over a finite time interval. Specifically, we utilize the Lagrangian coherent structures (LCS) in the flow field to investigate the flow characteristics around a jellyfish. LCS are separatrices or invariant manifolds, which separate the flow field into distinct regions. To locate the LCS in the flow, we employ the concept of the finite-time Lyapunov Exponent (FTLE), which measures the rate at which particles diverge from each other, and LCS are identified as the high-value ridges in the FTLE field. This method is implemented and validated by analysis on two-dimensional vortex dipole flow, two-dimensional experimental time-series data, and Hill\u2019s vortex sphere. This method is expected to extract LCS from three-dimensional experimental time-series data." }, { "name": "Graff, Emilio Casta\u00f1o", "degree": "PhD", "year": "2007", "title": "On the Development of Defocusing Digital Particle Image Velocimetry with Full Characterization", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-140239", "creators": [ { "name": { "family": "Graff", "given": "Emilio Casta\u00f1o" }, "id": "Graff-Emilio-Casta\u00f1o", "display_name": "Graff, Emilio Casta\u00f1o" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9HM56F8", "abstract": "Defocusing Digital Particle Image Velocimetry is the first volumetric, three-dimensional PIV method ever put into practice. This manuscript contains the details of its development, a detailed analysis of its performance (both through simulation and real measurements), and a series of experimental demonstrations of the capability of the technique. The system is capable of resolving upwards of 7,000 vectors per pair with an absolute error on the order of 0.03% of the volume size." }, { "name": "Kidd, Theresa Hiromi", "degree": "PhD", "year": "2007", "title": "Mechanical Characterization of Damage and Failure in Polymeric Foams and Glass/Epoxy Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102006-182329", "creators": [ { "name": { "family": "Kidd", "given": "Theresa Hiromi" }, "id": "Kidd-Theresa-Hiromi", "display_name": "Kidd, Theresa Hiromi" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G25Y-KE07", "abstract": "The mechanical characterization including evolution of damage and failure of foams and composites are becoming increasingly important, as they form the basic components of sandwich structures. Sandwich structures consist of two faceplates that surround a core material. In many modern applications, faceplates and cores are typically comprised of composite materials and polymeric foam, respectively. Knowledge of the failure behavior of these individual components is necessary for understanding the failure behavior and design of sandwich structures. A systematic investigation of the damage evolution and failure behavior of foams and composites was conducted using a variety of experimental techniques.
\r\n\r\nIn-situ ultrasonic measurements were used to track the damage behavior in PVC polymeric foams with densities ranging from 130 to 250 kg/m\u00b3. The wave speeds were measured by two quartz piezoelectric shear transducers with a resonant frequency of 5 MHz in the transmission mode. A fixture was developed and constructed to protect the transducers during compression, while allowing them to take sound speed measurements of the sample along the axis of the load train. This fixture was placed in a servo-hydraulic MTS (Materials Testing System) machine, where the load-displacement response of the foam was recorded. A digital image correlation (DIC) method was used to capture the progression of failure under compression. Two dominant failure modes, elastic buckling and plastic collapse, were identified \u2013 and their onsets corresponded to the change in elastic wave speeds in the material, measured by the in-situ ultrasonic technique.
\r\n\r\nThe transverse response of S-Glass/Epoxy unidirectional composites was investigated under varying degrees of confinement and strain rates. The experimental setup utilizes a fixture that allowed for independent measurement of the three principal stresses in a confined specimen. A servo-hydraulic materials testing system and a Kolsky (split Hopkinson) pressure bar generated strain rates between 10\u207b\u00b3 to 10\u2074 s\u207b\u00b9. Post-test scanning electron microscopy (SEM) observations suggest that under transverse loading at low-strain rates, confinement contributes to localized band formation. In addition, micrographs indicated that macroscopic transverse failure is dominated by shear stress, and occurs within these localized bands. These shear dominated failure bands were found inclined in a direction approximately 35\u00b0 to the direction of loading. Implications of this orientation deviation of failure bands from maximum shear trajectories at 45\u00b0 are discussed in reference to the state of confinement.
" }, { "name": "Klamo, Joseph Thomas", "degree": "PhD", "year": "2007", "title": "Effects of Damping and Reynolds Number on Vortex-Induced Vibrations", "advisor": "Leonard, Anthony; Gharib, Morteza; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-120631", "creators": [ { "name": { "family": "Klamo", "given": "Joseph Thomas" }, "id": "Klamo-Joseph-Thomas", "orcid": "0000-0003-1458-0379", "display_name": "Klamo, Joseph Thomas" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-advisor", "display_name": "Gharib, Morteza" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "co-advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "mecheng" ], "doi": "10.7907/S27Z-J533", "abstract": "Vortex-induced vibrations have been studied experimentally with emphasis on damping and Reynolds number effects. Our system was an elastically-mounted rigid circular cylinder, free to oscillate only transverse to the flow direction, with very low inherent damping. We were able to prescribe the mass, damping, and elasticity of the system over a wide range of values, with the damping controlled by a custom-made variable magnetic eddy-current damping system.
\r\n\r\nSpecial emphasis is put on a nontraditional parameter formulation. The advantages of this formulation are explained, and an important new parameter, effective stiffness, is introduced. Using this new formulation, the amplitude and frequency responses are only a function of damping, Reynolds number, and effective stiffness. We show the effects that damping and Reynolds number each have on the amplitude and frequency response profiles and make the interesting observation that changes in damping or Reynolds number have similar effects.
\r\n\r\nThe maximum amplitudes of our systems are studied in detail. We theoretically show that they should be functions of both damping and Reynolds number. This allows us to create constant-Reynolds-number curves of maximum amplitude over a large range of damping values, which we call a \"generalized\" Griffin plot. We also define maximum amplitudes in the case of zero damping as limiting amplitudes, and show that they are only a function of Reynolds number. We experimentally determine our limiting amplitude dependence on Reynolds number over the range 200 < Reynolds number < 5050.
\r\n\r\nDiscontinuities in the amplitude response profile are also investigated. The discontinuity between the initial branch and the large-amplitude, upper branch is studied in two ways. First, the time-averaged behavior is examined to understand what controls the discontinuity and look for damping and Reynolds number effects. Second, we track the cycle-by-cycle transient response through this discontinuous amplitude change, induced either by changes in the tunnel velocity or system damping. Finally, we also find a new discontinuity hysteresis region between the lower branch and the desynchronized region, which appears to be a low Reynolds number effect and is only seen in systems with Reynolds number < 1000.
" }, { "name": "Latini, Marco", "degree": "PhD", "year": "2007", "title": "Simulations and Analysis of Two- and Three-Dimensional Single-Mode Richtmyer-Meshkov Instability using Weighted Essentially Non-Oscillatory and Vortex Methods", "advisor": "Meiron, Daniel I.; Schilling, Oleg", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082006-124547", "creators": [ { "name": { "family": "Latini", "given": "Marco" }, "id": "Latini-Marco", "display_name": "Latini, Marco" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Schilling", "given": "Oleg" }, "id": "Schilling-O", "role": "advisor", "display_name": "Schilling, Oleg" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Schilling", "given": "Oleg" }, "id": "Schilling-O", "role": "member", "display_name": "Schilling, Oleg" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1397-GZ04", "abstract": "An incompressible vorticity-streamfunction (VS) method is developed to investigate the single-mode Richtmyer-Meshkov instability in two and three dimensions. The initial vortex sheet (representing the initial shocked interface) is thickened to regularize the limit of classical Lagrangian vortex methods. In the limit of smaller thickness, the initial velocity converges to the velocity of a vortex sheet. The vorticity on the Cartesian grid follows the vorticity evolution equation augmented by the baroclinic vorticity production term (to capture the effects of the instability on the layer) and a viscous dissipation term. The equations are discretized using a fourth-order in space and third-order in time semi-implicit Adams-Bashforth backward differentiation scheme. The convergence properties of the method with respect to varying the diffuse interface thickness and viscosity are investigated. It is shown that the small-scale structures within the roll-up are more sensitive to the diffuse interface thickness than to the viscosity. By contrast, the large-scale quantities, including the perturbation, bubble, and spike amplitudes are less sensitive. Fourth-order point-wise convergence is achieved, provided that a sufficiently fine grid is used.
\r\n\r\nIn two dimensions, the VS method is applied to investigate late-time nonlinear effects of the single-mode Mach 1.3 air(acetone)/SF_6 shock tube experiment of Jacobs and Krivets. The results are also compared to those from compressible ninth-order weighted essentially non-oscillatory (WENO) simulations. The density fields from the WENO and VS methods agree with the experimental PLIF images in the large-scale structures but differ in the small-scale structures. The WENO method exhibits small-scale disordered structure similar to that in the experiment, while the VS method does not capture such structure, but shows a strong rotating core. The perturbation amplitudes from the two methods are in good agreement and match the experimental data points well. The WENO bubble amplitude is smaller than the VS amplitude and vice versa for the spike amplitude. Comparing amplitudes from simulations with varying Mach number shows that as the Mach number increases, the differences in the bubble and spike amplitudes increase due to intensifying pressure perturbations not present in the incompressible VS method. The perturbation amplitude from the WENO and VS methods is also compared to the predictions of nonlinear amplitude growth models in which the growth rate was reduced to account for the diffuse initial interface. In general, the model predictions agree with the simulation amplitudes at early-to-intermediate times and underpredict at later times, corresponding to the late nonlinear regime.
\r\n\r\nThe WENO simulation is used to investigate reshock, which occurs when the transmitted shock reflects from the end wall of the test section and interacts with the evolving layer. The post-reshock mixing layer width agrees well with the predictions of reshock models for short times until the interaction of the reflected rarefaction with the layer.
\r\n\r\nThe VS simulation was also compared to classical Lagrangian and vortex-in-cell simulations as the Atwood number was varied. For low Atwood numbers, all three simulations agree. As the Atwood number increases, the VS simulation shows differences in the bubble and spike amplitudes compared to the Lagrangian and VIC simulations, as the baroclinic vorticity production for a diffuse layer is different from that of a thin layer. The simulation amplitudes agree with the predictions of nonlinear amplitude growth models at early times. The growth models underpredict the amplitudes at later times.
\r\n\r\nThe investigation is extended to three dimensions, where the initial perturbation is a product of sinusoids and the initial vorticity deposition is given by linear instability analysis. The instability evolution and dynamics of vorticity are visualized using the mass fraction and enstrophy isosurface, respectively. For the WENO and VS methods, two roll-ups corresponding to the bubble and spike regions form, and the vorticity shows the formation of a ring-like structure. The perturbation amplitudes from the WENO and VS methods are in excellent agreement. The bubble and spike amplitude are in good agreement at early times. At later times, the WENO bubble amplitude is smaller than the VS amplitude and vice versa for the spike. The nonlinear three-dimensional Zhang-Sohn model agrees with the simulation amplitudes at early times, and underpredicts later. In three dimensions, the enstrophy iso-surface after reshock shows significant fragmentation and the formation of small, short, tubular structures. Simulations with different initial amplitudes show that the mixing layer width after reshock does not depend on the pre-shock amplitude. Finally, the effects of Atwood number are investigated using the VS method and the amplitudes are compared to the predictions of the Zhang-Sohn model. The simulation and the models are in agreement at early times, while the models underpredict later.
\r\n\r\nThe VS method constitutes a useful numerical approach to investigate the Richtmyer-Meshkov instability in two and three dimensions. The VS method and, more generally, vortex methods are valid tools for predicting the large-scale instability features, including the perturbation amplitudes, into the late nonlinear regime.
" }, { "name": "Loumes, Laurence", "degree": "PhD", "year": "2007", "title": "Multilayer Impedance Pump: A Bio-Inspired Valveless Pump with Medical Applications", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-103832", "creators": [ { "name": { "family": "Loumes", "given": "Laurence" }, "id": "Loumes-Laurence", "display_name": "Loumes, Laurence" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MT2J-AR81", "abstract": "This thesis introduces the concept of multilayer impedance pump, a novel pumping mechanism inspired from the embryonic heart structure.
\r\n\r\nThe multilayer impedance pump is a composite two-layer fluid-filled elastic tube featuring a thick, gelatin-like internal layer similar in nature to the embryonic cardiac jelly, and that is used to amplify longitudinal elastic waves. Pumping is based on the impedance pumping mechanism. Elastic waves are generated upon small external periodic compressions of the elastic tube. They propagate along the tube\u2019s walls, reflect at the tube\u2019s extremities and drive the flow in a preferential direction. This fully coupled fluid-structure interaction problem is solved for the flow and the structure using the finite element method over a relevant range of frequencies of excitation. Results show that the two-layer configuration can be an efficient wave propagation combination, and that it allows the pump to produce significant flow for small excitations. The multilayer impedance pump is a complex system in which flow and structure exhibit a resonant behavior. At resonance, a constructive elastic wave interaction coupled with a most efficient energy transmission between the elastic walls and the fluid is responsible for the maximum exit flow. The pump efficiency reaches its highest at resonance, highlighting furthermore the concept of resonance pumping.
\r\n\r\nUsing the proposed multilayer impedance pump model, we are able to bring an additional proof on the impedance nature of the embryonic heart by comparing a peristaltic and an impedance multilayer pump both excited in similar fashion to the one observed in the embryonic heart.
\r\n\r\nThe gelatin layer that models the embryonic cardiac jelly occupies most of the tube walls and is essential to the propagation of elastic waves. A comparison between the exact same impedance pump with and without the additional gelatin layer sheds light on the dynamic role of the cardiac jelly in the embryonic heart and on nature's optimized design.
\r\n\r\nFinally, several biomedical applications of multilayer impedance pumping are presented. A physiologically correct model of aorta is proposed to test the pump as an implantable cardiovascular assist device.
\r\n" }, { "name": "Morris, Bradford S.", "degree": "PhD", "year": "2007", "title": "Charge-Exchange Collision Dynamics and Ion Engine Grid Geometry Optimization", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282007-154751", "creators": [ { "name": { "family": "Morris", "given": "Bradford S." }, "id": "Morris-Bradford-S", "display_name": "Morris, Bradford S." } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "member", "display_name": "Johnson, Lee K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W996-M220", "abstract": "The development of a new three-dimensional model for determining the absolute energy distribution of ions at points corresponding to spacecraft surfaces to the side of an ion engine is presented. The ions resulting from elastic collisions, both charge-exchange (CEX) and direct, between energetic primary ions and thermal neutral xenon atoms are accounted for. Highly resolved energy distributions of CEX ions are found by integration over contributions from all points in space within the main beam formed by the primary ions.
\r\n\r\nThe sputtering rate due to impingement of these ions on a surface is calculated. The CEX ions that obtain significant energy (10 eV or more) in the collision are responsible for the majority of the sputtering, though this can depend on the specific material being sputtered. In the case of a molybdenum surface located 60 cm to the side of a 30 cm diameter grid, nearly 90% of the sputtering is due to the 5% of ions with the highest collision exit energies. Previous models that do not model collision energetics cannot predict this. The present results agree with other models and predict that the majority of the ion density is due to collisions where little to no energy is transferred.
\r\n\r\nThe sputtering model is combined with a grid-structure model in an optimization procedure where the sputtering rate at specified locations is minimized by adjustment of parameters defining the physical shape of the engine grids. Constraints are imposed that require that the deflection of the grid under a specified load does not exceed a maximum value, in order to ensure survivability of the grids during launch. To faciliate faster execution of the calculations, simplifications based on the predicted behavior of the CEX ions are implemented. For diametrically opposed sputtering locations, a rounded barrel-vault shape reduces the expected sputtering rate by up to 30% in comparison to an NSTAR-shaped grid.
" }, { "name": "Mouton, Christopher Andre", "degree": "PhD", "year": "2007", "title": "Transition Between Regular Reflection and Mach Reflection in the Dual-Solution Domain", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01052007-125557", "creators": [ { "name": { "family": "Mouton", "given": "Christopher Andre" }, "id": "Mouton-Christopher-Andre", "display_name": "Mouton, Christopher Andre" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TEA0-Q468", "abstract": "A study of the shock-reflection domain for steady flow is presented. Conditions defining boundaries between different possible shock-reflection solutions are given, and where possible, simple analytic expressions for these conditions are presented. A new, more accurate estimate of the steady-state Mach stem height is derived based on geometric considerations of the flow. In particular, the location of the sonic throat through which the subsonic convergent flow behind the Mach stem is accelerated to divergent supersonic flow is considered. Comparisons with previous computational and experimental work show that the theory presented in this thesis more accurately predicts the Mach stem height than previous theories. The Mach stem height theory is generalized to allow for a moving triple point. Based on this moving triple point theory, a Mach stem growth rate theory is developed. This theory agrees well with computational and experimental results. Numerical computations of the effects of water vapor disturbances are also presented. These disturbances are shown to be sufficient to cause transition from regular reflection to Mach reflection in the dual-solution domain. These disturbances are also modeled as a simple energy deposition on one of the wedges, and an estimate for the minimum energy required to cause transition is derived.
\r\n\r\nExperimental results using an asymmetric wedge configuration in the Ludwieg tube facility at the California institute of Technology are presented. A Mach 4.0 nozzle was designed and built for the Ludwieg tube facility. This Mach number is sufficient to provide a large dual-solution domain, while being small enough not to require preheating of the test gas. The test time of the facility is 100ms, which requires the use of high-speed cinematography and a fast motor to rotate one of the two wedges. Hysteresis in the transition between regular to Mach reflection was successfully demonstrated in the Ludwieg tube facility. The experiments show that regular reflection could be maintained up to a shock angle approximately halfway between the von Neumann condition and the detachment condition.
\r\n\r\nEnergy deposition studies were performed using an Nd:YAG laser. Triggering transition in this manner is found to depend on the location of the energy deposition. This finding is consistent with the numerical work presented in this thesis. Experiments were also performed to measure the Mach stem height and its growth rate. These results are compared with the theoretical estimates presented in this thesis. Excellent agreement between the steady-state Mach stem height and the theoretical estimates is seen. Comparisons of Mach stem growth rate with theoretical estimates show significant differences, but do show good agreement regarding the time required to reach the steady-state height.
" }, { "name": "Rubel, Michael Thomas", "degree": "PhD", "year": "2007", "title": "A Theory of Stationarity and Asymptotic Approach in Dissipative Systems", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122007-114557", "creators": [ { "name": { "family": "Rubel", "given": "Michael Thomas" }, "id": "Rubel-Michael-Thomas", "display_name": "Rubel, Michael Thomas" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VWDE-GB16", "abstract": "The approximate dynamics of many physical phenomena, including turbulence, can be represented by dissipative systems of ordinary differential equations. One often turns to numerical integration to solve them. There is an incompatibility, however, between the answers it can produce (i.e., specific solution trajectories) and the questions one might wish to ask (e.g., what behavior would be typical in the laboratory?) To determine its outcome, numerical integration requires more detailed initial conditions than a laboratory could normally provide. In place of initial conditions, experiments stipulate how tests should be carried out: only under statistically stationary conditions, for example, or only during asymptotic approach to a final state. Stipulations such as these, rather than initial conditions, are what determine outcomes in the laboratory.
\r\n\r\nThis theoretical study examines whether the points of view can be reconciled: What is the relationship between one's statistical stipulations for how an experiment should be carried out--stationarity or asymptotic approach--and the expected results? How might those results be determined without invoking initial conditions explicitly?
\r\n\r\nTo answer these questions, stationarity and asymptotic approach conditions are analyzed in detail. Each condition is treated as a statistical constraint on the system--a restriction on the probability density of states that might be occupied when measurements take place. For stationarity, this reasoning leads to a singular, invariant probability density which is already familiar from dynamical systems theory. For asymptotic approach, it leads to a new, more regular probability density field. A conjecture regarding what appears to be a limit relationship between the two densities is presented.
\r\n\r\nBy making use of the new probability densities, one can derive output statistics directly, avoiding the need to create or manipulate initial data, and thereby avoiding the conceptual incompatibility mentioned above. This approach also provides a clean way to derive reduced-order models, complete with local and global error estimates, as well as a way to compare existing reduced-order models objectively.
\r\n\r\nThe new approach is explored in the context of five separate test problems: a trivial one-dimensional linear system, a damped unforced linear oscillator in two dimensions, the isothermal Rayleigh-Plesset equation, Lorenz's equations, and the Stokes limit of Burgers' equation in one space dimension. In each case, various output statistics are deduced without recourse to initial conditions. Further, reduced-order models are constructed for asymptotic approach of the damped unforced linear oscillator, the isothermal Rayleigh-Plesset system, and Lorenz's equations, and for stationarity of Lorenz's equations.
" }, { "name": "Sone, Kazuo", "degree": "PhD", "year": "2007", "title": "Modeling and Simulation of Axisymmetric Stagnation Flames", "advisor": "Dimotakis, Paul E.; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252007-170838", "creators": [ { "name": { "family": "Sone", "given": "Kazuo" }, "id": "Sone-Kazuo", "display_name": "Sone, Kazuo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DYGA-YJ20", "abstract": "Laminar flame modeling is an important element in turbulent combustion research. The accuracy of a turbulent combustion model is highly dependent upon our understanding of laminar flames and their behavior in many situations. How much we understand combustion can only be measured by how well the model describes and predicts combustion phenomena. One of the most commonly used methane combustion models is GRI-Mech 3.0. However, how well the model describes the reacting flow phenomena is still uncertain even after many attempts to validate the model or quantify uncertainties.
\r\n\r\nIn the present study, the behavior of laminar flames under different aerodynamic and thermodynamic conditions is studied numerically in a stagnation-flow configuration. In order to make such a numerical study possible, the spectral element method is reformulated to accommodate the large density variations in methane reacting flows. In addition, a new axisymmetric basis function set for the spectral element method that satisfies the correct behavior near the axis is developed, and efficient integration techniques are developed to accurately model axisymmetric reacting flow within a reasonable amount of computational time. The numerical method is implemented using an object-oriented programming technique, and the resulting computer program is verified with several different verification methods.
\r\n\r\nThe present study then shows variances with the commonly used GRI-Mech 3.0 chemical kinetics model through a direct simulation of laboratory flames that allows direct comparison to experimental data. It is shown that the methane combustion model based on GRI-Mech 3.0 works well for methane-air mixtures near stoichiometry. However, GRI-Mech 3.0 leads to an overprediction of laminar flame speed for lean mixtures and an underprediction for rich mixtures. This result is slightly different from conclusion drawn in previous work, in which experimental data are compared with a one-dimensional numerical solutions. Detailed analysis reveals that flame speed is sensitive to even slight flame front curvature as well as its finite extension in the radial direction. Neither of these can be incorporated in one-dimensional flow modeling.
" }, { "name": "Laurence, Stuart Jon", "degree": "PhD", "year": "2006", "title": "Proximal Bodies in Hypersonic Flow", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04242006-172719", "creators": [ { "name": { "family": "Laurence", "given": "Stuart Jon" }, "id": "Laurence-Stuart-Jon", "orcid": "0000-0001-8760-8366", "display_name": "Laurence, Stuart Jon" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Stevenson", "given": "David John" }, "id": "Stevenson-D-J", "orcid": "0000-0001-9432-7159", "role": "member", "display_name": "Stevenson, David John" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZJV-KJ48", "abstract": "The problem of proximal bodies in hypersonic flow is encountered in several important situations, both natural and man-made. The present work seeks to investigate one aspect of this problem by exploring the forces experienced by a secondary body when some part of it is within the shocked region created by a primary body travelling at hypersonic speeds.
\r\n\r\nAn analytical methodology based on the blast wave analogy is developed and used to predict the secondary force coefficients for simple geometries in both two and three dimensions. When the secondary body is entirely inside the primary shocked region, the nature of the lateral coefficient is found to depend strongly on the relative size of the two bodies. For two spheres, the methodology predicts that the secondary body will experience an exclusively attractive lateral force if the secondary diameter is larger then one-sixth the primary diameter. The analytical results are compared with numerical simulations carried out using the AMROC software and good agreement is obtained if an appropriate normalization for the lateral displacement is used.
\r\n\r\nResults from a series of experiments in the T5 hypervelocity shock tunnel are also presented and compared with perfect-gas numerical simulations, again with good agreement. In order to model this situation experimentally, a new force-measurement technique for short-duration hypersonic facilities has been developed, and results from the validation experiments are included.
\r\n\r\nFinally, the analytical methodology is used to model two physical situations. First, the entry of a binary asteroid system into the Earth's atmosphere is simulated. Second, a model for a fragmenting meteoroid in a planetary atmosphere is developed, and simulations are carried out to determine whether the secondary scatter patterns in the Sikhote-Alin crater field may be attributed to aerodynamic interactions between fragments rather than to secondary fragmentation. It is found that while aerodynamic interactions lead to increased secondary crater grouping, these groups do not exhibit the typically elliptical shape that we would expect secondary fragmentation to produce.
" }, { "name": "Lieberman, Daniel Howard", "degree": "PhD", "year": "2006", "title": "Detonation Interaction with Sharp and Diffuse Interfaces", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11172005-092205", "creators": [ { "name": { "family": "Lieberman", "given": "Daniel Howard" }, "id": "Lieberman-Daniel-Howard", "display_name": "Lieberman, Daniel Howard" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9JZE-X524", "abstract": "Detonation interaction with an interface was investigated, where the interface separated a combustible from an oxidizing mixture. The ethylene-oxygen combustible mixture had a fuel-rich composition to promote secondary combustion with the oxidizer in the turbulent mixing zone that resulted from the interaction. Both sharp and diffuse interfaces were studied.
\r\n\r\nDiffuse interfaces were created by the formation of a gravity current using a sliding valve that initially separated the test gas and combustible mixture. Opening the valve allowed a gravity current to develop before the detonation was initiated. By varying the delay between opening the valve and initiating the detonation it was possible to achieve a wide range of interface conditions. Sharp interfaces were created by using a nitro-cellulose membrane to separate the two mixtures. The membrane was destroyed by the detonation wave.
\r\n\r\nThe interface orientation and thickness with respect to the detonation wave have a profound effect on the outcome of the interaction. Diffuse interfaces result in curved detonation waves with a transmitted shock and following turbulent mixing zone. Sharp interfaces result in an interaction occurring at a node point similar to regular shock refraction (Henderson, 1989). The impulse was measured to quantify the degree of secondary combustion accounting for 5-6% of the total impulse. A model was developed that estimated the volume expansion of a fluid element due to combustion in the turbulent mixing zone (Dimotakis, 1991) to predict the impulse in the limit of infinite Damkohler number.
" }, { "name": "Parkin, Kevin L.G.", "degree": "PhD", "year": "2006", "title": "The Microwave Thermal Thruster and Its Application to the Launch Problem", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-160023", "creators": [ { "name": { "family": "Parkin", "given": "Kevin L.G." }, "id": "Parkin-Kevin-L-G", "orcid": "0000-0003-4521-8559", "display_name": "Parkin, Kevin L.G." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Barmatz", "given": "Martin B." }, "id": "Barmatz-M-B", "role": "member", "display_name": "Barmatz, Martin B." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Worden", "given": "Simon P." }, "id": "Worden-S-P", "role": "member", "display_name": "Worden, Simon P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T337-T709", "abstract": "Nuclear thermal thrusters long ago bypassed the 50-year-old specific impulse (Isp) limitation of conventional thrusters, using nuclear powered heat exchangers in place of conventional combustion to heat a hydrogen propellant. These heat exchanger thrusters experimentally achieved an Isp of 825 seconds, but with a thrust-to-weight ratio (T/W) of less than ten they have thus far been too heavy to propel rockets into orbit.
\r\n\r\nThis thesis proposes a new idea to achieve both high Isp and high T/W: The Microwave Thermal Thruster. This thruster covers the underside of a rocket aeroshell with a lightweight microwave absorbent heat exchange layer that may double as a re-entry heat shield. By illuminating the layer with microwaves directed from a ground-based phased array, an Isp of 700\u2013900 seconds and T/W of 50\u2013150 is possible using a hydrogen propellant. The single propellant simplifies vehicle design, and the high Isp increases payload fraction and structural margins. These factors combined could have a profound effect on the economics of building and reusing rockets.
\r\n\r\nA laboratory-scale microwave thermal heat exchanger is constructed using a single channel in a cylindrical microwave resonant cavity, and new type of coupled electromagnetic-conduction-convection model is developed to simulate it. The resonant cavity approach to small-scale testing reveals several drawbacks, including an unexpected oscillatory behavior. Stable operation of the laboratory-scale thruster is nevertheless successful, and the simulations are consistent with the experimental results.
\r\n\r\nIn addition to proposing a new type of propulsion and demonstrating it, this thesis provides three other principal contributions: The first is a new perspective on the launch problem, placing it in a wider economic context. The second is a new type of ascent trajectory that significantly reduces the diameter, and hence cost, of the ground-based phased array. The third is an eclectic collection of data, techniques, and ideas that constitute a Microwave Thermal Rocket as it is presently conceived, in turn selecting and motivating the particular experimental and computational analyses undertaken.
" }, { "name": "Zhang, Rongjing", "degree": "PhD", "year": "2006", "title": "Mechanical Characterization of Thin Films with Application to Ferroelectrics", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312006-170959", "creators": [ { "name": { "family": "Zhang", "given": "Rongjing" }, "id": "Zhang-Rongjing", "display_name": "Zhang, Rongjing" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Molinari", "given": "Alain" }, "id": "Molinari-A", "role": "member", "display_name": "Molinari, Alain" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CJR5-DK94", "abstract": "One important part of the motivation for this research work comes from the microelectromechanical systems (MEMS) technology. Its basic concept of high volume production and low unit cost can only be achieved when the devices made by microelectronics technique are reliable. The success in this area largely depends on the understanding of materials. However, the mechanical characterization is lagged behind the theoretical work and designing software development. The standard characterization method is still not established. For MEMS actuators, especially for active materials, the desired characterization system for obtaining mechanical properties requires load control feature and the capability of doing dynamic tests. However, there is no such method among the currently available tools for mechanical characterization.
\r\n\r\nThe other part of the motivation comes from the comprehensive research work of Caltech ferroelectric group. This group, which consists of nine faculty members, is aiming to develop new devices, especially new actuators, by the aid of multi-scale theory tools and selected experimental methods. The work presented in this dissertation is an important and key step of this ambitious project: the electromechanical characterization of devices. This will provide validation for the multi-scale materials modeling framework and help to increase the reliability of the actuators and devices.
\r\n\r\nIn this work, two techniques were developed for mechanical characterization, which satisfy the challenging requirements for thin film structures and devices: being able to do dynamic study on fragile ceramic thin film samples with load control feature. The first technique is a new method to characterize mechanical properties of released thin films under concentrated load. This technique can be used to apply load in the ?N?mN range with displacement measured with high accuracy of 0.1 ?m. The successful characterization of Si3N4 free-standing membranes demonstrated the capability and reliability of this new technique. The elastic modulus and residual stress of Si3N4 free-standing thin film were measured to be around 250 GPa and 450 MPa, respectively. These values were in close agreement with values obtained using a different technique as well as those found in the literature. This technique has the potential application on elastic-plastic characterization and characterization of other functional thin film materials such as shape memory alloys.
\r\n\r\nPressure bulge test technique, which is another type of load control method suitable for dynamic test, was also developed. The apparatus was designed to be compact to fit into the x-ray diffractometer for in-situ XRD study and had additional compatibility for polarized light microscopy study. Characterization of free standing thin film of single layer amorphous silicon nitride (Si3N4) and multi-layered PBT/Si3N4, and thick film of single crystal barium titanate (BaTiO3) showed the capability and reliability of this technique. Excellent agreement of the Si3N4 Young\u2019s modulus between these two developed methods gave the confidence for using these techniques to understand new materials.
\r\n\r\nIn situ x-ray diffraction study was carried out on the single crystal thick films which were loaded with distributed mechanical loading by pressure bulge setup. Direct evidence of 90o domain switching was obtained from the in situ XRD results with the intensity changing in both (002) and (200) orientations. Obvious changes in domain patterns were observed by using the polarized light microscope. The Young\u2019s modulus of this barium titanate single crystal thick film with thickness of 100 ?m was characterized before the XRD exam. Using this information, in-plane stress can be analyzed, and the relation between the driving force (the stress) and the microstructural change (volume fraction change in a-domain or c-domain) can be determined.
" }, { "name": "Zielonka, Matias Gabriel", "degree": "PhD", "year": "2006", "title": "Configurational Forces and Variational Mesh Adaption in Solid Dynamics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05112006-162905", "creators": [ { "name": { "family": "Zielonka", "given": "Matias Gabriel" }, "id": "Zielonka-Matias-Gabriel", "display_name": "Zielonka, Matias Gabriel" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V6RB-FR94", "abstract": "This thesis is concerned with the exploration and development of a variational finite element mesh adaption framework for non-linear solid dynamics and its conceptual links with the theory of dynamic configurational forces. The distinctive attribute of this methodology is that the underlying variational principle of the problem under study is used to supply both the discretized fields and the mesh on which the discretization is supported. To this end a mixed-multifield version of Hamilton's principle of stationary action and Lagrange-d'Alembert principle is proposed, a fresh perspective on the theory of dynamic configurational forces is presented, and a unifying variational formulation that generalizes the framework to systems with general dissipative behavior is developed. A mixed finite element formulation with independent spatial interpolations for deformations and velocities and a mixed variational integrator with independent time interpolations for the resulting nodal parameters is constructed. This discretization is supported on a continuously deforming mesh that is not prescribed at the outset but computed as part of the solution. The resulting space-time discretization satisfies exact discrete configurational force balance and exhibits excellent long term global energy stability behavior. The robustness of the mesh adaption framework is assessed and demonstrated with a set of examples and convergence tests." }, { "name": "Bergthorson, Jeffrey Myles", "degree": "PhD", "year": "2005", "title": "Experiments and Modeling of Impinging Jets and Premixed Hydrocarbon Stagnation Flames", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-165713", "creators": [ { "name": { "family": "Bergthorson", "given": "Jeffrey Myles" }, "id": "Bergthorson-Jeffrey-Myles", "orcid": "0000-0003-2924-7317", "display_name": "Bergthorson, Jeffrey Myles" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kuppermann", "given": "Aron" }, "id": "Kuppermann-A", "role": "member", "display_name": "Kuppermann, Aron" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7FQZ-EY88", "abstract": "To model the combustion of long-chain hydrocarbon fuels, an accurate kinetics mechanism must first be developed for the oxidation of small hydrocarbons, such as methane, ethane, and ethylene. Even for methane, a generally accepted mechanism is still elusive due to a lack of kinetically independent experimental data. In this work, a combined experimental and modeling technique is developed to validate and further optimize these mechanisms. This technique relies on detailed measurements of strained flames in a jet-wall stagnation flow using simultaneous Particle Streak Velocimetry (PSV) and CH Planar Laser Induced Fluorescence (PLIF). Stagnation flames are simulated using an axisymmetric, one-dimensional model with accurate specification of the requisite boundary conditions. Direct comparisons between experiment and simulation allow for an assessment of the various models employed, with an emphasis on the chemistry model performance.
\r\n\r\nThe flow field for a cold impinging laminar jet is found to be independent of the nozzle-to-plate separation distance if velocities are scaled by the Bernoulli velocity. The one-dimensional formulation is found to accurately model the stagnation flow if the velocity boundary conditions are appropriately specified. The boundary-layer-displacement-thickness corrected diameter is found to be an appropriate scale for axial distances and allows the identification of an empirical, analytical expression for the flow field of the impinging laminar jet.
\r\n\r\nStrained methane-air flame experiments confirm that the reacting flow is also independent of the nozzle-to-plate separation distance. Methane, ethane, and ethylene flames are studied as functions of the applied strain rate, mixture dilution, and mixture fraction. Mechanism performance is found to be relatively insensitive to both the mixture dilution and the imposed strain rate, while exhibiting a stronger dependence on the fuel type and flame stoichiometry. The approach and diagnostics presented here permit an assessment of the predictions of strained-hydrocarbon flames for several combustion chemistry mechanisms. The data presented in this thesis are made available to kineticists looking for optimization targets, with the goal of developing a predictive kinetics model for hydrocarbon fuels. The methodology described here can allow new optimization targets to be rapidly measured, reducing the experimental burden required to fully constrain the chemistry models.
" }, { "name": "Chatelain, Philippe", "degree": "PhD", "year": "2005", "title": "Contributions to the Three-Dimensional Vortex Element Method and Spinning Bluff Body Flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012005-061553", "creators": [ { "name": { "family": "Chatelain", "given": "Philippe" }, "id": "Chatelain-Philippe", "orcid": "0000-0001-9891-5265", "display_name": "Chatelain, Philippe" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YEDS-0V89", "abstract": "Several contributions to the three-dimensional vortex element method for incompressible flows are presented. We introduce redistribution schemes based on the hexagonal lattice in two dimensions, and the face-centered cubic lattice in three dimensions. Interpolation properties are studied in the frequency domain and are used to build high-order schemes that are more compact and isotropic than equivalent cubic schemes. We investigate the reconnection of vortex rings at small Reynolds numbers for a variety of configurations. In particular, we trace their dissipative nature to the formation of secondary structures.
\r\n\r\nA method for flows with moving boundaries is implemented. The contributions of rotating or deforming boundaries to the Biot-Savart law are derived in terms of surface integrals. They are implemented for rigid boundaries in a fast multipole algorithm. Near-wall vorticity is discretized with attached panels. The shape function and Biot-Savart contributions of these elements account for the presence of the boundary and its curvature. A conservative strength exchange scheme was designed to compute the viscous flux from these panels to free elements.
\r\n\r\nThe flow past a spinning sphere is studied for a Reynolds number of 300 and a wall velocity that is equal to half the free-stream velocity. Three directions of the angular velocity are considered. Good agreement with previous numerical and experimental measurements of the force coefficients is observed. Topological features such as the separation and critical points are investigated and compared amongst the configurations.
\r\n\r\nFinally, preliminary results for flapping motions are presented. Simple rigid geometries are used to model a fish swimming in a free-stream and a flapping plate.
" }, { "name": "Dabiri, John Oluseun", "degree": "PhD", "year": "2005", "title": "Unsteady Fluid Mechanics of Starting-Flow Vortex Generators with Time-Dependent Boundary Conditions", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112005-151435", "creators": [ { "name": { "family": "Dabiri", "given": "John Oluseun" }, "id": "Dabiri-John-Oluseun", "orcid": "0000-0002-6722-9008", "display_name": "Dabiri, John Oluseun" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/QV8Y-YZ12", "abstract": "Nature has repeatedly converged on the use of starting flows for mass, momentum, and energy transport. The vortex loops that form during flow initiation have been reproduced in the laboratory and have been shown to make a proportionally larger contribution to fluid transport than an equivalent steady jet. However, physical processes limit growth of the vortex loops, suggesting that these flows may be amenable to optimization. Although it has been speculated that optimal vortex formation might occur naturally in biological systems, previous efforts to quantify the biological mechanisms of vortex formation have been inconclusive. In addition, the unsteady fluid dynamical effects associated with starting flow vortex generators are poorly understood.
\r\n\r\nThis thesis describes a combination of new experimental techniques and in vivo animal measurements that determine the effects of fluid-structure interactions on vortex formation by starting flow propulsors. Results indicate that vortex formation across various biological systems is manipulated by these kinematics in order to maximize thrust and/or propulsive efficiency. An emphasis on observed vortex dynamics and transient boundary conditions facilitates quantitative comparisons across fluid transport schemes, irrespective of their individual biological functions and physical scales.
\r\n\r\nThe primary contributions of this thesis are the achievement of quantitative measures of unsteady vortex dynamics via fluid entrainment and added-mass effects, and the development of a robust framework to facilitate the discovery of general design principles for effective fluid transport in engineering technologies and biological therapies. The utility of this new research paradigm is demonstrated through a variety of examples.
" }, { "name": "Dooley, Bradley Scott", "degree": "PhD", "year": "2005", "title": "Stereo Digital Particle Image Velocimetry Investigation of a Free Surface Mixing Layer", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-180557", "creators": [ { "name": { "family": "Dooley", "given": "Bradley Scott" }, "id": "Dooley-Bradley-Scott", "display_name": "Dooley, Bradley Scott" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EH41-N436", "abstract": "Shear flows in the vicinity of a free surface are a problem with numerous applications, perhaps the most obvious being the wakes of seagoing surface vessels. The flow behind a full-scale ship is extremely complex \u2013 so much so that it is frequently more instructive to consider simpler cases highlighting particular elements of the larger problem. To that end, an experimental investigation has been conducted to study the behavior of a turbulent plane mixing layer intersecting a free surface at low Froude number. The local Reynolds number, based on the velocity differential across the layer and the momentum thickness, was approximately 10,000.
\r\n\r\nThe technique of Stereoscopic Digital Particle Image Velocimetry (SDPIV) was implemented to obtain instantaneous three-component velocity measurements within planar slices of the steady-state, spatially developing mixing layer flow. Guided by previous studies of the same flow conditions, specific depths were chosen at a single downstream station for investigation \u2013 specifically those in and around counter-rotating streamwise vortices known to exist in the mean flow very near the free surface. 3,000 consecutive SDPIV image pairs were recorded at a rate of 15 per second at each location, giving ample data for Reynolds decomposition and spectral analysis of the velocity fields.
\r\n\r\nThe present study has found that the anisotropy known to exist in some other free surface flows, such as surface-parallel submerged jets, is also present in the case of the mixing layer. Power spectra of all three velocity components are shown to capture part of the inertial subrange; the isotropic energy cascade seen to be present away from the free surface is also seen to disappear near the surface, as surface-normal velocity fluctuations are severely attenuated.
\r\n\r\nAdditionally, a low-frequency spanwise oscillation is deduced from the velocity power spectra and cospectra in the immediate vicinity of the mean streamwise vortices. Not present at all at significant depth, the motions at this frequency are also observed to markedly decrease \u2013 in all components \u2013 at locations closer to the surface. These observations appear to have both parallels and key differences compared to previously observed meandering of model boat wakes, and the possibility that the oscillation stems from the vortex-pair instability is discussed.
" }, { "name": "Faddy, James Malcolm", "degree": "PhD", "year": "2005", "title": "Flow Structure in a Model of Aircraft Trailing Vortices", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-163801", "creators": [ { "name": { "family": "Faddy", "given": "James Malcolm" }, "id": "Faddy-James-Malcolm", "display_name": "Faddy, James Malcolm" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RC42-JY40", "abstract": "We consider a model of incompressible trailing vortices consisting of an array of counter-rotating structures in a doubly periodic domain, infinite in the vertical direction. The two-dimensional vortex array of Mallier and Maslowe is combined with an axial velocity profile chosen proportional to the initial axial vorticity to provide an initial condition for the vortex wake. This base flow is a weak solution of the three component steady Euler equations in two dimensions thus allowing its linear stability properties to be investigated. These are used to interpret several stages in the development of vortex structure observed in fully three-dimensional DNS at Reynolds numbers Gamma/(2 pi nu)=O(1000). For sufficiently high axial velocity, itseffect can be seen, in that each vortex in the linear array first develops helical structures before undergoing a period of relaminarization. At later times the more slowly growing co-operative elliptical instabilities become apparent; however, the helical structure persists and the observed vortical structures remain coherent for longer periods than in the absence of axial velocity. Using the stretched vortex subgrid model, large-eddy simulation runs are performed at higher Reynolds numbers and a mixing transition identified at about Re = 1-2 x 10\u2074. Similar phenomena are observed in these simulations as are seen in the DNS. Next the spatial nature of the true aircraft wake is compared to the temporal approximation commonly employed to simplify the computational complexity of the problem. A model is formulated to acount for the average axial pressure gradients that develops in the spatial wake but is absent from the temporal simulation. The model enables jet- and wake-like axial flows to be distinguished and the subtle differences in the ensuing turbulent states investigated. Finally, the model is used to investigate co-rotating vortex merger, the new thrust term providing a mechanism to enhance the axial flow further destabilizing the base flow." }, { "name": "Fung, Jimmy", "degree": "PhD", "year": "2005", "title": "Coarse Analysis of Multiscale Systems: Diffuser Flows, Charged Particle Motion, and Connections to Averaging Theory", "advisor": "Murray, Richard M.; Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-165938", "creators": [ { "name": { "family": "Fung", "given": "Jimmy" }, "id": "Fung-Jimmy", "orcid": "0000-0002-6612-2209", "display_name": "Fung, Jimmy" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wn0z-gn57", "abstract": "We describe a technique for the efficient computation of the dominant-scale dynamics of a fluid system when only a high-fidelity simulation is available. Such a technique is desirable when governing equations for the dominant scales are unavailable, when model reduction is impractical, or when the original high-fidelity computation is expensive. We adopt the coarse analysis framework proposed by I. G. Kevrekidis (Comm. Math. Sci. 2003), where a computational superstructure is designed to use short-time, high-fidelity simulations to extract the dominant features for a multiscale system. We apply this technique to compute the dominant features of the compressible flow through a planar diffuser. We apply the proper orthogonal decomposition to classify the dominant and subdominant scales of diffuser flows. We derive a suitable coarse projective Adams-Bashforth time integration routine and apply it to compute averaged diffuser flows. The results include accurate tracking of the dominant-scale dynamics for a range of parameter values for the computational superstructure. These results demonstrate that coarse analysis methods are useful for solving fluid flow problems of a multiscale nature.
\r\n\r\nIn order to elucidate the behavior of coarse analysis techniques, we make comparisons to averaging theory. To this end, we derive governing equations for the average motion of charged particles in a magnetic field in a number of different settings. First, we apply a novel procedure, inspired by WKB theory and Whitham averaging, to average the variational principle. The resulting equations are equivalent to the guiding center equations for charged particle motion; this marks an instance where averaging and variational principles commute. Secondly, we apply Lagrangian averaging techniques, previously applied in fluid mechanics, to derive averaged equations. Making comparisons to the WKB/Whitham-style derivation allows for the necessary closure of the Lagrangian averaging formulation. We also discuss the Hamiltonian setting and show that averaged Hamiltonian systems may be derivable using concepts from coarse analysis. Finally, we apply a prototypical coarse analysis procedure to the system of charged particles and generate trajectories that resemble guiding center trajectories. We make connections to perturbation theory to derive guidelines for the design of coarse analysis techniques and comment on the prototypical coarse analysis application.
" }, { "name": "Jackson, Scott Irving", "degree": "PhD", "year": "2005", "title": "Gaseous Detonation Initiation Via Wave Implosion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-151253", "creators": [ { "name": { "family": "Jackson", "given": "Scott Irving" }, "id": "Jackson-Scott-Irving", "orcid": "0000-0002-6814-3468", "display_name": "Jackson, Scott Irving" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "co-chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "co-chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MKP3-VC84", "abstract": "Efficient detonation initiation is a topic of intense interest to designers of pulse detonation engines. This experimental work is the first to detonate propane-air mixtures with an imploding detonation wave and to detonate a gas mixture with a non-reflected, imploding shock. In order to do this, a unique device has been developed that is capable of generating an imploding toroidal detonation wave inside of a tube from a single ignition point without any obstruction to the tube flow path. As part of this study, an initiator that creates a large-aspect-ratio planar detonation wave in gas-phase explosive from a single ignition point has also been developed.
\r\n\r\nThe effectiveness of our initiation devices has been evaluated. The minimum energy required by the imploding shock for initiation was determined to scale linearly with the induction zone length, indicating the presence of a planar initiation mode. The imploding toroidal detonation initiator was found to be more effective at detonation initiation than the imploding shock initiator, using a comparable energy input to that of current initiator tubes.
" }, { "name": "Johnson, Michael Bernard", "degree": "Engineering Degree", "year": "2005", "title": "Aerodynamic Control and Mixing with Ramp Injection", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262005-112117", "creators": [ { "name": { "family": "Johnson", "given": "Michael Bernard" }, "id": "Johnson-Michael-Bernard", "display_name": "Johnson, Michael Bernard" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8EVK-FK75", "abstract": "Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility (S3L) to investigate the behaviour of a flow and geometry with many features that are potentially useful for a Supersonic Combustion Ramjet (SCRAMJET) engine - a recirculation zone for flameholding, enhanced mixing between fuel and air, and low total-pressure losses. In a subsonic diffuser configuration with no mass injection, the exit velocity and guidewall static-pressure profiles collapse over a large range of inlet Reynolds numbers. Significant control of exit velocity and guidewall pressure profiles is possible via injection through a perforated ramp into the freestream. The control authority on the overall pressure coefficient increases with increasing inlet Reynolds number. Simple control volume models put bounds on the overall pressure coefficient for the device.
\r\n\r\nIn low-supersonic flow, the area ratio calculated from measured pressures agrees well with the visual shear-layer thickness, illustrating the low total-pressure losses present.
\r\n\r\nFurther control is possible through variable heat release from a fast-chemical reaction between reactants carried in the two streams. At the highest heat release studied, mass injection requirements are lowered by, roughly, a factor of two. Measurements of mixing inferred from the temperature rise from such a reaction indicate a high level of mixing vs. classical free shear layers. As in free shear layers, however, the level of mixing begins to decrease with increasing heat release.
" }, { "name": "Kowalewsky, Olga", "degree": "PhD", "year": "2005", "title": "Theory of Complex Lattice Quasicontinuum and Its Application to Ferroelectrics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202004-182638", "creators": [ { "name": { "family": "Kowalewsky", "given": "Olga" }, "id": "Kowalewsky-Olga", "display_name": "Kowalewsky, Olga" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rb0c-9534", "abstract": "Complex lattice Quasicontinuum theory is developed and applied to the description of ferroelectric phenomena. Quasicontinuum theory is a multiscale theory that provides a unified description of materials by combining atomistic and continuum approaches. It provides a seamless transition between atomistics and continuum, but the description of the material is derived directly from the underlying atomic structure, using the computationally expensive atomistics only where needed, at the location of phenomena of atomistic origin.
\r\n\r\nComplex Lattice Quasicontinuum theory can be applied to complex lattice crystals consisting of many kinds of atoms. One highlight of it is treatment of each component lattice as separately and independently as possible. The component Quasicontinua are coupled through the microscopic forces within nodal clusters, making the complex atomistics of the heterogeneous lattice the basis of the description.
\r\n\r\nFerroelectrics are especially suited to the application of Quasicontinuum theory. The nature of defects in ferroelectric materials is atomistic, but their influence over the material is long ranged due to induced elastic fields. Many different ferroelectric phenomena involving the perovskite ferroelectrics Barium Titanate and Lead Titanate are investigated and simulated. For Barium Titanate: the 180 degree domain wall structure and quasistatic crack under load. For Lead Titanate: the 180 degree domain wall structure and a domain wall step.
\r\n\r\nThe results for the domain walls show that the domain wall thickness is atomistically small, of the order of few lattice constants, which is in agreement with recent ab initio molecular dynamics simulations, but we also observe long range effects resulting from the presence of the wall. During crack loading in the sample of Barium Titanate we observe polarization changes around the crack tip which are consistent with experimental observations of an increase of fracture toughness. The quasicontinuum study of a domain wall step gives an atomistical view into the equilibrium structure of the step.
\r\n\r\nQuasicontinuum is able to model these phenomena with atomistic precision around the defects and non-homogeneities, and also capture the influence of long-ranging effects in the samples. These studies could also give valuable modeling input for larger scale continuum approaches.
" }, { "name": "Papachristodoulou, Antonis", "degree": "PhD", "year": "2005", "title": "Scalable Analysis of Nonlinear Systems Using Convex Optimization", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082005-100243", "creators": [ { "name": { "family": "Papachristodoulou", "given": "Antonis" }, "id": "Papachristodoulou-Antonis", "orcid": "0000-0002-3565-8967", "display_name": "Papachristodoulou, Antonis" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Rantzer", "given": "Anders" }, "id": "Rantzer-A", "role": "member", "display_name": "Rantzer, Anders" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cds" ], "doi": "10.7907/5YG6-JG32", "abstract": "In this thesis, we investigate how convex optimization can be used to analyze different classes of nonlinear systems at various scales algorithmically. The methodology is based on the construction of appropriate Lyapunov-type certificates using sum of squares techniques.
\r\n\r\nAfter a brief introduction on the mathematical tools that we will be using, we turn our attention to robust stability and performance analysis of systems described by Ordinary Differential Equations. A general framework for constrained systems analysis is developed, under which stability of systems with polynomial, non polynomial vector fields and switching systems, as well as estimating the region of attraction and the L2 gain can be treated in a unified manner. Examples from biology and aerospace illustrate our methodology.
\r\n\r\nWe then consider systems described by Functional Differential Equations (FDEs), i.e., time-delay systems. Their main characteristic is that they are infinite dimensional, which complicates their analysis. We first show how the complete Lyapunov-Krasovskii functional can be constructed algorithmically for linear time delay systems. Then, we concentrate on delay-independent and delay-dependent stability analysis of nonlinear FDEs using sum of squares techniques. An example from ecology is given.
\r\n\r\nThe scalable stability analysis of congestion control algorithms for the Internet is investigated next. The models we use result in an arbitrary interconnection of FDE subsystems, for which we require that stability holds for arbitrary delays, network topologies and link capacities. Through a constructive proof, we develop a Lyapunov functional for FAST - a recently developed network congestion control scheme - so that the Lyapunov stability properties scale with the system size. We also show how other network congestion control schemes can be analyzed in the same way.
\r\n\r\nFinally, we concentrate on systems described by Partial Differential Equations. We show that axially constant perturbations of the Navier-Stokes equations for Hagen-Poiseuille flow are globally stable, even though the background noise is amplified as R3 where R is the Reynolds number, giving a 'robust yet fragile' interpretation. We also propose a sum of squares methodology for the analysis of systems described by parabolic PDEs.
\r\n\r\nWe conclude this work with an account for future research.
" }, { "name": "Ponchaut, Nicolas Frederic", "degree": "PhD", "year": "2005", "title": "Part I: 3DPTV: Advances and Error Analysis. Part II: Extension of Guderley's Solution for Converging Shock Waves", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312005-111401", "creators": [ { "name": { "family": "Ponchaut", "given": "Nicolas Frederic" }, "id": "Ponchaut-Nicolas-Frederic", "display_name": "Ponchaut, Nicolas Frederic" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/09ZH-9M66", "abstract": "This work is divided into two unrelated parts. In the first part, a full three-dimensional particle tracking system was developed and tested. Three images, from three separate CCDs placed at the vertices of an equilateral triangle, permit the three-dimensional location of particles to be determined by triangulation. Particle locations measured at two different times can then be used to create a three-component, three-dimensional velocity field. Key developments are the ability to accurately process overlapping particle images, offset CCDs to significantly improve effective resolution, treatment of dim particle images, and a hybrid particle tracking technique ideal for three-dimensional flows when only two sets of images exist. An in-depth theoretical error analysis was performed, which gives the important sources of error and their effect on the overall system. This error analysis was verified through a series of experiments, and a vortex flow measurement was performed.\r\n\r\nIn the second part, the problem of a cylindrically or spherically imploding and reflecting shock wave in a flow initially at rest was examined. Guderley's strong shock solution around the origin was improved by adding two more terms in the series expansion solution for both the incoming and the reflected shock waves. A series expansion was also constructed for the case where the shock is still very far from the origin. In addition, a program based on the characteristics method was written. Thanks to an appropriate change of variables, the shock motion could be computed from virtually infinity to very close to the reflection point. Comparisons were made between the series expansions, the characteristics program, and the results obtained using an Euler solver. These comparisons showed that the addition of two terms to the Guderley solution significantly increases the accuracy of the series expansion." }, { "name": "Thunnissen, Daniel Pierre", "degree": "PhD", "year": "2005", "title": "Propagating and Mitigating Uncertainty in the Design of Complex Multidisciplinary Systems", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072005-162147", "creators": [ { "name": { "family": "Thunnissen", "given": "Daniel Pierre" }, "id": "Thunnissen-Daniel-Pierre", "display_name": "Thunnissen, Daniel Pierre" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." } ], "option_major": [ "mecheng" ], "doi": "10.7907/0FX2-AM50", "abstract": "As humanity has developed increasingly ingenious and complicated systems, it has not been able to accurately predict the performance, development time, reliability, or cost of such systems. This inability to accurately predict parameters of interest in the design of complex multidisciplinary systems such as automobiles, aircraft, or spacecraft is due in great part to uncertainty. Uncertainty in complex multidisciplinary system design is currently mitigated through the use of heuristic margins. The use of these heuristic margins can result in a system being overdesigned during development or failing during operation.
\r\n\r\nThis thesis proposes a formal method to propagate and mitigate uncertainty in the design of complex multidisciplinary systems. Specifically, applying the proposed method produces a rigorous foundation for determining design margins. The method comprises five distinct steps: identifying tradable parameters; generating analysis models; classifying and addressing uncertainties; quantifying interaction uncertainty; and determining margins, analyzing the design, and trading parameters. The five steps of the proposed method are defined in detail. Margins are now a function of risk tolerance and are measured relative to mean expected system performance, not variations in design parameters measured relative to heuristic values.
\r\n\r\nAs an example, the proposed method is applied to the preliminary design of a spacecraft attitude determination and control system. In particular, the design of the attitude control system on the Mars Exploration Rover spacecraft cruise stage is used. Use of the proposed method for the example presented yields significant differences between the calculated design margins and the values assumed by the Mars Exploration Rover project.
\r\n\r\nIn addition to providing a formal and rigorous method for determining design margins, this thesis provides three other principal contributions. The first is an uncertainty taxonomy for use in the design of complex multidisciplinary systems with detailed definitions for each uncertainty type. The second is the modification of two simulation techniques, the mean value method and subset simulation, that can significantly reduce the computational burden in applying the proposed method. The third is a set of diverse application examples and various simulation techniques that demonstrate the generality and benefit of the proposed method.
" }, { "name": "Wheatley, Vincent", "degree": "PhD", "year": "2005", "title": "On the Richtmyer-Meshkov Instability in Magnetohydrodynamics", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-145538", "creators": [ { "name": { "family": "Wheatley", "given": "Vincent" }, "id": "Wheatley-Vincent", "orcid": "0000-0002-7287-7659", "display_name": "Wheatley, Vincent" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N407-2B54", "abstract": "The Richtmyer-Meshkov instability is important in a wide variety of applications including inertial confinement fusion and astrophysical phenomena. In some of these applications, the fluids involved may be plasmas and hence be affected by magnetic fields. For one configuration, it has been numerically demonstrated that the growth of the instability in magnetohydrodynamics is suppressed in the presence of a magnetic field. Here, the nature of this suppression is theoretically and numerically investigated.
\r\n\r\nIn the framework of ideal incompressible magnetohydrodynamics, we examine the stability of an impulsively accelerated, sinusoidally perturbed density interface in the presence of a magnetic field that is parallel to the acceleration. This is accomplished by analytically solving the linearized initial value problem, which is a model for the Richtmyer-Meshkov instability. We find that the initial growth rate of the interface is unaffected by the presence of a magnetic field, but for a finite magnetic field the interface amplitude asymptotes to a constant value. Thus the instability of the interface is suppressed. The interface behavior from the analytical solution is compared to the results of both linearized and non-linear compressible numerical simulations for a wide variety of conditions.
\r\n\r\nWe then consider the problem of the regular refraction of a shock at an oblique, planar contact discontinuity separating conducting fluids of different densities in the presence of a magnetic field aligned with the incident shock velocity. Planar ideal MHD simulations indicate that the presence of a magnetic field inhibits the deposition of vorticity on the shocked contact, which leads to the suppression of the Richtmyer-Meshkov instability. We show that the shock refraction process produces a system of five to seven plane waves that may include fast, intermediate, and slow MHD shocks, slow compound waves, 180\u00b0 rotational discontinuities, and slow-mode expansion fans that intersect at a point. In all solutions, the shocked contact is vorticity free and hence stable. These solutions are not unique, but differ in the type of waves that participate. The set of equations governing the structure of these multiple-wave solutions is obtained in which fluid property variation is allowed only in the azimuthal direction about the wave-intersection point. Corresponding solutions are referred to as either quintuple-points, sextuple-points, or septuple-points, depending on the number of participating waves. A numerical method of solution is described and examples are compared to the results of numerical simulations for moderate magnetic field strengths. The limit of vanishing magnetic field at fixed permeability and pressure is studied for two solution types. The relevant solutions correspond to the hydrodynamic triple-point with the shocked contact replaced by a singular structure consisting of a wedge, whose angle scales with the applied field magnitude, bounded by either two slow compound waves or two 180\u00b0 rotational discontinuities, each followed by a slow-mode expansion fan. These bracket the MHD contact which itself cannot support a tangential velocity jump in the presence of a non-parallel magnetic field. The magnetic field within the singular wedge is finite and the shock-induced change in tangential velocity across the wedge is supported by the expansion fans that form part of the compound waves or follow the rotational discontinuities. To verify these findings, an approximate leading order asymptotic solution appropriate for both flow structures was computed. The full and asymptotic solutions are compared quantitatively and there is shown to be excellent agreement between the two.
" }, { "name": "Wirz, Richard Edward", "degree": "PhD", "year": "2005", "title": "Discharge Plasma Processes of Ring-Cusp Ion Thrusters", "advisor": "Culick, Fred E. C.; Polk, James E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232005-162628", "creators": [ { "name": { "family": "Wirz", "given": "Richard Edward" }, "id": "Wirz-Richard-Edward", "orcid": "0000-0001-5309-3659", "display_name": "Wirz, Richard Edward" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "co-advisor", "display_name": "Polk, James E." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VKKE-PC20", "abstract": "This study has increased the viability of miniature ion thruster technology, advanced state-of-the-art discharge modeling, and revealed important aspects of discharge plasma processes. These extensions of existing ion thruster technology and understanding are necessary to fulfill the needs of future space missions. Experimental comparisons of the discharge performance of an array of miniature (3cm diameter) ion thruster discharge configurations were conducted and showed that a 3-ring configuration with length-to-diameter of 1.0 exhibited the best performance. A compact and lightweight version of this configuration, using small accelerator grid holes, exhibited discharge losses of 250-550eV/ion and propellant efficiency of as much as 87%. This performance represents a significant advancement in miniature (less than 5cm diameter) ion thruster technology and demonstrates that a miniature ion thruster of low magnet and thruster weight can yield desirable performance.
\r\n\r\nA multi-component hybrid 2-D computational Discharge Model was developed to help identify important ion thruster discharge processes and investigate miniaturization issues. Combining experimental and computational results reveals that magnetic field optimization for a miniature ion thruster is bracketed by considerations of primary electron utilization and discharge stability. Discharge Model analysis of the larger (30cm diameter) NSTAR thruster revealed that the peak observed in the NSTAR beam profile is due to double ions that are created by over-confinement of primary electrons on the thruster axis. Design sensitivity results show that, at the NSTAR thruster scale, efficient confinement of primary electrons is relatively easy to achieve; therefore, efforts to improve thruster performance should focus on effectively utilizing the primary electrons to minimize double ion production and maximize the number of single ions extracted to the beam.
\r\n\r\nThe observations from this study have furthered the understanding of discharge processes and should improve future ion thruster design and modeling efforts. The Discharge Model advances state-of-the-art ion thruster modeling and provides a framework for a complete thruster model that can be used for long-life performance assessment and life validation.
" }, { "name": "Barba, Lorena A.", "degree": "PhD", "year": "2004", "title": "Vortex Method for Computing High-Reynolds Number Flows: Increased Accuracy with a Fully Mesh-Less Formulation", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-030854", "creators": [ { "name": { "family": "Barba", "given": "Lorena A." }, "id": "Barba-Lorena-A", "orcid": "0000-0001-5812-2711", "display_name": "Barba, Lorena A." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TSR5-DE67", "abstract": "For the applications of high Reynolds number flows, the vortex method presents the advantage of being free from numerically dissipative truncation error. In practice, however, many vortex methods introduce some numerical dissipation in mesh-based spatial adaption stages, or schemes such as vortex particle splitting. The need for spatial adaption in vortex methods arises from the Lagrangian framework, which results in an increase of discretization error over time. Presently, a vortex method is devised that incorporates radial basis function (RBF) interpolation to provide spatial adaption in a fully mesh-less formulation. Numerical experiments show that there is a potential for higher accuracy in comparison with the standard remeshing techniques. The rate of convergence of the new spatial adaption method is exponential, however convection error limits the vortex method to second order convergence. Avenues for future research involve decreasing convection error, for example by means of deformable basis functions. Nevertheless, the RBF-based spatial adaption scheme has various advantages, in addition to a demonstrated higher accuracy and the obvious benefit of not requiring a regular arrangement of particles or mesh. One presently demonstrated advantage is automatic core size control for the core spreading viscous method, without the need for vortex particle splitting.
\r\n\r\nThree applications have been successfully treated with the presently developed vortex method. The relaxation of monopoles under non-linear perturbations has been computed, resulting in noticeable improvements compared to previously published results. The existence of a quasi-steady state consisting of a rotating tripole has been corroborated, for the case of large amplitude perturbations. The second application consists of the early adaptation of two co-rotating vortices at high Reynolds number, characterized by elliptical deformation of the cores, as well as small scale deformation in the weak areas of vorticity. This is considered to pose a severe test on the present method, or indeed any method. Comparison with results using spectral methods demonstrate in practice the potential for high accuracy computations using a mesh-less method, and in addition show that the naturally adaptive vortex method can result in considerably reduced problem sizes. Finally, for the calculation of non-symmetric Burgers vortices, a correction to the core spreading method for out-of-plane strain was developed. The results establish the capability of the vortex method for the computation of vortices under three-dimensional strain.
" }, { "name": "Bobba, Kumar Manoj", "degree": "PhD", "year": "2004", "title": "Robust Flow Stability: Theory, Computations and Experiments in Near Wall Turbulence", "advisor": "Doyle, John Comstock; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-143324", "creators": [ { "name": { "family": "Bobba", "given": "Kumar Manoj" }, "id": "Bobba-Kumar-Manoj", "display_name": "Bobba, Kumar Manoj" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0J1D-1B18", "abstract": "Helmholtz established the field of hydrodynamic stability with his pioneering work in 1868. From then on, hydrodynamic stability became an important tool in understanding various fundamental fluid flow phenomena in engineering (mechanical, aeronautics, chemical, materials, civil, etc.) and science (astrophysics, geophysics, biophysics, etc.), and turbulence in particular. However, there are many discrepancies between classical hydrodynamic stability theory and experiments. In this thesis, the limitations of traditional hydrodynamic stability theory are shown and a framework for robust flow stability theory is formulated. A host of new techniques like gramians, singular values, operator norms, etc. are introduced to understand the role of various kinds of uncertainty. An interesting feature of this framework is the close interplay between theory and computations. It is shown that a subset of Navier-Stokes equations are globally, non-nonlinearly stable for all Reynolds number. Yet, invoking this new theory, it is shown that these equations produce structures (vortices and streaks) as seen in the experiments. The experiments are done in zero pressure gradient transiting boundary layer on a flat plate in free surface tunnel. Digital particle image velocimetry, and MEMS based laser Doppler velocimeter and shear stress sensors have been used to make quantitative measurements of the flow. Various theoretical and computational predictions are in excellent agreement with the experimental data. A closely related topic of modeling, simulation and complexity reduction of large mechanics problems with multiple spatial and temporal scales is also studied. A nice method that rigorously quantifies the important scales and automatically gives models of the problem to various levels of accuracy is introduced. Computations done using spectral methods are presented.\r\n" }, { "name": "Chao, Tong Wa", "degree": "PhD", "year": "2004", "title": "Gaseous Detonation-Driven Fracture of Tubes", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04062004-165940", "creators": [ { "name": { "family": "Chao", "given": "Tong Wa" }, "id": "Chao-Tong-Wa", "display_name": "Chao, Tong Wa" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TEZP-YC46", "abstract": "An experimental investigation of fracture response of aluminum 6061-T6 tubes under internal gaseous detonation loading has been carried out. The pressure load, with speeds exceeding 2 km/s, can be characterized as a pressure peak (ranging from 2 to 6 MPa) followed by an expansion wave. The unique combination of this particular traveling load and tube geometry produced fracture data not available before in the open literature. Experimental data of this type are useful for studying the fluid-structure-fracture interaction and various crack curving and branching phenomena, and also for validation for multi-physics and multi-scale modeling.
\r\n\r\nAxial surface flaws were introduced to control the crack initiation site. Fracture threshold models were developed by combining a static fracture model and an extensively studied dynamic amplification factor for tubes under internal traveling loads. Experiments were also performed on hydrostatically loaded preflawed aluminum 6061-T6 tubes for comparison. Significantly different fracture behavior was observed and the difference was explained by fluid dynamics and energy considerations. The experiments yielded comparison on crack speeds, strain, and pressure histories.
\r\n\r\nIn other experiments, the specimens were also pre-torqued to control the propagation direction of the cracks. Measurements were made on the detonation velocity, strain history, blast pressure from the crack opening, and crack speeds. The curved crack paths were digitized. The Chapman-Jouguet pressure, initial axial flaw length, and torsion level were varied to obtain different crack patterns. The incipient crack kinking angle was found to be consistent with fracture under mixed-mode loading. High-speed movies of the fracture events and blast wave were taken and these were used in interpreting the quantitative data.
\r\n\r\nNumerical simulations were performed using the commercial explicit finite-element software LS-Dyna. The detonation wave was modeled as a traveling boundary load. Both non-fracturing linear elastic simulations and elastoplastic simulations with fracture were conducted on three-dimensional models. The simulated fracture was compared directly with an experiment with the same conditions. The overall qualitative fracture behavior was captured by the simulation. The forward and backward cracks were observed to branch in both the experiment and simulation.
" }, { "name": "Fago, Matthew Justin", "degree": "PhD", "year": "2004", "title": "Constrained Sequential Lamination: Nonconvex Optimization and Material Microstructure", "advisor": "Ortiz, Michael; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142004-144712", "creators": [ { "name": { "family": "Fago", "given": "Matthew Justin" }, "id": "Fago-Matthew-Justin", "display_name": "Fago, Matthew Justin" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "co-advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P1PK-E179", "abstract": "A practical algorithm has been developed to construct, through sequential lamination, the partial relaxation of multiwell energy densities such as those characteristic of shape memory alloys. The resulting microstructures are in static and configurational equilibrium, and admit arbitrary deformations. The laminate topology evolves during deformation through branching and pruning operations, while a continuity constraint provides a simple model of metastability and hysteresis. In cases with strict separation of length scales, the method may be integrated into a finite element calculation at the subgrid level. This capability is demonstrated with a calculation of the indentation of a Cu-Al-Ni shape memory alloy by a spherical indenter.
\r\n\r\nIn verification tests the algorithm attained the analytic solution in the computation of three benchmark problems. In the fourth case, the four-well problem (of, e.g., Tartar), results indicate that the method for microstructural evolution imposes an energy barrier for branching, hindering microstructural development in some cases. Although this effect is undesirable for purely mathematical problems, it is reflective of the activation energies and metastabilities present in applications involving natural processes.
\r\n\r\nThe method was further used to model Shield's tension test experiment, with initial calculations generating reasonable transformation strains and microstructures that compared well with the sequential laminates obtained experimentally.
" }, { "name": "Jewell, Joseph Stephen", "degree": "Senior Thesis", "year": "2004", "title": "Violence in the Medieval Church before the First Crusade", "advisor": "Brown, Warren C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06162014-194836973", "creators": [ { "name": { "family": "Jewell", "given": "Joseph Stephen" }, "id": "Jewell-Joseph-Stephen", "orcid": "0000-0002-4047-9998", "display_name": "Jewell, Joseph Stephen" } ], "advisors": [ { "name": { "family": "Brown", "given": "Warren C." }, "id": "Brown-Warren-C", "role": "advisor", "display_name": "Brown, Warren C." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "aeronautics", "history" ], "doi": "10.7907/33km-kt20", "abstract": "The attitude of the medieval church towards violence before the First Crusade in 1095 underwent a significant institutional evolution, from the peaceful tradition of the New Testament and the Roman persecution, through the prelate-led military campaigns of the Carolingian period and the Peace of God era. It would be superficially easy to characterize this transformation as the pragmatic and entirely secular response of a growing power to the changing world. However, such a simplification does not fully do justice to the underlying theology. While church leaders from the 5th Century to the 11th had vastly different motivations and circumstances under which to develop their responses to a variety of violent activities, the teachings of Augustine of Hippo provided a unifying theme. Augustine\u2019s just war theology, in establishing which conflicts are acceptable in the eyes of God, focused on determining whether a proper causa belli or basis for war exists, and then whether a legitimate authority declares and leads the war. Augustine masterfully integrated aspects of the Old and New Testaments to create a lasting and compelling case for his definition of justified violence. Although at different times and places his theology has been used to support a variety of different attitudes, the profound influence of his work on the medieval church\u2019s evolving position on violence is clear." }, { "name": "Malhotra, Sanjeev", "degree": "PhD", "year": "2004", "title": "On Combustion Instability in Solid Rocket Motors", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05062004-130913", "creators": [ { "name": { "family": "Malhotra", "given": "Sanjeev" }, "id": "Malhotra-Sanjeev", "display_name": "Malhotra, Sanjeev" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Flandro", "given": "G. A." }, "id": "Flandro-G-A", "role": "member", "display_name": "Flandro, G. A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V1WS-S833", "abstract": "An investigation of combustion instability in solid rocket motors was conducted using perturbation techniques, with particular emphasis placed upon understanding the fluid dynamics of the chamber environment. It was shown that although the phenomena generally manifests itself as oscillations of pressure, with the frequencies measured in tests well predicted by classical acoustic formulas, important aspects of the behavior cannot be explained without due recognition of the two basic processes of fluid dynamics\u2014i.e., the compressing/expanding process and the shearing process.
\r\n\r\nThus, a new framework for studying these instabilities that accommodated both linear and nonlinear behavior was developed. The approach differed from previous work in its use of linear stability eigenfunctions\u2014that satisfy the no-slip boundary condition\u2014as a basis for the expansion, with adjoints used to effect a spatial averaging. Among other things, this allowed for the self-consistent inclusion of vortical flow effects.
\r\n\r\nWith respect to the linear behavior, two dominant vorticity-related pathways were shown to exist: one because of sound creating vorticity, and the other, because of that vorticity, in turn, creating more sound. These effects cancel however and thus to leading order no net contribution exists. Though this finding had been reported in an earlier study, restrictive assumptions were introduced. In contrast, we establish that the result is independent of grain geometry and holds for any fluid motion, turbulent or otherwise.
\r\n\r\nA nonlinear coupling to the flame zone owing to vorticity creation was also identified. The term was left unevaluated however, since no satisfactory model of the flame response presently exists. To help circumvent this difficulty, i.e., that much remains to be done on modeling nonlinear processes, the amplitude equations were studied in a general way using perturbation techniques based on ideas of resonance. The advantage of such an approach is that the nonlinear coefficients need not be specified a priori\u2014only conditions on the linear behavior of the system need to be placed. Closed form results were derived for the limiting periodic behavior when the first mode is unstable and compared against results from numerical integration. Striking agreement was shown.
" }, { "name": "O'Gorman, Paul Ambrose", "degree": "PhD", "year": "2004", "title": "Theory and Simulation of Passive Scalar Mixing in the Presence of a Mean Scalar Gradient", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-150652", "creators": [ { "name": { "family": "O'Gorman", "given": "Paul Ambrose" }, "id": "O'Gorman-Paul-Ambrose", "display_name": "O'Gorman, Paul Ambrose" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K02H-HK48", "abstract": "The turbulent mixing of a passive scalar in the presence of a mean scalar gradient was investigated using theory and simulation. The velocity-scalar cospectrum measures the distribution of the mean scalar flux across scales. An inequality is shown to bound the magnitude of the cospectrum in terms of the shell-summed energy and scalar spectra. At high Schmidt number this bound limits the possible contribution of the sub-Kolmogorov scales to the scalar flux. At low Schmidt number we use an argument of Batchelor, Howells, and Townsend (1959) to derive a new asymptotic result for the cospectrum in the inertial-diffusive range, with a -11/3 power law wavenumber dependence. A comparison is made with results from large-eddy simulation at low Schmidt number.
\r\n\r\nThe sparse direct-interaction perturbation (SDIP) was used to calculate the cospectrum for a range of Schmidt numbers. The Kolmogorov type scaling result is recovered in the inertial-convective range, and the constant of proportionality was calculated. At high Schmidt numbers, the cospectrum is found to decay exponentially in the viscous-convective range, and at low Schmidt numbers the -11/3 power law is observed in the inertial-diffusive range. The stretched-spiral vortex model was used to calculate the cospectrum, and asymptotic expressions were found for the contribution to the cospectrum from the axial velocity in the vortex structures. Results are reported for the cospectrum from a direct numerical simulation at a Taylor Reynolds number of 265, and a comparison is made of results for the cospectrum from the SDIP, the stretched-spiral vortex model, simulation, and experiment.
\r\n\r\nThe stretched-spiral vortex model was also used to derive expressions for the modal time correlation functions of the velocity and scalar fields. These expressions were evaluated numerically and asymptotically. Winding by the vortex core is shown to lead to an inertial timescale, and movement of the vortex structures by the large scale flow leads to a sweeping timescale. The velocity and scalar modal time correlation functions were calculated in the direct numerical simulation. They coincide for large enough wavenumber, and are found to collapse to universal forms when a sweeping timescale is used.
" }, { "name": "O'Reilly, Gerard Kieran", "degree": "PhD", "year": "2004", "title": "Compressible Vortices and Shock-Vortex Interactions", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262004-145030", "creators": [ { "name": { "family": "O'Reilly", "given": "Gerard Kieran" }, "id": "O'Reilly-Gerard-Kieran", "display_name": "O'Reilly, Gerard Kieran" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FGJD-0Z31", "abstract": "Secondary instabilities on the organized, spanwise, vortical structures in incompressible shear layers, play an important role in generating the onset of three-dimensional turbulence in such flows. The effect of increasing compressibility on these instabilities is examined by using the compressible Stuart vortex as a model for a compressible shear layer. It is found that both two- and three-dimensional subharmonic instabilities cease to promote pairing events even at moderate free stream Mach numbers. The fundamental mode becomes dominant as the free stream Mach number is increased, and a new instability corresponding to an instability on a parallel shear layer is observed. The interaction of a shock with a compressible vortex may be viewed as a simplified model of the general interaction of a shock with the coherent structures in a turbulent flow field. An approximate theory for computing shock-compressible-vortex interactions is developed, based on Ribner (1954). The problem of convection of a frozen patern of vorticity, dilatation, temperature and entropy through a planar shock wave is considered. The refraction and modification of the upstream disturbances into the three basis modes permitted by the linear Euler equations is derived, as well as the perturbation to the shock wave. This theory is used to compute approximate post-shock states corresponding to shock-CSV interactions, a model for shock shear layer interactions. The method is verified by comparing its approximate post-shock fields with those computed explicitly using AMROC, a finite difference, AMR-WENO code. Finally, numerical solutions corresponding to a compressible analogue of the Mallier and Maslowe vortex (a periodic array of counter-rotating vortices) are presented. These solutions admit the existence of large regions of smooth supersonic flow, and could potentially be used to model the counter-rotating vortices arising from the single- and multi-mode Richtmyer-Meshkov instability." }, { "name": "Ringuette, Matthew James", "degree": "PhD", "year": "2004", "title": "Vortex Formation and Drag on Low Aspect Ratio, Normal Flat Plates", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292004-183807", "creators": [ { "name": { "family": "Ringuette", "given": "Matthew James" }, "id": "Ringuette-Matthew-James", "orcid": "0000-0002-8998-9489", "display_name": "Ringuette, Matthew James" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/907K-2F28", "abstract": "Experiments were done to investigate the role of vortex formation in the drag force generation of low aspect ratio, normal flat plates starting from rest. This very simplified case is a first, fundamental step toward understanding the more complicated flow of hovering flight, which relies primarily on drag for propulsion. The relative importance of the plate's free end, or tip, with varying aspect ratio was also studied.
\r\n\r\nIdentifying the relationship among aspect ratio, vortex formation, and drag force can provide insight into the wing aspect ratios and kinematics found nature, with the eventual goal of designing man-made flapping wing micro air vehicles.
\r\n\r\nThe experiments were carried out using flat plate models in a towing tank at a moderate Reynolds number of 3000. Two aspect ratios, 6 and 2, were considered, the latter in order to have a highly tip-dominated case. A force balance measured the time-varying drag, and multiple, perpendicular sections of the flow velocity were measured quantitatively using digital particle image velocimetry. Vorticity fields were calculated from the velocity data, and features in the drag force for different aspect ratios were related to the vortex dynamics. Finally, since the flow is highly three-dimensional, dye flow visualization was done to characterize its structure and to augment the two-dimensional digital particle image velocimetry data.
" }, { "name": "Wintenberger, Eric", "degree": "PhD", "year": "2004", "title": "Application of Steady and Unsteady Detonation Waves to Propulsion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222004-121013", "creators": [ { "name": { "family": "Wintenberger", "given": "Eric" }, "id": "Wintenberger-Eric", "display_name": "Wintenberger, Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2NXT-SE76", "abstract": "The present work investigates the applications of steady and unsteady detonation waves to air-breathing propulsion systems. The efficiency of ideal detonation-based propulsion systems is first investigated based on thermodynamics. We reformulate the Hugoniot analysis of steady combustion waves for a fixed initial stagnation state to conclude that steady detonation waves are less desirable than deflagrations for propulsion. However, a thermostatic approach shows that unsteady detonations have the potential for generating more work than constant-pressure combustion. The subsequent work focuses on specific engine concepts. A flow path analysis of ideal steady detonation engines is conducted and shows that their performance is limited and poorer than that of the ideal ramjet or turbojet engines. The limitations associated with the use of a steady detonation in the combustor are drastic and such engines do not appear to be practical. This leads us to focus on unsteady detonation engines, i.e., pulse detonation engnes. The unsteady generation of thrust in the simple configuration of a detonation tube is first analyzed using gas dynamics. We develop one of the first models to quickly and reliably estimate the impulse of a pulse detonation tube. The impulse is found to scale directly with the mass of explosive in the tube and the square root of the energy release per unit mass of the mixture. Impulse values for typical fuel-oxidizer mixtures are found to be on the order of 160 s for hydrocarbon-oxygen mixtures and 120 s for fuel-air mixtures at standard conditions. These results are then used as a basis to develop the first complete system-level performance analysis of a supersonic, single-tube, air-breathing pulse detonation engine. We show that hydrogen- and JP10-fueled pulse detonation engines generate thrust up to a Mach number of 4, and that the specific impulse decreases quasi-linearly with increasing flight Mach number. Finally, we find that the performance of our pulse detonation engine exceeds that of the ramjet below a Mach number of 1.35." }, { "name": "Yang, Qiang", "degree": "PhD", "year": "2004", "title": "Thermomechanical Variational Principles for Dissipative Materials with Application to Strain Localization in Bulk Metallic Glasses", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-152537", "creators": [ { "name": { "family": "Yang", "given": "Qiang" }, "id": "Yang-Qiang", "display_name": "Yang, Qiang" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6FV2-KV63", "abstract": "This thesis is concerned with variational principles for general coupled thermomechanical problems in dissipative materials including finite elastic and plastic deformation, non-Newtonian viscosity, rate sensitivity, arbitrary flow and hardening rule, as well as heat conduction. It is shown that there exists a potential function such that both the conservation of energy and balance of linear momentum are the Euler-Lagrange equations of its first variation. Inspired from the time-discretized version of the variational formulation, we present a procedure for variational thermomechanical update, which generalizes the isothermal approach under a variational thermodynamic framework. This variational formulation then serves as a basis for temperature change as well as constitutive updates.
\r\n\r\nAn important application of the variational formulation is to optimize the shear band thickness in strain localization processes. We show that this optimization takes the form of a configurational-force equilibrium and results in a well-defined band thickness. We further implement displacement discontinuities into a class of strain-localization finite elements. These elements consist of two surfaces, attached to the abutting volume elements, which can separate and slip relative to each other, and thus enable the accurate and efficient simulation of the dynamical formation of stain localization.
\r\n\r\nThe variational formulation also leads to a finite-deformation continuum modeling of bulk metallic glasses. It is shown that the strain softening of bulk metallic glasses is due to the increase of free volume (and thus the decrease of viscosity), while temperature rise accelerates the localization of the deformation. The model reproduces the constitutive behavior of Vitreloy 1 bulk metallic glass at various strain rates and temperatures.
" }, { "name": "Arienti, Marco", "degree": "PhD", "year": "2003", "title": "A Numerical and Analytical Study of Detonation Diffraction", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122003-152525", "creators": [ { "name": { "family": "Arienti", "given": "Marco" }, "id": "Arienti-Marco", "orcid": "0000-0001-8166-0016", "display_name": "Arienti, Marco" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MAGN-R628", "abstract": "An investigation of detonation diffraction through an abrupt area change has been carried out via two-dimensional, parallel simulations. The existence of critical conditions for successful diffraction is closely related to the occurrence of localized re-initiation mechanisms, and is relevant to propulsion and safety concepts concerning detonation transmission. Our analysis is specialized to a reactive mixture with perfect gas equation of state and a single-step reaction in the Arrhenius form. The concept of shock decoupling from the reaction zone is the simplest idea used to explain the behavior of a diffracting detonation front. Lagrangian particles are injected into the flow in order to identify the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in a shock-based reference system. Conveniently simplified, this equation provides an insight into the competition between the energy release rate and the expansion rate behind the diffracting front. We also examine the mechanism of spontaneous generation of transverse waves along the front. This mechanism is related to the sensitivity of the reaction rate to temperature, and it is investigated in the form of a parametric study for the activation energy. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behavior, super-, sub-, and near-critical diffraction. We review the applicability of existing shock dynamics models to the corner-turning problem. Numerical results from the parametric study are compared with predictions from these theories in the attempt to find a formula for shock decay in a quenching detonation. This estimate is then used in the simplified temperature rate of change equation to provide a relation between critical channel width and activation energy. We conclude this study by examining the spontaneous formation of transverse waves along the wavefront of a successfully transmitted detonation. The problem is simplified to a planar CJ detonation moving in a channel over a small obstacle to investigate how acoustic waves propagate within the reaction zone. Depending on the reaction kinetics, we show that such waves may be amplified due to feedback between the chemical reaction and fluid motion. The amplification can lead to shock steepening and formation of transverse detonation waves.\r\n" }, { "name": "Austin, Joanna Maria Karol", "degree": "PhD", "year": "2003", "title": "The Role of Instability in Gaseous Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-150534", "creators": [ { "name": { "family": "Austin", "given": "Joanna Maria Karol" }, "id": "Austin-Joanna-Maria-Karol", "orcid": "0000-0003-3129-5035", "display_name": "Austin, Joanna Maria Karol" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X7YH-T687", "abstract": "In detonation, the coupling between fluid dynamics and chemical energy release is critical. The reaction rate behind the shock front is extremely sensitive to temperature perturbations and, as a result, detonation waves in gases are always unstable. A broad spectrum of behavior has been reported for which no comprehensive theory has been developed. The problem is extremely challenging due to the nonlinearity of the chemistry-fluid mechanics coupling and extraordinary range of length and time scales exhibited in these flows. Past work has shown that the strength of the leading shock front oscillates and secondary shock waves propagate transversely to the main front. A key unresolved issue has emerged from the past 50 years of research on this problem: What is the precise nature of the flow within the reaction zone and how do the instabilities of the shock front influence the combustion mechanism?
\r\n\r\nThis issue has been examined through dynamic experimentation in two facilities. Key diagnostic tools include unique visualizations of superimposed shock and reaction fronts, as well as short but informative high-speed movies. We study a range of fuel-oxidizer systems, including hydrocarbons, and broadly categorize these mixtures by considering the hydrodynamic stability of the reaction zone. From these observations and calculations, we show that transverse shock waves do not essentially alter the classic detonation structure of Zeldovich-von Neumann-Doring (ZND) in weakly unstable detonations, there is one length scale in the instability, and the combustion mechanism is simply shock-induced chemical-thermal explosion behind a piecewise-smooth leading shock front. In contrast, we observe that highly unstable detonations have substantially different behavior involving large excursions in the lead shock strength, a rough leading shock front, and localized explosions within the reaction zone. The critical decay rate model of Eckett et al. (JFM 2000) is combined with experimental observations to show that one essential difference in highly unstable waves is that the shock and reaction front may decouple locally. It is not clear how the ZND model can be effectively applied in highly unstable waves. There is a spectrum of length scales and it may be possible that a type of \"turbulent\" combustion occurs. We consider how the coupling between chemistry and fluid dynamics can produce a large range of length scales and how possible combustion regimes within the front may be bounded.
" }, { "name": "Hung, Patrick Hin Fun", "degree": "PhD", "year": "2003", "title": "Algorithms for Reaction Mechanism Reduction and Numerical Simulation of Detonations Initiated by Projectiles", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-142744", "creators": [ { "name": { "family": "Hung", "given": "Patrick Hin Fun" }, "id": "Hung-Patrick-Hin-Fun", "display_name": "Hung, Patrick Hin Fun" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/H5GV-PV33", "abstract": "The evolution of a homogeneous, chemically reactive system with n species forms a dynamical system in chemical state-space. Under suitable constraints, unique and stable equilibrium exists and can be interpreted as zeroth-dimensional (point like) attractors in this n-dimensional space. At these equilibrium compositions, the rates of all reversible reactions vanish and can, in fact, be determined from thermodynamics independent of chemical kinetics.
\r\n\r\nGeneralizing this concept, an m-dimensional Intrinsic Low Dimensional Manifold (ILDM) represents an m-dimensional subspace in chemical state-space where all but the m-slowest aggregate reactions are in equilibrium, and these aggregate reactions are determined by eigenvalue considerations of the chemical kinetics. In this context, a certain composition is said to be m-dimensional if it is on an m-, but not an (m-1)-, dimensional ILDM.
\r\n\r\nTwo new algorithms are proposed that allow the dimensionality of chemical compositions be determined simply. The first method is based on recasting the Maas and Pope algorithm. The second, and more efficient, method is inspired by the mathematical structure of the Maas and Pope algorithm and makes use of the technique known as arc-length reparameterization. In addition, a new algorithm for the construction of ILDM, and the application of these ideas to detonation simulations, is discussed.
\r\n\r\nIn the second part of the thesis, numerical simulations of detonation waves initiated by hypervelocity projectiles are presented. Using detailed kinetics, only the shock-induced combustion regime is realized as simulating the conditions required for a stabilized detonation is beyond the reach of our current computational resources. Resorting to a one-step irreversible reaction model, the transition from shock-induced combustion to stabilized oblique detonation is observed, and an analysis of this transition based on the critical decay-rate model of Kaneshige (1999) is presented.
" }, { "name": "Koslowski, Marisol", "degree": "PhD", "year": "2003", "title": "A Phase-Field Model of Dislocations in Ductile Single Crystals", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-094155", "creators": [ { "name": { "family": "Koslowski", "given": "Marisol" }, "id": "Koslowski-Marisol", "orcid": "0000-0001-9650-2168", "display_name": "Koslowski, Marisol" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Molinari", "given": "Alain" }, "id": "Molinari-A", "role": "member", "display_name": "Molinari, Alain" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SFMJ-1B50", "abstract": "A phase-field theory of dislocations, strain hardening and hysteresis in ductile single crystals is developed. The theory accounts for an arbitrary number and arrangement of dislocation lines over a slip plane; the long-range elastic interactions between dislocation lines; the core structure of the dislocations; the interaction between the dislocations and an applied resolved shear stress field; and the irreversible interactions with short-range obstacles, resulting in hardening, path dependency and hysteresis.
\r\n\r\nWe introduce a variational formulation for the statistical mechanics of dissipative systems. The influence of finite temperature as well as the mechanics in the phase-field theory are modeled with a Metropolis Monte Carlo algorithm and a mean field approximation.
\r\n\r\nA chief advantage of the present theory is that at zero temperature it is analytically tractable, in the sense that the complexity of the calculations may be reduced, with the aid of closed form analytical solutions, to the determination of the value of the phase field at point-obstacle sites. The theory predicts a range of behaviors which are in qualitative agreement with observation, including hardening and dislocation multiplication in single slip under monotonic loading; the Bauschinger effect under reverse loading; the fading memory effect; the evolution of the dislocation density under cycling loading; temperature softening; strain rate dependence; and others.
\r\n\r\nThe model also reproduces the formation of dislocation networks observed in grain boundaries for different crystal structures and orientations. Simultaneously with the stable configurations the theory naturally predicts the equilibrium dislocation density independently of initial values or sources.
" }, { "name": "Kumar, Sanjay", "degree": "PhD", "year": "2003", "title": "An Experimental Investigation of Richtmyer-Meshkov Instability", "advisor": "Hornung, Hans G.; Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212003-140109", "creators": [ { "name": { "family": "Kumar", "given": "Sanjay" }, "id": "Kumar-Sanjay", "display_name": "Kumar, Sanjay" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NKDR-TT39", "abstract": "In this study, the interaction of a shock wave with an interface between two gases is studied experimentally. The basic mechanism for the initial growth of perturbations on the interface is the baroclinic generation of vorticity which results from the misalignment of the pressure gradient in the shock and the density gradient at the interface. The growth of perturbations soon enters into a nonlinear regime with the appearance of bubbles of light fluid rising into heavy fluid and spikes of heavy fluid falling into light fluid. In the nonlinear regime, interaction between various scales and the appearance of other instabilities, such as Kelvin-Helmholtz instability, along the boundaries of the spikes occur, which results in the breakup of the interface. These processes lead to a turbulent mixing zone (TMZ) which grows with time. The main focus of this study is to understand the growth of TMZ with time in a cylindrical geometry with square cross section and for the the first time study the effect of area convergence in a conical geometry on its growth rate. The present set of experiments is done in the GALCIT 17 in. shock tube with air and sulfur hexafluoride as light and heavy gases. The growth of the TMZ is studied in a straight test section for single-mode initial perturbation consisting of two different wavelength and amplitude combinations at incident shock Mach number of 1.55. The multimode initial perturbation growth at late times is studied in a conical geometry to study the effect of area convergence at incident Mach numbers of 1.55 and 1.39. The results are compared with the experiments of Vetter which were done in the same shock tube with a straight test section with no area convergence and at the same Mach number.
\r\n\r\nIn the study of the Richtmyer-Meshkov (RM) instability of single-scale perturbations on air/sulfur-hexafluoride interface in a straight test section, the initially sinusoidal interface is formed by a polymeric membrane of thickness 1.5 micron and the flow visualization is done using schlieren imaging technique. The interface thickness is measured visually from the photographs. It is found that the growth rate decreases rapidly with time with a small dependence on the initial wavelength persisting until late times.
\r\n\r\nIn the case of the RM instability, growth of multimode initial perturbations in a conical geometry, it is found from the schlieren flow visualization images that the interface thickness grows about 40-50 % more rapidly than in Vetter's experiments. Experimental results for laser-induced scattering at late times are presented for air/He gas combinations at the interface. In situations when the rear of the interface is not clearly demarcated, the thickness is determined by an image processing technique. This technique is also used to determine the possible dominant eddy/blob size in the TMZ from the schlieren images. Some inviscid computational studies, with a planar or spherical shock interacting with a planar or spherical initial interface in light-heavy (air/sulfur-hexafluoride) and heavy-light (air/He) configurations, are also presented. In the conical geometry there is a reflected shock originating from the triple point. This reflection is a consequence of the transition from the cylindrical shock tube to the converging cone. Due to the vorticity created by the interaction of reflected shock from the cone wall with the interface in initial stage, it is found that the interface curves toward or away from the apex of the cone, depending on the sign of density gradient. This curving of the interface could have a role to play in the diffuse rear boundary of the interface in schlieren flow visualization images but the laser-induced scattering image shows that the mixing zone indeed does not have a well-defined rear boundary. Rather, small blobs of fluids on the right are scattered in the mixing zone. An inviscid computational study is also done on cylindrical and conical test section geometries to study the effect of transverse reflected waves on the growth of small sinusoidal initial perturbations. It is found by comparison with cylindrical geometry (where reflected waves do not exist) that the transverse reflected waves do not affect the growth of perturbations on the interface.
" }, { "name": "Lew, Adri\u00e1n Jos\u00e9", "degree": "PhD", "year": "2003", "title": "Variational Time Integrators in Computational Solid Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262003-200254", "creators": [ { "name": { "family": "Lew", "given": "Adri\u00e1n Jos\u00e9" }, "id": "Lew-Adri\u00e1n-Jos\u00e9", "display_name": "Lew, Adri\u00e1n Jos\u00e9" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Sulsky", "given": "Deborah" }, "id": "Sulsky-D", "role": "member", "display_name": "Sulsky, Deborah" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6C74-GC16", "abstract": "This thesis develops the theory and implementation of variational integrators for computational solid mechanics problems, and to some extent, for fluid mechanics problems as well. Variational integrators for finite dimensional mechanical systems are succinctly reviewed, and used as the foundations for the extension to continuum systems. The latter is accomplished by way of a space-time formulation for Lagrangian continuum mechanics that unifies the derivation of the balance of linear momentum, energy and configurational forces, all of them as Euler-Lagrange equations of an extended Hamilton's principle. In this formulation, energy conservation and the path independence of the J- and L-integrals are conserved quantities emanating from Noether's theorem. Variational integrators for continuum mechanics are constructed by mimicking this variational structure, and a discrete Noether's theorem for rather general space-time discretizations is presented. Additionally, the algorithms are automatically (multi)symplectic, and the (multi)symplectic form is uniquely defined by the theory. For instance, in nonlinear elastodynamics the algorithms exactly preserve linear and angular momenta, whenever the continuous system does.
\r\n\r\nA class of variational algorithms is constructed, termed asynchronous variational integrators (AVI), which permit the selection of independent time steps in each element of a finite element mesh, and the local time steps need not bear an integral relation to each other. The conservation properties of both synchronous and asynchronous variational integrators are discussed in detail. In particular, AVI are found to nearly conserve energy both locally and globally, a distinguishing feature of variational integrators. The possibility of adapting the elemental time step to exactly satisfy the local energy balance equation, obtained from the extended variational principle, is analyzed. The AVI are also extended to include dissipative systems. The excellent accuracy, conservation and convergence characteristics of AVI are demonstrated via selected numerical examples, both for conservative and dissipative systems. In these tests AVI are found to result in substantial speedups, at equal accuracy, relative to explicit Newmark.
\r\n\r\nIn elastostatics, the variational structure leads to the formulation of discrete path-independent integrals and a characterization of the configurational forces acting in discrete systems. A notable example is a discrete, path-independent J-integral at the tip of a crack in a finite element mesh.
" }, { "name": "Pottebaum, Tait Sherman", "degree": "PhD", "year": "2003", "title": "The Relationship Between Near-Wake Structure and Heat Transfer for an Oscillating Circular Cylinder in Cross-Flow", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202003-145011", "creators": [ { "name": { "family": "Pottebaum", "given": "Tait Sherman" }, "id": "Pottebaum-Tait-Sherman", "display_name": "Pottebaum, Tait Sherman" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Richardson", "given": "Mark I." }, "id": "Richardson-M-I", "role": "member", "display_name": "Richardson, Mark I." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C9NQ-N832", "abstract": "A series of experiments were carried out in order to understand the relationship between wake structure and heat transfer for a transversely oscillating circular cylinder in cross-flow and to explore the dynamics of the vortex formation process in the wake. The cylinder's heat transfer coefficient was determined over a range of oscillation amplitudes up to 1.5 cylinder diameters and oscillation frequencies up to 5 times the stationary cylinder natural shedding frequency. The results were compared to established relationships between oscillation conditions and wake structure. Digital particle image thermometry/velocimetry (DPIT/V) was used to measure the temperature and velocity fields in the near-wake for a set of cases chosen to be representative of the variety of wake structures that exist for this type of flow. The experiments were carried out in a water tunnel at a Reynolds number of 690.
\r\n\r\nIt was found that wake structure and heat transfer both significantly affect one another. The wake mode, a label indicating the number and type of vortices shed in each oscillation period, is directly related to the observed heat transfer enhancement. The dynamics of the vortex formation process, including the trajectories of the vortices during roll-up, explain this relationship. The streamwise spacing between shed vortices was also shown to affect heat transfer coefficient for the 2S mode, which consists of two single vortices shed per cycle. The streamwise spacing is believed to influence entrainment of freestream temperature fluid by the forming vortices, thereby affecting the temperature gradient at the cylinder base. This effect may exist for other wake modes, as well.
\r\n\r\nThe cylinder's transverse velocity was shown to influence the heat transfer by affecting the circulation of the wake vortices. For a fixed wake structure, the effectiveness of the wake vortices at enhancing heat transfer depends on their circulation. Also, the cylinder's transverse velocity continually changes the orientation of the wake with respect to the freestream flow, thereby spreading the main source of heat transfer enhancement--the vortices near the cylinder base--over a larger portion of the cylinder surface.
\r\n\r\nPreviously observed heat transfer enhancement associated with oscillations at frequencies near the natural shedding frequency and its harmonics were shown to be limited to amplitudes of less than about 0.5 cylinder diameters.
\r\n\r\nA new phenomenon was discovered in which the wake structure switches back and forth between distinct wake modes. Temperature induced variations in the fluid viscosity are believed to be the cause of this mode-switching. It is hypothesized that the viscosity variations change the vorticity and kinetic energy fluxes into the wake, thereby changing the wake mode and the heat transfer coefficient. This discovery underscores the role of viscosity and shear layer fluxes in determining wake mode, potentially leading to improved understanding of wake vortex formation and pinch-off processes in general.
\r\n\r\nAspect ratio appears to play a role in determining the heat transfer coefficient mainly for non-oscillating cylinders. The heat transfer is also affected by aspect ratio for oscillation conditions characterized by weak synchronization of the wake to the oscillation frequency.
" }, { "name": "Thoutireddy, Pururav", "degree": "PhD", "year": "2003", "title": "Variational Arbitrary Lagrangian-Eulerian Method", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-113845", "creators": [ { "name": { "family": "Thoutireddy", "given": "Pururav" }, "id": "Thoutireddy-Pururav", "display_name": "Thoutireddy, Pururav" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DQT0-5104", "abstract": "This thesis is concerned with the development of Variational Arbitrary Lagrangian-Eulerian method (VALE) method. VALE is essentially finite element method generalized to account for horizontal variations, in particular, variations in nodal coordinates. The distinguishing characteristic of the method is that the variational principle simultaneously supplies the solution, the optimal mesh and, in case problems of shape optimization, optimal shape. This is accomplished by rendering the functional associated with the variational principle stationary with respect to nodal field values as well as with respect to the nodal positions of triangulation of the domain of analysis. Stationarity with respect to the nodal positions has the effect of the equilibriating the energetic or configurational forces acting in the nodes. Further, configurational force equilibrium provides precise criterion for mesh optimality. The solution so obtained corresponds to minimum of energy functional (minimum principle) in static case and to the stationarity of action sum (discrete Hamilton's stationarity principle) in dynamic case, with respect to both nodal variables and nodal positions. Further, the resulting mesh adaption scheme is devoid of error estimates and mesh-to-mesh transfer interpolation errors. We illustrate the versatility and convergence characteristics of the method by way of selected numerical tests and applications, including the problem of semi-infinite crack, the shape optimization of elastic inclusions and free vibration of 1-d rod." }, { "name": "Chasiotis, Ioannis", "degree": "PhD", "year": "2002", "title": "The Strength of Polycrystalline Silicon at the Micro- and Nano-Scales with Applications to MEMS", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142005-105805", "creators": [ { "name": { "family": "Chasiotis", "given": "Ioannis" }, "id": "Chasiotis-Ioannis", "display_name": "Chasiotis, Ioannis" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JPRZ-P277", "abstract": "Three aspects concerning the reliability of MicroElectroMechanical Systems (MEMS) are discussed in this work. These aspects are: (1) the development of a new tensile testing technique for measuring the elastic modulus and rupture strengths of thin films, (2) an assessment of stress concentration and specimen size effects in failure of micron-sized specimens and (3) the consequences of Hydrofluoric Acid (HF) chemical treatment on the microstructural integrity and the tensile strength of polycrystalline silicon.
\r\n\r\nA new method for tensile testing of thin films by means of an improved apparatus has been developed to measure the elastic properties (Young's modulus, tensile strength) of surface micromachined polycrystalline silicon specimens. The newly designed tensile tester makes use of an Ultraviolet (UV) light curable adhesive to clamp micron-sized specimens. It permits for the first time the testing of thin film materials possessing high failure strength. The properties determination utilizes surface topologies of deforming specimens, acquired with an Atomic Force Microscope (AFM), for determining strain fields by means of Digital Image Correlation (DIC). This full-field, direct and local measurements technique provides the capability of testing any type of thin film materials with nanometer resolution. The gage section of the specimens tested in this study varied between 200 and 1000 \u00b5m in length, 6 and 50 \u00b5m in width, all for a nominal thickness of 2 \u00b5m.
\r\n\r\nThe dependence of fracture strength on micron and sub-micron sized geometries was studied by means of specimens containing various degrees of stress concentrations. A systematic study of small-scale size effects was thus performed by tensioning elliptically perforated specimens (minimum radius of curvature of 1 gm) so as to: (a) vary the stress concentration with constant radius of curvature, (b) increasing radius of curvature of micronotches relative to the grain size. The results demonstrate a strong influence of the size of the highly strained domain (decreasing notch radii) on the failure strength of MEMS scale specimens, while the effect of varying the stress concentration factor is rather insignificant. In addition, tests performed on unnotched tensile specimens of varying dimensions revealed a specimen size effect by which the values of strength scaled with the specimen length. The Young's modulus, however, is found to be rather insensitive to the specimen dimensions at the scale of microns.
\r\n\r\nIn an effort to assess the unexplained and puzzling large variation in properties reported for very small polysilicon specimens a study was conducted to search for a cause. Contrary to the common belief that 49% HF wet release represents a safe post-process for manufacturing polycrystalline silicon, this study has clearly identified the release process as a key item in determining thin film failure properties. It is found that surface roughness as characterized by groove formation at the grain boundaries depends distinctly on the HF release time. In addition, while the actual failure mechanism in polysilicon follows a transgranular fracture, moderate exposure in HF results in partial intergranular fracture at the film surface that is responsible for complete failure. Long exposures yield films of low mechanical strength that demonstrate clear intergranular failure.
" }, { "name": "Gonz\u00e1lez Li\u00f1ero, Luis", "degree": "PhD", "year": "2002", "title": "Global Fracture Analysis of Laminated Composite Materials for Aerospace Structures", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032011-085654224", "creators": [ { "name": { "family": "Gonz\u00e1lez Li\u00f1ero", "given": "Luis" }, "id": "Gonz\u00e1lez-Li\u00f1ero-Luis", "display_name": "Gonz\u00e1lez Li\u00f1ero, Luis" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FCJ8-EW63", "abstract": "The failure process of laminated composite materials originating from precut sharp cracks, as well as their propagation, is studied from a \"global\" perspective,\r\nappropriate for structural analysis. The size effect in the damage development is explored and the question of \"scaling\" of the results is addressed.\r\n\r\nTwo globally orthotropic sets of panels with the notches aligned along the axes of orthrotopy are studied. The internally evolving damage in the crack tip region is\r\nexamined through enhanced x-ray radiographic inspection and surface strain fields are measured by means of the Digital Image Correlation method (the applicability and limitations of which are analyzed and discussed). The results obtained from these two experimental techniques are joined to assess the feasibility of identifying internal damage solely from surface measurements.\r\n\r\nThe shape of the region of influence of the crack is described and its extension measured. A simplified model for damage progression analysis is proposed.\r\n\r\nThe process of initiation of the damage propagation is described in detail and the different responses for the two different layups are discussed. The maximum stress/strain and the Tsai-Hill failure criteria are compared with the experimental results on the laminates, and their reliability and limitations are addressed.\r\n\r\nThe effective properties of the two sets of laminates are measured at three different loading rates and compared to theory, and the relevance of the time dependence of the material is studied.\r\n" }, { "name": "Nguyen, Olivier Thanh", "degree": "PhD", "year": "2002", "title": "Cohesive Models of Fatigue Crack Growth and Stress-Corrosion Cracking", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032004-161201", "creators": [ { "name": { "family": "Nguyen", "given": "Olivier Thanh" }, "id": "Nguyen-Olivier-Thanh", "display_name": "Nguyen, Olivier Thanh" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C3KP-4M44", "abstract": "The aim of this dissertation was to develop models of fatigue crack growth and stress-corrosion cracking by investigating cohesive theories of fracture. These models were integrated in a finite-element framework embedding a contact algorithm and techniques of remeshing and adaptive meshing.\r\n\r\nFor the fatigue model, we developed a phenomenological cohesive law which exhibits unloading-reloading hysteresis. This model qualitatively predicts fatigue crack growth rates in metals under constant amplitude regime for short and long cracks, as well as growth retardation due to overload. Quantitative predictions were obtained in the case of long cracks.\r\n\r\nWe developed a chemistry-dependent cohesive law which serves as a basis for the stress-corrosion cracking model. In order to determine this cohesive law, two approaches, based on energy relaxation and the renormalization group, were used for coarse-graining interplanar potentials. We analyzed the cohesive behavior of a large--but finite--number of interatomic planes and found that the macroscopic cohesive law adopts a universal asymptotic form. The resulting stress-corrosion crack growth rates agreed well with those observed experimentally in 'static' fatigue tests given in the literature.\r\n" }, { "name": "Xu, Luoyu Roy", "degree": "PhD", "year": "2002", "title": "Dynamic Failure Characteristics in Layered Materials and Structures", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-111825843", "creators": [ { "name": { "family": "Xu", "given": "Luoyu Roy" }, "id": "Xu-Luoyu-Roy", "display_name": "Xu, Luoyu Roy" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wver-8342", "abstract": "Systematic investigations were carried out to understand the general nature of dynamic failure mechanisms in layered materials and structures such as composite and\r\nsandwich structures, thin films, layered armors and layered rock. A series of impact experiments on model-layered specimens were conducted using high-speed photography\r\nand dynamic photoelasticity.\r\n\r\nFor the first time, the sequence and interaction of two major dynamic failure modes in layered materials-inter-layer cracking and intra-layer cracking were revealed\r\nin real time. For heterogeneous three-layer systems, shear-dominated inter-layer cracking was always the first failure event for specimens subjected to low-speed impact. Interlayer cracking generally nucleated from interfacial locations where the inter-layer shear stress acquired a local maximum. Depending on impact speed and bond strength\r\ncharacteristics, inter-layer cracks were very transient and often became intersonic even under moderate impact speeds. Intra-layer cracking always initiated after the development of inter-layer cracks as a result of inter-layer crack kinking into the adjacent layer. The resulting intra-layer mode I cracks often accelerated and branched as they\r\nattained high speeds, causing core layer fragmentation. For homogenous-layered systems composed of bonded layers of Homalite, intra-layer cracks appeared in the form of cracks\r\nradiating from the impact site. As soon as these cracks approached an interface, interlayer cracks were often induced depending on the angle between the crack path and the interface. Direct experimental evidence of the dynamic equivalent of \"Cook-Gordon mechanism\" was recorded, i.e., two intersonic interfacial cracks nucleated and propagated along the interface before a fan of mode I incident cracks was ever able to reach the interface. Also, significant dependence of the failure characteristics on impact speeds and interfacial strengths was found. For the heterogeneous three-layer system subjected to a high impact speed, two clear shear shock waves associated with the intersonic inter-layer cracks were observed at the specimen center. Shock waves were also observed along the interface in heterogeneous three-layer systems featuring weak and ductile bonds. The impact momentum and loading duration were identified as two important parameters in damage spreading for a given impact energy.\r\n\r\nMotivated by the experimental observations of crack deflection/penetration at an interface, a novel wedge-loaded impact specimen was designed to explore the basic\r\nmechanics nature of this phenomenon. The deflection/penetration behavior of an incoming dynamic crack at an interface was found to depend on the interfacial angle and the interfacial fracture toughness. A dynamic fracture model, together with an energy criterion, were proposed and were found to agree reasonably well with the experimental observations." }, { "name": "Zhuang, Shiming", "degree": "PhD", "year": "2002", "title": "Shock Wave Propagation in Periodically Layered Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102011-141326530", "creators": [ { "name": { "family": "Zhuang", "given": "Shiming" }, "id": "Zhuang-Shiming", "display_name": "Zhuang, Shiming" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Grady", "given": "Dennis E." }, "id": "Grady-D-E", "role": "member", "display_name": "Grady, Dennis E." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/988X-1V27", "abstract": "Mathematically, a shock wave is treated as a discontinuity in a medium. In reality, however, a shock wave is always structured, i.e., its front takes a finite time to rise from an initial material state to the final shocked state. The structuring of a shock front is due to the competition between the nonlinearity of material behavior and the dissipation processes occurring during the wave propagation. There are many mechanisms which may be responsible for the dissipation and/or dispersion of shock wave energy. In homogeneous media, such as metals, one common interpretation for the structuring of a shock wave is that the viscoplasticity processes (dislocation, twinning, etc.) are responsible for the dissipation of energy. While in heterogeneous composites, besides the viscous dissipative processes existing in each of its constituents, due to the existence of internal interfaces, the scattering induced by the interface during shock compression could be another important mechanism.\r\n\r\nIn this study, the interface scattering effects on shock wave propagation in heterogeneous media were investigated by subjecting periodically layered composites to planar impact loading with a flyer plate. The flyer plate was accelerated to a desired velocity using a powder gun loading system. In order to measure shock particle velocity time history at an internal or the free surface of the specimen, the so-called VISAR (Velocity Interferometry System for Any Reflector) diagnostic system was constructed and used during shock compression experiments. Manganin stress gages were embedded inside the specimen at selected internal interfaces to measure shock stress time history. To study the scattering mechanisms of the interface to waves, two-component composite specimens with different interface mechanical properties and heterogeneity were prepared and tested. Different types of composites were prepared with differing mechanical impedance. Specimens with different heterogeneity were obtained by changing the geometrical configuration (length scale) of the layered stack. Two-dimensional numerical simulations were also carried out to understand the process of shock wave evolution in the layered composites.\r\n\r\nExperimental and numerical studies show that periodically layered composites support steady structured shock waves. The influence of internal interfaces on the shock wave propagation is through the scattering mechanism, i.e., multiple reflection of waves in the layers and their interaction with the shock wave. The interface scattering affects both the bulk and the deviatoric response of the composite to shock compression. The influence of scattering on the bulk behavior is to slow down the velocity of the shock wave in the composites, while its influence on the deviatoric response is to structure the shock wave profile. If all the dissipative and dispersive effects are collectively termed as viscosity, which causes the shock front structuring, i.e., the shock front rise-time increasing, then the effective shock viscosity increases with the increase of interface impedance mismatch and decreases with the increase of interface density (interface area per unit volume) and shock loading strength. The existing mixture model for constructing the constitutive relation for composites based on the known properties of its component materials can only, at best, reasonably predict the response of the composites under strong shock loading conditions. In order to fully describe the response of a heterogeneous composite to shock compression loading, accurate physics-based constitutive relations need to be formulated to take into account the scattering effects induced by the heterogeneous microstructure.\r\n" }, { "name": "Burcsu, Eric Noboru", "degree": "PhD", "year": "2001", "title": "Investigation of Large Strain Actuation in Barium Titanate", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-10232001-192042", "creators": [ { "name": { "family": "Burcsu", "given": "Eric Noboru" }, "id": "Burcsu-Eric-Noboru", "display_name": "Burcsu, Eric Noboru" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "co-chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XT3Y-Z860", "abstract": "Sensors and actuators based on ferroelectric materials have become indispensable in the fields of aerospace, high technology, and medical instruments. Most devices rely on the linear piezoelectric behavior of formulations of PZT which offer high bandwidth, linear actuation but very low strains of around 0.1%. The nonlinear electromechanical behavior of these materials is largely governed by the motion of domains and is highly affected by stress as well as electric field. The recent theories of Shu and Bhattacharya have sought to address some of the issues related to the structure and behavior of these materials at the mesoscale. One result of the theories is the prediction of another mode of actuation in ferroelectric crystals based on a combined electrical and mechanical loading that could result in strains of up to 6%.
\r\n\r\nDescriptions of the phenomenological theories of ferroelectrics are presented including the classical Landau-Ginsburg-Devonshire theory and the more recent theory of Shu and Bhattacharya. Predictions are made, based on the theory, of the electromechanical behavior of ferroelectric crystals that are addressed by the experiments. An experimental setup has been designed to investigate large strain actuation in single crystal ferroelectrics based on combined electrical and mechanical loading. An investigation of the stress dependence of the electrostrictive response has been carried out with in situ observations of the domain patterns under constant compressive stress and variable electric field. Experiments have been performed on initially single domain crystals of barium titanate with (100) and (001) orientation at compressive stresses between 0 and 5 MPa. Global strain and polarization histories have been recorded. The electrostrictive response is shown to be highly dependent on the level of applied stress with a maximum strain of 0.9% measured at a compressive stress of about 2 MPa. An unusual secondary hysteresis has been observed in the polarization signal at high levels of stress that indicates an intermediate structural configuration, possibly the orthorhombic state. Polarized light microscopy has been used to observe the evolution of the domain pattern simultaneously with the strain and polarization measurement. These results are discussed and suggestions for future work are proposed.
" }, { "name": "Ching, Weng Ki", "degree": "PhD", "year": "2001", "title": "Disinfection by Pulsed Power Discharges", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07252005-142630", "creators": [ { "name": { "family": "Ching", "given": "Weng Ki" }, "id": "Ching-Weng-Ki", "display_name": "Ching, Weng Ki" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Nealson", "given": "Kenneth H." }, "id": "Nealson-K-H", "orcid": "0000-0001-5189-3732", "role": "member", "display_name": "Nealson, Kenneth H." }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." } ], "option_major": [ "envreng" ], "doi": "10.7907/RV3M-0849", "abstract": "We study the disinfection of Escherichia coli in a pulsed power discharge reactor. The pulsed power discharge process is an electrohydraulic phenomenon characterized by a rapid release of electrical energy across a submerged electrode pair.
\r\n\t\r\nThe survival kinetics of pure strains of E. coli suspensions exposed to 5.5 kV, 90 kA electrohydraulic discharges (EHD) is investigated. The probability of survival Pn of a 2 x 10\u2077 E. coli CFU mL\u207b\u00b9 population after 50 consecutive EHD's follows a logit distribution that corresponds to lethal doses of LD\u2085\u2080 = 2.2 and L:D\u2089\u2080 = 10.8 EHDs. Variation of the initial cell concentration produced nearly constant values of LD\u2085\u2080 = 0.9\u00b10.1 in the range 2 x 10\u00b3 \u2264 E. coli/CFU mL\u207b\u00b9 \u2264 2 x 10\u2076. Beyond 10\u2076 CFU mL\u207b\u00b9, the LD\u2085\u2080 values increase exponentially due to nonlinear light absorbance with increasing E. coli concentrations. Qualitatively similar initial cell concentration dependence is observed for survival under low intensity 254 nm irradiation, in contrast with lower values of LD\u2085\u2080 obtained in denser colonies to 20 kHz power ultrasound exposure.
\r\n\r\nThe high intensity (3.3 x 10\u00b9\u2070 W m\u207b\u00b2) ultraviolet radiation emitted by the electrohydraulic discharge is completely suppressed in the presence of less than 100 mg L\u207b\u00b9 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-disulfonic acid (BP9), a well-known sunscreen agent. Concentrations of BP9, in the range (0 - 100) mg L\u207b\u00b9, are varied to measure the sterilization kinetics of ~3 x 10\u2077 CFU mL\u207b\u00b9 suspensions to varying degrees of high intensity UV exposure. The slope of the logit plots of E. coli as function of BP9 concentration is consistent with the screening of radiation as the sole lethal agent. Computed values of biologically available light fluences are 5.0 x 10\u00b9\u00b9 photons CFU\u207b\u00b9 for high intensity, high power, pulsed EHD experiments and 6.6 x 10\u2078 photons CFU\u207b\u00b9 for separate low power continuous UV experiments. The net availability of 3 orders of magnitude more photons during high intensity UV exposure suggests the possibility of a multiphotonic disinfection mechanism at play in the EHD process relative to low intensity case.
\r\n\r\nThe overall resistance to long term exposure to EHD is also investigated. Selective pressure experiments with E. coli exposed to 11 cycles of 50 consecutive EHDs each show a weak kinetic change in the dose-response curves reflected in the nearly constant values of LD\u2085\u2080 - 0.24 \u00b1 0.03. A greater than 98% metabolic similarity in carbon source consumption between initial and final E. coli populations are enzymatically related. In addition, the results indicate that no bacterial contaminants are propagated throughout the experiment.
" }, { "name": "Chow, Benjamin Bin", "degree": "PhD", "year": "2001", "title": "Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures", "advisor": "Rosakis, Ares J.; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-103246", "creators": [ { "name": { "family": "Chow", "given": "Benjamin Bin" }, "id": "Chow-B-B", "display_name": "Chow, Benjamin Bin" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/745f-mb29", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. A drop of up to 40% in the value of dynamic initiation toughness, [...], is discovered for loading rates in the range of [...]. This range of loading rate corresponds to the typical rates found in an aircraft fuselage experiencing explosive loading conditions. A dramatic increase in the value of dynamic crack initiation toughness is also found for loading rates above [...]. Based on these results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate the residual strength of aircraft structures.\r\n\r\nA methodology to determine residual strength of dynamically loaded structures based on global structural analysis coupled with local finite element analysis is introduced. Local finite element calculations were performed for different loading rates, [...], ranging from [...] to [...], to simulate the conditions encountered in an explosively loaded aircraft fuselage. Simulations were conducted at a number of loading rates for the following cases of relevance to aircraft fuselage: (i) center cracked panels, (ii) rivet holes with wing cracks, (iii) biaxially loaded panels and (iv) panels prestressed to simulate pressurization. The results from the analyses were then used in conjunction with the experimental results for the dynamic fracture toughness of a 2024-T3 aluminum alloy as a function of loading rate, [...], to determine the time to failure, [...], for a given loading rate. A failure envelope, [...], based on the failure model and finite element analysis, is presented for the different cases and the implications for the residual strength of aircraft structures is discussed.\r\n\r\nMixed mode dynamic crack initiation in aluminum 2024-T3 alloy is investigated by combining experiments with numerical simulations. Pre-fatigued single edge notched specimens and three point bend specimens are subjected to dynamic symmetric and asymmetric loading to generate a range of mode mixity at the cracktip. The optical technique of coherent gradient sensing (CGS) and a strain gage method are employed to study the evolution of the mixed mode stress intensity factors. The dynamic mixed mode failure envelope is obtained using the crack initiation data from the experiments at a nominal loading rate of [...] and is compared with the static counterpart for 2024-T3 aluminum alloy. The fracture surfaces near the crack initiation site are investigated using a scanning electron microscope and reveal ductile void growth and coalescence. Numerical simulations of the experiments are conducted to both help in designing the experiments and to validate the results of the experiments. The numerical simulations show good correlation with the experimental results." }, { "name": "Coker, Demirkan", "degree": "PhD", "year": "2001", "title": "Dynamic Initiation and Propagation of Cracks in Unidirectional Composite Plates", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-152127073", "creators": [ { "name": { "family": "Coker", "given": "Demirkan" }, "id": "Coker-Demirkan", "orcid": "0000-0001-7385-7089", "display_name": "Coker, Demirkan" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yrm2-4b88", "abstract": "Dynamic crack growth along weak planes is a significant mode of failure in composites and other layered/sandwiched structures and is also the principal mechanism of shallow crustal earthquakes. In order to shed light on this phenomenon dynamic crack initiation and propagation characteristics of a model fiber-reinforced unidirectional graphite/epoxy composite plate was investigated experimentally. Dynamic fracture experiments were conducted by subjecting the composite plates to in-plane, symmetric and asymmetric, impact loading. The lateral shearing interferometric technique of coherent gradient sensing (CGS) in conjunction with high-speed photography was used to visualize the failure process in real time. It was found that mode-I cracks propagated subsonically with crack speeds increasing to the neighborhood of the Rayleigh wave speed of the composite. Also in mode-I, the dependence of the dynamic initiation fracture toughness on the loading rate was determined and was found to be constant for low loading rates and to increase rapidly above K̇dI > 10\u2075. The dynamic crack propagation toughness, KID, was observed to decrease with crack tip speed up to the Rayleigh wave speed of the composite.
\r\n\r\nFor asymmetric, mode-II, types of loading the results revealed highly unstable and intersonic shear-dominated crack growth along the fibers. These cracks propagated with unprecedented speeds reaching 7400 m/s which is the dilatational wave speed of the composite along the fibers. For intersonic crack growth, the interferograms featured a shock wave structure typical of disturbances traveling with speeds higher than one of the characteristic wave speeds in the solid. In addition high speed thermographic measurements are conducted that show concentrated hot spots behind the crack tip indicating non-uniform crack face frictional contact. In addition, shear dominated dynamic crack growth is investigated along composite/Homalite interfaces subjected to impact loading. The crack growth phenomenon was observed usivvvvng dynamic photoelasticity in conjunction with high-speed photography. Three quantized intersonic and supersonic crack tip speed regimes were identified. First conclusive evidence of crack growth at supersonic speeds with respect to lower speed material and sonic speeds with respect to the unidirectional composite was obtained. Furthermore, this investigation documents the first experimental observation of a mother/daughter crack mechanism allowing a subsonic crack to evolve into an intersonic crack.
\r\n\r\n" }, { "name": "Duchemin, Olivier Bernard", "degree": "PhD", "year": "2001", "title": "An investigation of ion engine erosion by low energy sputtering", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242002-122344", "creators": [ { "name": { "family": "Duchemin", "given": "Olivier Bernard" }, "id": "Duchemin-O-B", "display_name": "Duchemin, Olivier Bernard" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "co-chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Brophy", "given": "John R." }, "id": "Brophy-J-R", "role": "member", "display_name": "Brophy, John R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K408-J123", "abstract": "Unlike chemical propulsion systems, which are fundamentally limited in performance by propellant energy density, electric propulsion devices, such as ion engines, are limited in iotal deliverable impulse by maximum propellant throughput due to engine wear.\r\n\r\nIn order to perform realistic modeling of engine lifetime, the erosion mechanisms involved must be understood. In particular, the damage---or sputtering---caused by slow ions on solid surfaces is extremely difficult to quantify. We first review the engine failure modes in which sputtering of molybdenum by slow xenon ions plays a critical role. We then present the relevant physical mechanisms, and describe a model for estimating the minimum kinetic energy necessary to dislodge a surface atom.\r\n\r\nOver seventeen analytical approaches to the energy dependence of sputtering have been published in the literature. We implement the four that are most relevant to ion engine erosion processes. In addition, we use the Monte-Carlo simulation program TRIM to calculate sputtering yields. We find, in particular, that the relative sensitivity of sputtering yield to surface binding energy increases dramatically near the sputtering threshold energy. Although the surface binding energy is a (weak) function of temperature, we show that the sputtering yield should not increase significantly at temperatures typical of ion engine operation.\r\n\r\nAn experimental approach to the measurement of low energy sputtering yields is implemented and validated. Based on the Quartz Crystal Microbalance (QCM) technique, this method takes advantage of the differential mass sensitivity exhibited by the piezoelectric quartz resonator used in this study. Because of the importance of surface contamination in low energy sputtering, a surface kinetics model is presented to describe a surface under the simultaneous cleaning effect of ion bombardment, and background gas flow contamination.\r\n\r\nA special case of simultaneous surface contamination and erosion occurs during engine ground testing, where carbon is backsputtered on the accelerator grid from the facility. We describe experiments to measure ion-induced desorption cross-sections for carbon on molybdenum, before concluding that the protective effect of the carbon contamination is unlikely to significantly affect engine erosion, so that ground testing results are applicable to space operations" }, { "name": "Eckett, Christopher Adam", "degree": "PhD", "year": "2001", "title": "Numerical and Analytical Studies of the Dynamics of Gaseous Detonations", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-143255", "creators": [ { "name": { "family": "Eckett", "given": "Christopher Adam" }, "id": "Eckett-Christopher-Adam", "display_name": "Eckett, Christopher Adam" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/83ME-8076", "abstract": "This thesis examines two dynamic parameters of gaseous detonations, critical energy and cell size. The first part is concerned with the direct initiation of gaseous detonations by a blast wave and the associated critical energy. Numerical simulations of the spherically symmetric direct initiation event with a simple chemical reaction model are presented. Local analysis of the computed unsteady reaction zone structure identities a competition between heat release rate, front curvature and unsteadiness. The primary failure mechanism is found to be unsteadiness in the induction zone arising from the deceleration of the shock front. On this basis, simplifying assumptions are applied to the governing equations, permitting solution of an analytical model for the critical shock decay rate. The local analysis is validated by integration of reaction zone structure equations with detailed chemical kinetics and prescribed unsteadiness. The model is then applied to the global initiation problem to produce an analytical equation for the critical energy. Unlike previous phenomenological models, this equation is not dependent on other experimentally determined parameters. For different fuel-oxidizer mixtures, it is found to give agreement with experimental data to within an order of magnitude. The second part of the thesis is concerned with the development of improved reaction models for accurate quantitative simulations of detonation cell size and cellular structure. The mechanism reduction method of Intrinsic Low-Dimensional Manifolds, originally developed for flame calculations, is shown to be a viable option for detonation simulations when coupled with a separate model in the induction zone. The agreement with detailed chemistry calculations of constant volume reactions and one-dimensional steady detonations is almost perfect, a substantial improvement on previous models. The method is applied to a two-dimensional simulation of a cellular detonation in hydrogen-oxygen-argon. The results agree well with an earlier detailed chemistry calculation and experimental data. The computational time is reduced by a factor of 15 compared with a detailed chemistry simulation." }, { "name": "Guduru, Pradeep Reddy", "degree": "PhD", "year": "2001", "title": "An investigation of dynamic failure events in steels using full field high-speed infrared thermography and high-speed photography", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052003-085740", "creators": [ { "name": { "family": "Guduru", "given": "Pradeep Reddy" }, "id": "Guduru-P-R", "display_name": "Guduru, Pradeep Reddy" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3w5m-qb27", "abstract": "An infrared (IR) imaging system has been developed recently at Caltech for measuring the temperature increase during the dynamic deformation of materials. The system consists of an 8x8 HgCdTe focal plane array, with 64 parallel preamplifiers. Outputs from the 64 detector/preamplifiers are digitized using a row-parallel scheme. In this approach, all 64 signals are simultaneously acquired and held using a bank of track and hold amplifiers. An array of eight 8:1 multiplexers then routes the signals to eight 10MHz digitizers, acquiring data from each row of detectors in parallel. The maximum rate is one million frames per second.\r\n\r\nCrack tip temperature rise during dynamic deformation is known to alter the fracture mechanisms and consequently the fracture toughness of a material. However, no direct experimental measurements have ever been made to determine the same because of limited diagnostic tools. Further, the temperature rise in the vicinity of the crack tip could potentially be used as a direct measure of loading and could serve as a diagnostic tool in order to extract appropriate fracture parameters. By transcending the existing experimental limitations, this investigation presents detailed, real time evolution of the transient crack tip temperature fields in two different steels (C300 and HY100 steels), using the 2-D high speed IR camera. The crack tip temperature rise at initiation in C300 steel was found to be about 55K. In case of HY100, the crack tip temperature rise was above 90K and was seen to be a strong function of loading rate. HRR elastic-plastic singular field has been used to extract J integral evolution from the measured temperature field. Critical value of J integral at initiation was seen to increase with loading rate.\r\n\r\nAn experimental investigation has been conducted to study the initiation and propagation characteristics of dynamic shear bands in C300 maraging steel. Pre-fatigued single edge notched specimens were impacted on the edge under the notch to produce shear dominated mixed mode stress fields. The optical technique of coherent gradient sensing (CGS) was employed to study the evolution of the mixed mode stress intensity factors. Simultaneously, the newly developed 2-D high speed infrared (IR) camera was employed to obtain the temperature field evolution during the initiation and propagation of the shear bands. A criterion for shear band initiation is proposed in terms of a critical mode II stress intensity factor. The IR images, for the first time, revealed the transition of crack tip plastic zone into a shear band and also captured the structure of the tip of a propagating shear band. These thermographs support the notion of a diffuse shear band tip and reveal \"hot spots\" distributed along the length of a well developed shear band." }, { "name": "Huang, Ying", "degree": "PhD", "year": "2001", "title": "Scanning Tunneling Microscopy and Digital Image Correlation in Nanomechanics Investigations", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212010-112400412", "creators": [ { "name": { "family": "Huang", "given": "Ying" }, "id": "Huang-Ying", "display_name": "Huang, Ying" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/exy7-5z58", "abstract": "Probe microscopy (scanning tunneling microscopy and atomic force microscopy) and digital image correlation together serve as a potentially powerful tool for experimentally\r\ninvestigating the mechanical behaviors of materials at the sub-micron and nanometer scales. Based on the tunneling effect in quantum physics, the scanning tunneling\r\nmicroscope (STM) records surface topography quantitatively and can achieve angstrom resolution. The digital image correlation (DIC) extracts the displacements and gradients\r\nfrom the undeformed and deformed topographical images.\r\nIn this work, a calibration has been performed on the existing STM built \"in-house\" and the coefficients used in the STM system were confirmed. Major improvements on several\r\ncomponents of the system have been made, including constructing a new actuator probe to decouple its in-plane and out-of-plane movements, designing and implementing a new\r\nfirst-stage amplifier to reduce the noise output by a factor of 10 and modeling of the controller in the STM feedback loop.\r\nFurther, systematic study of the digital image correlation has been conducted. In the simple case of one-dimensional correlation, key parameters involved are the subset size,\r\nvariables in the displacement representation, frequency content of the signal and noise. The one-dimensional study was then extended to two dimensions. In addition to those\r\nkey parameters identified in the one-dimensional study, the sampling rate poses substantial influence on the correlation accuracy. Low amplitude, high frequency noise\r\nstill increases the correlation error significantly." }, { "name": "Isella, Giorgio Carlo", "degree": "PhD", "year": "2001", "title": "Modeling and Simulation of Combustion Chamber and Propellant Dynamics and Issues in Active Control of Combustion Instabilities", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012006-093758", "creators": [ { "name": { "family": "Isella", "given": "Giorgio Carlo" }, "id": "Isella-Giorgio-Carlo", "display_name": "Isella, Giorgio Carlo" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/k1rf-a525", "abstract": "A method for a comprehensive approach to analysis of the dynamics of an actively controlled combustion chamber, with detailed analysis of the combustion models for the case of a solid rocket propellant, is presented here. The objective is to model the system as interconnected blocks describing the dynamics of the chamber, combustion and control (including sensors and actuators).
\r\n\r\nThe analytical framework for the analysis of the dynamics of a combustion chamber is based on spatial averaging, as introduced by Culick. This method results in the determination of a set of coupled oscillator equations that are then integrated with the appropriate forcing terms deriving from combustion and control.
\r\n\r\nCombustion dynamics are analyzed for the case of a solid propellant. Considerable data exists suggesting that the response functions for many solid propellants tend to have higher values, in some ranges of frequencies, than predicted by the conventional quasi-steady theory. Hence, quasi-steady theory is extended to include the dynamics of the gas-phase and also of a surface layer interposed between the gaseous flame zone and the heated solid phase of the propellant. The models are constructed so that they produce a combustion response function for the solid propellant that can be immediately introduced in the our analytical framework. The principal objective of this analysis is to determine which characteristics of the solid propellant are responsible for the large sensitivity, observed experimentally, of propellant burning response to small variations in the conditions. We show that velocity coupling, and not pressure coupling, has the potential to be the mechanism responsible for that high sensitivity. Some issues related to the modeling of solid propellant are also discussed, namely the importance of particulate modeling and its effect on the global dynamics of the chamber and a revisited interpretation of the intrinsic stability limit for burning of solid propellants.
\r\n\r\nActive control is also considered in the analysis. A critical discussion about the most commonly used control strategies used in combustion allows us to define which are the most promising algorithms to use on future experiments. Particular attention is devoted to the effect of time delay (between sensing and actuation) on the control strategy; several methods to compensate for it are presented and discussed, with numerical examples based on the approximate analysis produced by our framework.
\r\n\r\nExperimental results are presented for the case of a Dump Combustor. The combustor exhibits an unstable burning mode, defined through the measurement of the pressure trace and shadowgraph imaging. The transition between stable and unstable modes of operation is characterized by the presence of hysteresis, also observed in other experimental works, and hence not a special characteristic of this combustor. Control is introduced in the form of pulsed secondary fuel. We show the capability of forcing the transition from unstable to stable burning, hence extending the stable operating regime of the combustor. The transition, characterized by the use of a shadowgraph movie sequence, is attributed to a combined fluid-mechanic and combustion mechanism.
" }, { "name": "Krueger, Paul Samuel", "degree": "PhD", "year": "2001", "title": "The Significance of Vortex Ring Formation and Nozzle Exit Over-Pressure to Pulsatile Jet Propulsion", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142005-111030", "creators": [ { "name": { "family": "Krueger", "given": "Paul Samuel" }, "id": "Krueger-Paul-Samuel", "display_name": "Krueger, Paul Samuel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3QWF-8G05", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPulsatile jet propulsion can be accomplished using a fully-pulsed jet (i.e., a periodic series of starting jets or pulses), the unsteady nature of which engenders vortex ring formation. The significance of vortex ring formation for this type of propulsion is studied experimentally using a piston-cylinder mechanism to generate starting and fully-pulsed, round jets of water into water at a maximum jet Reynolds number of 13,000. Starting jets are considered separately since they are the limiting case of a fully-pulsed jet at zero pulsing frequency. Direct measurements of the total impulse per pulse (starting jets) and time-averaged thrust (fully-pulsed jets) are made using a force balance. Hotfilm anemometry is used to measure the jet velocity and Digital Particle Image Velocimetry (DPIV) is used to measure vortex ring position, vorticity, energy, circulation, and impulse.\r\n\r\nThe pulses for both types of jets are generated using piston stroke to diameter ratios (L/D) in the range 2 to 8 for piston velocity programs in a generally positive-sloping (PS) or negative-sloping (NS) family. The range of L/D considered brackets the transition between the case where an individual vortex ring is produced with each pulse (small L/D) and the case where the vortex ring stops growing and pinches off from its generating jet, producing a trailing jet (large L/D). This transition occurs at a higher L/D for the PS ramps, allowing the effects of vortex ring formation and pinch off to be illuminated by comparison of the results for the NS and PS ramps.\r\n\r\nThe significance of vortex ring formation is first analyzed for starting jets. Measurements of the total impulse per pulse as a function of L/D show that a leading vortex ring adds more impulse per unit L/D than a trailing jet. This leads to a maximum in the average thrust during a pulse at the L/Ds just before vortex ring pinch off is observed for both the PS and NS ramps. The propulsive benefit provided by a leading vortex ring over a trailing jet is connected to over-pressure at the nozzle exit plane during vortex ring formation. DPIV measurements demonstrate that nozzle exit over-pressure also makes an important contribution to energy and circulation. It is shown that this over-pressure can be related to the momentum that must be supplied by the forming vortex ring to ambient fluid in the form of added and entrained mass. A model is proposed for nozzle exit over-pressure near the initiation of an impulsive velocity program where entrainment can be ignored. The model readily accounts for the pressure contribution to circulation in the NS ramps, but modeling of entrainment is required to properly determine impulse and energy.\r\n\r\nFor the fully-pulsed jet experiments, a normalized thrust, [...], is introduced to characterize the pressure effects associated with vortex ring formation. The pulsing frequency is expressed in dimensionless form as [...], which is between 0 and 1 for all fully-pulsed jets. A propulsive benefit from pressure ([...]) is observed for all L/D and [...] considered. At low [...], the results are similar to those for the starting jets. At higher [...], [...] decreases with L/D as with the starting jets, which is related to the existence of vortex ring pinch off for all observed [...]. At a fixed L/D, two dominant decreasing trends in [...] with [...] appear and seem to be related to the effects of previously ejected pulses on forming vortex rings. No dramatic increase in [...] with [...] (associated with the increased convective velocity of multiple coaxial vortex rings over that of individual vortex rings) is observed since (a) the ring separation is never reduced low enough to see an increase in the ring velocity (even for [...]), and (b) the vortex rings don't remain coaxial or coherent as [...]." }, { "name": "Lokhandwalla, Murtuza", "degree": "PhD", "year": "2001", "title": "Damage Mechanisms in Shock Wave Lithotripsy (SWL)", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162005-130412", "creators": [ { "name": { "family": "Lokhandwalla", "given": "Murtuza" }, "id": "Lokhandwalla-Murtuza", "display_name": "Lokhandwalla, Murtuza" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZWS-7Z85", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock wave lithotripsy is a 'non-invasive' therapy for treating kidney stones. Focused shock waves fragment stones to a size that can be passed naturally. There is, however, considerable tissue injury associated with this treatment, and the mechanisms of stone fragmentation and tissue injury are not well understood. This work investigates potential tissue damage mechanisms, with an aim towards modifying the wave-field parameters, so as to enhance stone fragmentation and minimize tissue damage.\r\n\r\nLysis of red blood cells (RBC's) due to in vitro exposure to shock waves was considered as a model of cellular level damage. Fluid flow-fields induced by a non-uniform shock wave, as well as radial expansion/implosion of a bubble was hypothesized to cause lysis of cells. Both the above flow-fields constitute an unsteady, extensional flow exerting inertial as well as viscous forces on the RBC membrane. The resultant membrane tension and the membrane areal strain ([Delta]A/A) due to the above flow-fields were estimated. Both were found to exert a significantly higher inertial force (50 - 100 mN/m) than the critical membrane tension (10 mN/m). Bubble-induced flow-field was estimated to last for a longer duration ([...]) compared to the shock-induced flow ([...]) and hence, was predicted to be lytically more effective, in typical in vitro experimental conditions. However, in vivo conditions severely constrain bubble growth, and cell lysis due to shock-induced shear could be dominant.\r\n\r\nHemolysis due to shock-induced shear, in absence of cavitation, was experimentally investigated. The lithotripter-generated shock wave was refocused by a parabolic reflector. This refocused wave-field had a tighter focus (smaller beam-width and a higher amplitude) than the lithotripter wave-field. Cavitation was eliminated by applying overpressure to the fluid. A novel passive cavitation detector (HP-PCD) operating at high overpressure (upto 7 MPa) was used to measure acoustic emission due to bubble activity. Aluminum foils were also used to differentiate cavitational from non-cavitational mode of damage. RBC's suspended in phosphate-buffered saline PBS) were exposed to the reflected wave-field from the parabolic reflector and also from a flat reflector, the latter serving as a control experiment. Exposure to the wave-field from the parabolic reflector increased hemolysis four-fold compared to untreated controls and was twice that of cell lysis with the flat reflector. This result corroborated the hypothesis of shock-induced shear as a cell damage mechanism in the absence of cavitation.\r\n" }, { "name": "Molinari, Jean-Francois Roland", "degree": "PhD", "year": "2001", "title": "Three dimensional finite element analysis of impact damage and erosion of metallic targets", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-102656", "creators": [ { "name": { "family": "Molinari", "given": "Jean-Francois Roland" }, "id": "Molinari-J-R", "display_name": "Molinari, Jean-Francois Roland" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6ZJV-B162", "abstract": "This dissertation is concerned with the development of a robust three-dimensional finite-element framework for the simulation of complex problems in mechanics and physics of solids. This approach is intended to shine light on impact and erosion mechanisms among other multiscale, multiphysics problems. The components of the computational framework are a contact algorithm including friction, wear, finite deformation plasticity, heat generation, heat transfer, and adaptive meshing coupled with error estimation. The adaptive meshing is a key development that enhances the efficiency and robustness of the method. We demonstrate the ability of the methodology to simulate diverse problems such as shear banding, impact, and wear.\r\n" }, { "name": "Ol, Michael Volf", "degree": "PhD", "year": "2001", "title": "The Passage Toward Stall of Nonslender Delta Wings at Low Reynolds Number", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192010-085724406", "creators": [ { "name": { "family": "Ol", "given": "Michael Volf" }, "id": "Ol-Michael-Volf", "display_name": "Ol, Michael Volf" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/016w-2332", "abstract": "Separated flow over the leeside of relatively nonslender delta wings was studied experimentally. Such flowfields are more complex than those of the slender delta wing\r\nof very low aspect ratio. A version of Stereo Digital Particle Image Velocimetry was applied to measurements in a low speed water tunnel, at Reynolds numbers below 20,000, for delta wing models of 50\u00b0 and 65\u00b0 leading edge sweep angles and 30\u00b0 windward-side leading edge bevels. Since the objective was to draw comparisons to the stall of classical high aspect ratio wings, low angles of attack were emphasized, with most data points taken in the 5\u00b0-20\u00b0 angle of attack range. Measurements were taken over the starboard portion of the wing planform in crossflow planar slices near the apex region, yielding all three components of the velocity field, albeit restricted to planar cuts.\r\nVorticity and circulation were calculated from these measurements. All three components of vorticity were obtained in select cases, by central-differencing velocity\r\ndata across triplets of adjacent interrogation planes. In addition, flow visualization by dye injection into the windward apex stagnation region was used to confirm the presence of primary and secondary leading edge vortices, to qualitatively verify the locations of vortex breakdown, and to verify the stereo digital particle image velocimetry results.\r\nBoth delta wings exhibit stable, coherent leading edge vortices at very low angles of attack, down to 2.5\u00b0. Results for the 65\u00b0 wing were in accordance with the literature. The 50\u00b0 wing, however, exhibited flow characteristics akin to both slender delta wings, and wings of high aspect ratio, and generally exhibited stronger and more robust leading edge vortices than usually observed. For the 50\u00b0 wing, the primary leading edge vortices were stable below 10\u00b0 angle of attack, with gradual and steady upstream progression of the vortex breakdown region with increasing angles of attack, from aft of the trailing\r\nedge to approximately the midchord. Secondary leading edge vortices were found to decay more abruptly, and at lower angle of attack than the primaries, all but disappearing\r\nby 10\u00b0 angle of attack. This fact has the potential of serving as the basis for a predictive criterion for breakdown of the primary vortices.\r\nThe entire vortex system undergoes large-scale instabilities in the 12\u00b0-20\u00b0 angle of attack range. While the flow visualization was inconclusive, particle image\r\nvelocimetry confirmed that breakdown sweeps over the entire forward third of the wing planform in going from 12.5\u00b0 to 15\u00b0 angle of attack. This change is characterized by a\r\nsharp drop in axial velocity in the primary leading edge vortex core region, along with a loss of coherent vortical structure normally associated with this region. The leading edge shear layer, however, remains in an organized rolled-up state. By 20\u00b0, the flow over the leeward side of the wing is at the threshold of complete separation, with flow along the wing centerline stalling as the left and right separated regions grow and merge.\r\nBoth wings exhibited a largely stagnant region outboard of the primary LEV and inboard of the leading edge shear layer, especially at angles of attack beyond 10\u00b0. This\r\nphenomenon is consistent with some prior observations at Reynolds numbers on the order of 20,000 and below, and differs sharply from that at higher Reynolds numbers. Further experiments are necessary to elucidate the cause and extent of Reynolds number influence on separation near the leeward surface. Also, the 50\u00b0 wing is probably of too\r\nhigh sweep to be a true limiting case for the existence of coherent leading edge vortices, for the conditions of the present experiment. But the abruptness of its stall and the close relationship between the leading edge vortex flow and the leeward surface boundary layer are qualitatively indicative of such a transitional case from slender delta wing separation to classical airfoil stall." }, { "name": "Rasheed, Adam", "degree": "PhD", "year": "2001", "title": "Passive Hypervelocity Boundary Layer Control Using an Ultrasonically Absorptive Surface", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08192001-143746", "creators": [ { "name": { "family": "Rasheed", "given": "Adam" }, "id": "Rasheed-Adam", "display_name": "Rasheed, Adam" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "busecon" ], "doi": "10.7907/EFZZ-X764", "abstract": "A series of exploratory boundary layer transition experiments was performed on a sharp 5.06 degree half-angle round cone at zero angle-of-attack in the T5 Hypervelocity Shock Tunnel in order to test a novel hypersonic boundary layer control scheme. Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface that would damp the second mode (Mack mode). The cone used in the experiments was constructed with a smooth surface on half the cone (to serve as a control) and an acoustically absorptive porous surface on the other half. It was instrumented with flush-mounted thermocouples to detect the transition location. Test gases investigated included nitrogen and carbon dioxide at M = 5 with specific reservoir enthalpy ranging from 1.3 MJ/kg to 13.0 MJ/kg and reservoir pressure ranging from 9.0 MPa to 50.0 MPa. Detailed comparisons were performed to insure that previous results obtained in similar boundary layer transition experiments (on a regular smooth surface) were reproduced and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the hole size was significantly smaller than the viscous length scale." }, { "name": "Samudrala, Omprakash", "degree": "PhD", "year": "2001", "title": "Subsonic and intersonic crack growth along weak planes and bimaterial interfaces", "advisor": "Knauss, Wolfgang Gustav; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-134248309", "creators": [ { "name": { "family": "Samudrala", "given": "Omprakash" }, "id": "Samudrala-Omprakash", "display_name": "Samudrala, Omprakash" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/51b0-1c87", "abstract": "A combined experimental and analytical study has been conducted to investigate the phenomena of intersonic crack propagation along weak planes in homogeneous solids and dissimilar material interfaces. A single edge notch/crack oriented along a weak plane in a brittle polymer or along a polymer/metal interface was loaded in shear by impacting the specimen with a high velocity projectile fired from a gas gun. Homalite-100 or PMMA was chosen for the polymer and 6061 Aluminum or 4340 steel was chosen for the metal. The stress field information around the propagating crack tip was recorded in real time by two different optical techniques which provide complimentary information - photoelasticity and coherent gradient sensing (CGS), in conjunction with high speed photography. Along weak planes in Homalite-100, dynamic shear cracks were observed to initiate and propagate at speeds exceeding the shear wave speed (c_s) of the polymer. The isochromatic fringe patterns reveal two distinct lines of strong stress field discontinuity (Mach waves) emanating from the crack tip. Intersonic cracks were observed to initially accelerate up to the longitudinal wave speed (c_l) of Homalite and thereafter slow down to propagate at a near constant velocity slightly above \u221a2c_s . A series of short secondary opening cracks parallel to each other and at a steep angle to the weak plane (\u2248 80\u00b0) were also observed to initiate behind the main intersonic crack tip. Motivated by the experimental observations, an asymptotic analysis was performed to obtain the near tip fields for an intersonically propagating steady state mode II crack with a finite sized shear cohesive zone in front of it. The cohesive shear stress was chosen to be either a constant or to depend linearly on the magnitude of the local slip rate. Decohesion was chosen to occur when the relative slip between the two cohesive surfaces reaches a material/interface specific critical value. Unlike the case of a point sized dissipative region, it is shown that with a finite cohesive zone, the dynamic energy release rate is finite through out the intersonic regime. The influence of crack plane shear strength and of the rate parameter on the crack propagation behavior is investigated. Isochromatic fringe patterns were constructed using the cohesive crack tip fields, which compare favorably with the experimentally observed fringe patterns, and an attempt is made to extract the relevant analytical parameters. Unlike for a mode-I crack, a cohesive stress distribution that decreases with the local slip rate is found to match the experimental observations. The rate parameter was extracted by fitting the secondary crack angle observed in the experiments to that predicted by the analytical solution based on a maximum principal stress fracture criterion. Edge notches/cracks on polymer/metal interfaces were loaded under different impact configurations and the conditions governing the attainment of intersonic crack growth along a bimaterial interface were investigated. High resolution isochromatic fringe patterns were obtained to study the nature of the crack tip fields during subsonic/intersonic transition. Careful observations of the transition of an interface crack into the intersonic regime showed the formation of crack face contact at speeds beyond c_R of the polymer. Subsequently, the contact zone is observed to expand in size, detach from the intersonic crack tip and finally vanish. The recorded isochromatic fringe patterns showed multiple Mach wave formation associated with such a scenario. Along PMMA/ Al and PMMA/steel bimaterial interfaces, dynamic cracks initiating from edge notches were observed to accelerate to speeds higher than c_l of PMMA (supersonic), almost reaching c_R of aluminum. The resulting crack growth was observed to be highly transient and the gradients of in-plane normal stress components were recorded using CGS interferometry. Motivated by the aforementioned experimental observations, an asymptotic analysis was performed to obtain the stress and deformation fields around a steadily propagating intersonic crack on an elastic-rigid interface with a finite zone of crack face frictional sliding contact located a finite distance behind the tip. A linear frictional contact model is adopted, wherein the shear stress is proportional to the normal stress through a constant, the coefficient of dynamic friction. Isochromatic fringe patterns predicted by the near-tip fields exhibit the essential features observed during the experiments. Frictional sliding contact is shown to be possible only for velocities between c_s and \u221a2c_s of the polymer. The relevant analytical parameters were predicted by comparing the model to the experimental isochromatic fringe patterns and comments are made on the merits of the model presented." }, { "name": "Sane, Sandeep Bhalchandra", "degree": "PhD", "year": "2001", "title": "Time-dependent compressibility of poly (methyl methacrylate) (PMMA) : an experimental and molecular dynamics investigation", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:04262011-100757709", "creators": [ { "name": { "family": "Sane", "given": "Sandeep Bhalchandra" }, "id": "Sane-S-B", "display_name": "Sane, Sandeep Bhalchandra" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/saw5-7p32", "abstract": "This thesis contains three chapters, which describe different aspects of an investigation of the bulk response of Poly(Methyl Methacrylate) (PMMA). The first chapter describes the physical measurements by means of a Belcher/McKinney-type apparatus. Used earlier for the measurement of the bulk response of Poly(Vinyl Acetate), it was now adapted for making measurements at higher temperatures commensurate with the glass transition\r\ntemperature of PMMA. The dynamic bulk compliance of PMMA was measured at atmospheric pressure over a wide range of temperatures and frequencies, from which the master curves for the bulk compliance were generated by means of the time-temperature superposition principle. It was found that the extent of the transition ranges for the bulk and shear response were comparable. Comparison of the shift factors for bulk and shear responses supports the idea that different molecular mechanisms contribute to shear and\r\nbulk deformations.\r\n\r\nThe second chapter delineates molecular dynamics computations for the bulk response for a range of pressures and temperatures. The model(s) consisted of 2256 atoms\r\nformed into three polymer chains with fifty monomer units per chain per unit cell. The time scales accessed were limited to tens of pico seconds. It was found that, in addition to the typical energy minimization and temperature annealing cycles for establishing equilibrium models, it is advantageous to subject the model samples to a cycle of\r\nrelatively large pressures (GPa-range) for improving the equilibrium state. On comparing the computations with the experimentally determined \"glassy\" behavior, one finds that,\r\nalthough the computations were limited to small samples in a physical sense, the primary limitation rests in the very short times (pico seconds). The molecular dynamics computations do not model the physically observed temperature sensitivity of PMMA, even if one employs a hypothetical time-temperature shift to account for the large\r\ndifference in time scales between experiment and computation. The values computed by the molecular dynamics method do agree with the values measured at the coldest\r\ntemperature and at the highest frequency of one kiloHertz.\r\n\r\nThe third chapter draws on measurements of uniaxial, shear and Poisson response conducted previously in our laboratory. With the availability of four time or frequency-dependent material functions for the same material, the process of interconversion between different material functions was investigated. Computed material functions were\r\nevaluated against the direct experimental measurements and the limitations imposed on successful interconversion due to the experimental errors in the underlying physical data\r\nwere explored. Differences were observed that are larger than the experimental errors would suggest.\r\n" }, { "name": "Seywert, Claude", "degree": "PhD", "year": "2001", "title": "Combustion Instabilities: Issues in Modeling and Control", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252007-135242", "creators": [ { "name": { "family": "Seywert", "given": "Claude" }, "id": "Seywert-Claude", "display_name": "Seywert, Claude" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JKFD-7W43", "abstract": "This study deals with various aspects in the development of active control of combustion instabilities.\r\n\r\nA low-order model is developed, reconciling along the way two different approaches taken by researchers to attack the description of combustion instabilities. The model is demonstrated with application to a Rijke tube and compared to experiments. The Rijke burner experiments suggest two major discrepancies with the model: the presence of a hysteresis loop is unaccounted for and the model does not describe the seemingly random fluctuations in the amplitude of the pressure oscillations in the 'unstable' regime. So far no explanation for the hysteresis can be given; however, this phenomenon is successfully exploited by using a novel nonlinear control technique to expand the stable operating range of the burner. The origin of the 'noise' in the pressure trace is explained by considering entropy and vorticity waves in the combustor. Their presence leads to a slight modification of the original model, introducing stochastic source terms into the oscillator equations. The consequences of the presence of these terms is analyzed by means of simulations. One interesting result is that they allow for the identification of model parameters from a single experimental run of a stable combustion system.\r\n\r\nFinally, a unified approach to controlling combustion instabilities is presented. The formulation and analysis account for truncation to a few modes; uncertainties in the description of the system (including uncertain sensing and actuating); external disturbances; and intrinsic noise sources. An explicit expression is derived against which any controller can be checked for stability." }, { "name": "Shan, Wei-Jen Jerry", "degree": "PhD", "year": "2001", "title": "Mixing and Isosurface Geometry in Turbulent Transverse Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082002-152648", "creators": [ { "name": { "family": "Shan", "given": "Wei-Jen Jerry" }, "id": "Shan-Wei-Jen-Jerry", "display_name": "Shan, Wei-Jen Jerry" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0R6S-DY34", "abstract": "Mixing and the geometry of jet-fluid-concentration level sets in turbulent transverse jets were experimentally studied. Jet-fluid concentration fields were measured with laser-induced fluorescence and digital imaging techniques for Reynolds numbers between 1000 and 20000. The scalar field is assessed in terms of classical measures, such as two-dimensional power spectra, as well as probability-density functions (PDFs). Enhanced scalar mixing with increasing Reynolds number is found in the evolution of PDFs of jet-fluid concentration. In the far field of the transverse jet, the scalar PDF is seen to evolve from a monotonically-decreasing function to a strongly-peaked distribution with increasing Reynolds number. Turbulent mixing is found to be flow dependent, based on differences between PDFs of scalar fields in transverse jets and axisymmetric, turbulent jets. The distribution of scalar increments is also studied for separations of varying distance and direction. A novel technique for whole-field measurement of scalar increments is introduced. Probability-density functions of scalar increments are found to trend toward exponential-tailed distributions with decreasing separation distances. The scalar field is anisotropic with decreasing scale, as seen in the two-dimensional power spectra, directional scalar microscales, and in directional PDFs of scalar increments.\r\n\r\nThe geometric complexity of level-sets (iso-concentration contours) in turbulent mixing is assessed within the framework of fractal geometry.\r\nGeneralized coverage statistics are introduced for anisotropic, non-self-similar geometries. This generalized coverage counting involves covering with parallelepipeds of varying size and aspect ratio. A scale-dependent measure of the anisotropy of a set is also introduced. It is shown that this scale-dependent measure transforms the generalized coverage count to isotropy through a scale-dependent normalization of the coordinates. Level sets of jet-fluid concentration in the transverse jet are found to be anisotropic at both large and small scales. The small-scale anisotropy is explained by vertically-oriented extensional strain caused by a counter-rotating vortex pair, while the large-scale anisotropy is associated with the horizontally-elongated shape of the cross-section of the transverse jet. For the special case of isotropic box-counting, the scale-dependent coverage dimension is found to vary from unity, at the smallest length scales, to 2, at the largest length scales, indicating that the isosurfaces produced by turbulent mixing are more complex than can be described by power-law fractals" }, { "name": "Su, Wei-Jen", "degree": "Engineering Degree", "year": "2001", "title": "Aerodynamic Control for a Subsonic Diffuser", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-145002", "creators": [ { "name": { "family": "Su", "given": "Wei-Jen" }, "id": "Su-Wei-Jen", "display_name": "Su, Wei-Jen" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xqg4-r486", "abstract": "Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of mass injection in subsonic diffusers.
\r\n\r\nThe goal of the experiment is to study aerodynamic control in subsonic diffusers by investigating downstream velocity profiles. These experiments were designed to address several key issues like effects due to velocity change (for one-stream and two-stream flows), and effects due to density variation. The effect of the separation bubble (stall flow) on the performance of the diffuser has also been investigated.
\r\n\r\nOne-stream experiments were performed with non-reacting (cold) runs using N\u2082 in the high-speed section at different velocities and zero velocity at the low-speed section. Detailed analysis of data obtained shows a slight dependency of the reattachment point of the separation bubble on Reynolds number. As the flow rate in the high-speed section increases, the reattachment point of the separation bubble shifted slightly downstream. Two-stream flow (low- and high-speed sections) experiments were performed using [...] in the high-speed section and a density-matched mixture of Argon/Helium in the low-speed section. As the mass injection is increased in the low-speed section, the reattachment point of the separation bubble moved further downstream. While keeping the same velocity ratio (low- and high-speed sections), as the overall flow velocity increases, the reattachment point moved further downstream. Also, experiments with a higher density ratio using Argon in the low-speed section and N\u2082 in the high-speed section were performed. As the density of the low-speed section increases, the reattachment point of the separation bubble moved upstream due to shear-layer entrainment effect. Finally, as the reattachment point of the separation bubble shifted further downstream, the diffuser pressure coefficient decreases, therefore, the performance of the diffuser is degraded.
\r\n\r\nSchlieren flow visualization and pressure probes were used in the experiments.
" }, { "name": "Yu, Chengxiang Rena", "degree": "PhD", "year": "2001", "title": "Three-Dimensional Cohesive Modeling of Impact Damage of Composites", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-130530819", "creators": [ { "name": { "family": "Yu", "given": "Chengxiang Rena" }, "id": "Yu-Chengxiang-Rena", "orcid": "0000-0003-4176-0324", "display_name": "Yu, Chengxiang Rena" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/nd8e-tc84", "abstract": "The objective of this work is to establish the applicability of cohesive theories of fracture in situations involving material interface, material heterogeneity (e.g., layered composites), material anisotropy(e.g., fiber-reinforced composites), shear cracks, intersonic dynamic crack growth and dynamic crack branching. The widely used cohesive model is extended to orthotropic range. The so-developed computational tool, completed by a self-adaptive fracture procedure and a frictional contact algorithm, is capable of following the evolution of three-dimensional damage processes, modeling the progressive decohesion of interfaces and anisotropic materials. The material parameters required by cohesive laws are directly obtained from static experiments. The ability of the methodology to simulate diverse problems such as delamination between fibers of graphite/epoxy composites, as well as sandwich structures and branching within brittle bulk materials has been demonstrated.
" }, { "name": "Zuhal, Lavi Rizki", "degree": "PhD", "year": "2001", "title": "Formation and Near-Field Dynamics of a Wing Tip Vortex", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072013-122723580", "creators": [ { "name": { "family": "Zuhal", "given": "Lavi Rizki" }, "id": "Zuhal-Lavi-Rizki", "display_name": "Zuhal, Lavi Rizki" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VNJW-6592", "abstract": "The search for a more efficient method to destroy aircraft trailing vortices requires\r\na good understanding of the early development of the vortices. For that purpose, an\r\nexperimental investigation has been conducted to study the formation and near-field\r\ndynamics of a wing tip vortex.
\r\n\r\nTwo versions of the Digital Particle Image Velocimetry (DPIV) technique were\r\nused in the studies. Planar DPIV was used to obtain velocity fields adjacent to the wing\r\nsurface. Stereoscopic DPIV, which allows instantaneous measurements of all three\r\ncomponents of velocity within a planar slice, was used to measure velocity fields behind\r\nthe wing. The trailing vortex was produced by a rectangular half-wing model with an\r\nNACA 0012 profile. All measurements were made at Reynolds number, based on chord\r\nlength, of 9040.
\r\n\r\nThe present study has found that the wing sheds multiple vortices. A structure\r\nthat closely resembles a wing tip vortex is first observed on the suction side of the wing\r\nnear the tip at the mid-chord section of the wing. At the trailing edge of the wing, a\r\nsmaller vortex with an opposite sense of rotation is observed next to the tip vortex. In\r\naddition to the two vortices, two vortex layers with opposite sense of rotation, one on the\r\npressure side and one on the suction side, are apparent at the trailing edge. Farther\r\ndownstream, most of the vorticity in the vortex layer, with the same sense of rotation as\r\nthe tip vortex, rolls up into the wing tip vortex. The vortices, with opposite sense of\r\nrotation, break up into smaller vortices which orbit around the tip vortex. At least one\r\nrelatively strong satellite vortex appears in some of the instantaneous fields. The studies\r\nfound that the interaction of the tip vortex and satellite vortices give rise to the unsteady\r\nmotion of the wing tip vortex. In addition, the studies also examined the effects of the\r\nboundary layer and the tip geometry to the strength and motion of the trailing vortex.
" }, { "name": "Brady, Mark A.", "degree": "PhD", "year": "2000", "title": "Regularized vortex sheet evolution in three dimensions", "advisor": "Pozrikidis, Constantine; Pullin, Dale Ian; Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-145525634", "creators": [ { "name": { "family": "Brady", "given": "Mark A." }, "id": "Brady-M-A", "display_name": "Brady, Mark A." } ], "advisors": [ { "name": { "family": "Pozrikidis", "given": "Constantine" }, "id": "Pozrikidis-C", "role": "advisor", "display_name": "Pozrikidis, Constantine" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pbyj-k986", "abstract": "A computational method is presented to follow the evolution of regularized three-dimensional (3D) vortex sheets through an otherwise irrotational, inviscid, constant-density fluid. The sheet surface is represented by a triangulated mesh with interpolating functions locally defined inside each triangle. C^1 continuity is maintained between triangles via combinations of cubic B\u00e9zier triangular interpolants. The self-induced sheet motion generally results in a highly deformed surface which is adaptively refined as needed to capture regions of increasing curvature and to avoid severe Lagrangian deformation. Automatic mesh refinement is implemented with an advancing front technique. Sheet motion is regularized by adding a length scale cut-off to the BiotSavart kernel. Velocity evaluation takes less time than the standard O(N^2) scaling, due to utilization of multi-pole expansions of the kernel. Zero, singly, and doubly periodic vortex sheets are simulated, modeling vortex rings, vortex/jet combinations and standard shear layers. Comparisons with previous two-dimensional (2D) results are favorable and 3D simulations are presented. The perturbed 3D planar shear layer is simulated and compared with a similar experiment revealing qualitatively similar results and agreement on the mechanism by which streamwise vorticity is created. We find the ratio of spanwise to streamwise vorticity to vary between 7 and 9 during early stages of roll-up.\r\n\r\nA new technique for estimating the curvature singularity time of true vortex sheets (i.e., non-regularized motion) is presented. The motion and singularity time of a planar, doubly periodic sheet, evolving from a 3D normal mode perturbation, is found to reduce to that of a well known singly periodic (and only two-dimensional) problem, an unexpected extension of Moore's [38] non-linear analysis for 2D vortex sheets." }, { "name": "Haberman, Keith Scott", "degree": "Engineering Degree", "year": "2000", "title": "A Micromechanical Constitutive Model for the Dynamic Response of Brittle Materials \"Dynamic Response of Marble\"", "advisor": "Rosakis, Ares J.; Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-113248", "creators": [ { "name": { "family": "Haberman", "given": "Keith Scott" }, "id": "Haberman-Keith-Scott", "display_name": "Haberman, Keith Scott" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/smj0-cq27", "abstract": "A micromechanically based constitutive model for the dynamic inelastic behavior of brittle materials, specifically \"Dionysus-Pentelicon marble\" with distributed microcracking is presented. Dionysus-Pentelicon marble was used in the construction of the Parthenon, in Athens, Greece. The constitutive model is a key component in the ability to simulate this historic explosion and the preceding bombardment form cannon fire that occurred at the Parthenon in 1678. Experiments were performed by Rosakis (1999) that characterized the static and dynamic response of this unique material. A micromechanical constitutive model that was previously successfully used to model the dynamic response of granular brittle materials is presented. The constitutive model was fitted to the experimental data for marble and reproduced the experimentally observed basic uniaxial dynamic behavior quite well. This micromechanical constitutive model was then implemented into the three dimensional nonlinear lagrangain finite element code Dyna3d(1998). Implementing this methodology into the three dimensional nonlinear dynamic finite element code allowed the model to be exercised on several preliminary impact experiments. During future simulations, the model is to be used in conjunction with other numerical techniques to simulate projectile impact and blast loading on the Dionysus-Pentelicon marble and on the structure of the Parthenon." }, { "name": "Jeon, David S.", "degree": "PhD", "year": "2000", "title": "On Cylinders Undergoing One- and Two-Degree of Freedom Forced Vibrations in a Steady Flow", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302010-151500998", "creators": [ { "name": { "family": "Jeon", "given": "David S." }, "id": "Jeon-David-S", "display_name": "Jeon, David S." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ky58-en52", "abstract": " Formation of vortices in the near wake of circular cylinders is discussed. Two different cases are compared: starting flow around an initially stationary cylinder and flow around an oscillating cylinder in a steady freestream. The effects of formation time on the morphology of the vortices are shown, as well as some consequences thereof.\r\n\r\n For starting flows, the critical formation time defines the point where the wake transitions from the initially symmetrical state to the intermediate asymmetrical state. The asymmetrical state breaks down into the periodic shedding state normally associated with cylinder flows. It appears that the wake reaches a critical level of vorticity annihilation at the critical time. This triggers an exponential growth of asymmetry in the near wake. Evidence of this process can also be seen in the early time force data.\r\n\r\n For oscillating flows, the critical time defines the transition from vortex to vortex-and-tail morphology. First, phase averaged vorticity fields are presented showing the changes in the wake with forcing frequency and streamwise motion. These changes are related to the formation time, and related to similar effects seen in other flows. In addition, prolonged formation is related to the observed switch in the phase of the vortex shedding. The effects of streamwise motion are also shown, including the increased phase coherence of the shedding via coordination of the shedding process and the ability to adjust formation time via streamwise acceleration. The latter was used to demonstrate a plausible explanation for the vortex pair formation process observed by some researchers by showing how the formation process affects the number of vortices generated per cycle." }, { "name": "Moeleker, Piet", "degree": "PhD", "year": "2000", "title": "The filtered advection-diffusion equation : Lagrangian methods and modeling", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-114741410", "creators": [ { "name": { "family": "Moeleker", "given": "Piet" }, "id": "Moeleker-P", "display_name": "Moeleker, Piet" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2q17-4g27", "abstract": "This research focuses on the incompressible scalar advection-diffusion equation. After applying a Gaussian filter, an infinite series expansion is found for the advection term to obtain a closed equation. Only the first two terms in this expansion are retained yielding the tensor-diffusivity subgrid model. This model can be interpreted as a tensor-diffusivity term which is proportional to the rate-of-strain tensor of the large-scale\r\nfiltered velocity field. Due to the negative diffusion in the stretching directions, care needs to be taken in the choice of a numerical method.\r\n\r\nThe scalar field is decomposed in a collection of anisotropic or axisymmetric Gaussian particles. Equations of motion for the location and the shape/size of the particles are derived using an expansion in Hermite polynomials. A novel, accurate remeshing scheme was found resulting in explicit expressions for the amplitudes of the new set of particles.\r\n\r\nA stagnation flow was used for illustrative purposes and validation. Using a 2D time-dependent velocity field yielding chaotic advection, both axisymmetric and\r\nanisotropic particles yield good agreement with filtered direct numerical simulations and compare favorably with the Smagorinsky subgrid model. Computational efficiency\r\nmakes axisymmetric particles the preferred choice.\r\n\r\nA literature study using a 3D stationary one-parameter chaotic velocity field was used to validate model and particle-method in 3D. For highly chaotic fields good\r\nagreement was obtained with this study. Computations have been performed for 3D forced isotropic periodic turbulence to study scalar mixing. Comparisons with literature are made.\r\n\r\nIt was shown that when the unfiltered velocity field is known, the most accurate results are obtained by moving particles using this field. It was concluded that a good\r\nsubgrid model modifies the equation of motion to get a good approximation to the unfiltered velocity field.\r\n" }, { "name": "Schlamp, Stefan", "degree": "PhD", "year": "2000", "title": "Laser-induced thermal acoustic velocimetry", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-130705165", "creators": [ { "name": { "family": "Schlamp", "given": "Stefan" }, "id": "Schlamp-S", "display_name": "Schlamp, Stefan" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/skm0-tk82", "abstract": "Laser-Induced Thermal Acoustics (LITA) is a non-intrusive, remote, four-wave mixing laser diagnostic technique for measurements of the speed of sound and of the thermal diffusivity in gases. If the gas composition is known, then its temperature and density can be inferred. Beam misalignments and bulk fluid velocities can influence the time history and intensity of LITA signals. A closed-form analytic expression for LITA signals incorporating these effects is derived. The magnitude of beam misalignment and the flow velocity can be inferred from the signal shape using a least-squares fit of this model to the experimental data. High-speed velocimetry using homo dyne detection is demonstrated with NO_2-seeded air in a supersonic blow-down nozzle. The measured speed of sound deviates less than 2% from the theoretical value assuming isentropic quasi-1D flow. Boundary layer effects degrade the velocity measurements to errors of 20%. Heterodyne detection is used for low-speed velocimetry up to Mach number M = 0.1. The uncertainty of the velocity measurements was ~ 0.2 m/s. The sound speed measurements were repeatable to 0.5%. The agreement between theory and experiments is very good. A one-hidden-layer feed-forward neural network is trained using back-propagation learning and a steepest descent learning rule to extract the speed of sound and flow velocity from a heterodyne LITA signal. The effect of the network size on the performance is demonstrated. The accuracy is determined with a second set of LITA signals that were not used during the training phase. The accuracy is found to be better than that of a conventional frequency decomposition technique while being computationally as efficient. This data analysis method is robust with respect to noise, numerically stable, and fast enough for real-time data analysis. The accuracy and uncertainty of non-resonant LITA measurements is investigated. The error in measurements of the speed of sound and of the thermal diffusivity initially decreases with increasing signal intensity (excitation beam pulse energy) and increases again after passing a minimum. The location of the minimum error for the speed of sound and for the thermal diffusivity coincide. The errors at the minimum are 0.03% and 1%, respectively. The uncertainties for the speed of sound and the thermal diffusivity decrease monotonically to 0.25% and 5%, respectively. The increased error for high excitation beam pulse energies results from finite-strength waves that cannot be treated using the linearized equations of motion." }, { "name": "Schultz, Eric", "degree": "PhD", "year": "2000", "title": "Detonation Diffraction Through an Abrupt Area Expansion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-180459", "creators": [ { "name": { "family": "Schultz", "given": "Eric" }, "id": "Schultz-Eric", "display_name": "Schultz, Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/96F1-QR61", "abstract": "The problem of a self-sustaining detonation wave diffracting from confinement into an unconfined space through an abrupt area change is characterized by the geometric scale of the confinement and the reaction scale of the detonation. Previous investigations have shown that this expansion associated with a detonation transitioning from planar to spherical geometry can result in two possible outcomes depending upon the combustible mixture composition, initial thermodynamic state, and confining geometry. Competition between the energy release rate and expansion rate behind the diffracting wave is crucial. The sub-critical case is characterized by the rate of expansion exceeding the energy release rate. As the chemical reactions are quenched, the shock wave decouples from the reaction zone and rapidly decays. The energy release rate dominates the expansion rate in the super-critical case, maintaining the coupling between the shock and reaction zone which permits successful transition across the area change. A critical diffraction model has been developed in the present research effort from which the initial conditions separating the sub-critical and super-critical cases can be analytically determined. Chemical equilibrium calculations and detonation simulations with validated detailed reaction mechanisms provide the model input parameters. Experiments over a wide range of initial conditions with single- and multi-sequence shadowgraphy and digital chemiluminescence imaging support the model derivation and numerical calculations. Good agreement has been obtained between the critical diffraction model and experimental results." }, { "name": "Swenson, Grant Douglas", "degree": "PhD", "year": "2000", "title": "Numerical simulations of combustion instabilities in gas turbine combustors, with applications", "advisor": "Culick, Fred E. C.; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-140810", "creators": [ { "name": { "family": "Swenson", "given": "Grant Douglas" }, "id": "Swenson-G-D", "display_name": "Swenson, Grant Douglas" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3QG6-JN34", "abstract": "Recent advances in technology have opened up a potential market for small gas turbine power systems in the 50-100 MW range. In an effort to improve their systems, the gas-turbine industry is interested in understanding and controlling combustion instabilities as well as reducing pollutant production. To understand the dynamics inherent in a combustion system, information about the flow field behavior is required. Because of a scarcity of available experimental or numerical results for full-scale gas-turbine combustors, we decided to use numerical simulations to provide the required information about the flow field dynamics. The ability of the numerical simulations to reproduce unstable behavior in combustion environments will be presented. The investigation of the flow field dynamics has been conducted for three test cases; a planar heat source in a tube, premixed flow in a dump combustor, and premixed and diffusion flames in a full-scale gas turbine combustor. The numerically determined unsteady acoustic modes will be shown to compare well with theory and experiments. An investigation of the local heat release response to an unsteady flow field is conducted for incorporation into an approximate analysis method. The results of including a Helmholtz resonator in a dump combustor as a passive control mechanism will be presented. The production of NOx and CO will be compared between stable and unstable flow configurations. The pollutant results indicate that for the planar flame in a tube and the dump combustor, the NOx levels at the exit plane are reduced when the system is unstable.\n" }, { "name": "Voelkl, Tobias", "degree": "PhD", "year": "2000", "title": "A physical-space version of the stretched-vortex subgrid-stress model for large-eddy simulation of incompressible flow", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-154618", "creators": [ { "name": { "family": "Voelkl", "given": "Tobias" }, "id": "Voelkl-T", "display_name": "Voelkl, Tobias" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/d900-mk74", "abstract": "In large-eddy simulations of turbulence, the large scales of the flow are resolved by a numerical solution of the equations of motion for these scales, but the contribution of the fine-scale turbulence must be modeled. The stretched-vortex model estimates the influence of these unresolved subgrid-scale turbulence fluctuations on the resolved-scale velocities by using kinematic results for homogeneous, anisotropic turbulence consisting of locally straight, unidirectional vortex structures [D. I. Pullin and P. G. Saffman, Phys. Fluids 6 (5), 1994]. A new method is presented to dynamically determine the value of model constants related to the subgrid kinetic energy. For this purpose, a relation between the resolved-scale velocity structure function of second order and the energy spectrum is derived based on the kinematics of the model vortex structures, and therefore without the assumption of isotropy. Implementation of this relation using a local, circular average allows application of the model to wallbounded turbulent flows without special modifications. The resulting algebraic model is completely localized, i.e., no global flow quantities like the resolved-scale spectrum are required. This facilitates the application of the model in physical-space numerical methods using, for example, finite differences or Lagrangian-interpolation polynomials. The model includes an estimate of the subgrid kinetic energy, which is used to compute subgrid contributions to low-order turbulence statistics of the full flowfield. Results will be shown for the decay of kinetic energy and energy spectra of decaying, isotropic turbulence, for mean velocities, root-mean-square velocity fluctuations and turbulence-kinetic-energy budgets of channel flow up to a Reynolds number of approximately 23 000 (based on channel halfwidth and centerline velocity), and for mean velocities and turbulence kinetic energy of channel flow under spanwise rotation. The results are compared to unfiltered data from direct numerical simulations and experiment." }, { "name": "Bond, Christopher Llewellyn", "degree": "PhD", "year": "1999", "title": "Reynolds number effects on mixing in the turbulent shear layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242005-162912", "creators": [ { "name": { "family": "Bond", "given": "Christopher Llewellyn" }, "id": "Bond-C-L", "display_name": "Bond, Christopher Llewellyn" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3KKM-HB66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments have been performed in turbulent shear layers to assess the effects of Reynolds number on mixing. The experiments extend the upper range of incompressible, chemically-reacting flow data from [...] to [...] and, in a subsequent collaboration with M. Slessor and others, to 7 x 10[...]. The experiments address an ambiguity in recent measurements of mixing in compressible shear layers, whose differences from measurements in incompressible shear layers could have been due either to compressibility or Reynolds number effects. The current results, collectively with previous results, show that the decrease of mixing with increasing Reynolds number first seen by Mungal et al. (1985) continues to the Reynolds numbers studied, but do not show a further decrease in mixing. The conclusions must be tempered by the presence of changes in the initial boundary layers and acoustic environment, and by the compressibility ([...] = 0.25) of the highest Reynolds number (Re = 7 x 10[...]) case.\r\n" }, { "name": "Davis, Jean-Paul", "degree": "PhD", "year": "1999", "title": "High-enthalpy shock/boundary-layer interaction on a double wedge", "advisor": "Sturtevant, Bradford; Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-125333", "creators": [ { "name": { "family": "Davis", "given": "Jean-Paul" }, "id": "Davis-J", "display_name": "Davis, Jean-Paul" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4C98-MN23", "abstract": "Interaction between a shock wave and a boundary layer at a compression corner can produce a region of separated flow. The length of separation is important in determining aerodynamic forces, and the heat transfer at reattachment is important for the design of thermal protection systems. The effects of high-enthalpy flow on these phenomenon, particularly separation length, are not well known. Experiments to measure separation length and reattachment heating are performed in the T5 Hypervelocity Shock Tunnel using nitrogen test gas and a double-wedge geometry which allows greater control over local flow conditions at separation and, at high incidence angle, may produce real-gas effects due to dissociation behind the leading shock. Local external flow conditions were found by computational reconstruction of the inviscid nonequilibrium flow field.\n\nApplication of results from asymptotic theory to a simple model for separation leads to a new scaling parameter which approximately accounts for wall temperature effects on separation length for a laminar nonreacting boundary layer and extends previous results to arbitrary viscosity law. A. classification is introduced which divides mechanisms for real-gas effects into those acting internal and external to viscous regions of the flow, with internal mechanisms further subdivided into those arising upstream and downstream of separation. Application of the ideal dissociating gas model to a scaling law based on local external flow parameters and a nonreacting boundary layer shows that external mechanisms due to dissociation decrease separation length at low incidence but depend on the free-stream dissociation at high incidence, and have only a small effect on peak heating. A limited numerical study of reacting boundary layers shows that internal mechanisms due to recombination in the upstream boundary layer cause a slight decrease in separation length and a large increase in heat flux relative to a nonreacting boundary layer with the same external conditions.\n\nCorrelations are presented of experimentally measured separation length using local external flow parameters computed for reacting flow, which scales out external mechanisms but not internal mechanisms. These show the importance of the new scaling parameter in high-enthalpy flows, a linear relationship between separation length and reattachment pressure ratio as found previously for supersonic interactions, and a Reynolds-number effect for transitional interactions. A significant increase in scaled separation length is observed for high-enthalpy data in the laminar regime, and this is attributed to an internal recombination mechanism occurring in the separated shear layer. Experimental data for reattachment heat flux are found to agree roughly with existing correlations and to exhibit an increase due to an internal recombination mechanism, but cannot provide further insight due to large scatter." }, { "name": "Deshpande, Nitin Ashok", "degree": "Engineering Degree", "year": "1999", "title": "An Experimental Investigation of High-Shear-Strain-Rate Behavior of Metals", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-080229", "creators": [ { "name": { "family": "Deshpande", "given": "Nitin Ashok" }, "id": "Deshpande-Nitin-Ashok", "display_name": "Deshpande, Nitin Ashok" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/naah-mx91", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe present study investigated the mechanical behavior of metals under high-shear-strain-rates and large shear strains. Numerical and experimental investigation of different specimen geometries for shear testing of materials was carried out. Results of numerical simulations showed that shear stress-strain curves calculated from boundary measurement of load and displacement did not match with the constitutive law for the material. The yield stress for the shear stress-strain curve from the boundary measurement was considerably lower than that of the constitutive law whereas hardening exponent was almost the same for two curves. Considerable bending was observed in the shear zone. The results from the boundary measurements were close to the constitutive law for H specimen, an analogue of axisymmetric top hat specimen with top replaced by tool steel punch. A planar version of axisymmetric top hat specimen geometry was studied using finite element analysis. The plane specimen was chosen since it is suitable for temperature measurements in the shear zone. In order to reduce the bending, three types of constraints were considered in the experiments.\r\n\r\nQuasi-static and high strain rate experiments were carried out on different geometries in the strain rate range, 10[...] to 10[...] s[...]. Relatively rate insensitive material, 2024-T3 aluminum was used to establish the relationship between numerical and experimental results. Experimental results for the axisymmetric top hat specimen were found to be in good agreement with the finite element results, but there was discrepancy between the stress-strain curve from the boundary measurements and the constitutive law. Shear stress-strain curve from the quasi-static test for the plane specimen with external constraint reproduced the results of numerical simulation. A planar specimen with built-in constraint was fabricated using wire EDM. Both quasi-static and high strain rate results matched with the numerical simulation of the same specimen geometry. High shear strains of the order of 1.5 were reached in the experiments on the Kolsky pressure bar. Some amount of thermal softening was observed in high strain rate experiments.\r\n\r\nIt was concluded that both numerical simulations and experiments are required in order to obtain accurate constitutive behavior of the material using top hat specimen geometries. A relationship can be established between the numerical tests and the experiments by conducting the experiments at strain rates where the constitutive behavior of the metal is well known. This relationship then can be used to predict the constitutive law at higher strain rates from the experimental data obtained at high strain rates." }, { "name": "Gharib, Mohammad Reza", "degree": "PhD", "year": "1999", "title": "Vortex-induced vibration, absence of lock-in and fluid force deduction", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132005-133506", "creators": [ { "name": { "family": "Gharib", "given": "Mohammad Reza" }, "id": "Gharib-M-R", "display_name": "Gharib, Mohammad Reza" } ], "advisors": [], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CF0Y-5A59", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nVortex-induced vibration (VIV) of elastically supported cylinders in cross-flow is studied experimentally for cylinder mass ratios (average cylinder density / fluid density), [...]. For small mass ratios below 10, a new VIV mode is discovered which does not involve a lock-in behavior. The oscillation and the shedding frequencies coalesce and deviate slightly from the nominal Strouhal frequency of St=0.2 to smaller values with increasing free stream velocity U. With increasing mass ratio above 10 (m*>10), the frequency growth with free stream velocity U appears to approach the lock-in limit while the amplitude and the frequency range of oscillations diminish. Additionally, a novel technique is employed to deduce the unsteady lift coefficient on the body using VIV time traces of the cylinder displacement and their numerical derivatives.\n\nAn analytical study of the dynamical equation shows that the oscillation amplitude (A/D) is inversely proportional to effective stiffness, [...], where U represents the non-dimensional flow speed and [...], the ratio of the oscillation to natural frequencies. It is hence maintained that at high mass ratio cases studied previously (m*>100), lock-in behavior ([...] for U ~ 1) is a prerequisite for nominal vibration amplitudes. At low values of mass ratio, however, [...] is minimized naturally without a need for lock-in.\n\nThrough a detailed study of a large number of cases with low to medium mass ratios in different experimental settings, it is additionally argued that lock-in is a sporadic phenomenon that appears at various mass ratios. The few occurrences of lock-in at low mass ratios with nominal damping and the unexpected absence of any oscillations at medium mass ratios (m*~30), except for a few cases exhibiting lock-in tendencies indicate that lock-in is not as common as classically believed.\n" }, { "name": "Leyva, Ivett A.", "degree": "PhD", "year": "1999", "title": "Shock detachment process on cones in hypervelocity flows", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-162753", "creators": [ { "name": { "family": "Leyva", "given": "Ivett A." }, "id": "Leyva-I-A", "display_name": "Leyva, Ivett A." } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/62TN-GA26", "abstract": "The shock detachment process on cones in hypervelocity flows is one of the most sensitive flows to relaxation effects. The critical angle for shock detachment under frozen conditions can be very different from the critical angle under chemical and thermal equilibrium. The rate of increase of the detachment distance with cone angle is also affected by the relaxation rate.
\r\n\r\nThe purpose of this study is to explain the effects of nonequilibrium on the shock detachment distance and its growth rate on cones in hypervelocity flows. The study consists of an experimental and a computational program. The experimental part has been carried out at Caltech's hypervelocity reflected shock tunnel (T5). Six different free-stream conditions have been chosen, four using N2 as the test gas and two using CO2. About 170 shots were performed on 24 cones. The cones range in diameter from 2 cm to 16 cm with half-angles varying from 55\u00b0 to 75\u00b0. The experimental data obtained are holographic interferograms of every shot, and surface temperature and pressure measurements for the bigger cones. Extensive numerical simulations were made for the N2 flows and some were also made for the CO2 flows. The code employed is a Navier-Stokes solver that can account for thermal and chemical nonequilibrium in axisymmetric flows.
\r\n\r\nThe experimental and computational data obtained for the shock detachment distance confirms a previous theoretical model that predicts the detachment distance will grow more slowly for relaxing flows than for frozen or equilibrium flows. This difference is explained in terms of the behavior of the sonic line inside the shock layer. Different growth rates result when the detachment distance is controlled by the diameter of the cone (frozen and equilibrium cases) than when it is controlled by the extent of the relaxation zone inside the shock layer (nonequilibrium flows). The experimental data are also complemented with computational data to observe the behavior of the detachment distance from the frozen to equilibrium limits for a given cone half-angle and free-stream condition. As deduced by a previous simple scaling argument, the ratio of the detachment distance to the diameter of the cone is constant in the two extremes and rapidly switches from one value to the other for cone diameters of about 2 cm to 16 cm. The experimental interferograms are also compared with numerical ones in terms of the detachment distance, the number of fringes in the shock layer, and the shape of the fringes.
\r\n\r\nThe heat flux traces obtained from the temperature measurements show different behaviors for the attached and detached cases, but these effects can be related to the conditions at the edge of and inside the boundary layer and to the Reynolds number of the flow rather than to nonequilibrium effects. The pressure measurements were insensitive to the degree of nonequilibrium.
\r\n" }, { "name": "Maheo, Patrice Michel", "degree": "PhD", "year": "1999", "title": "Free-Surface Turbulent Shear Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-104541", "creators": [ { "name": { "family": "Maheo", "given": "Patrice Michel" }, "id": "Maheo-Patrice-Michel", "display_name": "Maheo, Patrice Michel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCTV-BM26", "abstract": "The structure and dynamics of turbulent wakes and shear layers in the presence of a clean free surface have been investigated experimentally using digital particle image velocimetry (DPIV). The purpose of this study was to determine the extent and characteristics of the influence, if any, of the free surface on these underlying turbulent shear flows.
\r\n\r\nThe free surface was found to affect the dynamics of turbulence within a surface layer on the order of one half-width of the submerged wake and one half of the local vorticity thickness of the submerged shear layer. Within this layer, the vertical velocity fluctuations are inhibited and the turbulence kinetic energy is redistributed to the horizontal components. The self-induced motion of surface-parallel vortical structures under the influence of their images was shown to lead to large-scale mean streamwise secondary flows and associated outward surface currents-symmetric for the wake and asymmetric for the shear layer. This motion was the origin of the significantly higher lateral spreading rates of these surface shear flows compared to the spreading rates of their fully-submerged counterparts \u2014 20% and 25% for the wake and shear layer respectively. In addition, the evolution of the streamwise and surface-normal enstrophy components within the surface layer was consistent with the normal connection of vortical structures required at a free surface.
\r\n\r\nThe influence of the secondary flows was tracked back to the splitter plate's turbulent boundary layers where they were hence deduced to originate. A simple analysis of the mixed-boundary corner flows of the splitter plate made using the mean streamwise vorticity equation coupled with the evolution of the values of the transverse velocity confirmed the latter. In this picture of the mean flow, the secondary flows present in the near-surface edges of these shear flows were related to the pair of outer secondary vortices generated thereby. Furthermore, using a simplified equation for the surface-normal Reynolds stress, it was shown that the mutual interaction of the surface-parallel vortical structures with their images yielded a decrease in vertical velocity fluctuations as the free surface was approached. This equation shed further light on the redistribution of the vertical kinetic energy of turbulence into the other two Reynolds normal stresses. The resulting free-surface Reynolds-stress anisotropy in turn gave birth to the two streamwise secondary flows.
\r\n\r\n\r\n" }, { "name": "Shariff, Shaun", "degree": "PhD", "year": "1999", "title": "Numerical simulation of viscous reacting hypersonic flow past cones", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-155520", "creators": [ { "name": { "family": "Shariff", "given": "Shaun" }, "id": "Shariff-S", "display_name": "Shariff, Shaun" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D6TR-5Z18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThe stepback and partial grid techniques were used in the numerical simulation of laminar viscous reacting flows past cones at incidence. The stepback technique is a method for computing exactly flows which are truly conical, and can be an effective approximate method for nearly conical flows such as viscous flow past cones. The partial grid technique uses a stepback solution as the upstream boundary condition for a time-marching calculation, and is more accurate than the stepback method. Both frozen and chemically active equilibrium flow were considered, using the Ideal Dissociating Gas model. Computations were performed for frozen hypersonic flow past a 10[...] half-angle cone inclined at 24[...] incidence, and for hypervelocity flow past a 15[...] half-angle cone at 30[...] incidence with active dissociation and recombination chemistry. These computations were compared with experiments, and the effects of equilibrium and non-equilibrium chemistry were observed. These calculations also show that the effects of chemistry on heat transfer and separation location are small and of the same order as the errors associated with the stepback method. Therefore, for high accuracy in computing reacting flows, the partial grid method should be used.\r\n" }, { "name": "Lee, Sangwook", "degree": "PhD", "year": "1998", "title": "Failure of laminated composites at thickness discontinuities under complex loading and elevated temperatures", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222008-140642", "creators": [ { "name": { "family": "Lee", "given": "Sangwook" }, "id": "Lee-Sang", "display_name": "Lee, Sangwook" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9p36-ht49", "abstract": "Failure initiation of laminated composites with discontinuous thickness is examined in terms of typical structural load description (tension, shear force and bending moment) rather than in terms of micromechanics considerations. Because transverse shear produced relatively small effects in failure initiation, results are presented as tension-bending interactions. Two loading frames were designed to apply moments and tension simultaneously. Four types of specimens of different stacking sequence were examined to determine failure initiation, and analyzed subsequently via a finite element analysis (ABAQUS). Depending on the stacking sequence across the interface of the step, two different failure modes are identified: For uni-directional fiber orientation across the interface in the tension direction, failure occurs through cracking and delamination which is governed by a fracture mechanics criterion. While the initiation strength for this failure mode is higher than for the cross-ply configurations, the residual strength after initiation is only marginally higher, providing virtually no margin of safety (10%). For cases involving cross-plies on either side of the interface, failure initiation occurs by matrix cracking, with a critical strain across the fibers providing a universal failure criterion. In these cases the residual load bearing capability was 30 to 45% higher than the failure initiation loads. The interaction between moment and tension at failure initiation is linear, an observation that does not hold for the delamination failure driven by crack propagation. It is found that all failures can be described in terms of a common fracture principle; the stress or strain criteria are interchangeable with the fracture energy computations, provided one allows for a range of values of associated fracture energies. Assuming that time dependent aspects of the failure process are not dominant, elevated temperatures did not change the general results of how bending and tension loads interact, provided one accounts for residual thermal stresses; however, the stress magnitude at which the failure initiation occurs decreases with increasing temperature.\r\n" }, { "name": "Park, Han G.", "degree": "PhD", "year": "1998", "title": "A Study of Heat Transport Processes in the Wake of a Stationary and Oscillating Circular Cylinder Using Digital Particle Image Velocimetry/Thermometry", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-150955", "creators": [ { "name": { "family": "Park", "given": "Han G." }, "id": "Park-Han-G", "display_name": "Park, Han G." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C9KN-RQ12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\t\t\t\t\t\r\nAn experimental investigation is carried out on the processes of heat transfer associated with a heated circular cylinder in crossflow. Two studies are made. First, a study of the transport of heat in the near wake (x/D<5) of a stationary and transversely oscillated cylinder is made at Reynolds number of 610. Second, a study is made of the surface heat transfer from a cylinder which is undergoing forced oscillations in the transverse direction.\r\n\r\nThe studies are made using the technique of Digital Particle Image Velocimetry/Thermometry (DPIV/T) which allows simultaneous measurements of both the velocity and temperature fields of the flow. The temperature is measured by seeding the flow with thermochromic liquid crystal (TLC) particles which change their reflected wavelength as function of temperature. By calibrating reflected wavelength versus temperature using a color multi-CCD camera, the local temperature of the flow may be deduced. The velocity is measured by using the same particles as Lagrangian flow tracers, and local velocity or displacement of the flow may be measured by cross-correlating two sequential images. A limitation of DPIV/T, which is the low level of precision (5% - 20% of the temperature span of TLC particles), may be overcome by a process in which the temperature at a given location is computed by averaging the temperatures of the particles within a specified sampling window. This process increases the precision to 2% - 10%.\r\n\r\nIn the study of the heat transport in the near wake, the velocity and temperature measurements obtained from DPIV/T are decomposed into their mean, coherent, and incoherent components using the triple decomposition. It is found that the heat from the cylinder is transported down the wake mostly by the mean heat flux and is laterally transported out of the wake by the coherent and the incoherent heat fluxes. In examining the direction of the turbulent heat flux vectors, the vectors are found not to be co-linear with the gradient of mean temperature. This misalignment implies that the gradient transport models are inappropriate for modeling the turbulent heat transport in the near wake of a circular cylinder. In examining the production of turbulence, it is found that that kinetic energy fluctuations are produced in the saddle regions (regions where the fluid is being stretched in one direction and compressed in another) while the temperature fluctuations are produced at the edges of center regions (regions where the fluid is rotating), i.e., the edges of the vortex cores.\r\n\r\nFrom the study of the heat convection from a cylinder as function of forced oscillation frequency [...] and amplitudes (A/D=0.1, 0.2), it is found that besides the previously known increase near the natural vortex shedding frequency, there also exists a large increase in the heat transfer at approximately three times this frequency for A/D=0.1. For A/D=0.2, there exist large increases at roughly two and three times the natural vortex shedding frequency. From a DPIV/T study, it is found that the wake pattern becomes synchronized with the mechanical oscillation of the cylinder at these frequencies where the heat transfer increases significantly. At the frequencies corresponding to roughly two and three times the unforced vortex shedding frequency, the wake pattern may become synchronized by processes of period doubling and tripling with respect to the cylinder oscillation period, respectively. The increase in the heat transfer rate is found to correlate with the distance at which vortices roll-up behind the cylinder. The distance is observed to decrease sharply at the frequencies corresponding to a sharp increase in the heat transfer. Therefore, the near wake is found to play a critical role in the heat transfer from the surface of a circular cylinder, and the cause of the increase in heat transfer is believed to the removal of the stagnant and low heat convecting fluid at the base of the cylinder during the roll-up of the vortices." }, { "name": "Patel, Bibhuti Bhusan", "degree": "Engineering Degree", "year": "1998", "title": "An Experimental Investigation of Wave Propagation in Fractured Brittle Material", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232004-112403", "creators": [ { "name": { "family": "Patel", "given": "Bibhuti Bhusan" }, "id": "Patel-Bibhuti-Bhusan", "display_name": "Patel, Bibhuti Bhusan" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/w1t3-1f55", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental method for visualizing and analyzing the propagation of plate stress waves in a brittle plate is developed. A procedure has been developed to cast Break-Away glass (a low molecular weight polystyrene material) plate specimens in an open mold. The specimens are loaded with short duration (200 [...]s) stress pulses on one edge by an electromagnetic stress wave generator. The propagating stress waves generate out-of-plane deformations on the specimen surface, which are observed using Twyman-Green interferometry. The fringe patterns created by the propagating stress waves are captured using a high speed camera - pulsing laser combination at 4[...]s intervals.\r\n\r\nA generalized \"Fringe Analysis Procedure\" is developed to subtract the reference interferogram from the subsequent interferograms. The \"Fringe Analysis Procedure\" employs a fringe edge detection algorithm to obtain the sharp edge lines of the fringes in an interferogram. A digitizer is used to extract points on these edge lines and assign them fringe numbers. The \"griddata\" option in the commercial software \"Matlab\" is utilized to interpolate the deformation field on to the nodes of a uniform grid. The field values at these nodes in the reference image are then subtracted from corresponding values in the subsequent images to obtain the actual deformation patterns generated by the propagating stress waves. The \"Fringe Analysis Procedure\" has eliminated the subjective element introduced by human judgment in manual fringe tracing procedures.\r\n\r\nThe developed experimental method and the image analysis technique is used to investigate the propagation of stress waves in Break-Away glass plate specimens." }, { "name": "Radovitzky, Raul A", "degree": "PhD", "year": "1998", "title": "Error estimation and adaptive meshing in strongly nonlinear dynamic problems", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-113427", "creators": [ { "name": { "family": "Radovitzky", "given": "Raul A" }, "id": "Radovitzky-R-A", "display_name": "Radovitzky, Raul A" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MF7F-YK03", "abstract": "This dissertation is concerned with the development of a general computational framework for mesh adaption such as is required in the three-dimensional lagrangian finite element simulation of strongly nonlinear, possibly dynamic, problems. It is shown that, for a very general constitutive framework, the solutions of the incremental boundary value problem obey a minimum principle, provided that the constitutive updates are formulated appropriately. This minimum principle is taken as a basis for asymptotic error estimation. In particular, we chose to monitor the error of a lower-order projection of the finite element solution. The optimal mesh size distribution then follows from a posteriori error indicators which are purely local, i. e., can be computed element-by-element.\n\nA sine qua non condition for the successful accomplishment of the kind of analysis envisioned in this work is the possibility to mesh the deforming domains of analysis. In the first section of this thesis a method is presented for mesh generation in complex geometries and general--possibly non-manifold--topologies.\n\nThe robustness and versatility of the computational framework is demonstrated with the aid of convergence studies and selected examples of application and the results contrasted with previous approaches" }, { "name": "Repetto, Eduardo A.", "degree": "PhD", "year": "1998", "title": "On the fatigue behavior of ductile F.C.C. metals", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-133649", "creators": [ { "name": { "family": "Repetto", "given": "Eduardo A." }, "id": "Repetto-E-A", "display_name": "Repetto, Eduardo A." } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/zkfb-sr87", "abstract": "A micromechanically based model for fatigue crack nucleation in ductile F.C.C. metals is developed. The theory includes a model of F.C.C. crystal-plasticity in finite deformations that takes into account the Bauschinger effect, dipole annihilation in the persistent slip bands (PSBs), with vacancy generation and PSB elongation as a byproduct, as well as coupled vacancy diffusion and the attendant surface motion due to the flux of vacancies out of the body.\r\n\r\nFinite element simulations are performed in order to establish the predictive capability of the theory. Detailed modelling of the intersection of the PSB with a free surface, enhanced by the use of remeshing and surface evolution techniques, enable the prediction of nucleation sites, life expectancy, surface profile, alternate slip between the sides of the PSB and strain localization at the grooves.\r\n\r\nIn an attempt to resolve the dislocation structures experimentally observed during cyclic loading, a theory based on the non-convexity of a pseudo-energy density is developed. Non-homogeneous minimizers are found containing variants oriented in coincidence with the dislocation walls observed experimentally. Due to the latent hardening and geometrical softening, the minimizing structures are found to consist of regions of single slip which is in accordance with the observed \"patchy slip.\"" }, { "name": "Shiels, Douglas G.", "degree": "PhD", "year": "1998", "title": "Simulation of Controlled Bluff Body Flow with a Viscous Vortex Method", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162004-133652", "creators": [ { "name": { "family": "Shiels", "given": "Douglas G." }, "id": "Shiels-Dpouglas-G", "display_name": "Shiels, Douglas G." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/49A0-VA12", "abstract": "Bluff body flows controlled in various manners are simulated with a high-resolution, gridless vortex method. Two-dimensional, unsteady, viscous simulations are utilized to illuminate the physical phenomenon underpinning certain flows of this class. Flows past a rotationally oscillating circular cylinder and flows past an elastically mounted circular cylinder are studied, providing a variety of new insights about these systems. A computational method facilitating longtime, high-resolution vortex simulations is developed whose grid-free nature enables future extension to complex geometries.\r\n\r\nThe significant fluid forces experienced by bluff bodies are of much practical concern and are induced by flowfields that are often complex. The studies in this thesis aim to contribute to the understanding of the relation between wake development and forces and how to exploit this relationship to achieve flow control. A circular cylinder undergoing rotational oscillation is known to experience a significant deviation in forces from unforced flow. Computations from Re=150-15000 verify past experimental observation of significant drag reduction for certain forcing parameters. These simulations also illuminate the mechanism which renders this control effective - a forced boundary layer instability triggering premature shedding of multipole vortex structures.\r\n\r\nNew insights were also provided by studies of flow over a model of an elastically mounted cylinder. A two-dimensional cylinder modeled as a damped oscillator can serve as an approximation to three-dimensional situations such as a cable under tension. Simulations clarified the behavior of such a two-dimensional system and, contrary to a line of classical thinking, revealed an unexpected adaptivity in wake evolution. New scaling is also suggested which better classifies these systems under certain conditions.\r\n\r\nVortex methods are well-suited for incompressible bluff body flow in many ways. However, the handling of viscous diffusion causes complications for such simulations. A relatively unexplored approach, the core expansion method, is studied, extended, and implemented in this work in order to balance accuracy with preservation of the gridless foundation of vortex methods. This viscous technique is found to enable long-time calculations that are prohibitive with other techniques while preserving a high level of accuracy." }, { "name": "Slessor, Michael David", "degree": "PhD", "year": "1998", "title": "Aspects of turbulent-shear-layer dynamics and mixing", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292005-085835", "creators": [ { "name": { "family": "Slessor", "given": "Michael David" }, "id": "Slessor-M-D", "display_name": "Slessor, Michael David" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K55F-8589", "abstract": "Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shearlayer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described.\r\n\r\nChemically-reacting and non-reacting flows were investigated, the former relying on the (H2 + NO/F2) chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of \"flip\" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows.\r\n\r\nBoth inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are \"remembered\" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, i. e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from all other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces laxge-scale entrainment and turbulent growth, but slightly enhances smallscale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.\r\n" }, { "name": "Adam, Philippe H.", "degree": "PhD", "year": "1997", "title": "Enthalpy Effects on Hypervelocity Boundary Layers", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-111636", "creators": [ { "name": { "family": "Adam", "given": "Philippe H." }, "id": "Adam-Philippe-H", "display_name": "Adam, Philippe H." } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YF0K-HK91", "abstract": "More than 50 shots with air and 35 shots with carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 5\u00b0 half-angle cone measuring approximately 1 meter in length. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer and, when applicable, the transition location.\r\n\r\nTransitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases as well. The stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. These effects do not appear when the transition location is normalized with the edge conditions. Further normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code.\r\n\r\nThe observation that the reference conditions seem more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel data are around an order of magnitude below the flight data. This is commonly attributed to the fact that disturbance levels in tunnels are high, causing the boundary layer to transition prematurely. However, when the conditions at the reference temperature are used instead, the data come within striking distance of one another although the trend with enthalpy seems to be a destabilizing one for the flight data. This difference could be due to the cone bending and blunting observed during the reentry.\r\n\r\nExperimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the noncatalytic and frozen chemistry models. The results for carbon dioxide, however, are inconclusive. This is, perhaps, because of inadequate modeling of the actual reactions. Experimentally, an anomalous yet repeatable, rise in the laminar heat transfer level can be seen at medium enthalpies in carbon dioxide boundary layers.\r\n" }, { "name": "Chea, Limdara Ong", "degree": "Engineering Degree", "year": "1997", "title": "Finite Element Simulation and Analysis of Local Stress Concentration in Polymers with a Nonlinear Viscoelastic Constitutive Model", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082008-095104", "creators": [ { "name": { "family": "Chea", "given": "Limdara Ong" }, "id": "Chea-Limdara-Ong", "display_name": "Chea, Limdara Ong" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/13SD-9N16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nGiven a nonlinear viscoelastic (NLVE) constitutive model for a polymer, this numerical study aims at simulating local stress concentrations in a boundary value problem with a corner stress singularity. A rectangular sample of Polyvinyl Acetate (PVAc)-like cross-linked polymer clamped by two metallic rigid grips and subjected to a compression and tension load is numerically simulated.\r\n\r\nA modified version of the finite element code FEAP, that incorporated a NLVE model based on the free volume theory, was used. First, the program was validated by comparing numerical and analytical results. Two simple mechanical tests (a uniaxial and a simple shear test) were performed on a Standard Linear Solid material model, using a linear viscoelastic (LVE) constitutive model. The LVE model was \r\nobtained by setting the proportionality coefficient [...] to zero in the free volume theory equations. Second, the LVE model was used on the corner singularity boundary value problem for three material models with different bulk relaxation functions K(t). The time-dependent stress field distribution was investigated using two sets of plots: the stress distribution contour plots and the stress time curves. Third, using the NLVE constitutive model, compression and tension cases were compared using the stress results (normal stress [...] and shear stress [...]). These two cases assessed the effect of the creep retardation-creep acceleration phenomena.\r\n\r\nThe shift between the beginning of the relaxation moduli was shown to play an important role. This parameter affects strongly the fluctuation pattern of the stress curves. For two different shift values, in one case, the stress response presents a 'double peak' and 'stress inversion' characteristic whereas, in the other case, it presents a 'single peak' and no 'inversion'. Another important factor was the material's compressibility. In the case of a nearly-incompressible material, the LVE and NLVE models yielded identical results; thus, the simpler LVE model is preferable.\r\n\r\nHowever, in the case of sufficient volume dilatation (or contraction), the NLVE model predicted correct characteristic responses, whereas LVE results were erroneous. This proves the necessity of using the NLVE model over the LVE model.\r\n" }, { "name": "Gonzalez, Javier Gonzalez", "degree": "Engineering Degree", "year": "1997", "title": "Full Field Study of Strain Distribution Near the Crack Tip in the Fracture of Solid Propellants Via Large Strain Digital Image Correlation and Optical Microscopy", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212004-164817", "creators": [ { "name": { "family": "Gonzalez", "given": "Javier Gonzalez" }, "id": "Gonzalez-Javier-Gonzalez", "display_name": "Gonzalez, Javier Gonzalez" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HRM1-RJ74", "abstract": "A full field method for visualizing deformation around the crack tip in a fracture process with large strains is developed. A digital image correlation program (DIC) is used to incrementally compute strains and displacements between two consecutive images of a deformation process. Values of strain and displacements for consecutive deformations are added, this way solving convergence problems in the DIC algorithm when large deformations are investigated. The method developed is used to investigate the strain distribution within 1 mm of the crack tip in a particulate composite solid (propellant) using microscopic visualization of the deformation process." }, { "name": "Gornowicz, Galen Gerald", "degree": "Engineering Degree", "year": "1997", "title": "Continuous-Field Image-Correlation Velocimetry and its Application to Unsteady Flow Over an Airfoil", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062004-141142", "creators": [ { "name": { "family": "Gornowicz", "given": "Galen Gerald" }, "id": "Gornowicz-Galen-Gerald", "display_name": "Gornowicz, Galen Gerald" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/52KD-JX10", "abstract": "Continuous-field Image Correlation Velocimetry (ICV) is an extension to the ICV technique of Tokumaru & Dimotakis (1995). The method determines the optical flow in sequences of images, and relies on a convected Lagrangian marker, e.g., a conserved scalar field, or particles, etc. The method has been applied to several simulated-flow test cases and results are presented for the error of the method, with and without noise added to the correlated test-images. The results of further tests are reported, for two laboratory flows; a NACA-0012 airfoil at high angle of attack, and a transverse jet in a coflowing stream.\r\n" }, { "name": "Hodowany, Jon", "degree": "PhD", "year": "1997", "title": "On the conversion of plastic work into heat", "advisor": "Ravichandran, Guruswami; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-074409", "creators": [ { "name": { "family": "Hodowany", "given": "Jon" }, "id": "Hodowany-J", "display_name": "Hodowany, Jon" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FENH-ZK36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe present study investigated heat evolution in metal plasticity. Specifically, experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations. The fraction of plastic work converted into heat has implications in a wide range of thermomechanical phenomena, including shear bands, dynamic fracture, ballistic penetration and high speed machining.\r\n\r\nKolsky bars, in compression and torsion, were used to determine mechanical properties at strain rates between [...] and [...]. For dynamic loading, in-situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. Specially designed infrared optics, configured in tandem with the HgCdTe detector and the Kolsky bar constituted a novel experimental configuration for determining the fraction of plastic work converted into heat, and thus, the amount of energy stored in metals. The temperature detection system was ideally suited for small temperature excursions from ambient conditions, and was sensitive to temperature changes as little as 0.5 \u00b0C. The emissivity of metals was found to increase above certain high levels of plastic strain due to changes in surface roughness, which can affect the validity of temperature calibration. A technique of sample recovery, rough surface layer removal, and reloading was employed to obtain large plastic strains in the Kolsky bar. A Materials Testing System (MTS) servo-hydraulic load frame was used to measure mechanical properties at lower strain rates, [...] to [...] When temperature measurement was needed within this range of strain rates, a fast E-type thin wire thermocouple, with a time response of 1 ms, was employed.\r\n\r\nThe fraction of plastic work converted into heat, [beta], was treated as a constitutive function of strain and strain rate in the heat conduction equation. 2024 aluminum alloy and commercially pure [alpha]-titanium were the metal systems used in the current study to determine the functional dependence of [beta] on strain and strain rate. The T351, T4 and T6 tempers of 2024 aluminum did not exhibit strain rate dependence in flow stress over the entire range of strain rates tested. At low levels of plastic strain, all tempers of 2024 aluminum stored more than 50% of the input plastic work. At some level of plastic strain, depending on temper, 2024 aluminum could no longer store plastic work. After this point, [beta] increased to a value near 1.0 and remained nearly constant during subsequent plastic deformation. When averaged over all strains, [beta] was 0.85-0.95 depending on the particular heat treatment. The fraction of plastic work dissipated as heat was not found to be sensitive to strain rate over a wide range of strain rates. In contrast, the flow stress of [alpha]-titanium was strongly dependent on strain rate. The initial flow stress increased by more than 15% between strain rates of [...] and [...]. In addition, the strain hardening was also observed to be rate dependent. For fixed plastic strain, the tangent modulus increased as strain rate increased. Titanium dissipated a greater proportion of energy as heat at low strains than all tempers of 2024 aluminum. The ability to store energy in titanium decreased with increasing plastic strain. For plastic strains above 0.3, titanium dissipated nearly all input plastic work as heat. The proportion of energy dissipated as heat at fixed strain increased as strain rate increased.\r\n" }, { "name": "Krok, James Christopher", "degree": "PhD", "year": "1997", "title": "Jet Initiation of Deflagration and Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-181337", "creators": [ { "name": { "family": "Krok", "given": "James Christopher" }, "id": "Krok-James-Christopher", "display_name": "Krok, James Christopher" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kirschvink", "given": "Joseph L." }, "id": "Kirschvink-J-L", "orcid": "0000-0001-9486-6689", "role": "member", "display_name": "Kirschvink, Joseph L." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PSTR-T717", "abstract": "We have constructed a facility for the study of jet-initiated deflagration and detonation in hydrogen-air-steam mixtures. The facility is built around two pressure vessels. Mixtures of hydrogen, oxygen and nitrogen are spark-ignited in the driver vessel, generating a hot mixture of combustion products. The pressure rise ruptures a diaphragm, venting the products into the receiver vessel through nozzles of 12.7-92 mm diameter. The receiver is filled with hydrogen-air and hydrogen-oxygen mixtures diluted with either nitrogen or steam.
\r\n\r\nThe deflagration tests studied the lean and maximum-dilution limits of hydrogen-air mixtures ignited by a hydrogen-steam jet. The lean limit of 6% hydrogen was comparable to other studies. The maximum dilution limit for steam was 60%. This is higher than the limit found in spark/glow plug ignition experiments. Shock oscillations in the receiver increased with nozzle size.
\r\n\r\nFurther tests studied the initiation of detonation in both hydrogen-air and stoichiometric hydrogen-oxygen-diluent mixtures. In terms of jet diameter, D, and receiver detonation cell size, \u03bb, we found initiation limits of 2 < D/\u03bb < 7, where other experiments required a D/\u03bb of 11 or more. We propose that the D/\u03bb model does not adequately characterize jet initiation, as it does not reflect the conditions in the driver.
\r\n\r\nThe tests indicated that shock focusing plays an important role, promoting strong secondary explosions with or without prompt initiation of detonation. Mixtures with steam dilution were prone to DDT near the detonation limit, as the slower flame speed allows shock reflection and pressurization to occur before the reactants are consumed. Tests with nitrogen dilution had no DDT regime. Because of DDT and shock focusing, peak pressures were highest in mixtures that were slightly less sensitive than the detonation threshold. Schlieren movies confirmed the formation of a detonation near the nozzle exit.
" }, { "name": "Lu, Hongbing", "degree": "PhD", "year": "1997", "title": "Nonlinear thermo-mechanical behavior of polymers under multiaxial loading", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072003-103136", "creators": [ { "name": { "family": "Lu", "given": "Hongbing" }, "id": "Lu-H", "display_name": "Lu, Hongbing" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SH42-W153", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [?]. Abstract is included in .pdf document.\n\nIn order to better understand phenomena related to \"yield-like\" behavior of polymers, the nonlinear thermo-mechanical behavior of Polymethyl Methacrylate (PMMA) under combined axial (tension, compression) and shear stress states (torsion) is investigated on thin walled cylindrical specimens at temperatures between 22[degrees] and 100[degrees]C. A non-contact measurement technique based on digital image correlation method is developed to determine the surface deformations on curved cylindrical specimens at various temperatures, including temperatures close to the glass transition when the specimens become soft. The study indicates that in contrast to tile mutual independence of shear and dilatational response under conditions appropriate for linearized viscoelasticity, one observes an increasingly strong coupling between all deformation or stress invariants as assessed in creep experiments for strains in excess of' 0.4%. While shear stresses alone elicit nonlinear response in creep (rates) as \"intrinsically\" nonlinear shear response, the superposition of small positive dilatation accelerates shear deformations while negative dilatation retards it in quantitative agreement with free volume arguments. Passing below the glass transition still produces greater creep acceleration from positive dilatation than from a decrease in specific volume, but the dominance of the intrinsic shear nonlinearity vis-a-vis the dilatational ilifluence increases below [...] as the temperature drops. A constitutive model based oil free volume consideration is modified from the models proposed by Losi and Knauss (1992). Comparison of experimental results with model prediction indicates a good qualitative agreement, and reasonably good quantitative agreement." }, { "name": "Mackey, Ryan Murrill Ezekiel", "degree": "Engineering Degree", "year": "1997", "title": "Soap Film Thickness Imaging by Infrared Methods", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-01182008-085524", "creators": [ { "name": { "family": "Mackey", "given": "Ryan Murrill Ezekiel" }, "id": "Mackey-Ryan-Murrill-Ezekiel", "display_name": "Mackey, Ryan Murrill Ezekiel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7bv0-m741", "abstract": "A new method of studying soap film flows is introduced and discussed from several viewpoints. Using a commercial infrared camera and a cold background as an infrared light source, one can recover nonintrusively a measurement of the film thickness distribution. Once the thickness is known it is easy to compute the two-dimensional pressure in the film, allowing one to compute other film properties as well.
\r\n\r\nBlackbody and infrared detector theory are covered in brief and a simple theory of operation is introduced to explain the connection between emissivity and thickness. This theory is demonstrated to behave similarly to the physical system, predicting detected temperature values as a function of thickness of the same approximate magnitude as observed, but is too simple to provide a perfect match. An empirical calibration routine is demonstrated allowing one to calculate the film thickness to a high degree of precision.
\r\n\r\nThe infrared method is applied to a number of familiar test problems as a demonstration. A gravity driven soap film tunnel has been constructed, and infrared images of the film surface are provided for unobstructed flow, separated flow past a cylinder held at one wall, and turbulent flow through a grid. These images are presented in raw and processed formats and the phenomena observed are discussed.
" }, { "name": "Noca, Flavio", "degree": "PhD", "year": "1997", "title": "On the Evaluation of Time-Dependent Fluid-Dynamic Forces on Bluff Bodies", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102005-132659", "creators": [ { "name": { "family": "Noca", "given": "Flavio" }, "id": "Noca-Flavio", "display_name": "Noca, Flavio" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K2Z0-9016", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe present some exact expressions for the evaluation of time-dependent forces on a body in an incompressible and viscous cross-flow which only require the knowledge of the velocity field (and its derivatives) in a finite and arbitrarily chosen region enclosing the body.\r\n\r\nGiven a control volume V with external surface S which encloses an arbitrary body, the fluid-dynamic force F on the body can be evaluated from one of the following three expressions (in abbreviated form):\r\n\r\nF = [...] + body motion terms,\r\n\r\nF = [...] + body motion terms,\r\n\r\nF = no volume integral terms + [...] + body motion terms,\r\n \r\nwhere N is the space dimension, u is the flow velocity, [...] is the vorticity, x is the position vector, and the tensors [...], [...], [...] depend only on the velocity field u and its (spatial and temporal) derivatives.\r\n\r\nThe first equation is already known for either simply connected domains or inviscid flows. We re-derive it here for viscous flows in doubly connected domains (i.e. domains which include a body). We then obtain the second and third equation through a simple algebraic manipulation of the first equation.\r\n\r\nThese expressions are particularly useful for experimental techniques like Digital particle Image Velocimetry (DPIV) which provide time sequences of 2D velocity fields but not pressure fields.\r\n\r\nThey are tested experimentally with DPIV on two-dimensional, low Reynolds number circular cylinder flows. Both steady and unsteady motions are studied." }, { "name": "Papalexandris, Miltiadis Vassilios", "degree": "PhD", "year": "1997", "title": "Unsplit Numerical Schemes for Hyperbolic Systems of Conservation Laws with Source Terms", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-161139", "creators": [ { "name": { "family": "Papalexandris", "given": "Miltiadis Vassilios" }, "id": "Papalexandris-Miltiadis-Vassilios", "display_name": "Papalexandris, Miltiadis Vassilios" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW7S-AR36", "abstract": "In this thesis, a new method for the design of unsplit numerical schemes for hyperbolic systems of conservation laws with source terms is developed. Appropriate curves in space-time are introduced, along which the conservation equations decouple to the characteristic equations of the corresponding one-dimensional homogeneous system. The local geometry of these curves depends on the source terms and the spatial derivatives of the solution vector. Numerical integration of the characteristic equations is performed on these curves.\r\n\r\nIn the first chapter, a scalar conservation law with a stiff, nonlinear source term is studied using the proposed unsplit scheme. Various tests are made, and the results are compared with the ones obtained by conventional schemes. The effect of the stiffness of the source term is also examined.\r\n\r\nIn the second chapter, the scheme is extended to the one-dimensional, unsteady Euler equations for compressible, chemically-reacting flows. A numerical study of unstable detonations is performed. Detonations in the regime of low overdrive factors are also studied. The numerical simulations verify that the dynamics of the flow-field exhibit chaotic behavior in this regime.\r\n\r\nThe third chapter deals with the development and implementation of the unsplit scheme, for the two-dimensional, reactive Euler equations. In systems with more than two independent variables there are one-parameter families of curves, forming manifolds in space-time, along which the one-dimensional characteristic equations hold. The local geometry of these manifolds and their position relative to the classical characteristic rays are studied. These manifolds might be space-like or time-like, depending on the local flow gradients and the source terms.\r\n\r\nIn the fourth chapter a numerical study of two-dimensional detonations in performed. These flows are intrinsically unstable and produce very complicated patterns, such as cellular structures and vortex sheets. The proposed scheme appears to be capable of capturing many of the the important details of the flow-fields. Unlike traditional schemes, no explicit artificial-viscosity mechanisms need to be used with the proposed scheme." }, { "name": "Prochazka, Aurelius", "degree": "PhD", "year": "1997", "title": "Stability and structure of stretched vortices", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-091416", "creators": [ { "name": { "family": "Prochazka", "given": "Aurelius" }, "id": "Prochazka-A", "display_name": "Prochazka, Aurelius" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Grether", "given": "David M." }, "id": "Grether-D-M", "role": "member", "display_name": "Grether, David M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/sc0x-1g40", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nWe investigate, numerically and analytically, the structure and stability of steady and quasi-steady solutions of the Navier-Stokes equations corresponding to steady stretched vortices embedded in a uniform nonsymmetric straining field, [...], [...], one principal axis of extensional strain of which is aligned with the vorticity. These are known as nonsymmetric Burgers vortices studied first by Robinson and Saffman (1984). We consider vortex Reynolds numbers [...] where [...] is the vortex circulation and [...] the kinematic vorticity, in the range [...], and a broad range of strain ratios [...] including [...], and in some cases [...]. A pseudo-spectral method is used to obtain numerical solutions corresponding to steady vortex states over our whole ([...] parameter space including [...], where arguments proposed by Moffatt, Kida, and Ohkitani (1994) suggest the nonexistence of steady solutions. When [...] and [...], we find an accurate asymptotic form for the vorticity in a region [...], giving, in some cases, near machine-precision agreement with our numerical solutions. This suggests the existence of an extended region where the exponentially small vorticity is confined to a near cat's-eye shaped region of the almost two-dimensional flow, and takes a constant value nearly equal to [...] on bounding streamlines. This allows an estimate of the leakage rate of circulation to infinity as [...] = [...] with corresponding exponentially slow decay of the vortex when [...]. This leakage rate differs substantially from that estimated by Moffatt, Kida, and Ohkitani. The normal-mode linear stability of the axisymmetric Burgers vortex [...] to two-dimensional disturbances is calculated in detail and the vortex is found to be stable at all Reynolds numbers. An iterative technique based on the Power method is used to estimate the largest eigenvalues for the nonsymmetric case [...]. Stability is found for [...], and a neutrally convective mode of instability is found and analyzed analytically for [...]. Our general conclusion is that the generalized nonsymmetric Burgers vortex is unconditionally stable to two-dimensional disturbances for all [...], and that the vortex will tend to move with the background strain when [...], but maintain its structure which will change only through exponentially slow leakage of vorticity, indicating extreme robustness in this case.\n" }, { "name": "Warncke, Amy E.", "degree": "PhD", "year": "1997", "title": "The Effects of Surfactants on Free-Surface Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-092233", "creators": [ { "name": { "family": "Warncke", "given": "Amy E." }, "id": "Warncke-Amy-E", "display_name": "Warncke, Amy E." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1xg2-yy62", "abstract": "This experimental investigation into the nature of free surface flows is to study the effects of surfactants on the boundary condition at the free surface and the resulting flow field. In particular, the flow field associated with a stationary Reynolds ridge was investigated as well as the wake behind a surface-piercing cylinder, where experimental techniques such as Digital Particle Image Velocimetry and a new surface slope measurement technique were utilized.\r\n\r\nResults show a large change in the flow field in the free-surface vicinity depending on the presence of surface tension gradients and thus shear stresses at the free surface. In particular, the boundary layer beneath a Reynolds ridge was measured and it is shown that the primary source of vorticity at the free surface can be attributed to the free surface deceleration at the ridge. Also, in the wake of the cylinder, depending on the surface condition, the connection of the shedding vortex filaments was found to be greatly altered with the propensity of surface tension gradients to redirect the vorticity near the free surface to that of the surface-parallel component. Thus it is shown that surfactants can dramatically alter the flow field due to the change in the free-surface boundary condition and resulting vorticity generation and conversion in the vicinity of the free surface." }, { "name": "Burnley, Victor Scott", "degree": "PhD", "year": "1996", "title": "Nonlinear Combustion Instabilities and Stochastic Sources", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012005-140017", "creators": [ { "name": { "family": "Burnley", "given": "Victor Scott" }, "id": "Burnley-Victor-Scott", "display_name": "Burnley, Victor Scott" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Levine", "given": "Jay" }, "id": "Levine-J", "role": "member", "display_name": "Levine, Jay" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/013z-q287", "abstract": "An investigation of combustion instabilities was conducted using an approximate analysis which allows any relevant physical processes to be included. The resulting system of coupled nonlinear oscillator equations was studied using the methods of dynamical systems theory. Previous investigations have further simplified the system using the method of time-averaging and truncation to a small number of modes. We have investigated the consequences of using these additional approximations, a case which had not been addressed completely in the literature. It was determined that application of the method of time-averaging introduces a stability boundary which limits the range in which the averaged equations are valid.
\r\n\r\nTransverse oscillations in a cylindrical chamber were also treated. It was established that in addition to its role in energy transfer between modes, nonlinear gasdynamics also provides a means of shifting the frequencies of oscillations to integral multiples of the fundamental. This additional role can reduce the efficiency of energy transfer, thus increasing the acoustic amplitudes. An example of a low amplitude transverse oscillation was produced suggesting a means by which the amplitudes of transverse modes, as well as nonintegral longitudinal modes, may be reduced.
\r\n\r\nThe coupling between combustion processes and acoustic oscillations was studied as a possible explanation of the phenomenon known as triggering. Using several ad hoc models, the effects of nonlinear pressure coupling and velocity coupling on the behavior of the system were investigated. Substantial regions of possible triggering were produced when using a model of velocity coupling with a threshold, but only if nonlinear gas dynamics was also included.
\r\n\r\nThe interaction between combustion noise and acoustic instabilities has received relatively little attention. The sources of noise in a combustion chamber are associated with vorticity and entropy waves. By including these contributions in the approximate analysis, the general forms of the stochastic excitations were obtained. Subsequently, the efects of these excitations on the amplitudes of acoustic modes were studied. When only nonlinear gasdynamics was included, no cases of bimodal probability density functions, characteristic of triggering, were found. However, when the model of velocity coupling with a threshold is added, bimodal probability densities can occur.
" }, { "name": "Cates, Joseph Eugene", "degree": "PhD", "year": "1996", "title": "Studies of shock wave focusing using geometrical shock dynamics", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-142406", "creators": [ { "name": { "family": "Cates", "given": "Joseph Eugene" }, "id": "Cates-J-E", "display_name": "Cates, Joseph Eugene" } ], "advisors": [], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bfhf-3w47", "abstract": "A finite-difference numerical method for geometrical shock dynamics has been developed, based on the analogy between the equations and the supersonic potential equation. The method has proven to be a valuable tool for analyzing the complex nonlinear processes that occur in shock focusing. The approximate shock dynamics theory is able to capture the effects of initial Mach number and aperture angle on the focal region. The numerical results duplicate the strong, moderate, and weak shock behaviors observed in experiments, with good agreement for focal pressure and triple-point path. The primary error arises due to the inability of shock dynamics to allow regular reflection along the centerline. Adequate resolution of the focal region proves to be particularly important to properly judge the accuracy of the shock dynamics solution. The appropriate shock dynamics equations are developed for the case of shock propagation into a nonuniform media for a general equation of state with nonuniform freestream velocity. The modification of the numerical method to this more general problem is straightforward. The complete shock dynamics equations are derived for both perfect gas and water using the modified Tait equation. The results for propagation of a planar shock over cylindrical gas inhomogeneities shows excellent agreement with experimental results.\n\nThe propagation of sonic booms through the atmosphere provides examples of all major types of weak shock behavior. The extensive seismic network in Southern California, consisting of over two hundred sites covering over 50,000 square kilometers, is used to map primary and secondary sonic boom carpets. The results show sonic boom ground exposure under the real atmosphere is much larger than previously expected.\n" }, { "name": "Catrakis, Haris J.", "degree": "PhD", "year": "1996", "title": "Mixing and the Geometry of Isosurfaces in Turbulent Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312005-152819", "creators": [ { "name": { "family": "Catrakis", "given": "Haris J." }, "id": "Catrakis-Haris-J", "display_name": "Catrakis, Haris J." } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GPS6-DW08", "abstract": "Experiments have been conducted to investigate mixing and the geometry of scalar isosurfaces in turbulent jets. Specifically, images of the jet-fluid concentration in the far-field of round, liquid-phase, turbulent jets have been recorded at high resolution and signal-to-noise ratio using laser-induced-fluorescence digital-imaging techniques, in the Reynolds number range 4.5 x 10\u00b3 \u2264 Re \u2264 18 x 10\u00b3. Analysis of these data indicates that this Reynolds-number range spans a mixing transition in the far field of turbulent jets. This is manifested in the probability-density function of the scalar field, as well as in other scalar-field and scalar-isosurface measures. Classical as well as fractal measures of the isosurfaces have been computed, from small to large spatial scales, and are found to be functions of both scalar threshold and Reynolds number. The coverage of level sets of jet-fluid concentration in the two-dimensional images is found to possess a scale-dependent-fractal dimension that increases continuously with increasing scale, from near unity, at the smallest scales, to 2, at the largest scales. The geometry of the scalar isosurfaces is, therefore, more complex than power-law fractal, exhibiting an increasing complexity with increasing scale. This behavior necessitates a scale-dependent generalization of power-law-fractal geometry. A connection between scale-dependent-fractal geometry and the distribution of scales is established and used to compute the distribution of spatial scales in the flow. A lognormal model of scales is proposed. The data also indicate a lognormal distribution of size of the isoscalar islands and lakes, and a powerlaw distribution of shape complexity, with values of the latter that increase with increasing size.
" }, { "name": "Howard, Danny Dwayne", "degree": "PhD", "year": "1996", "title": "Part I. Mechanisms of injury associated with extracorporeal shock wave lithotripsy; Part II. Exsolution of volatiles", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-083544", "creators": [ { "name": { "family": "Howard", "given": "Danny Dwayne" }, "id": "Howard-D-D", "display_name": "Howard, Danny Dwayne" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/995X-8517", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nPart I - Shock waves are focused in extracorporeal shock wave lithotripsy (ESWL) machines to strengths sufficient to fracture kidney stones. Substantial side effects-most of them acute-have resulted from this procedure, including injury to soft tissue. The focusing of shock waves through various layers of tissue is a complex process which stimulates many bio-mechano-chemical responses.\n\nThis thesis presents results of an in vitro study of the initial mechanical stimulus. Planar nitrocellulose membranes of order 10 um thick were used as models of thin tissue structures. Two modes of failure were recorded: Failure due to cavitation collapsing on or near the membranes, and failure induced by altering the structure of shock waves. Tests were done in water at and around F2 to characterize the extent of cavitation damage, and was found to be confined within the focal region, 1.2 cm along the axis of focus.\n\nScattering media were used to simulate the effects of acoustic nonuniformity of tissue and to alter the structure of focusing shock waves. 40 um diameter (average) hollow glass spheres were added to ethylene glycol, glycerine and castor oil to vary the properties of the scattering media. Multiple layer samples of various types of phantom tissue were tested in degassed castor oil to gauge the validity of the scattering media. The scattering media and tissue samples increased the rise time decreased strain rate in a similar fashion. Membranes were damaged by the decreased strain rate and accumulated effects of the altered structure: After about 20 or so shocks immersed in the scattering media and after about 100 shocks behind the tissue samples. The mode of failure was tearing with multiple tears in some cases from about .1 cm to about 3 cm depending of the number of shocks and membrane thickness.\n\nPart II - This work examines the exsolution of volatiles-carbon dioxide from water-in a cylindrical test cell under different pressure conditions. Water was supersaturated with carbon dioxide under various pressures (620 to 1062 kPa), and depressurized rapidly to investigate how carbon dioxide is undissolved, exsolution, and its effects on the surrounding environment. Cavities grow as a result of convective diffusion: They move before depleting carbon dioxide in a given region. The radius of a cavity in this environment grows at a faster rate [...] than that of a cavity at rest [...]. Bubble growth rates were inferred by measuring the bulk liquid using high speed motion pictures. Water in the test-cell is accelerated as a result of buoyancy induced by cavity growth. Cavities are elliptical in shape and grow until mutual interaction causes them to fragment. Accelerations range from 10 to 100 g were measured with velocities ranging from 7 to 13 m/s.\n" }, { "name": "Kuzo, David Matthew", "degree": "PhD", "year": "1996", "title": "An experimental study of the turbulent transverse jet", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232005-160358", "creators": [ { "name": { "family": "Kuzo", "given": "David Matthew" }, "id": "Kuzo-D-M", "display_name": "Kuzo, David Matthew" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xa4v-qb95", "abstract": "An experimental study that examines the mean flow properties of the turbulent transverse jet using Digital Particle Image Velocimetry (DPIV) is reported.
\r\n\r\nThis study examines various jet flows over a range of Reynolds numbers based upon jet velocity and diameter. Within this range it is documented that mean flow fields, identified as alternate mean flow states, other than the symmetric vortex pair exist. These alternate flow states are characterized by unsteadiness, asymmetry, and multiple streamwise vortices. Flow visualization shows that these alternate flow states are formed during initial jet roll-up, and persist far downstream without developing into the (expected) vortex pair. A map of the domain of existence, in velocity ratio - Reynolds number space, of these alternate states is provided, and a discussion of the underlying physics is included.
\r\n\r\nWith this new understanding, selected symmetric jet flows at velocity ratios of 5, 10, and 20 are generated and studied using DPIV. The mean flow is quantified through measurements of vortex circulation, size, and impulse, and the relationship of these properties to the (initial) jet momentum flux is examined.
" }, { "name": "Moore, Cyrille Dennis", "degree": "PhD", "year": "1996", "title": "Experiments in axisymmetric supersonic jets", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-151911", "creators": [ { "name": { "family": "Moore", "given": "Cyrille Dennis" }, "id": "Moore-C-D", "display_name": "Moore, Cyrille Dennis" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1g15-nz55", "abstract": "An experimental study of the effects of exit Mach number and density ratio on the development of axisymmetric jets is described in this thesis. Jet exit Mach numbers of 1.41, 2.0, and 3.0, were studied for jets of helium, argon, and nitrogen. The jets exit into a gas at rest (velocity ratio = 0), in order to better isolate the effects of compressibility and density ratio. Density ratios vary from 0.23 to 5.5.\n\nIn order to generate shock free-jets, unique nozzles were designed and constructed for each gas and Mach number combination. A plating method for the construction of the nozzles was developed to ensure high-accuracy and a good surface finish at a cost significantly less than direct-machining techniques.\n\nThe spreading rate of the jet for several downstream locations is measured with a pitot probe. Centerline data are used to characterise the length of the potential core of the jet, which correlates well with the relative spreading rates. Limited frequency data is obtained through the use of piezo-resistive pressure probes. This method is promising for flows that are not conducive to hot-wire probes.\n\nSpark shadography is used to visualize both the mean and instantaneous flow, with the minimum spark time being 20 nanoseconds. The convection velocity of large-scale disturbances is estimated from the visible Mach-type acoustic waves emanating from the jet.\n\nFor a wide range of jet Mach and Reynolds numbers, the convection velocity of the large scale disturbances in the potential core region of the jet is approximately 0.8 times the jet velocity, the approximate velocity of the first helical instability mode of the jet.\n\nThe main objectives of the present work were to investigate the effects of compressibility and density on the initial development of the axisymmetric jet. Although the data are not sufficient to determine if the convective Mach number concept used in 2-d shear layer research will work in the case of an axisymmetric jet, it is clear that the axisymmetric data do not collapse onto the 2-d curve. However, the density ratio scaling used for the 2-d shear layer appears to work well for the axisymmetric jet, based on the available data.\n\nThe data appear to indicate that the initial development of the jet is dominated by instability modes of the jet as a whole, rather than the shear layers.\n\nOne anomaly noted was that there were long period variations in the centerline total pressure, with times on the order of 3000 jet time scales. The fluctuations did not appear to be experimental artifacts." }, { "name": "Moore, Kevin C.", "degree": "PhD", "year": "1996", "title": "Experiments on the interaction of a coflowing light gas jet with a weak oblique shock wave", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072013-095344022", "creators": [ { "name": { "family": "Moore", "given": "Kevin C." }, "id": "Moore-K-C", "display_name": "Moore, Kevin C." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/qgz4-en52", "abstract": "Results of experiments performed in the GALCIT Supersonic Wind Tunnel involving\r\na coflowing helium jet in a Mach 2.4 air freestream are presented. Measurements\r\nof the undisturbed jet arc compared with those made after the jet interacts with\r\ndifferent weak oblique shock waves. Data collected using stagnation temperature\r\nand pitot pressure probes is used to form time averaged cross sectional views of the\r\nflow for different downstream stations. These views show that the baroclinic vorticity\r\ngenerated when the jet passes through the shock wave causes the jet to develop\r\ninto a pair of counter-rotating vortices whose axes are aligned with the flow. Previously\r\nproposed models for the circulation deposited on the jet-freestream interface\r\nand characteristic time of an analogous unsteady two-dimensional flow are adapted\r\nto this flow. Comparison of the jet cross sections for corresponding characteristic\r\ntimes shows agreement with experiments and analysis previously performed on the\r\nuustcady two-dimensional analogy. Shear between the jet and the freestream is not\r\nseen to materially affect the development of the flow, but the development of the\r\njet is seen to strongly depend on the strength of the oblique shock. Scattering of\r\na laser light sheet off of ice crystals present in the air but absent from the helium\r\nprovides time-resolved flow visualization pictures which show large departures from\r\nthe mean as the flow moves downstream. This demonstrates the need to consider\r\nturbulence effects which were not considered in previous two-dimensional studies.\r\nThey also show that the presence of the shock wave increases the apparent randomness\r\nof the flow as well as the spreading rate of the jet, likely increasing mixing.\r\nA jet cross section extracted from the average of several Rayleigh scattered images\r\nagrees well with the general size and shape of the jet cross section taken from the\r\ncorresponding time averaged temperature data. The design and construction of the\r\nactive feedback control loop in a gas blending system used to independently control\r\nthe mass flowrate and temperature of the jet is described.\r\n" }, { "name": "Valluri, Siddhartha", "degree": "PhD", "year": "1996", "title": "Bluff Body Flows in the Presence of a Free Surface", "advisor": "Roshko, Anatol; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082007-075443", "creators": [ { "name": { "family": "Valluri", "given": "Siddhartha" }, "id": "Valluri-Siddhartha", "display_name": "Valluri, Siddhartha" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2wbk-9k81", "abstract": "An experimental study is performed in a water tunnel (Re = 40,000 to Re = 60,000) to study the interaction between the wake of a circular disk and the free surface. The deformation of the free surface is correlated with the behavior of the wake by utilizing surface pictures, wake flow visualization, drag measurement and Digital Particle Image Velocimetry techniques. It is observed that the wake can exist in two modes with different stabilities. The flow can switch between these two modes and the switching process exhibits hysteresis. The topological differences between these modes and their relation to the observed surface patterns are discussed. The changes in the wake are reflected by an increase in Cd which reaches a maximum value when the upper edge of the disk is 0.125 diameters from the surface. Comparison is also made with a disk approaching a solid boundary." }, { "name": "Breton, Fabienne Anne", "degree": "Engineering Degree", "year": "1995", "title": "A large deformation analysis of plates or membranes for the determination of Young's modulus and Poisson's ratio", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292007-093444", "creators": [ { "name": { "family": "Breton", "given": "Fabienne Anne" }, "id": "Breton-F-A", "display_name": "Breton, Fabienne Anne" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0c9r-ve54", "abstract": "An analytical method for determining Young's modulus and the Poisson's ratio of thin films is considered; the method is based on the load-deflection behavior of a rectangular membrane of finite aspect ratio n = b/a subjected to uniform pressure (c.f. figure 0.1). Following numerical analysis, previously published model results are shown to be inaccurate, especially for aspect ratios greater than 1.5.\r\n\r\nAn improved model description decomposes the displacement field into two parts: following the Timoshenko formulation, the deflection is assumed to be sinusoidal near the edges, but for aspect ratios larger than unity the central portion parallel to the longer sides is assumed to bear two-dimensional character (the displacement field is independent of the coordinate parallel to the longer side).\r\n\r\nUsing energy methods and including the effects of the residual stress, the load-deflection relationship for a rectangular membrane of arbitrary aspect ratio n = b/a, under uniform pressure, is obtained.\r\n\r\nExperiments are simulated by using numerical analysis. By comparing the numerical data of load-versus-deflection behavior to that for the energy based approximation, Young's modulus can be determined to within 2% of the value specified for the numerical analysis, provided that Poisson's ratio, v, is known. If the latter is not the case, the error increases to 14%, if the full range of Poisson's ratio (0 <= v <= 0.5) is admitted. Narrowing of the uncertainty through bounding Poisson's ratio is demonstrated. This result constitutes a significant improvement over the previous models which were shown to elicit errors on the order of 45%.\r\n\r\nA method to evaluate Poisson's ratio is also proposed. Making use of the load-deflection relationship for a rectangular plate of any aspect ratio, Poisson's ratio may be evaluated through the comparison of the load-deflection behavior of membranes of different aspect ratios. This method was found to be valid for materials with Poisson's ratio in the range {0.25, 0.5}.\r\n\r\nSince it is generally difficult to obtain homogeneous films, this study was extended to considerations for bimaterial plates in terms of an effective thickness that is well defined. A layer of the material under examination is deposited onto a well-characterized substrate so that a sandwich film results. Young's modulus of the material can then be deduced from the load-deflection data of the bimaterial film." }, { "name": "Chen, Weinong", "degree": "PhD", "year": "1995", "title": "Dynamic failure behavior of ceramics under multiaxial compression", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-101839", "creators": [ { "name": { "family": "Chen", "given": "Weinong" }, "id": "Chen-Weinong", "display_name": "Chen, Weinong" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0NNE-JD20", "abstract": "An experimental technique has been developed that is capable of (1) dynamically loading the specimen in multiaxial compression; (2) controlling the stress state in the specimen in the range from uniaxial stress to uniaxial strain; and (3) allowing the recovery of the sample after loaded by a single, well defined pulse for the characterization of the failure mode. In this technique, cylindrical ceramic specimens were loaded in the axial direction using a split Hopkinson pressure bar modified to apply a single loading pulse, and were confined laterally either by shrink fit sleeves, or by eletro-magnetic force.\r\n\r\nQuasi-static and dynamic multiaxial compression experiments have been performed on a machinable glass ceramic, Macor, and a monolithic engineering ceramic, sintered aluminum nitride (A1N). The cylindrical ceramic specimens were confned laterally by shrink fit sleeves: the amount of confining pressure (0-230 MPa) was varied by using different sleeve materials. The quasi-static axial load was applied by a hydraulic driven Material Test System (MTS), whereas the dynamic axial load was provided by a modified split Hopkinson (Kolsky) pressure bar (SHPB). Under both quasi-static and dynamic loading conditions, the experimental results for both materials showed that the failure mode changed from fragmentation by axial splitting under conditions of uniaxial stress (without lateral confinement) to localized deformation on faults under moderate lateral confinement. The fault initiation process was studied experimentally in detail. Based on the experimental results, a compressive brittle failure process was summarized. A transition from brittle to ductile behavior was observed in Macor under high confinement pressure which was achieved using a second sleeve around the inner sleeve. The compressive failure strengths of both materials increased with increasing confinement pressure under both quasi-static and dynamic loading conditions. The highest dynamic compressive strengths of Macor and A1N measured in the experiments were 1.35 GPa and 5.40 GPa, respectively, whereas their quasi-static compressive strength were measured to be 0.43 GPa and 2.5 GPa, respectively.\r\n\r\nBased on the experimental results on A1N together with available data in the literature, a failure/flow criterion was developed for ceramic materials under multiaxial loading. A Mohr-Coulomb criterion and an improved Johnson-Holmquist model were found to fit the experimental data for brittle failure, whereas the materials exhibited pressure insensitive plastic flow at high pressures. Observations made in other types of dynamic experiments (e.g., shock wave loading) were rationalized based on the postulated failure mechanisms and the possibility of plastic flow beyond the Hugoniot elastic limit (HEL). The effect of various material properties on the failure behavior was investigated using the proposed failure criterion. The applicability of the present model to a range of ceramics was also explored and the limitations of the model were outlined.\r\n" }, { "name": "Cummings, Eric Bryant", "degree": "PhD", "year": "1995", "title": "Laser-Induced Thermal Ccoustics", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182007-085047", "creators": [ { "name": { "family": "Cummings", "given": "Eric Bryant" }, "id": "Cummings-Eric-Bryant", "display_name": "Cummings, Eric Bryant" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/p7mb-d967", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLaser-induced thermal acoustics (LITA) is a new technique for remote nonintrusive measurement of thermophysical gas properties. LITA involves forming, via opto-acoustic effects, grating-shaped perturbations of gas properties using intersecting beams from a short-pulse laser. A third beam scatters coherently into a signal beam off the perturbation grating via acousto-optical effects. The evolution of the gas perturbations modulates the scattered signal beam. Accurate values of the sound speed, transport properties, and composition of the gas can be extracted by analyzing the signal beam.\r\n\r\nAn analytical expression for the spectrum, absolute magnitude, and time history of the LITA signal is derived. The optoacoustic effects of thermalization and electrostriction are treated. Finite beam-diameter, beam-duration, and thermalization-rate effects are included in the analysis. The expression accurately models experimental signals over a wide range of gas conditions.\r\n\r\nExperimental tests using LITA have been conducted on pure and [...]-seeded air and helium at pressures ranging from ~0.1 kPa-14 MPa. Carbon dioxide has been explored near its liquid-vapor critical point. Accuracies of 0.1% in sound speed measurements have been achieved in these tests. Accuracies of ~1% have been achieved in measurements of thermal diffusivity, although beam misalignment effects have typically degraded this accuracy by a factor of ~10-20. Using LITA, susceptibility spectra have been taken of approximately a femtogram of [...]. The effects of fluid motion and turbulence have been explored. LITA velocimetry has been demonstrated, in which the Doppler shift of light scattered from a flowing fluid is measured. LITA velocimetry requires no particle seeding, has a coherent signal beam, and can be applied to pulsed flows. LITA has also been applied to measure single-shot [...] or \"Rayleigh scattering\" spectra of a gas using a technique of wavelength-division multiplexing, called multiplex LITA. The LITA apparatus used in these tests costs about one-tenth that of many conventional laser diagnostics. Narrowband LITA measurements of the sound speed and transport properties and multiplex LITA measurements of the spectral properties of gases may be taken in a single laser shot.\r\n" }, { "name": "Min, Inki A.", "degree": "PhD", "year": "1995", "title": "Transport, stirring and mixing in two-dimensional vortex flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182007-132306", "creators": [ { "name": { "family": "Min", "given": "Inki A." }, "id": "Min-I-A", "display_name": "Min, Inki A." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8y2c-8203", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nTo understand the basic contribution of vortex motion in the transport and mixing of passive fluid, we study a system of N discrete vortices. With variation of N and [...] (a vorticity distribution parameter), we are able to experiment with a range of vortex dynamics sufficient to capture many of the features of two-dimensional turbulence in their elementary form - such as vortex merging (inverse cascade of energy), filamentation (enstrophy cascade), etc. With this model the mixing of the fluid is numerically studied via stretch statistics and the spatial distribution of a non-diffusive scalar interface. The spectrum of spatial distribution of scalars as a result of the stirring motion of the N vortices is particularly important in view of the recent (as well as historical) interest in the characterization of the scalar distribution in turbulence. We also examine the velocity field statistics and the Lagrangian motion of fluid particles. It is also instructive to look at the kinematic causes behind the types of statistics that are obtained for the velocity structure functions. A 'building block' approach to understanding these effects in turbulence may lie in building up from a collection of discrete vortices, as done in this thesis, to adding vortices of different scales and the three-dimensional effects. It is in the context of these wider issues that we study the N-vortex problem.\n\nIn the final part of this thesis we investigate the two-dimensional mixing produced by large scale vortical structures during the evolution of a spatially developing mixing layer. Although the advent of three-dimensionality and fully developed turbulence are essential features of mixing layers, it is still dominated by the large scale two-dimensional structures and its effect on the mixing is illustrated here.\n" }, { "name": "Rousset, Bernard", "degree": "Engineering Degree", "year": "1995", "title": "Calibration and Study of the Contoured Nozzle of the T5 Free-Piston Hypervelocity Shock Tunnel", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192007-094437", "creators": [ { "name": { "family": "Rousset", "given": "Bernard" }, "id": "Rousset-Bernard", "display_name": "Rousset, Bernard" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A82S-0J92", "abstract": "A pitot pressure survey of the contoured nozzle of the T5 shock tunnel was performed over a wide range of reservoir conditions and in the region of the exit plane of the nozzle. A rake of thirteen pitot probes was used for this purpose. The survey includes an investigation of the repeatability of the facility and an analysis of the accuracy of the measurements. The features of the pitot pressure distribution across the exit plane are a pronounced minimum near but not exactly on the centerline, and a pronounced drop near the nozzle wall. The concave profile may be quantified in terms of the curvature of the pitot pressure distribution, which increases markedly as the enthalpy is decreased and as the area ratio is increased. The normalized value of the minimum pitot pressure is found to be independent of the reservoir enthalpy, in contrast to the behavior obtained by numerical computation of inviscid flows. The results of this survey show clearly, that the use of a contoured nozzle should be restricted to conditions very close to the design condition. Since flexibility in the reservoir enthalpy and pressure, as well as area ratio, is an important feature of a shock tunnel, the results of this survey strongly suggest the use of a conical nozzle.\r\n" }, { "name": "Sanderson, Simon Ralph", "degree": "PhD", "year": "1995", "title": "Shock wave interaction in hypervelocity flow", "advisor": "Sturtevant, Bradford; Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092004-094744", "creators": [ { "name": { "family": "Sanderson", "given": "Simon Ralph" }, "id": "Sanderson-S-R", "display_name": "Sanderson, Simon Ralph" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3GPK-5G29", "abstract": "The interaction of a weak oblique shock with the strong bow shock ahead of a blunt body in supersonic flow produces extreme heat transfer rates and surface pressures. Although the problem has been studied extensively in low enthalpy flows, the influences of high enthalpy real gas effects are poorly understood. Existing perfect gas models predict greatly increased heating with increasing Mach number and decreasing ratio of specific heats.\r\n\r\nExperiments are conducted in a free piston shock tunnel to determine the effects of thermochemistry on the problem at high enthalpy. The flow topology is simplified by studying the nominally two-dimensional flow about a cylinder with a coplanar impinging shock wave. High resolution holographic interferometry is used to investigate changes in the flow structure as the location of the impinging shock wave is varied. Fast response heat transfer gauges provide time resolved measurements of the model surface temperature. The data that are obtained do not support the existing predictions of greatly increased heat transfer at high enthalpy.\r\n\r\nA model is developed to study the thermochemical processes occurring in the interaction region. The phenomenon arises because the stagnation streamline is forced to pass through a system of oblique shock waves that produce less entropy than the undisturbed bow shock. Peak heating is shown to result from a balancing of the strengths of the oblique shock waves. This condition is demonstrated to simultaneously minimize the influence of thermochemistry on the flow. Real gas effects are shown to become important at lower Mach numbers (< 7.5) and for shock angles weaker or stronger than that which produces maximum heating. The model accurately reproduces the experimental observations.\r\n\r\nA nonequilibrium approximation is introduced that applies when the oblique waves are weak with respect to the undisturbed bow shock. Within the scope of the approximation, non-monotonic behavior with the reaction rate is predicted. The reaction rate is not varied as an independent parameter in the current experiments.\r\n" }, { "name": "Tierney, C. Michael", "degree": "Engineering Degree", "year": "1995", "title": "Plume characteristics of a multiple ion source thruster", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07112007-133241", "creators": [ { "name": { "family": "Tierney", "given": "C. Michael" }, "id": "Tierney-C-M", "display_name": "Tierney, C. Michael" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/mj8f-q926", "abstract": "This report describes ion plume characteristics of a multiple ion source thruster that are important to propulsion subsystem, spacecraft system, and mission design engineers with respect to incorporation of the segmented ion thruster (SIT) within a space mission. These characteristics will address issues related to operational performance, lifetime, thruster interaction with a host spacecraft, multiple ion beam interaction, and repeatability of construction and operation. Information contained within this report can be helpful in evaluating subsystem / mission performance, and resolve possible thruster / spacecraft integration issues.\n\nCharacteristics of the exhausted ion beam(s) were evaluated through two sets of experiments. The first involved measuring the two-dimensional ion current density distribution at several downstream locations from the thruster with concurrent operation of up to three ion sources. Assessments were made of plume symmetry, plume development as a function of downstream position, interactions between multiple ion beams, and beam divergence angles were calculated for individually operated ion sources. Ion beam asymmetries about the ion source centerline were observed. Construction of multiple ion source current density profiles through superposition of data obtained from operation of individual ions sources was attempted. Charge exchange effects appear to have impacted the analyses and some discrepancies between 'real' and 'constructed' results were observed. Beam divergence angles for R = 0.893 cases ranged from 10\u00b0 to 18\u00b0 and from 16\u00b0 to 22\u00b0 for R = 0.643 cases.\n\nThe second set of experiments involved collection of ion charge state data with the use of an ExB mass spectrometer placed downstream of the thruster. Charge state data was collected along the ion source centerline for 3 fixed propellant flow rates and varible beam currents. Data was also collected for a fixed flow rate and beam current at positions located along the horizontal and vertical axes passing through the ion source centerline. Correction factors for thrust and propellant utilization based upon doubly charged ion production, as well as propellant backflow into the discharge chamber were determined. Asymmetries in the radial profiles, as well as inconsistencies between the profiles of singly and doubly charged ions and charge state ratio, were observed." }, { "name": "Al Juhany, Khalid Ahmed Bin Talal", "degree": "PhD", "year": "1994", "title": "Supersonic Film Cooling Including the Effect of Shock Wave Interaction", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-084103", "creators": [ { "name": { "family": "Al Juhany", "given": "Khalid Ahmed Bin Talal" }, "id": "Al-Juhany-Khalid-Ahmed-Bin-Talal", "display_name": "Al Juhany, Khalid Ahmed Bin Talal" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7ry6-fy87", "abstract": "The current work is an investigation of supersonic film cooling effectiveness including interactions with a two-dimensional shock wave. Air and helium, which are either heated or cooled, are injected at Mach numbers between 1.2 and 2.2 into a Mach 2.4 air freestream. The adiabatic wall temperature is measured directly. The injection velocity and mass flux are varied by changing the total temperature and Mach number while maintaining matched pressure conditions.
\r\n\r\nHeated injection, with the injectant to freestream velocity ratios greater than 1, exhibit a rise in wall temperature downstream of the slot yielding effectiveness values greater than one. The temperature rise, which also occurs for cooled injection, is attributed to the merging of the injectant boundary layer and the lip-wake. As a result comparisons between heated and cooled injection may not be valid. With the exception of heated helium runs, larger injection Mach numbers slightly increase the effective cooling length per mass injection rate. The results for helium injection indicate an increase in effectiveness as compared to that for air injection. The experimental results are compared with studies in the literature.
\r\n\r\nFlow profiles at several axial locations, up to 90 slot heights, indicate that for the same Mach number the helium injections induce a larger wake and a thicker boundary layer than air injection.
\r\n\r\nThe influence of the shock impingement on the recovery temperature is not large if the flow remains attached. Once separation occurs the temperature changes drastically with downstream distance. The shock strength for incipient separation is smaller when helium is injected than when no film coolant is present. However, the converse is true with air injection even though, for the same Mach number, the momentum flux for the air injection is less than that for the helium injection. The induced separation in the case of helium is attributed to the reduced fullness of its momentum flux profile prior to interaction. This research demonstrates how the performance of supersonic film cooling for thermal control is undermined by the susceptibility to shock induced separation, and raises concerns about hydrogen film cooling for N.A.S.P.
" }, { "name": "Germain, Patrick", "degree": "PhD", "year": "1994", "title": "The boundary layer on a sharp cone in high-enthalpy flow", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-112714", "creators": [ { "name": { "family": "Germain", "given": "Patrick" }, "id": "Germain-P", "display_name": "Germain, Patrick" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hfje-z896", "abstract": "An exploratory study of the laminar, transitional and turbulent boundary layer on a 5 deg. half-angle cone in hypervelocity flow was conducted in the high-enthalpy shock tunnel T5 by measurement of the heat flux distribution and by qualitative flow visualization. A novel flow visualization technique using sodium seeding to increase the sensitivity of conventional interferometric techniques by resonant enhancement of the refractivity of the medium was developed to study the boundary layer structure. The experiments were designed to cover a large range of specific reservoir enthalpy, ranging from the perfect-gas regime to the range where significant oxygen and some nitrogen dissociation and recombination effects may be expected in the boundary layer. The presence of atomic species is due to the combined effect of nozzle freezing and frictional heating in the boundary layer. In the laminar regime and in the latter range, the following effects were found to be present: At the same nominal conditions, heat flux levels are higher in air than in nitrogen because of a larger heat release from oxygen recombination at the wall. By varying the reservoir specific enthalpy in air and nitrogen, and from measurements in carbon dioxide, it was found that real-gas effects stabilize the boundary layer. If the transition Reynolds number is renormalized by evaluating it at the reference temperature, the data for a given gas becomes correlated in a plot against reservoir enthalpy. Increasing enthalpy stabilizes the flow. The stabilizing effect is stronger with gases whose lowest activation energy is low. This behavior is opposite to the prediction made by the linear stability theory regarding the second linear mode of instability. The linear stability theory predicts, however, that real-gas effects stabilize the Tollmien-Schlichting mode. Flow visualization results suggest that the dominant instability mode in the present experiments was the Tollmien-Schlichting mode. Finally, the flow visualization pictures show structures that are not qualitatively different from those of an incompressible turbulent boundary layer, but they do not indicate if real-gas effects change significantly the structure of the turbulent boundary layer. The heat transfer measurements compare well with semi-empirical predictions." }, { "name": "Lambros, John", "degree": "PhD", "year": "1994", "title": "Dynamic decohesion of bimaterial interfaces", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042007-075432", "creators": [ { "name": { "family": "Lambros", "given": "John" }, "id": "Lambros-J", "display_name": "Lambros, John" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/36hw-c185", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn the present work, findings of an experimental study of dynamic decohesion of bimaterial systems composed of constituents with a large material property mismatch are presented. PMMA/steel or PMMA/aluminum bimaterial fracture specimens are used. Dynamic one point bend loading is accomplished with a drop weight tower device (for low and intermediate loading rates) or a high speed gas gun (for high loading rates). High speed interferometric measurements are made using the lateral shearing interferometer of Coherent Gradient Sensing in conjunction with high speed photography. Very high crack propagation speeds (terminal crack tip speeds up to [...], where [...] is the shear wave speed of PMMA) and high accelerations ([...], where g is the acceleration of gravity) are observed and reported. Issues regarding data analysis of the high speed interferograms are discussed. The effects of near tip three dimensionality are also analyzed. In crack propagation regions governed by large crack tip accelerations it is found that for accurate analysis of the optical data use of a transient elastodynamic crack tip field is necessary. Otherwise use of a Kd-dominant analysis is sufficient. Using the dynamic complex stress factor histories obtained by fitting the experimental data, a dynamic crack growth criterion is proposed. In the subsonic regime of crack growth it is seen that the opening and shearing displacements behind the propagating crack tip remain constant, i.e., the crack retains a self-similar profile during crack growth at any speed. This forms the basis of the proposed dynamic interfacial fracture criterion. It is also found that the process of dynamic interfacial fracture is highly unstable. This is corroborated by both the very large measured values of crack tip speed and acceleration and by the observation that the energy release rate at the propagating crack tip decreases with increasing crack tip speed. A mechanism of energy transfer from the metal to the PMMA side of the specimen is believed to be responsible for the high transient and transonic effects. An analysis and discussion of this phenomenon is also presented in this work.\n" }, { "name": "Sugawara, Satoshi", "degree": "Engineering Degree", "year": "1994", "title": "An experimental investigation of fracture at an interface between two epoxies", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-160254018", "creators": [ { "name": { "family": "Sugawara", "given": "Satoshi" }, "id": "Sugawara-S", "display_name": "Sugawara, Satoshi" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/850e-8c88", "abstract": " The growth of a crack located at the interface between two linearly elastic solids is investigated experimentally. The requirements for the test pieces are strong bonding between the two materials, a well-defined, planar interface, and a pronounced difference in the stiffness between the two materials. To attain these requirements, castable liquid epoxy resins are used. It is demonstrated that the manufacturing process, which follows previously established procedures for the bi-material solid composed of Solithane, is also applicable for epoxy. To investigate the toughness of the interface crack, the measurement of crack speed and the estimation of stress intensity factors are carried out for several different temperatures. Master curves of crack speed for either of the two materials and for the bimaterial are presented. The experimentally obtained fracture toughness data are compared with the expected values by Knauss's model (1971). By varying the mode mixity at the crack tip, it is found that the crack might advance by kinking into the soft material or by propagating along the interface itself, depending on the applied loading conditions. Although the number of data points is small, the fracture data gathered from tests performed at two different temperatures indicate that rate effects significantly influence the kinking behavior. Crack tip speeds after kinking are also recorded." }, { "name": "Vendroux, Guillaume", "degree": "PhD", "year": "1994", "title": "Scanning tunneling microscopy in micromechanics investigations", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-06162005-104436", "creators": [ { "name": { "family": "Vendroux", "given": "Guillaume" }, "id": "Vendroux-G", "display_name": "Vendroux, Guillaume" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KVSX-Q863", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nA new experimental method is proposed for studying deformations of micromechanical material systems at the submicron scale. To that end, a Scanning Tunneling Microscope (STM) was designed and built to allow placement on a mechanically deforming specimen. Operating in constant current mode, this digitally controlled STM records detailed topographies of specimen surfaces with a resolution of 10.15 nm in-plane and [...] out-of-plane, over a [...] area.\n\nA pattern recognition type algorithm was written to extract the 3-D displacement field from topographies of a given specimen area but under different loading conditions. This Digital Image Correlation (DIC) scheme was found to have very robust convergence characteristics and a higher resolution than that of the images it compares. The accuracy of the DIC code on STM scans was assessed by measuring displacement fields resulting from a translation of the specimen under the microscope. Two major causes of noise were identified, namely drifting of the specimen during scan acquisition and hysteresis distortion of the scan grid. An experimental procedure was devised to limit the occurrence of such perturbations and under these guidelines the resolution of the DIC scheme was found to be 4.8 nm for in-plane displacement measurements and 1.5 nm for out-of plane's.\n\nA micromechanical study of the deformation mechanism of PolyVinylChloride (PVC) was undertaken. Analysis of STM scans revealed that, upon first loading the surface of PVC specimens is deformed irreversibly even at low strain levels. The size of the strain induced topographic changes suggests that, at the scale of [...], a continuum type constitutive modeling of PVC may not be appropriate. This investigation also uncovered the present limitations of the STM-DIC scheme in measuring displacement fields consistently at the nanometer scale." }, { "name": "Wen, Chihyung", "degree": "PhD", "year": "1994", "title": "Hypervelocity flow over spheres", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212004-092435", "creators": [ { "name": { "family": "Wen", "given": "Chihyung" }, "id": "Wen-C", "display_name": "Wen, Chihyung" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5DDV-GW34", "abstract": "The nature of the nonequilibrium flow of dissociating gases over spheres was investigated experimentally, numerically and theoretically. A series of experiments with three different gases, nitrogen, air and carbon dioxide, was performed in the shock tunnel T5 at GALCIT. Five spheres of different radii equipped with thermocouples for surface heat flux measurements were used. The state-of-the-art numerical method by Candler (1988) was used to conduct a parallel study which strongly complemented the experimental and theoretical efforts.\n\nExperimental heat flux measurements are presented. Good agreement was observed among the measured stagnation point heat transfer rates, computational results and Fay and Riddell\u2019s theoretical predictions. For nitrogen and air, the measured heat flux distributions were also in good agreement with numerical computation results and Lees\u2019 theory. For carbon dioxide, large deviations were observed. Early transition tripped by surface roughness is a possible cause for the deviation of heat flux distribution from the theory. The experimental differential interferograms were compared with the images constructed from computational flowfields. Good agreement of fringe pattern and shock shape was observed.\n\nAn analytical solution is obtained for inviscid hypervelocity dissociating flow over spheres. The solution explains the correlation between the dimensionless stand-off distance and the dimensionless reaction rate parameter previously observed by Hornung (1972) for nitrogen. The physics of the correlation can be shown as the binary scaling. Based on the solution, a new dimensionless reaction rate parameter is defined to generalize Hornung\u2019s correlation for more complex gases than nitrogen. Experimental and numerical results confirm the new correlation.\n\nThe effect of nonequilibrium recombination downstream of a curved two-dimensional shock was also addressed. An analytical solution for an ideal dissociating gas was obtained, giving an expression for dissociation fraction as a function of temperature on a streamline. The solution agrees well with the numerical result and provides a rule of thumb to check the validity of binary scaling for the experimental conditions. The effects upon the binary scaling of the large difference in freestream temperature between flight and free-piston shock tunnel conditions are discussed." }, { "name": "Belanger, Jacques", "degree": "PhD", "year": "1993", "title": "Studies of Mixing and Combustion in Hypervelocity Flows with Hot hydrogen injection", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-092852", "creators": [ { "name": { "family": "Belanger", "given": "Jacques" }, "id": "Belanger-Jacques", "display_name": "Belanger, Jacques" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/012K-GE91", "abstract": "The ability to build an air-breathing single-stage-to-orbit propulsion system requires examination of key elements such as turbulent mixing rates, especially at the \"zero shear\" fuel-air mixing condition, and combustion efficiency. The required data can only be obtained in experiments which simultaneously match the flight total pressure and total enthalpy as well as the fuel conditions. GALCIT, with its new free piston shock tunnel T5, has the capability to do some of these combustion experiments. But prior to these tests, it was felt that there was a need to simulate the gas dynamical processes in the free piston shock tunnel and also in a new combustion driven shock tunnel built for these experiments so that both systems could be used as efficiently as possible. The numerical code helped explain the piston motion in the free piston shock tunnel. The code was also very useful for the design of the combustion driven shock tunnel.
\r\n\r\nBecause hydrogen has to be injected into the combustion chamber of the propulsion system after being used as a cooling fluid, a combustion driven shock tunnel was built to reproduce this \"hot\" hydrogen fuel. The system has been used successfully to supply hydrogen at up to 1500 K for the experiments. To reduce the complexity of the problem, a very basic configuration for the hydrogen injection system was tested. This was first done with an injection system mounted flush with the surface of a flat plate in the test section of T5. Different test conditions as well as Mach 2 and 5 nozzle injectors at angles of 15\u00b0 or 30\u00b0 were tested to determine criteria for significant combustion. Lower limits in pressure and enthalpy were found where hydrogen combustion becomes very limited using this \"hot\" hydrogen fuel. The second set of experiments still used an injection system mounted flush with the surface but involved a small combustor model previously tested in the hypervelocity HYPULSE facility. Low pressure experiments were performed to reproduce some of the HYPULSE tests and excellent agreement was found. Experiments at high pressure were also performed to better match the real flight total pressure and some hydrogen combustion was detected in these tests.
" }, { "name": "Bridges, David Henry", "degree": "PhD", "year": "1993", "title": "Tip effects on the vortex wake of an axisymmetric body at angle of attack", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-081713", "creators": [ { "name": { "family": "Bridges", "given": "David Henry" }, "id": "Bridges-D-H", "display_name": "Bridges, David Henry" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Peck", "given": "Charles W." }, "id": "Peck-C-W", "role": "member", "display_name": "Peck, Charles W." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DZ4H-M010", "abstract": "Experiments on the effects of conditions at the tip of an axisymmetric body on the vortex wake of the body at large angle of attack in incompressible flow have been performed. The separation patterns that occur at the nose of a cone with a hemispherical tip have been documented for ranges of Reynolds number based on tip radius and of relative angle of attack. Tips with cross sections that vary smoothly from elliptic to circular have been designed and tested on a cone. The effectiveness of the tips in varying the cone side force coefficient as the tip is rotated has been demonstrated. The relation between tip roll angle and side force coefficient has been shown to be essentially independent of Reynolds number, for the range of Reynolds number tested, as well as cone base conditions and roll direction. The relation between tip roll angle and side force coefficient has been shown to be a strong function of angle of attack. The reasons for nonsmooth variation of side force coefficient with tip roll angle at higher angles of attack have been determined by examinations of the vortex wake geometry. Peaks in the magnitude of the side force coefficient after zero crossings have been shown to be caused by a rapid shift in the wake vortices away from a symmetric configuration as the tip rotates away from a symmetry condition. Reductions in magnitude of the side force coefficient between magnitude peaks have been demonstrated to be a result of the near vortex crossing over the cone centerline. This vortex crossover has been shown to occur near and after the breakaway from the cone of the far vortex. The ability of one of the elliptic cross section tips to produce smooth variations of side force coefficient with roll angle ahead of vortex breakaway has been demonstrated, suggesting that the tip might be an effective yaw control device for aircraft at high angle of attack." }, { "name": "Cardell, Gregory Scott", "degree": "PhD", "year": "1993", "title": "Flow past a circular cylinder with a permeable wake splitter plate", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012005-092116", "creators": [ { "name": { "family": "Cardell", "given": "Gregory Scott" }, "id": "Cardell-G-S", "display_name": "Cardell, Gregory Scott" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/25C5-1150", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMeasurements in the near wake region of a circular cylinder in a uniform flow in the Reynolds number range [...] with permeable splitter plates spanning the wake center plane are presented. Permeability is defined by the pressure drop across the plates, and the relationship between permeability and plate solidity is determined for a set of plates constructed from woven wire mesh, permitting unambiguous characterization of the splitter plates by the solidity. The effects of different solidities on the flow in the near wake are investigated using smoke wire flow visualization, hot-wire anemometry, and measurements of the mean pressure at the cylinder surface, and the results are related to cylinder flow without a splitter plate.\n\nFlow visualization results demonstrate that the introduction of low solidity splitter plates does not change the basic near wake structure, and that sufficiently high solidity uncouples the large-scale wake instability from the body, with the primary vortex formation occurring downstream of the separation bubble due to instability of the wake profile. Hotwire and surface pressure measurements confirm and quantify the flow visualization results, showing that the permeable splitter plates reduce the drag and modify the primary wake frequency. When the solidity is high enough that the wake is convectively unstable, the base pressure is independent of the Reynolds number and solidity. For a wide range of solidities, the same asymptotic value of the Strouhal number is reached at high Reynolds numbers. The relationship between the Strouhal number and the base pressure is discussed.\n\nDetailed measurements in the separating shear layers with splitter plates moderating the primary vortex formation show that in the mean the development of the separating shear layers is similar to that of the plane mixing layer. The presence of the splitter plates enhances shear layer development, and it is found that for all solidities the instability amplifies a broad frequency band without discrete spectral features. Turbulent transition in the shear layer and its role in the pronounced Reynolds number dependency of the flow in this Reynolds number range is discussed. Acoustic excitation of the separated shear layers confirms the broad band frequency response of the shear layer instability, and the effect of the driven shear layers on the near wake is investigated." }, { "name": "Geubelle, Philippe H.", "degree": "PhD", "year": "1993", "title": "Nonlinear effects in interfacial fracture", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-104817", "creators": [ { "name": { "family": "Geubelle", "given": "Philippe H." }, "id": "Geubelle-P-H", "display_name": "Geubelle, Philippe H." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rkt0-7k90", "abstract": "The issue of the non-coplanar quasi-static propagation of a crack in homogeneous and bimaterial sheets is investigated. Through a preliminary linear analysis, it is shown that the interface crack kinking problem is confronted, in most practical cases, with difficulties which do not arise in the homogeneous situation: the crack path as predicted by the maximum energy release rate criterion cannot be determined uniquely and an additional length parameter, absent in the homogeneous case, needs to be specified to assure uniqueness. Following that development, the assumption of small deformations is relinquished and it is shown how the size of the nonlinear zone imparts possibly the physical significance of the additional length parameter. The analysis is performed numerically in the homogeneous and bimaterial cases within the framework of the nonlinearly elastic theory of plane stress and using a \"boundary-layer\" approach. Material and geometrical nonlinearities are combined through the use of the Generalized Neo-Hookean (GNH) model. As the length of the crack extension becomes comparable to the size of the nonlinear zone, a transition is observed between the value of the energetically most favorable kink angle predicted by the linear theory and a unique \"nonlinear\" value which is found to be independent of the crack extension length and the far-field loading conditions.\n\nThe results of the crack propagation analysis are related to those of a detailed asymptotic analysis of the structure of the near-tip stress and deformation fields for the GNU class of hyperelastic materials. The investigation addresses a) the symmetric (mode I) and non-symmetric (mixed-mode) homogeneous situations, b) the rigid substrate case and c) the general bimaterial problem which allows for an arbitrary choice, on both sides of the interface, of the three material parameters characterizing the GNH model. The asymptotic analysis allows to quantify the effect of the \"hardening\" characteristics on the blunting of the crack and the associated stress and strain singularities, and shows that the near-tip fields corresponding to a general nonsymmetric loading are, in the homogeneous situation, related to those of the symmetric (mode I) case through a rotation which depends on the material characteristics and the far-field loading conditions. A somewhat similar property is obtained in the bimaterial problem, where the existence of a non-oscillatory and \"contact-free\" solution is confirmed for all material combinations." }, { "name": "Hammer, Jay A.", "degree": "PhD", "year": "1993", "title": "Lifted turbulent jet flames", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-131353", "creators": [ { "name": { "family": "Hammer", "given": "Jay A." }, "id": "Hammer-J-A", "display_name": "Hammer, Jay A." } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fn1k-za85", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nExperiments were conducted on lifted, turbulent jet diffusion flames. An automated technique using a linear photodiode array was implemented to measure the temporal history of the liftoff height h. The measurements enabled accurate determination of the mean liftoff height [...] under a wide range of flow conditions, including several fuels, nozzle diameters, and exit velocities [...]. The results showed an approximately linear relationship between [...] and [...], with a slight dependence on Reynolds number. A strain-rate model for liftoff, based on far-field scaling of turbulent jets, provides an explanation for the linear dependence of [...] on [...]. Measurements were also made in which the nozzle fluid contained varying amounts of air, where it was found that the slope of the [...] vs. [...] line increases faster than predicted by far-field scaling of turbulent jets. The discrepancy is attributed to near-field effects.\n\nThe amplitudes of the fluctuations in h were found to be of the order of the local large scale of the jet. There is a slight increase in normalized fluctuation level [...] with [...], and there is some variation of [...] with fuel type. The time scales of the fluctuations of h were found to be considerably longer than the local large-scale time of the turbulence [...]. By using fuels of different chemical times to vary [...], the measured correlation time [...] normalized by [...] was found to collapse with Richardson number [...]. Experiments in which the nozzles were oriented horizontally showed no change in [...], however. Additional experiments were conducted to investigate alternative explanations for the variation of [...] with [...]. These experiments included measuring the flame length L simultaneously with h, and measuring the visible radiation I simultaneously with h. L(t) was found to be nearly uncorrelated with h(t), dismissing the possibility that a feedback mechanism from L to h controls the fluctuations of h. Although I(t) is highly correlated with h(t) for the most sooting fuel, acetylene, it is not deemed responsible for the longer correlation times of that fuel. This was deduced from experiments using mixtures of hydrogen with other fuels, which produce very little radiation, but which have values of [...] comparable to those of acetylene flames.\n\nAnother experiment was conducted in which two-dimensional images of fuel concentration (CH4) and reaction zones (indicated by CH) were obtained. The images showed a wide variety of structure types, indicating that there is no universal description of the flow field at the flame base. The flame stabilization position showed large fluctuations in both the axial and radial directions. The shot to shot variation in methane number density at the flame base was also large." }, { "name": "Koumoutsakos, Petros D.", "degree": "PhD", "year": "1993", "title": "Direct numerical simulations of unsteady separated flows using vortex methods", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-082957", "creators": [ { "name": { "family": "Koumoutsakos", "given": "Petros D." }, "id": "Koumoutsakos-P-D", "display_name": "Koumoutsakos, Petros D." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCQ9-9C86", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nNumerical simulations are presented for viscous incompressible flows with and without solid wall boundaries. Our numerical method is based on vortex methods. The classical inviscid scheme is enhanced to account for viscous effects via the method of particle strength exchange. The method is extended to account for the enforcement of the no-slip boundary condition as well by appropriately modifying the strength of the particles. Computations are possible for extended times by periodically remeshing the vorticity field.\n\nThe particles are advanced using the Blot-Savart law for the evaluation of the velocity. Computations are made using up to [...](10[superscript 6]) vortex particles by efficiently implementing the method of multipole expansions for vector computer architectures to obtain an [...](N) algorithm.\n\nThe method is used to simulate the inviscid evolution of an elliptical vortex in an unbounded fluid as well as unsteady separated flows around circular cylinders for a wide range of Reynolds numbers (40 - 9500). Direct comparisons are made of the results of the present method with those from a variety of theoretical, computational and experimental studies. The results exhibit the robustness and validity of the present method and allow to gain physical insight as to vorticity formation and its relation to the forces experienced by the body." }, { "name": "Lappas, Tasso", "degree": "PhD", "year": "1993", "title": "An adaptive Lagrangian method for computing 1-D reacting flows, and, The theory of Riemann invariant manifolds for the compressible Euler equations", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192007-130342", "creators": [ { "name": { "family": "Lappas", "given": "Tasso" }, "id": "Lappas-T", "display_name": "Lappas, Tasso" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bw0e-2789", "abstract": "In the first part of this thesis, a method for computing one-dimensional, unsteady compressible flows, with and without chemical reactions, is presented. This work has focused on accurate computation of the discontinuous waves that arise in such flows. The main feature of the method is the use of an adaptive Lagrangian grid. This allows the computation of discontinuous waves and their interactions with the accuracy of front-tracking algorithms. This is done without the use of additional grid points representing shocks, in contrast to conventional, front-tracking schemes. The Lagrangian character of the present scheme also allows contact discontinuities to be captured easily. The algorithm avoids interpolation across discontinuities in a natural and efficient way. The method has been used on a variety of reacting and non-reacting flows in order to test its ability to compute complicated wave interactions accurately and in a robust way.\r\n\r\nIn the second part of this thesis, a new approach is presented for computing multidimensional flows of an inviscid gas. The goal is to use the knowledge of the one-dimensional, characteristic problem for gas dynamics to compute genuinely multidimensional flows in a mathematically consistent way. A family of spacetime manifolds is found on which an equivalent 1-D problem holds. These manifolds are referred to as Riemann Invariant Manifolds. Their geometry depends on the local, spatial gradients of the flow, and they provide locally a convenient system of coordinate surfaces for spacetime. In the case of zero entropy gradients, functions analogous to the Riemann invariants of 1-D gas dynamics can be introduced. These generalized Riemann Invariants are constant on the Riemann Invariant Manifolds. The equations of motion are integrable on these manifolds, and the problem of computing the solution becomes that of determining the geometry of these manifolds locally in spacetime.\r\n\r\nThe geometry of these manifolds is examined, and in particular, their relation to the characteristic surfaces. It turns out that they can be space-like or time-like, depending on the flow gradients. An important parameter is introduced, which plays the role of a Mach number for the wave fronts that these manifolds represent. Finally, the issue of determining the solution at points in spacetime, using information that propagates along space-like surfaces is discussed. The question of whether it is possible to use information outside the domain of dependence of a point in spacetime to determine the solution is discussed in relation to the existence and uniqueness theorems, which introduce the concept of domain of dependence.\r\n\r\nThis theory can be viewed as an extension of the method of characteristics to multidimensional, unsteady flows. There are many ways of using the theory to develop practical, numerical schemes. It is shown how it is possible to correct a conventional, second-order Godunov scheme for multidimensional effects, using this theory. A family of second-order, conservative Godunov schemes is derived, using the theory of Riemann Invariant Manifolds, for the case of two-dimensional flow. The extension to three dimensions is straightforward. One of these schemes is used to compute two standard test cases and a two-dimensional, inviscid, shear layer.\r\n" }, { "name": "Lisoski, Derek Lee Ashton", "degree": "PhD", "year": "1993", "title": "Nominally 2-Dimensional Flow About a Normal Flat Plate", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04042005-105646", "creators": [ { "name": { "family": "Lisoski", "given": "Derek Lee Ashton" }, "id": "Lisoski-Derek-Lee-Ashton", "display_name": "Lisoski, Derek Lee Ashton" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AZEG-2T16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nTowing tank and water channel experiments and a two-dimensional vortex element numerical model were used to study the forces experienced by a bluff flat plate set normal to a nominally two-dimensional flow. Intrinsic (small scale) and extrinsic (large scale) three-dimensional motions in the experimental flow were isolated and their separate and combined effects on forces and overall wake development were studied. Transient flow development starting from rest, as well as steady flow conditions, were investigated.\r\n\r\nA force balance was used to measure the unsteady lift and drag of vertically oriented models projecting through a free surface with various lower end conditions; simultaneous LIF flow visualizations imaged the structure of the vortices in the wake. Plate aspect ratio, lower end condition and angle of attack were varied to effect changes in large scale three-dimensional motions, while changes in Reynolds number and Richardson number (flow stratification) modified the small scale three dimensionality intrinsic to the flow.\r\n\r\nTowing tank experiments indicated that normal plates required sixty to one hundred chord lengths of travel to establish steady vortex shedding. An initial drag peak during acceleration was followed by a drag minimum of [...] reached while the wake was confined to a symmetric vortex bubble. Subsequent to the breakdown of this bubble, a region of symmetric flow with [...] and no vortex shedding was apparent for twenty to thirty chord lengths, followed by the final onset of vortex shedding which occurred exponentially. During this onset forces overshot their final steady-state values [...]. Flows with less large scale extrinsic three dimensionality (higher aspect ratio, \"more two-dimensional\" end conditions, and stratified flow) had longer development times and higher subsequent overshoot levels.\r\n\r\nSmall geometric asymmetries (angle of attack variations) increased the minimum drag level seen after the acceleration and resulted in an earlier breakdown of the closed wake, followed by an immediate transition to steady shedding. The breakdown of the initial bubble in this case was more coherent spanwise and did not result in a long-lasting symmetric nonshedding flow.\r\n\r\nDuring \"steady-state\" shedding, modulation in the vortex shedding amplitude at a time scale of five to ten Strouhal periods resulted in a twenty percent fluctuation in mean drag level, with a corresponding increase in rms lift. This modulation accompanied a slow oscillation in the formation distance of the shed vorticity, the period of which was Reynolds number independent but decreased with increasing aspect ratio, reaching a minimum value of six Strouhal periods for aspect ratios greater than ten.\r\n\r\nAgreement between three-dimensional experimental and two-dimensional numerical-model results was good at early times, indicating the experiments were two-dimensional until the breakdown of the closed wake bubble following the initial acceleration. Prior to this breakdown the numerical model of a normal plate gave a drag coefficient [...], similar to that given by the Kirchhoff-Rayleigh free-streamline prediction but lower than experiments. Small asymmetries of the 2d model resulted in an increase in the minimum drag level to [...] . Subsequent to the closed wake breakdown, drag levels of [...] are 65% higher than steady-state experimental values.\r\n\r\nAlthough no region corresponding to the post-acceleration non-vortex-shedding seen experimentally was found in the basic numerical results, the addition of circulation decay to the numerical-model resulted in a region which appeared qualitatively similar. This circulation decay also decreased mean drag levels [...] and gave an exponential shedding onset with subsequent long period shedding modulation.\r\n\r\nStabilizing spanwise stratification of the experimental flow had little effect for Richardson numbers [...] (based on chord). For [...] and [...] a longer lasting post-acceleration closed wake was followed by strong initial shedding and a large drag overshoot, with a subsequent decrease in shedding amplitude and increase in formation distance to the levels seen in the unstratified [...] case, which exhibited considerable Reynolds number dependence. For plates at [...] angle of attack the symmetric nonvortex shedding region was reduced in duration and subsequent \"steady-state\" drag levels were increased ten to fifteen percent [...] from the unstratified case." }, { "name": "Pulos, Guillermo C.", "degree": "PhD", "year": "1993", "title": "Nonsteady crack propagation and craze behavior in PMMA", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312007-104217", "creators": [ { "name": { "family": "Pulos", "given": "Guillermo C." }, "id": "Pulos-G-C", "display_name": "Pulos, Guillermo C." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4kqe-ec90", "abstract": "This work is devoted to the study of nonsteady crack propagation under cyclic loading in polymers, specifically PMMA. The first part deals with the delineation of a precision loading facility allowing ultra-precise load or displacement control commensurate with the high resolution measurements of crack tip material response.\r\n\r\nA method of determining the advance of crack tip through combined microscope and computer-analyzed observation is presented. In particular, the experimental set up and software development is described by which these measurements are achieved. It is shown that automated crack tip location is possible with a precision of one to two microns, which is amply sufficient for present purposes to make definitive statements about the smoothness or discontinuity of crack propagation.\r\n\r\nThe craze and crack opening displacements are measured near the free surface of the specimen both under quasi-static step loading and cyclic loading. Eleven craze opening profiles for equal load increments are acquired during a single cycle under fatigue loading. A multi-linear craze stress model is used to match the opening displacements to the measurements. While the primordial thickness can be defined from the Lorentz-Lorenz equation and from the assumption of a constant index of refraction for the quasi-static loading, the effect of load history may prevent such determinations for cyclic loading. The damage accumulated through cyclic deformation reduces the strength of the fibrils in the middle of the craze and produces a drop in the middle of the stress distribution. The craze and crack opening displacement are monitored in connection with a jump-like crack/craze advance constituting 50% of the craze length. The newly-drawn craze fibrils after the jump show mechanical behavior that is different from their behavior before the jump and exhibit no deterioration in their stress-displacement relation." }, { "name": "Togami, Kenji", "degree": "Engineering Degree", "year": "1993", "title": "Hypervelocity dissociating flow over a spherically blunted cone", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282007-141027", "creators": [ { "name": { "family": "Togami", "given": "Kenji" }, "id": "Togami-K", "display_name": "Togami, Kenji" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/kewn-2m49", "abstract": "Recently several hypersonic vehicles are being developed in several countries. For the design of these vehicles, understanding the flow physics is necessary. Recently, the free piston driver for large shock tunnels became practical and it enables us to simulate the hypervelocity flow in the ground based facilities. Also the computing resources have grown dramatically and it enables us to compute the hypervelocity flow which is chemically and thermally nonequilibrium in a reasonable computation time. In this thesis the combined approach of experiment and computation has been applied to the hypervelocity flow on a spherically blunted cone.\n\nThe experiments are conducted in the newly developed free piston shock tunnel called T5 at the Graduate Aeronautical Laboratories, California Institute of Technology. Three kinds of the gases, nitrogen, air and carbon dioxide are used. The flow fields are computed by a CFD code using the two temperature model by Park. Since the flow field in the experiments is visualized with the differential interferogram, the computed density field is used to generate the differential interferogram. It can be concluded that the two temperature model CFD code can reproduce the basic flow feature such as the inflection point in the shock wave.\n\nHeat transfer at the stagnation point is then examined. It correlates well with the equation by Fay and Riddell. Subsequently, the after body heat flux can be predicted by Lees' theory very well. The heat flux on after body is well correlated with Stanton number and local Reynolds number for each gas but the difference between the gases are significant. This is partly because the recombination plays a more important role in the after body flow. The results of the experiments and the computations points to the necessity of other correlation parameters for the after body heat transfer in hypervelocity flows.\n\nThen the difference between the shock tunnel experiment and actual flight was examined. The most dominant factor is the difference of free stream temperature. One method to estimate the heat flux in actual flight from experimental data was proposed and this method compensates the difference of the temperature. The result shows very good agreement with numerical computational results.\n" }, { "name": "Tsuyuki, Richard M.", "degree": "Engineering Degree", "year": "1993", "title": "Buckling of thermoviscoelastic structures under temporal and spatial temperature variation", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152011-095226678", "creators": [ { "name": { "family": "Tsuyuki", "given": "Richard M." }, "id": "Tsuyuki-R-M", "display_name": "Tsuyuki, Richard M." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T54W-0694", "abstract": "The problem of lateral instability of a viscoelastic in-plane loaded structure is considered in terms of thermorheologically simple materials. As an example of a generally in-plane loaded structure, we examine the simple column under axial load: Both cyclic loading is considered (with constant or in-phase variable temperature excursions) as well as the case of constant load in the presence of thermal gradients through the thickness of the structure.\r\nThe latter case involves a continuous movement of the neutral axis from the center to the colder side and then back to the center.\r\n\r\nIn both cases, one finds that temperature has a very strong effect on the rate at which instabilities evolve, and under in-phase thermal cycling the critical loads are reduced compared to those at constant (elevated) temperatures. The primary effect of thermal gradients beyond that of thermally-induced rate accelerations is a rate increase occasioned by the generation of an \"initial imperfection\" or \"structural bowing.\" This latter effect, which is proportional to both the temperature gradient and the coefficient of thermal expansion (presumed homogeneous in this study), can in fact be dominant. Because the coefficient of thermal expansion tends to be large for many polymeric materials, it may be necessary to take special care in lay-up design of composite structures intended for use under compressive loads in high-temperature applications. Finally, the implications for the temperature\r\nsensitivities of composites to micro-instability (fiber crimping) are also apparent from the results delineated here.\r\n" }, { "name": "Yeung, Moon-Tai", "degree": "Engineering Degree", "year": "1993", "title": "Chemical Reactions in a Scramjet Combustor and Two-Dimensional Nozzles", "advisor": "Kubota, Toshi; Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152011-095847676", "creators": [ { "name": { "family": "Yeung", "given": "Moon-Tai" }, "id": "Yeung-Moon-Tai", "display_name": "Yeung, Moon-Tai" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/vw7e-nq49", "abstract": "Finite-rate chemistry of hydrogen-air combustion is to be investigated numerically in a one-dimensional constant pressure SCRAMJET combustor and two-dimensional nozzles. Detailed reaction mechanisms and temperature dependent thermodynamics are to be used in the models. The aspects of interest include the combustion characteristics at different fuel-air ratios, pressures and initial temperatures in the combustor. Methods for enhancing the combustion rate in the combustor is to be studied also. The effect of expansion rate on the hydrogen-air reactions is the prime focus of the nozzle calculation. The results from different inlet conditions and wall geometries are to be analyzed.
\r\n\r\nA computer model for a one-dimensional (channel-flow) combustor is constructed based on the chemical kinetics subroutine library CHEMKIN. Subsequent calculations show that the initial temperature is the most important parameter in the combustor. It is further discovered that certain reaction steps are responsible for the initial delay exhibited in all hydrogen-air combustion processes. Low temperature behavior is studied extensively and augmentation methods are developed. The introduction of a small percentage of the hydrogen radical into the initial mixture is found to be the most effective in reducing the reaction delay. The combustor pressure enters the overall reaction process in a linear manner. The calculations over five combustor pressures show that the initial delay in hydrogen-air reaction and the following period of explosion are proportional to the combustor pressure raised to certain powers.
\r\n\r\nThe nozzle model is two-dimensional, steady and inviscid with no conductivity and diffusivity. Two schemes are developed to handle the boundary conditions. One is based on pure numerical interpolation/extrapolation methods while the other imposes analytical supersonic characteristic equations. The former scheme is found to be more efficient while the latter is more accurate. In analysing the response of the combustion product to an expansion, it is found that the formation of water is favoured by an expansion. A closer examination reveals that the behavior can be attributed to the abundance of free radicals in the nozzle inlet composition. Freezing is not clearly observed except for the NOx species.
\r\n" }, { "name": "Bonazza, Riccardo", "degree": "PhD", "year": "1992", "title": "X-ray measurements of shock-induced mixing at an air/xenon interface", "advisor": "Sturtevant, Bradford; Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232005-111112", "creators": [ { "name": { "family": "Bonazza", "given": "Riccardo" }, "id": "Bonazza-R", "display_name": "Bonazza, Riccardo" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "co-advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3h5j-yb71", "abstract": "A new experimental technique to measure the density of a high atomic number gas at an interface has been developed and demonstrated. It is based on the absorption of X-rays by the high atomic number gas, and it was implemented in a vertical square shock tube for the study of shock-accelerated air/xenon interfaces. These were prepared by retracting a metal plate initially separating the two gases, prior to the release of the shock wave. Thus the interfaces were all of initial finite thickness. Interfaces of two types, quasi-sinusoidal and nominally flat, were examined. Object of study were the amplitude of large wavelength (25 - 100 mm) perturbations on the interface, and the thickness of the interface. An integral definition for the interface mean line (proposed in a previous numerical work at GALCIT) was adopted; a new integral definition for the interface thickness was proposed, making it feasible to study for the first time the thickness of quasi sinusoidal interfaces. Experiments were performed to image interfaces having interacted with the incident shock, the incident and the reflected shock, or a series of weak waves reverberating between the interface and the shock tube end wall. The results for the growth rates of the amplitudes were compared against a model based on the linear theory: The measured values are larger than the predicted ones in the case when the interface only interacts with the incident and the first reflected shocks. They are smaller than the theoretical ones in the case of multiple reverberations. The interface thickness exhibits essentially no growth upon interaction with the incident shock. The interaction of the reflected shock with the turbulent boundary layer behind the incident one generates random acoustical disturbances which reach the interface and cause the subsequent thickness growth. The thickness growth rates of nominally flat interfaces are larger than those previously found at GALCIT in a schlieren visualization experiment, in the case of two shock interactions. They are smaller in the case of multiple interactions. In the case of two shock interactions, wall vortices generated by the interaction of the reflected shock with the boundary layer behind the incident one severely affected the measurements. A correction was proposed to account for this effect in the measurements of the interface thickness. The need remains for a different experimental technique, capable of eliminating these adverse effects altogether." }, { "name": "Bowen, John Murray", "degree": "Engineering Degree", "year": "1992", "title": "An experimental investigation of fracture at a bimaterial interface", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-092222", "creators": [ { "name": { "family": "Bowen", "given": "John Murray" }, "id": "Bowen-J-M", "display_name": "Bowen, John Murray" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/esfz-eb60", "abstract": "The growth of a crack located at the interface between two linearly (visco)elastic solids is investigated experimentally. It is found that the crack may advance by kinking into either of the adherends or by propagating along the interface itself, depending on the applied loading. For the separation problem, in which crack advance occurs along the bimaterial interface, it is demonstrated that the time-dependent unbonding of the two joined viscoelastic solids follows a rate-dependent fracture process that can be described to a large extent by the viscoelastic properties of the two adherends. Moreover, the strength of the interfacial bond can be characterized in terms of an equilibrium interface-intrinsic fracture energy, the magnitude of which represents the bond strength quantitatively. In particular, interface strength on the same order as those of the adherends is achieved. In contrast to the time-dependent approach developed for the separation problem, the propensity of the interface crack to kink out of the interface upon loading is evaluated in the context of (time-independent) linearly elastic fracture mechanics. It is demonstrated that crack propagation along the interface occurs for a finite range of load mixity, a phenomenon predicted by linear analysis of the bimaterial joint but absent from the corresponding homogeneous development. Agreement between observed kinking behavior and analytical results is seen to improve by suitable manipulation of a presumably material characteristic length, the origin of which is rooted in the linearized analysis. The influence of material rate effects on the crack kinking behavior \nis also investigated.\n" }, { "name": "Budzinski, John Michael", "degree": "PhD", "year": "1992", "title": "Planar Rayleigh Scattering Measurements of Shock Enhanced Mixing", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-130628", "creators": [ { "name": { "family": "Budzinski", "given": "John Michael" }, "id": "Budzinski-John-Michael", "display_name": "Budzinski, John Michael" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pwj0-h036", "abstract": "This investigation was concerned with the mixing which occurs after the unsteady interaction of a shock wave with a laminar jet of helium. The jet of helium was injected normal to the direction of the propagation of the shock. The vorticity created at the boundaries of the jet during the shock interaction generates a stream of air which divides the initial circular cross section of the jet into two lobes. Each lobe is further divided into a tail region and a vortex core. The vortex cores from each lobe form a vortex pair that pulls ahead of the tail regions. In the present investigation the primary diagnostic, planar Rayleigh scattering, had sufficient spatial and temporal resolution to resolve the smallest diffusion scales present and allowed helium mole fractions to be measured in two-dimensional planes normal to the original jet flow direction. The amount of molecular mixing was evaluated with a mass distribution function at increasing times after the shock interaction. The total masses of helium contained in regions where the molar concentration of helium was at least 30% and 50% were also calculated. The shock Mach number was varied, and the effect of a reflected shock was studied. The velocity and spacing of the vortex pairs was measured. It was found that shock interactions can significantly increase the mixing between the air and helium. As the Mach number increases, better mixing occurs as the stream of air divides the jet. However, less mixing occurs at the later times when the vortex pairs are moving ahead of the tails. A rough collapse of the mixing data occurs when time is normalized with the change in velocity of the air behind the shock. The measured velocities and estimated values of the circulation agree very well with previous computational results. An increase in the enhancement of mixing occurred after the interaction with the reflected shock." }, { "name": "Frieler, Clifford Eugene", "degree": "PhD", "year": "1992", "title": "Mixing and reaction in the subsonic 2-D turbulent free shear layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292005-135259", "creators": [ { "name": { "family": "Frieler", "given": "Clifford Eugene" }, "id": "Frieler-C-E", "display_name": "Frieler, Clifford Eugene" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fsen-at31", "abstract": "Several aspects of mixing and reaction in a turbulent two-dimensional shear layer have been studied. Experiments have been performed with reacting H2, F2, and NO in inert diluent gases. Sensing the heat release by these reactions, several aspects of the mixing process can be examined without the usual resolution limitations. For example, in contrast with direct measurements of composition, the amount of mixed fluid can be conservatively estimated with the results of the \"flip\" experiments. These have been performed over a range of density ratios, Reynolds numbers and heat release.\r\n\r\nThe effects of initial conditions are of primary importance when comparisons to other studies are undertaken. Aspects as fundamental as growth rate of the turbulent region, or as obscure as the mixed fluid flux ratio depend strongly on the boundary conditions of this flow. These effects are examined in conjunction with those of Reynolds number and density ratio. For most cases studied here, tripping of the high speed boundary layer led to growth rate decreases. An exception was found for the case of high density ratio where the opposite effect was observed. This anomalous result occurred at conditions under which a new mode of instability has been shown to exist. Parallels exist between this unusual result and those of Batt in the uniform density case.\r\n\r\nAn extensive study of the effects of density ratio on the mixing and reaction in the 2-D shear layer has been performed. Results indicate that several aspects of the mixing process are remarkably similar. Profiles of mixed fluid change little as the density ratio varies by a factor of 30. The integral amount of mixed fluid varies less than 6% for all density ratios examined. This insensitivity contrasts with that of the profiles of mixed fluid composition. While having very similar shapes the profiles are offset by an amount which depends very strongly upon the density ratio. The entrainment into the mixing layer has also been examined. Power spectral densities of the temperature time series were calculated and found to collapse upon normalization with the adiabatic flame temperature and large structure passage frequency. Least squares fits of the probability density functions were also examined.\r\n\r\nThe initial work of Mungal and Frieler (1988) on the effects of chemical kinetics on the formation of product in the 2-D mixing layer have been greatly expanded. Measurements have been extended to include a wider range of NO concentrations and have been performed for two other stoichiometries. Results indicate that the simple model envisioned in Mungal and Frieler may only be suited for cases with extreme stoichiometry (very high or very low). Further investigations have turned up a serious discrepancy reflecting both on the experimental technique and on theory and modeling of this reacting flow. Experiments run under otherwise identical conditions demonstrate that more product is formed when F2 is the rich reactant than when H2 is the rich reactant. This dependence upon molecular character is counter intuitive and stems from a coupling of the effects of differing diffusivity and chemical kinetics. Numerical calculations based on simplified flow models are reported which demonstrate this coupling. These results indicate that even subtle diffusion effects can measurably effect reacting flows and imply that assumptions common among current modeling efforts must be re-examined.\r\n\r\nThe effects of Reynolds number on mixing and reaction in the 2-D turbulent mixing layer have been examined. Evidence of the remnants of the initial roll up and mixing transition are seen for Reynolds numbers as large as 30,000. Indications of a resonance with the acoustic mode of the apparatus exist which affect results for Reynolds numbers up to 60,000. Natural transition of the high and low speed boundary layer on the splitter plate complicate comparisons of the high Reynolds number data with the remainder. In spite of all of these qualifications, the amount of mixed fluid is nearly constant. Over the range of Reynolds numbers 10,000 to 200,000, it varies by less than 12%. No evidence of an asymptotic decline in the amount of mixed fluid is observed.\r\n" }, { "name": "Gortsema, Steven Craig", "degree": "Engineering Degree", "year": "1992", "title": "An Experimental Investigation of the Failure of a Stepped Composite Plate", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-110435", "creators": [ { "name": { "family": "Gortsema", "given": "Steven Craig" }, "id": "Gortsema-Steven-Craig", "display_name": "Gortsema, Steven Craig" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4R72-Y162", "abstract": "The progression of damage in a stepped composite plate has been investigated experimentally. This study is intended to provide insight into the failure behavior of co-cured, stringer-reinforced composite plates and shells. The specimens were constructed of four different lay-ups of carbon-fiber-reinforced epoxy and were subjected to various combinations of moment, tension, and shear static loadings.
\r\n\r\nThe primary means of damage observation was in situ microscopic inspection of the specimen edges. These observations were supplemented by penetrant-dye inspection, microscopic inspection of the plate face, and ultrasonic C-scanning of specimens which were unloaded prior to catastrophic failure. In addition to providing detailed descriptions of the damage development, this thesis presents hypotheses which attempt to explain the mechanisms involved in the failure process.
\r\n\r\nThe immediate goal of this work was to gather the experimental evidence needed to evaluate a recently proposed failure criterion. The criterion attempts to predict failure for an arbitrary lay-up by studying the behavior of the computed stresses within an extremely small vicinity of the singularity. The tests described in this thesis revealed that damage initiation does not always occur on the plate-stringer interface, as assumed in the failure criterion. Furthermore, it was discovered that in some lay-ups, damage initiates at a distance of over one lamina thickness away from the singularity. This fact makes it impossible to predict failure accurately with any criterion which is based solely on a computed stress singularity.
" }, { "name": "Lu, Lingyun", "degree": "PhD", "year": "1992", "title": "On the development and application of a modified boundary element method for the analysis of three-dimensional elastostatic problems in thick plates", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-131209", "creators": [ { "name": { "family": "Lu", "given": "Lingyun" }, "id": "Lu-L", "display_name": "Lu, Lingyun" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tkxp-f839", "abstract": "A modified three-dimensional Boundary Element Method (BEM) is developed. This method is specially tailored towards applications in three-dimensional elasticity, involving regions containing two parallel planar surfaces. Typical structures are the three-dimensional plate structures. The formulation makes use of the three-dimensional fundamental solution of a concentrated load applied in an infinite three-dimensional plate of uniform finite thickness (obtained by Benitez and Rosakis in 1985). The most attractive feature of this modified BEM is that, for the class of problems involving structures described above subjected to traction-free boundary conditions on the planar surfaces, discretization is only required on the lateral surfaces of the plate and the surfaces of the cavities, holes, and cracks in the plate. No discretization is needed on the planar surfaces of the plate. In this initial study, three problems involving a pressurized hole in an infinite three-dimensional plate are analyzed. The shapes of the holes include a circular hole and two elliptical holes with the aspect ratios of 4 and 10, respectively. In all the cases, the accuracy of the modified BEM is established by direct comparison of its results with those of finite element calculations. The results of the modified BEM are also compared with the plane-stress and plane-strain approximations of the problems under consideration. This comparison make it possible to access the important three-dimensional effects near the surface of the elliptical hole." }, { "name": "Minahen, Timothy M.", "degree": "PhD", "year": "1992", "title": "Structural instabilities involving time dependent materials : theory and experiment", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08082007-100442", "creators": [ { "name": { "family": "Minahen", "given": "Timothy M." }, "id": "Minahen-T-M", "display_name": "Minahen, Timothy M." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Christman", "given": "Tom" }, "id": "Christman-T", "role": "member", "display_name": "Christman, Tom" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7h70-2p51", "abstract": "The creep buckling of viscoelastic structures is studied analytically and experimentally to investigate structural stability in the presence of time dependent materials. The theory of linear viscoelasticity is used to model polymeric column specimens subjected to constant compressive end loads. A strength of materials approach (Euler-Bernoulli beam theory) is employed to model the moment-curvature relation for the column. The growth of initial imperfections is calculated using the hereditary integral formulation. Solution techniques are developed for small displacements and then generalized to include the effects of large displacements and rotations. A failure criterion based on maximum deformation allows the column life to be estimated directly from the material relaxation modulus. A discussion generalizing the results to include plates and shells is presented.\n\nRectangular cross-section polymethylmethacrylate (PMMA) specimens with hinged boundary conditions are used to study viscoelastic buckling experimentally. Constant compressive end loads are applied using a servo-controlled load frame while the specimens are kept in a temperature cabinet at elevated temperatures (accelerating the creep behavior). Specimen shortening and out-of-plane deflections are monitored during the tests. The relaxation modulus of PMMA is approximated by a Prony-Dirichlet series and the model is used to simulate the laboratory experiments. Model and experimental results show good agreement during the \"glassy\" and slow growth phases of the column response. As the growth rate increases some deviations between theory and experiment are seen. It is shown that the deviations are not a result of geometric nonlinearities, but may, in part, be explained by material nonlinearities not accounted for in the model.\n" }, { "name": "Nadiga, Balasubramanya T.", "degree": "PhD", "year": "1992", "title": "A study of multi-speed discrete-velocity gases", "advisor": "Sturtevant, Bradford; Broadwell, James E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092007-090234", "creators": [ { "name": { "family": "Nadiga", "given": "Balasubramanya T." }, "id": "Nadiga-B-T", "display_name": "Nadiga, Balasubramanya T." } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "advisor", "display_name": "Broadwell, James E." } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tz85-x511", "abstract": "The applicability of multi-speed discrete-velocity gases to compressible flow situations is considered. First, the equation of state, the anisotropies and the advection velocities for any multi-speed model on the square and triangular lattices are derived. The dependence on the model of any of these to leading order in the flow velocity is shown to be only through a fourth moment of the stationary equilibrium speed distribution. Next, a computation scheme is introduced, wherein adjacent cells in a cell network interact through an exchange of particles, commensurate with the equilibrium fluxes of mass, momentum, and energy. This corresponds to the infinite collision rate limit of the model gas, resulting in very low viscosities. Finally, a simple multi-speed model, the nine-velocity model is studied in detail: Solving the shock tube flow with the model yields almost all phenomenology associated with a perfect gas. An exact shock profile is computed for the model and is compared to a Navier-Stokes shock profile. An adiabatic channel flow is simulated with the model and the results compared to an integral solution of the Navier-Stokes equation. The comparisons in both the cases are excellent. It is also shown that the nine-velocity gas does not permit steady supersonic flow." }, { "name": "Sullivan, Gregory Daniel", "degree": "PhD", "year": "1992", "title": "An investigation of mixing and transport at a sheared density interface", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152007-082818", "creators": [ { "name": { "family": "Sullivan", "given": "Gregory Daniel" }, "id": "Sullivan-G-D", "display_name": "Sullivan, Gregory Daniel" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/931s-r394", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nScalar transport is investigated at a density interface imbedded in a turbulent shear flow. This problem is investigated first experimentally, and based on the experimental findings, a physical model for entrainment is developed.\n\nSteady-state interfacial shear flows are generated in a laboratory water channel for layer Richardson numbers, Ri, between about 1 and 10. The flow field is made optically homogeneous, enabling the combined use of laser-Doppler velocimetry and laser-induced fluorescence with photodiode array imaging to measure the velocity and concentration fields at high resolution.\n\nFalse-color images of the concentration field provide valuable insight into mixing and transport at the interface. The dominant interfacial mixing mechanism is found to depend on the local mean shear Richardson number, [...] for [...] less than about 0.40 to 0.45, local mixing is dominated by Kelvin-Helmholtz (K-H) instabilities; for somewhat larger values of [...], mixing is dominated by interfacial wave breaking. In both cases, vertical transport of mixed fluid into adjacent turbulent layers is accomplished by large-scale turbulent eddies which impinge on the interface and scour fluid from its outer edges.\n\nBased on the experimental results, a model for interfacial mixing and entrainment is developed. A local equilibrium is assumed in which the rate of loss of interfacial fluid by eddy scouring is balanced by the rate of production (local mixing) by interfacial instabilities and molecular diffusion. In the case of one-sided entrainment, the model results are as follows: when interfacial mixing is diffusion dominated, [...] and [...], where [...] is the interface thickness, h is the boundary layer thickness, Pe is the Peclet number, and E is the normalized entrainment velocity; when mixing is wave breaking dominated, [...] and [...]; and when mixing is K-H dominated, [...] and [...]. In all cases the maximum concentration anomaly is [...]. The model for single-sided entrainment is simply extended to the case in which both layers are entraining. In the latter case it is found that entrainment depends on combinations of parameters from both layers.\n\nThe proposed entrainment model is supported by experimental results from this and previous studies. The data from this study are in agreement with [...] and are consistent with model results for [...]; results from previous studies support model predictions for E and [...]." }, { "name": "Wissler, John B.", "degree": "PhD", "year": "1992", "title": "Transmission of thin light beams through turbulent mixing layers", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08162007-133929", "creators": [ { "name": { "family": "Wissler", "given": "John B." }, "id": "Wissler-J-B", "display_name": "Wissler, John B." } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pw33-qc68", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nLight transmission through incompressible gaseous turbulent mixing layers is investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments are done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considers both the unequal density (high-speed [...] and low-speed [...]) and equal density (high-speed [...] and low-speed [...]) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure ([...]) white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wanders under the influence of the passing coherent structures.\n\nThe study finds that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the span-wise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs. The rms fluctuations of the streamwise and spanwise deflection angles increase rapidly during mixing transition, peaking at 380 high-speed-side momentum thicknesses downstream from the splitter plate, then decrease far down-stream to asymptotic values of 0.6 to 0.8 as scaled by the static pressure and the Gladstone-Dale constant shift across the mixing layer. The data suggest that a possible mechanism for the deflections is the interaction of the beam with the thin interfaces which bound relatively uniform bodies of fluid inside the structures." }, { "name": "Gilbrech, Richard Joseph", "degree": "PhD", "year": "1991", "title": "An experimental investigation of chemically-reacting, gas-phase turbulent jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06272007-091419", "creators": [ { "name": { "family": "Gilbrech", "given": "Richard Joseph" }, "id": "Gilbrech-R-J", "display_name": "Gilbrech, Richard Joseph" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/p80s-h321", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nA new high pressure combustion facility was built to investigate mixing in axisymmetric, turbulent jets exiting into quiescent reservoirs. The facility uses fluorine and nitric oxide, diluted with nitrogen, for chemical product formation that is accompanied by heat release. The average temperature was measured by a set of long, thin, resistance wire thermometers stretched across the jet centerline at 16 downstream locations from x/d[subscript 0] = 30 to 240. Runs at several stoichiometric mixture ratios [phi], for Reynolds numbers ranging from 10,000 [...] Re [...] 150,000, were performed to determine any dependence of flame length on Reynolds number. The Reynolds number was varied through density, i.e., pressure, while the jet exit velocity and exit diameter were held constant. The time-averaged line integral of temperature, measured along the transverse axis of the jet by the wires, displays a logarithmic dependence on x/d* within the flame zone, and asymptotes to a constant value beyond the flame tip, as predicted from scaling and similarity arguments for a momentum-dominated, turbulent jet. The main result of the work is that the flame length, as estimated from the temperature measurements, varies with changes in Reynolds number, suggesting that the mixing process is not Reynolds number independent up to Re = 150,000. Specifically, the normalized flame length Lf/d* displays a linear dependence on [phi], with a slope that decreases from Re = 10,000 to 20,000, and then remains constant for Re > 20,000. Additionally, the measurements revealed a \"mixing virtual origin,\" defined as the far-field flame length extrapolated to [phi] = 0, that increases with increasing Re for Re [...]20,000 and then decreases with increasing Re for Re > 20, 000. A separate set of experiments indicated that the runs described above were momentum dominated to the farthest measuring station and that the kinetics of the chemical reactions were fast compared to the characteristic mixing time. The transition of the jet flow from a momentum- dominated to a buoyancy-dominated regime was identified in another set of experiments." }, { "name": "Hall, Jeffery Lawrence", "degree": "PhD", "year": "1991", "title": "An experimental investigation of structure, mixing and combustion in compressible turbulent shear layers", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232005-141544", "creators": [ { "name": { "family": "Hall", "given": "Jeffery Lawrence" }, "id": "Hall-J-L", "display_name": "Hall, Jeffery Lawrence" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T0MN-J472", "abstract": "Two-dimensional, compressible, turbulent shear layers are studied in a new wind tunnel facility. Both reacting and non-reacting flows are investigated, with one free stream velocity supersonic and the other subsonic. The combustion experiments are based on the use of low concentrations of hydrogen, nitric oxide and fluorine gases. Side-view Schlieren photographs of these reacting and non-reacting flows appear devoid of the two-dimensional, large-scale structures seen in incompressible flows. Comparison with all-subsonic flows produced in the same facility suggests that this lack of two-dimensional structure is due to the presence of the supersonic high-speed free stream velocity. Travelling shock and expansion waves are observed in the high compressibility flows, evidently created by turbulent structures convecting at supersonic velocities. Such waves are seen only in the low-speed fluid, with apparent convection velocities much higher than those predicted on the basis of isentropic pressure-matching arguments. The measured shear layer growth rates agree with previous results by other experimenters, except for a few cases at low compressibility and low density ratio. The fast chemistry regime is attained in some of the high compressibility flows tested. \"Flip\" experiments conducted in this regime indicate that the volume fraction of mixed fluid in the layer is substantially reduced as compared to previous incompressible results. These same flip experiments also reveal that compressibility significantly alters the entrainment ratio. Finally, it is observed that the shear layer growth rate is relatively insensitive to incident shock /expansion waves and significant heat release inside the shear layer." }, { "name": "Hill, Larry Glenn", "degree": "PhD", "year": "1991", "title": "An experimental study of evaporation waves in a superheated liquid", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-103224", "creators": [ { "name": { "family": "Hill", "given": "Larry Glenn" }, "id": "Hill-L-G", "display_name": "Hill, Larry Glenn" } ], "advisors": [], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NF49-ME48", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nEvaporation waves in superheated liquids are studied using a rapid-depressurization facility consisting of a vertical glass test cell situated beneath a large, low-pressure reservoir. The objective of this study is to learn more about the physical mechanisms of explosive boiling (of which an evaporation wave is a specific example), as well as properties of the flow it produces.\r\n\r\nThe test cell is initially sealed from the reservoir by a foil diaphragm, and is partially filled with a volatile liquid (Refrigerant 12 or 114). An experiment is initiated by rupturing the diaphragm via a pneumatically driven cutter. The instrumentation consists of fast-response pressure measurements, high-speed motion pictures, and spark-illuminated still photographs. The liquid temperature is typically 20\u00b0C; the liquid superheat is controlled by setting the reservoir pressure to values between vacuum and 1 atm. The pressures subsequent to depressurization are very much less than the critical pressure, and the initial temperatures are sufficiently low that, although the test liquid is highly superheated, the superheat limit is not approached. Evaporation waves in which bubble nucleation within the liquid column is suppressed entirely are considered almost exclusively.\r\n\r\nWhen the diaphragm is ruptured, the liquid pressure drops to virtually the reservoir value within a few milliseconds. Provided that the liquid superheat so obtained is sufficiently high, the free surface then erupts in a process known as explosive boiling, which is characterized by violent, fine-scale fragmentation of the superheated liquid and extremely rapid evaporation. The explosive boiling process proceeds as a \"wavefront\" into the liquid column, producing a highspeed, two-phase flow that travels upward into the low-pressure reservoir, emptying the test cell in a few hundred milliseconds. The speed of the wavefront varies between 0.2 and 0.6 m/s, depending on run conditions; the corresponding two-phase flow varies between about 5 and 35 m/s.\r\n\r\nIn the highest superheat case for the more volatile liquid (Refrigerant 12), explosive boiling usually initiates by the rapid formation of nucleation sites at random spots on the liquid free surface and at the glass/free-surface contact line. Boiling spreads to the remaining surface within 160 [...]. In the highest superheat case for the less volatile liquid (Refrigerant 114), nucleation begins only at the glass/free-surface contact line. Boiling then spreads radially inward toward the center. In the lower superheated cases for both liquids, nucleation begins at one or more sites on the glass/free-surface contact line, and propagates across the free surface.\r\n\r\nAt the higher superheats, explosive boiling initiates within a few milliseconds from diaphragm burst, the same time scale as that of liquid depressurization. No distinction is made between the onset of nucleation and that of explosive boiling. However, if the reservoir pressure is raised above a certain approximate value, the onset of explosive boiling is delayed. During the delay period, relatively slow bubbling (initiated at one or more nucleation sites at the glass/free-surface contact line) occurs, and a cluster of bubbles forms in the vicinity of the initial site. The bubble cluster then \"explodes,\" marking the transition to explosive boiling. The delay period increases significantly as the reservoir pressure is raised slightly further. Reservoir pressures corresponding to a delay period of order 100 ms define an approximate self-start threshold pressure, above which the transition to explosive boiling does not occur. \r\n\r\nWithin about 10 ms of initiation, the wave reaches a quasi-steady condition in which the average wave speed, two-phase flow speed, and base and exit pressures are constant. However, the instantaneous propagation rate and the mechanisms that generate the mean flow are observed to be highly nonsteady. The wavefront appears to propagate by heterogeneous bubble nucleation at its leading edge, and any given region of the wavefront tends to propagate in surges associated with new nucleation and/or very fine-scale surface perturbations. Measurements of the instantaneous position of the upstream tip of the wavefront indicate that local velocity fluctuations are the same order as the mean velocity. The leading-edge bubble lifetimes and diameters are statistically distributed; mean values are of order 1 ms and 1 mm, respectively. The leading-edge bubbles are fragmented in violent \"bursts\" of aerosol. Bursts have a tendency to sweep over the leading-edge bubble layer in a wavelike manner: They are \"large-scale structures\" associated with the fragmentation of many bubbles.\r\n\r\nFragmentation, rapid evaporation, flow acceleration, and pressure drop occur primarily within about 1 cm of the leading edge. Downstream of this region, the average speed and appearance of the flow are virtually constant. This developed flow is a highly nonuniform, two-phase spray containing streaklike structures. Its liquid phase is composed of drops (with a maximum diameter of about 100 [...]), as well as clusters and chains of bubbles (with a diameter of a few hundred microns). A thin liquid layer begins climbing the wall upon wave initiation. Its speed is a few m/s-significantly slower than that of the two-phase flow through the center. Exit pressure measurements indicate that the flow chokes for sufficiently low reservoir pressure; at higher reservoir pressures the flow is unchoked.\r\n\r\nThe self-start threshold is not a propagation threshold, as waves are observed to propagate at somewhat lower superheats if started artificially. This is accomplished in Refrigerant 114 by \"jump-starting\" the wave, using the more volatile Refrigerant 12. For sufficiently high reservoir pressures, an \"absolute\" threshold is reached at which the quasi-steady rapid evaporation processes break down.\r\n\r\nPossible mechanisms for explosive boiling are discussed in light of the present results. While neither of the two previous schools of thought (interfacial instability hypotheses and the secondary nucleation hypothesis) are alone adequate to explain the observed behavior, there is evidence that both may play a role. It is here proposed that the bursting phenomenon and bubble nucleation at the wavefront leading edge are mutually interactive processes-bursting occurring as the violent breakup of interstitial bubble liquid, and nucleation (and fine-scale perturbations) being caused by burst-generated aerosol striking the leading-edge surface. It is not understood what role interfacial instability may play in the bursting process.\r\n\r\nAn evaporation wave is analogous to a premixed flame in that both are classified as \"weak deflagration\" waves in gasdynamic theory. It is shown that using several approximations that are valid for the type of evaporation waves studied, the conservation equations (jump conditions) can be reduced to a single, simple expression in terms of readily measured and inferred properties.\r\n" }, { "name": "Kubr, Thomas J.", "degree": "Engineering Degree", "year": "1991", "title": "Stresses near a change of thickness in a continuous-fiber-composite plate", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072007-105324", "creators": [ { "name": { "family": "Kubr", "given": "Thomas J." }, "id": "Kubr-T-J", "display_name": "Kubr, Thomas J." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rra5-sv66", "abstract": "This thesis presents the results of a numerical investigation of the stresses near an abrupt change in thickness of a composite plate. The plate is a laminate of unidirectional, continuous fiber plies. The study is aimed at gaining insight into the failure behavior of co-cured stringer reinforced composite plates and shells.\n\nThe analysis is performed in a plane normal to the stringer axis. The problem formulation is similar to plane strain. Because orthotropic materials are involved, a solution method allowing three-dimensional displacements as functions of two spatial variables is applied. The method is called plane-coupled strain. Failure is assumed to initiate at the sharp 90\u00b0 reentrant corner of the step-down geometry due to a rise in stresses. The resulting stress singularity is characterized for different combinations of stacking orders in the stepped plate. Stresses in the structure are determined by means of the finite element method.\n\nThe results are presented in two parts: The first describes the differences obtained with plane-coupled strain and classical plane strain; the second characterizing the stress singularity. The more computer intensive plane-coupled strain solution produces significantly different results for the stresses near the singularity. The character of the stress singularity is found to be highly dependent on the fiber direction of the material at the sharp corner.\n\nThe results for the stress singularity are used in an example failure criterion. Stacking sequences are examined with respect to their susceptibility to failure under different combinations of in-plane loading." }, { "name": "Pfaff, Richard D.", "degree": "PhD", "year": "1991", "title": "Three-dimensional effects in nonlinear fracture explored with interferometry", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07102007-104514", "creators": [ { "name": { "family": "Pfaff", "given": "Richard D." }, "id": "Pfaff-R-D", "display_name": "Pfaff, Richard D." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6jnw-kh62", "abstract": "The prospects for understanding fracture mechanics in terms of a general material constitutive description are explored. The effort consists of three distinct components.\n\nFirst, optical interferometry, in its various forms (Twyman-Green, diffraction moire, etc.), can potentially be used under a wide range of conditions to very accurately measure the displacement and strain fields associated with the deformation surrounding a cracktip. To broaden the range of fracture problems to which interferometry may be applied, certain of the necessary experimental improvements have been developed:\n\n1. High speed camera designs capable of extremely high (> 10(9) frames/second) framing rates with large array sizes, (> 4000 x 4000 pixels per frame) so that the application of optical techniques to solid mechanics may be considered without limitation on the rate of deformation.\n\n2. An accurate and adaptable device for dynamic loading of fracture specimens to high load levels utilizing electromagnetic (Lorentz force) loading with ultrahigh (> 2,000,000 Amp/cm(2)) current flux densities.\n\n3. Implementation of high sensitivity (2 nm), large range (2 nm x 3,200,000) interferometry achieved with wide field array sizes of 50,000 x 50,000 and 8 bit gray scale (error restricted to 1 bit) for surface deformation measurements on fracture specimens.\n\nSecond, functional descriptions for certain aspects of the displacement fields associated with fracture specimens are developed. It is found that the fully three-dimensional crack tip field surrounding a through-thickness crack in a plate of elastic-plastic material shows a hierarchical structure of organization and that the primary aspects of the deformation field would seem to have a relatively simple form of expression if the deformation is viewed in a properly normalized form.\n\nThird, a comparison is made between interferometrically measured surface displacements for a notched 3-point-bend speciemn of a ductile heat treatment of 4340 steel and a numerical simulation of the specimen based on a material constitutive description determined from uniaxial tests performed on the same material. The small but finite notch tip radius (0.15 mm) fabricated by a wire-cutting electrical discharge machine allows one to explore the limits of applicability of standard continuum plasticity theories without involving a process zone model for the very near tip region extent in a cracked specimen geometry.\n" }, { "name": "Schultheisz, Carl R.", "degree": "PhD", "year": "1991", "title": "Comparison of experimental and computational crack-tip deformations using Moire interferometry and finite elements", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-132245", "creators": [ { "name": { "family": "Schultheisz", "given": "Carl R." }, "id": "Schultheisz-C-R", "display_name": "Schultheisz, Carl R." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/etqv-z784", "abstract": "The large plastic deformations at the tip of a crack in a ductile heat treatment of 4340 steel are studied experimentally and numerically to investigate the details of the deformation in a tough material. The specimen is loaded in a three-point-bend arrangement. The finite-element model of the experiment uses a small-strain, incremental plasticity law, with a power-law hardening behavior. Both the in-plane and out-of-plane deformations were measured on the same specimen at the same time.\n\nThe experimental technique of moire interferometry is used to measure the in-plane displacements. This technique is described in detail, including an analysis of the effect of out-of-plane rotations on the use of the technique. A four-beam interferometer for measuring orthogonal displacement components is described, and its performance analyzed.\n\nThe three-dimensional, finite-element model has 11913 degrees of freedom, and provides data for comparison with the experiment between 4000 N (linear behavior) up to 73.5 kN (continuous fracture of the steel specimen). The model material properties are determined from a uniaxial test on specimens taken from the same bar as the fracture specimens and with identical heat treatment. This model characterizes the crack as a rounded notch to match the notch in the steel fracture specimen. The effects of tunneling of the crack are introduced through the release of nodes along the crack plane corresponding to measured crack profiles.\n\nResults indicate that the numerical model matches the experiment quite well up to a load of 52.3 kN; mismatch at higher loads may be caused by a lack of finite-strain formulation in the code. The finite notch tip negates the singularity in either the stress or strain fields; the HRR field seems to have no region of dominance. However, the function of the J-integral appropriate to the HRR field does normalize the stresses and strains well, indicating that the J-integral is still a good fracture criterion. The effects of the added tunnel indicate that failure of the material depends on both the plastic strain and the hydrostatic stress." }, { "name": "Sugioka, Ichiro", "degree": "PhD", "year": "1991", "title": "Particle Transport by Rapid Vaporization of Superheated Liquid", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-082412", "creators": [ { "name": { "family": "Sugioka", "given": "Ichiro" }, "id": "Sugioka-Ichiro", "display_name": "Sugioka, Ichiro" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "co-chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sieh", "given": "Kerry E." }, "id": "Sieh-K-E", "role": "member", "display_name": "Sieh, Kerry E." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZS1H-VE29", "abstract": "Superheated liquid vaporizing explosively in a particle bed inside a cylindrical test cell has been studied using a rapid depressurization apparatus. The experiments provide insights into the explosive vaporization phenomenon and the multiphase flow which is generated by the rapid production of vapor.
\r\n\r\nInside the sealed test cell, spherical glass particles are immersed in a volatile liquid, Refrigerant 12 or 114 at 300K. When the diaphragm at the upper end of the test cell is ruptured, the liquid pressure is reduced to a predetermined pressure within milliseconds. Since the liquid temperature is higher than the boiling temperature at reduced pressure, the liquid achieves a superheated state and nucleate boiling begins among the particles. The particle-liquid-vapor flow produced by the rapid release of vapor has been found to differ depending on whether the pressure is reduced below a critical level, which is 55% of the vapor pressure in the experiments conducted. When the final pressure is greater than critical, vapor pockets continue to grow throughout the particle bed and displace a liquid-particles mixture out from the test cell. When the final pressure is below critical, the particles are dispersed by a wave-like phenomenon (disruption front) where explosive vaporization appears to be localized in a narrow region. A disruption front in R12 travels at about 380 cm/s, and at about 200 cm/s in R114.
\r\n\r\nExperiments have been performed at various conditions to study the vaporization and transport process. High-speed cinematography and fast response pressure gauges have provided data on the particle acceleration process. The inertial effect on particle acceleration has been studied by conducting similar experiments in a centrifuge. Using this data, the transport process associated with the disruption front has been examined in detail. An empirical relationship between the particle weight and viscous drag is presented for this particular case. This study concludes with discussions based on analytical models of the disruption front to approximate flows properties which are intractable experimentally. It is suggested that a disruption front is an expansion process which maximizes vaporization and entropy.
" }, { "name": "Tokumaru, Phillip Takeo", "degree": "PhD", "year": "1991", "title": "Active control of the flow past a cylinder executing rotary motions", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-141454", "creators": [ { "name": { "family": "Tokumaru", "given": "Phillip Takeo" }, "id": "Tokumaru-P-T", "display_name": "Tokumaru, Phillip Takeo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/v7p7-d977", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\t\t\t\t\t\r\nExploratory experiments have been performed on circular cylinders executing forced rotary motions in a steady uniform flow. These motions include harmonic oscillations, steady rotation, and combinations of the two. Flow visualization and laser-Doppler velocimetry measurements were used to characterize the wake structure, and to estimate the convection speed, spacing, and strength of the vortical structures. Laser-Doppler velocimetry measurements were also made to estimate the cylinder drag coefficient and wake displacement thickness. In addition, the periodic flow close the cylinder and in the near wake region was mapped for a particular forced case. The data show that a considerable amount of control can be exerted over the flow by such means. In particular, a large increase, or decrease, in the resulting displacement thickness, estimated cylinder drag, and associated mixing with the free stream can be achieved, depending on the frequency and amplitude of oscillation. In order to assess the effects of oscillatory forcing on a cylinder with a net (mean) rotation rate, a novel method for estimating the steady lift forces was employed. Using this method, it was also found that the addition of forced rotary oscillations to the steady rotation of the cylinder helped to increase [...] in the cases where the wake would normally be separated in the steadily rotating case, and decrease it otherwise. Results obtained for a steadily rotating cylinder (no forced oscillations) compare favorably with similar data published in the literature." }, { "name": "Waitz, Ian Anton", "degree": "PhD", "year": "1991", "title": "An Investigation of Contoured Wall Injectors for Hypervelocity Mixing Augmentation", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-083103", "creators": [ { "name": { "family": "Waitz", "given": "Ian Anton" }, "id": "Waitz-Ian-Anton", "display_name": "Waitz, Ian Anton" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MPJS-1Q71", "abstract": "A parametric study of a class of contoured wall fuel injectors is presented. The injectors were aimed at enabling shock-enhanced mixing for the supersonic combustion ramjet engines currently envisioned for applications on hypersonic vehicles. Short combustor residence time, a requirement for fuel injection parallel to the freestream, and strong sensitivity of overall vehicle performance to combustion efficiency motivated the investigation. Several salient parametric dependencies were investigated. Injector performance was evaluated in terms of mixing, losses, jet penetration and heating considerations.
\r\n\r\nA large portion of the research involved a series of tests conducted at the NASA Langley High - Reynolds Number Mach 6 Wind-Tunnel. Helium was used as an injectant gas to simulate hydrogen fuel. The parameters investigated include injector spacing, boundary layer height, and injectant to freestream pressure and velocity ratios. Conclusions concerning injector performance and parameter dependencies are supported by extensive three-dimensional flow field surveys as well as data from a variety of flow visualization techniques including Rayleigh scattering, Schlieren, spark-shadowgraph, and surface oil flow.
\r\n\r\nAs an adjunct to these experiments, a three-dimensional Navier-Stokes solver was used to conduct a parametric study which closely tracked the experimental effort. The results of these investigations strongly complemented the experimental work. Use of the code also allowed research beyond the fairly rigid bounds of the experimental test matrix. These studies included both basic investigations of shock-enhanced mixing on generic injectors, and applied efforts such as combining film-cooling with the contoured wall injectors.
\r\n\r\nLocation of an oblique shock at the base of the injection plane was found to be a loss-effective method for enhancing hypervelocity mixing through baroclinic generation of vorticity and subsequent convection and diffusion. Injector performance was strongly dependent on the displacement effect of the hypersonic boundary layer which acted to modify the effective wall geometry. Strong dependence on injectant to freestream pressure ratio was also displayed. Mixing enhancement related to interaction of the unsteady component of the boundary layer with both steady and unsteady components of the flow field was found to be secondary, as were effects due to variation in mean shear between the injectant and the freestream in the exit plane.
" }, { "name": "Chua, Kiat", "degree": "PhD", "year": "1990", "title": "Vortex Simulation of Separated Flows in Two and Three Dimensions", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-142847", "creators": [ { "name": { "family": "Chua", "given": "Kiat" }, "id": "Chua-Kiat", "display_name": "Chua, Kiat" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9ENS-EP36", "abstract": "This thesis is concerned with the applications of vortex methods to the problem of unsteady, separated flows in two and three dimensions, and can be divided into three parts. In the first part, an improved method for satisfying the boundary conditions on a flat plate is developed and applied to the two-dimensional separated flow problem. In this method, boundary layers on both side of the plate are represented by stacks of multiple vortex panels, the strength of which are determined by enforcing both the no-through flow and no-slip boundary conditions at the plate. Vortex shedding at the sharp edge of the plate is represented as the separation of the boundary vortex elements. Both forced and unforced flows are studied and comparisons to experiments are carried out. For the case without forcing, large discrepancy between calculations and experiments, which is also reported by other workers using a different vortex method or Navier-Stokes calculations, is observed. In the case with forcing, the discrepancy is reduced with lateral forcing at low amplitude; and eliminated, regardless of amplitude, with streamwise forcing (acceleration). In the second part, an improved three-dimensional vortex particle method is developed. In this method, vortex elements of vorticity that move with the local velocity and are stretched and rotated according to the local strain field, are used. To mimic the effects of vorticity cancellations, close pairs of opposite sign vortex elements are replaced by high order dipoles. The method is designed to handle complex high Reynolds number vortical flows and a non-linear viscosity model is included to treat small-scale effects in such flows. Applications to two problems involving strong interactions of vortex tubes are carried out and core deformation with complex internal strucures and induced axial flow within vortex tubes are observed. Qualitative comparison to experiments are encouraging. In the third part, the two-dimensional method developed in the first part is modified and extended to three dimensions. Here, solenoidal condition for vorticity is considered and closed vortex loops are used to represent the boundary layer vorticity and the vorticity at shedding. For the evolution of the vortex wake, the vortex particle method developed in the second part is used. Applications to the flow past a normal square plate is carried out and the early stages of the flow are studied.
" }, { "name": "Fric, Thomas Frank", "degree": "PhD", "year": "1990", "title": "Structure in the Near Field of the Transverse Jet", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232007-075829", "creators": [ { "name": { "family": "Fric", "given": "Thomas Frank" }, "id": "Fric-Thomas-Frank", "display_name": "Fric, Thomas Frank" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JVHG-E582", "abstract": "Photographs of an axisymmetric turbulent jet issuing from a wall into a crossflow display the four types of vortical structures which exist in the near field: the jet shear layer vortices, the nascent far field vortex pair, the near wall horseshoe vortices, and a system of vortices in the wake of the jet.
\r\n\r\nAdditionally, results of hot-wire measurements in the wake of the transverse jet are presented. Among these results are characteristic wake Strouhal frequencies, which vary with the jet to crossflow velocity ratio, and wake velocity profiles.
\r\n\r\nIt is found that the wake vorticity is not \"shed\" from the jet but is formed from vorticity which originated in the wall boundary layer. Therefore, analogies between the wakes of transverse jets and the wakes of solid cylinders are incorrect. Since the jet is not a solid obstacle to the crossflow, as a cylinder is, new vorticity is not generated at the interface between the jet and the crossflow. Instead, the boundary layer on the wall from which the jet issues separates near the downstream side of the jet because it cannot negotiate the adverse pressure gradient imposed on it by the flow around the jet, which is not \"separated\" as it is for a cylinder. The wake vortices subsequently formed are found to be most coherent near a jet to crossflow velocity ratio of four.
\r\n\r\nThe near field development of the counterrotating vortex pair, which is the dominant structure of the far field jet, is also addressed. It is argued that the source of vorticity for the vortex pair is the vorticity from the boundary layer within the jet nozzle. Estimates for the strength of these vortices are obtained by considering the flux of vorticity emanating from the nozzle.
\r\n\r\nPossible implications for mixing are briefly discussed.
" }, { "name": "Goldstein, David Benjamin", "degree": "PhD", "year": "1990", "title": "Investigations of a Discrete Velocity Gas", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-093505", "creators": [ { "name": { "family": "Goldstein", "given": "David Benjamin" }, "id": "Goldstein-David-Benjamin", "display_name": "Goldstein, David Benjamin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DK4P-AK28", "abstract": "A new model of molecular gasdynamics with discrete molecular velocity components has been implemented for parallel computation. When the suitably normalized velocity components can take only integer values and time is discretized for digital computation, the particles travel between a regular array of points in physical and velocity space, and the gas is called a \"lattice gas.\" Calculations of molecular motions are thereby simplified. The outcome of binary collisions between particles is determined by reflections about axes of symmetry in the center-of-mass frame of reference. The procedure speeds calculations of collisions. Of interest is the insight the discrete model provides into complex physical behavior and the effect that physically realistic simplifications have on the accuracy and speed of parallel calculations of a flow.
\r\n\r\nThe equilibrium state of a discrete-velocity gas and the influence of limited velocity resolution are explained. It is found that the equilibrium velocity distribution functions of the present model agree with those of the discrete Boltzmann equation at very low velocity resolution and the continuous-velocity Boltzmann equation at higher velocity resolution. The time development of non-equilibrium velocity distribution functions is presented. The model is applied to unsteady flows involving strong shock waves, heat transfer between solid surfaces, and unsteady shear layer development.
\r\n\r\nWhen the model is applied to gas mixtures, numerical experiments show that the required number of values of each component of molecular velocity depends strongly upon the mass ratios of the particle species involved. However, fewer than ten values of each velocity component are necessary to produce results of satisfactory accuracy in calculations of a shock wave in a single species gas. A unique, self-adaptive mesh for parallel computation, used either for the present lattice gas model or earlier direct simulation Monte Carlo (Bird, 1976) models, is described. The mesh balances the load between the processors of the multicomputer and maintains the cell size at approximately a fixed number of local mean free paths throughout the flow field.
" }, { "name": "Ide, Kayo", "degree": "PhD", "year": "1990", "title": "Regular and chaotic motion of uniform elliptical vortices in external linear time dependent velocity fields", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-092941", "creators": [ { "name": { "family": "Ide", "given": "Kayo" }, "id": "Ide-K", "display_name": "Ide, Kayo" } ], "advisors": [], "committee": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "chair", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/sc2s-3749", "abstract": "The motion of a uniform vorticity of an elliptical shape (UEV) induced by an external linear flow field and a self induced effect in a two dimensional incompressible inviscid flow is investigated. The fluid particle motion around the UEV is also investigated. The techniques from dynamical systems are intensively used. In particular, we develop some modified versions of the Melnikov techniques which show how the perturbations influence the dynamics and allow us to predict the perturbed dynamics by knowing the unperturbed dynamics.\n\nThe UEV motions in steady external linear flow fields are regular, however there are quite a few possibilities for types of motion depending on the UEV initial configuration and the external linear flow field parameters. When time periodic perturbation is imposed, the UEV motion drastically changes and various new types of motion become possible. This includes transition dynamics (i.e., the UEV changes its type of motion), chaotic motion, irregular oscillation and rotation, and quasiperiodic motion. The Melnikov techniques tell that the excess kinetic energy play significant roles in determining the UEV dynamics.\n\t\nA periodic motion of the UEV in a steady external linear flow field results in the generation of chaotic fluid particle mixing regions around the UEV where the fluid particles from distinct flow regions are chaotically transported. Our study emphasizes on the finite core size effect of the UEV in comparison to flow fields induced by a point vortex in unsteady external linear flow fields. We show that the size of the UEV core and the UEV initial configuration are important factors in determining the size of the mixing region.\n" }, { "name": "Jahnke, Craig C.", "degree": "PhD", "year": "1990", "title": "Application of Dynamical Systems Theory to Nonlinear Aircraft Dynamics", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092007-134504", "creators": [ { "name": { "family": "Jahnke", "given": "Craig C." }, "id": "Jahnke-Craig-C", "display_name": "Jahnke, Craig C." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9KZS-XC46", "abstract": "A continuation method has been used to determine the steady states of three nonlinear aircraft models: a general aviation aircraft with a canard configuration, a generic jet fighter, and the F-14. The continuation method calculated the steady states of the aircraft as functions of the control surface deflections. Bifurcations of these steady states were determined and shown to cause instabilities which resulted in qualitative changes in the state of the aircraft. A longitudinal instability which resulted in a deep stall was determined for the general aviation aircraft. Roll-coupling and high angle of attack instabilities were determined for the generic jet fighter, and wing rock, directional divergence and high angle of attack instabilities were determined for the F-14.
\r\n\r\nKnowledge of the control surface deflections at which bifurcations occurred was used to either put limits on the control surface deflections or to program the control surface deflections such that a combination of control surface deflections at which bifurcations occur could not be attained. Simple control systems were included in the aircraft models to determine the effects of control systems on the instabilities of each aircraft. Steady spin modes were determined for each aircraft. A successful recovery technique was determined for the general aviation aircraft, but no successful recovery technique could be found for the F-14.
" }, { "name": "Losi, Giancarlo Umberto Maria", "degree": "PhD", "year": "1990", "title": "Nonlinear thermoviscoelastic behavior of polymers", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-103818", "creators": [ { "name": { "family": "Losi", "given": "Giancarlo Umberto Maria" }, "id": "Losi-G-U-M", "display_name": "Losi, Giancarlo Umberto Maria" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2dk7-z575", "abstract": "The rheological behavior of polymers in the neighborhood of the glass transition has been investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition was modified to account for the effect of the residual volume of vacancies below the glass transition; this modification was accomplished by modelling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecules. The changes in mechanical properties going across the glass transition follow from the freezing-in of relaxation mechanisms and of free volume. The pressure dependence of the glass transition was found to be in qualitative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities was found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery domains. The predictions of the model for the problem of transient and residual thermal stresses were compared with those of two simpler models.\n\nThe second part of the thesis studies the consequences of the nonlinear viscoelastic behavior on the decohesion zone in front of a crack propagating through an adhesive layer. The softening of the material response in the cohesive zone is taken to be effected by free volume induced change in relaxation times of the cohesive material and by void growth; the latter is assumed to depend on a critical value of strain at the beginning of the cohesive zone. The stress intensity factor for steady crack propagation is obtained by imposing the finiteness of strains at the crack tip. For the case where the properties of the adherends are the same as the linearized properties of the adhesive, the predictions show three regimes of crack propagation: a low speed regime where the adherends behave elastically with the rubbery properties, an intermediate range where their response becomes increasingly stiffer, and a high speed regime characterized by glassy behavior of the adherends and control of the crack growth process exclusively by the nonlinearly viscoelastic behavior of the failing material." }, { "name": "Pepin, Francois Michel", "degree": "PhD", "year": "1990", "title": "Simulation of the flow past an impulsively started cylinder using a discrete vortex method", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-08162005-104131", "creators": [ { "name": { "family": "Pepin", "given": "Francois Michel" }, "id": "Pepin-F-M", "display_name": "Pepin, Francois Michel" } ], "advisors": [], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7svd-7213", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nVortex methods are a powerful tool for the simulation of incompressible flows at high Reynolds number. They rely on a discrete Lagrangian representation of the vorticity field to approximately satisfy the Kelvin and Helmholtz theorems which govern the dynamics of vorticity for inviscid flows.\r\n\r\nA time splitting technique can be used to include viscous effects. The diffusion equation is considered separately after convecting the particles with an inviscid vortex method. In this thesis, the viscous effects are represented by the so-called deterministic method. The approach was extended to problems where a flux of vorticity is used to enforce the no-slip boundary condition. The ability of such a scheme to create the right amount of vorticity at the wall and to adequately redistribute it within the fluid is demonstrated by simulating the viscous flow induced by an oscillating cylinder.\r\n\r\nIn order to accurately compute the viscous transport of vorticity, gradients need to be well resolved. As the Reynolds number is increased, these gradients get steeper and more particles are required to achieve the requisite resolution. In practice, the computing cost associated with the convection step dictates the number of vortex particles and puts an upper bound on the Reynolds number that can be simulated with confidence.\r\n\r\nThat threshold can be increased by reducing the asymptotic time complexity of the convection step from [...] to [...]. The near-field of every vortex particle is identified. Within that region, the velocity is computed by considering the pairwise interaction of vortices. The speed-up is achieved by approximating the influence of the rest of the domain, the far-field. In that context, the interaction of two vortex particles is treated differently depending on their spatial relation. The resulting computer code does not lend itself to vectorization but has been successfully implemented on concurrent computers.\r\n\r\nThe combination of a fully viscous vortex method with a fast parallel algorithm is used to simulate the flow past an impulsively started cylinder. Experiments have shown that this flow is characterized by the presence of a secondary eddy within the main recirculating region. The secondary structures over a wide range of Reynolds number (Re=550 to 9500). It was observed that the secondary phenomenon can lead to a major flow reorganization by drastically altering the transport of vorticity. The separating boundary layer acts as a source of vorticity and, at Re=550, the resulting vortex sheet smoothly rolls up into the primary vortex. For Re=3000 and 9500, however, the secondary eddy interferes with that process and the flux of vorticity is redirected toward the cylinder where it accumulates into a new vortical structure.\r\n\r\nThe impulsive start is followed by a [...] singularity in the drag coefficients. The numerical simulations captured this behavior and the computed drag history for short times is in close agreement with the one predicted by a matched asymptotics analysis." }, { "name": "Smedley, Gregory Todd", "degree": "PhD", "year": "1990", "title": "A study of immiscible liquids, liquid behavior at zero gravity, and dynamic contact lines and angles", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182004-154208", "creators": [ { "name": { "family": "Smedley", "given": "Gregory Todd" }, "id": "Smedley-G-T", "display_name": "Smedley, Gregory Todd" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AQR1-4B73", "abstract": "The work reported here covers three topics that were investigated as part of preparation for a space based experiment. The intention of the proposed experiment was to study the relationship between container geometry and interface geometry for a free liquid surface at zero gravity.\n\nA mathematical theory proposed by Paul Concus and Robert Finn in 1974 and recently developed by Finn yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. It is possible to find geometrical criteria that promise a particular liquid location. A unified graphical presentation of four geometries is given that can be used directly for the design of containments for liquids at zero gravity. As one application of these design curves, a container was built and tested in a series of 2 second droptower experiments at NASA Lewis Research Center.\n\nIt was apparent that the space based experiment would require use of sophisticated optical instrumentation that would be most effective if a pair of immiscible liquids were used rather than a single liquid under its vapor. This work identifies 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with plexiglas (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful noninvasive technique for determining interfacial tensions is explained and used.\n\nThe contact angle is a critical parameter in the consideration of liquid behavior at zero gravity, therefore, a technique, based on laser light refraction, was developed to objectively measure it. Dynamic contact line experiments were conducted at various velocities, both advancing and receding, using one of the 121 immiscible liquid pairs (nonane/formamide) in contact with glass.\n" }, { "name": "Washabaugh, Peter D.", "degree": "PhD", "year": "1990", "title": "An experimental investigation of mode-I crack tip deformation", "advisor": "Knauss, Wolfgang Gustav; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-101356", "creators": [ { "name": { "family": "Washabaugh", "given": "Peter D." }, "id": "Washabaugh-P-D", "display_name": "Washabaugh, Peter D." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wv0e-g535", "abstract": "The out-of-plane displacement of amorphous polymethylmethacrylate plates rupturing at slow (0.1 mm/s), and fast (0.5 to 0.9 mm/\u00b5s) rates are measured using a Twymann-Green interferometer. The measured surface shapes within one plate thickness of the crack-tip do not compare well with the two-dimensional planar asymptotic approximation, but compare favorably with the published slopes for three-dimensional finite element solutions when normalized with the static material properties. Discrepancies, on the order of ten percent, between the magnitude of the three-dimensional finite element solutions suggest that the stress intensity factor does not fully characterize the near tip deformations.\n\nA dynamically propagating crack is found to move in a non-steady, periodic, submicrosecond fashion. This result is supported both by the surface measurements and the fracture morphology. The material toughening, as measured by the surface roughness, correlates well with the stress intensity factor and not with the crack velocity. The details of the sub-microsecond propagation and toughening was not resolvable with the microsecond temporal resolution of the experiment.\n\nInhibiting the material toughening at the crack tip by artificially introducing a weak material plane augments the crack motion to velocities close to the material's shear wave speed. The crack propagates more steadily along the weak plane than through a virgin solid, while maintaining the character of the out-of-plane displacement of a crack propagating in an unsullied material.\n" }, { "name": "Zhuang, Mei", "degree": "PhD", "year": "1990", "title": "An investigation of the inviscid spatial instability of compressible mixing layers", "advisor": "Dimotakis, Paul E.; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-094001", "creators": [ { "name": { "family": "Zhuang", "given": "Mei" }, "id": "Zhuang-M", "display_name": "Zhuang, Mei" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "co-advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/650s-9t96", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe behavior of both unbounded and bounded compressible plane mixing layers with respect to two- and three-dimensional, spatially growing wave disturbances is investigated using linear stability analysis. The mixing layer is formed by two parallel streams with different gases and the flow is assumed to be inviscid and non-reacting.\r\n\r\nFor unbounded mixing layers, the effects of the free stream Mach number, velocity ratio, temperature ratio, gas constant (molecular weight) ratio and the ratios of specific heats on the linear spatial instability characteristics of a mixing layer are determined. A nearly universal dependence of the normalized maximum amplification rate on the convective Mach number is found for two-dimensional spatially growing disturbances. The effects of the mean flow profiles on the instability behavior of the mixing layers are also studied. It is shown that decreasing the thickness of the total temperature profile relative to the mean velocity profile, or adding a wake component in the mean velocity profile can make the normalized amplification rate decrease slower as the convective Mach number increases for both subsonic and supersonic convective Mach numbers.\r\n\r\nFor an unbounded mixing layer with subsonic convective Mach numbers, there is only one unstable mode propagating with a phase velocity [...] approximately equal to the isentropically estimated convective velocity of the large scale structures [...]. As the convective Mach number approaches or exceeds unity, there are always two unstable spatial modes. One is with a phase velocity [...] (slow mode and the other is with a phase velocity [...] (fast mode). For the low supersonic convective Mach numbers, the fast mode is more unstable than the slow mode when the heavy gas is on the low speed side and the slow mode is dominant when the heavy gas is on the high speed side.\r\n\r\nThe effect of parallel flow guide walls on a spatially growing mixing layer is also investigated. It is shown that, in this case, if the convective Mach number exceeds a critical value of approximately unity, there are many supersonic unstable modes. The maximum amplification rates of mixing layers approach an asymptotic value and this maximum amplification rate increases to a maximum value and decreases again as the distance between the walls decreases. For a mixing layer inside parallel flow guide walls, the growth rate of three-dimensional modes is larger than the corresponding two-dimensional mode at high convective Mach numbers. But the growth rate of two-dimensional supersonic instability waves has a larger value than their three-dimensional counterparts for a mixing layer inside a rectangular duct (Tam & Hu [1988], [1989]). Contour plots of the pressure perturbation fields for both unbounded and bounded mixing layers indicate that there are waves propagating outward from the mixing layer along the Mach angle, and that the walls provide a feedback mechanism between the growing mixing layer and this compression/expansion wave system. The bounded mixing layers are more unstable than the corresponding free mixing layers for supersonic convective Mach numbers. The streaklines of the flow confirm that the spreading rate of the mixing layer is unusually small for supersonic disturbances.\r\n" }, { "name": "Anilkumar, A. V.", "degree": "PhD", "year": "1989", "title": "Experimental Studies of High-Speed Dense Dusty Gases", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-130447", "creators": [ { "name": { "family": "Anilkumar", "given": "A. V." }, "id": "Anilkumar-A-V", "display_name": "Anilkumar, A. V." } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/5B1B-AY62", "abstract": "An experimental study of the flow of high-speed dense dusty gases has been conducted in a novel shock tube facility. The flow is generated through rapid depressurization and subsequent fluidization of a stationary packed bed of particles loaded under pressure in the vertical driver section of the shock tube. The flow was studied with high-speed photography and fast-response pressure transducers.
\r\n\r\nThe studies have been exploratory in nature. The entire process of lofting and disassembly of packed particle beds has been documented. A wide spectrum of dusty flows with particle loadings ranging from that of a fully packed plug to that of a dilute disperse particle flow was observed in this facility. Only extreme flow fields like packed plug flows and very dilute disperse particle flows were found to be uniform. All other flow fields, with intermediate particle loadings, were characterized by the simultaneous presence of dense filamentary structures and dilute dispersions of particles. Typically, while operating with 0.5 mm glass beads, flows reached speeds of 60 meters per second in a period of 25 milliseconds.
\r\n\r\nTwo lofting configurations of the packed beds were set up. In the first configuration, the rapid depressurization of the interstitial bed fluid and the consequent initiation of bed expansion was examined. Bed expansion starts along horizontal fractures that partition the bed into slabs. While the bed is accelerating, particles rain down from the bottom surfaces of the slabs partitioning the fractures into bubbles with a characteristic honeycomb pattern. The bubbles eventually compete and the dominant ones prevail. The observed instability of the bottom surfaces of the slabs is analogous to the Rayleigh-Taylor instability observed in continuous media. The flow development in this configuration was not influenced by any wall effects.
\r\n\r\nThe second lofting configuration is a high-speed fluidization configuration. Here, the role of the fluid entering from below the bed, in continuing the bed expansion initiated by the rapid depressurization of the interstitial bed fluid, was examined. The bed expansion occurs along expanding and elongating bubbles and the bubble walls are stretched into dense filamentary structures. Beds initially stacked with a gradient in particle size or density or both showed drastic differences in response to fluidization. The morphology of the expanded flow field in all cases was essentially the same: nonuniform, interspersed with dense filamentary structures and dilute dispersions of particles.
\r\n\r\nIn the second lofting configuration, only the late stages of flow development were influenced by wall effects. Wall effects manifest as faster moving fluid along the walls and denser accumulation of flow structures towards the center of the channel. The bottom of the dusty flow is characterized by the presence of a tail; a concentric dense particle column formed by the accumulation of particles, initially present in the bottom regions of the flow. The tail terminates in a bulbous and streamlined bottom from which particles are slowly eroded by the coflowing fluid.
\r\n\r\nA multi-transducer probe was installed in the dusty gas flow for making dynamic pressure measurements and for correlating observations with those made through extensive flow visualization.
" }, { "name": "Beran, Philip Stewart", "degree": "PhD", "year": "1989", "title": "An Investigation of the Bursting of Trailing Vortices Using Numerical Simulation", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-105641", "creators": [ { "name": { "family": "Beran", "given": "Philip Stewart" }, "id": "Beran-Philip-Stewart", "display_name": "Beran, Philip Stewart" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/chyb-nk54", "abstract": "Solutions of the Navier-Stokes equations are obtained for the flow of an isolated, trailing vortex, and for the swirling flow through a frictionless pipe. In both cases, the flow is assumed to be steady, incompressible and rotationally symmetric. Solutions are computed using Newton's method and Gaussian elimination for a wide range of values of two parameters: Reynolds number, Re, and vortex strength, V. Pseudo-arclength continuation is employed to facilitate the computation of solution points in the parameter space. The numerical procedure is validated through comparison of solutions with solutions obtained in previous investigations for the case of a trailing vortex. Solutions are also compared with results reported by Brown and Lopez (1988) for the case of flow through a pipe.
\r\n\r\nSolutions of the quasi-cylindrical equations are obtained for the flow of a trailing vortex. Solutions are computed using an explicit, space-marching scheme, and are compared with solutions of the Navier-Stokes equations.
\r\n\r\nProvided that Re is about 200, or larger, four vortex states are observed.
\r\n\r\n1. When V is sufficiently small, the flow is entirely supercritical.
\r\n\r\n2. As V is increased, the flow at an axial station becomes critical and a transition point forms. At the point, the flow departs from an upstream state that is supercritical to a downstream state that is marked by large-amplitude, spatial oscillations of core radius. When Re is large, the downstream state is nearly periodic. The general features of transition are well described by the conjugate-flow theory of Benjamin 1967). Failure of the quasi-cylindrical equations is found to be a necessary and sufficient condition for the existence of a transition point. As V is further increased, the transition point moves upstream. Reversed flow is not observed.
\r\n\r\n3. Over a narrow range of vortex strengths, a small bubble of reversed flow is observed downstream of the transition point.
\r\n\r\n4. When V is large, the entire flow is marked by large-amplitude, spatial oscillations of core radius. A transition point is not evident within the computational domain. Typically, large regions of reversed flow are observed.
" }, { "name": "Brouillette, Martin", "degree": "PhD", "year": "1989", "title": "On the Interaction of Shock Waves with Contact Surfaces Between Gases of Different Densities", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-102505", "creators": [ { "name": { "family": "Brouillette", "given": "Martin" }, "id": "Brouillette-Martin", "display_name": "Brouillette, Martin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9JGS-ZX78", "abstract": "The interaction of shock waves with a contact surface between gases of different densities has been studied experimentally and theoretically. The basic mechanism for the instability of perturbations at the interface is baroclinic vorticity generation resulting from the misalignment of the pressure gradient of the shock and the density gradient of the interface. In the present study, the effects of interface density contrast and initial thickness, and incident wave strength on the development of the instability at the interface are investigated. The experiments were performed in a new vertical shock tube facility where the interaction of a shock wave with either a discontinuous interface, formed by a thin (0.5 \u00b5m) plastic membrane, or a continuous interface, created by retracting a metal plate initially separating the two gases, was studied. Air was used on one side of the interface and either helium, carbon dioxide, refrigerant-22 or sulphur hexafluoride was used on the other side as the test gas.
\r\n\r\nExperiments to study the time evolution of quasi-sinusoidal perturbations on a continuous interface have shown that the growth rates are reduced as the interface thickness is increased. It has been observed that growth rates of perturbations of wavelength \u03bb ~ 25 mm on interfaces of thickness \u03b4 ~ 10 mm are about three times smaller than those predicted by the linear theory for the impulsive acceleration of discontinuous interfaces. A new model that accounts for the growth rate reduction caused by the presence of a finite density gradient on the interface has been proposed, and good agreement was obtained with the present experimental results.
\r\n\r\nExperiments were also performed to observe the schlieren visual thickness of plane discontinuous or continuous interfaces with random small-scale perturbations after interaction with the incident shock wave and its reverberations. The interface was initially located near the end wall of the shock tube to permit the observation of the development of the interface phenomena after the arrival of the incident shock and its reverberations. It is found that the interaction of a shock wave with a discontinuous interface causes the appearance of a turbulent mixing zone between the two gases, whose growth rate slows down as time increases, owing to a decrease in turbulence intensity and the action of viscosity. Because of the large uncertainty associated with the measurements a short time after the interaction with the incident shock, the accurate determination of a possible universal power law governing the thickening of the interface is not feasible. Results for the interaction of the first reverberation of the primary wave with the already turbulent interface have demonstrated that this growth is sensitive to the initial pre-growth state of the interface. It also appears that the thickening of the turbulent mixing zone is accomplished by the merging of large structures within the interface. However, since the energy available for the turbulent motions at the impulsively accelerated interface remains constant after the interaction with the shock and also depends on the wavelength of the initial perturbation, it is not certain whether the development of mixing at the interface achieves an asymptotic stage of self-similar turbulence independent of initial conditions, as has been observed for the gravity-driven interfaces. Also, it has been found that the growth rates measured in the present experiments with discontinuous interfaces are nearly an order of magnitude lower than those reported by previous investigators. The continuous interfaces formed by the retracting plate are smoothed by molecular diffusion, and thus the combination of low density gradient and small initial perturbations is such that they exhibit growth only after being perturbed by acoustic noise introduced by the reverberation of waves between the interface, the side walls and the end of the shock tube.
\r\n\r\nThe development of viscous boundary layers on the side walls of the test section can cause the bifurcation of waves reflected from the end wall of the shock tube, and, thereafter, the formation of wall bubbles and interface contaminating jets. Moreover, the generation of vortical structures by the baroclinic instability excited by the interaction of reflected waves with the distorted interface within the boundary layer has been demonstrated. Significant contamination of the test gas can by achieved by these structures, even if reflected-wave bifurcation is absent. Moreover, the strain induced by the vorticity in these wall structures tends to thin the interface; the magnitude of this effect on the growth rates in the present plane interface experiments is estimated to be of order 10% for discontinuous interfaces and 50% for continuous interfaces.
\r\n" }, { "name": "Krishnaswamy, Sridhar", "degree": "PhD", "year": "1989", "title": "On the Domain of Dominance of the Asymptotic Elastodynamic Crack-Tip Fields", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-134326", "creators": [ { "name": { "family": "Krishnaswamy", "given": "Sridhar" }, "id": "Krishnaswamy-Sridhar", "display_name": "Krishnaswamy, Sridhar" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/cfz9-nk80", "abstract": "A substantial part of the experimental data in dynamic fracture mechanics has been obtained under the assumption that the two-dimensional asymptotic elastodynamic stress-intensity factor field (the KdI-field) is dominant over at least the region around the crack-tip over which the experimental measurements are made. The validity of this assumption is investigated in this thesis both experimentally and through finite-element simulations of the experiments.
\r\n\r\nThe experiments reported in this work were on 4340 steel, three-point bend specimens loaded dynamically using a drop-weight tower. The two cases of dynamically loaded stationary cracks and dynamically propagating cracks were considered. An optical configuration is proposed that leads to a bifocal high-speed camera capable of focusing on two different planes simultaneously. This was used in conjunction with the method of caustics to measure the apparent stress-intensity factor simultaneously from two different regions (initial-curves) around the crack-tip. If the initial-curves lie within the domain of dominance of the asymptotic field, the measured values of the dynamic stress-intensity factor must agree to within experimental error. By suitably adjusting the optical set-up, a range of initial-curves was scanned in an attempt to map the domain of dominance of the KdI-field.
\r\n\r\nThe impact hammer and supports of the drop-weight loading device were instrumented in order to monitor the time dependent loads acting on the specimen. These loads were subsequently used as boundary tractions in dynamic two- and three-dimensional finite-element simulations of the experiments. The simulations were carried only up to the point of crack initiation. Comparison of the numerical simulations with the experimental results help in identifying the role of three-dimensionality and transient conditions on the measured stress-intensity factor values.
\r\n\r\nOn the basis of both the experimental results as well as the numerical simulations, no sizeable annulus of dominance for the asymptotic elastodynamic field was found for the laboratory situation studied. It appears that the assumption of an underlying KdI-dominant (or two-dimensional) field might not hold to a level of accuracy that would warrant many of the conclusions made in the literature regarding the crack-initiation toughness values as well as the uniqueness of the dynamic fracture toughness - crack velocity relation or its specimen and acceleration dependence.
" }, { "name": "Schneider, Steven Philip", "degree": "PhD", "year": "1989", "title": "Effects of Controlled Three-Dimensional Perturbations on Boundary Layer Transition", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142007-094214", "creators": [ { "name": { "family": "Schneider", "given": "Steven Philip" }, "id": "Schneider-Steven-Philip", "display_name": "Schneider, Steven Philip" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZJ0M-GG83", "abstract": "The laminar-turbulent transition in a flat plate boundary layer was studied experimentally using a spanwise array of computer-controlled surface heating elements. The elements were used to introduce disturbances at a point just downstream of the critical Reynolds number. When sinusoidal heating at an unstable frequency is carried out, instability waves develop and grow as they travel downstream. Measurements were made using flush-mounted hot-film wall shear sensors, and the later stages of transition were visualized using dye injection. Oblique Tollmien-Schlichting waves were successfully introduced, and their downstream development into the turbulent regime was studied. Exploratory studies of other types of 3D forcing are also reported.
\r\n\r\nMeasurements of oblique waves in the linear region yielded phase speeds and wave angles that were consistent with the linear theory. Subharmonics of the oblique-wave wall shear were seen downstream, in the nonlinear region. Surprisingly, the amplitude of these subharmonic waves decreased abruptly with increasing oblique-wave angle, so that an oblique wave of about 10 degrees had a subharmonic amplitude which was an order of magnitude below that for a 2D wave. Waves of larger oblique angles did not produce detectable subharmonics. A simple explanation of this behavior is given, in terms of the wave-interaction theory.
\r\n\r\nThe intermittency, defined as the fraction of time in which the wall shear is turbulent, was measured to determine the relative location of transition. These measurements, carried out further downstream, show that the introduction of a 2D wave is most effective in moving the transition point upstream, for a given power input. This upstream movement of transition slowly decreases as the oblique wave angle is increased. The fact that there is no abrupt movement of transition corresponding to the abrupt disappearance of the subharmonic nonlinear breakdown mechanism suggests there should be a simpler explanation for the nonlinear breakdown.
" }, { "name": "Winckelmans, Gr\u00e9goire St\u00e9phane", "degree": "PhD", "year": "1989", "title": "Topics in Vortex Methods for the Computation of Three- and Two-Dimensional Incompressible Unsteady Flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-112216", "creators": [ { "name": { "family": "Winckelmans", "given": "Gr\u00e9goire St\u00e9phane" }, "id": "Winckelmans-Gr\u00e9goire-St\u00e9phane", "display_name": "Winckelmans, Gr\u00e9goire St\u00e9phane" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/19HD-DF80", "abstract": "Contributions to vortex methods for the computation of incompressible unsteady flows are presented. Three methods are investigated, both theoretically and numerically.
\r\n\r\nThe first method to be considered is the inviscid method of vortex filaments in three dimensions, and the following topics are presented: (a) review of the method of regularized vortex filaments and of convergence results for multiple-filament computations, (b) modeling of a vortex tube by a single filament convected with the regularized Biot-Savart velocity applied on the centerline: velocity of the thin filament vortex ring and dispersion relation of the rectilinear filament, and (c) development of a new regularization of the Biot-Savart law that reproduces the lowest mode dispersion relation of the rectilinear vortex tube in the range of large to medium wavelengths.
\r\n\r\nNext the method of vortex particles in three dimensions is investigated, and the following contributions are discussed: (a) review of the method of singular vortex particles: investigation of different evolution equations for the particle strength vector and weak solutions of the vorticity equation, (b) review of the method of regularized vortex particles and of convergence results, and introduction of a new algebraic smoothing with convergence properties as good as those of Gaussian smoothing, (c) development of a new viscous method in which viscous diffusion is taken into account by a scheme that redistributes the particle strength vectors, and application of the method to the computation of the fusion of two vortex rings at Re = 400, and (d) investigation of the particle method with respect to the conservation laws and derivation of new expressions for the evaluation of the quadratic diagnostics: energy, helicity and enstrophy.
\r\n\r\nThe third method considered is the method of contour dynamics in two dimensions. The particular efforts presented are (a) review of the classical inviscid method and development of a new regularized version of the method, (b) development of a new vector particle version of the method, both singular and regularized: the method of particles of vorticity gradient, (c) development of a viscous version of the method of regularized particles and application of the method to computation of the reconnection of two vortex patches of same sign vorticity, and (d) investigation of the particle method with respect to the conservation laws and derivation of new expressions for the evaluation of linear and quadratic diagnostics.
" }, { "name": "Dowling, David Russell", "degree": "PhD", "year": "1988", "title": "Mixing in Gas Phase Turbulent Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06132005-160404", "creators": [ { "name": { "family": "Dowling", "given": "David Russell" }, "id": "Dowling-David-Russell", "display_name": "Dowling, David Russell" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9233-5476", "abstract": "This work is an experimental investigation of the mixing of the nozzle fluid of a round, turbulent jet with the entrained reservoir fluid, using laser-Rayleigh scattering methods. The measurements, at Reynolds numbers of 5,000 and 16,000, cover the axial range from 20 to 90 jet exit diameters and resolve the full range of temporal and spatial concentration scales. The measured mean and rms values of the concentration, and the mean scalar dissipation rate, when estimated from the time derivative of concentration, are consistent with jet similarity laws. Concentration fluctuation power spectra are found to be self-similar along rays emanating from the virtual origin of the jet, and are consistent with the universal form of scalar spectra proposed by Gibson (1968 II). The probability density functions for the concentration, the time derivative of concentration, and the square of the time derivative of concentration, are compiled and are also found to be self-similar along rays. Features of the measured distributions and spectra are consistent with the existence of large-scale structures within the flow that span the local diameter of the jet's turbulent cone. On the centerline of the jet, the scaled probability density function of jet gas concentration is found to be almost independent of the Reynolds number while the local mixing rate in the inner part of jet is not. The usual assumptions concerning isotropy and correlation of derivatives are found to lead to erroneous results for the probablility density function of the scalar dissipation rate.
" }, { "name": "Giezen, Jurgen Johannes", "degree": "PhD", "year": "1988", "title": "Plastic Buckling of Cylinders Under Biaxial Loading", "advisor": "Babcock, Charles D.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212007-083506", "creators": [ { "name": { "family": "Giezen", "given": "Jurgen Johannes" }, "id": "Giezen-Jurgen-Johannes", "display_name": "Giezen, Jurgen Johannes" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "co-advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Singer", "given": "Josef" }, "id": "Singer-J", "role": "member", "display_name": "Singer, Josef" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ycv3-kp17", "abstract": "An experimental investigation is carried out to study the effects of nonproportional loading in the plastic range on a buckling load. The discrepancy between experimental and theoretical results points to some principal shortcoming in the analysis. The problem has been simplified by applying axial tensile load and external press to simple cylindrical shell specimen and observing the buckling load for various nonproportional load-paths. Results are compared to numerical predictions (BOSOR5) using classical type plasticity models such as J\u2082 deformation and J\u2082 incremental theory. Significant discrepancy was found an attributed to inadequate modeling of the nonlinear material behavior. The effects of geometrical imperfections and large deflections were found to insignificant, thereby leading to an idea how much of the discrepancy between test and theory is due to a use of inadequate plastic model. The introduction of the Southwell plot into elastic shell buckling problem reduced the already minor effects of geometric imperfections.
\r\n\r\nThe Christoffersen-Hutchinson corner theory model was introduced into BOSAR5 in its simplest form as presented by Poh-Sang Lam. Results obtained with this model, which allows corners to form on an initially smooth yield surface, displayed better agreement with experimental data. However, increased computational time and problems related to abrupt changes in load-path at the corner are a major concern at this present time.
\r\n" }, { "name": "Pugh, Jeffrey David", "degree": "PhD", "year": "1988", "title": "Finite Amplitude Waves in Plane Poiseuille Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-104253", "creators": [ { "name": { "family": "Pugh", "given": "Jeffrey David" }, "id": "Pugh-Jeffrey-David", "display_name": "Pugh, Jeffrey David" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XHFQ-MJ23", "abstract": "Nonlinear behavior in plane Poiseuille flow has attracted theoretical interest over the last decade, both because of its tractability and because it is believed that some of the results may be applicable to phenomena occurring in the boundary layer. We have investigated the existence of three-dimensional finite amplitude waves in plane Poiseuille flow, in the hope of finding candidates for a class of simple flows which might provide insight into the nature of turbulence. These so-called vortical states would exist as attractors for the turbulent flow and mimic many of its properties.
\r\n\r\nOne of the requisite properties of these simple flows is existence at the low Reynolds numbers observed in experimental studies of transition to turbulence in plane Poiseuille flow. Although no such three-dimensional solutions were found in our study, a number of new insights have been made into the structure and stability of two- and three-dimensional steady wave solutions in plane Poiseuille flow. These in turn suggest new areas of investigation for finding vortical states.
" }, { "name": "Waas, Anthony Marius", "degree": "PhD", "year": "1988", "title": "Compression Failure of Fibrous Laminated Composites in the Presence of Stress Gradients: Experiment and Analysis", "advisor": "Babcock, Charles D.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-092741", "creators": [ { "name": { "family": "Waas", "given": "Anthony Marius" }, "id": "Waas-Anthony-Marius", "orcid": "0000-0002-5258-2749", "display_name": "Waas, Anthony Marius" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "co-chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "co-chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Singer", "given": "Josef" }, "id": "Singer-J", "role": "member", "display_name": "Singer, Josef" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PP86-PE50", "abstract": "A series of experiments were performed to determine the mechanism of failure in compressively loaded laminated plates in the presence of stress gradients generated by a circular cutout. Real time holographic interferometry and in-situ photomicrography of the hole surface, were used to observe the progression of failure.
\r\n\r\nThe test specimens are multi-layered composite flat plates, which are loaded in compression. The plates are made of two material systems, T300/BP907 and IM7/8551-7. Two different lay-ups of T300/BP907 and four different lay-ups of IM7/8551-7 are investigated.
\r\n\r\nThe load on the specimen is slowly increased and a series of interferograms are produced during the load cycle. These interferograms are video-recorded. The results obtained from the interferograms and photo-micrographs are substantiated by sectioning studies and ultrasonic C-scanning of some specimens which are unloaded prior to catastrophic failure, but beyond failure initiation. This is made possible by the servo-controlled loading mechanism that regulates the load application and offers the flexibility of unloading a specimen at any given instance in the loadtime history.
\r\n\r\nAn underlying objective of the present investigation is the identification of the physics of the failure initiation process. This required testing specimens with different stacking sequences, for a fixed hole diameter, so that consistent trends in the failure process could be identified.
\r\n\r\nIt is revealed that the failure is initiated as a localized instability in the 0\u00b0 plies at the hole surface, approximately at right angles to the loading direction. This instability emanating at the hole edge and propagating into the interior of the specimen within the 0\u00b0 plies is found to be fiber microbuckling. The microbuckling is found to occur at a local strain level of \u2243 8600 \u00b5strain at the hole edge for the IM material system. This initial failure renders a narrow zone of fibers within the 0\u00b0 plies to loose structural integrity. Subsequent to the 0\u00b0-ply failure, extensive delamination cracking is observed with increasing load. The through thickness location of these delaminations is found to depend on the position of the 0\u00b0 plies.
\r\n\r\nThe delaminated portions spread to the undamaged areas of the laminate by a combination of delamination buckling and growth, the buckling further enhancing the growth. When the delaminated area reaches a critical size, about 75-100% of the hole radius in extent, an accelerated growth rate of the delaminated portions is observed. The culmination of this last event is the complete loss of flexural stiffness of each of the delaminated portions leading to catastrophic failure of the plate. The levels of applied load and the rate at which these events occur depend on the plate stacking sequence.
\r\n\r\nA simple mechanical model is presented for the microbuckling problem. This model addresses the buckling instability of a semi-infinte layered half-plane alternatingly stacked with fibers and matrix, loaded parallel to the surface of the half-plane. The fibers are modelled using Bernoulli-Navier beam theory, and the matrix is assumed to be a linearly elastic foundation. The predicted buckling strains are found to overestimate the experimental result. However, the dependence of the buckling strain on parameters such as the fiber volume fraction, ratio of Youngs moduli of the constituents and Poisson's ratio of the matrix are obtained from the analysis. It is seen that a high fiber volume fraction, increased matrix stiffness, and perfect bonding between fiber and matrix are desirable properties for increasing the compressive strength.
" }, { "name": "Arakeri, Jaywant H.", "degree": "PhD", "year": "1987", "title": "Structure Measurements in a Synthetic Turbulent Boundary Layer", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-085206", "creators": [ { "name": { "family": "Arakeri", "given": "Jaywant H." }, "id": "Arakeri-Jaywant-H", "display_name": "Arakeri, Jaywant H." } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FABW-YZ77", "abstract": "Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number.
\r\n\r\nThe large eddy is composed of a pair of primary counter-rotating vortices about five \u03b4 long in the streamwise direction and about one \u03b4 apart in the spanwise direction, where \u03b4 is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer flow. A stretching mechanism is important in matching spanwise vorticity close to the wall to variations in turbulent shearing stress. Regions where the stretching term is large coincide with regions of large wall shearing stress and large turbulence production.
" }, { "name": "Lacerda, Nehemias Lima", "degree": "PhD", "year": "1987", "title": "On the Start Up of Supersonic Underexpanded Jets", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-081340", "creators": [ { "name": { "family": "Lacerda", "given": "Nehemias Lima" }, "id": "Lacerda-Nehemias-Lima", "display_name": "Lacerda, Nehemias Lima" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W3CX-2Z48", "abstract": "An impulsively started jet can be formed by a gas confined in a high pressure reservoir that escapes suddenly through an exit orifice, into a controlled atmosphere. Supersonic gas jets of this type are unsteady and differ from the steady jet that develops later by the presence of a bow shock, a jet head and a nonstationary Mach disk. The effects of the pressure ratio between the high pressure gas inside the reservoir and the lower pressure atmospheric gas, as well as the gas combination used, are studied experimentally. The gases used for the jet and the atmosphere were selected from helium, nitrogen and sulfur hexafluoride.
\r\n\r\nThe data acquisition consisted of: high resolution flash photography to obtain detail from the pictures; high-speed movie pictures to obtain the time development of selected features; and fast-response pressure transducers located at the reservoir end plate, the tank end plate and the jet exit. The initial development of the jet is highly time dependent. During this phase, the shape that the jet assumes varies with pressure ratio and with the choice of gas. In particular an extremely light gas exhausting into a heavy atmosphere, exhibits an uncommon shape. It develops as a bubble wrapped by the bow shock, that increases its volume with flow time and pressure ratio. As the pressure ratio increases, it becomes more tightly wrapped by the bow shock. At later times the jet assumes conventional linear growth.
\r\n\r\nAfter the jet starts, a Mach disk is observed close to the jet exit which moves downstream as the exit pressure builds up. The monotonic increase in exit pressure is caused by the slow breaking of the diaphragm. The position of the Mach disk is furthest from the jet exit when the exit pressure is a maximum. After that it oscillates around the location predicted by the steady theory of Ashkenas and Sherman (1966) at a frequency close to one of the resonant frequencies of the reservoir. The features observed for the inner structure of the jet were verified to agree with those obtained for impulsive flow generated by a muzzle blast.
\r\n\r\nThe frontal part of the jet forms the jet head, whose shape changes with the flow conditions. The initial evolution of the jet head is linear but after propagating a distance of around ten exit diameters, it reaches asymptotic behavior with an evolution that is approximately proportional to square root of time. The head creates a bow shock ahead of it that propagates downstream and increases the pressure of the atmospheric gas. This bow shock was found to be less attenuated than in spherically symmetric explosions. The asymptotic behavior of the bow shock was reached after about eight exit diameters.
" }, { "name": "Lin, Jane Ming-Chin", "degree": "PhD", "year": "1987", "title": "Transient Gas Jets into Liquid", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262004-113723", "creators": [ { "name": { "family": "Lin", "given": "Jane Ming-Chin" }, "id": "Lin-Jane-Ming-Chin", "display_name": "Lin, Jane Ming-Chin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4qp0-4x37", "abstract": "An experimental investigation of the development of high velocity, impulsively initiated gas jets into liquid was conducted in an effort to understand some of the physical processes that occur for a jet of very light fluid into a dense ambient atmosphere. Four gases, refrigerants 12 and 22, nitrogen, and helium were injected into water at nozzle exit Mach numbers from 1.0 to 2.2.
\r\n\r\nThe study showed that a gas jet into water develops in at least three stages: startup, transition, and global steady state. The startup is characterized by bubble growth; the growth rate is well predicted by classical bubble-growth theory. Jet transition is marked by axially directed flow, which penetrates through the startup bubble and which forms a cylindrical protrusion along the axis of symmetry. A combination of strong recirculating flow and liquid entrainment causes the startup bubble to deflate and to lift off and move downstream. In the steady state, instantaneous photographs show small-scale fluctuations of the jet boundary, but time-averaged photographs show the expected conical spreading of the steady jet; the measured spreading angles range from 18-25 degrees.
\r\n\r\nHowever, the most significant finding of this study is that under some conditions, the gas jet into liquid never reaches the global steady state. Instead, the jet boundary exhibits chugging: large nonlinear oscillations which lead to irregular collapses of the gas column followed by explosive outward bursts of gas. The unsteadiness observed is much more violent than the familiar fluctuations typical of constant-density jets. The length scale of the motion is generally on the order of several jet diameters; the time scale is on the order of the period for bubble collapse.
\r\n\r\nIt was found that the amplitude and frequency of chugging are strongly dependent on the ratio of the liquid density to the gas density, the jet Mach number, and the operating pressure ratio. The conditions under which unsteadiness occurs were determined experimentally. In particular, a quantitative measure of jet susceptibility to unsteadiness has been established. Steady jets can be achieved in two ways: by being discharged from deLaval nozzles (increasing the exit Mach number) or by being overpressured.
\r\n\r\nThe unsteady behavior is modeled as the collapse of a bubble in liquid; comparisons of collapse times show good agreement. A mechanism for the unsteadiness is discussed. It is proposed that the chugging is the response of the jet boundary to a pressure difference between the jet and surrounding liquid, which arises as the result of the rapid expansion of a light fluid into a dense ambient atmosphere. The flow is shown to be similar to the discharge of a gas from a nozzle into a channel of larger cross section. An upper limit to the pressure difference is determined based on estimates of the minimum base pressure for such channel flows; a lower limit is established for the collapse time. All experimental values are within the bounds. The derived values indicate that the pressure differences between the jet and liquid may be more than 90 percent of the ambient pressure.
" }, { "name": "Papamoschou, Dimitri", "degree": "PhD", "year": "1987", "title": "Experimental Investigation of Heterogeneous Compressible Shear Layers", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-085328", "creators": [ { "name": { "family": "Papamoschou", "given": "Dimitri" }, "id": "Papamoschou-Dimitri", "display_name": "Papamoschou, Dimitri" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "member", "display_name": "Blandford, Roger D." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "member", "display_name": "Lees, Lester" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M7PQ-Y494", "abstract": "The compressible, two-dimensional shear layer is investigated experimentally in a novel facility. In this facility, it is possible to flow similar or, dissimilar gases of different densities and to select different Mach numbers for each stream over a wide range of Reynolds numbers. In the current experiments, ten combinations of gases and Mach numbers are studied in which the freestream Mach numbers range from 0.2 to 4, the density ratio varies from 0.2 to 9.2, and the velocity ratio varies from 0.13 to 1. The growth of the turbulent region of the layer is measured by means of pitot pressure profiles obtained at several streamwise locations. The resulting growth rate is estimated to be about 80% of the visual growth rate. The transition from laminar to turbulent flow, as well as the structure of the turbulent layer, are observed with Schlieren photographs of 20 nanosecond duration. Streamwise pressure distribution and total pressures are measured by means of a Scanivalve-pressure transducer system.
\r\n\r\nAn underlying objective of this investigation was the definition of a compressibility-effect parameter that correlates and consolidates the experimental results, especially the turbulent growth rates. A brief analytical investigation of the vortex sheet suggests that such a parameter is the Mach number in a frame of reference moving with the phase speed of the disturbance, called here the convective Mach number. In a similar manner, the convective Mach number of a turbulent shear layer is defined as the one seen by an observer moving with the convective velocity of the dominant waves and structures. It happens to have about the same value for each stream. In the current experiments, it ranges from 0 to 1.9.
\r\n\r\nThe correlations of the growth rate with convective Mach number fall approximately onto one curve when the growth rate is normalized by its incompressible value at the same velocity and density ratios. The normalized growth rate, which is unity for incompressible flow, decreases gradually with increasing convective Mach number, reaching an asymptotic value of about 0.25 for supersonic convective Mach numbers. The above behavior is in qualitative agreement with results of linear stability theory as well as with those of previous, one-stream experiments.
\r\n\r\nLarge-scale structures, resembling those observed in subsonic shear layers, are evident in the Schlieren photographs. It is estimated that the mean structure spacing, normalized by the local thickness, is reduced to about half its incompressible value as the convective Mach number becomes supersonic.
\r\n\r\nAn estimate of the transition Reynolds number has been obtained from the photographs of two shear layers having quite different convective Mach numbers, one low subsonic and the other sonic. In both cases, it is about 2 x 105, based on distance to transition and properties of the high unit Reynolds number stream, thus suggesting that, in this experiment, transition is dominated by instabilities of the wake, rather than of the shear layer.
\r\n" }, { "name": "Schatzle, Paul Russell", "degree": "PhD", "year": "1987", "title": "An Experimental Study of Fusion of Vortex Rings", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232004-092555", "creators": [ { "name": { "family": "Schatzle", "given": "Paul Russell" }, "id": "Schatzle-Paul-Russell", "display_name": "Schatzle, Paul Russell" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KK00-ZJ41", "abstract": "A two-component laser-Doppler velocimeter with frequency bias is used to measure the velocity field produced by the oblique collision of two laminar vortex rings. The Reynolds number, defined here as the ratio of ring circulation to kinematic viscosity, is about 1800. The rings are generated underwater and approach each other along intersecting paths. The plane defined by the two paths is a plane of symmetry, and is the plane in which the measurements were done. The out-of-plane components of vorticity and strain rate are computed from finite differences of the velocity data. The state of the rings prior to the collision is determined in order to provide a set of starting conditions for future numerical simulations. In addition, the circulation of each vortex core is computed as a function of time during the collision.
\r\n\r\nThe principal result of this work is that the circulation of each vortex core is observed to decrease during the interaction; furthermore, the fluid viscosity is shown to be responsible for this decrease. The exact mechanism by which the reduction in circulation is effected is unclear, but it appears to be related to the out-of-plane stretching. A time scale is proposed for this cancellation process which combines the effects of viscosity and stretching.
\r\n\r\nThe measurements also show that the structure of the vorticity field changes during the collision. In particular, each vortex core is observed to split into two vortices under the action of the local in-plane strain field.
" }, { "name": "Dubois, Pascale Claude", "degree": "Engineering Degree", "year": "1986", "title": "Study of the Stall-Spin Phenomena Using Analysis and Interactive 3-D Graphics", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242008-113141", "creators": [ { "name": { "family": "Dubois", "given": "Pascale Claude" }, "id": "Dubois-Pascale-Claude", "display_name": "Dubois, Pascale Claude" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SFMF-Z114", "abstract": "The purpose of this study is to gain a better understanding of the nonlinear stall-spin phenomenon through numerical analysis and interactive 3-D graphics.
\r\n\r\nThe linear aerodynamic range was thoroughly examined for the NAVION, a light aviation aircraft. Nonlinear aerodynamic behavior was modeled by adding nonlinearities to the lift, pitching and rolling moments. The results of this analysis are promising; however, a more sophisticated model is needed to fully simulate the stall-spin phenomenon.
\r\n\r\nA graphic tool is described which allows the user to interact with the simulation process. This gives the user a \"feel\" for the dynamics of aircraft and effectively displays the characteristic features of the dynamic model.
\r\n" }, { "name": "Freeman, Janet Elizabeth", "degree": "Engineering Degree", "year": "1986", "title": "Design of One-Kilometer-Long Antenna Sticks and Support Structure for a Geosynchronous Satellite", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242008-104934", "creators": [ { "name": { "family": "Freeman", "given": "Janet Elizabeth" }, "id": "Freeman-Janet-Elizabeth", "display_name": "Freeman, Janet Elizabeth" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0cpe-gh28", "abstract": "This study develops a preliminary structural design for three one-kilometer-long antenna sticks and an antenna support structure for a geosynchronous earth-imaging satellite. On each of the antenna sticks is mounted a linear array of over 16,000 antenna elements. The antenna sticks are parallel to each other, and are spaced 1 km apart so that they form the corners of an imaginary triangular tube. This tube is spinning about its long axis. Antenna performance requires that the position of each antenna element be known to an accuracy of 0.5 cm, and that the spacecraft's spin axis be parallel to the earth's spin axis within one degree. Assuming that the position of each joint on each antenna stick is known, the antenna sticks are designed as beams under a uniformly distributed acceleration (due to spacecraft spin) to meet the displacement accuracy requirements for the antenna elements. Both a thin-walled round tube and a three-longeron double-laced truss are considered for the antenna stick structure. A spacecraft spinrate is chosen by considering the effects of environmental torques on the precession of a simplified spacecraft. A preliminary truss-like support structure configuration is chosen, and analyzed in quasi-static equilibrium with control thrusters firing to estimate the axial loads in the structural members. The compressive loads found by this analysis are used to design the support structure members to be buckling-critical three-longeron double-laced truss columns. Some tension-only members consisting of Kevlar cord are included in the design to eliminate the need for bulkier members. The lateral vibration modes of the individual structural members are found by conventional analysis -- the fundamental frequencies are as low as 0.0066 Hz. Finite element dynamic analyses of the structure in free vibration confirm that simplified models of the structure and members can be used to determine the structural modes and natural frequencies for design purposes." }, { "name": "Kawasaki, Kazunori", "degree": "Engineering Degree", "year": "1986", "title": "Monte Carlo Calculation of the Flow of Granular Materials", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-110816", "creators": [ { "name": { "family": "Kawasaki", "given": "Kazunori" }, "id": "Kawasaki-K", "display_name": "Kawasaki, Kazunori" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6b67-x610", "abstract": "The flow of granular materials has been investigated theoretically using the Direct Simulation Monte Carlo (DSMC) method for rarefied gas flows implemented on the Caltech concurrent 64-node Cosmic Cube computer. A fundamental understanding of the behavior of a heavily loaded gas under conditions for which collisions among the solid particles suspended in the gas are frequent is very important for a variety of problems, e.g., grain explosions and the performance of metallized solid-propellant rockets. At one extreme of particulate flow (granular material flow), the effect of the interstitial fluid is negligible. In particular, the numerical method has been applied to the problem of sedimentation and channel flow.\r\n\r\nBird's method has been applied to granular material flows by using a hard, rough-sphere particle model and introducing restitution and slip coefficients for particle-particle and particle-boundary collisions, respectively. In the DSMC method, physical space is divided into many cells, each containing several simulated particles. The distance between particles is much greater than the particle diameter. Using the concurrent computer, cells are assigned singly or in groups to individual processors (nodes). Calculations of particle-particle collisions are carried out locally by each node and information is communicated between adjacent nodes. Using the concurrent computer has enabled powerful computational ability to be brought to bear on the DSMC calculation.\r\n\r\n For a gas sedimentation calculation simulating the gravitational collapse of a uniform atmosphere, significant thermal and wave effects are observed. For flow in a channel at Mach number 2.76 and Reynolds number 32.6, differences are observed between the behavior of granular material flow and gas flow. For both cases significant \"slip\" at the wall is observed. For the flow of granular material, the boundary layer is thin and the velocity reduction near the wall is small." }, { "name": "Papantoniou, Dimitris Antony", "degree": "PhD", "year": "1986", "title": "Observations in Turbulent Buoyant Jets by Use of Laser-Induced Fluorescence", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-03142008-142149", "creators": [ { "name": { "family": "Papantoniou", "given": "Dimitris Antony" }, "id": "Papantoniou-Dimitris-Antony", "display_name": "Papantoniou, Dimitris Antony" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "eng" ], "doi": "10.7907/SX4D-3555", "abstract": "The entrainment mechanism and mixing process are investigated in the far field of a liquid phase buoyant jet issuing into an unconfined, quiescent medium, by an experimental technique based on laser-induced fluorescence (LIF). Visualization experiments show the existence of a large scale organization in the far field, with structures spanning the radial extent of the conical flow region. Quantitative, high-resolution measurements of scalar concentration were performed along the radial direction in the far field region. For each data set, a large number of successive instantaneous concentration profiles were obtained by combining LIF techniques with linear photodiode array imaging and high speed data acquisition. The measurements revealed that the instantaneous profile bears no resemblance to the time-averaged profile. The flow interior is characterized by large spatial gradients of concentration, associated with interfaces between mixed jet fluid and fresh, entrained ambient fluid transported to regions deep into the flow. This is inconsistent with the description of transport by gradient diffusion concepts. The probability of finding unmixed ambient fluid and the concentration variance are greatly increased under the action of buoyancy. At any axial location, the arrival of a structure front is marked by a spatially coherent (along the radial direction) increase in the local concentration level. It is found that, within the structure, values of the concentration are generally decreasing in the upstream direction; substantial uniformity within the mixed fluid portion is observed along the radial direction. In the conical flow field of the momentum jet, a central region (in fixed spatial coordinates) may be identified within which the local mixed fluid composition is relatively uniform. This is not the case for the buoyancy driven plume, due to a greater variance in the position of the large structure and the high value of the intermittency. It is suggested that fluid is entrained by vortical motions mainly from the back and side regions of the large structure. Flow visualization reveals vorticity in the axial direction which enhances the mixing process; this vorticity appears stronger in the buoyancy driven flow. The results of these experiments are interpreted through a simple conceptual model of entrainment and mixing that encompasses the observed large scale organization of the buoyant jet flow.
" }, { "name": "Robey, Harry Francis, III", "degree": "PhD", "year": "1986", "title": "The Nature of Oblique Instability Waves in Boundary Layer Transition", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-150746", "creators": [ { "name": { "family": "Robey", "given": "Harry Francis, III" }, "id": "Robey-Harry-Francis-III", "display_name": "Robey, Harry Francis, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7VG8-Y513", "abstract": "An experimental study of both the weakly non-linear as well as the three-dimensional nature of boundary layer transition is conducted using the active surface heating technique of Liepmann et al. In the present study, this technique is extended to provide a means for controllably and repeatably introducing three-dimensional disturbances into a laminar boundary layer. A review of the surface heating technique is presented along with a discussion of some peculiarities encountered in extending this technique to three-dimensional geometries. A thorough description of the design and operation of a programmable 32-element heater array and the supporting instrumentation are given as well.
\r\n\r\nThe heater array is first used to study the effect of weak nonlinearity on boundary layer transition. By keeping the forced disturbances as two-dimensional as possible, it is shown that the effects of weak non-linearity are relatively benign. The growth rates are seen to follow the linear theory up to perturbation amplitudes (\u03c4'w\u03c4̅w) of nearly twelve percent. The only deviation from the linear theory arises in the form of non-linearly generated harmonics phase-locked to the fundamental. It is concluded that although these non-linearly generated harmonics do alter the wave behavior to some extent, they are by themselves not sufficient to explain the transition from small linear oscillations to the large amplitude, broad-band, three-dimensional oscillations characteristic of a fully turbulent boundary layer.
\r\n\r\nThe effect of three-dimensionality on boundary layer transition is then investigated through an analytical and experimental study of single oblique instability waves. This subject has remained largely unexplored, as such disturbances were generally thought to be more stable and therefore less dangerous than their two-dimensional counterparts. Through a series of experiments, however, it is shown that certain conditions exist for which oblique waves are observed to be more unstable than any two-dimensional wave. It is shown that oblique waves exhibit a non-stationary period-doubling behavior that is not seen in two-dimensional disturbances. A vortex pairing mechanism is proposed to explain this behavior, and is shown to occur in a manner consistent with the Biot-Savart law for the induced velocity field.
" }, { "name": "Sigurdson, Lorenz Willard", "degree": "PhD", "year": "1986", "title": "The Structure and Control of a Turbulent Reattaching Flow", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-104655", "creators": [ { "name": { "family": "Sigurdson", "given": "Lorenz Willard" }, "id": "Sigurdson-Lorenz-Willard", "display_name": "Sigurdson, Lorenz Willard" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/prfm-x404", "abstract": "An unsteady and three-dimensional large-scale structure is proposed for the reattachment region of a separation bubble, based on a visualization study of the flow over a plate with a square leading edge and its axisymmetric counterpart, a flat-faced circular cylinder aligned coaxially with the free-stream. The initial free shear layer structures are primarily two-dimensional but evolve into boundary layer type structures as they near reattachment and interact with the wall. Some segments form \"loops\" which convect away from the wall and downstream, while spanwise adjacent parts convect toward the wall and upstream. The loops are sometimes clearly arranged in a staggered pattern. Their legs form a series of counter-rotating streamwise vortex pairs which bridge the reattachment zone. These observations reconcile apparently contradictory propositions concerning the fate of the structures as they encounter reattachment. The interaction between successive vortices at alternating spanwise locations is fundamental to several flows. The structure of turbulent wakes is also discussed.
\r\n\r\nAn experimental study was made of the effect of a periodic velocity perturbation on the separation bubble downstream of the sharp- edged blunt face of a circular cylinder aligned coaxially with the free stream. Velocity fluctuations were produced with an acoustic driver located within the cylinder and a small circumferential gap located immediately downstream of the fixed separation line to allow communication with the external flow. The flow could be considerably modified when forced at frequencies lower than the initial Kelvin-Helmholtz frequencies of the free shear layer, and with associated vortex wavelengths comparable to the bubble height. Reattachment length, bubble height, pressure at separation, and average pressure on the face were all reduced. The effects on the large-scale structures were studied on flow photographs obtained by the smoke-wire technique. The forcing increased the entrainment near the leading edge.
\r\n\r\nIn both forced and unforced cases it was concluded that the final vortex of the shear layer before reattachment is an important element of the flow structure. There are two different instabilities involved, the Kelvin-Helmholtz instability of the free shear layer and the \"shedding\" type instability of the entire bubble. The latter results from an interaction with the image vortices due to the presence of the wall. A method of frequency scaling is proposed that correlates data for a variety of bubbles and supports an analogy with Karman vortex shedding.
\r\n\r\nNew methods for approximating axisymmetric flows are presented. Transition of shear-layers and separation bubbles is also discussed.
" }, { "name": "Taylor, Stephen", "degree": "PhD", "year": "1986", "title": "The Effects of Large-Eddy Manipulator Devices on the Turbulent Spot and the Turbulent Boundary Layer", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-083411", "creators": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-Stephen", "orcid": "0000-0003-0264-1453", "display_name": "Taylor, Stephen" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7520-qj30", "abstract": "Recent experimental studies indicate that net drag reductions can be achieved in a turbulent boundary layer by placing a tandem configuration of large-eddy manipulator blades in the outer region of the boundary layer. However, the mechanisms responsible for the observed wall-shear reductions are not well understood. Furthermore, discrepancies exist among independent experimental studies regarding the magnitude of the attainable net drag reduction.
\r\n\r\nA fundamental argument is made regarding the source of the observed wall-shear reductions. It is shown that the tandem manipulator is not a low-drag device. The implication is that the momentum deficit in the wake of the manipulator is a prominent contributor to the observed wall-shear reductions, not necessarily that the ability of the large eddies to transport momentum is hampered. The behavior of the wall shear downstream of the device, obtained using hot-film wall-shear sensors, is consistent with the entrainment, mixing, and consequent deceleration of low-momentum fluid from the wake of the manipulator.
\r\n\r\nWith the aid of direct measurements of wall shear, an upper bound is placed on the attainable net drag reduction by establishing a lower bound for the device drag. It is concluded that small net reductions (~ 5 percent) may be attained at large downstream distances (\u2273 100 boundary-layer thicknesses). This conclusion is consistent with most net drag assessments made independently by others in which the momentum-balance technique was employed. However, the result is not consistent with reports of large net reductions (~ 20 percent) over shorter distances (~ 50 boundary-layer thicknesses).
\r\n\r\nEfforts are also made to explain the observed effects in terms of turbulent structure. The turbulent spot is employed as a prototype structure for the large-scale, organized motions in the turbulent boundary layer. Dramatic wall-shear reductions occur in the region of the spot occupied by the large vortex structure. Such reductions are also evident when the spot is propagating in transitional and fully turbulent ambient boundary layers. Although the transport properties of the vortex structure may be affected by the manipulator, it is proposed that an important source of the wall-shear reductions is the transport by the large vortex of low-momentum fluid in the wake of the manipulator.
\r\n\r\nSome effects of a three-dimensional manipulator are also explored. The design of the device is based on a crude model of the three-dimensional structure of the turbulent spot. Although it appears that the device inhibits the spanwise growth of the spot, its overall effect on the wall shear of the spot and the turbulent boundary layer does not represent an improvement over the effectiveness of a comparable tandem configuration.
" }, { "name": "Aaron, Kim Maynard", "degree": "PhD", "year": "1985", "title": "Edgetones and Acoustic Resonances in a Duct", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222007-092606", "creators": [ { "name": { "family": "Aaron", "given": "Kim Maynard" }, "id": "Aaron-Kim-Maynard", "display_name": "Aaron, Kim Maynard" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bfy8-1995", "abstract": "Undesirable sound generation in the combustion chamber of segmented solid propellant rocket motors has been attributed to vortex shedding from obstructions that are uncovered as the propellant burns back. This phenomenon has been investigated experimentally and the mechanism explained.
\r\n\r\nA pair of aluminum baffles within a lucite duct through which air is drawn models the important aspects which enable the sound generation mechanism to operate. The baffles form an edgetone system which interacts with the longitudinal acoustic modes of the chamber. Acoustic tones occur spontaneously, at frequencies determined by the acoustic resonances, when the spacing between the baffles satisfies certain criteria.
\r\n\r\nFlow visualization using smoke and a strobe light triggered by the pressure oscillations indicate that vortex shedding occurs at the first baffle in phase with the acoustic velocity oscillations there. The interaction of these vortices with the downstream baffle drives the acoustic resonance which, in turn, triggers the formation of new vortices at the upstream separation point.
\r\n\r\nThe phase relations for this feedback to operate require that there be close to an integral number of wavelengths, or vortices, from the separation point to the impingement point.
\r\n\r\nA model has been developed which predicts the experimentally observed behaviour well. Pressure amplitudes are predicted within an order of magnitude. Mean flow rates and baffle spacings yielding maximum response are determined correctly by the model.
" }, { "name": "Dahm, Werner Johann Anton", "degree": "PhD", "year": "1985", "title": "Experiments on Entrainment, Mixing and Chemical Reactions in Turbulent Jets at Large Schmidt Number", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062006-104125", "creators": [ { "name": { "family": "Dahm", "given": "Werner Johann Anton" }, "id": "Dahm-Werner-Johann-Anton", "orcid": "0000-0002-0779-3280", "display_name": "Dahm, Werner Johann Anton" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/k93g-jh12", "abstract": "Entrainment, mixing and chemical reactions are investigated in the far field of steady, axisymmetric, momentum-driven, turbulent jets issuing into an unconfined, quiescent medium in the large Schmidt number (liquid-phase) regime. Visualization experiments using both passive and chemically sensitive planar laser induced fluorescence (LIF) techniques show the importance of large scale transport in the jet far field, and suggest that entrainment, mixing and chemical reactions in the far field are dominated by a large scale organization of the flow. Successive instantaneous profiles of the jet fluid concentration along the axial and radial directions in the jet far field are measured by combining these LIF techniques with direct, high-resolution, linear photodiode array imaging and high-speed digital data acquisition. These imaging measurements have revealed an axial similarity concentration variable for which probability density functions (PDFs) in the jet far field are self-similar along rays. A chemical reaction method is presented which allows the self-similar form of these PDFs to be measured with full resolution at all scales of transport and mixing. Furthermore, these imaging measurements have shown that instantaneous radial profiles of the jet fluid concentration do not resemble the mean concentration profile. Specifically, unmixed ambient fluid is found deep within the jet and the composition of molecularly mixed fluid within large regions in the jet is approximately uniform. The results from these experiments are interpreted in the context of a simple conceptual model for large scale organization of entrainment, mixing and chemical reactions in the far field of turbulent jets.
" }, { "name": "Elyada, Dov", "degree": "PhD", "year": "1985", "title": "Structural Analysis of Imperfect Three-Legged Truss Columns for Large Space Structures Applications", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11182004-161353", "creators": [ { "name": { "family": "Elyada", "given": "Dov" }, "id": "Elyada-Dov", "display_name": "Elyada, Dov" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YXNE-YE65", "abstract": "Three-legged truss columns are basic structural components of many envisioned large outer-space structures. They constitute three longerons ('legs') forming, in the column cross-section, the vertices of an equiliateral triangle. Their longerons are held together by uniformly spaced battens while a shear web, usually made of diagonals, restrains shear deformation.
\r\n\r\nThis work deals with configurations characterized by having relatively stiff battens, longerons which are pinned to the battens and prestressed string diagonals. Considered are only simply-supported slender columns having slender longeron segments and relatively thin and lightly preloaded diagonals. The columns are allowed to have global (overall) as well as local (longeron segment) geometrical imperfections - not necessarily small ones.
\r\n\r\nInvestigated is the static structural behavior of such columns when loaded by purely axial compressive concentrated forces acting at the supports. Addressed are the topics of global and local buckling, post-buckling, imperfection sensitivity, global-local mode interaction, complete non-linear response, limit loads and diagonals slackening and post-slackening.
\r\n\r\nThe approach is a theoretical one; a system of non-linear, ordinary differential equations is set up which represents the column, and results, mostly in closed form, are obtained by solving that system for a variety of cases of varying generality.
\r\n\r\nFirst, a highly idealized case is studied in detail, in which the diagonals are removed and infinite shear rigidity is postulated instead. The results exhibit most of the essential features of the more complicated cases. Next, the case of the undeflected or only-slightly deflected column is considered. Results include the prebuckling behavior, slackening and local buckling loads, global buckling load, initial post-buckling behavior and imperfection sensitivities. Diagonals slackening in a deflecting column is studied next. This is done by means of slackening loci constructed in the load-deflection plane. Solutions are obtained for some special cases of a deflecting column. These include a complete analysis of the locally-perfect case and the cases of small load and high defection. Also obtained is an engineering-oriented load-deflection working relation valid for the most general case but based on generalization rather than on rigorous solution. A torsion-compression mode, dominant in post-slackening, is also analyzed. The work is concluded by investigating the error committed in treating continuous longerons as if they were discontinuous-pinned.
\r\n" }, { "name": "Frost, David Lawrence", "degree": "PhD", "year": "1985", "title": "Effects of Ambient Pressure on the Instability of a Liquid Boiling Explosively at the Superheat Limit", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-081638", "creators": [ { "name": { "family": "Frost", "given": "David Lawrence" }, "id": "Frost-David-Lawrence", "orcid": "0000-0002-3579-6091", "display_name": "Frost, David Lawrence" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8J3K-PS54", "abstract": "The effect of ambient pressure on the dynamical behaviour of a single droplet (1-2 mm diameter) of volatile liquid boiling explosively at the limit of superheat is studied experimentally and theoretically. In a series of experiments it is shown that the evaporative instability, observed earlier by Shepherd & Sturtevant (1982) during the rapid vapourization of butane droplets at atmospheric pressure, is suppressed at high pressure. Three other fluids (pentane, isopentane, and ether) are tested to establish the generality of the instability and other transient processes previously observed. Direct evidence is obtained showing that during violently unstable boiling small liquid particles are torn from the liquid-vapour interface. This ejection of fine droplets from the evaporating surface produces a mass flux orders of magnitude greater than that characteristic of ordinary boiling.
\r\n\r\nRaising the ambient pressure lowers the superheat attained at the superheat limit, which decreases the vapourization rate. At high pressure boiling consists of normal slow vapourization from a smooth interface. Observed bubble growth rates show reasonable agreement with theory. At intermediate pressures a transitional regime of stability occurs in which a drop initially vapourizes stably for several milliseconds while incipient instability waves develop on the evaporating interface. When only a small amount of liquid remains in the drop in the shape of a thin cap, heat transfer from the surrounding hot host fluid initiates violent boiling at the edge of the liquid cap. The subsequent rapid vapourization generates a radiated pressure field two orders of magnitude larger than during stable boiling, and sets the bubble into violent oscillation. The bubble is subject to the Rayleigh-Taylor instability and rapidly disintegrates into a cloud of small bubbles.
\r\n\r\nLowering the ambient pressure decreases the time delay between nucleation and onset of unstable boiling. For example, in ether at atmospheric pressure the instability is triggered less than 8 \u00b5sec after nucleation, shortly after the smooth vapour bubble contacts the droplet surface. Heterogeneous nucleation spreads out along the surface of the drop while disturbances (with a length scale of 100 \u00b5m) distort the unstably evaporating interface within the drop, substantially enhancing the vapourization rate. At early times, droplets torn from the evaporating surface evaporate before the instability-driven jet impinges upon the surrounding fluid, bulging the bubble surface. The last portion of liquid in a drop boils particularly violently and droplets ejected from the evaporating interface at this time remain intact to splatter the bubble surface. At subatmospheric pressures the most rapid vapourization occurs and temperature gradients within a drop produce spatial variations in vapourization rate.
\r\n\r\nThe Landau mechanism for the instability of laminar flames is adapted to the case of evaporation to investigate the effects of variable ambient pressure. A spherical version of the theory, applicable before the vapour bubble contacts the droplet surface, predicts absolute stability at atmospheric pressure. At later times the spherical constraint is inappropriate and planar theory yields results in general agreement with observation. Differences in fluid properties make some fluids more prone to instability than others. The product of the maximum growth rate with the time interval the interface is predicted to be linearly unstable measures the susceptibility to instability. For practical estimates it is suggested that a value of 3 of this parameter be taken as the lower limit for instability. The sensitivity of the instability to temperature suggests that small temperature nonuniformities may be responsible for quantitative departures of the behaviour from predictions.
\r\n" }, { "name": "Hermanson, James Carl", "degree": "PhD", "year": "1985", "title": "Heat Release Effects in a Turbulent, Reacting Shear Layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06132007-075717", "creators": [ { "name": { "family": "Hermanson", "given": "James Carl" }, "id": "Hermanson-James-Carl", "display_name": "Hermanson, James Carl" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/y722-za34", "abstract": "The effects of heat release were studied in a planar, gaseous reacting mixing layer formed between free streams containing hydrogen and fluorine in inert diluents. Sufficiently high concentrations of reactants were employed to produce adiabatic flame temperature rises of up to 940 K (1240 K absolute). The Reynolds number at the measuring station, based on velocity difference, 1% temperature thickness and cold kinematic viscosity was approximately 6x104. The temperature field was measured with cold wire resistance thermometers and thermocouples. Flow visualization was accomplished by schlieren spark and motion picture photography. Mean velocity information was extracted from mean pitot probe dynamic pressure measurements.
\r\n\r\nThough the displacement thickness of the layer, for zero streamwise pressure gradient, increased with increasing heat release, the actual growth rate of the layer did not increase, but instead decreased slightly. The overall entrainment into the layer was seen to be substantially reduced as a consequence of heat release. Calculations showed that the decrease in layer growth rate can be accounted for by a corresponding reduction in turbulent shear stress.
\r\n\r\nThe mean temperature rise profiles, normalized by the adiabatic flame temperature rise, were not greatly changed in shape by heat release. A small decrease in normalized mean temperature rise with heat release was observed. Large scale coherent structures were observed to persist at all levels of heat release in this investigation. The mean structure spacing decreased with increasing temperature. This decrease exceeded the rate of layer growth rate reduction, and suggests that the mechanisms of vortex amalgamation were, to some extent, inhibited by heat release.
\r\n\r\nImposition of a favorable pressure gradient resulted in additional thinning of the layer, and caused a slight increase in the mixing and amount of chemical product formation. The change in layer growth rate can be shown to be related to a change in free stream velocity ratio induced by pressure gradient.
" }, { "name": "Roberts, Fredrick Allen", "degree": "PhD", "year": "1985", "title": "Effects of a Periodic Disturbance on Structure and Mixing in Turbulent Shear Layers and Wakes", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-144801", "creators": [ { "name": { "family": "Roberts", "given": "Fredrick Allen" }, "id": "Roberts-Fredrick-Allen", "display_name": "Roberts, Fredrick Allen" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "chair", "display_name": "Broadwell, James E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/syy5-a334", "abstract": "Large scale structure and mixing processes are investigated in chemically reacting wakes and shear layers to which a periodic disturbance is applied. The experiments employ a diffusion-limited acid-base reaction to directly measure the extent of mixing. Optical diagnostics used include laser absorption and laser induced fluorescence. Absorption of laser light by reacted product provides a measure of cross-stream average product. Fluorescence was measured by a self-scanning linear photodiode array using high speed computer data acquisition to obtain the product distribution across the layer.
\r\n\r\nPrevious results showing that forcing alters the structure and growth rate of shear layers are confirmed. Forcing artificially extends the lifetime of vortices whose size is consistent with the disturbance wavelength. Amalgamation of smaller vortices is enhanced over that in the natural layer until the frequency locked scale is achieved. At high Reynolds number product measurements show reduction of product with forcing. At moderate Reynolds numbers, on the other hand, there is an increase in product when forced. In one case a five fold increase in product was observed. The differences are related to the different effects of forcing on entrainment, composition ratio and secondary structure.
\r\n\r\nA dramatic, order of magnitude increase in mixing was discovered for certain forced wake flows. This effect is strongly associated with an interaction between the spanwise organized wake vortices and the test-section side walls.
\r\n" }, { "name": "R\u00f6sgen, Thomas", "degree": "PhD", "year": "1985", "title": "Second Sound Scattering in Superfluid Helium", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-161340", "creators": [ { "name": { "family": "R\u00f6sgen", "given": "Thomas" }, "id": "R\u00f6sgen-Thomas", "display_name": "R\u00f6sgen, Thomas" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/r8ge-j070", "abstract": "Focusing cavities are used to study the scattering of second sound in liquid helium II. The special geometries reduce wall interference effects and allow measurements in very small test volumes.
\r\n\r\nIn a first experiment, a double elliptical cavity is used to focus a second sound wave onto a small wire target. A thin film bolometer measures the side scattered wave component. The agreement with a theoretical estimate is reasonable, although some problems arise from the small measurement volume and associated alignment requirements.
\r\n\r\nA second cavity is based on confocal parabolas, thus enabling the use of large planar sensors. A cylindrical heater produces again a focused second sound wave. Three sensors monitor the transmitted wave component as well as the side scatter in two different directions. The side looking sensors have very high sensitivities due to their large size and resistance. Specially developed cryogenic amplifiers are used to match them to the signal cables.
\r\n\r\nIn one case, a second auxiliary heater is used to set up a strong counterflow in the focal region. The second sound wave then scatters from the induced fluid disturbances.
\r\n\r\nAttempts to observe scattering from quantized vortex lines in the rotating parabolic cavity ultimately did not succeed, although a theoretical estimate seems to indicate a basic feasibility.
" }, { "name": "Chang, Samuel Kwang Yeh", "degree": "Engineering Degree", "year": "1984", "title": "Crack Propagation in Viscoelastic Materials under Transient Loading with Application to Adhesively Bonded Structures", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102005-155309", "creators": [ { "name": { "family": "Chang", "given": "Samuel Kwang Yeh" }, "id": "Chang-Samuel-Kwang-Yeh", "display_name": "Chang, Samuel Kwang Yeh" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZHV3-TK46", "abstract": "Linear viscoelasticity theory is applied to the fatigue problem of solids sensitive to the deformation rate. A series of experiments have been performed to investigate the range of applicability in whch the theory is valid and to examine the accuracy of the theory. The experimental results are compared with an existing theory." }, { "name": "Cimbala, John Michael", "degree": "PhD", "year": "1984", "title": "Large Structure in the Far Wakes of Two-Dimensional Bluff Bodies", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132005-131650", "creators": [ { "name": { "family": "Cimbala", "given": "John Michael" }, "id": "Cimbala-John-Michael", "orcid": "0000-0003-3210-6347", "display_name": "Cimbala, John Michael" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZ05-YC02", "abstract": "Smoke-wire flow visualization and hot-wire anemometry have been used to study near and far wakes of two-dimensional bluff bodies. For the case of a circular cylinder at 70 < Re < 2000, a very rapid (exponential) decay of velocity fluctuations at the Karman vortex street frequency is observed. Beyond this region of decay, larger-scale (lower wave-number) structure can be seen. In the far wake (beyond one hundred diameters) a broad band of frequencies is selectively amplified and then damped, the center of the band shifting to lower frequencies as downstream distance is increased.
\r\n\r\nThe far-wake structure does not depend directly on the scale or frequency of the original Karman vortices; the growth of this structure is due to hydro-dynamic instability of the developing mean wake profile; it is not caused by amalgamation of the Karman vortices. Under certain conditions amalgamation can take place, but is purely incidental, and is not the driving mechanism responsible for the growth of larger-scale structure. Similar large structure is observed downstream of porous flat plates (Re \u2248 6000), which do not initially shed Karman-type vortices into the wake.
\r\n\r\nHot-wire measurements show that two-dimensional locally-parallel inviscid linear stability theory is adequate to explain the growth of downstream structure. Namely, measured prominent frequencies in the cylinder wake are in close agreement with those predicted by the theory, when streamwise growth of wake width is taken into account.
\r\n\r\nFinally, three-dimensionality in the far wake of a circular cylinder is briefly discussed.
" }, { "name": "Haas, Jean-Fran\u00e7ois Luc", "degree": "PhD", "year": "1984", "title": "Interaction of Weak Shock Waves and Discrete Gas Inhomogeneities", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232005-110318", "creators": [ { "name": { "family": "Haas", "given": "Jean-Fran\u00e7ois Luc" }, "id": "Haas-Jean-Fran\u00e7ois-Luc", "orcid": "0000-0002-7730-5107", "display_name": "Haas, Jean-Fran\u00e7ois Luc" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T37C-X215", "abstract": "An experimental investigation of the interaction of shock waves with discrete gas inhomogeneities is conducted in the GALCIT 15 cm diameter shock tube. The gas volumes are cylindrical refraction cells of 5 cm diameter with a 0.5 \u00b5m thick membrane separating the test gas (helium or Freon 22) from the ambient air and large spherical soap bubbles containing the same gases. The incident wave Mach numbers are nominally 1.09 and 1.22. The wave pattern and the deformation of the gas volumes are documented by shadowgraphs. The transmitted and diffracted wave pressure profiles are recorded by pressure transducers at various distances behind the cylinders. The basic phenomena of acoustic wave refraction, reflection and diffraction by cylindrical acoustic lenses, with indices of refraction appropriate to the gases used in the experiments, are illustrated with computer-generated ray and wave-front diagrams.
\r\n\r\nIn the case of a Freon 22-filled cylinder, the wave diffracted externally around the body precedes the wave transmitted from the interior which goes through a focus just behind the cylinder, while in the case of the helium-filled cylinder the expanding transmitted wave runs ahead of the diffracted wave. Both sets of waves merge a few cylinder diameters downstream. The wave patterns inside the cylinder, showing initially the refracted waves and later the same waves reflected internally, present some interesting phenomena.
\r\n\r\nThe mechanisms by which the gas volumes are transformed into vertical structures by the shock motion are observed. The unique effect of shock acceleration and Rayleigh-Taylor instability on the spherical volume of helium leads to the formation of a strong vortex ring which rapidly separates from the main volume of helium. Measurements of the wave and gas-interface velocities are compared to values calculated for one-dimensional interactions and for a simple model of shock-induced Taylor instability. The behavior of thin liquid membranes accelerated by shocks under varying conditions is documented by high speed photography.
\r\n\r\nIn a related experiment, shock waves of Mach number between 1.005 and 1.36 interact with a dense random array of 2 mm diameter helium filled soap bubbles. Experimental results (based on shadowgraphs and pressure measurements) show that very weak shock waves (Ms \u2264 1.01) are strongly scattered by the array, which is left undisturbed by the shock, and that stronger shock waves, only locally disturbed by each bubble, maintain undisturbed pressure profiles because of nonlinear effects, while the array undergoes shock-induced mixing. A simple criterion for multiple scattering shows that the combined effect of many bubbles is necessary in order to produce important modifications on the shock wave pressure profile.
" }, { "name": "Koochesfahani, Manoochehr Mohseni", "degree": "PhD", "year": "1984", "title": "Experiments on Turbulent Mixing and Chemical Reactions in a Liquid Mixing Layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132006-131143", "creators": [ { "name": { "family": "Koochesfahani", "given": "Manoochehr Mohseni" }, "id": "Koochesfahani-Manoochehr-Mohseni", "orcid": "0000-0002-7001-8455", "display_name": "Koochesfahani, Manoochehr Mohseni" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y7BR-C556", "abstract": "The processes of entrainment and mixing are investigated in reacting and non-reacting, uniform density, liquid mixing layers over a wide range of Reynolds numbers. In non-reacting cases, a passive scalar technique is used to measure the probability density function (pdf) of the composition field. Chemically reacting experiments employ a diffusion-limited acid-base reaction to directly measure the extent of mixing. The diagnostics are based entirely on the laser induced fluorescence technique. The fluorescence signal is measured by self-scanning linear photodiode arrays using high speed, real-time computer data acquisition. The system is capable of yielding species concentration data with a spatial resolution of 100 \u00b5m and a temporal resolution of 0.8 msec.
\r\n\r\nResults show that the vertical structures in the mixing layer initially roll up with a large excess of high speed fluid in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but the composition also changes. It is found that the pdf of the mixed fluid, above the mixing transition, is quite uniform across the entire transverse extent of the layer. Furthermore, it is asymmetric and biased toward the high speed fluid. Experimental evidence indicates that the turbulent transport, in the cases studied, is dominated by large scale structures and is not adequately described by standard gradient-diffusion models. The fluid composition in the mixing layer, suggested by the present results, is in qualitative agreement with many aspects of the recent theoretical model of Broadwell and Breidenthal. The amount of product formed in the layer is compared to Mungal's measurements in gas, and, it is observed that the liquid layer has about 50% less product. The mean concentration of the mixed fluid, for a mixing layer at a velocity ratio of 0.38, becomes constant at 0.57 above the mixing transition. This corresponds to an entrainment ratio of 1.32, in agreement with the gaseous result of Konrad at the same velocity ratio.
" }, { "name": "Lim, Christopher Sy", "degree": "Engineering Degree", "year": "1984", "title": "I. Mixing in Doorway Flows. II. Entrainment in Fire Plumes", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212006-153204", "creators": [ { "name": { "family": "Lim", "given": "Christopher Sy" }, "id": "Lim-Christopher-Sy", "display_name": "Lim, Christopher Sy" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MWGY-CY05", "abstract": "The motion of hot combustion products through a burning structure plays a dominant role in fixing the spread of the fire and the spread of toxic gases. The first part of this report is concerned with the effect of door geometry on the rate of turbulent mixing between the hot and cold layers near a doorway. The second part of the report deals with the entrainment rates in the near field of a buoyant diffusion methane flame.\r\n\r\nIn the study of the motion of the hot combustion products near a doorway, the gas in the burning room is assumed to be divided into two homogeneous layers--the ceiling layer which contains the hot combustion products and the floor layer which contains the denser fresh air. Temperature and carbon dioxide measurements are taken from a half-scale room which uses a pump and furnace to simulate the entrainment and heating of the fresh air by the fire plume. The mass transfer rates are calculated from these measurements and are found to be a function of a Richardson number that uses the interface height measured from the floor as the characteristic length and the average inflow velocity of fresh air as the characteristic velocity. This form for Ri(0) is derived from an analysis based on Taylor's entrainment hypothesis. For a given fire size, i.e., for a given mass flow of fresh air into the room, the effect of reducing the door area is to reduce the value of Ri(0), and hence increase the mixing rate in the room. The door height is found to be a much stronger influence on the mixing rate and interface height than the door width.\r\n\r\nThe entrainment rates of fresh air in the near field of a buoyant diffusion methane flame whose flames extend well above the interface between the hot gas layer and the fresh air layer are measured for several interface heights. In the experiments, the ceiling layer-fire plume interaction is simulated by placing a large steel hood over an axisymmetric burner. The hood may be raised or lowered to change the interface height. The entrainment measurements are obtained from a chemical analysis of a dried sample of combustion products taken from the ceiling layer. The measured species concentrations are compared with the theoretical equilibrium composition of the ceiling layer gas. For a given interface height, the ceiling layer gas temperature is found to be a linear function of the fuel-air ratio up to the stoichiometric fuel-air ratio. Increasing the fuel-air ratio above the stoichiometric value did not change the gas temperature significantly. This maximum temperature is observed to decrease with interface height. The air entrainment rates are found to be a weak function of the fuel-air ratio at very low elevations of the interface." }, { "name": "Wang, Chiun", "degree": "PhD", "year": "1984", "title": "The Effects of Curvature on Turbulent Mixing Layers", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222007-142548", "creators": [ { "name": { "family": "Wang", "given": "Chiun" }, "id": "Wang-Chiun", "display_name": "Wang, Chiun" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BC48-BE98", "abstract": "Experimental studies have been conducted in a curved mixing layer in which both the velocity ratio and the density ratio were variable. Flow visualization studies and profile measurements covered a wide range of experimental conditions. The structures observed experimentally were examined in the light of three different instability mechanisms which can exist in the same mean flow.
\r\n\r\nFor the case of mixing layers with uniform density, it was found that the normal large spanwise vortex structures can be weakened or inhibited by Taylor-Gortler instability if the inner stream is faster than the outer stream. For the case of mixing layers with different densities, three-dimensionality is greatly enhanced by Rayleigh-Taylor instability if the inner stream is heavier than the outer stream, and especially if the inner stream is also faster. In the former case the growth rate of the mixing layer was found to be insensitive to changes in the velocity ratio.
\r\n\r\nThe effects of curvature on the structure of the curved turbulent mixing layer were explored in terms of length scales and celerity for the large spanwise structures where these structures could be observed. Other things being equal, the celerity of the large structures was found to depend on density ratio and velocity ratio but not on the sense of the mean streamline curvature.
" }, { "name": "Gharib, Morteza (Mory)", "degree": "PhD", "year": "1983", "title": "The Effect of Flow Oscillations on Cavity Drag, and a Technique for their Control", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-133001", "creators": [ { "name": { "family": "Gharib", "given": "Morteza (Mory)" }, "id": "Gharib-Morteza", "orcid": "0000-0003-0754-4193", "display_name": "Gharib, Morteza (Mory)" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "member", "display_name": "Blandford, Roger D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JJYA-CK31", "abstract": "The phenomenon of cavity flow oscillation is investigated to determine the conditions for onset of periodic oscillations and to understand the relationship between the state of the shear layer and the cavity drag. Experiments have been performed in a water tunnel using a 4\" axisymmetric cavity model instrumented with a strip heater on the nose cone and pressure taps in and around the cavity. A complete set of measurements of oscillation phase, amplitude amplification along the flow direction, distribution of shear stress and other momentum flux is obtained by means of a laser Doppler velocimeter. Drag measurements were made by integrating the mean pressure over the solid surfaces of the cavity. Results indicated exponential cavity drag dependence on the length of the cavity. A jump in the cavity drag coefrcient is observed as the cavity flow shows a bluff body wake type behavior. An independent estimate of the drag, which is obtained by integration of shear and mean momentum transfer terms over the peripheral area of the cavity, confirms the exponential dependence of drag on the length of the cavity. Results, also reveal that the drag of the cavity in the non-oscillating mode is less than the case if the cavity were replaced by a solid surface. Natural and forced oscillations of the cavity shear layer spanning the gap are studied. The forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of the gap, For a sufficiently large gap, self-sustained periodic oscillations are observed while for smaller gaps, which do not oscillate naturally, periodic oscillations can be obtained by external forcing through the strip-heater. In the latter case resonance is observed whenever the forcing frequency satisfies the phase criterion \u03c6/(2\u03c0) = N, and its amplitude exceeds certain threshold levels, but the phenomenon is non-self-supporting. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. For naturally occurring oscillations, it is possible for two waves to co-exist in the shear layer (natural and forced). Also, it is possible to completely eliminate mode switching by applying external forcing. For the first time a test is performed to cancel or dampen the amplitude of Kelvin-Helmholtz wave in the cavity shear layer. This is done through introducing an external perturbation with the same frequency of the natural component but having a different phase. Reduction by a factor of 2 is obtained in the amplitude of the oscillation.
" }, { "name": "Heymans, Luc J.", "degree": "PhD", "year": "1983", "title": "An Engineering Analysis of Polymer Film Adhesion to Rigid Substrates", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-111322", "creators": [ { "name": { "family": "Heymans", "given": "Luc J." }, "id": "Heymans-Luc-J", "display_name": "Heymans, Luc J." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." }, { "name": { "family": "Fornberg", "given": "Bengt" }, "id": "Fornberg-Bengt", "role": "member", "display_name": "Fornberg, Bengt" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3GQW-YP87", "abstract": "An important source of interface fracture contributing to adhesive failure in a bimaterial sandwich, consisting of a rigid substrate and a viscoelastic encapsulant material, arises from residual stresses. The encapsulant is often deposited on the substrate above its glass transition temperature region but used below this temperature range. In order to determine the magnitude of the residual stresses a viscoelastic stress analysis of a bimaterial sandwich is carried out, taking into account the time-dependent material properties of the polymeric layer and the environmental \"loading\" conditions. The theoretical analysis is paralleled by an experimental examination of the time-dependent out-of-plane deformation of thin, circular sandwiches.
\r\n\r\nPolyvinyl acetate was chosen as a model material exhibiting significant viscoelastic effects under room test conditions. Therefore the pertinent physical and mechanical properties of PYAc are determined; these include the thermal coefficient of expansion, the shear creep compliance and the relaxation modulus. In the experimental work BK-7 glass is taken as the \"rigid\" substrate. The measurements connected to the stress analysis are monitored with laser interferometry (Newton's rings). A comparison between theory and experiment completes the viscoelastic stress analysis.
\r\n\r\nIn the second part of this study time dependent adhesive failure of rubbery materials is investigated. Polymeric materials are being used increasingly for a wide variety of applications. Some of these materials are applied as protective layers to isolate their substrates from a hostile environment. Others achieve remarkable structural bond strengths thereby displacing the traditional mechanical fasteners like bolts and rivets. If one wants to investigate the long time integrity of a layer assembly the time dependence of the material properties of the adhesives needs to be carefully analyzed. This time dependence is also reflected in the energy required to create new surfaces as interfacial debonding proceeds the adhesive fracture energy is one of the dominant parameters in time dependent adhesive failure. In our investigation it is characterized through peel testing.
\r\n\r\nWith the knowledge of the pertinent material properties as well as of the adhesive fracture energy, we then proceed to formulate a criterion for continuing interfacial crack propagation. The analysis is carried out for elastic solids, with the effect of viscoelastic behavior incorporated later on. Debond tests provide a way to check how well the theoretical predictions correspond to experimental debond results.
" }, { "name": "Magaldi, Anthony", "degree": "Engineering Degree", "year": "1983", "title": "Low Velocity Impact Damage and its Propagation Under Compressive Load in Curved, Graphite/Epoxy Panels", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-082416", "creators": [ { "name": { "family": "Magaldi", "given": "Anthony" }, "id": "Magaldi-Anthony", "display_name": "Magaldi, Anthony" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ekat-8g08", "abstract": "An experimental study was conducted to investigate the influence of plate curvature on low-velocity impact damage and its propagation under compressive load in thick, Graphite/Epoxy laminates. High-speed photography coupled with the oblique-shadow moire technique indicates that initial impact damage and its subsequent propagation through delamination buckling act as separate mechanisms during the catastrophic failure process.\r\n\r\nResults of an initial-postbuckling analysis for the buckling of thin cylindrical plates in axial compression were used to assess the effect of plate curvature on the conditions necessary for delamination buckling. Although curvature was found to increase the buckling load at the expense of a greater imperfection sensitivity, the effect is insignificant in thin shells if the plate width (i.e. initial delamination width) is small compared to the plate's radius.\r\n\r\nWhen compared with the experimental and analytic findings of similar studies involving flat Gr/Ep laminates, results reveal that the 15 inch plate radius used for this series of experiments had a negligible influence on the inital damage and delamination propagation mechanisms." }, { "name": "Mungal, Mark Godfrey", "degree": "PhD", "year": "1983", "title": "Experiments on Mixing and Combustion with Low Heat Release in a Turbulent Shear Flow", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-144655", "creators": [ { "name": { "family": "Mungal", "given": "Mark Godfrey" }, "id": "Mungal-Mark-Godfrey", "display_name": "Mungal, Mark Godfrey" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "chair", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QZ4F-V692", "abstract": "A new blowdown facility to study mixing and combustion in a turbulent shear layer has been built. The system is capable of 100 m/s for three seconds in a 5 x 20 cm exit area on the high speed side, and 50 m/s in a 10 x 20 cm exit area on the low speed side. Dilute concentrations of hydrogen and fluorine, carried in an inert gas, react when both fluid streams meet at the tip of a splitter plate. The reaction is spontaneous, rapid, and highly exothermic. The resulting temperature field has been studied using a rake of eight fast response thermometers placed across the width of the layer. Runs have been performed for low heat release over a wide range of equivalence (concentration) ratios, at a Reynolds number of 30,800 based on velocity difference and vorticity thickness. The heat release is sufficiently low so that the overall properties of the mixing layer are not significantly changed from the cold case.
\r\n\r\nThe results show the presence of large, hot structures within the flow together with cool, irrotational tongues of freestream fluid that penetrate deep into the layer. Thus, it is possible for the entire width of the layer to be quite hot, owing to the passage of a large structure, or for the layer to be quite cool, owing to the presence of the cool fluid tongues. The mean temperature results from a duty cycle whereby a given point in the flow sees alternating hot and cool fluid which averages into the local mean. The mean temperature profiles do not achieve the adiabatic flame temperature at any location across the layer, with the maximum mean temperature, depending upon the equivalence ratio, varying from 54% to 67% of the adiabatic flame temperature. The location of the maximum mean temperature shifts by about 25% of the visual thickness of the layer for a change of equivalence ratio by a factor of 64. The amount of product formed in the layer is compared to earlier measurements in water, and, it is found that at a speed ratio of 0.40, there exists 20 to 25% more product in gaseous flows, implying that molecular diffusion, or in nondimensional form the Schmidt number, plays a role in mixing at large Reynolds number. The present results compare favorably with the recent theoretical model of Broadwell and Breidenthal for mixing and chemical reaction in a turbulent shear layer. With this model it is possible to bring the results for gases and liquids into quantitative agreement.
" }, { "name": "Sargent, William Stapf", "degree": "PhD", "year": "1983", "title": "Natural Convection Flows and Associated Heat Transfer Processes in Room Fires", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052007-132409", "creators": [ { "name": { "family": "Sargent", "given": "William Stapf" }, "id": "Sargent-William-Stapf", "display_name": "Sargent, William Stapf" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/n7kr-k165", "abstract": "This report presents the results of experimental investigations of natural convection flows and associated heat transfer processes produced by small fires in rooms with a single door or window opening. Calculation procedures have been developed to model the major aspects of these flows.
\r\n\r\nTwo distinct sets of experiments were undertaken.
\r\n\r\nFirst, in a roughly 1/4 scale facility, a slightly dense solution of brine was allowed to flow into a tank of fresh water. The resulting density difference produced a flow which simulated a very small fire in a room with adiabatic walls. Second, in an approximately 1/2 scale test room, a nearly stoichioinetric mixture of air and natural gas was burned at floor level to model moderate strength fires. In this latter facility, we directly measured the heat conducted through the walls, in addition to determining the gas temperature and composition throughout the room.
\r\n\r\nThese two facilities complemented each other. The former offered good flow visualization and allowed us to observe the basic flow phenomena in the absence of heat transfer effects. On the other hand, the latter, which involved relatively larger fires, was a more realistic simulation of an actual room fire, and allowed us to calculate the convective heat transfer to the ceiling and walls. In addition, the stronger sources present in these 1/2 scale tests produced significant secondary flows. These secondary flows along with heat transfer effects act to modify the gas temperature or density profiles within the room from those observed in the 1/4 scale experiments.
\r\n\r\nSeveral calculation procedures have been developed, based on the far field properties of plumes when the density differences are small (the Boussinesq approximation). The simple point source plume solution is used along with hydraulic analysis of flow through an orifice to estimate the temperatures of the hot ceiling layer gas and of the cooler floor zone fluid, as well as the height of the interface between them. A finite source plume model is combined with conservation equations across the interface to compute the evolution of the plume above the interface. This calculation then provides the starting point for an integral analysis of the flow and heat transfer in the turbulent ceiling jet.
\r\n\r\nThe computed results both for the average floor and ceiling zone gas temperatures, and for the connective heat transfer in the ceiling jet agreed reasonably well with our experimental data. This agreement suggests that our computational procedures can be applied to answer practical questions, such as whether the connective heat flux from a given fire in a real room would be sufficient to trigger sprinklers or other detection systems in a given amount of time.
" }, { "name": "Bauer, Thomas Patrick", "degree": "PhD", "year": "1982", "title": "Low-Thrust Perturbation Guidance", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-133355", "creators": [ { "name": { "family": "Bauer", "given": "Thomas Patrick" }, "id": "Bauer-Thomas-Patrick", "display_name": "Bauer, Thomas Patrick" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Wood", "given": "Lincoln" }, "id": "Wood-L", "role": "chair", "display_name": "Wood, Lincoln" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "member", "display_name": "Muhleman, Duane Owen" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TVQ3-FV70", "abstract": "Low-thrust perturbation guidance, as applied to the minimum time problem of an Earth to Mars rendezvous, has been reexamined and shown to perform orders of magnitude better, as measured by the terminal state error, than previous studies indicated. The orbits of Earth and Mars were assumed to be inclined and elliptical. The only forces considered were the Sun's gravity and that of the constant thrust rocket engine.
\r\n\r\nFirst order necessary conditions of the calculus of variations were developed for the nominal trajectory. The resulting nonlinear two-point boundary value problem was solved with the Backward Sweep Method. Feedback gain related and trajectory information is stored on a file during the optimization of the nominal trajectory to be retrieved later in the guidance programs by a high order interpolator.
\r\n\r\nTwo guidance schemes, Time-To-Go Guidance and Minimum Distance Guidance, were investigated for several initial perturbations in velocity and position. The performance of the two schemes was found to be clearly acceptable although not quite as good as reoptimization. The two schemes are equivalent in performance. Moreover, a simplified version of the schemes, Current Time Guidance, was found to be comparable in performance to the more elaborate guidance schemes.
\r\n\r\nA comparison of the current results with those of previous studies was made showing that terminal state errors can be reduced 100 to 10,000 times more than found earlier. This apparent improvement may possibly be explained by the use of a high fidelity integrator and other enhancements implemented in the software, although algorithm and programming mistakes in the earlier studies are suspected.
\r\n\r\nA similar minimum time problem, that of a two-dimensional Earth to Mars orbit transfer using a solar sail, was also reexamined. The optimized trajectory was found to be very similar to those obtained by most earlier studies. A recent report which prompted the study was found to have an error in a transversality condition causing anomalous results.
" }, { "name": "Catherasoo, Christopher Jeyaparan", "degree": "PhD", "year": "1982", "title": "Shock Dynamics in Non-Uniform Media", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-143337", "creators": [ { "name": { "family": "Catherasoo", "given": "Christopher Jeyaparan" }, "id": "Catherasoo-Christopher-Jeyaparan", "display_name": "Catherasoo, Christopher Jeyaparan" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7knb-5s50", "abstract": "The theory of shock dynamics in two dimensions is reformulated to treat shock propagation in a non-uniform medium. The analysis yields a system of hyperbolic equations with source terms representing the generation of disturbances on the shock wave as it propagates into the fluid non-uniformities. The theory is applied to problems involving the refraction of a plane shock wave at a free plane gaseous interface. The \"slow-fast\" interface is investigated in detail, while the \"fast-slow\" interface is treated only briefly. Intrinsic to the theory is a relationship analogous to Snell's law of refraction at an interface. The theory predicts both regular and irregular (Mach) refraction, and a criterion is developed for the transition from one to the other. Quantitative results for several different shock strengths, angles of incidence and sound speed ratios are presented. An analogy between shock refraction and the motion of a force field in unsteady one-dimensional gasdynamics is pointed out. Also discussed is the limiting case for a shock front to be continuous at the interface. Comparison of results is made with existing experimental data, with transition calculations based on three-shock theory, and with the simple case of normal interaction.
" }, { "name": "Chai, Herzl", "degree": "PhD", "year": "1982", "title": "The Growth of Impact Damage in Compressively Loaded Laminates", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-084629", "creators": [ { "name": { "family": "Chai", "given": "Herzl" }, "id": "Chai-Herzl", "display_name": "Chai, Herzl" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Corcoran", "given": "William Harrison" }, "id": "Corcoran-W-H", "role": "member", "display_name": "Corcoran, William Harrison" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/58D3-ZZ41", "abstract": "The thesis is divided into two chapters. The first chapter describes an experimental program carried out to determine the phenomenological aspects of composite panel failure (graphite/epoxy laminate) under simultaneous in-plane compression and low velocity transverse impact (0-250 ft/sec). High-speed photography and the shadow moire technique were used to record a full-field surface deformation history of the impacted plate. The information gained from these records, supplemented by plate sectioning and observation for interior damage, has shown that the predominant failure mechanism is the coupled effect of delamination and buckling.
\r\n\r\nIn chapter 2, this process of failure is modelled by delamination buckling wherein the local delamination stability, growth or arrest are governed by an energy release rate criterion. Various degrees of problem simplifications are employed, starting with a one-dimensional, delaminated-beam model. In the most sophisticated treatment, it is assumed that the damaged area has an elliptical shape. It was found that this model is capable of describing the growth conditions and the growth behavior of the damaged area. It was also found that the predominant parameter controlling delamination growth or arrest is the fracture energy associated with delamination.
\r\n\r\nIn the appendix at the end of this work, the fracture energy of a composite laminate is considered. A modified cleavage analysis is developed, and is applied to evaluate this quantity for two composite materials of current interest. The test results are then examined with reference to impact damage tolerance data available for these materials. A viscoelastic characterization of the two resins used to fabricate the two composites mentioned above is also provided. The results of these measurements are then examined with reference to long-term applicability of the matrix material.
" }, { "name": "Nosenchuck, Daniel Mark", "degree": "PhD", "year": "1982", "title": "Passive and Active Control of Boundary Layer Transition", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-135720", "creators": [ { "name": { "family": "Nosenchuck", "given": "Daniel Mark" }, "id": "Nosenchuck-Daniel-Mark", "display_name": "Nosenchuck, Daniel Mark" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CKFA-E875", "abstract": "It is well known that laminar-turbulent boundary layer transition is initiated by the formation of Tollmien-Schlichting laminar instability waves. The amplification rates of these waves are strongly dependent on the shape of the boundary layer velocity profile. Consequently, the transition process can be controlled by modifying the velocity profile. This can be accomplished by controlling the pressure gradient (dp/dx), using boundary layer suction, installing surface roughness elements, or by surface heating or cooling. Methods used to modify the transition process through changes in the mean velocity profile are called \"passive\" in this paper. There exists a large set of experiments and theory on the application of passive methods for boundary layer control. In the present work only surface heating will be addressed.
\r\n\r\nTransition measurements were made on a heated flat plate in water. Results are presented for several plate wall temperature distributions. An increase by a factor of 2.5 in transition Reynolds number was observed for a 5\u00b0C isothermal wall overheat. Buoyancy effects on transition were minimal due to the small Richardson and Grashof numbers encountered in the experiments.
\r\n\r\nThe amplification of laminar instability waves is comparatively to process, taking place over many boundary layer thicknesses. After the slow amplification of the laminar instability waves, transition occurs by a strong three dimensional dynamic instability. It appears possible to attenuate (or reinforce) the instability waves by introducing amplitude-and phase-controlled perturbations into the laminar boundary layer using feedback control system. This method is called \"active\" control and forms the larger part of the research reported in this thesis.
\r\n\r\nA combination of sensors, activators and feedback control electronics is required for active control. The sensors used in the experiments are flush-mounted hot film wall shear robes. A new type of activator was developed using thin, flush-mounted surface heating elements to excite instability waves in the laminar boundary layer by periodic (active) heating.
\r\n\r\nExperimental evidence is presented illustrating the effects of periodically heated flush mounted strips in perturbing a flat plate boundary layer in water. The results of superposition of forced laminar instability waves are also given. Finally, an active feedback-control system using a single hot film probe and strip heater was developed to control natural laminar instability waves in real time. It is shown that when the natural waves were attenuated, the transition length was increased by 25%, requiring only 10 watts of strip heater power. To accomplish the same transition delay using passive heating, the internal heating pads had to supply 1900 watts of power.
" }, { "name": "Ravi-Chandar, K.", "degree": "PhD", "year": "1982", "title": "An Experimental Investigation into the Mechanics of Dynamic Fracture", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-104624", "creators": [ { "name": { "family": "Ravi-Chandar", "given": "K." }, "id": "Ravi-Chandar-K", "display_name": "Ravi-Chandar, K." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZSX5-Q128", "abstract": "Current theories of dynamic fracture are based on elastodynamic analyses of mathematically sharp plane cracks and as such do not explain the observed terminal velocities or the phenomenon of crack branching satisfactorily. The present investigation addresses the above problems by using both microscopic and macroscopic interpretations. The experimental scheme that is used in this investigation is the configuration of a pressure loaded semi-infinite crack in an infinite medium. The loading is achieved through an electromagnetic device which provides highly repeatable loading. The method of caustics is used in conjunction with a high speed camera to obtain the time histories of the crack tip stress intensity factor and the crack position.
\r\n\r\nThe problems of crack initiation and crack arrest are explored. The stress intensity factor at initiation is found to be independent of the rate of applied loading when the latter is below about 104MPA/sec, but the initiation stress intensity factor increases considerably when the loading rate is increased further. Crack arrest is obtained in large specimen by using very low energy loading pulses. It was found that the stress intensity factor at crack arrest was constant and also that, within the time resolution of the high speed camera (5 \u03bcsec), the crack comes to a stop abruptly.
\r\n\r\nThe crack propagation and branching aspects were investigated first using post-mortem analysis of the fracture surfaces and high speed photomicrography to get an idea of the microscopic processes that occur in the fracure process. From this investigation, it was found that crack propagation involving high stress intensity factor and high velocity situations takes place by the growth and interaction of microcracks, due to the voids present in the material. A surprising result of this investigation was that cracks propagated at a constant velocity, although the stress intensity factor varied. Current theories of dynamic fracture cannot explain such behaviour. The crack branching process was found to be a continuous process arising out of propagation along a straight line. High speed photomicrographs of the branching process indicated the presence of a number of part-through attempted branches that interact with one another and finally the successful emergence of a few full fledged branches.
\r\n\r\nThe microscopic observations on the crack propagation and branching process leads to a new interpretation of dynamic fracture that attempts to qualitatively explain the constancy of the velocity of propagation, the terminal velocity and crack branching. The crack branching mechanism is a logical continuation of the mechanism for crack propagation.
\r\n" }, { "name": "Shieh, An Huh", "degree": "PhD", "year": "1982", "title": "Non-Stationary Lattice Theory", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-112813", "creators": [ { "name": { "family": "Shieh", "given": "An Huh" }, "id": "Shieh-An-Huh", "display_name": "Shieh, An Huh" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xknf-r113", "abstract": "No abstract submitted." }, { "name": "Trebitz, Bernd Otto", "degree": "PhD", "year": "1982", "title": "Acoustic Transmission Imaging for Flow Diagnostics", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-145444", "creators": [ { "name": { "family": "Trebitz", "given": "Bernd Otto" }, "id": "Trebitz-Bernd-Otto", "display_name": "Trebitz, Bernd Otto" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pnsp-rk30", "abstract": "Wave propagation through a given flow field can be utilized to obtain information about the flow. Acoustic waves in particular offer the possibility of measuring velocity fields, because sound waves are convected with the flow, and temperature fields, because the acoustic index of refraction is a strong function of temperature. This work concentrates on situations where the first effect is dominating compared to the latter one.
\r\n\r\nA sound system capable of \"illuminating\" a flow field with ultrasonic waves and measuring the amplitude and phase distribution of the transmitted wave as a function of time was constructed. A large area transmitter and a linear receiving array were used as transducers. Parallel signal processing and interleaved data conversion and acquisition result in a maximum frame rate of 10 kHz.
\r\n\r\nThe feasibility of measuring velocity disturbances with ultrasound was demonstrated by transmitting sound through a vortex, which was generated in a duct by an airfoil swirl generator. Assuming an exponential fit for the tangential velocity component, inner core radius and circulation can be determined directly from the phase change of the transmitted wave due to the vortex. A more accurate representation of the radial velocity profile can be found by digital reconstruction via the Abel inversion formula, which allows reconstruction of rotationally symmetric objects from line projections. Even though the flow field under investigation was steady, this is neither a restriction of the technique, nor of the apparatus. However, the repetition rate for consecutive data frames depends on the operating procedure.
" }, { "name": "Bernal, Luis Paulino", "degree": "PhD", "year": "1981", "title": "The Coherent Structure of Turbulent Mixing Layers. I. Similarity of the Primary Vortex Structure. II. Secondary Streamwise Vortex Structure", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08262005-154143", "creators": [ { "name": { "family": "Bernal", "given": "Luis Paulino" }, "id": "Bernal-Luis-Paulino", "display_name": "Bernal, Luis Paulino" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z52D-SA34", "abstract": "The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated. Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of the large scale vortices. It was found that after an initial transition region mean properties of the large scale vortices reach the expected linear growth with downstream distance required by similarity. In the self-similar region, the vortex core area and visual thickness increase continuously during its life-span.
\r\n\r\nA theoretical model of probability distribution function for the large-scale vortex circulation was developed. This distribution is found to be lognormal and to have a standard deviation, normalized with the mean of 0.28. From this model the mean life-span of the vortices could also be obtained and was found to be 0.67 times the mean life-span position.
\r\n\r\nThe streamwise streak pattern observed by Konrad (1976) and Breidenthal (1978) in plan-view pictures of the mixing layer was investigated, using flow visualization and spanwise concentration measurements. It was confirmed that this pattern is the result of a secondary vortex structure dominated by streamwise, counterrotating vortices. A detailed description of its spatial relation to the primary, spanwise vortex structure is presented. From time average flow pictures, the onset position and initial scale of the secondary structures were determined. From concentration measurements, spanwise variations in mean properties, resulting from the secondary structure, were found. This also showed an increase of the spanwise scale with downstream distance and the existence of the streamwise vortices in the fully developed turbulent region. In this region the mean spacing is found approximately equal to the vorticity thickness.
" }, { "name": "Doan, Phuc The", "degree": "Engineering Degree", "year": "1981", "title": "Computing the Development of Disturbances in the Blasius Boundary Layer Due to Localized Unsteady Two-Dimensional Wall Injection", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052006-115727", "creators": [ { "name": { "family": "Doan", "given": "Phuc The" }, "id": "Doan-Phuc-The", "display_name": "Doan, Phuc The" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bt7y-zn32", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe localized unsteady two-dimensional wall injection of fluid into the Blasius boundary layer was mathematically modeled as a mixed initial-value boundary-value problem. Here the magnitude of the initial disturbance was sufficiently small so that the problem was linear. For the case of parallel mean flow, detailed formulation was discussed, and then, as an illustration, the problem of instantaneous blowing through a narrow slit in the wall was specifically analyzed and computed at a Reynolds number based on displacement thickness of 750 with the result showing a wave packet traveling at .44 times the speed of the freestream, amplifying like [...], spreading like 0.1x, where x is the distance from the slit, and eventually containing only frequencies whose imaginary parts lie between 0.009 and -0.010. To account for the effect of the boundary layer growth on the evolution of the disturbance, a perturbation method based on the idea of multiple scales was presented." }, { "name": "Glezer, Ari", "degree": "PhD", "year": "1981", "title": "An Experimental Study of a Turbulent Vortex Ring", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092006-080016", "creators": [ { "name": { "family": "Glezer", "given": "Ari" }, "id": "Glezer-Ari", "display_name": "Glezer, Ari" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RC4P-DA56", "abstract": "An apparatus has been constructed to study the formation and dynamics of vortex rings. The rings are formed in water by a momentary jet discharge downward into a glass tank from an orifice in a submerged plate. The necessary impulse is provided by a pressurized reservoir and is controlled by a fast programmable solenoid valve.
\r\n\r\nA particular turbulent vortex ring with a relatively thin core was chosen for detailed study. The velocity field of this ring was measured at numerous locations in the tank, using a two-channel laser-Doppler velocimeter with digital tracking electronics. Beamsplitting and frequency-shifting were accomplished by two partially-overlapping radial phase gratings driven by hysteresis-synchronous motors.
\r\n\r\nThe main aim of the research was to verify the similarity properties of the turbulent vortex ring and to determine mean particle paths and mean vorticity contours in the appropriate nonsteady similarity coordinates x/t\u00bc, r/t\u00bc. Some novel pattern-recognition techniques were developed to overcome the problem of dispersion in the trajectories of individual vortices.
" }, { "name": "Ruth, Edward Kenneth", "degree": "PhD", "year": "1981", "title": "Experiments with Unconventional Cross Flow Heat Exchangers", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-110003", "creators": [ { "name": { "family": "Ruth", "given": "Edward Kenneth" }, "id": "Ruth-Edward-Kenneth", "display_name": "Ruth, Edward Kenneth" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P6TP-GR40", "abstract": "These experiments consisted of measurements of pressure losses and heat transfer rates for two unconventional crossflow heat exchanger configurations.\r\n\r\nThe first type consisted of an arrangement of circular tubes in a sawtooth pattern. Performance of this type did not appear to be an improvement over more conventional heat exchangers.\r\n\r\nThe second type used exchanger tubes of a special lenticular cross section so spaced as to keep the velocity of the fluid flowing outside the tubes nearly constant in magnitude reducing separation and drag. The lenticular tubes' performance was superior to the conventional types, especially at higher Reynolds numbers." }, { "name": "Shih, Choon-Foo", "degree": "PhD", "year": "1981", "title": "Failure of Liquid Storage Tanks Due to Earthquake Excitation", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132018-090928397", "creators": [ { "name": { "family": "Shih", "given": "Choon-Foo" }, "id": "Shih-Choon-Foo", "display_name": "Shih, Choon-Foo" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/m0v8-hs31", "abstract": "Above ground liquid storage tanks have suffered serious damage during earthquakes. The damage of tanks can vary from local yielding or buckling of the tank wall, to loss of contents, or to collapse which leads to an unrepairable tank. Considerable work has been carried out on this problem with varying degree of success. However, the results are largely directed toward response rather than failure prediction. The information on failure mechanisms is very limited. The present work consists of scale model testing, correlation with existing analysis and failure prediction with laboratory verification. The scale model testing incorporates dynamic similarity of the fluid/structure interaction problem. The model study shows that small plastic models can be useful in studying the dynamics and buckling of liquid-filled tanks under ground excitation even though the model does not display complete similitude. The buckling criterion proposed in this study is based upon static considerations and the complex stress field in the shell wall is supplanted by a simple field for which analytical/experimental results are available. Harmonic buckling tests demonstrate that the static buckling criterion is satisfactory even though the prebuckling stress field is time dependent. The harmonic buckling tests, when correlated with the stresses from a response analysis, also indicate that the buckling is largely dependent upon the n = 1 response, Transient buckling tests are also carried out and the results show that the linear analysis together with the static buckling criterion gives a good prediction of the failure of a full fluid-filled tank. The test parameters in these buckling tests include water depth, title angle, thickness of tank wall, top end condition, ground excitation pattern, etc. In addition, buckling tests of unanchored tanks are conducted to study the influence of changing the anchorage of the tank base. An analytical model is suggested to predict the response of an unanchored tank due to overturning moment. The current design criterion of an un\u00adanchored tank is also assessed in this study. The results of this investigation, in addition to those carried out previously, provide a better understanding of the forced vibration problem, failure criterion and appropriate design procedure for a liquid storage tank.
\r\n" }, { "name": "Kyriakides, Stelios", "degree": "PhD", "year": "1980", "title": "On the Propagating Buckle and Its Arrest", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-134840", "creators": [ { "name": { "family": "Kyriakides", "given": "Stelios" }, "id": "Kyriakides-Stelios", "display_name": "Kyriakides, Stelios" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/c81x-nk02", "abstract": "If an offshore pipeline locally buckles in the presence of sufficiently large external pressure, a propagating buckle is initiated. The buckle propagates along the pipeline until it encounters a region of adverse conditions -- low pressure or an arresting device. The lowest pressure at which a buckle propagates is defined as the Propagation Pressure. An experimental study of this quantity is presented and a semiempirical expression derived by examining various models of the phenomenon. The dynamics of the Propagating Buckle are also examined and a parametric study of the steady state velocity of Propagation is carried out. A systematic way of empirically deriving the parametric dependence of arresting devices is presented and experimental results of two such arrestors are discussed. During this study a unique \"flip-flop\" mode of propagation was discovered and studied. An explanation of the phenomenon is also attempted." }, { "name": "Liechti, Kenneth Macdougall", "degree": "PhD", "year": "1980", "title": "The Application of Optical Interferometry to Time Dependent Unbonding: Parts 1, 2, and 3", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-135400", "creators": [ { "name": { "family": "Liechti", "given": "Kenneth Macdougall" }, "id": "Liechti-Kenneth-Macdougall", "display_name": "Liechti, Kenneth Macdougall" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9yk1-v212", "abstract": "Improved methods of adhesive joining for constructing structural elements have led to an increase in the use of bonding. Bonding is already widely used in the aerospace industry. It allows potential for greater weight and manufacturing cost savings when compared to mechanical fastening as well as providing better fatigue resistant capabilities. More accurate design or life prediction based on a better understanding of adhesive joint failure will allow far more extensive and safer use of adhesively bonded structures. The possibility of time dependent failure is introduced in bonding,by the fact that many adhesives are polymers and measurably viscoelastic under many circumstances. Failure can occur by unbonding at the adherend-adhesive interface or totally within the adhesive. Here the time dependent failure by unbonding at the interface is addressed as one initial investigation of the whole problem.\r\n\r\nIn many engineering problems the modelling of failure has been based on linear fracture mechanics. The extent to which the use of the linear theory can be justified is often questionable in view of the nonlinearity of the local crack front deformation field. One aspect of the current investigation is therefore the measurement of the local crack front deformation to examine the limits of the validity for the linear theory and to provide a basis for future modelling, Within this framework, particular attention is paid to the aspects of local failure mode interaction and the time dependence of the unbonding process.\r\n\r\nThe small displacements in the crack front region require a resolution on the order of a wavelength of light. The experimental techniques used are therefore based on optical interferometry. The displacements applied to the adherends are controlled to the same order by a novel, thermally actuated servoloading device.\r\n\r\nThe thesis is divided into three distinct parts. The first part deals with the development of the experimental techniques used to measure the unbound profiles as well as to measure and control the displacements applied to the adherends. For stationary cracks, the second part describes experiments which examine the extent of the nonlinearity in the crack front deformation field while fracture criteria are developed and compared for unbonding rates in steadily propagating cracks. Finally, proposals for improvement of the experimental techniques and further experiments are discussed in the third part." }, { "name": "Mullainathan, M.", "degree": "Engineering Degree", "year": "1980", "title": "Finite-Difference Solution of Steady Two-Dimensional Boundary-Layer Equations with Heat Transfer", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-134715", "creators": [ { "name": { "family": "Mullainathan", "given": "M." }, "id": "Mullainathan-M", "display_name": "Mullainathan, M." } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rawg-2g03", "abstract": "The incompressible boundary layer equations in two dimensions, with heat transfer have been solved numerically using three different methods and the results are compared. All three methods solve these equations when the pressure distribution is prescribed on the boundary, suction or blowing at the wall and the temperature distribution at the wall. The first method is the second-order Keller's box scheme and the second method is the fourth-order scheme using the Euler-Maclurin formula to replace an integral. The proposed third scheme is also a fourth-order scheme which uses a four point formula to replace an integral. All these schemes use a variable mesh in both coordinates. When the truncation error is specified the first scheme chooses an optimum spacing in the direction normal to the wall." }, { "name": "Nomoto, Hideki", "degree": "Engineering Degree", "year": "1980", "title": "Acoustic Waves Generated by Vortex Shedding", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-110713", "creators": [ { "name": { "family": "Nomoto", "given": "Hideki" }, "id": "Nomoto-Hideki", "display_name": "Nomoto, Hideki" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ghk0-az55", "abstract": "An internal flow self-sustained oscillation system, which consists of a two-dimensional duct and a pair of baffles inside, is investigated experimentally. This system produces a high amplitude pure tone when certain flow and geometrical conditions are satisfied. The frequency of this generated tone seems to be determined by the longitudinal acoustic modes of the duct, while the dependence of pure tone production on flow and geometrical conditions seems to be related to the interaction between vortex shedding and acoustic feed back mechanism.\r\n\r\nSome features on self-sustained oscillation systems are reviewed briefly and Rossiter's idea on the cavity tone system is applied for interpretation of the mechanism of the pure tone production.\r\n\r\nFlow visualization shows stable vortical structure of the flow between the baffles when a pure tone is produced." }, { "name": "Turner, Timothy Neal", "degree": "PhD", "year": "1980", "title": "Second Sound Shock Waves and Critical Velocities in Liquid Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132006-075044", "creators": [ { "name": { "family": "Turner", "given": "Timothy Neal" }, "id": "Turner-Timothy-Neal", "display_name": "Turner, Timothy Neal" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/cg05-6436", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLarge amplitude second-sound shock waves have been generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts is calculated and compared to experimental data. Theoretically it is shown that at T = 1.88\u00b0K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse will evolve into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. The theoretical dependence of the shock induce temperature jump on the Mach number is successfully verified for large amplitudes ([...]) after the response of a thin-film superconducting temperature sensor is analyzed.\r\n\r\nThe ability of second-sound shock waves to simultaneously produce and measure very large relative velocities in regions away from the disruptive influence of walls makes them an invaluable tool in the study of critical velocities intrinsic to the fluid. It was experimentally discovered that very large second-sound shock waves initiate a breakdown in the superfluidity of helium II, which is dramatically displayed as a limit to the maximum attainable shock strength. Although the observed breakdown could not be definitely attributed to a critical velocity, the value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium II. The observed limits within which superfluidity was still maintained (w=3.67 m/sec at T = 1.45\u00b0K, and w = 3.20 m/sec at T = 1.85\u00b0K) are the largest counterflow velocities ever obtained outside of restricted geometries." }, { "name": "Breidenthal, Robert Edward", "degree": "PhD", "year": "1979", "title": "A Chemically Reacting, Turbulent Shear Layer", "advisor": "Roshko, Anatol; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10272006-111937", "creators": [ { "name": { "family": "Breidenthal", "given": "Robert Edward" }, "id": "Breidenthal-Robert-Edward", "display_name": "Breidenthal, Robert Edward" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hj67-9h91", "abstract": "A chemically reacting turbulent shear layer was investigated in a new, blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. Using optical densitometry techniques, the amount of product was measured as a function of Reynolds number, at a relatively high Schmidt number of approximately 600. The results were compared with both the previous mixing measurements of Konrad in a gaseous shear layer (Sc = 0.7) and the simple mixing model of Broadwell.\r\n\r\nThe product was found to be distributed, as expected, in concentrated lumps associated with the large, spanwise-coherent structures of the turbulence. The time averaged amount of product in the layer exhibited a rapid transition at a large-structure Reynolds number of about 5 x 10(3) for a velocity ratio of 0.38. Above the transition, the amount of product within the layer was independent of Reynolds number.\r\n\r\nThis transition is related to the introduction of small scale, three-dimensional motions into the layer. In the initial region, where the flow was already unsteady and contained large structures but was strictly two-dimensional, very little mixing was observed. Downstream the flow became unstable to three-dimensional perturbations and small scale, three-dimensional motions were introduced into the layer. Across this transition, the aqueous mixing increased by an order of magnitude, indicating the sensitivity of mixing to small scales of the turbulence in a high Schmidt number fluid. At high Reynolds numbers, changing the Schmidt number by three orders of magnitude only altered the molecular mixing by about a factor of two or less. The mixing model of Broadwell, which addresses the effect of Schmidt number, is in satisfactory qualitative agreement with the observations.\r\n\r\nThe unique flow visualization of the visible reaction product in water permitted a study of the three-dimensional instability and evolution of small scale motions in the layer. Streamwise streaks which had been previously observed in the Brown-Roshko gas apparatus were found to originate from a spanwise-sinuous wiggle which appeared at a large-structure Reynolds number which varied with velocity ratio, indicating an influence of initial conditions on the instability." }, { "name": "Oey, Nicolaus Kiam Thian", "degree": "PhD", "year": "1979", "title": "Leading Edge Flutter of a Supercavitating Hydrofoil", "advisor": "Babcock, Charles D.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032006-091936", "creators": [ { "name": { "family": "Oey", "given": "Nicolaus Kiam Thian" }, "id": "Oey-Nicolaus-Kiam-Thian", "display_name": "Oey, Nicolaus Kiam Thian" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Davis", "given": "Leverett" }, "id": "Davis-Leverett", "role": "member", "display_name": "Davis, Leverett" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9DGB-DW93", "abstract": "Leading edge flutter is a problem that is unique to a super-cavitating hydrofoil. At high speed, the leading edge portion has been observed to oscillate while the trailing edge remains motionless.
\r\n\r\nIn this study, several flat plate hydrofoils were tested. The experimental results indicate that the phenomenon is a complex function of speed, angle of attack, cavitation number and mass ratio. Leading edge flutter was also observed to cause cavity pinching. A theoretical study was also conducted. Two mathematical models are presented here. The first one models the flexible chord foil as a rigid chord foil hinged at the trailing edge; the second model treats the fluid-structure interaction problem of a flexible chord foil cantilevered at the trailing edge. Both models resemble leading edge flutter near zero cavitation number in some respects. At short and moderate cavity lengths, leading edge flutter phenomenon is influenced by the cavity closure condition.
\r\n" }, { "name": "Rogers, Philip Louis", "degree": "Engineering Degree", "year": "1979", "title": "Experimental Investigation of Second Sound Shock Waves in Liquid Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012006-135258", "creators": [ { "name": { "family": "Rogers", "given": "Philip Louis" }, "id": "Rogers-Philip-Louis", "display_name": "Rogers, Philip Louis" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/y2bj-vw94", "abstract": "Second sound shock waves in liquid helium II were studied experimentally using superconducting thin film detectors. The temperature waves were generated electrically using an evaporated thin film heater and the effects of variations in pulse power (input power to the heater as large as 150 Watts/cm(2)) and pulse duration (from less than 100 \u00b5sec to 10 msec) were examined. A number of different materials were tested for use as detectors with the best results obtained from evaporated gold on tin.\r\n\r\nQualitative agreement with Khalatnikov's theory was obtained; however, breakdown of the theoretical model was observed for heater input powers greater than 20 - 30 Watts/cm(2), in agreement with other known results. Quantitative data for shock strength, i.e., temperature amplitude, wave speed, and pulse power, were obtained. The critical counterflow velocities calculated from these data, w = 2.51 to 3.77 m/sec, indicate that heat fluxes at least an order of magnitude greater than those reported for steady channel flow can be transported using the pulsed techniques." }, { "name": "Sava\u015f, \u00d6mer", "degree": "PhD", "year": "1979", "title": "Some Measurements in Synthetic Turbulent Boundary Layers", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012006-083249", "creators": [ { "name": { "family": "Sava\u015f", "given": "\u00d6mer" }, "id": "Sava\u015f-\u00d6mer", "display_name": "Sava\u015f, \u00d6mer" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XZ05-2555", "abstract": "Synthetic turbulent boundary layers were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1.7 x 106. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft which displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e., the probability of observing turbulent flow at a particular point in space and time. The results are reported in numerous x-t diagrams showing the evolution of various synthetic flows along the plate. The celerity or phase velocity of the large eddies was found to be 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows which contained appreciable laminar regions. The large eddies shifted in formation to new positions, intermediate to their original ones, while preserving their hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, were used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study. The values recommended are: spanwise period/thickness \u22483.2, streamwise period/thickness \u224811." }, { "name": "Vinkler, Aharon P.", "degree": "PhD", "year": "1979", "title": "Optimal Controller Design Methods for linear Systems with Uncertain Parameters: Development, Evaluation and Comparison", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312006-104019", "creators": [ { "name": { "family": "Vinkler", "given": "Aharon P." }, "id": "Vinkler-Aharon-P", "display_name": "Vinkler, Aharon P." } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9fwb-er39", "abstract": "In many physical systems, an accurate knowledge of certain parameters is very difficult or very expensive to obtain. The designer of a remotely piloted vehicle flight control system, for example, frequently has available little data regarding aerodynamic coefficients, due to a lack of wind tunnel tests. Commonly used controller design methods, based on nominal values of plant parameters, often fail to achieve a satisfactory design in the face of parameter uncertainty.\r\n\r\nIn this work two methods have been developed for the design of linear, constant gain feedback controllers for systems with uncertain parameters:\r\n\r\n1) The multistep guaranteed cost control method is based on the concept of minimizing an upper bound of a cost functional in the face of parameter uncertainty. An algorithm has been developed to analyze the effect of parameter uncertainties on closed-loop system stability. An extension of this algorithm results in a technique for choosing constant feedback gains which guarantee a stable closed-loop system that possesses some of the desirable features of optimally designed control systems.\r\n\r\n2) The minimum discrete expected cost method is based on the concept of minimizing the expected value of a cost functional over a finite number of points in the range of parameter uncertainty. The design process makes use of statistical information about the uncertain parameters and incorporates in its cost functional whatever effects accompany a large departure in the plant parameters from their nominal values.\r\n\r\nAn extensive comparison of these two methods, together with the guaranteed cost control method, the minimax method, and the uncertainty weighting method, has been done in the context of the design of a fifth-order lateral autopilot for an RPV with uncertain aerodynamic coefficients. All five methods were evaluated on the bases of performance and design effort required. Both new methods were found to avoid some of the drawbacks associated with other techniques. The two newly developed methods are easy to implement and offer the designer tools for use in real control system design." }, { "name": "Wise, Jack LeRoy, III", "degree": "PhD", "year": "1979", "title": "Experimental Investigation of First- and Second-Sound Shock Waves in liquid Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032006-095703", "creators": [ { "name": { "family": "Wise", "given": "Jack LeRoy, III" }, "id": "Wise-Jack-LeRoy-III", "display_name": "Wise, Jack LeRoy, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/c49w-bh82", "abstract": "The cryogenic shock tube is used to generate a gasdynamic shock which propagates through saturated helium vapor and subsequently reflects from the upper surface of a column of LHeII. Superconducting thin-film detectors, produced by evaporation of aluminum in an oxygen atmosphere, yield highly repeatable arrival time data for the incident gasdynamic shock and the resultant first- and second-sound shocks in the liquid. Accurate x-t diagrams of the shock trajectories have been constructed for initial liquid temperatures of T(0) = 1.522, 1.665, 1.751, 1.832, 1.989, 2.031, and 2.095\u00b0K. Consistent discrepancies are observed between experimental and theoretical wave trajectories.\r\n\r\nThe detector signals qualitatively verify theoretical predictions that the temperature decreases through the pressure shock and increases through the temperature shock. Amplitude measurements based on static detector calibrations indicate that the magnitude of the temperature jump across the pressure shock agrees approximately with the theoretical calculation. Temperature jump measurements for the coupled second-sound shock imply shock-induced relative velocities, w =v(n)-v(s), on the order of 2.5 m/sec.\r\n\r\nFor initial conditions close to the [lambda]-transition (e.g., T(0) = 2.095\u00b0K), the pressure jump across the first-sound shock is sufficient to cause a change in phase from LHeII to LHeI. This change is experimentally evidenced by detector outputs indicating the absence of the temperature shock in the wake of a sufficiently strong pressure shock." }, { "name": "Koenig, Keith", "degree": "PhD", "year": "1978", "title": "Interference Effects on the Drag of Bluff Bodies in Tandem", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-140552", "creators": [ { "name": { "family": "Koenig", "given": "Keith" }, "id": "Koenig-Keith", "display_name": "Koenig, Keith" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EXEV-R625", "abstract": "The objective of this study is to obtain better understanding of the flow over two tandemly positioned bluff bodies in close enough proximity to strongly interact with each other. This interaction is often beneficial in that the drag of the overall system is reduced. Prototypes for this problem come from tractor-trailer and cab-van combinations and from various add-on devices designed to reduce their drag.\r\n\r\nThe object of the present investigation is an axisymmetric configuration which seems to have first been studied by Saunders (1966). A disc of diameter d1 is coaxially placed in front of a flat faced cylinder of diameter d2. For a given ratio d1/d2, there is a value of gap ratio, g*/d2 for which the drag of the system is a minimum. In the most optimum configuration, d1/d2 = 0.75, g*/d2 = 0.375, and the corresponding drag coefficient is 0.01, a remarkable reduction from the value of 0.72 for the cylinder alone. For each value of d1/d2, the minimum drag configuration g*/d2 appears to correspond to a condition in which the separation streamsurface just matches (joins tangentially onto) the rearbody. Support for this idea is furnished by comparison with results derived from free-streamline theory and from flow visualization experiments. However, when g*/d2 exceeds a critical value of about 0.5, the value of CD, while still optimum, is almost an order of magnitude higher than for subcritical optimum gap ratios. The increase seems to be connected with the onset of cavity oscillations.\r\n\r\nMeasurements of the velocity field in the vicinity of the forebody have been made using a frequency-shifted laser-Doppler velocimeter. These measurements indicate an order of magnitude difference in the shear stress along the separation surface between optimum subcritical and supercritical geometries.\r\n\r\nThe drag characteristics of the axisymmetric forebody system are altered by modifying the shape of the component bodies. Modifications that change the conditions at separation from the frontbody, interfere with the cavity flow or effect the flow on the rearbody face can produce significant changes in the forebody drag.\r\n\r\nFor non-axisymmetric geometry (square cross-sections) the separation surface cannot exactly match the rear body and the subcritical minimum values of drag are higher than for circular cross-sections." }, { "name": "Ly, Uy-Loi", "degree": "Engineering Degree", "year": "1978", "title": "A Direct Method for Designing Optimal Control Systems That Are Insensitive to Arbitrarily Large Changes in Physical Parameters", "advisor": "Cannon, Robert H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302006-142840", "creators": [ { "name": { "family": "Ly", "given": "Uy-Loi" }, "id": "Ly-Uy-Loi", "display_name": "Ly, Uy-Loi" } ], "advisors": [ { "name": { "family": "Cannon", "given": "Robert H." }, "id": "Cannon-Robert-H", "role": "advisor", "display_name": "Cannon, Robert H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/z992-rx27", "abstract": "A new concept has been developed for designing optimal feedback controllers that will be insensitive to given, arbitrarily large variations in physical parameters. The method uses as a single figure of merit the expected value of a quadratic performance index, the minimization of which determines directly (without trial and error) the desired set of feedback gains. These values of the feedback gains (where such exist) guarantee at the outset closed-loop stability for all possible values of physical parameters in the prescribed domain of uncertainty.\r\n\r\nThe new method extends the well known method for the optimal regulator design where physical parameters have single, precisely known values, to the case where they may have a range of values. In addition, it encompasses (as a special case) the Minimax design developed also for handling systems whose physical parameters may have a range of values (which the Minimax explores by trial and error while the new method accounts automatically for the entire range).\r\n\r\nAn essential feature of the new procedure is that it includes exactly in its cost criterion whatever effects accompany large departures in the plant parameters from their nominal values. This is why the new method is able to guarantee stability over the whole range of parameter values, where perturbation techniques are not.\r\n\r\nThe feasibility and usefulness of the new design technique are illustrated by numerical examples in which control systems are designed for second-order plants each of whose parameters may have a given range of values. Comparisons which results using standard optimal design and the Minimax technique are given.\r\n\r\nApplication to high-order systems will need to be accompanied by further development of appropriate computational procedures." }, { "name": "Magiawala, Kiran Ramanlal", "degree": "PhD", "year": "1978", "title": "Measurements of Energy Exchange Between Acoustic Fields and Non-Uniform Steady Flow Fields", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302006-154249", "creators": [ { "name": { "family": "Magiawala", "given": "Kiran Ramanlal" }, "id": "Magiawala-Kiran-Ramanlal", "display_name": "Magiawala, Kiran Ramanlal" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TR93-1793", "abstract": "Study of the unsteady burning of solid propellants can be best carried out under widely varying conditions and at relatively inexpensive cost in a simple test device known as the T-burner. This simple configuration is used to observe the spontaneous growth and decay of oscillations. Knowing the losses involved in the system, one can infer the frequency response of the burning surface within the approximations of linearity.\r\n\r\nA significant undertainty in the interpretation of data taken with T-burners arises because very little has been known about some of the acoustics, in particular the influence of the exhaust vent. The present investigation is a study of the influence of a subsonic exhaust vent. The primary apparatus is a resonance tube operated at room temperature with different resonance frequencies of the first longitudinal mode of oscillation. Experiments have been done over ranges of the average Mach number of the flow in the resonance tube, and with vent having different sizes and shapes.\r\n\r\nAccording to the one-dimensional linear stability analysis, the attenuation constant associated with the influence of the exhaust vent is given by the product of four times the resonance frequency of oscillation times the average Mach number of the flow in the resonance tube. The following major conclusions were predicted and verified:\r\n\r\n (i) the vent produces a gain of acoustic energy proportional to the average Mach number of the flow in main resonance tube\r\n\r\n (ii) the gain is proportional to the frequency of the fundamental longitudinal mode\r\n\r\n (iii) the gain is independent of the shape and size of the vent. \r\n\r\nThe influence of the exhaust vent, hence, cannot be neglected in the interpretation of T-burner data." }, { "name": "Tangren, Ernst Norman", "degree": "Engineering Degree", "year": "1978", "title": "An Experimental Investigation of Convective Flows Associated with Room Fires", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302006-095405", "creators": [ { "name": { "family": "Tangren", "given": "Ernst Norman" }, "id": "Tangren-Ernst-Norman", "display_name": "Tangren, Ernst Norman" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2d9y-x090", "abstract": "This thesis presents an experimental investigation of the fluid dynamic aspects of a room fire and the applicability of a theoretical model. The model, developed by Zukoski, considers a single room containing a point heat source with or without an opening to the outside. For the case of an opening the interest is in the height and density of the ceiling layer of hot air and combustion products. The case without an opening concerns itself with the time required to fill a room with smoke.\r\n\r\nWater was used as the fluid medium and a flow of salt brine represented the heat source. The experiments investigated the effects of fire strength, opening geometry, fire location and fire geometry for the open room case. For the closed room the movement of the ceiling layer interface and the general flow field were investigated." }, { "name": "Wadcock, Alan James", "degree": "PhD", "year": "1978", "title": "Flying-Hot-Wire Study of Two-Dimensional Turbulent Separation on an NACA 4412 Airfoil at Maximum Lift", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312006-095330", "creators": [ { "name": { "family": "Wadcock", "given": "Alan James" }, "id": "Wadcock-Alan-James", "display_name": "Wadcock, Alan James" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5TB8-1G75", "abstract": "Hot-wire measurements have been made in the boundary layer, the separated region, and the near wake for flow past an NACA 4412 airfoil at maximum lift. The Reynolds number based on chord was about 1,500,000. Special care was taken to achieve a two-dimensional mean flow. The main instrumentation was a flying hot wire; that is, a hot-wire probe mounted on the end of a rotating arm. The probe velocity was sufficiently high to avoid the usual rectification problem by keeping the relative flow direction always within a range of \u00b130 degrees to the probe axis. A digital computer was used to control synchronized sampling and storage of hot-wire data at closely spaced points along the probe arc. Data were obtained at several thousand locations in the flow field. These data include intermittency, two components of mean velocity, and mean values for three double, four triple, and five quadruple products of two velocity fluctuations. No information was obtained about the third (spanwise) velocity component. The data are available on punched cards in raw form and also in processed form, after use of smoothing and interpolation routines to obtain values on a fine rectangular mesh aligned with the airfoil chord. The data are displayed as contour plots of the fifteen variables." }, { "name": "Berg, Dale Evan", "degree": "PhD", "year": "1977", "title": "Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142006-154140", "creators": [ { "name": { "family": "Berg", "given": "Dale Evan" }, "id": "Berg-Dale-Evan", "display_name": "Berg, Dale Evan" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2S44-JV38", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations.\r\n\r\nThe boundary layer was found to respond gradually and to attain new equilibrium profiles, for both the mean and the fluctuating properties, some 10 to 25 [...] downstream of the step change. Mean flow self-similarity was the first to establish itself, followed by the mass flux fluctuations, followed in turn by the total temperature fluctuations.\r\n\r\nUse of a modified Van Driest transformation resulted in good correlation of smooth and rough wall data in the form of the incompressible law of the wall. This is true even in the nonequilibrium vicinity of the step for small roughness heights.\r\n\r\nThe present data are found to correlate well with previously published roughness effect data from low and high speed flows when the roughnesses are characterized by an equivalent sand grain roughness height.\r\n\r\nExisting correlations based on low speed data were found to be unsuccessful in predicting the effect of this roughness on the skin friction and velocity profile. The indiscriminate use of low speed roughness effects correlations to predict the effects of roughness on supersonic and hypersonic flows must therefore be regarded as a procedure subject to gross errors.\r\n\r\nSignificant pressure and temperature history effects were observed throughout the boundary layer. The existence of these effects was found to create a nozzle wall boundary layer whose properties were far different than those in a boundary layer on a flat plate in the freestream, raising questions about the validity of simulating the flat plate boundary layer with the nozzle wall boundary layer." }, { "name": "Craig, James Eldon", "degree": "PhD", "year": "1977", "title": "Weak Shocks in Open-Ended Ducts with Complex Geometry", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302006-133224", "creators": [ { "name": { "family": "Craig", "given": "James Eldon" }, "id": "Craig-James-Eldon", "display_name": "Craig, James Eldon" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QAFR-PS29", "abstract": "The dynamics of weak shocks in ducts of complex geometry and the sound radiation produced by the reflection of a weak shock from the open end of a duct have been investigated. Duct geometries include expansion chambers with and without inlet or outlet tubes extended and enclosed perforated tubes. Internal and external pressure histories of the interaction of weak shocks with simple muffler elements have been recorded using a standard one-shot shock tube and a resonating shock tube. The excitation shock Mach number ranged from 1.05 to 1.55. Analytical investigations, including a synthesis of existing works on internal weak-shock interactions of an acoustic treatment of the sound radiation produced by weak shock waves, are presented. Combining the above analyses, models for the reduction in radiated sound per unit of incident shock amplitude, as a result of inserting a muffler between the source and the tailpipe exit, are developed.\r\n\r\nFor expansion chambers with and without extensions, the dependence of the transmitted and reflected waves and of the radiated sound on area ratio is compared with predictions. In particular, measured transmission coefficients for expansion chambers agree reasonably well with the predictions for all shock strengths; however, for large area ratios, the predicted sound attenuation is not observed, as waves diffracted at the upstream junction cause more sound to be radiated. For expansion chambers with internal extensions, sound attenuation is increased for low incident shock strengths; while for increasing incident shock strength, the internal transmission characteristics deteriorate, the reducing the sound attenuation.\r\n\r\nFor enclosed perforated tubes, the dependence of the transmitted and reflected waves and of the radiated sound on the perforated area ratio and incident shock strength is compared with predictions. For perforated tubes with infinite enclosure, the transmission and reflection coefficients depend on both incident shock strength and perforated area ratio, as predicted. However, agreement with data is obtained only after inserting a perforated discharge coefficient with the perforated area ratio in the theory. The reduction of sound radiation with perforated area ratio is measured for one incident shock strength and then compared with predictions. For small area ratios, there is agreement but for large area ratios the measurements show that less sound is radiated than predicted. For large area ratios, gradual compressions with smooth fronts (not shock fronts) are transmitted, resulting in less radiated sound. Enclosures have no effect on the sound attenuation for small perforate area ratios; however, as the perforate area ratio increases, the enclosure eventually inhibits further increase in sound attenuation." }, { "name": "Higuchi, Hiroshi", "degree": "PhD", "year": "1977", "title": "Experimental Investigation on Axisymmetric Turbulent Wakes with Zero Momentum Defect", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282006-111227", "creators": [ { "name": { "family": "Higuchi", "given": "Hiroshi" }, "id": "Higuchi-Hiroshi", "display_name": "Higuchi, Hiroshi" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/121B-VN50", "abstract": "An experimental investigation of a turbulent axisymmetric wake with zero momentum defect was carried out. The experiment was conducted in a low speed wind tunnel with a circular tube mounted parallel to the stream. A controlled amount of air was injected into the stream at the end of the model to cancel the drag produced by the turbulent boundary layer on the model. The measurements on the mean flow and the fluctuation quantities were carried up to 90 diameters downstream. By adjusting the strength of the injections the behavior of the pure wake, the co-flowing jet and the matched injection were examined, and the self similar properties both in the mean velocity and the turbulent intensity were found to exist in these cases. Rapid decays off the centerline velocity and the maximum turbulent intensity were observed in the matched injection case. The effect of the initial condition was studied by artificially thickening the boundary layer on the model, and it was observed that the wake relaxes into the final decay law sooner. The unmatched cases, both strong and weak injections, were also investigated; the strong injection case was found to relax into the self-similar weak jet profile and the weaker injection case was observed to approach to the similar wake profile.\r\n\r\nFlow visualization was conducted on the plane of symmetry and the entrainment process by the engulfing large eddies was visualized in the pure wake and in the co-flowing jet.\tA lack of large rotations was observed in the matched injection case and the lack of production of turbulent energy was attributed to the faster decay of the flow properties." }, { "name": "Konrad, John Harrison", "degree": "PhD", "year": "1977", "title": "An Experimental Investigation of Mixing in Two-Dimensional Turbulent Shear Flows with Applications to Diffusion-Limited Chemical Reactions", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-105700", "creators": [ { "name": { "family": "Konrad", "given": "John Harrison" }, "id": "Konrad-John-Harrison", "display_name": "Konrad, John Harrison" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZE81-ZM79", "abstract": "The extent of molecular mixing in several two-dimensional free turbulent shear flows was measured using a concentration probe with a frequency response of 100 kHz and a spatial resolution of 0.1 mm. The flows investigated were (i) a shear layer in which the gases on either side of the layer are of unequal density, (ii) a shear layer in which the gases on either side of the layer are of equal density, and (iii) a wake in which the gases on either side of the wake are of unequal densities. The extent of mixing was measured as a function of Reynolds number for the first case.
\r\n\r\nIt was found that at a critical Reynolds number the extent of molecular mixing sharply increased (25%). Power spectral density curves of the concentration time histories also indicated a marked increase in the high frequency fluctuations above this Reynolds number. A shadowgraph investigation of this phenomenon revealed that three-dimensional Taylor-type vortices whose axes of rotation are basically in the flow direction exist in the flow in addition to the two-dimensional large structures previously observed. These Taylor vortices were found to be unstable above the critical Reynolds number and were producing the increase in molecular mixing. The growth and development of the two-dimensional large structures were found to be basically unaffected by this instability. It is proposed that the fully developed turbulence of shear flows is maintained by a combination of the development of the large structures and of the coupling between the large structures and these unstable Taylor vortices.
\r\n\r\nThese data were also used to predict results for shear flows in which diffusion-limited chemical reactions have been incorporated.
\r\n" }, { "name": "Shah, Piyush Chimanlal", "degree": "PhD", "year": "1977", "title": "Estimation of Properties in Petroleum Reservoirs", "advisor": "Gavalas, George R.; Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-081055", "creators": [ { "name": { "family": "Shah", "given": "Piyush Chimanlal" }, "id": "Shah-Piyush-Chimanlal", "display_name": "Shah, Piyush Chimanlal" } ], "advisors": [ { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "advisor", "display_name": "Gavalas, George R." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7DC3-EX92", "abstract": "The determination of parameters in a dynamical system, on the basis of noisy observations of its state is variously known as parameter estimation, identification or the inverse problem. In this work, the determination of porous rock property distribution in a petroleum reservoir using the production rate records and observed pressures (the history matching problem) is considered.\r\n\r\nThe history matching problem is inherently underdetermined because of the large number of unknown parameters relative to the available data. The number of unknowns can be reduced by representing the distributions by a small number of parameters (parameterization). The commonly used zonation approach involves a parameterization, but introduces a considerable modeling error. In chapter 1, Bayesian estimation theory is extended to history matching as an alternative to zonation; it is sought to alleviate the underdeterminacy through specification of a priori statistical information about the unknown parameters. Application of Bayesian estimation and zonation to the problem of porosity and permeability estimation in a one-dimensional single-phase reservoir indicates that the former yields superior estimates; this holds true even when the prior statistics involve large errors. The application of the conjugate gradient and the Gauss-Newton (or Marquardt's) algorithms for history matching is investigated, and the numerical effort for zonation and Bayesian estimation in one- and two-dimensional reservoirs is estimated in detail.\r\n\r\nIn chapter 2, analytic expressions are derived for the sensitivities of an observed oil pressure to small, arbitrary changes in the porosity and permeability distributions in a one-dimensional reservoir. The results indicate that highly oscillatory components of either have very small influence on the pressure and thus cannot be determined by history matching. Further, the dependence of all the observed pressures on the unknown parameters is linearized, for small deviation, about two reference property distributions. The linear relation is analyzed to yield quantitative information concerning the statistical properties of the problem. Iterative corrections in the history matching algorithms are identified with various pseudo-inverses of the linear relation, thus explaining the properties of the resulting estimates. The nature of the linear relation is found to be not strongly dependent on the reference property distributions used for linearization; thus such analysis can be performed prior to estimation. It is discussed how the linearized analysis can be used to determine the determinacy of any given parameterization.\r\n\r\nThe information derived from the linearized analysis and that in the a priori statistics is synthesized in chapter 3 to predict covariances for the zonation and Bayesian estimates. Since the results of the linearized analysis depend only weakly on the reference distribution, the predicted covariances are valid for a class of reservoirs having \"true\" property distributions with identical prior statistics. A good agreement is found when the predicted variances are compared with actual mean square estimate errors in simulations with four distributions with given prior statistics. The sensitivity of the estimates and their covariance to changes and errors in the specification of the prior statistics are investigated in considerable detail. The determination of zonation with smallest trace of estimate covariance for a given problem is considered. The design of Marquardt's algorithm to yield the smallest expected total estimate error for a given zonation is discussed." }, { "name": "Wojcik, Gregory Lynn", "degree": "PhD", "year": "1977", "title": "Self-Similar Elastodynamic Solutions for the Plane Wedge", "advisor": "Sechler, Ernest Edwin; Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132006-080224", "creators": [ { "name": { "family": "Wojcik", "given": "Gregory Lynn" }, "id": "Wojcik-Gregory-Lynn", "display_name": "Wojcik, Gregory Lynn" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E1D3-0T11", "abstract": "Wave propagation in a two-dimensional elastic wedge is fundamental to a large class of problems in elastodynamic theory, however until now analytical solutions to all but certain degenerate cases were unknown. In this thesis a general elastodynamic solution is derived for the wedge in a state of plane strain. Surface tractions are, restricted to uniform normal and shear loads spreading from the wedge vertex at constant velocity. The geometry and loading then allow self-similar solutions of the governing differential equations and boundary conditions in hyperbolic and elliptic domains. Hyperbolic solutions are found in terms of the elliptic solutions by the method of characteristics, while elliptic solutions are reduced using analytic function theory to two independent Fredholm integral equations of the second kind in one dimension. Although numerical solutions are beyond the scope of the investigation, the integral equations are solvable by standard techniques. Such solutions can be used to solve a number of plane elastodynamic problems involving an edge." }, { "name": "Bofah, Kwasi Kete", "degree": "PhD", "year": "1976", "title": "A Study of the Trailing Vortices Behind a Ring Wing", "advisor": "Liepmann, Hans Wolfgang; Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092006-132109", "creators": [ { "name": { "family": "Bofah", "given": "Kwasi Kete" }, "id": "Bofah-Kwasi-Kete", "display_name": "Bofah, Kwasi Kete" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/050Z-4228", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe flow field of a laminar vortex wake behind a ring wing was investigated. Experiments were conducted in the GALCIT Low Speed Water Channel, using laser Doppler velocimetry techniques to measure vertical and axial velocity components in the trailing vortex wake. A thin cylindrical ring wing model was tested at various axial angles of attack and free stream velocities. Velocity profiles were measured at several downstream stations from the trailing edge to 45 wing diameters downstream.\r\n\r\nThe inviscid roll-up of the trailing vortex sheet shed by a ring wing was numerically examined. A line vortex representation was used to calculate the evolution of the initially cylindrical vortex sheet. The vortex sheet was found to distort in shape and then smoothly roll up into a pair of doubly connected spirals whose centers originate from approximately the center of gravity of vorticity in the upper quadrants of the ring wing's circular trailing edge. (This origin is at an angle of 38\u00b0 measured from the horizontal wing diameter.)\r\n\r\nThe experimental and flow visualization results are consistent with the numerical data and show that a pair of counter-rotating vortices do develop from the rolling up of the vortex sheet shed by a ring wing in a nonaxial flow. The vortices trail, downstream of the wing, with their vorticity centroids spaced by [...]/4 wing diameters.\r\n\r\nSaffman and Moore's theory of axial flow in laminar trailing vortices was adapted and found to be in reasonable agreement with the experimental results. The flow field near the trailing edge was found to be in fair agreement with Weissinger's inviscid calculations." }, { "name": "Cantwell, Brian Joseph", "degree": "PhD", "year": "1976", "title": "A Flying Hot Wire Study of the Turbulent Near Wake of a Circular Cylinder at a Reynolds Number of 140,000", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-085806", "creators": [ { "name": { "family": "Cantwell", "given": "Brian Joseph" }, "id": "Cantwell-Brian-Joseph", "display_name": "Cantwell, Brian Joseph" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QKGW-CA84", "abstract": "An experiment was performed in the GALCIT 10-foot wind tunnel to study the flow in the near wake of a circular cylinder at a Reynolds number of 140,000.\r\n\r\nThe main objective of this investigation was to study the phenomenology of the processes of vortex formation and transport in the near wake, at a Reynolds number sufficiently high to insure a fully turbulent wake, but low enough to insure a laminar separation. The latter requirement anticipates the eventual use of the results as a test case for advanced calculation codes.\r\n\r\nMuch current experimental work on turbulent flows is concerned with large, coherent, organized vortex structures which have a relatively long lifetime and which account for much of the transport of mass, momentum and heat in turbulent shear flows. High Reynolds number flow past a cylinder is one case where such structures dominate.\r\n\r\nThe apparatus developed for measuring this flow consists of x-array hot wire probes mounted on the ends of a pair of whirling arms. In such a flow, where large changes in flow direction occur, a fixed hot wire would rectify the velocity signal and give ambiguous results. However, by applying a large enough bias velocity to the wires, the relative velocity vector can be maintained within the [+/-]30 degree range of sensitivity of the x-array. One useful property of this technique is that a rotation of the arms in a uniform flow applies a wide range of relative flow angles to the x-arrays, making them inherently self-calibrating in pitch.\r\n\r\nThe most important element of the instrumentation concomitant to the flying hot wire is a computer controlled data acquisition system which is slaved to the position of the rotating arm and which manages, monitors, edits and records the vast profusion of data which is continuously poured out by the device. A fast sensor responding to model surface pressure was used to generate a signal synchronized with the vortex-shedding process. This signal was recorded along with the hot wire data and used later to sort the data into populations having the same phase. Ensemble averages conditioned this way yield an average picture of the instantaneous flow field in which the vortices are frozen as they would be in a photograph.\r\n\r\nIn addition to the conventional velocity, pressure and stress data, results are presented which show the instantaneous (in the sense of an average at constant phase) velocity, intermittency, vorticity and stress fields as a function of phase for the first six diameters of the near wake.\r\n\r\nIn the present study, the Reynolds stresses are broken up into the contribution from large scale periodic motions and that from background or random turbulence, and, when dissected in this way, permit an enlightening look at the anatomy of this turbulent flow. Laid against the background of the instantaneous velocity, vorticity and intermittency, the stresses in the near wake emerge as a concatenation of peaks and valleys, some the result of strong induced motions in the outer flow which cause free stream fluid to move rapidly inward toward the center of the wake, others the result of the random motions of the background turbulence." }, { "name": "Cosner, Raymond Robert", "degree": "PhD", "year": "1976", "title": "Experiments on Thin Airfoils Spanning a Transonic Shear Flow", "advisor": "Zukoski, Edward E.; Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-134453", "creators": [ { "name": { "family": "Cosner", "given": "Raymond Robert" }, "id": "Cosner-Raymond-Robert", "display_name": "Cosner, Raymond Robert" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YJNQ-ZP43", "abstract": "A wind tunnel was built at the California Institute of Technology to provide two uniform coflowing streams at Mach numbers of 0.6 and l.4 with a plane mixing layer in between. Preliminary studies were made of this free shear layer, indicating a region of self-similar behavior and general agreement in growth rate with previous studies.\r\n\r\nA program of experimental and theoretical work was completed in which wedges were installed in the supersonic stream to create shock waves incident on the shear layer. Similar studies were performed with wedges in the subsonic stream. Good agreement was found between the analytic first-order theory and experiment in showing that the upstream propagation of pressure disturbances ahead of their source in the uniform subsonic stream is limited to about 0.6 subsonic layer thicknesses.\r\n\r\nThe problem of an airfoil in spanwise-varying transonic shear was studied experimentally with the goal of understanding the interactions in the shear region between the supersonic and subsonic streams, especially in terms of deviations from quasi-two-dimensional behavior. The effect of modest angle of attack was also examined." }, { "name": "Shea, John Richard, III", "degree": "PhD", "year": "1976", "title": "A Chemical Reaction in a Turbulent Jet", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282006-152216", "creators": [ { "name": { "family": "Shea", "given": "John Richard, III" }, "id": "Shea-John-Richard-III", "display_name": "Shea, John Richard, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Wulf", "given": "Oliver Reynolds" }, "id": "Wulf-O-R", "role": "member", "display_name": "Wulf, Oliver Reynolds" }, { "name": { "family": "Setchell", "given": "Robert E." }, "id": "Setchell-R-E", "role": "member", "display_name": "Setchell, Robert E." }, { "name": { "family": "Kaufmann", "given": "Aaron" }, "id": "Kaufmann-A", "role": "member", "display_name": "Kaufmann, Aaron" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJQT-9A50", "abstract": "The turbulent mixing and subsequent chemical reaction of gases is an essential part of many technological processes ranging from gas furnaces to chemical lasers. Surprisingly, there is very little information, either theoretical or experimental, about the actual rate of the chemical reaction in such processes. Generally the chemical kinetics are well understood, but the process of turbulent mixing is not. Many measurements of mixing in turbulent jets have been made in the past, but they have generally failed to distinguish essentially unmixed gas in the turbulent mixing zone from gas which is mixed on a molecular scale. Knowledge of where turbulent fluid is mixed on a molecular scale is critical for predicting chemical reaction rates in the flow.
\r\n\r\nIn this experiment the rate of a chemical reaction in an axisymmetric turbulent jet is studied, and the results are used to determine the rate of molecular mixing in the jet. A turbulent jet containing dilute ozone in an inert mixture of nitrogen and oxygen flows into a stagnant tank of nitric oxide and nitrogen. When the gases mix on a molecular scale, the ozone and nitric oxide rapidly react to produce oxygen and nitrogen dioxide. The rate at which the mixing and chemical reaction proceeds is determined by using an ultraviolet light absorption technique to measure the time averaged ozone concentration at points throughout the jets mixing zone.
\r\n\r\nThe experiment establishes a criterion for determining when a reaction of known chemical kinetics is sufficiently rapid that chemical nonequilibrium has a negligible effect on the mean reactant profile. When a reacting jet satisfies this criterion for equilibrium chemistry, the reactant profiles are found to be independent of jet Reynolds numbers from 4,000 to 32,000 based on the nozzle diameter.
\r\n\r\nIn addition, a mixing fraction, η, is defined to measure the extent of local molecular scale mixing independently of a chemical reaction occurring in the jet. The fraction assumes values of unity in the unmixed primary jet, zero in unmixed ambient fluid, and intermediate fractions for mixtures of all proportions. Points on nonreacting jet profiles are related to time averages of η. A limiting highly reacting ozone profile, found when a large excess of nitric oxide is present in the ambient fluid, is related to the time average of an intermittency function, J(η), defined equal to unity when η is within a specified neighborhood of one and zero elsewhere. Thus the experimental measurements of ozone profiles are directly related to the statistics of molecular scale mixing in the jet.
" }, { "name": "Bremmer, David Franklin", "degree": "Engineering Degree", "year": "1975", "title": "An Efficient Approximate Solution Method for Predicting the Buckling of Axially Compressed Imperfect Cylindrical Shells", "advisor": "Babcock, Charles D.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-112038866", "creators": [ { "name": { "family": "Bremmer", "given": "David Franklin" }, "id": "Bremmer-David-Franklin", "display_name": "Bremmer, David Franklin" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S3M9-NT50", "abstract": " A theoretical investigation of an efficient numerical solution scheme to solve approximately the nonlinear Donnell equations for imperfect isotropic cylindrical shells with edge restraints and under axial compression was carried out.\r\n\r\n The nonlinear partial differential equations have been reduced to an equivalent set of nonlinear ordinary differential equations. The resulting two-point boundary value problem was solved, first, by using \"Newton's Method of Quasilinearization\" to obtain a set of linearized differential equations for the correction terms and, secondly, these differentials were approximated as finite differences to cast the linearized system of equations into the form of a block tridiagonal matrix equation. The Potters' Method solution scheme was used to solve efficiently the block tridiagonal matrix equation. By successive iterations a solution to the set of nonlinear ordinary differential equations was obtained.\r\n\r\n The use of this method makes it possible to investigate how the axial load level at the limit point is affected by the following factors: the choice of inplane boundary conditions, the prebuckling growth caused by the radial edge constraint, the orientation and shape of the axisymmetric and asymmetric imperfection components, and the finite length of the shell." }, { "name": "Chang, Liang-Chou", "degree": "PhD", "year": "1975", "title": "Theoretical Investigations of Turbulent Boundary Layer Over a Wavy Surface", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122015-115400945", "creators": [ { "name": { "family": "Chang", "given": "Liang-Chou" }, "id": "Chang-Liang-Chou", "display_name": "Chang, Liang-Chou" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ANTA-K262", "abstract": "The important features of the two-dimensional incompressible\r\nturbulent flow over a wavy surface of wavelength comparable with the boundary\r\nlayer thickness are analyzed.
\r\n\r\nA turbulent field method using model equation for turbulent\r\nshear stress similar to the scheme of Bradshaw, Ferriss and Atwell\r\n(1967) is employed with suitable modification to cover the viscous\r\nsublayer. The governing differential equations are linearized based\r\non the small but finite amplitude to wavelength ratio. An orthogonal\r\nwavy coordinate system, accurate to the second order in the amplitude\r\nratio, is adopted to avoid the severe restriction to the validity of\r\nlinearization due to the large mean velocity gradient near the wall.\r\nAnalytic solution up to the second order is obtained by using the method\r\nof matched-asymptotic-expansion based on the large Reynolds number\r\nand hence the small skin friction coefficient.
\r\n\r\nIn the outer part of the layer, the perturbed flow is practically\r\n\"inviscid.\" Solutions for the velocity, Reynolds stress and also the\r\nwall pressure distributions agree well with the experimental measurement. \r\nIn the wall region where the perturbed Reynolds stress plays an\r\nimportant role in the process of momentum transport, only a qualitative\r\nagreement is obtained. The results also show that the nonlinear\r\nsecond-order effect is negligible for amplitude ratio of 0.03.\r\nThe discrepancies in the detailed structure of the velocity, shear\r\nstress, and skin friction distributions near the wall suggest modifications\r\nto the model are required to describe the present problem.
" }, { "name": "Kulkarny, Vijay Anand", "degree": "PhD", "year": "1975", "title": "An Experimental Investigation on Focussing of Weak Shock Waves in Air", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-082903", "creators": [ { "name": { "family": "Kulkarny", "given": "Vijay Anand" }, "id": "Kulkarny-Vijay-Anand", "display_name": "Kulkarny, Vijay Anand" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KK7V-6827", "abstract": "The behavior of focussing weak shock waves is experimentally investigated with a view to observe and understand the processes occurring near the focus, especially the processes that control the maximum amplitude. Concave reflectors are used against the endwall of a large 17\" diameter shock tube, to focus the plane incident shock. Reflectors producing line and point foci, and cusped and smooth caustics are examined for incident shock Mach numbers ranging between 1.005 to 1.5. The flowfield is observed with spark shadowgraphs to visualize the motion of various wavefronts. Pressure histories measured at various points in the flow with miniature piezoelectric gauges provide additional information about the various processes occurring near the focus.\r\n\r\nShadowgraphs show that for weak shocks, the observed foci are predominantly nonlinear, even though away from the focus, the shockfronts appear to be almost acoustic. Thus a weak shockfront, after the focus, crosses itself and forms a loop, which is an essential feature of acoustic wavefronts. Nonetheless, at the focus, distortion in the geometry of the fronts due to nonlinear effects is very prominent. Inherently nonlinear phenomena, such as formation of three-shock intersections, lead to foci of finite size, in which, as the pressure measurements show, the amplitudes are finite.\r\n\r\nThe amplitude dependence of these phenomena confirms that they are basically nonlinear. The geometrical distortion and the focus are larger for stronger shock waves, and the maximum amplification is smaller. Further, when the distortion becomes significant compared to the size of the initial shockfront, a transition occurs in the geometry of the focussed shockfront. In this case, the focussed front does not cross and remains \"unlooped\", which is consistent with the nonlinear behavior predicted by shock dynamics.\r\n\r\nThe transition in the geometry of the wavefronts is related to the behavior of the three-shock intersections formed near the focus. In fact, it is shown that the occurrence of crossed or uncrossed shockfronts is very parallel to the occurrence of regular or Mach reflection, respectively, in the case of a shock diffracted by a wedge. (The reflecting wedge surface corresponds to the axis of symmetry in a focussing process.) The dependence on the steepness of the approaching waves is also similar in the two cases; rapid convergence of waves suppresses nonlinear effects, whereas in a slow convergence, nonlinear effects gain prominence.\r\n\r\nThe pressure histories at various locations, when correlated with the waves occurring there, show that nonlinear diffraction processes are very important. In fact, it is shown that the formation of the three-shock intersection occurs due to nonlinear distortion and breaking of a compressive diffraction, and that, in the focus, the limiting and reduction of the peak amplitude occurs by a diffracted expansion overtaking the shock due to nonlinear effects." }, { "name": "Moronval, Marc Jules", "degree": "PhD", "year": "1975", "title": "Optimization of Arch and Shell Structures", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-093909310", "creators": [ { "name": { "family": "Moronval", "given": "Marc Jules" }, "id": "Moronval-Marc-Jules", "display_name": "Moronval, Marc Jules" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EMCP-7017", "abstract": "Structural optimization of structures with respect to their shape and thickness distribution is studied using a variational approach. The behavioral constraint is either the state of stress or the stiffness.\r\nThe boundary value problems, derived using Optimal Control theory, are solved with the parallel shooting technique. For statically determinant arches subjected to a uniform pressure, the contribution of the shear force is included in the behavioral constraints to prevent the problems from being singular. For the case of membrane shells of revolution supporting a combined pressure and end traction loading case, solutions were obtained up to a critical value of the load coefficient. A physical interpretation of the singularity is obtained by including the possibility\r\nof discrete rings in the formulation. A set of optimality conditions for shells of revolution described by the bending theory, satisfying a stiffness constraint, is derived. The problem is found to be ill posed when the shear contribution is not included in the structural operator.\r\n" }, { "name": "Sarohia, Virendra", "degree": "PhD", "year": "1975", "title": "Experimental and Analytical Investigation of Oscillations in Flows over Cavities", "advisor": "Roshko, Anatol; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032007-131245", "creators": [ { "name": { "family": "Sarohia", "given": "Virendra" }, "id": "Sarohia-Virendra", "display_name": "Sarohia, Virendra" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WJC1-X942", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this study, an analytical and experimental approach has been used to investigate the phenomenon of flow induced oscillations in cavities. Laminar axisymmetric flows over shallow cavities at low subsonic speeds were experimentally investigated using constant temperature hot-wire anemometry. This study comprised the following: study of the effect of the freestream and cavity configuration on onset of cavity oscillations; measurements of cavity shear layer under a wide range of cavity and flow configurations, and the distribution of the phase of the propagating disturbances during both first and second mode of cavity oscillation for a fixed Reynolds number at the upstream corner. Both motion and instant pictures of cavity shear flow, visualized by smoke injection, were obtained. Experiments were also done to investigate the effect of artificial excitation and of mass injection on the onset of cavity oscillations.\r\n\r\nThe present study indicates that the cavity depth has little effect on oscillations in shallow cavities, except when the depth is of the order of the thickness of the cavity shear flow. For such cavity configurations, measurements indicate a strong stabilizing effect of depth on laminar cavity shear layer. Results of motion pictures and hot-wire surveys of the cavity shear layer show that, close to the downstream cavity corner, large lateral motion of the shear layer occurs, which results in a periodic shedding of vortices at a frequency of cavity oscillations. Mean velocity measurements show growth rates as high as [...] 0.022 where [...] is the shear layer momentum thickness and x is the streamwise coordinate. These are attributed to strong imposed velocity fluctuations on the flow, by the oscillating cavity system.\r\n\r\nPhase measurements indicate that the disturbances propagate at a constant phase speed through the cavity shear layer. The wave length of the propagating disturbance bears an approximate integral relation to cavity width, in each mode of cavity oscillation given by [...] where b is the cavity width, [...] the wave length of the propagating disturbance and N is an integer, which takes values 0, 1, 2, ... etc. depending upon the mode of oscillation.\r\n\r\nStability calculations of the measured mean velocity profile were made by numerically integrating the governing equation of motion. These numerical results were used to compute the phase and the integrated amplification of the growing disturbances, through the cavity shear layer. Finally, the mode of cavity oscillation can be predicted for a given cavity flow by studying simultaneously the phase and integrated amplification of various disturbance frequencies through the shear layer and applying the mode relation." }, { "name": "Smith, Gordon Carl", "degree": "PhD", "year": "1975", "title": "An Experimental Investigation of the Dynamic Fracture of a Brittle Material", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-082245", "creators": [ { "name": { "family": "Smith", "given": "Gordon Carl" }, "id": "Smith-Gordon-Carl", "display_name": "Smith, Gordon Carl" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/35AK-XJ82", "abstract": "A new method of experimentally investigating the behavior of a crack in a stress wave environment has been developed and used to study the initial stages of dynamic crack propagation in Homalite 100, a polyester. The experimental method, which employs an electromagnetic loading device, permitted the application of pressure pulses to the surfaces of an 18 inch crack. The amplitude (51 psi to 1020 psi) and duration (~ 200 \u00b5sec) of the pulses were highly repeatable. The experimental configuration simulates, in the vicinity of the crack tip, a tension wave impacting a stationary semi-infinite crack in an infinite two-dimensional body where the wave front is parallel to the crack. A high speed framing camera, synchronized with the loading device, was used to record the time required for the crack to begin to propagate and its subsequent extension and velocity. The experimental results were analyzed within the bounds of linearly elastic fracture mechanics and a correlation was made between the dynamic stress intensity factor and the time at which the cracks began to propagate. It was found that the critical stress intensity factor increased dramatically with increasing loading rates at very high rates, which contrasts with quasi-static loading where the critical stress intensity factor decreases with an increasing loading rate. A simple model suggests that temperature effects at the crack tip may account for the observed increase in the critical stress intensity factor at high loading rates. Crack branching of running cracks was observed but unlike previous reports of branching, the cracks in this study branched mostly into three separate fast-running cracks." }, { "name": "Toda, Susumu", "degree": "Engineering Degree", "year": "1975", "title": "The Effects of Elliptic and Rectangular Cutouts on the Buckling of Cylindrical Shells Loaded by Axial Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-090542", "creators": [ { "name": { "family": "Toda", "given": "Susumu" }, "id": "Toda-Susumu", "display_name": "Toda, Susumu" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/473V-C743", "abstract": "The results of experimental investigations of the effect of elliptic cutouts on the buckling of thin cylindrical shells under axial compression are presented. The experiments were performed on Mylar shells with a radius to thickness ratio of 400 and with two diametrically opposed circular, elliptic or rectangular holes. The results show that, for a given shell geometry, the area of a cutout determined the shell buckling behavior, but that the configuration of the cutout had little influence on the buckling loads.\r\n\r\nA simplified analytical study based on Van Dyke's stress analysis and a strictly empirical design formula which gives a lower bound for the existing experimental data are also presented." }, { "name": "Hoeijmakers, Hendrik Willem Marie", "degree": "Engineering Degree", "year": "1974", "title": "Effects of Planform Curvature in Supersonic Wings", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-092227", "creators": [ { "name": { "family": "Hoeijmakers", "given": "Hendrik Willem Marie" }, "id": "Hoeijmakers-Hendrik-Willem-Marie", "display_name": "Hoeijmakers, Hendrik Willem Marie" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6DFV-0J65", "abstract": "In this thesis a method is developed for calculating supersonic wings with curved subsonic leading edges. The linearized theory is used throughout the thesis.\r\n\r\nThe wing with the curved subsonic leading edges is transformed into a wing with straight subsonic leading edges by means of a transformation as used by Coene for quasi-homogeneous approximations to the solution of this problem. The Mach cone is invariant under the transformation.\r\n\r\nThe solution of the transformed Prandtl-Glauert equation is expressed in terms of Fenain's solutions for the delta wing. In general the solution is an infinite sum of terms, each term related to a solution for the delta wing. However, a condition is formulated under which certain families of wings with curved leading edges possess solutions in closed form. It is shown that any boundary value problem for such wings can be solved by the superposition of these exact solutions of the Prandtl-Glauert equation. The problem is thus reduced to determining the number of terms necessary to approximate the given boundary values within satisfactory bounds, and within a satisfactory region of the wing.\r\n\r\nOne family of wings with curved leading edges that has a solution in closed form is found. The flat plate with these leading edges is studied in detail. In order to find a reasonable approximation to the flat plate, in a satisfactory region of the wing, up to five solutions are superposed. It has been found that the curvature has a considerable effect on the perturbation velocity and the leading edge suction force. The leading edge suction force thus found is compared with that calculated by some other approximate methods.\r\n" }, { "name": "Kendall, Frank, III", "degree": "Engineering Degree", "year": "1974", "title": "An Experimental Investigation of the Nonlinear Vibration of Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-083549862", "creators": [ { "name": { "family": "Kendall", "given": "Frank, III" }, "id": "Kendall-Frank-III", "display_name": "Kendall, Frank, III" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q4F6-C984", "abstract": "An experimental investigation of the nonlinear vibrations of\r\ncylindrical shells was undertaken. An aluminum shell was vibrated by means of an induction shaker. An optical device was used to obtain radial displacement measurements. Several modes of vibration were studied in detail. Various nonlinear effects were observed. These included nonlinearity in the driven mode frequency response\r\ncurve, the participation of the companion mode, and the participation of axisymmetric response at twice the driven frequency. The experimental results indicated only a softening type nonlinearity. The response of the companion mode was significant in several of the modes studied and was of a more complex nature than was predicted by previous theoretical work.\r\n" }, { "name": "Knight, Doyle Dana", "degree": "PhD", "year": "1974", "title": "An Analytical Investigation of Turbulent Flow Over a Wavy Boundary", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-151736905", "creators": [ { "name": { "family": "Knight", "given": "Doyle Dana" }, "id": "Knight-Doyle-Dana", "display_name": "Knight, Doyle Dana" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T9PD-TM13", "abstract": "The linearized, two-dimensional flow of an incompressible fully turbulent fluid over a sinusoidal boundary is solved using the method of matched asymptotic expansions in the limit of vanishing skin friction.\r\nA phenomenological turbulence model due to Saffman\r\n(1970, 1974) is utilized to incorporate the effects of the wavy boundary on the turbulence structure.\r\nArbitrary lowest order wave speed is allowed in order to consider both the stationary wavy wall, and the water wave moving with arbitrary positive or negative velocity.\r\nGood agreement is found with measured tangential velocity profiles and surface normal stress coefficients. The phase shift of the surface normal stress exhibits correct qualitative behavior with both positive and negative wave speeds, although predicted values are low.\r\n" }, { "name": "Rizk, Magdi Hanna", "degree": "PhD", "year": "1974", "title": "Nonsteady Fluid Mechanics of Vehicles in Tubes", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-152813759", "creators": [ { "name": { "family": "Rizk", "given": "Magdi Hanna" }, "id": "Rizk-Magdi-Hanna", "display_name": "Rizk, Magdi Hanna" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8PJF-8H92", "abstract": "A theoretical study is performed to investigate the drag\r\nexperienced by vehicles travelling in tubes, the pressure distribution and flow velocities resulting from the vehicle's motion. The study deals with both the cases of vehicles accelerating from rest in the tube and vehicles entering a tube at finite speed. The effect of having a vent in the tube is also studied.\r\n\r\nThe unsteady compressible equations are used to describe\r\nthe flow in the tube. Before the boundary layer fills the tube, an inviscid core-boundary layer formulation is used. However, it is found that the simpler one-dimensional formulation is adequate for describing the flow in the tube. The quasi-steady near-field assumption agrees well with the unsteady near-field solution except for the initial period of low velocities.\r\n\r\nThe solution is compared to that in which compressibility\r\nis neglected. It is found that the effect of compressibility is not large for short tubes, low blockage ratios and small velocities. However, its importance increases as the values of these parameters increase. Compressibility may not be neglected during the initial period in the case of vehicles entering tubes at finite speeds.\r\n" }, { "name": "Sidor, Laurent Bernard", "degree": "Engineering Degree", "year": "1974", "title": "An Investigation of the Ejector-Powered Jet-Flap", "advisor": "Stewart, Homer Joseph; Harris, Gordon L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-143232435", "creators": [ { "name": { "family": "Sidor", "given": "Laurent Bernard" }, "id": "Sidor-Laurent-Bernard", "display_name": "Sidor, Laurent Bernard" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Harris", "given": "Gordon L." }, "id": "Harris-Gordon-L", "role": "advisor", "display_name": "Harris, Gordon L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D5X4-X160", "abstract": "The inviscid and incompressible potential flow aspects associated with a two-dimensional ejector-powered jet-flap configuration are investigated. The energy addition due to the mixing process in the ejector results in a non-homogeneous flow and is represented by an actuator disk located between the lifting surfaces and a powered\r\nwake. A set of singularities is developed to represent the lifting surfaces, to include camber and flap deflection, and the powered\r\nwake. A numerical procedure is used to compute the total system\r\nvorticity needed to satisfy exactly all the prescribed boundary conditions. The lift and moment coefficients are evaluated as a function of the head change prescribed across the actuator disk. A simple interpretation of the resulting lift curves is proposed in terms of analytical results obtained for single-airfoil configurations - a flat-plate airfoil and sink system, and a conventional single element jet flap. The sink effect of the actuator accounts for a finite lift at zero angle of attack, and the lift increment due to angle of attack only can be predicted by using Spence's theory of the jet flap.\r\n" }, { "name": "Uehara, Sachio", "degree": "PhD", "year": "1974", "title": "Theoretical Investigation of Minimum Time Loop Maneuvers of Jet Aircraft", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-111949185", "creators": [ { "name": { "family": "Uehara", "given": "Sachio" }, "id": "Uehara-Sachio", "display_name": "Uehara, Sachio" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZTAZ-J396", "abstract": "Minimum time loop maneuvers of high performance jet aircraft have been investigated by means of the calculus of variations. A number of simplifying assumptions have been made in the atmospheric conditions, aerodynamic parameters, and the number of controls and their upper and lower bounds, in order to obtain general features and basic characteristics of the problem. The optimal control (lift coefficient and thrust) has been determined as a function of the state variables and Lagrange multipliers. It is found that subarcs with variable thrust, or with variable lift coefficient and minimum thrust do not occur on time optimal paths. Possible transitions among the five optimal subarcs have been established by applying the corner conditions of variational calculus. These relationships are applicable to any minimum time maneuver in the vertical plane. The effects of the magnitudes of maximum lift coefficient and maximum thrust on the control program, maneuver time, final speed, and final. horizontal distance for minimum time loop maneuvers are explored through numerical computation. It is found that the control history in lift and thrust and the minimum time required for a loop maneuver depend strongly on the magnitudes of maximum lift coefficient and maximum thrust. A limited numerical exploration using more realistic aerodynamic and atmospheric parameters and a state-dependent maximum thrust yielded results in qualitative agreement with the more extensive analysis based on simplified parameters. Normal acceleration constraints are analyzed by considering the maximum lift coefficient to be a function of altitude and speed. New design criteria for the inlet, duct and engine are suggested by consideration of the problem of engine surge." }, { "name": "Bhatia, Prem", "degree": "PhD", "year": "1973", "title": "Buckling of Imperfect Circular Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08302010-162439924", "creators": [ { "name": { "family": "Bhatia", "given": "Prem" }, "id": "Bhatia-Prem", "display_name": "Bhatia, Prem" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FS7M-8D46", "abstract": "In this project, the buckling of imperfect circular cylindrical shells under uniform axial compression has been investigated. The imperfection considered is prismatic and is in the form of flat spots along the complete length of the shell. The problem is solved by considering it as an interaction problem between curved and flat panels. Shell equations are satisfied in the curved portions of the shell while flat plate equations are used in the flat spot regions. At the common edge between two adjacent panels, forces and displacements are matched to arrive at the eigenvalue problem for the critical load of the shell. Two flat spot configurations have been studied. In the first case, a single flat spot along the complete length of the shell is considered. Curved and flat panels join to form sharp corners at their common edges. Numerical results are presented to show the effect of the width of the flat spot, thickness ratio and length to radius ratio of the shell, on the buckling load of the shell. In the second case, the imperfection is in the form of two or more identical flat spots distributed uniformly along the circumference of the shell. Between two consecutive flat spots is a uniform radius cylindrical panel joining smoothly to the flat panels. This analysis is valid for any integral number of identical flat spots. Numerical results are presented for 2, 3, 4, 8-flat spots. The effect of width of flat spots, radius of curved panels, thickness ratio of the shell has been investigated. The results, presented in this paper, clearly demonstrate a very significant reduction in the buckling load of the shell below its classical value. This is true even in the presence of relatively small flat spots. This reduction becomes more severe with a decrease in the thickness of the shell or an increase in the width of the flat spot. " }, { "name": "Cummings, John Chester", "degree": "PhD", "year": "1973", "title": "I. Development of a Cryogenic Shock Tube. II. Experimental Investigation of the Interaction of a Shock Wave with Liquid Helium and I and II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-095321580", "creators": [ { "name": { "family": "Cummings", "given": "John Chester" }, "id": "Cummings-John-Chester", "display_name": "Cummings, John Chester" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AM0F-DB64", "abstract": "I. Development of a cryogenic shock tube
\r\n\r\nA cryogenic shock tube has been developed as a tool for research in fluid mechanics and low temperature physics. The shock tube is designed to operate with the test section immersed in a cryogenic liquid. A unique diaphragm changing mechanism makes this shock tube an economical and practical device.
\r\n\r\nThere are several advantages in operating a shock tube at cryogenic temperatures. Shock waves of very large Mach number can be produced. The flow field can be accurately calculated using ideal shock tube - perfect gas theory. Boundary layer effects are decreased so that long test times are possible.
\r\n\r\nThe cases which have been studied are test gas temperatures of 300, 77, 4.2, and 2.3\u00b0K. Helium is used as both test and driver gas. The largest Mach numbers which have been observed range from 2.4 at 300\u00b0K to 32 at 2.3\u00b0K (several runs at 1.46\u00b0K have produced Mach 40 shocks). As the test gas temperature is decreased the observed Mach numbers approach those calculated using the ideal shock tube equation. The observed test times can be interpreted using laminar or turbulent boundary layer theory if the effects of shock formation distance and wall temperature rise are taken into account.
\r\n\r\nAs a laboratory tool the cryogenic shock tube may be applied in many areas and modified for use in even more. Large Mach number shocks and large Reynolds number flows can be produced with this device. The rapid increase in temperature and pressure across a shock wave is useful for studies of sublimation, evaporation, or chemical reactions. Quantum mechanical effects in cryogenic materials, superconductors, or superfluid helium can also be investigated.
\r\n\r\nII. Experimental investigation of the interaction of a shock wave with liquid helium I and II
\r\n\r\nThe flow field produced by a shock wave reflecting from a helium gas -liquid interface has been investigated using a new cryogenic shock tube. Incident and reflected shock waves have been observed in the gas; transmitted first and second sound shocks have been observed in the liquid. Wave diagrams have been constructed to compare the data to theoretical wave trajectories. Qualitative agreement between data and theory has been shown. Quantitative differences between data and theory indicate a need for further analysis of both the gas-liquid interface and the propagation of nonlinear waves in liquid helium.
\r\n\r\nThis work is essentially a first step in the experimental investigation of a very complex nonequilibrium state. The well controlled jump in temperature and pressure across the incident shock wave provides unique initial conditions for the study of dynamic phenomena in superfluid helium.
\r\n\r\nThe results clearly demonstrate the usefulness of the cryogenic shock tube as a research tool.
" }, { "name": "Ditchey, Robert Louis", "degree": "Engineering Degree", "year": "1973", "title": "The Effect of Imperfections on the Buckling of Thin Walled Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-145835690", "creators": [ { "name": { "family": "Ditchey", "given": "Robert Louis" }, "id": "Ditchey-Robert-Louis", "display_name": "Ditchey, Robert Louis" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TPE9-EM80", "abstract": "A theoretical study of the effect of imperfections on the buckling load of a circular cylindrical shell under axial compression was carried out. The nonlinear shell equations of Donnell are solved in an approximate manner using the Potential Energy Theorem. The method of derivation and the resulting algebraic equations are com-pared to previous derivations which use a different method of solution. It was found that the resulting equations are identical to the ones derived by Galerkin's procedure, lending credence to that method. A parametric study of an imperfection model was carried out numerically. The imperfection model is similar to that originally used by Donnell, having amplitude decay with increasing wave number. The results show the effect of various rates of decay of amplitude with wave number, as well as the effect of various assumed amplitudes. Using these parameters, it is shown when shell buckling is dominated by long wave imperfections as opposed to classical short wave imperfections. It was found that if the decay of asymmetric imperfections with axial wave number is sufficiently high, that long wave imperfections can dominate. In the range of values chosen for these parameters, changes in the axisymmetric imperfection model had little effect on buckling behavior as compared to the changes in sensitivity to long waves which occur as the asymmetric model is varied." }, { "name": "Glaser, Robert James", "degree": "Engineering Degree", "year": "1973", "title": "Gravity Gradiometer Data Reduction", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272010-080449842", "creators": [ { "name": { "family": "Glaser", "given": "Robert James" }, "id": "Glaser-Robert-James", "display_name": "Glaser, Robert James" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "chair", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Dergarabedian", "given": "Paul" }, "id": "Dergarabedian-Paul", "role": "member", "display_name": "Dergarabedian, Paul" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5VY1-7Z44", "abstract": "Two existing gravity gradiometers are discussed and a single signal equation is developed for both instruments. Equations are derived for calculating the gradiometer signal from known spherical harmonic coefficients. The result is a signal equation in the same form as the harmonic expansion but with a \"gradiometer\" polynomial. Next, an integral curvefit procedure is developed for calculating the harmonic coefficients of the gravitational field from known gradiometer data. The procedure only requires calculation of a theoretical observation matrix, thus the orbit determination part of the algorithm is the rate determining step. This increases in cost as the fourth power of the maximum harmonic degree considered. Calculations using parts of the algorithm are discussed and procedures for dealing with error sources are described. Finally, a brief description of a complete gradiometer data reduction program is presented.
" }, { "name": "Ikawa, Hideo", "degree": "PhD", "year": "1973", "title": "Turbulent Mixing Layer Experiment in Supersonic Flow", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-154352889", "creators": [ { "name": { "family": "Ikawa", "given": "Hideo" }, "id": "Ikawa-Hideo", "display_name": "Ikawa, Hideo" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4MBK-D880", "abstract": "A supersonic, two-dimensional, turbulent free mixing layer\r\nwas experimentally investigated in the GALCIT Supersonic wind tunnel to clarify the Mach number dependence of this flow field. The tests were conducted with a nominal Mach number of 2.47 with an ambient stagnation condition. Self similarities of the mean and turbulent flow fields were established.\r\n\r\nThe mean and fluctuating flow measurements were made. In\r\naddition, the actual entrainment rate of the turbulent free mixing layer through the low speed interface was also measured and it was verified that this quantity equals the growth rate of momentum thickness. The spreading rate, the entrainment rate and the maximum shear stress were appreciably smaller than the respective incompressible\r\nvalues. Velocity profile scaled to an incompressible form.\r\nby a linear transformation of the lateral coordinate. The maximum streamwise velocity fluctuation was approximately 1/3 of the incompressible value. The flow field of turbulent free mixing layer was found to be highly dependent upon the supersonic compressibility\r\neffect.\r\n" }, { "name": "Kosmicki, James Joseph", "degree": "Engineering Degree", "year": "1973", "title": "Experimental Study of the Separation and Reattachment in a Partially Confined Jet", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-133626", "creators": [ { "name": { "family": "Kosmicki", "given": "James Joseph" }, "id": "Kosmicki-James-Joseph", "display_name": "Kosmicki, James Joseph" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/14DA-WA82", "abstract": "By use of various lengths of shroud an experimental study was made of a partially confined jet to examine the transition between the flow configuration for a free jet to that of a confined jet. An examination of the reattachment pressure distributions and the parameters at the entrance of the abrupt channel expansion was made. A smooth transition of mean flow quantities was found to occur in the transition from a free jet to a partially confined jet and then to a fully confined jet. The distance to reattachment was measured for various shroud lengths and shown to exhibit an asymptotic value which was Reynolds number dependent. Associated with this maximum reattachment length was a maximum pressure recovery factor. The range of Reynolds numbers - based upon the jet diameter - for the present study was 80,000 to 280,000." }, { "name": "Lee, Peter Hoong-Yee", "degree": "PhD", "year": "1973", "title": "An Investigation of Collisionless Plasma Beam Interaction with a Nonhomogeneous Magnetic Field", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262010-104719284", "creators": [ { "name": { "family": "Lee", "given": "Peter Hoong-Yee" }, "id": "Lee-Peter-Hoong-Yee", "display_name": "Lee, Peter Hoong-Yee" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XNF6-9D90", "abstract": "The interaction between a rarefied flowing plasma and an externally imposed nonhomogeneous magnetic field is studied experimentally in a collisionless plasma wind tunnel, where a collisionless plasma beam is directed through a current loop. The collisionless plasma is generated by an electron bombardment engine. Nominal values of ion flow speed, number density, electron temperature and magnetic induction of the loop are U ~10^4 m/s, N ~5 x 10^7/cc, kT_e ~0.2 eV and B ~10 Gauss, respectively. Due to lack of probe theories in the presence of nonhomogeneous magnetic fields and failure of conventional Langmuir probe methods, a new, simple method of diagnostics is developed. This method employs two probes of different geometry and obtains information on the ion density and flow speed from the ion-saturation region of the probe characteristic. Radial density profiles in the wake of the current loop mapped by the \"two-probe\" method indicate annular density \"peaks\" at certain radial positions. In order to understand this non-uniform \"pinching\" process, a theoretical analysis is attempted. It is found that the experimentally observed phenomenon can be qualitatively described by the collision-less two-fluid equations, but turbulent \"friction\" is required to improve the two-fluid model. A heuristic turbulent model is used, and evidence of turbulence in the flow field is also obtained through measurements of the fluctuating probe currents." }, { "name": "Mahale, Narayan Krishna", "degree": "Engineering Degree", "year": "1973", "title": "Failure of Precracked Fiber Reinforced Composite Plate", "advisor": "Knauss, Wolfgang Gustav; Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192010-160559026", "creators": [ { "name": { "family": "Mahale", "given": "Narayan Krishna" }, "id": "Mahale-Narayan-Krishna", "display_name": "Mahale, Narayan Krishna" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DPK2-YA94", "abstract": "In the following pages a theoretical and experimental investigation of the fracture of a precracked carbon fiber reinforced composite is presented. The work deals mainly with a unidirectional composite having the crack aligned parallel to the fibers. We put forth some ideas on how to extend the failure criterion of the above restricted case to a more general one of multidirectional composites.\r\nThe failure criterion proposed is based on an energy argument similar to that proposed by Griffith for isotropic solids. For the purpose of stress analysis the material under consideration is assumed to be homogeneous and orthotropic. Lekhnitskii's complex variable method\r\nof stress analysis of the two dimensional elasticity problems for anisotropic bodies is used in the theoretical investigation.\r\n" }, { "name": "Masoni, Harry Joseph", "degree": "Engineering Degree", "year": "1973", "title": "A Communications Satellite System Design with Educational Television for the Republic of Indonesia", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-090107696", "creators": [ { "name": { "family": "Masoni", "given": "Harry Joseph" }, "id": "Masoni-Harry-Joseph", "display_name": "Masoni, Harry Joseph" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W9SX-GB37", "abstract": "The purpose of this thesis is to apply a feasible and comprehensive systems approach to the design and analysis of a communications satellite system with educational television for an underdeveloped country. The\r\nquestion of the effectiveness of educational television in concept is treated through revelation of historical evidence and case studies pertaining to existing educational television programs throughout the world. The\r\napplicability of blending educational television with a complete satellite communications system is illustrated through the detailed design of a system for the Republic of Indonesia. A system providing educational television, national television, and telephony is proposed and all systems elements and technical analyses are subsequently described. The economic viability of the system is illustrated through a detailed financial analysis\r\nwith both operating and cash flow results. Comparison of the proposed satellite system with an equivalent terrestrial system is briefly made in Appendix C, to demonstrate the cost-effectiveness of the satellite approach.\r\n" }, { "name": "Rebollo-Rebollo, Manuel", "degree": "PhD", "year": "1973", "title": "Analytical and Experimental Investigation of a Turbulent Mixing Layer of Different Gases in a Pressure Gradient", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-091455869", "creators": [ { "name": { "family": "Rebollo-Rebollo", "given": "Manuel" }, "id": "Rebollo-Rebollo-Manuel", "display_name": "Rebollo-Rebollo, Manuel" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6YB5-CJ15", "abstract": "An analytical and experimental study has been made of the turbulent mixing layer in a pressure gradient. Theory predicts the possible existence of equilibrium flows, and this was confirmed experimentally for turbulent shear layers between streams of helium and nitrogen. \r\nThe only case for which similarity is possible is for P2 U_2^2 = P1 U_1^2 since then P_2 (x) = P_1 (x). These equilibrium flows are of the form U_1 ~x^ \u03b1 and \u03b4~X, where \u03b1=x/U_1 dU_1/dx is non \u2013dimensional pressure gradient parameter. \r\nThe experimental investigation was conducted in the facility designed by Brown to produce turbulent flows at pressures up to 10 atmospheres. The adjustable walls of the test section of the apparatus were modified in order to set the pressure gradient. \r\nShadowgraphs of the mixing zone for \u03b1 = 0 and \u03b1 = - 0.18, at different Reynolds numbers, revealed a large scale structure noticeably different for each \u03b1. \r\nThe similarity properties of the shear layer were established from mean profiles of total head and density. In addition, the rms density fluctuations were found to be self-preserving. From the mean profiles, the spreading rate, turbulent mass diffusion, Reynolds stress and Schmidt number distributions were calculated from the equations of motion. \r\nThe experimental results show that the spreading rate for the adverse pressure gradient is 60% A greater than for the \u03b1 = 0 case. The maximum shearing stress is 70% larger and the maximum value of the turbulent mass diffusion is 20% larger than their \u03b1 = 0 counterparts. The maximum rms density fluctuations are approximately 0.2 in both flows. \r\nSurprisingly low values of turbulent Schmidt numbers were found; e. g., at the dividing streamline Sc_t = 0.16 for \u03b1 = 0 and Sc_t = 0. 33 for \u03b1 = - 0. 18.\r\n" }, { "name": "Rupert, Viviane Claude", "degree": "PhD", "year": "1973", "title": "Experimental Study of Shock Wave Strengthening by a Positive Density Gradient in a Cryogenic Shock Tube", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272010-083731520", "creators": [ { "name": { "family": "Rupert", "given": "Viviane Claude" }, "id": "Rupert-Viviane-Claude", "display_name": "Rupert, Viviane Claude" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZXBM-7809", "abstract": "An experimental investigation of the strengthening of a shock wave propagating through an isobaric region of increasing density is presented. A new experimental configuration consisting of a pressure-driven shock tube mounted vertically with the test section partially immersed in a cryogenic bath is used. The resulting test gas density distribution consists of a uniform region of low density near the shock tube diaphragm, then a strong local gradient followed by another uniform region of high density. The\r\nMach number of the shock initiated at the diaphragm is determined as the shock emerges from the gradient from velocity and temperature measurements for various initial conditions.\r\nThe experimental data are compared with predictions from approximate theoretical models and a numerical integration of the exact flow equations for the shock-gradient interaction. The measured Mach numbers are considerably higher than these predictions indicating that the models are not adequate to represent the experimental configuration. Calculations show that the additional strengthening of the shock results from multiple interactions between waves generated within the gradient and flow nonuniformities due to the shock formation mechanism.\r\n" }, { "name": "Storm, Erik", "degree": "PhD", "year": "1973", "title": "Part I. Investigation of Strong Shock Waves in a Conical Convergent Channel. Part II. Spectroscopic Investigation of Strong Shockwaves in a Conical, Convergent Channel", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-104952", "creators": [ { "name": { "family": "Storm", "given": "Erik" }, "id": "Storm-Erik", "display_name": "Storm, Erik" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TJFS-6964", "abstract": "ABSTRACT OF PART I:
\r\n\r\nThe behavior of an initially plane, strong shock wave propagating into a conical convergence is investigated experimentally and theoretically. In the experiment a 10\u00b0 half-angle cone is mounted on the end of a pressure-driven shock tube. Shock waves with initial Mach numbers varying from 6.0 to 10.2 are generated in argon at a pressure of 1.5 torr. During each run local shock velocities at several positions along the cone axis are measured using a thin, multi-crystal piezoelectric probe inserted from the vertex. This technique produces accurate velocity data for both the incident and reflected shock waves. In the corresponding analysis, a simplified characteristics method is used to obtain an approximate solution of the axisymmetric diffraction equations derived by Whitham (1959).
\r\n\r\nBoth the shock velocity measurements and the axisymmetric diffraction solution confirm that the incident shock behavior is dominated by cyclic diffraction processes which originate at the entrance of the cone. Each diffraction cycle is characterized by Mach reflection on the cone wall followed by Mach reflection on the axis. These cycles evidently persist until the shock reaches the cone vertex, where the measured velocity has increased by as much as a factor of three. Real-gas effects, enhanced in the experiment by increasing the initial Mach number and decreasing the pressure, apparently alter the shock wave behavior only in the region near the vertex. Velocity measurements for the reflected shock within the cone show that the shock velocity is nearly constant throughout most of the convergence length.
\r\n\r\nABSTRACT OF PART II:
\r\n\r\nThe thermodynamic conditions behind the incident and reflected shock wave close to the vertex of a convergent channel are investigated spectroscopically. The investigation was initiated in order to better determine the possible uses of such a geometrical device as a tool for high temperature plasma research. Using argon at an initial pressure of 1.5 torr, the shock Mach number prior to the entrance of the cone is 10.2. Two windows are mounted at x/1 = 0.9 in the cone, where the Mach number has increased to 24, and the emitted radiation is monitored for both time-resolved (Monochromator - Photomultiplier) and time-integrated (Spectrograph) analysis. The relative line intensity method is used to measure the electron temperature. The Stark broadened profile of the 6965.4 \u00c5 neutral argon line, and continuum intensity measurements are used to determine the electron number density.
\r\n\r\nFrom initial values of 13200\u00b0K and 1.4 x 10\u00b9\u2077 cm\u207b\u00b3, both the electron temperature and number density profiles behind the incident shock are dominated by the previous shock diffraction processes. The general trend is a gradual increase, presumably due to the continuing compression of the gas shocked at successively earlier times. Superimposed upon this is the effect of hot slugs of gas from previous localized regions of very high Mach number. The reflected shock wave heats and compresses the gas even further. The subsequent expansion results in a series of rapid exponential decreases in temperature, density and pressure. Immediately after the reflected shock wave has passed, the gas appears to be in a nonequilibrium state with a population inversion among the upper excited atomic energy levels. There is an indication of the presence of a second reflected wave. The effects of self-absorption on Stark broadened lines is studied. An equation is derived, demonstrating the effect of individual corrections that are necessary before accurate interpretations of measured quantities can be made. Simple self-absorption correction schemes are demonstrated and shown to be self-consistent.
" }, { "name": "Su, Tsung-Chow Joe", "degree": "Engineering Degree", "year": "1973", "title": "Viscous-Inviscid Flow Interaction in Stratified Flow Over a Barrier", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182010-154704323", "creators": [ { "name": { "family": "Su", "given": "Tsung-Chow Joe" }, "id": "Su-Tsung-Chow-Joe", "display_name": "Su, Tsung-Chow Joe" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XNJM-ES87", "abstract": "The gross effect of boundary layer separation on the flow field of stratified flow over a barrier was studied by means of the integral method of Lees and Reeves.
\r\n\r\nThe complete integral formulation of both inner and outer flow field of stratified flow over a barrier was obtained.
\r\n\r\nFurthermore, an iteration scheme of computation is proposed for the simple case of incompressible homogeneous flow over a barrier with viscous-inviscid interaction included.
\r\n\r\nHowever, in viewing the increasing importance, a considerable amount of work remains to be done on this problem.
" }, { "name": "Tamura, Yukio Stephen", "degree": "Engineering Degree", "year": "1973", "title": "Dynamic Stability of Cylindrical Shells Under Step Loading", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092009-105825918", "creators": [ { "name": { "family": "Tamura", "given": "Yukio Stephen" }, "id": "Tamura-Yukio-Stephen", "display_name": "Tamura, Yukio Stephen" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MSMN-N280", "abstract": "A study has been made to determine the dynamic stability of an imperfect circular cylindrical shell subject to a step loading in the axial direction. In the analysis, the radial displacement of the shell is approximated by a finite degree of freedom system. To assure that the created model is proper, its static buckling behavior was studied. It was found that the model gives the proper imperfection sensitivity behavior.\r\n\r\nThe dynamic analysis includes not only the effect of the radial inertia, but also that due to the axial inertia in an approximate manner. The critical loads are determined by numerical integration of the equation of motion. In addition a study is carried out to consider the effects of wave number of the radial mode shape, mass on the loaded edge of the shell and damping of the axial motion. Compared with the static case, there is a significant reduction of the dynamic buckling load for the high wave numbers of the radial modes. Also, there is a critical clamping value, above which the dynamic buckling load is close to the static buckling load. The dynamic buckling load approaches half of the static buckling load with increasing mass on the loading edge. Through the parametric studies of the wave number, mass, and damping factor it is concluded that due to frequency coupling between axial and radial motions, the axial inertia plays an essential role in characterizing the dynamic instability of a finite length shell.\r\n" }, { "name": "Wiley, Robert Freeland", "degree": "Engineering Degree", "year": "1973", "title": "On the Use of Fixed Attitude Propulsive Arcs for Transfer Between Neighboring Coplanar Keplerian Orbits", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-115331989", "creators": [ { "name": { "family": "Wiley", "given": "Robert Freeland" }, "id": "Wiley-Robert-Freeland", "display_name": "Wiley, Robert Freeland" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/456S-YS44", "abstract": "The question of whether or not a coplanar, fixed attitude, constant acceleration burn in a central force field can result in a post-burn orbit that does not intersect the pre-burn orbit was investigated for small changes in the orbit. This was done by developing a criterion for separation between coplanar elliptical orbits, solving\r\nthe linearized equations of motion given in reference 1 for a coplanar, fixed attitude, constant acceleration burn, and evaluating the criterion. Regions in which an initial alignment of the acceleration vector may be chosen to result in orbital separation at some point in the burn and the alignments of the acceleration vector to do this were found numerically. However, it appears that the distances between the separated orbits and the time over which the orbits separate for a particular alignment are too small to make the phenomenon of much practical use for small orbital changes.\r\n" }, { "name": "Chen, Jay-Chung", "degree": "PhD", "year": "1972", "title": "Nonlinear Vibration of Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-085617930", "creators": [ { "name": { "family": "Chen", "given": "Jay-Chung" }, "id": "Chen-Jay-Chung", "display_name": "Chen, Jay-Chung" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CBC4-MP23", "abstract": "The large amplitude vibrations of a thin-walled cylindrical shell are analyzed using the Donnell's shallow-shell equations. A perturbation method is applied to reduce the nonlinear partial differential equations into a system of linear partial differential equations. The simply-supported boundary condition and the circumferential periodicity condition are satisfied. The resulting solution indicates that in addition to the fundamental modes, the response contains asymmetric modes as well as axisymmetric modes with the frequency twice that of the fundamental modes. In the previous investigations in which the Galerkins procedure was applied, only the additional axisymrnetric modes were assumed.\r\nVibrations involving a single driven mode response are investigated. The results indicate that the nonlinearity is either softening or hardening depending on the mode. The vibrations involving both a driven mode and a companion mode are also investigated. The region where the companion mode participates in the vibration is obtained and the effects due to the participation of the companion mode are studied.\r\nAn experimental investigation is also conducted. The\r\nresults are generally in agreement with the theory. \"Non-stationary4 response is detected at some frequencies for large amplitude response where the amplitude drifts from one value to another. Various nonlinear phenomena are observed and quantitative comparisons with the theoretical results are made.\r\n" }, { "name": "Davis, Joseph Eugene", "degree": "PhD", "year": "1972", "title": "Non-Planar Wings in Non-Planar Ground Effect", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-162542308", "creators": [ { "name": { "family": "Davis", "given": "Joseph Eugene" }, "id": "Davis-Joseph-Eugene", "display_name": "Davis, Joseph Eugene" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NNF7-GV39", "abstract": " A numerical method is developed for solving the problem of a wing in arbitrary non-planar ground effect. The linearized equations of unsteady motion for an arbitrary non-planar wing in non-planar ground effect are presented. Numerical calculations were made to determine all the aerodynamic characteristics and stability derivatives for various thin, uncambered planar and non-planar wings (including two wings connected in tandem) in planar and non-planar ground effect. These calculations were incorporated into the equations of unsteady motion to determine the dynamic stability characteristics of these wings in the various ground effect situations. Several wings were found to be longitudinally stable, but only in rare cases were they found to be laterally stable.\r\n \r\n An experiment was conducted to compare some of the numerical calculations with reality. The agreement was reasonable.\r\n" }, { "name": "Dolait, Jean-Pierre", "degree": "Engineering Degree", "year": "1972", "title": "Transonic Wind Tunnel for Investigation of Turbomachinery Blades", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01062016-155803211", "creators": [ { "name": { "family": "Dolait", "given": "Jean-Pierre" }, "id": "Dolait-Jean-Pierre", "display_name": "Dolait, Jean-Pierre" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4D2K-SR72", "abstract": "The design of a two-stream wind tunnel was undertaken to allow\r\nthe simulation and study of certain features of the flow field around\r\nthe blades of high-speed axial-flow turbomachineries. The mixing of\r\nthe two parallel streams with designed Mach numbers respectively\r\nequal to 1.4 and 0.7 will simulate the transonic Mach number distribution\r\ngenerally obtained along the tips of the first stage blades in\r\nlarge bypass-fan engines.
\r\n\r\nThe GALCIT hypersonic compressor plant will be used as an\r\nair supply for the wind tunnel, and consequently the calculations contained\r\nin the first chapter are derived from the characteristics and\r\nthe performance of this plant.
\r\n\r\nThe transonic part of the nozzle is computed by using a method\r\ndeveloped by K. O. Friedrichs. This method consists essentially of\r\nexpanding the coordinates and the characteristics of the flow in power\r\nseries. The development begins with prescribing, more or less arbitrarily,\r\na Mach number distribution along the centerline of the nozzle.\r\nThis method has been programmed for an IBM 360 computer to define\r\nthe wall contour of the nozzle.
\r\n\r\nA further computation is carried out to correct the contour for\r\nboundary layer buildup. This boundary layer analysis included geometry,\r\npressure gradient, and Mach number effects. The subsonic nozzle\r\nis calculated {including boundary layer buildup) by using the same\r\ncomputer programs. Finally, the mixing zone downstream of the splitter\r\nplate was investigated to prescribe the wall contour correction necessary\r\nto ensure a constant-pressure test section.
" }, { "name": "Giraudbit, Jean-No\u00ebl", "degree": "Engineering Degree", "year": "1972", "title": "Optimal Simple Structures with Bending and Membrane Stresses", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10132010-094217970", "creators": [ { "name": { "family": "Giraudbit", "given": "Jean-No\u00ebl" }, "id": "Giraudbit-Jean-No\u00ebl", "display_name": "Giraudbit, Jean-No\u00ebl" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/29PJ-3X76", "abstract": "Structural optimization of elastic solid structures with membrane and bending stresses is studied. A necessary and sufficient optimality condition for maximum stiffness is derived using an energy formulation (minimum potential energy). In the case of pure membrane or pure bending stress states, maximum stiffness and maximum strength are governed by the same optimality condition (uniform strength design). For mixed stress states (membrane and bending), this result is not true, and a general method of approach to find a necessary condition for maximum strength is developed by means of the calculus of variation. Two particular statically indeterminate problems with one design variable to be optimized (clamped-clamped beam, clamped-clamped arch) are treated by this method, and, in both examples, maximum. strength is achieved by a uniform strength design." }, { "name": "Hulcher, Gregory Don", "degree": "Engineering Degree", "year": "1972", "title": "Hypersonic Viscous-Inviscid Flow Interactions Including Boundary Layer Separation on a Flat Plate at Angle of Attack", "advisor": "Behrens, Wilhelm", "url": "https://resolver.caltech.edu/CaltechTHESIS:09032010-111033039", "creators": [ { "name": { "family": "Hulcher", "given": "Gregory Don" }, "id": "Hulcher-Gregory-Don", "display_name": "Hulcher, Gregory Don" } ], "advisors": [ { "name": { "family": "Behrens", "given": "Wilhelm" }, "id": "Behrens-W", "role": "advisor", "display_name": "Behrens, Wilhelm" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PZCP-FT88", "abstract": "Experimental measurements of mean flow properties over the leeward surface and in the near wake of an adiabatic thin flat plate at an angle of attack of \u03b1 = 15\u00b0 were obtained at Mach 6 and Reynolds number based on the chord length of 186,000. The leading edge thickness is the predominant variable which affects the pre-separation interaction region. The effects of the large windward pressure, which separates the boundary layer at \u2113/L \u2243 .7 are felt at points considerably forward of the separation point. The pressure rise in the separation region is similar to the rise on a flat plate-ramp model, and the data correlate according to Chapman's parameters. Also, the leeward side flow of the thin flat plate is found to be very similar to the flow over a wedge whose leeward side is inclined to the same angle. The wake centerline quantities behave similar to those behind a flat plate at zero angle of attack, but the streamwise gradients are less than those behind an inclined wedge. The flow appears to remain laminar throughout the entire field of measurement." }, { "name": "Kulkarni, Arun Narayan", "degree": "Engineering Degree", "year": "1972", "title": "Analysis of the Airline Systems Performance by Varying Inputs, Viz. Jet Aircraft, Routes and Scheduling", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07102007-093646", "creators": [ { "name": { "family": "Kulkarni", "given": "Arun Narayan" }, "id": "Kulkarni-Arun-Narayan", "display_name": "Kulkarni, Arun Narayan" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C94H-PP45", "abstract": "This is a systems analysis study of the commercial airlines. In essence, it provides a systematic procedure for determining a combination of decisions regarding the aircraft, routes and scheduling which maximizes overall effectiveness.\r\n\r\nThe model treats the aircraft, route and the scheduling as basic inputs, passenger-mile or ton-mile as basic outputs, revenue and cost as the monetary output and input respectively, to the airline system. Out of the numerous and diverse management objectives, the profit is chosen as a performance parameter, however noting that the return on investment would be a more realistic parameter. As a simplification, a multiple relationship between the direct and the indirect operating cost is used to eliminate indirect operating cost, and the attention is focused on the direct operating cost. The core idea of the profit computation is the deterministic approach to the costs and the probabilistic approach to the revenues.\r\n\r\nFour major steps can be observed, namely:\r\n\r\n1. Collection and systematic presentation of the relevant data about the aircraft and routes, taking into account the operational and technical constraints. This system reduces the number of possible alternatives, thus simplifying decision analysis. The pictorial representation of this system appears on the next sheet.\r\n\r\n2. A set of equations for the direct operating cost computation is developed, employing a technique of multiple regression analysis, by observing U. S. domestic experience of major airlines using B707-320B, B727-100 C/QC, DC9-30 aircraft. (All data is obtained from CAB-Wash.) DOC is further divided into flying, maintenance and depreciation. With the help of these equations, the direct operating cost could be predicted knowing the characteristics of the aircraft (number of engines, operating empty weight, fuel consumption), routes (average stage length) and scheduling (utilization).\r\n\r\n3. The probabilistic revenue calculations are carried out using a simplified Monte Carlo simulation and expected value approach. The impact of alternative modes of transportation and the competition on the route has been given proper weightage. Even though calculations are done for three station problems, an extension is possible for complicated route networks.\r\n\r\n4. By judging the profit performance, a feedback system is proposed." }, { "name": "Logan, Samuel Ernest", "degree": "PhD", "year": "1972", "title": "Laser Velocimeter Measurement of Reynolds Stress and Turbulence in Dilute Polymer Solutions", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-110214903", "creators": [ { "name": { "family": "Logan", "given": "Samuel Ernest" }, "id": "Logan-Samuel-Ernest", "display_name": "Logan, Samuel Ernest" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BD39-BV19", "abstract": "Measurements of Reynolds stress and axial and transverse\r\nturbulence intensities have been made in drag-reducing\r\nturbulent pipe flow of a dilute solution of high molecular\r\nweight polymer and compared to measurements made with pure\r\nwater. A newly developed laser velocimeter capable of\r\nmeasuring these turbulence parameters has been utilized and\r\nis described in detail.\r\n\r\nAxial turbulence intensities measured in polymer solution\r\nare consistent with previous polymer results and\r\nviscous sublayer thickening is observed. New results include\r\ndemonstration that the turbulent shearing stress is\r\nreduced in the turbulent core by an amount proportional to\r\nthe observed decrease in pressure gradient at the wall, and\r\nextrapolates to a wall value in agreement with calculated\r\nlocal wall shear. Near the wall polymer solution Reynolds\r\nstress is reduced below that measured for water consistent\r\nwith observed velocity profiles. Polymer radial turbulence\r\nintensities are comparable with those for water in the\r\nturbulent core, but exhibit similar dramatic suppression\r\nnear the wall. These and other recent results strongly\r\nsuggest that dilute polymer solution drag reduction is\r\nprimarily a wall phenomenon. Polymers appear to have little\r\nor no effect on turbulent flow away from a solid boundary\r\nwhere turbulent velocities scale with u_\u03c4, the shear\r\nvelocity based on the observed wall shear.\r\n" }, { "name": "Miyata, Gavien Nobuyuki", "degree": "Engineering Degree", "year": "1972", "title": "The Effect of a Spanwise Blowing Jet on the Separation Bubble Length Behind a Rearward Facing Step", "advisor": "Harris, Gordon L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172010-162416535", "creators": [ { "name": { "family": "Miyata", "given": "Gavien Nobuyuki" }, "id": "Miyata-Gavien-Nobuyuki", "display_name": "Miyata, Gavien Nobuyuki" } ], "advisors": [ { "name": { "family": "Harris", "given": "Gordon L." }, "id": "Harris-Gordon-L", "role": "advisor", "display_name": "Harris, Gordon L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EFBF-0016", "abstract": "The problem of the effect of a spanwise blowing jet on the\r\nflow past a rearward facing step is considered both theoretically and experimentally. The primary flow is considered to be a finite two dimensional jet blowing past a step and the spanwise jet is assumed to blow perpendicular to this primary flow. The equations predicting\r\nthe separation bubble length are de rived by assuming that the two dimensional jet is thin enough so that its radius of curvature can be determined by the pressure difference across the primary jet and the jet momentum. Then by doing a momentum balance at the reattachment point, the angle of reattachment is determined and the bubble geometry is fixed. The effect of the spanwise blowing jet is modeled by a two-dimensional sink with the sink strength given by the mass entrainment per unit length of a round jet in a semi-confined space.\r\n\r\nThe experimental work, which measured the bubble length\r\nas a function of the two-dimensional jet thickness and the strength of the spanwise blowing jet, is matched with the theoretical predictions giving the spreading parameters of the shear layers on both sides of the primary jet.\r\n" }, { "name": "Nieuwstadt, Fransiscus", "degree": "Engineering Degree", "year": "1972", "title": "Numerical Solution of Steady, Symmetric and Laminar Flow Around a Circular Cylinder", "advisor": "Roshko, Anatol; Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-160650145", "creators": [ { "name": { "family": "Nieuwstadt", "given": "Fransiscus" }, "id": "Nieuwstadt-Fransiscus", "display_name": "Nieuwstadt, Fransiscus" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A6ET-VQ44", "abstract": "A numerical integration of the Navier-Stokes\r\nequations is given for the steady, symmetric flow around\r\na circular cylinder. The problem is formulated in terms of\r\na streamfunction and the vorticity. The method used is the\r\nsemi-analytical one of series truncation, in which the\r\nstreamfunction and the vorticity are expanded in a finite\r\nFourier sine series with argument \u03b2, the polar angle.\r\nSubstitution of the truncated series into the Navier-\r\nStokes equations yields a system of non linear, coupled,\r\nordinary differential equations for the Fourier coefficients\r\nwhich is subjected to boundary conditions on the cylinder\r\nand at infinity. In order to be able to do a numerical calculation the free stream conditions at infinity are replaced by the asymptotic Oseen conditions at a finite distance from the cylinder. The resulting two point boundary value problem for the system of differential equations is solved numerically by a finite difference method. This method gives rise to a non linear system of algebraic difference equations. Four different iteration methods are discussed to solve this algebraic system. The most efficient iteration method seems to be Newton's method, which needs only about three iterations to converge to a solution of the difference equations. The approximation of the solution of the finite difference equations to the exact solution of the differential equations is improved by performing a Richardson\r\nextrapolation.\r\n\r\nIt can be concluded that a very efficient scheme\r\nhas been obtained to solve the system of ordinary differential equations which follow from the application of the method of series truncation. It has been found however\r\nthat the number of terms in the Fourier series needed to\r\ndescribe the flow adequately and correspondingly the\r\ncomputation time increase considerably with the Reynolds\r\nnumber. Nevertheless, it is believed that the method\r\ndeveloped here is much more efficient than previous ones.\r\nCalculations have been done for R = 0.5, 2.0, 3.5 and 5.0\r\nwhere R = Ua/ \u03b3 (a is the radius of the cylinder). The results compare reasonably well with previous numerical\r\ncalculations of Keller-Takami and Dennis-Chang." }, { "name": "Palaniswamy, Karuppagounder", "degree": "PhD", "year": "1972", "title": "Crack Propagation under General In-Plane Loading", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252010-104555143", "creators": [ { "name": { "family": "Palaniswamy", "given": "Karuppagounder" }, "id": "Palaniswamy-Karuppagounder", "display_name": "Palaniswamy, Karuppagounder" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M7WW-G964", "abstract": "The problem of crack extension in brittle materials under\r\ngeneral loading conditions is investigated. Methods of solution of the related two-dimensional elasto-static boundary value problem are discussed. Using Kolosov-Muskhelishvili stress functions, an approximate solution is obtained. The effect of the approximation on the results is estimated by solving two related problems exactly. Then using two postulates the critical loads and crack extension direction are determined under loading conditions\r\nunsymmetrical to the crack axis. Results are compared with those obtained using a different set of postulates.\r\n" }, { "name": "Pu\u010dik, Thomas Antone", "degree": "PhD", "year": "1972", "title": "Elastostatic Interaction of Cracks in the Infinite Plane", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-083924490", "creators": [ { "name": { "family": "Pu\u010dik", "given": "Thomas Antone" }, "id": "Pu\u010dik-Thomas-Antone", "display_name": "Pu\u010dik, Thomas Antone" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BVJ3-BV94", "abstract": " The stress boundary value problem of an infinite, planar region with embedded rectilinear cracks is investigated from the viewpoint of two-dimensional, static, linear elasticity theory (plane strain or generalized stress). Any finite number of cracks may be considered. Their orientation may be arbitrary, so long as they do not intersect. Boundary loadings may take the form of quite general in-plane tractions along the crack surfaces, together with a bounded in-plane stress field at infinity.\r\n\r\n Using Muskhelishvili\u2019s solution for colinear cracks, the problem is reduced to a set of one-dimensional Fredholm integral equations. A simple numerical technique is presented for the approximate solution of these equations. The method is established to possess an extremely high rate of convergence.\r\n\r\n Results are presented for a number of two-crack interaction problems. As expected, the interaction of the cracks generally tends to reduce the fracture strength of a material, relative to the strength that would exist with either crack acting independently. However, for certain orientations, it is found that the interaction phenomenon can actually increase the resistance to fracture." }, { "name": "Setchell, Robert Earle", "degree": "PhD", "year": "1972", "title": "Shock Tube Investigations of Strong Shock Waves in a Convergent Channel", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-154300", "creators": [ { "name": { "family": "Setchell", "given": "Robert Earle" }, "id": "Setchell-Robert-Earle", "display_name": "Setchell, Robert Earle" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RVJ0-B836", "abstract": "The behavior of the incident and reflected shock waves in a convergent channel is investigated in order to determine if such a geometrical device could be used as a means of producing high-enthalpy gas samples. A 10\u00b0 half-angle conical convergence is mounted on the end of a pressure-driven, six-inch shock tube. Using argon at an initial pressure of 1.5 torr, initial shock Mach numbers are varied from 6.0 to 10.2. During each run local shock velocities at several positions along the cone axis are measured using a small, multi-crystal, axial piezoelectric probe inserted from the cone vertex.
\r\n\r\nThe incident shock velocity profiles show that the shock behavior is dominated by multiple diffraction processes which originate at the cone entrance. Sudden increases in shock velocity at certain positions along the axis are observed, corresponding to the intersection of stemshocks formed by Mach reflection on the cone wall. These increases are separated by regions of deceleration and acceleration, corresponding to the growth and decline of a center shock formed by Mach reflection on the cone axis. Near the vertex the shock velocity has increased by as much as a factor of three, indicating that high temperatures and pressures are generated. By varying the initial Mach number and pressure, real gas effects are found to influence the diffraction process only in a region near the vertex.
\r\n\r\nReflected shock profiles show that the shock velocity is nearly constant for much of the convergence length, in contrast to the power-law decline predicted by the similarity solution. During this period the shock propagates into fluid originally set into steady, uniform motion outside the cone entrance. Small variations in the velocity result from weak interactions with localized nonuniformities and secondary waves. Beyond the cone entrance the shock decelerates towards the velocity corresponding to reflection from a plane end wall. A departure from ionization equilibrium is likely near the vertex during the rapid expansion which occurs behind the reflected shock.
" }, { "name": "Steinhilper, Eric Anthony", "degree": "PhD", "year": "1972", "title": "Electron Beam Measurements of the Shock Wave Structure: Part I. The Inference of Intermolecular Potentials from Shock Wave Experiments. Part II. The Influence of Accommodation on Reflecting Shock Waves", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-094927", "creators": [ { "name": { "family": "Steinhilper", "given": "Eric Anthony" }, "id": "Steinhilper-Eric-Anthony", "display_name": "Steinhilper, Eric Anthony" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AWTA-PA12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA technique has been developed in which accurate measurements of shock wave structure and an exact molecular theory of shock waves are used to determine intermolecular potentials. Shock wave density profiles in neon, argon, krypton, and xenon are measured in the GALCIT 17-inch diameter shock tube. The theory is a numerical molecular simulation technique (developed by G. Bird of the University of Sidney) in which the only adjustable parameter is the intermolecular potential. Parameters for the exp-6 and Lennard-Jones potentials are determined by matching the experimental shock wave density profiles with those predicted by the Monte Carlo simulation technique. The experimental data are taken at shock Mach number of about 8; consequently, these results fall in an energy range midway between the molecular beam measurements and low temperature transport property results.\r\n\r\nAfter the potentials for neon, argon, krypton, and xenon have been determined, they are tested for conformity to the Law of Corresponding States. Plots of the potentials in corresponding states coordinates, [...] vs.[...], show that the exp-6 potential model issuperior to the Lennard-Jones. This is an important result, because for the first time this statement can be made on the basis of one set of measurements. Previously it had been necessary to adduce molecular beam results in order toprove that the inverse twelfth-power repulsive part of the Lennard-Jones potential is too strong. Comparisons show that the exp-6, Lennard-Jones, simple repulsive, and hard sphere molecular potentials predict the experimental shock structure with successively decreasing accuracy. However, their accuracy is sufficient that any one of the potentials would predict any flow accurately enough to give an indication of the relative importance of the parameters governing the flow. This point is emphasized by the need for both the most precise experimental measurements and the use of the Law of Corresponding States in order to provide the basis for ranking the potentials. Moreover, changing the potentials has given a better understanding of the mechanisms by which intermolecular forces influence shock structure.\r\n\r\nMeasurements of density profiles during the reflection of thick shock waves in argon from the end wall of the GALCIT 17-inch diameter shock tube were reported previously. A mass balance using these profiles had revealed that as much as 20% of the gas which should have been between the end wall and the reflected shock was simply not present. Comparison with theory was not possible because no theory incorporated a loss of mass. Currently available theories for the reflection process include a Monte Carlo flow simulation technique for a thermally accommodating wall.\r\n\r\nIt is found that this technique can correctly predict either the reflected shock trajectory or the thermal layer near the wall, but the inability to duplicate both implies that there is a second important effect which we assume to be adsorption.\r\n\r\nAdditional experiments are conducted in neon which has a lower thermal accommodation coefficient than argon. If thermal accommodation is the only wall boundary condition, then according to the Monte Carlo calculations the shock should reflect faster in neon, and the thermal layer should be thinner. However, the measured density profiles show that the reflected shock trajectory is nearly the same as in argon but that there is only half as much \"missing\" mass. Thus, the neon results provide the most significant confirmation of adsorption.\r\n\r\nBecause this unexpected violation of the continuity equation was observed, a comprehensive review of instrumental effects and the data reduction technique is made. Several hypothetical effects are shown to have no influence on the loss of mass. However, improving the mass balance calculations accounts for approximately 25% of the missing mass. Correcting for multiple scattering of the electron beam accounts for another 10%, but this correction applies only at the highest densities. Therefore, the \"missing\" mass of the previous experiment is verified but is reduced somewhat in magnitude." }, { "name": "Trijonis, John Charles, Jr.", "degree": "PhD", "year": "1972", "title": "An Economic Air Pollution Control Model-Application: Photochemical Smog in Los Angeles County in 1975", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechTHESIS:06262014-113258422", "creators": [ { "name": { "family": "Trijonis", "given": "John Charles, Jr." }, "id": "Trijonis-John-Charles", "display_name": "Trijonis, John Charles, Jr." } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/hxbp-pc89", "abstract": "An economic air pollution control model, which determines the least cost of reaching various air quality levels, is formulated. The model takes the form of a general, nonlinear, mathematical programming problem. Primary contaminant emission levels are the independent variables. The objective function is the cost of attaining various emission levels and is to be minimized subject to constraints that given air quality levels be attained.
\r\n\r\nThe model is applied to a simplified statement of the photochemical smog problem in Los Angeles County in 1975 with emissions specified by a two-dimensional vector, total reactive hydrocarbon, (RHC), and nitrogen oxide, (NOx), emissions. Air quality, also two-dimensional, is measured by the expected number of days per year that nitrogen dioxide, (NO2), and mid-day ozone, (O3), exceed standards in Central Los Angeles.
\r\n\r\n\r\nThe minimum cost of reaching various emission levels is found by a linear programming model. The base or \"uncontrolled\" emission levels are those that will exist in 1975 with the present new car control program and with the degree of stationary source control existing in 1971. Controls, basically \"add-on devices\", are considered here for used cars, aircraft, and existing stationary sources. It is found that with these added controls, Los Angeles County emission levels [(1300\r\ntons/day RHC, 1000 tons /day NOx) in 1969] and [(670 tons/day RHC, 790 tons/day NOx) at the base 1975 level], can be reduced to 260 tons/day RHC (minimum RHC program) and 460 tons/day NOx (minimum NOx program).
\r\n\r\n\"Phenomenological\" or statistical air quality models provide the relationship between air quality and emissions. These models estimate the relationship by using atmospheric monitoring data taken at one (yearly) emission level and by using certain simple physical assumptions, (e. g., that emissions are reduced proportionately at all points in space and time). For NO2, (concentrations assumed proportional to NOx emissions), it is found that standard violations in\r\nCentral Los Angeles, (55 in 1969), can be reduced to 25, 5, and 0 days per year by controlling emissions to 800, 550, and 300 tons /day, respectively. A probabilistic model reveals that RHC control is much more effective than NOx control in reducing Central Los Angeles ozone. The 150 days per year ozone violations in 1969 can be reduced to 75, 30, 10, and 0 days per year by abating RHC emissions to 700, 450, 300, and 150 tons/day, respectively, (at the 1969 NOx emission level).
\r\n\r\nThe control cost-emission level and air quality-emission level relationships are combined in a graphical solution of the complete model to find the cost of various air quality levels. Best possible air quality levels with the controls considered here are 8 O3 and 10 NO2 violations per year (minimum ozone program) or 25 O3 and 3 NO2 violations per year (minimum NO2 program) with an annualized cost of $230,000,000 (above the estimated $150,000,000 per year for the new car control program for Los Angeles County motor vehicles in 1975).
\r\n" }, { "name": "Van Dillen, David Edwin", "degree": "Engineering Degree", "year": "1972", "title": "Vibrations of a Three-Layer Beam with a Viscoelastic Middle Layer", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262010-162507540", "creators": [ { "name": { "family": "Van Dillen", "given": "David Edwin" }, "id": "Van-Dillen-David-Edwin", "display_name": "Van Dillen, David Edwin" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P2BD-K350", "abstract": "The equations governing a three-layer beam in which the middle layer is viscoelastic were derived by means of a variational principle. These equations were solved subject to arbitrary time dependent boundary conditions of both the simply-supported and cantilever type. In the simply-supported case, an eigenfunction expansion was constructed after the governing equations had been transformed through operation by a differential operator. In the cantilever case, the solution was obtained by Fourier transform with respect to time, and inversion by residue theory. An analysis of the theoretical response of the cantilever beam to steady state sinusoidal loading was carried out, and an experiment was conducted for comparison." }, { "name": "Barcelo, Brian Thomas", "degree": "PhD", "year": "1971", "title": "Electron Beam Measurements of the Shock Wave Structure. Part 1. Determination of the Interaction Potential of the Noble Gases from Shock Wave Structure Experiments. Part II. Feasibility of a Modified Electron Beam Densitometer Technique to Measure Diffusive Separation in Shock Waves in Helium-Argon Mixtures", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-092506", "creators": [ { "name": { "family": "Barcelo", "given": "Brian Thomas" }, "id": "Barcelo-Brian-Thomas", "display_name": "Barcelo, Brian Thomas" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QH9Z-BH10", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock wave experiments were conducted in the GALCIT* seventeen-inch low density shock tube to measure the interaction potential of the following nonradioactive noble gases: neon, argon, krypton, and xenon. The experimental shock profiles obtained by employing the electron beam densitometer technique were compared to the Monte Carlo numerical simulation of the shock wave structure. The comparison determined the intermolecular potential for these gases, a potential assumed to be of the form [...] = const/r[superscript s]. The values resulting for the free parameter s in the inverse repulsive power law were 9, 10, 11, and 12 for xenon, krypton, argon, and neon, respectively.\r\n\r\nIn a second phase of the experiments, the feasibility of a modified electron beam densitometer technique was investigated for measuring the shock wave structure in a binary mixture of helium and argon. It was desired to obtain both the argon and helium density profiles through the shock wave by varying the electron beam energy in two experiments of identical shock conditions (gas concentrations, Mach number, initial pressure, etc.). Theoretical calculations of the collision cross-section indicated only a slight possibility of separating the density profiles of the two species with the range of electron energy possible in the experimental apparatus (7000 to 15000 volts). Experiments conducted with initial gas concentrations of 10%, 20%, 50%, and 80% argon in shock waves with a Mach number of approximately four confirmed these suspicions but permitted qualitative conclusions in agreement with other similar investigations.\r\n\r\n*Graduate Aeronautical Laboratories California Institute of Technology." }, { "name": "Davey, Robert Frederick", "degree": "PhD", "year": "1971", "title": "An Experimental Investigation of the Effect of a Density Gradient on Shear Layer Instability", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-131624", "creators": [ { "name": { "family": "Davey", "given": "Robert Frederick" }, "id": "Davey-Robert-Frederick", "display_name": "Davey, Robert Frederick" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YJF7-DV47", "abstract": "Measurements of mass flow rate and mean density have been made in separated laminar boundary layers having large transverse density gradients. A 3/8 in. by 1 1/2 in. rectangular half-jet was used to generate a two-dimensional shear layer and the density heterogeneity was produced in an incompressible flow by exhausting one gas into a reservoir of another gas having a different molecular weight. Two Freons were used having a density ratio of 1.98 and unique properties which permitted the measurement of the mass flow rate in all mixtures of the gases with a single hot wire.\r\n\r\nMean density and mass flow rate profiles were compared to the Holmboe model used in theoretical hydrodynamic stability analyses. Fluctuations in the mass flow rate were analyzed and the frequency, wave number and amplification rate of the most unstable oscillation were measured and compared to theoretically predicted values. The oscillations were found to have a higher amplification rate, lower wave number and lower frequency than homogeneous flow when the lighter gas flowed into the heavier one, in agreement with the theoretical predictions. Opposite trends were observed with the heavy gas flowing.\r\n\r\nThe development of harmonic frequency oscillations in the non-linear region is discussed briefly." }, { "name": "Elachi, Charles", "degree": "PhD", "year": "1971", "title": "Electromagnetic Wave Propagation and Source Radiation in Space-Time Periodic Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-143115", "creators": [ { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-Charles", "display_name": "Elachi, Charles" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WYFR-GR84", "abstract": "The electromagnetic wave equations for the fields, potentials and Hertz vectors are derived and a Lorentz gauge is given for space-time dependent media. Electromagnetic wave propagation, electric and magnetic dipole radiation, and Cerenkov and transition radiation in sinusoidally space-time periodic dielectric, plasma and uniaxial plasma are studied and numerous radiation patterns are given. A special radiation effect in the uniaxial plasma is investigated. Finally the study is extended to general space-time periodic media (i.e., \u03b5 = \u03b50\u03b5r [1 + \u03b51 f(Kz - \u03a9t)] where f(\u03be) is a periodic function)." }, { "name": "Imbert, Jean-Fran\u00e7ois", "degree": "Engineering Degree", "year": "1971", "title": "The Effect of Imperfections on the Buckling of Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05012008-155801", "creators": [ { "name": { "family": "Imbert", "given": "Jean-Fran\u00e7ois" }, "id": "Imbert-Jean-Fran\u00e7ois", "display_name": "Imbert, Jean-Fran\u00e7ois" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RHXA-BJ33", "abstract": "A theoretical investigation of the effect of general imperfections on the buckling of a cylindrical shell under axial compression was carried out. A limit point analysis was performed to determine the buckling loads using a simplified imperfection and displacement model consisting of one axisymmetric and two asymmetric components with the same circumferential wave number.\r\n\r\nThe wave number dependence of imperfections for a class of shells obtained by the same manufacturing processes was characterized by using an imperfection model to fit the experimental imperfection coefficients available. Buckling load calculations were performed using both experimental and fitted data as imperfection coefficients.\r\n\r\nFor the experimental data available the three-mode solution was found to have only a small additional effect with respect to the two-mode solution. In addition, by extrapolating imperfection coefficients for high wave numbers by means of the imperfection model, it was found that a strong interaction effect would exist between a low wave number axisymmetric mode and two classical asymmetric modes." }, { "name": "Liu, Ting-Lung", "degree": "Engineering Degree", "year": "1971", "title": "An Energy Approach to the Dynamic Buckling of Spherical Caps", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-153153", "creators": [ { "name": { "family": "Liu", "given": "Ting-Lung" }, "id": "Liu-Ting-Lung", "display_name": "Liu, Ting-Lung" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8JD0-W843", "abstract": "An experimental study to determine the dynamic buckling load of a spherical cap under impulsive loading was carried out. Impulsive loading was realized experimentally by use of a spray deposited explosive (Silver Acetylide-Silver Nitrate). The experimental dynamic buckling loads were compared to the dynamic buckling loads as calculated by using an energy criterion. The critical load from the energy criterion was determined by the conducting static pressure volume tests on the spherical caps. It was found that experimental results were consistently below the dynamic buckling load as predicted by the energy criterion. It was thought that this inconsistency resulted from the fact that transition state found in the static experiment was not the same as the dynamic transition state." }, { "name": "Ramaswamy, Mathagondapally A.", "degree": "PhD", "year": "1971", "title": "Experimental Investigation of the Effect of Cooling on Near Wake of Circular Cylinder at Mach Number Six", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152011-112031398", "creators": [ { "name": { "family": "Ramaswamy", "given": "Mathagondapally A." }, "id": "Ramaswamy-Mathagondapally-A", "display_name": "Ramaswamy, Mathagondapally A." } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8ZZ8-PC49", "abstract": "An experimental investigation has been conducted to study the near wake of a two-dimensional circular cylinder of 0.2 in. diameter at M_\u221e = 6. Mean flow properties were determined from Pitot pressure, static pressure, and hot-wire recovery temperature measurements at free stream Reynolds number of 0.905 X 10^4 and 2.95 X 10^4 for both adiabatic and cooled models, the latter at 0.19 T_o.
\r\n\r\nThe near-wake was laminar for the adiabatic model at both\r\nthe Reynolds numbers tested. For the cold model, the near-wake was laminar for the lower Reynolds number and transition occurred in the near wake at the higher Reynolds number. The wake shocks, the shear layer edge and the thermal layer edge moved closer to the wake centerline with cooling and with increase in Reynolds number. The base pressure decreased with cooling and the sonic point moved closer to the model on cooling. In the recirculating region, the total temperature distributions exhibited a minimum close to the dividing stream line for all the cases, and the total temperature on the centerline was nearly constant and equal to the value at the rear stagnation point (0.5 T_o for the cold models) indicating that the heat transfer in this region was mainly by convection. The existence of a thin thermal layer on the base was evident for the cold models.
\r\n\r\nPreliminary experiments on the two-dimensionality of the\r\nflow and an emperical formulation for the viscous corrections to the measured Pitot pressure have been included in the Appendices.
\r\n" }, { "name": "Shollenberger, Carl Alvin", "degree": "PhD", "year": "1971", "title": "An Investigation of a Two-Dimensional Propulsive Lifting System", "advisor": "Lissaman, Peter B. S.; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312010-081235652", "creators": [ { "name": { "family": "Shollenberger", "given": "Carl Alvin" }, "id": "Shollenberger-Carl-Alvin", "display_name": "Shollenberger, Carl Alvin" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GZNT-1X61", "abstract": " Several aspects of the nonhomogeneous flow associated with a system combining lifting and propulsive requirements of an aircraft are considered in detail by analytical and experimental methods. The basic geometry of the problem is that of two lifting surfaces with an actuator disk located between them. The resulting flow consists of two regions of different total energies.\r\n\r\n Propulsive lift systems are prototypes of many similar multi-energy flow problems. The principles governing flow with energy addition are examined. Basic equations and boundary conditions are developed for the complete inviscid and incompressible analysis for the two-dimensional case. The corresponding flow singularities are discussed and the integral equations which completely specify the system are derived.\r\n \r\n The two special cases of small and large energy addition are considered in detail including solutions.\r\n\r\n A numerical procedure is developed to solve the full problem including allowance for the wake deflection. Appropriate vorticity forms are used to represent the entire system. Wake vorticity is provided the freedom to move in the plane. An iterative scheme is presented which rapidly converges to a solution for the magnitude and location of the system vorticity distributions. Forces and moments are evaluated on the propulsive lift system.\r\n\r\n Analytical results are given from the numerical solution for various values of the geometric and energy parameters. Comparison of the numerical result with the solutions for extreme values of energizing is given.\r\n\r\n Results from a wind tunnel study of the two-dimensional propulsive-lift system provide a check on the importance of real effects. Comparison of the analytical and experimental results is given in detail. The experimentally determined wake development is observed to be similar to the predicted shape. In addition, the lift augmentation is similar for the theoretical and experimental cases. Further, the airfoil pressure distributions and resulting pitching moments are seen to exhibit the behavior expected from the calculations.\r\n" }, { "name": "Sigal, Asher", "degree": "PhD", "year": "1971", "title": "An Experimental Investigation of the Turbulent Boundary Layer Over a Wavy Wall", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-101022816", "creators": [ { "name": { "family": "Sigal", "given": "Asher" }, "id": "Sigal-Asher", "display_name": "Sigal, Asher" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VK9A-XA44", "abstract": " An experimental investigation of turbulent boundary layer flow over wavy surfaces was conducted at low speed.\r\n\r\n Two models with the ratio of the amplitude to the wave length a/\u03bb = 0.03 and wave lengths \u03bb = 6\" and 12\" were tested in an open-circuit wind tunnel. The free stream velocity was 15.4 m/sec, giving Reynolds number Re = 2.54 X 10^4 per inch. Boundary-layer thickness varied from \u03b4 = 1.5\" to \u03b4 = 4. 1\" by means of boundary-layer trips of various height, in order to change the ratio \u03bb/6.\r\n \r\n The following measurements were taken:\r\n * Wall pressure distribution\r\n * Average velocity and turbulence level, using a single element hot-wire probe\r\n * Wall stress distribution, using Preston's tube\r\n * Static and total pressures\r\n * Turbulence intensities and shear stress using X-array hot-wire probe.\r\n\r\n An appreciable modulation of all the flow quantities, imposed by the wavy boundary, is observed throughout the investigation. Wall pressure is much lower than predicted by uniform, inviscid theory and is slightly non-symmetric. Wall stress distribution has a peak with C_f/C_fo = 1.2 upstream of the crest and a dip of C_f/C_fo = 0. 6 upstream of the trough. Static pressure decays exponentially in the outer layer while its gradient is decreased toward the surface in the wall layer.\r\n\r\n The turbulence intensities and shear stress distributions near the wall show oscillatory modulation superimposed on the reference flat plate profiles. The amplitude of the oscillations decay exponentially toward the edge of the layer, so that in the outer part of the layer the turbulence quantities are practically independent of the longitudinal position.\r\n\r\n It was found that Coles' Law of the Wall does not apply in the present situation because of the modulation of the slope of the semi-logarithmic portion of the velocity profiles. A presentation of velocity profiles is suggested through the use of total velocity defined by U^t = (U^2 + 2(p\u2013p_\u221e)/p)^(1/2). This quantity obeys the Law of the Wake. Mixing length and eddy viscosity profiles based on the derivative \u2202U^t/\u2202y are reduced into one curve which is the reference flat plate distribution.\r\n" }, { "name": "Wu, Jiunn-Jenq", "degree": "Engineering Degree", "year": "1971", "title": "An Experimental Study of Hypersonic Wakes Behind Wedges at Angle of Attack", "advisor": "Behrens, Wilhelm", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222010-130843966", "creators": [ { "name": { "family": "Wu", "given": "Jiunn-Jenq" }, "id": "Wu-Jiunn-Jenq", "display_name": "Wu, Jiunn-Jenq" } ], "advisors": [ { "name": { "family": "Behrens", "given": "Wilhelm" }, "id": "Behrens-W", "role": "advisor", "display_name": "Behrens, Wilhelm" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/682B-HB46", "abstract": "Experimental measurements of mean flow properties of hypersonic wakes behind wedges of 20\u00b0 included angle were conducted for angles of attack up to 25\u00b0 at Mach number 6, with Reynolds number based on wedge base height ranging from 7000 to 55000. The near and far wake structures were determined, including streamlines and velocity profiles, over a downstream distance of 60 base heights. The base pressure is insensitive to angle of attack within about 17\u00b0. At higher incidence, flow separation occurs on the leeward surface. The far viscous wake (x/H Z 4) changes with increasing angle of attack mainly because of the increasing differences of the inviscid flow parameters at the leeward and windward edges of the viscous wake. Transition from laminar to turbulent flow moves upstream as \r\nangle of attack increases." }, { "name": "Blumenthal, Donald Lawrence", "degree": "PhD", "year": "1970", "title": "Experimental Study of Satellite Wakes in a Simulated Ionospheric Plasma", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092010-100552106", "creators": [ { "name": { "family": "Blumenthal", "given": "Donald Lawrence" }, "id": "Blumenthal-Donald-Lawrence", "display_name": "Blumenthal, Donald Lawrence" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PYM3-H107", "abstract": "Wakes of simple bodies (discs, strips) were investigated using an electrostatically accelerated stream of argon \r\n\r\nions and electrons. Typical conditions are: beam ion energy is 80 eV, ion density is 10^7-10^8 cm^(-3), electron \r\n\r\ntemperature 1-3 eV, ion thermal speed very small compared to mean ion velocity. The dimensionless parameters \r\n\r\nclosely approximate satellite flight conditions, with the exception of the electron-ion temperature ratio, which \r\n\r\nis near unity in flight and large in these experiments.\r\n\r\nThe dependence of principal near wake features (such as the large ion current peak on the centerline behind the \r\n\r\nbody) on the shape of the body was investigated systematically. All trends can be explained qualitatively by \r\n\r\nrecognizing the dominant role of those portions of the sheath where the free stream ion velocity is tangential to \r\n\r\nthe body.\r\n\r\nThe far wake of a strip (downstream of the ion current peak) displays a decaying radial distribution on the scale \r\n\r\nof the body size, somewhat similar to what is expected from a neutral gas. For axial symmetric models, the far \r\n\r\nwake displays a small structure on the scale of the ion current peak. The evolution of these disturbances\r\nis qualitatively explained by a simple, linearized two fluid theory. These features are initiated by the \r\n\r\ninteraction of the inwardly deflected ion streams behind the body. At least in certain regions of the flow field, \r\n\r\nthis interaction involves two-humped ion distribution functions, which may play a role in the further development \r\n\r\nof the far wake.\r\n\r\nThe effects on the simulation of varying the vacuum chamber background pressure was also examined in detail.\r\n" }, { "name": "Cassady, Phillip Earl", "degree": "PhD", "year": "1970", "title": "An Investigation of Non-Equilibrium Effects in an Argon Free-Jet Plasma", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-092851271", "creators": [ { "name": { "family": "Cassady", "given": "Phillip Earl" }, "id": "Cassady-Phillip-Earl", "display_name": "Cassady, Phillip Earl" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WHYP-RZ81", "abstract": "The non-equilibrium effects present in the formation of a strong normal shock wave in a low density, slightly ionized argon flow field, particularly as evidenced by the appearance of a dark region upstream of the shock wave, have been analyzed both theoretically and experimentally. A model for the flow through the shock wave was formulated which incorporates a quantum mechanical theory to explain the existence of the dark region, and the problem was solved numerically to yield flow field property distributions. A precursor region of high electron temperature was found to exist upstream of the main body of the heavy-particle shock wave.\r\n\r\nAn experimental investigation of the phenomenon was carried out in an arc heated free jet flow field. A test facility was constructed in which the goal has been to attain operation at low enough enthalpies to allow precise and extensive diagnostic testing while still high enough to exhibit the interesting non-equilibrium effects. Extensive study was carried out on the effect of electrode design and gas flow phenomena on the stability of the arc discharge. The completed unit was instrumented fully for measurement of the operating parameters and a computer program was developed to monitor its operation as a supply of slightly ionized argon for free-jet experiments.\r\n\r\nThe non-equilibrium aspects of the free-jet were analyzed both theoretically and experimentally. A theoretical model was developed and numerically solved for the free-jet expansion of slightly ionized argon. Pitot pressure measurements were completed and compared favorably with predictions calculated from this theoretical model.\r\n\r\nElectron temperature and ion density profiles were measured both along the axis of the empty free-jet and through the normal shock wave in front of a cooled blunt body using a new type of cooled Langmuir probe, the operation of which was theoretically analyzed. The existence of a region of electron temperature in front of a strong normal shock wave coincident with the observed dark region was experimentally verified." }, { "name": "Chu, Billie Mae", "degree": "PhD", "year": "1970", "title": "Rheological Properties of Soft Extensible Animal Tissue in Both Living and Excised States", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-153606301", "creators": [ { "name": { "family": "Chu", "given": "Billie Mae" }, "id": "Chu-Billie-Mae", "display_name": "Chu, Billie Mae" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/48T9-AD89", "abstract": "A mechanical characterization, over a wide range of response, \r\nof a particular soft extensible animal tissue, the mesentery of the cat, \r\nis presented. The structure of the mesenteric tissue is made up of a \r\ncomplicated array of components and the mechanical response is \r\ninfluenced not only by local factors, but also by adjustments of higher \r\ncontrol centers of the animal. Certain individual aspects of the \r\nresponse of living mesenteric membrane per se have been studied and \r\ncontrasted with (1) membrane strongly influenced by or containing \r\nlarge blood vessels, (2) excised membrane and (3) membrane after \r\ncirculatory collapse and accompanying sustained gut contraction.\r\n\r\n\tA freely floating segment of mesentery exists in a state of \r\ntension which can be demonstrated by making an incision through the \r\nplane of the mesentery. A technique has been developed to determine \r\nthe magnitude of this tension and also the corresponding stretch which \r\nis designated here as the initial configuration length. The tension \r\nlevel in the tissue at the initial configuration length is not unique but \r\ncan vary significantly according to the activity of the components of \r\nthe membrane per se as well as the state of the gut and the large \r\nblood vessels. The most nearly unique length of the tissue which can \r\nbe detected by these experimental methods is a relaxed length determined \r\nby excising a piece of tissue of known dimensions and \r\nmeasuring the freely floating (in a physiologic solution) dimensions\r\nto which the tissue relaxes. There is no marked material anisotropy\r\nin the plane of the membrane, i.e. the two principal dimensions in the \r\nplane of the mesentery do not vary by more than five percent even with \r\nwide history variations just prior to excision.\r\n\r\n\tThe temperature of the test preparation was monitored during \r\nthe course of the tests and maintained at the level of the core temperature \r\nof the animal. Since this temperature could drop as much as \r\nthree or four \u00b0C as a result of the anesthesia, the influence of \r\ntemperature variations on the force-stretch response of the tissue was \r\nstudied and was found to be less significant than the influence of \r\nmechanical degradation in successive loading cycles.\r\n\r\n\tA theoretical characterization that correlates rather well with \r\nthe data of the loading curves for the various tissues has been \r\nproposed. The limitations and assumptions incorporated in this \r\ntreatment have been discussed and when appropriate additional experimental \r\ndata are procured then the analytical treatment can likewise be \r\nextended to a more adequate characterization.\r\n\r\n\tPhotographic materials on pp. 53, 54, 55, 56, 58, 59, 60, 61, \r\n63, 64, 66, 67, 71, 72, 83, 89, 90 and 93 are essential and will not \r\nreproduce clearly on Xerox copies. Photographic copies should be \r\nordered.\r\n" }, { "name": "El Raheb, Michel Sadek", "degree": "PhD", "year": "1970", "title": "Some Approximations in the Dynamic Shell Equations", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212013-152121344", "creators": [ { "name": { "family": "El Raheb", "given": "Michel Sadek" }, "id": "El-Raheb-Michel-Sadek", "display_name": "El Raheb, Michel Sadek" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ejzn-dy90", "abstract": "A theoretical analysis was performed on the linear dynamic\r\nequations of thin cylindrical shells to find the error committed by the\r\nDonnell assumption and the neglect of inplane inertia.
\r\n\r\nThe Donnell approximation was found to be valid at high\r\nfrequencies as compared to the ring frequencies, for all admissible\r\nsets of boundary conditions for finite length thin shells.
\r\n\r\nThe error from neglecting tangential inertia is appreciable for\r\nlong circumferential and axial wave lengths, independent of shell\r\nthickness.
\r\n\r\nThe effect of boundary conditions was investigated from an\r\nexact solution of the linear eigenvalue problem. The inplane boundary\r\nconditions proved to be very influential in the neighborhood of the\r\nminimum frequency. An approximate technique which accounts for the\r\ninplane boundary conditions was then developed and shown to be in good\r\nagreement with the exact solution.
\r\n\r\nFinally, the effect of an elastic end ring on the eigenfrequencies\r\nwas studied. The out-of-plane and torsional rigidities of the ring were\r\nfound to govern the overall shell stiffness. Considerable mode inter action\r\nwas noticed at low circumferential wave numbers for low values\r\nof ring stiffness. The computed eigenfrequencies were found to be in\r\ngood agreement with the experimental results.
\r\n\r\n" }, { "name": "Fisher, Raymond Kurt", "degree": "PhD", "year": "1970", "title": "Resonance Cones in the Field Pattern of a Short Radio Frequency Probe in a Warm Anisotropic Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062012-143738636", "creators": [ { "name": { "family": "Fisher", "given": "Raymond Kurt" }, "id": "Fisher-Raymond-Kurt", "display_name": "Fisher, Raymond Kurt" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/909M-7S46", "abstract": "An experimental investigation of the angular field pattern of a small radio frequency probe in a plasma in a magnetic field is described. The field is observed to become very large along a resonance cone whose axis is parallel to the static magnetic field and whose opening angle is observed to vary with incident probe frequency, electron cyclotron frequency, and electron plasma frequency in agreement with simple cold plasma dielectric theory. The use of the resonance cone angle as a diagnostic tool to measure the plasma density in a plasma in a magnetic field is discussed. It is noted that similar cones might be expected near the ion cyclotron frequency.
\r\n\r\nThe relationship of these cones to the limiting phase- and group-velocity cones which appear in the theory of plane wave propagation is discussed. The necessity for examining the allowed directions of the group velocity rather than the allowed directions of the phase velocity and customary phase velocity plots when determining whether propagation between two remote points in a plasma is possible, is emphasized.
\r\n\r\nThe addition of electron thermal velocities to the theory is examined in the limit of a large static magnetic field. The resonance cone angle is shifted to a slightly smaller angle than that predicted by cold plasma theory, and a fine structure appears inside the cones and is shown to result from an interference between a fast electromagnetic wave and a slow plasma wave. The interference structure is observed experimentally, and measurements of the angular interference spacing are shown to agree with the warm plasma theory.
" }, { "name": "Govindaraju, Shakkottai P.", "degree": "PhD", "year": "1970", "title": "Part I. An Analysis of Reiner's Centripetal Pump. Part II. A Study of Some Turbulent Flows Using a Model for Inhomogeneous Turbulence", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-150404", "creators": [ { "name": { "family": "Govindaraju", "given": "Shakkottai P." }, "id": "Govindaraju-Shakkottai-P", "display_name": "Govindaraju, Shakkottai P." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C143-TT24", "abstract": "Part I:\tA centripetal pump consists of a self-aligning rotor in rotation close to a fixed plane stator. In such an apparatus Reiner observed an excess air pressure in the gap between the discs over ambient and a consequent repulsive force between the discs. Reiner interpreted this repulsive force to be the result of non-Newtonian properties of air. Since this hypothesis is in contradiction with known behavior of air in other similar situations, we try to explain it as due to imperfections of the apparatus used and consider three possibilities: dynamic unbalance of the rotor, instability of the rotor and vibrations of the stator. The results of the analyses show that the third possibility can explain Reiner's observations under some reasonable assumptions. It is concluded that Reiner's hypothesis is unjustified.
\r\n\r\nPart II: A model for inhomogeneous turbulence, due to Saffman, describes turbulence in terms of two scalar densities governed by nonlinear diffusion equations. Using this model some turbulent flows are studied to assess the value of the model as a basis for analyzing turbulent flows. The specific problems studied include the two-dimensional wake, the two-dimensional jet, the turbulent couette flow, flow in a channel and the turbulent trailing vortex. Predictions based on the model agree fairly well with experimental results except for the turbulent trailing vortex. Some shortcomings of the model as evident from the application are discussed.
" }, { "name": "O'Pray, John Edwin", "degree": "Engineering Degree", "year": "1970", "title": "A Semi-Inverse Design Technique for Leading Edge Slats", "advisor": "Lissaman, Peter B. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-144546", "creators": [ { "name": { "family": "O'Pray", "given": "John Edwin" }, "id": "O'Pray-John-Edwin", "display_name": "O'Pray, John Edwin" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9X7D-HQ81", "abstract": "A design technique for analytically generating a leading edge slat which will induce the modulating field required to match a specified pressure distribution on the nose of an elliptical airfoil was developed. This planar potential flow solution can be readily generalized to the design of slats to prevent boundary-layer separation at the nose of an arbitrary airfoil. The technique is described as semi-inverse because the singularity representation for the slat is constrained so that only realistic slat shapes will be generated.
\r\n\r\nThe elliptical airfoil is mapped to a half-plane. In this domain, the slat is represented by a finite series of distributed singularities on an inclined chord line which is placed along a zero order nose flow streamline. These distributed singularities correspond to the singular and regular camber and thickness modes of thin airfoil theory. A suitable slat chord location in the half-plane is selected by examination of the distribution of the specified modulating velocity. For a fixed slat location, the slat-induced velocity field can be written explicitly in terms of the unknown series coefficients. A least squares matching to the specified modulating field is used to select the coefficients. The velocity distribution along the chord line is integrated to determine the slat surface streamlines which are then transformed back to the ellipse plane.
\r\n\r\nThe digital computer program for the semi-inverse solution can be executed rapidly. Once an appropriate slat chord location in the half-plane has been selected, an accurate matching of the specified pressure distribution on the airfoil can be achieved. The airfoil nose flow calculated by the semi-inverse solution agrees very closely with the flow computed by the Douglas-Neumann direct solution for the same slat geometry.
\r\n\r\nThe airfoil nose flow is very sensitive to the distribution of camber and thickness along the chord line. In some test cases, a modified semi-inverse solution was required in which the minimum acceptable slat thickness was prescribed and a restricted inversion solution was conducted to select the camber mode coefficients required to match the specified modulating field. For a thin airfoil with a severe nose suction peak, a small, thin, highly-cambered slat which is located close to the airfoil nose is desirable.
" }, { "name": "Snel, Hermanus", "degree": "Engineering Degree", "year": "1970", "title": "The Motion of a Sphere in a Cylinder Filled with a Viscous Liquid and with a Diameter Slightly Larger than the Sphere Diameter", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-111117", "creators": [ { "name": { "family": "Snel", "given": "Hermanus" }, "id": "Snel-Hermanus", "display_name": "Snel, Hermanus" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DAYS-G298", "abstract": "The flow around a sphere, moving under the influence of gravity in a long cylinder filled with a viscous liquid, is investigated, for the case where the inside diameter of the tube is only slightly larger than the diameter of the sphere.\r\n\r\nFor low Reynolds numbers, an extension of the Christopherson and Dowson (1) theory is obtained in the form of a first order Reynolds number correction. It is shown that the fluid exerts a first order inertial force on the ball, tending to increase the eccentricity ratio. The sideways motion of the ball due to this force has been calculated approximately.\r\n\r\nFor very high Reynolds numbers, a potential flow solution has been found in the form of a Fourier series. This solution also yields a force tending to increase the eccentricity ratio.\r\n\r\nExperiments have been done for intermediate Reynolds numbers. The motion of the ball appears to be unstable when the Reynolds number exceeds a critical value (about 10)." }, { "name": "Starnes, James Herbert, Jr.", "degree": "PhD", "year": "1970", "title": "The Effect of a Circular Hole on the Buckling of Cylindrical Shells", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012009-110903", "creators": [ { "name": { "family": "Starnes", "given": "James Herbert, Jr." }, "id": "Starnes-James-Herbert-Jr", "display_name": "Starnes, James Herbert, Jr." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VGHN-EQ52", "abstract": "An experimental and theoretical investigation of the effect of a circular hole on the buckling of thin cylindrical shells under axial compression was carried out. The experimental program consisted of tests performed on seamless electroformed copper shells and Mylar shells with a lap joint seam. The copper shells were tested in a controlled displacement testing machine equipped with a noncontacting surface displacement measuring device. Three-dimensional surface plots obtained in this manner showed the changes in the displacement field over the entire shell, including the hole region, as the applied load was increased. The Mylar shells were tested in a controlled load testing machine and demonstrated the effect of increasing the hole radius on the buckling loads of the cylinder.
\r\n\r\nThe theoretical solution was based on a Rayleigh-Ritz approximation. The solution provided an upper bound for the buckling stresses of the cylinders tested for hole radii less than ten per cent of the shell radii. The theoretical solution also identified the governing parameter of the problem as being related to the hole radius, the shell radius, and the shell thickness.
\r\n\r\nThe theoretical part of the investigation showed that even a small hole should significantly reduce the buckling stresses of circular cylinders. Experimentally, it was found that the effect of a small hole is masked by the effects of initial deformations but, at larger hole radii, the reduction in buckling stress took the form predicted by the theory. The experimental results also showed that the character of the shell buckling was dependent on the hole size. For very small holes the shell buckled into the general collapse configuration and there was no apparent effect of the hole on the buckling mode of the shell. For slightly larger holes the shell still buckled into the general collapse configuration, but the buckling stresses of the shell were sharply reduced as the hole size increased. For still larger holes the buckling stresses did not decrease as sharply as the hole size increased and the shell buckled into a stable local buckling configuration.
\r\n" }, { "name": "Wilcox, David Clinton", "degree": "PhD", "year": "1970", "title": "The Motion of a Disc at Angle of Attack in a Rapidly Rotating Fluid", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04032009-113521", "creators": [ { "name": { "family": "Wilcox", "given": "David Clinton" }, "id": "Wilcox-David-Clinton", "display_name": "Wilcox, David Clinton" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EJBR-X182", "abstract": "The motion of a thin disc in a slightly viscous incompressible rotating fluid is studied. The axis of rotation is termed the vertical axis and the fluid and disc are in a container which is bounded by horizontal planes. Nonlinear inertia terms and unsteady effects are assumed small relative to the Coriolis acceleration and hence neglected. Of most importance is the fact that the disc is inclined to the container walls at an angle, \u03b1, which is not necessarily small. The angle is assumed to be large enough so that there are no closed geostrophic contours between the disc and the walls.\r\n\r\nSince the equations of motion are linear, the motions in the six degrees of freedom are considered independently. In all cases, a Taylor column is present although, in all but one case, there is fluid flowing across the boundary of the column. The detailed structure of the shear column is examined for infinitesimal angle of incidence. It is shown that it is possible to solve for the geostrophic flow without actually doing the detailed solution for the shear column structure.\r\n\r\nA static stability study is done and the disc is found to be unstable to small disturbances.\r\n\r\nThe motion of an elliptical plate at finite angle of attack for which the Taylor column is circular is studied. Using the techniques developed for infinitesimal \u03b1, an equation relating the geostrophic flow inside and outside the Taylor column is proposed. This equation is general enough to be used for arbitrary motion of any thin plate. However, only the solution for horizontal translation in a specific direction of the elliptical plate is done.\r\n" }, { "name": "Cheung, Man Cheong", "degree": "PhD", "year": "1969", "title": "The Static and Dynamic Stability of Clamped Shallow Circular Arches", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-081618", "creators": [ { "name": { "family": "Cheung", "given": "Man Cheong" }, "id": "Cheung-Man-Cheong", "display_name": "Cheung, Man Cheong" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8MXG-DE89", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the relationship between the dynamic buckling and the static buckling phenomenon was carried out.\r\n\r\nThe first half of the paper studies the stability of shallow arches subjected to lateral forces. Concentrated static and step loads were applied to circular arches with geometric parameters 7 < [...] < 20. Equilibrium path and the dynamic response at the loading position were recorded. Dynamic buckling is distinct. Supercritical and subcritical responses were separated by [...] of the total load. The sensitivity of the arch to loading imperfection was studied. The effect was pronounced in the static tests but moderate in the dynamic responses.\r\n\r\nThe second half of the paper studies the response of clamped circular arches under lateral impulse. The motion of the arch was recorded by a high speed camera and the deflected arch shape was measured in detail. The response was expressed in terms of the average displacement and three generalized displacement coordinates representing the amplitudes of the assumed mode shapes. The critical impulse is defined as the impulse level at the inflection point of the curve of maximum response versus impulse." }, { "name": "Collins, Donald James", "degree": "PhD", "year": "1969", "title": "The Near Wake of a Two-Dimensional Hypersonic Blunt Body with Mass Addition", "advisor": "Roshko, Anatol; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-144356", "creators": [ { "name": { "family": "Collins", "given": "Donald James" }, "id": "Collins-Donald-James", "display_name": "Collins, Donald James" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZHBC-A772", "abstract": "An experimental investigation of the steady, laminar nearwake flow field of a two-dimensional, adiabatic, circular cylinder with surface mass transfer has been made at a free-stream Mach number of 6. 0, and free-stream Reynolds numbers Re\u221e,d=0.9 and 3.0x104.
\r\n\r\nA flush-mounted porous section was used to transfer argon, nitrogen or helium into the near wake of the circular cylinder to determine the flow field associated with the addition of a passive scalar. Two cases were studied: mass transfer from the forward stagnation region, and mass transfer from the base. The pressure field was mapped by standard Pitot- and static-pressure measurements. The mass-concentration field was monitored by a continuous sampling mass-spectrometer system which utilized the output of a single mass peak to determine the relative mass-concentration levels.
\r\n\r\nFor mass addition from the base, a recirculating vortex remains in the near-wake flow and the characteristic near-wake pressure is the pressure at the stagnation point created by the interaction of the reversed flow with the injected fluid. This pressure, and the entire near-wake flow field, correlates with the ratio of the momentum flux of the injected fluid to the momentum flux in the cylinder boundary layer upstream of separation, and not the mass flow of the injected fluid as predicted by Chapman.
\r\n\r\nFor mass addition from the base, the axial mass concentration decays rapidly away from the base as a consequence of the countercurrent diffusion of mass into the oncoming recirculating flow. In addition, strong transverse mass-concentration gradients exist in the region between the two stagnation points and a local maximum occurs in the vicinity of the u = 0 locus for those cases in which ReSc > 0(1) for the reversed flow.
\r\n\r\nWith moderate mass addition from the forward stagnation region, the near-wake pressure field is unperturbed. In addition, because there is no source in the base region, the near-wake mass-concentration field is nearly uniform in the region of reversed flow. Bounding the uniform region, in the vicinity of the viscous shear layers, narrow diffusion layers govern the transport of mass into the outer flow.
\r\n\r\nIn the intermediate-wake region, immediately downstream of the neck, the mass-concentration fields for both forward and base injection are explained by a single model which incorporates the influence both of the accelerating axial velocity and of an assumed Gaussian distribution for the mass-concentration of argon. This model predicts the axial decay of mass concentration in the intermediate wake, and establishes the location of the virtual origin of the asymptotic far wake in terms of the mass-concentration profile parameters at the neck.
\r\n" }, { "name": "Delph, Terry Joseph", "degree": "Engineering Degree", "year": "1969", "title": "The Dynamic Stability Under Impulsive Loading of Shallow Arches with Elastic End Restraints", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-104435", "creators": [ { "name": { "family": "Delph", "given": "Terry Joseph" }, "id": "Delph-Terry-Joseph", "display_name": "Delph, Terry Joseph" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GRVF-AN95", "abstract": "A theoretical and experimental study of the buckling under impulsive load of an arch with rotational end restraints was carried out.\r\n\r\nImpulsive loading was realized experimentally by use of the spray deposited explosive silver nitrate-silver acetylide. The experimental buckling loads were compared to those obtained by a theoretical analysis. It was found that the theoretical analysis yields a quite conservative lower bound on the magnitude of load necessary for buckling. Both uniform and nonuniform loadings were considered.\r\n\r\nIt was found that there exists a critical value of rotational spring constant above which dynamic buckling may not occur in the rigorous mathematical sense. An expression for this critical value was found." }, { "name": "Fernandez, Fernando Lawrence", "degree": "PhD", "year": "1969", "title": "Two-Dimensional Viscous Flows with Large Distributed Surface Injection. Part I. Boundary Layer Flows with Large Injection and Heat Transfer. Part II. Experiments in Supersonic Turbulent Flow with Large Distributed Surface Injection. Part III. The Effect of Finite Plate Length", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-155216", "creators": [ { "name": { "family": "Fernandez", "given": "Fernando Lawrence" }, "id": "Fernandez-Fernando-Lawrence", "display_name": "Fernandez, Fernando Lawrence" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCCK-HT69", "abstract": "This report is concerned primarily with the effect of surface injection on viscous two-dimensional flows. More precisely, the investigation centers on surface injection rates where the wall shear has been considerably reduced below the no-injection value, but where the momentum of the injectant is still negligible compared to that in the free stream. Three separate problems are investigated to try to obtain an understanding of the physical mechanisms which control the flow.
\r\n\t\r\nFor the case of laminar boundary-layer flow, asymptotic solutions are obtained for large injection and heat transfer. It is found in this case that the boundary layer may be divided into two regions: (1) an inner region adjacent to the surface where viscous mixing plays a minor role; (2) a viscous layer where the transition occurs from the inner solution to the inviscid flow outside the boundary layer. In the case of the insulated wall the viscous layer contributes only small corrections to the boundary-layer properties. For the highly-cooled wall the boundary layer is strongly influenced by the viscous mixing between the inviscid outer flow and the high density low-speed gas adjacent to the wall.
\r\n\t\r\nFor turbulent flow, experiments with constant distributed surface injection at M\u221e=2.6 have been performed. These show that large injection leads to a constant pressure self-similar flow with linear growth. The experimental results are shown to be in good agreement with low Mach number experiments when the normal coordinate is stretched by using a Howarth-Dorodnitsyn transformation at the same value of the ratio of wall mass flow per unit area to that in the free stream.
\r\n\t\r\nFinally, the third part considers the upstream effect of the termination of injection on the flow in the \"blown\" layer. An analysis, using an integral approach is presented which agrees with the experimentally observed effects. In particular, as injection rates approaching the maximum value which can be entrained by a constant pressure mixing layer are approached, the analysis predicts that virtually the entire porous region experiences a falling pressure. It is postulated that this effect provides for a smooth transition from a boundary-layer flow to one where mixing is negligible, except in a thin layer near the streamline which divides the injected and freestream gas. Therefore, the analysis provides the step which gives a quantitative estimate for the range of injection rates in turbulent flow where the effect of mixing can be neglected and inviscid flow models utilized.
" }, { "name": "Foster, Michael Ralph", "degree": "PhD", "year": "1969", "title": "I. The Rotation of a Gravitating Sphere in a Monatomic Gas. II. The Drag of a Body Moving Transversely in a Confined Stratified Fluid", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132006-084851", "creators": [ { "name": { "family": "Foster", "given": "Michael Ralph" }, "id": "Foster-Michael-Ralph", "display_name": "Foster, Michael Ralph" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/89KW-B656", "abstract": "Part I - The Rotation of a Gravitating Sphere in a Monatomic Gas
\r\n\r\nThe flow resulting from the steady rotation of a gravitating sphere in a monatomic gas at rest is studied in a variety of special cases. The low speed rotation problem involves the solution of non-uniform Stokes equations and exhibits the interesting property that, if the field is large enough to make a \"scale height\" very small compared to the sphere radius, the motion is very weak and occurs primarily in a thin boundary layer on the sphere. The asymptotic theory for the gravitational field strength very large with arbitrary rotation speed shows essentially the same boundary layer, regardless of Reynolds number; the perturbation theory presents some interesting mathematical problems as well. The high speed rotation case is finally considered, and solutions have been obtained only for a gas with small Prandtl number. Even then, the flow structure is very complex. Depending on the relative sizes of the Prandtl number and inverse Reynolds number, there are six possibilities. In every case, there is a thin Prandtl boundary layer on the surface of the sphere and an essentially incompressible jet in the equatorial plane. In some cases, a thermal layer outside the Prandtl boundary layer is required to adjust the temperature, and in every case but one, it is necessary to infer the existence of still another layer, which is inviscid but rotational, that adjusts the uniform flow into the layer required by the strong hydrostatic constraints on the outer flow to that necessary for Prandtl boundary layer entrainment. In some cases these layers are unstable to small disturbances if the temperature on the sphere is sufficiently large.
\r\n\r\nPart II - The Drag of a Body Moving Transversely in a Confined Stratified Fluid
\r\n\r\nThe motion of a body through a stratified fluid bounded by vertical plates is studied in the case when the motion of the body is sufficiently slow to make the inertia of the fluid negligible. The case studied is for a very small coefficient of diffusion (for salt in water, for example). The density changes are quite large, and the drag is quite easily computed without appeal to the structure of any boundary layers or shear layers, depending only on changes of potential energy of the fluid. The solution exhibits regions where the fluid is unstably stratified, and hence mixes. Depending upon how complete the mixing process is, the body might experience a thrust!
\r\n\r\nThe equations for boundary layers are given, but details of their solution are not dealt with here, because of their quasi-linear nature. The horizontal shear layers consist of a simple density adjustment layer surrounded by a thicker and quite complicated non linear dynamical layer. The more conventional Stewartson layers do not appear here, these layers, because of the non linearities, are quite complex, and details of their structure have not yet been fully worked out.
" }, { "name": "Ko, Denny Ru-sue", "degree": "PhD", "year": "1969", "title": "I. Supersonic Laminar Boundary Layer Along a Two-Dimensional Adiabatic Curved Ramp. II. Non-Linear Stability Theory for a Laminar, Incompressible Wake", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102003-093156", "creators": [ { "name": { "family": "Ko", "given": "Denny Ru-sue" }, "id": "Ko-Denny-Ru-sue", "display_name": "Ko, Denny Ru-sue" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DM2V-N712", "abstract": "In Part I, the integral method of Lees and Reeves is applied to study a supersonic laminar boundary layer along a two-dimensional adiabatic curved ramp. The present method of solution requires no prior knowledge of the separation point and can be used to treat relatively weak interaction, including a fully attached flow. It starts with small perturbations of the self-induced interaction on a flat plate; consequently, it can be applied to flows with the hypersonic interaction parameter \u03a7\u0305, based on the distance of the beginning station of interaction to the leading edge, of the order 1. The effect of the radius of curvature on the separation phenomena is then investigated using this method. The effect of finite ramp length on the interaction is examined by making use of the characteristics of the singularities associated with the set of moment equations. Satisfactory agreement with the theory is obtained for the corresponding experiments conducted in the Mach 6 wind tunnel at the Graduate Aeronautical Laboratories of the California Institute of Technology.
\r\n\r\nIn Part II, a non-linear theory for the stability of the laminar wake behind a flat plate in an incompressible flow is presented. An integral method is used to investigate the effects of a finite amplitude disturbance on the flow. The flow is decomposed into a mean part, which is independent of time and a fluctuating part, which has a zero time average. The mean flow is assumed to be characterized by two parameters: the centerline velocity defect w[subscript c] and the wake half-width b. By using a two-length expansion procedure, the assumption of local, parallel mean flow is justified for the solution of the fluctuating component to the order considered in the present study. The fluctuation is assumed to be represented by an ascending power series of the amplitude A. The coefficients of the power series, as functions of the radial distance y, are then obtained in terms of the two mean flow parameters wc and b. The three unknowns b, wc and A are then obtained by solving the integral conservation equations of mean momentum, mean energy and fluctuation energy. In this integral method, the higher-order effects are introduced systematically by truncating the expansion for the fluctuation at various orders. The coupling between the mean flow and the fluctuation is found to be the most important mechanism in limiting the fluctuation amplitude and determining the mean flow. Satisfactory agreements with the experiment of Sato-Kuriki in the mean flow quantities and the relative development of the fluctuations are obtained, including the observed effect of free-stream Reynolds number.
" }, { "name": "Lake, Bruce Meno", "degree": "PhD", "year": "1969", "title": "Velocity Measurements Ahead of a Semi-Infinite Body in Magnetohydrodynamic Flow with Aligned Fields", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-142805", "creators": [ { "name": { "family": "Lake", "given": "Bruce Meno" }, "id": "Lake-Bruce-Meno", "display_name": "Lake, Bruce Meno" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PN2X-JB97", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments are described in which velocities were measured ahead of a semi-infinite Rankine body moving parallel to a uniform magnetic field in a conducting fluid. The flow disturbance in front of the body is found to increase in length as [...], where N is the interaction parameter. In most of the experiments this parameter was varied from 4 to about 50. Measurements made along the axis of symmetry in the flow show that there is a relatively short region of stagnant fluid directly ahead of the body. The major part of the disturbance is found to consist of a much longer region in which the flow undergoes transition from conditions in the freestream to conditions near the body. Velocity profiles across the flow in this region show that for increased N, at a fixed distance ahead of the body, the velocity defect increases and the disturbance becomes more confined radially. Although the radial gradients in the flow increase with N, they are found to be much smaller than would be expected in a flow containing thin current layers. A physical model of the flow which has currents and pressures consistent with these results is discussed." }, { "name": "Morel, Jean-Pierre Georges", "degree": "Engineering Degree", "year": "1969", "title": "Theoretical Solutions for the Jet Flap Diffuser", "advisor": "Lissaman, Peter B. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-140840", "creators": [ { "name": { "family": "Morel", "given": "Jean-Pierre Georges" }, "id": "Morel-Jean-Pierre-Georges", "display_name": "Morel, Jean-Pierre Georges" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y75H-MC77", "abstract": "This study proposes a jet sheet as an alternative to a rigid diffuser for a momentum propulsor. This appears attractive technically. The diffuser shape can be tailored by modulating jet momentum and angle and can be switched off in forward flight since its main function is increasing thrust/power ratio at static speeds. Theoretical analysis for a steady inviscid incompressible flow predicts impressive thrust augmentations. Taking into account the energy required to feed the jet sheet, it appears that in some cases propulsor thrust can be more than doubled. It could be applied to ducted fans, jet engines and seems particularly attractive for ejector thrust systems.\r\n\r\nA first approach of the study of the flow is made in the planar and axisymmetric cases by assuming that the velocity is uniform in each section. For the planar problem a linearized solution is presented. A conformal mapping transforms it into a half-plane boundary value problem of the Riemann-Hilbert-Poincare type. It is solved by combining Filbert Transforms, asymptotic expansion and a digital computer program. Then the nonlinear two-dimensional problem is presented with some references to the way it could be solved." }, { "name": "Parthasarathy, Shakkottai P.", "degree": "PhD", "year": "1969", "title": "I. The Transient Boundary Layer Produced by a Sink on a Plane Wall. II. Flow of Dusty Gases", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012009-085458", "creators": [ { "name": { "family": "Parthasarathy", "given": "Shakkottai P." }, "id": "Parthasarathy-Shakkottai-P", "display_name": "Parthasarathy, Shakkottai P." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GAFK-2R04", "abstract": "Part I: The solution for the problem of the transient boundary layers generated by a sink on a plane wall is obtained by an integral method. The incompressible flow is similar and the similarity solutions are obtained for the two dimensional and axisymmetric cases. The velocity layer reaches a steady state and the thermal layer does not. For large times, when the thermal layer is much thicker than the velocity layer, a solution for the temperature field is obtained ignoring the velocity layer. With some approximations to the flow near the sink, similar solutions for compressible flow are also obtained.\r\n\r\nPart IIa: By using the integrated equations of motion, the development of a laminar, two-dimensional, dusty jet issuing from a slit is considered. The solutions are simple in the limits \u03c4 \u2192 0 and \u03c4 \u2192 \u221e, where \u03c4 is the particle relaxation time. For arbitrary \u03c4, a numerical example is given. With some assumptions, the turbulent dusty jet is also considered.\r\n\r\nPart IIb: There are three parameters in the problem of steady motion of a dusty gas around a sphere. These are the Reynolds number R, particle parameter \u03c3 and the mass concentration of dust f[subscript \u221e]. Solutions are obtained by the perturbation method by expanding in terms of R with \u03c3 or \u03c3/R fixed, in the limit R \u2192 0. Solutions are also obtained for the limit R tending to infinity with f < < 1. In both cases critical values of \u03c3 exist, below which the sphere does not capture dust. The efficiency of capture as a function of \u03c3 is calculated in both cases." }, { "name": "Robinson, William McKinley, Jr.", "degree": "PhD", "year": "1969", "title": "Mass Spectrometric Studies of Ionization Precursors Ahead of Strong Shock Waves", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11222005-155153", "creators": [ { "name": { "family": "Robinson", "given": "William McKinley, Jr." }, "id": "Robinson-William-McKinley-Jr", "display_name": "Robinson, William McKinley, Jr." } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0QN4-MY03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study was conducted to identify the nature and origin of precursor ions produced by photoionization ahead of strong shock waves in xenon. A magnetic mass spectrometer is mounted at the end of a hydrogen-driven shock tube. Ions produced upstream of a shock wave are sampled by the spectrometer and the collected current provides a continuous time history of a particular ionic species. A mass spectrum is obtained in the precursor region for all impurities found in the shock tube. The incident shock Mach number is varied from 11.9 to 21.3, the initial pressure is varied from 0.050 to 0.500 torr, and the impurity level is altered. In all the conditions studied, the dominant ion present in the precursor is Xe+, although in certain instances, the impurity ion currents are found to be of the same order of magnitude as the xenon ion current. For small impurity levels, photoionization processes in xenon and impurities are apparently independent. Independent double probe measurements determine the total ion density to be about [...] at the shock front, the observable precursor extending about 150 cm from the shock wave.\r\n\r\nA theoretical model accounting for one-step and multi-step photoionization of xenon and impurities is used to find the ionization level ahead of a shock wave. The calculated ion density profiles agree well with experimental observations at the low pressures, where it appears that one-step photoionization predominates. Lack of agreement at high pressures, where, apparently, multi-step ionization is more efficient than the single-step process, suggests inadequacies in the treatment of photoexcitation and multi-step photoionization. Additional areas for experimental study are suggested.\r\n\r\nThe mass spectrometric data yield a better understanding of the role of radiation in shock structure, of the kinetics of photoionization processes in rare gases, and of the influence of impurities in the experimental facility on the radiation mechanisms." }, { "name": "Rose, James Robert", "degree": "PhD", "year": "1969", "title": "An Analysis of the Incompressible Two-Dimensional Jet Ejector", "advisor": "Lissaman, Peter B. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-093813", "creators": [ { "name": { "family": "Rose", "given": "James Robert" }, "id": "Rose-James-Robert", "display_name": "Rose, James Robert" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q1EZ-AW49", "abstract": "A general method for calculating the performance of two-dimensional jet ejector systems is presented, with special emphasis on those qualities desired in thrust augmenter devices. The nature of the viscous-inviscid interaction problem is examined and a \"frictionless\" model is defined. The equations are solved for the particular parametric problem of a single jet in a finite length shroud of uniform height. The flow in the \"recovery\" or confined-mixing region is discussed for this model and techniques are developed which may be applied to devices with diffusing systems.\r\n\r\nThe solutions presented for the free-mixing or interaction region are shown to agree with the simple channel flow studied analytically and experimentally by Curtet." }, { "name": "Stavro, William C.", "degree": "Engineering Degree", "year": "1969", "title": "Low Thrust Trajectories Using the Two Variable Asymptotic Expansion Method", "advisor": "Stewart, Homer Joseph; Wesseling, Pieter", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-143046", "creators": [ { "name": { "family": "Stavro", "given": "William C." }, "id": "Stavro-William-C", "display_name": "Stavro, William C." } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Wesseling", "given": "Pieter" }, "id": "Wesseling-P", "role": "advisor", "display_name": "Wesseling, Pieter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2DZ1-3033", "abstract": "An approximate analytic solution is derived in this thesis for the variables which describe a heliocentric low-thrust trajectory. The two-variable asymptotic expansion procedure is used. It is assumed that the thrust acceleration varies as the inverse of the distance to the central body raised to an arbitrary power \u03b1. Thus the value of \u03b1 = 1.4 will represent a solar-electric propulsion system, and the value of \u03b1 = 0 will represent a nuclear-electric system. It is also assumed that the mass of the spacecraft remains constant and that the direction of the thrust vector is arbitrary but remains constant. The results are compared to numerical integrations and to other integrating low-thrust programs." }, { "name": "Stevenson, Robert George", "degree": "Engineering Degree", "year": "1969", "title": "An Experimental Study of the Flow of a Subsonic and Turbulent Boundary Layer Over a Forward-Facing Step", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-132132", "creators": [ { "name": { "family": "Stevenson", "given": "Robert George" }, "id": "Stevenson-Robert-George", "display_name": "Stevenson, Robert George" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BECB-V842", "abstract": "The incompressible flow over a normal step in a channel was investigated by making measurements of the static wall pressures upstream of the step, on the step face, and downstream of the step. Several parameters were varied in order to determine their influence on the pressure field. These parameters included the free stream velocity, step height, channel height, and the boundary layer thickness. Tests were made using water as the working medium.\r\n\r\nThe results indicate that the pressure field in the vicinity of the step base is highly dependent on the ratio of step height to boundary layer thickness, and that the far field is influenced strictly by the ratio of channel height to step height. This distinction becomes more clear when the step is at least two times the boundary layer thickness." }, { "name": "Thach, Nathan Raymond, Jr.", "degree": "Engineering Degree", "year": "1969", "title": "The Flow of a Rarefied Gas Through a Circular Orifice and a Two-Dimensional Slit", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162005-104414", "creators": [ { "name": { "family": "Thach", "given": "Nathan Raymond, Jr." }, "id": "Thach-Nathan-Raymond", "display_name": "Thach, Nathan Raymond, Jr." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B8GW-KD14", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments were conducted to measure the mass flow of helium through a circular orifice and a two-dimensional slit over a wide range of Reynolds number for large pressure ratios across the test apertures. The Reynolds number, defined as [...] for the orifice and [...] for the slit, ranged nominally from 5 x [...] to 3 x [...]. The upstream-to-downstream pressure ratio, [...], was at all times greater than 100:1 so that the Mach number, defined as [...], was at all times approximately unity.\r\n\r\nThe results of the present experiments on the circular orifice are found to compare favorably with the results of experimental and theoretical work on the circular orifice by previous investigators. The results of the present experiments on the two-dimensional slit (which appear to be the first of this nature) do not compare favorably with the results of the meager amount of theoretical work on the two-dimensional slit.\r\n\r\nThe transition from free-molecule flow to continuum-limit flow for the circular orifice appears to be substantially complete within the range [...]. The two-dimensional slit behaves very much like the circular orifice for [...]. Unlike the circular orifice, however, the transition from free-molecule flow to continuum-limit flow for the two-dimensional slit appears to cover the range [...]." }, { "name": "Tombach, Ivar Harald", "degree": "PhD", "year": "1969", "title": "Velocity Measurements with a New Probe in Inhomogeneous Turbulent Jets", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-110134", "creators": [ { "name": { "family": "Tombach", "given": "Ivar Harald" }, "id": "Tombach-Ivar-Harald", "display_name": "Tombach, Ivar Harald" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V2CR-0Q19", "abstract": "Velocity profiles have been measured in subsonic, inhomogeneous, axisymmetric turbulent jets, using a new velocity measuring probe. This probe creates a train of heat pulses at one point in the flow and measures the time interval between the time a pulse is created and the time at which it is convected by the flow past a sensing wire a short distance downstream. In a turbulent flow the detected pulses are highly disturbed, but reconstruction of a mean pulse, by a digital computer, from several hundred pulses enabled calculation of a mean velocity and a velocity fluctuation level.\r\n\r\nMeasurements were made with this probe from near the nozzle to 48 diameters downstream in several combinations of jet gas and ambient gas (air-air, air-He, He-air, and He-SF[subfield 6]) having a range of jet/ambient density ratios from 0.03 to 7.25. Axial profiles of the variation with the density ratio of the jet width, mean velocity, and turbulence level were obtained from these measurements, showing the entrainment and approach to homogeneity of the inhomogeneous jet. A jet which is less dense than the ambient fluid is seen to entrain the ambient fluid more vigorously than the denser jet, as is demonstrated by its higher turbulence levels, more rapid growth, and more rapid axial decay of the mean velocity." }, { "name": "Victoria, Keith Jordis", "degree": "PhD", "year": "1969", "title": "The Hypersonic Laminar Boundary Layer Near a Sharp Expansion Corner", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-06172009-151827", "creators": [ { "name": { "family": "Victoria", "given": "Keith Jordis" }, "id": "Victoria-Keith-Jordis", "display_name": "Victoria, Keith Jordis" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EZX3-M918", "abstract": "The integral moment method for treating interactions between a laminar boundary layer and an external supersonic flow is applied to the problem of the hypersonic laminar boundary layer near sharp and slightly rounded convex (expansion) corners. The general features of this type of interacting flow are established by an analytical solution of the integral equations using the method of matched asymptotic expansions for the case of small interaction parameter. Numerical solutions are obtained for flows for which the interaction parameter can no longer be considered small.
\r\n\r\nAn experimental study is carried out in the GALCIT Mach 8 hypersonic wind tunnel in order to study the two-dimensional laminar boundary layer expansion. Major emphasis is placed on the acquisition of detailed data near the corner region. The basic measurements consist of the model surface pressure distribution and pitot pressure surveys of the boundary layer and inviscid flow field between the boundary layer and the leading edge shock wave both upstream and downstream of the corner region. The surface pressure measurements illustrate the striking departure of the flow field at hypersonic speeds from the classical Prandtl-Meyer description.
\r\n\r\nThese data with appropriate assumptions made regarding the static pressure and temperature fields at points away from the model surface allow calculation of the distributions of profile functions defined in the integral moment method formulation. These distributions along with the surface pressure distribution are compared directly with solutions of the moment equations.
\r\n" }, { "name": "Arbocz, Johann", "degree": "PhD", "year": "1968", "title": "The Effect of General Imperfections on the Buckling of Cylindrical SheIls.", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292005-080202", "creators": [ { "name": { "family": "Arbocz", "given": "Johann" }, "id": "Arbocz-Johann", "display_name": "Arbocz, Johann" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DSCT-G640", "abstract": "An experimental and theoretical investigation of the effect of general imperfections on the buckling load of a circular cylindrical shell under axial compression was carried out.\r\n\r\nA non-contact probe has been used to make complete imperfection surveys on electroformed copper shells before and during the loading process up to the buckling load. The data recording process has been fully automated and the data reduction was done on an IBM 7094. Three-dimensional plots were obtained of the measured initial imperfection surfaces and of the growth of these imperfections under increasing axial load. The modal components of the measured imperfection surfaces were also obtained.\r\n\r\nThe theoretical solution located the limit points of the post-buckled states. A simplified imperfection model was used consisting of one axisymmetric and one asymmetric component. For global buckling the correlation between the theoretical buckling loads and the experimental values was found to be good." }, { "name": "Chao, Chia-Chun", "degree": "Engineering Degree", "year": "1968", "title": "Constant-Pressure Laminar Mixing of a Shear Layer with a Quiescent Fluid", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112005-153627", "creators": [ { "name": { "family": "Chao", "given": "Chia-Chun" }, "id": "Chao-Chia-Chun", "display_name": "Chao, Chia-Chun" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8FYR-SB25", "abstract": "The constant-pressure laminar mixing of an initial shear layer with a quiescent fluid is studied theoretically. The line of singularities at the starting point is removed by abandoning the conventional restriction that the dividing streamline must coincide with the x-axis. Instead, the shape of this streamline in the \"near-field\" is determined by properly matching inner and outer flow regions so as to cancel any additional induced normal velocity and pressure disturbances in the outer flow. The \"far-field\" is obtained by applying the momentum integral technique beginning with the profiles determined by the near-field solution some distance downstream of the start of mixing. Universal functions are obtained that enable the progress of the mixing process to be followed both for a Blasius initial profile and an initial profile with a finite slip." }, { "name": "Crespo Mart\u00ednez, Antonio", "degree": "PhD", "year": "1968", "title": "I. Theoretical Investigation of the Reflection of Ionizing Shocks. II. Theoretical Study of Sound and Shock Waves in a Two-Phase Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05102005-094142", "creators": [ { "name": { "family": "Crespo Mart\u00ednez", "given": "Antonio" }, "id": "Crespo-Mart\u00ednez-Antonio", "display_name": "Crespo Mart\u00ednez, Antonio" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3XYJ-AC18", "abstract": "PART I\r\n\r\nThe reflection of an ionizing shock from the end wall of a shock tube is studied theoretically following the experimental model of J. Smith. The observed perturbations in the wall pressure history are found to agree with this theory. To describe the first perturbation, a decrease in pressure due to the ionization part in the reflected shock structure, the flow equations are linearized but the rate equations are used in nonlinear form. The second perturbation, an increase in pressure due to the ionization part of the incident shock structure, is studied using Whitham's theory and assuming equilibrium behind the reflected shock.\r\n\r\nPART II\r\n\r\nThe propagation of sound and shock waves in a two-phase medium is studied theoretically using the flow equations for each component. It is shown that the assumption of constant mass ratio during the sound propagation, used previously in the literature for the case of bubbles suspended in a liquid, is only valid for low frequencies. For high frequencies a larger sound speed is obtained. These two sound speeds give two different Mach numbers. It is found that when both Mach numbers are larger than one, the shock structure in a liquid containing bubbles is given by an initial increase of the pressure, followed by a region in which it oscillates around its final equilibrium value. When the low frequency Mach number is larger than one, and the high frequency Mach number smaller than one, the oscillations disappear and the transition is uniform.\r\n\r\nThe speed of sound of the mixture is also calculated by evaluating the scattering by the suspended phase." }, { "name": "Fersht, Rena Scher", "degree": "PhD", "year": "1968", "title": "Buckling of Cylindrical Shells with Random Imperfections", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-105632", "creators": [ { "name": { "family": "Fersht", "given": "Rena Scher" }, "id": "Fersht-Rena-Scher", "display_name": "Fersht, Rena Scher" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KF7B-XA89", "abstract": "The buckling stability analysis of long cylindrical shells with random imperfections subjected to axial load is treated using two different approaches. The first study is based on a Lyapunov method which enables one to establish sufficient conditions for buckling stability of a long cylindrical shell with axisymmetric random imperfections. A perturbed system of equations in the neighborhood of the prebuckling solution is investigated. By reducing the problem to a system of integral equations, it is observed that the stability boundary value problem of a long shell is similar to that of a dynamical system with random parametric excitations.\r\n\r\nInitial imperfections were assumed to have Gaussian distribution and an exponential cosine correlation function. The critical load was obtained as a function of the root mean square of the imperfections. Results obtained are qualitatively similar to those of Koiter for a periodic imperfection (Ref. 1).\r\n\r\nThe second part is based on the approximate method of truncated hierarchy. The prebuckling state of equilibrium for asymmetric imperfections is found by a successive substitution technique. A homogeneous variational system of equations is set up in order to examine the existence of bifurcation in the neighborhood of the equilibrium state. These last equations involve random parametric terms. The truncated hierarchy method is applied and characteristic equations are obtained. Various exponential cosine correlation functions associated with asymmetric imperfections are examined numerically. Qualitatively the results obtained are as anticipated." }, { "name": "Majumdar, Suarindranath", "degree": "Engineering Degree", "year": "1968", "title": "Buckling of Thin Annular Plates Due to Radial Compressive Loading", "advisor": "Sechler, Ernest Edwin; Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112005-152910", "creators": [ { "name": { "family": "Majumdar", "given": "Suarindranath" }, "id": "Majumdar-Suarindranath", "display_name": "Majumdar, Suarindranath" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QAE9-G437", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nBuckling of circular annular plates with the outer edge clamped and the inner edge free loaded with a uniform radial compressive force applied at the outside edge has been studied both theoretically and experimentally. A differential equation of equilibrium of the buckled plate has been developed for any general deflection pattern and solutions corresponding to the buckled form [...] Cos n 0 have been sought. The differential equation has been solved exactly for n = 0 and n = l and approximately for higher values of n as well as for n = 0 and 1. The solutions indicate that, for small ratios of inner to outer radius, the plates buckle into a radially symmetric buckling mode, but for the ratio of inner to outer radius exceeding a certain minimum value the minimum buckling load corresponds to buckling modes with waves along the circumference, the number of which depends on the particular ratio of the inner and outer radii. Tests were carried out using thin aluminum plates and the results agreed reasonably well with the theoretical predictions." }, { "name": "Mueller, Hans-Karl Christian Alfred", "degree": "PhD", "year": "1968", "title": "Stable Crack Propagation in a Viscoelastic Strip", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-142505", "creators": [ { "name": { "family": "Mueller", "given": "Hans-Karl Christian Alfred" }, "id": "Mueller-Hans-Karl-Christian-Alfred", "display_name": "Mueller, Hans-Karl Christian Alfred" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MGSD-R362", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA crack of length 2a which propagates with small, constant speed through a viscoelastic strip of width 2b is considered. The strip is strained by displacing its shearfree edges. Linear theory is applied. The stress on the line of crack advancement and the shape of the crack surface are calculated for a state of plane stress.\r\n\r\nThe stress intensity factor which is independent of material properties is given as a function of a/b. It exhibits a maximum at [...]. For a/b > 1.5 the stress intensity factor becomes essentially independent of crack length. The crack surface deflection is obtained in the form of a superposition integral and is a function of material properties and crack speed.\r\n\r\nThe energy which is released when the crack extends a small distancee is calculated. This crack energy depends on the crack speed and involves the creep function of the material. A characteristic length enters in the course of its derivation. This length does not appear in the case of an elastic material and is considered as an additional material property necessary to describe viscoelastic crack propagation.\r\n\r\nThe energy conservation equation is established by considering a small control volume surrounding the crack tip. A relationship emerges from this equation which implicitly gives a stable crack speed as a function of applied strain, temperature, and material properties. The creep function is the controlling factor in this equation.\r\n\r\nThe relevant material properties are discussed and presented for a Polyurethane rubber (Solithane 113 - 50/50). The lower bound of the surface energy is determined from fracture tests on the swollen material. The results of the material characterization are used to calculate the crack speed as a function of applied strain and temperature. Good agreement is found to exist between theory and experiment." }, { "name": "Piva, Hugo de Oliveira", "degree": "PhD", "year": "1968", "title": "Electron Beam Measurements of Density in Shock Waves Reflecting From a Cold Wall", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292005-131010", "creators": [ { "name": { "family": "Piva", "given": "Hugo de Oliveira" }, "id": "Piva-Hugo-de-Oliveira", "display_name": "Piva, Hugo de Oliveira" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EDZS-EA78", "abstract": "The normal shock wave is a rarefied-gas flow in which large departures from thermodynamic equilibrium and strong non-linearities occur and it is the simplest such flow due to its one-dimensionality and the absence of solid boundaries. Because of this, both theoretical and experimental studies of the structure of normal shock waves have been used successfully in recent years to get a better understanding of such phenomena. The present work is an extension of the earlier studies to the more complicated problem of shock-wave reflection. The density distribution of a normal shock wave in argon is measured during its reflection from a heat-conducting wall using an electron beam densitometer in the GALCIT 17-in diameter shock tube at incident Mach numbers 6.00, 4.00 and 2.96.\r\n\r\nDuring each run a density history is obtained at a certain distance from the wall by measuring electron-beam current as a function of time. By defining a consistent zero of time for all runs at the same conditions, these histories are converted by a cross-plot to families of density profiles at different times. x-t diagrams are obtained from the density history plots, and a wall-density history is obtained from the density profiles. Measured in terms of the ideal conditions behind the incident shock wave, the distances extend from 0.25 to 56 mean free paths from the wall and the times to 160 mean collision times after the beginning of the reflection.\r\n\r\nThe results presented here give both quantitative and qualitative information about the interaction of the incident shock wave with the wall, the effects of the wall heat transfer and accommodation on the density near the wall, the formation of the reflected shock wave, its strength and trajectory on the x-t diagram, and the nature of the flow field lying between the thermal layer and the reflected shock wave at large times." }, { "name": "Weidman, Patrick Dan", "degree": "Engineering Degree", "year": "1968", "title": "Wake Transition and Blockage Effects on Cylinder Base Pressures", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-153638", "creators": [ { "name": { "family": "Weidman", "given": "Patrick Dan" }, "id": "Weidman-Patrick-Dan", "display_name": "Weidman, Patrick Dan" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/95CE-1189", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nBase pressure measurements of circular cylinders at Reynolds numbers from 100 to 3 x [...] were obtained in a low speed wind tunnel. Pressure distributions from [...] to [...] were also obtained.\r\n\r\nIn the Reynolds number region from the first appearance of an unsteady wake to the critical Reynolds number the base pressure coefficient shows two maximums and two minimums. The first maximum (Rd [...] 50) coincides with the first appearance, of the Karman vortex street. The succeeding minimum (Rd [...] 300) probably corresponds to the movement of the onset of transition from the end of the vortex-formation region into the free shear layers. The following maximum (Rd [...] 2200) is accompanied by a small discontinuity in the base pressure curve and a decrease in the Strouhal number. The final minimum corresponds to the end of the Schiller-Linke region, at which point transition to turbulence occurs in the free shear layers very near to the shoulder of the cylinder.\r\n\r\nA comparison of the blockage correction theories of Maskell and Allen and Vincenti was made at [...] = 6 x [...]. The value of the base pressure coefficient in an unlimited stream at this Reynolds number was found to be [...] = -1.215 for cylinders of one particular roughness, though this value depends on other unit Reynolds number effects. These effects can also result in a significant Reynolds number shift of the base pressure coefficients." }, { "name": "Alber, Irwin Emanuel", "degree": "PhD", "year": "1967", "title": "Integral Theory for Turbulent Base Flows at Subsonic and Supersonic Speeds", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-141417", "creators": [ { "name": { "family": "Alber", "given": "Irwin Emanuel" }, "id": "Alber-Irwin-Emanuel", "display_name": "Alber, Irwin Emanuel" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0YEZ-H062", "abstract": "The integral near wake analysis of Reeves and Lees developed for supersonic laminar base flows is extended to the case of fully turbulent separated adiabatic flow behind a rearward facing step at both subsonic and supersonic speeds. A turbulent eddy viscosity model is formulated for the shear stress scaling of the dissipation integral in the mechanical energy equation. It is shown that the eddy viscosity can be described simply by one incompressible constant (valid for both shear layers and wakes) and one reference density \u03c1r. Using a compressibility transformation, theoretical solutions for the spreading rates of free shear layers are found to agree with experiment when the reference density is chosen to be the centerline density for the wake flow.
\r\n\r\nTwo alternate methods are presented for joining the wake flow solution to the body first, through a turbulent free shear layer mixing solution, and then through the use of a two parameter family of velocity profiles valid near the body. A simple conservation model is presented to relate the viscous sublayer after expansion to the initial boundary layer ahead of the step.
\r\n\r\nFor free stream Mach numbers M1 \u2264 2.3, the integral theory is found to give good estimates for the length scales and centerline pressure variations measured experimentally for both wake flows and step flows (where reattachment is to a solid surface).
\r\n\r\nAn iterative method of solution for the incompressible wake flow problem is presented as an extension of the work of Green. The calculation proposes the proper criteria for obtaining a convergent solution. The base pressure coefficient is found to be equal to the difference between the momentum thicknesses in the far wake and at the base.
\r\n" }, { "name": "Batt, Richard George", "degree": "PhD", "year": "1967", "title": "Experimental Investigation of Wakes Behind Two-Dimensional Slender Bodies at Mach Number Six", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-132450", "creators": [ { "name": { "family": "Batt", "given": "Richard George" }, "id": "Batt-Richard-George", "display_name": "Batt, Richard George" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3WW3-B746", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation has been conducted to determine mean flow properties for both near and far wakes behind several two-dimensional slender bodies at M[...] = 6. Three adiabatic wall models consisting of a flat plate model and two 20 [degree] included angle wedge models (H = .15\", H = .3\") were tested. The effect of wall temperature on wake properties was examined by cooling the larger of these two wedge models with the internal flow of liquid nitrogen ([...] = .19). Free stream Reynolds numbers were varied from [...] to [...] for each of these four configurations. In the far wake, measurements of total temperature, as determined with hot wire probes, and Pitot and static pressures were used to derive all other mean flow properties. The effect of transition on these far wake data was determined. Near wake flows were laminar for all adiabatic wall tests and at least for the two lowest test Reynolds numbers of the cold wall wedge. Base region flow field mappings and shear layer profiles were obtained for the .3\"H wedge model by combining Pitot pressure data with hot wire measurements of total temperature and mass flux. These results illustrated that for slender bodies with flat bases, the basic structure for laminar near wakes is appreciably more complex for hypersonic than for supersonic flow primarily because, in hypersonic flow, the corner expansion fan extends into the separated shear layers and base region shocks now become imbedded within the viscous portion of the shear layers." }, { "name": "Chen, Jay Chung", "degree": "Engineering Degree", "year": "1967", "title": "Extreme Value Analysis of Fluctuating Air Loads Acting on a Cylinder", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-134521", "creators": [ { "name": { "family": "Chen", "given": "Jay Chung" }, "id": "Chen-Jay-Chung", "display_name": "Chen, Jay Chung" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/37E4-WS51", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe fluctuating air loads over the surface of a smooth, cantilevered circular cylinder perpendicular to a flow in the supercritical Reynolds number ranging from [...] to [...] have been investigated according to Gumbel's extreme value theory.\r\n\r\nThe envelope of the extreme values of the pressure was found to be much greater than the static pressure and the root-mean-square values and decreased with increasing Reynolds number.\r\n\r\nOn the other hand, the envelope of the extreme values of the resultant force was generally unrelated with Reynolds number." }, { "name": "Eddington, Robert Barnes", "degree": "Engineering Degree", "year": "1967", "title": "Investigation of Supersonic Shock Phenomena in a Two-Phase (Liquid-Gas) Tunnel", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292006-133727", "creators": [ { "name": { "family": "Eddington", "given": "Robert Barnes" }, "id": "Eddington-Robert-Barnes", "display_name": "Eddington, Robert Barnes" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9RJT-A855", "abstract": "Homogeneous two-phase flows of dispersed liquid and gas having gas-to-liquid volume ratios around 1:1 exhibit the characteristics of a continuum flow with a greatly reduced sound propagational velocity that approaches 66 ft/sec at atmospheric pressure, and that is reduced further in value as the square root of the pressure. Flows of such mixtures at velocities in excess of the local velocity of sound can produce shock phenomena similar to that experienced in supersonic gaseous media. A supersonic two-phase tunnel was designed and built with such versatility and precision that normal and oblique shock structures can be photographed and analyzed in the absence of boundary-layer interference. The applicability of the isothermal continuum theory to such flows is confirmed empirically for volume ratios near 1:1, and the theory is mathematically extended for both normal and oblique shocks over a wide range of volume ratios centered about the 1:1 value. Auxiliary flow devices were constructed for the measurement of such difficult flow parameters as the relative phase velocity, local void ratio, coefficient of friction, and stagnation pressure. A general change in the flow model matrix was found at volume ratios approaching 1:1. Pressure gradients and relative phase velocities were correlated with the proposed flow models with generally good agreement. The coefficient of friction measured for supersonic flow was found to be a simple function of the local void ratio. Stagnation pressures measured for a wide range of flow conditions approximate an isentropic relation for a substantial part of the lower velocity spectrum. At higher velocities, the stagnation pressure closely approaches the normal shock plus isentropic slowdown theory. Considerable photographic information pertaining to shock structure and phase movement is obtained over the spectrum of flow conditions with Mach numbers ranging from 2 to 20." }, { "name": "Flandro, Gary Arnold", "degree": "PhD", "year": "1967", "title": "Rotating Flows in Acoustically Unstable Rocket Motors", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272004-154250", "creators": [ { "name": { "family": "Flandro", "given": "Gary Arnold" }, "id": "Flandro-Gary-Arnold", "display_name": "Flandro, Gary Arnold" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BYWJ-5Q96", "abstract": "One of the most interesting manifestations of acoustic combustion instability in solid propellant rocket motors is the formation of strong vortices in the combustion chamber. A single vortex filament stretching along the motor axis from the head-end has been observed in several experiments in association with gas oscillations in the frequently occurring traveling tangential mode of instability. These flows are sometimes accompanied by a quite noticeable axial torque on the motor itself, and this effect has given rise to flight performance difficulties in a number of instances. Previous theoretical studies of the vortex generation effect have been inadequate in several respects. The present work is an attempt to place the theory on a more firm base and to clarify the connection between traveling wave motions and the generation of vortices and torques.
\r\n\r\nIt is readily shown that traveling waves transport momentum, and in the case of traveling tangential waves in a cylindrical combustion chamber this represents a steady axial component of angular momentum in the gas. This observation gives rise to a simple conceptual model of the vortex generation effect. Thus the presence of a steady mass flux about the axis implies the existence of a layer of vorticity at the chamber walls which may be represented by a vortex sheet composed of axially oriented bound vortex filaments. In the three-dimensional case these vortices are shed either at the end of propellant grain or at the periphery of the nozzle; the other ends of the filaments traverse the fore-end closure to the center and are combined and shed in an intense vortex filament along the symmetry axis of the motor.
\r\n\r\nDue to the production of gas at the chamber wall, tangential forces at the wall are produced by the interaction of this mean flow with the bound vortices. Angular momentum arguments must be used in this conceptual mechanism to estimate the strength of the axial vortex filament, and it is readily shown that the sense of the vortex must be opposite to the direction of travel of the waves. The direction and magnitude of the torque on the motor depend on the mean flow Mach number at the wall and must be established by calculation of the wall shear stresses.
\r\n\r\nThe detailed calculations are guided by the mechanism just outlined. All physical features of the problem which appear to be significant are simulated mathematically. In particular, the effects of the three dimensional mean flow pattern in the chamber and the pressure-sensitive combustion region at the burning surface are represented. Also considered are the effects of freedom of motion of the rocket motor in the plane normal to the symmetry axis. Both inviscid and viscous theories are developed using multi-parameter asymptotic perturbation expansion techniques. It is proved that traveling tangential waves are subject to amplification under conditions existing in typical solid propellant rockets, and that a steady transport of gas about the chamber axis accompanies this motion as a second-order perturbation. The equations of motion admit of only a vortex-like steady second-order azimuthal solution. This must be superimposed on the acoustic wave motions in such a way that angular momentum is conserved (due consideration being given to body forces on the gas and tangential forces at the wall). Thus the net pattern of steady circumfer vential mass flux at a given motor cross-section consists of a drift of fluid in the direction of the wave adjacent to the wall with a rapid transition to an oppositely spinning vortex flow as the longitudinal axis is approached. Introduction of the viscous corrections gives rise to a boundary. condition which sets the vortex strength, and a formal connection with the classical acoustic streaming effect is established. Since momentum is dissipated in the shear region at the wall, a torque appears on the chamber itself. This roll moment is opposite in sense to the wave travel during amplification of the acoustic waves, and numerical calculations give torque magnitudes which are in agreement with experimental data from several sources.
\r\n" }, { "name": "Harstad, Kenneth Gunder", "degree": "PhD", "year": "1967", "title": "Steady Laminar Compressible Magneto-Fluid-Dynamic Gas Flows in Channels.", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172002-144944", "creators": [ { "name": { "family": "Harstad", "given": "Kenneth Gunder" }, "id": "Harstad-Kenneth-Gunder", "display_name": "Harstad, Kenneth Gunder" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5T8X-8S80", "abstract": "Numerical computations are carried out for the core flow of subsonic MFD generator channels with a large length-to-height ratio and fine electrode segmentation. The working fluid is taken as potassium seeded argon. Variable transport properties and radiation effects are considered. It is shown that transverse variations in fluid properties are very important in Faraday generators; a one-dimensional analysis of the flow is not adequate. Axial currents in nonequilibrium flows can be kept low if the right value of the Hall parameter can be obtained; this also depends critically on the Mach number and load parameter. Mach numbers much less than one and high load parameters are to be avoided. Attainment of very large Hall parameters and fields cannot be expected." }, { "name": "Henderson, Arnold Herbert", "degree": "Engineering Degree", "year": "1967", "title": "Construction and Testing of a Rarefied Gas Flow Facility", "advisor": "Zukoski, Edward E.; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-083819", "creators": [ { "name": { "family": "Henderson", "given": "Arnold Herbert" }, "id": "Henderson-Arnold-Herbert", "display_name": "Henderson, Arnold Herbert" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CCG6-QV79", "abstract": "A low-density gasdynamic facility, suitable for measurement of mass flow through small (approximately 1 mm diameter) nozzles, tubes, and orifices, was designed and constructed. The system is capable of producing and measuring mass flows at 100:1 upstream/downstream pressure ratios for the entire spectrum from continuum to free molecular flow.\r\n\r\nResults of preliminary tests on an orifice are shown and compared with the work of previous investigators. The regime of transition flow is apparently shown to extend to higher Knudsen numbers than previously postulated. The ratio, of actual mass flow to theoretical free-molecule mass flow is shown to increase smoothly from a limiting value of 1.0 at high Knudsen numbers to an apparent limiting value at very low continuum-flow Knudsen numbers." }, { "name": "Hoffman, Alan Lowell", "degree": "PhD", "year": "1967", "title": "Magnetohydrodynamic Shock Production and Current Sheet Diffusion", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-135853", "creators": [ { "name": { "family": "Hoffman", "given": "Alan Lowell" }, "id": "Hoffman-Alan-Lowell", "display_name": "Hoffman, Alan Lowell" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WVH-W290", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nCurrent sheets in inverse pinch MHD shock tubes exhibit the strange property of forming shocks in the very rear of the sheet when accelerating heavy gases. When accelerating light gases, shocks are formed further to the front in the sheet, but in no case do the shocks separate from the driving current sheet. This \"piston dragging shock\" effect is explained on the basis of a single-fluid model with variable conductivity. Shocks are shown to always form within current sheets which move at supersonic speeds with respect to the driven gas. The relevant parameters for determining the shock position are the Mach number and the magnetic Reynolds number. Large magnetic Reynolds numbers and small Mach numbers enhance forward shock formation. These conditions are obtained in light gases with high speeds of sound. Similarity methods are developed to estimate gas conductivities, electron temperatures, and degrees of ionization for the experiments which are conducted. In hydrogen typical electron temperatures of 4 ev are produced by the ohmic heating, but twice this value is shown necessary to achieve separation at the current sheet speeds of 2-3 [...] used. Higher current sheet speeds produce shocks in the rear of the current sheet where separation can never occur. The correct method of procedure and the relevant design parameters to achieve separation are given. The success of single-fluid methods in explaining plasma phenomena is especially notable, and these methods can be extended to other similar problems. Based on these methods, multiple-fluid and microscopic effects are easily detectable and can be accounted for." }, { "name": "Klein, Alan Frank", "degree": "PhD", "year": "1967", "title": "I. The Use of a Large Conventional Shock Tube as a Pre-Ionizer for an Inverse Pinch Shock Tube. II. The Application of Thin-Film Heat Transfer Gauges and Flush Electrostatic Probes to Partially Ionized Flows in Shock Tubes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-133945", "creators": [ { "name": { "family": "Klein", "given": "Alan Frank" }, "id": "Klein-Alan-Frank", "display_name": "Klein, Alan Frank" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G7GV-GX76", "abstract": "Part 1.
\r\n\r\nA large diameter (17\"), conventional shock tube has been used as the pre-ionizer for an inverse pinch shock tube in an attempt to achieve separation of the shock front and the current sheath in the inverse pinch. The inverse pinch was mounted in the endwall of the shock tube and was operated without an anode, either behind the incident or reflected shock wave generated by the pre-ionizer shock tube. The test gases used were Xenon, Argon, and Helium. Separation was not achieved, but in Argon the pressure front did move closer to the front of the current sheath. In Xenon, no improvement in the performance of the inverse pinch was observed as a result of the pre-ionization, and in one case it was noticeably degraded, with the piston appearing to leak excessively. Because of test time limitations it was only possible to operate the inverse pinch behind the incident shock wave in Xenon. By measuring the ionization relaxation time in Xenon it was found that for all the conditions of the present experiments, ionization equilibrium was not attained in the times available. Therefore, the inverse pinch was being operated in a slightly ionized, relaxing gas. The electrical conductivity of such a gas was calculated for Xenon and Argon and the results in Argon were found to be in good agreement with previous shock tube measurements of the conductivity. The relaxation time measurements, conducted primarily in the GALCIT 6\" shock tube, show that P\u2081\u03c4, the product of the initial pressure and the relaxation time behind the incident shock, depends strongly upon the magnitude of P\u2081, especially for P\u2081 < .5 mm Hg of Xenon. The dependence decreases as the Mach number is increased in the range 10 < Ms < 20.6.
\r\n\r\nPart 2.
\r\n\r\nPrevious shock tube observations of \"spurious\" signals in the output of thin-film heat gauges at Mach number for which the shocked gas becomes partially ionized are summarized. It is shown that these effects, and those observed the the present experiments in Xenon, cannot be explained in terms of a shorting gauge model. It is demonstrated that the effects are due to the gauge acting more as an electrostatic probe than as a heat gauge. Under these conditions it is shown that the heat gauge provides an accurate measurement of the ionization relaxation time as well as still being useful for determining the shock velocity. The thin-film is also operated as a flush electrostatic probe to measure the ion density in the shock tube wall boundary layer, and the experimental results are in good agreement with the theoretical predictions of two solutions of the boundary layer problem: one based on an approximate solution of the transformed boundary layer equations, and the other based on the solution of the equivalent Couette flow problems. The applicability of these solutions is found to be limited to conditions for which the ionization relaxation time is either very long or very short. Because of the computational simplifications involved it is seen that the Couette flow solution is preferred under most conditions.
" }, { "name": "Lewis, John Eldon", "degree": "PhD", "year": "1967", "title": "Experimental Investigation of Supersonic, Laminar, Two-Dimensional, Boundary Layer Separation in a Compression Corner with and without Cooling", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-102455", "creators": [ { "name": { "family": "Lewis", "given": "John Eldon" }, "id": "Lewis-John-Eldon", "display_name": "Lewis, John Eldon" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R0FB-DD20", "abstract": "An experimental investigation of the boundary layer separation associated with a compression corner was conducted in the GALCIT Mach 6 wind tunnel, and a supplementary study was performed in the JPL supersonic wind tunnel. Special emphasis was placed on the development of a wind tunnel model which approximated true two-dimensional flow, and which could be run in either a highly cooled or an adiabatic configuration. The basic measurements consist of the model surface pressure and temperature, and Pitot surveys of the boundary layer. The surface pressure distributions for the adiabatic wall configurations are compared with the theory of Lees and Reeves (modified by Klineberg and Lees). The surface pressure distribution for the cold wall was compared with the adiabatic configuration for a laminar interaction, and the dependence on Reynolds number for both laminar and transitional interactions are observed. The \"free interaction\" similarity suggested by Chapman is empirically tested and found to be a good approximation for the adiabatic configuration, but it fails to correlate the cooled with the adiabatic case. The scaling suggested by Curle was tested and found to eliminate this deficiency." }, { "name": "McGill, James Alexander", "degree": "Engineering Degree", "year": "1967", "title": "Low-Density Gas Dynamic Facility", "advisor": "Marble, Frank E.; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-081030", "creators": [ { "name": { "family": "McGill", "given": "James Alexander" }, "id": "McGill-James-Alexander", "display_name": "McGill, James Alexander" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P04W-KX13", "abstract": "The question of optimizing nozzle contours for micro-thrust rockets led to the design, construction, and testing of a low-density gas dynamic facility. The primary objective was to investigate the mass flow rates of a gas through various profiles in the slip and transition flow regimes at high pressure ratios.\r\n\r\nAn initial test was conducted with an orifice as the test profile. The results showed that the facility can be used to investigate mass flow rates from the threshold of the free-molecule, through the transition and slip, to the continuum regimes. These results compare favorably with those of two previous investigators, and asymptotically approach the theoretical continuum and free-molecule limits. The ratio of mass flow rate to theoretical free-molecule mass flow rate is shown to transition smoothly from one theoretical limit to the other. A local maximum may occur in this ratio in the slip regime, and the attainment of the theoretical free-molecule limit appears to occur more slowly than expected." }, { "name": "Navarro-Cantero, Carlos", "degree": "Engineering Degree", "year": "1967", "title": "The Thermal Rayleigh Problem in Perfect and Ionized Gases", "advisor": "Saffman, Philip G.; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-135817", "creators": [ { "name": { "family": "Navarro-Cantero", "given": "Carlos" }, "id": "Navarro-Cantero-Carlos", "display_name": "Navarro-Cantero, Carlos" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X3H0-7367", "abstract": "The problem of a heated gas at rest in contact with a cold wall has applications in shock tubes when a shock wave reflects at the end wall. A boundary layer arises that can be solved for constant conditions outside the boundary layer. In this paper, this condition is relaxed and the gas is permitted to undergo variations of pressure.\r\n\r\nThe equation has been derived for the boundary layer under those conditions, and a similarity solution was found for isentropic variations of a perfect gas outside the boundary layer. This solution is only valid for a temperature of the gas much greater than the temperature of the wall, unless the latter would follow a determined variation with time. Two cases were studied; one with thermal conductivity of the gas proportional to a power of the temperature, and the other with conductivity proportional to temperature. In the first case, an integral method has to be used, which gives an excellent approximation. For the second case, the solution is worked out either by similarity procedures or by series expansions.\r\n\r\nHeat transfer and temperature in the boundary layer are seen to depend on the pressure, which acts like a weighting factor on time.\r\n\r\nFor ionized gases, two cases were considered; frozen and equilibrium flow. Similarity solutions do not exist for variable pressure outside the boundary layer unless the variations of pressure with time are small enough. In this case, pressure acts again like a weighting factor on time, although the variations outside the boundary layer cannot be assumed isentropic anymore. At the same time, new equations for the equilibrium boundary layer were derived, in which the excited state of ions and atoms is taken into account.\r\n\r\nThe effect of the weighting factor of the pressure is applied to explain the experimental results obtained at the end wall of a shock tube, giving explanation to certain differences between experiment and theory." }, { "name": "Smith, Jerome Allan", "degree": "PhD", "year": "1967", "title": "An Experimental Investigation of the Structure of Reflecting, Ionizing Shocks in Xenon", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092002-160549", "creators": [ { "name": { "family": "Smith", "given": "Jerome Allan" }, "id": "Smith-Jerome-Allan", "display_name": "Smith, Jerome Allan" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KSPH-2V57", "abstract": "The results of an experimental investigation of the reflection of strong shocks in xenon from the end wall of the GALCIT 6\" shock tube are presented. The reflection of the incident shock structure, consisting of a frozen shock front, a region of relatively uniform frozen flow, and an ionization front, was observed with a fast-rise (0.3 [mu] sec) pressure gauge mounted in the shock tube end wall. The interaction between the reflecting shock and the ionizing gas in the incident shock structure was of particular interest. This interaction produces a complicated series of shock and rarefaction waves; those waves that propagate back to the end wall were observed with the pressure gauge. The incident shock Mach number was varied from 11 to 20, and the initial pressure was varied from 0.1 to 1.5 mm Hg.\r\n\r\nA simple model which includes the gross features of the shock reflection process is used to calculate end wall pressures. The calculated pressures agree well with the experimental observations. In addition, ionization relaxation times for xenon behind the incident and reflected shocks are determined from this simple model and the measured pressure histories. The relaxation time data yield a better understanding of the ionization relaxation process in monatomic gases and provide an estimate for the electron-atom, inelastic excitation cross section for xenon." }, { "name": "Suzuki, Bob Hiro", "degree": "Engineering Degree", "year": "1967", "title": "Magnetofluid-Dynamic Drag Measurements on Semi-Infinite Bodies in Aligned Fields", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-154514", "creators": [ { "name": { "family": "Suzuki", "given": "Bob Hiro" }, "id": "Suzuki-Bob-Hiro", "display_name": "Suzuki, Bob Hiro" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JWK4-BM31", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments are described in which measurements were made of the drag of semi-infinite bodies moving parallel to a uniform magnetic field in a conducting fluid. Two of these bodies were moderately streamlined halfbodies and a third was a blunt halfbody. The drag coefficients of all three bodies were found to increase monotonically as a function of the interaction parameter, N. This parameter was varied in the experiments from 0 to about 24. The drag coefficients of the streamlined halfbodies were found to increase linearly with N for N <= 0(1) in agreement with a simple theory based on a calculation of the Joule dissipation. On the other hand, for the same range of N, the drag coefficient of the blunt halfbody was found to increase negligibly from its zero-field value of 0.66. For N>>1, the drag coefficients of all three bodies were of 0(1) and appeared to be asymptotically converging to some common limiting value. Although the drag could not be calculated for large, finite values of N, an inviscid theoretical model of the flow is described from which it is concluded that the drag coefficient of any halfbody must approach unity as [...].\r\n\r\nIn addition to the experiments with the semi-infinite bodies, experiments are also described in which measurements were made of the non-magnetic drag of impulsively-started flat disks. Some unexpected and interesting transient variations in this drag were observed and are attributed to the vortex formation process in the wake." }, { "name": "Tuan, Dorothy Yung-Hsun", "degree": "PhD", "year": "1967", "title": "Part I. Interaction of DNA and Histone in Native Nucleohistone. Part II. Dormancy Associated with the Repression of Genetic Activity", "advisor": "Bonner, James Frederick", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-162144", "creators": [ { "name": { "family": "Tuan", "given": "Dorothy Yung-Hsun" }, "id": "Tuan-Dorothy-Yung-Hsun", "display_name": "Tuan, Dorothy Yung-Hsun" } ], "advisors": [ { "name": { "family": "Bonner", "given": "James Frederick" }, "id": "Bonner-J-F", "role": "advisor", "display_name": "Bonner, James Frederick" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "bioch" ], "doi": "10.7907/X7X3-QH34", "abstract": "Part I. Interaction of DNA and histone in nucleohistone \r\n\r\nChapter 1. SELECTIVE DISSOCIATION OF HISTONE FROM NUCLEOHISTONE\r\n\r\nWith increasing concentration of NaCl solution, an increasing amount of histone is dissociated from dissolved nucleohistone. The dissociated histone fractions are identified by gel electrophoresis. The lysine rich histone fraction I is dissociated from nucleohistone in the range 0.3-0.5 F NaCl; slightly lysine rich histone II in the range 0.8-1.6 F NaCl; arginine rich histone III+IV in the range 0.9-1.6 F NaCl. The results suggest that both electrostatic and non-electrostatic interactions contribute to the strength of binding between DNA and histones.\r\n\r\nChapter 2. OPTICAL ROTATORY DISPERSION STUDIES ON HISTONES\r\n\r\nThe optical rotatory dispersion spectra of histones free and in reconstituted nucleohistone (in which histone is complexed to DNA) are recorded. By the criterion of optical rotatory dispersion at wavelengths below 220 mu, histone I is the least helical of the histones, histone II the most helical. The helicity of DNA-bound histones in reconstituted nucleohistone is greater than that of free histones, but the order, histone II most helical and histone I least, is still preserved.\r\n\r\nChapter 3. OPTICAL ROTATORY DISPERSION STUDIES ON THE DNA OF NATIVE NUCLEOHISTONE AND OF PARTIALLY DEHISTONIZED NUCLEOHISTONES\r\n\r\nThe conformation of DNA in native nucleohistone is altered by the DNA-histone interaction. The dissociation of histone I does not produce significant conformational change in DNA of nucleohistone but removal of histone II and of histone III+IV bring about changes which cause the conformation of DNA in nucleohistone to resume virtually that characteristic of free DNA. The possibility of DNA supercoiling in nucleohistone is discussed.\r\n\r\nPart II. Dormancy associated with repression of genetic activity\r\n\r\nChapter 1. THE DORMANCY OF POTATO BUDS\r\n\r\nChromatin of the buds of dormant potato tubers is almost totally incapable of the support of DNA-dependent RNA synthesis in the presence of added exogenous RNA polymerase. The chromatin of non-dormant buds of potato tubers (in which dormancy has been broken by treatment with ethylene chlorohydrin) is highly effective in the support of DNA-dependent RNA synthesis by added exogenous RNA polymerase. It is therefore concluded that the genetic material of the buds of dormant potato tubers is largely in a repressed state, and that the breaking of dormancy is accompanied by derepression of the genetic material.\r\n\r\nChapter 2. THE DORMANCY OF ONION BULBS\r\n\r\nThe chromosomal material of non-growing and non-dividing onion buds possesses template activity in support of in vitro DNA-dependent RNA synthesis. If we define dormancy not only by the absence of visible growth and mitotic division, but also by the lack of ability to direct in vitro DNA-dependent RNA synthesis, potato buds are then dormant but onion buds are not. And the block to onion bud growth must lie somewhere else than in the repression of genetic material.\r\n\r\nChapter 3. ISOLATION OF GLADIOLUS CHROMATIN\r\n\r\nGladiolus corms contain very little isolatable chromatin material and the isolated chromatin is highly contaminated by the presence of starchy material." }, { "name": "Tyson, Thomas Janney", "degree": "PhD", "year": "1967", "title": "Laminar Boundary Layers in the Neighborhood of Abrupt Spatial Disturbances", "advisor": "Sechler, Ernest Edwin; Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-111459", "creators": [ { "name": { "family": "Tyson", "given": "Thomas Janney" }, "id": "Tyson-Thomas-Janney", "display_name": "Tyson, Thomas Janney" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S72R-AM75", "abstract": "Supersonic, steady laminar boundary layers exhibiting \"strong\" local interaction with the outer flow are considered. The general behavior of such flows on a flat adiabatic plate are studied by means of the \"moment method\" equations and by finite difference solutions of the full boundary layer equations, including the transverse momentum equation. A one-parameter family of \"free interaction\" solutions is generated with the finite difference approach. These include separated reverse flow solutions. The infinite plate solution is established from the leading edge through weak interaction by both techniques. Expansive corner flow solutions are developed using both methods. In the \"moment method\" study the nature of the leading edge, Blasius point and \"critical\" line singularities is developed by numerical investigation." }, { "name": "Walsh, Myles Alexander, III", "degree": "PhD", "year": "1967", "title": "On the Turbulent Flow of Dilute Polymer Solutions", "advisor": "Blatz, Paul J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-140727", "creators": [ { "name": { "family": "Walsh", "given": "Myles Alexander, III" }, "id": "Walsh-Myles-Alexander", "display_name": "Walsh, Myles Alexander, III" } ], "advisors": [ { "name": { "family": "Blatz", "given": "Paul J." }, "id": "Blatz-P-J", "role": "advisor", "display_name": "Blatz, Paul J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6NTP-AH77", "abstract": "This paper is concerned with the problem of explaining the anomalous decrease in turbulent skin friction observed in the turbulent flow of very dilute polymer solutions.\r\n\r\nThe experimental evidence for dilute solutions is summarized.\r\n\r\nThe polymer molecule in solution is examined from a theoretical point of view, using the Rouse model. It is found that the model predicts that the molecule will locally store energy as a function of the local strain rate of the solution.\r\n\r\nThe experimental evidence is reexamined and it is concluded that the anomalous decrease in turbulent momentum transport results because the molecules manage to alter the energy balance of the small disturbances at the edge of the viscous sublayer. By slightly altering this balance the molecules allow viscous dissipation to destroy disturbances which would have had sufficient energy to grow had the molecules not been present. By decreasing the number of small disturbances which grow per unit area and time and move out from the edge of the viscous sublayer, the addition of polymer molecules ultimately changes the structure of the turbulence in the outer part of the boundary layer. This change results in lower Reynolds stresses and hence lower turbulent momentum transport.\r\n\r\nWith the help of the relation for local energy storage derived from the Rouse model, parameters are developed to characterize the phenomenon. These parameters appear to be useful in understanding the experimental evidence to date." }, { "name": "Walter, Uso", "degree": "Engineering Degree", "year": "1967", "title": "A Study of the Longitudinal Low Frequency (Phugoid) Motion of an Airplane at Supersonic and Hypersonic Speeds", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-105053", "creators": [ { "name": { "family": "Walter", "given": "Uso" }, "id": "Walter-Uso", "display_name": "Walter, Uso" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CNZT-1P02", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe character of the longitudinal low frequency (phugoid) motion of a rigid airplane with controls fixed is investigated for the flight Mach number range from 1.25 to 8.0 using the physical and aerodynamic data of the North American X-15 research airplane.\r\n\r\nThe validity of the simplifying assumptions made in most low speed airplane stability investigations (symmetry of the airplane and of the air flow, small perturbations) is established for the problem under consideration.\r\n\r\nThe equations of longitudinal motion have been solved for the flight altitudes: sea level, 20,000 ft., 40,000 ft., and 60,000 ft.; and in, addition the roots of the simplified equations resulting from the phugoid approximation have been calculated for the same flight situations. It is found that the deviation of these approximate solutions from the solutions of the complete longitudinal equations is below 5 per cent throughout the considered range of flight conditions, and for most calculated points is less than 2 per cent. The phugoid roots are complex at 60,000 ft. altitude and real at sea level, with transition from one mode to the other at the intermediate flight altitudes. The real part of the roots is always negative, i. e., there is no divergence of the motion. Using the phugoid approximation, a criterion for the de-generation of the periodic phugoid mode into aperiodic modes is derived in form of a critical value of the lift to drag ratio [...].\r\n\r\nIn an appendix, the influence of an additional damping force (thrust control by the auto-pilot) on the character of the phugoid roots is shown." }, { "name": "Wang, Charles Chang-Ping", "degree": "PhD", "year": "1967", "title": "Mass Spectrometric Studies of Ionization in Shock Heated Gas Mixtures", "advisor": "Sturtevant, Bradford; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-104254", "creators": [ { "name": { "family": "Wang", "given": "Charles Chang-Ping" }, "id": "Wang-Charles-Chang-Ping", "display_name": "Wang, Charles Chang-Ping" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GN3Q-Y356", "abstract": "The initial stage of thermal ionization in gas mixtures behind strong normal shock waves has been studied using a mass spectrometer. The sampling process, the unique role of mass spectrometric analysis, the ionization mechanism and the effect of impurities on the ionization relaxation time of the inert gases are discussed. A detailed analysis of ion diffusion through the end wall thermal boundary layer to investigate the effect of the sampling process on the reaction and reaction products are described. The experiments were conducted in argon and xenon at temperatures of from 10,000 \u00baK to 30,000 \u00baK and pressures from 15 mmHg to 80 mmHg. A large number of different ions were detected in \"pure\" (the estimated level of naturally occurring impurities was 50 ppm) argon. H+ and O+ were found in much greater amounts than any of the other products. The roles of H and O were studied further by mixing a small amount of H2 or O2 in argon. The activation energy and the effective cross section for ionization were obtained from the measured ionization rate. For argon, the activation energy agrees within experimental accuracy with the result of Kelly (1966). For hydrogen the activation energy is about 10 ev, and this value coincides with its first excited state. The effective cross section is a thousand times larger than the corresponding effective cross section for the ionization of argon. This explains why small amounts of hydrogen affect the argon ionization relaxation time." }, { "name": "Wesseling, Pieter", "degree": "PhD", "year": "1967", "title": "The Driving Mechanism of Strongly Developed Taylor Vortex Flow", "advisor": "Lagerstrom, Paco A.; Saffman, Philip G.; Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechTHESIS:06132025-213106117", "creators": [ { "name": { "family": "Wesseling", "given": "Pieter" }, "id": "Wesseling-Pieter", "display_name": "Wesseling, Pieter" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/00y0-xt20", "abstract": "The purpose of this thesis is to explain how strongly\r\ndeveloped Taylor vortex flow is kept motion. On the basis of this\r\nexplanation approximate torque calculations for high Taylor numbers\r\nhave been made. Agreement with experiment is satisfactory. Axial\r\nsymmetry is assumed throughout." }, { "name": "Witte, Arvel Benjamin", "degree": "PhD", "year": "1967", "title": "Part I. Experimental Investigation of an Arc-Heated Supersonic Free Jet. Part II. Analysis of One-Dimensional Isentropic Flow for Partially Ionized Argon", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022005-082626", "creators": [ { "name": { "family": "Witte", "given": "Arvel Benjamin" }, "id": "Witte-Arvel-Benjamin", "display_name": "Witte, Arvel Benjamin" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/STEK-4N18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nI. Experimental Investigation of an Arc-Heated Supersonic Free Jet.\r\n\r\nAn experimental investigation of the flow field of a highly ionized supersonic free jet has been carried out in a continuous-flow test facility. Measurements of impact pressure, mass flux, total enthalpy and stagnation point heat transfer profile were made in this flow field with two water cooled probes.\r\n\r\nArgon gas, at a flowrate of 0.5 gm/sec, was heated in a magneto-plasma-dynamic arc heater without an external magnetic field operating from between 200 amp and 40 volts to 1000 amp and 25 volts. The total pressure ranged from between 20 and 35 mm Hg, at constant flowrate, and the atom-ion number density was approximately [...] cm[...] at the exit plane. The average total enthalpy calculated from a heat balance ranged from between about 5,000 to 10,000 BTU/[...], while the probe measurements showed that the peak total enthalpy on the jet centerline near the exit plane was about three times the average total enthalpy.\r\n\r\nThe impact and mass flux measurements showed that the flow was hypersonic, source-like, chemically frozen, and in other details very much like the under-expanded free jet flow of a perfect gas. By combining these measurements with the total enthalpy measurements it was shown that the fraction of the total energy contained in ionization was about 0.6 which is quite close to the equilibrium stagnation value. For equilibrium stagnation conditions, the total temperature ranges from between 12,000\u00b0 to 20,000\u00b0K. The species mass fraction ranges from 0.2 for the atoms and 0.8 for the singly-ionized ions, to 0.8 for the singly-ionized ions and 0.2 for doubly-ionized ions.\r\n\r\nExamination of the electron energy equation showed that within a few diameters from the exit plane the electrons become energetically isolated from the ions and the electron heat conduction term dominates.\r\n\r\nA preliminary attempt to correlate the stagnation point heat transfer measurements along the axis shows that the electron temperature (TE [...] TI in general) plays an important role.\r\n\r\nII. Analysis of One-Dimensional Isentropic Flow for Partially Ionized Argon.\r\n\r\nOne-dimensional isentropic-flow variables of partially ionized argon have been calculated by coupling the isentropic flow equations with the partition-function method of deriving equilibrium thermodynamic properties. Tabulated gas properties and flow variables are presented for stagnation conditions of 0.1, 0.5, 1.0, 2.0, and 3.0 atm pressure and temperatures from 6,000 to 14,000\u00b0K in 1,000\u00b0K increments. The gas properties computed for this flow process include the sound speed, entropy, enthalpy, electron concentration, ionization fraction, electrical conductivity and static-to-stagnation ratios of temperature, pressure, and density. Flow variables include velocity, mass flux, area ratio, and Reynolds number per centimeter. Compared to results obtainable from perfect gas relationships (neglecting excitation and ionization), the results indicate that electronic excitation, and especially ionization effects, significantly alter the flow variables, particularly at the lower stagnation pressures and higher temperatures considered. However, with the exception of the effect of one excited state (the first excited state of the ion) on the equilibrium-composition equation, the thermodynamic properties calculated by neglecting excitation yielded results which were within 1% of those predicted by including excitation." }, { "name": "Zien, Tse-Fou", "degree": "PhD", "year": "1967", "title": "A Class of Three-Dimensional Optimum Wings in Hypersonic Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302005-135648", "creators": [ { "name": { "family": "Zien", "given": "Tse-Fou" }, "id": "Zien-Tse-Fou", "display_name": "Zien, Tse-Fou" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X1J8-JK85", "abstract": "The idea of using streamlines of a certain known flow field to construct generally three-dimensional lifting surfaces together with the method of evaluating the aerodynamic forces on the surfaces, developed by Nonweiler, Jones and Woods, has been extended and applied to axisymmetric hypersonic flow fields associated with a class of slender power-law shock waves of the form r ~ \u03c4xn in the limit of infinite free stream Mach number. For this purpose, the basic flow fields associated with concave shocks (n > 1) have first been calculated numerically at a fixed value of the ratio of specific heats \u03b3 = 1.40, and the results are presented in tabulated form, covering a wide range of values of n. The method of constructing a lifting surface either by prescribing its leading edge shape on the basic shock or by specifying its trailing edge shape in the plane x = 1 is then discussed. Expressions for lift and drag on the surface are derived. A class of optimum shapes giving minimum pressure drag at a fixed value of lift has been determined for every basic flow field with n ranging from 1/2 to 10 at \u03b3 = 1.40.\r\n" }, { "name": "Beebe, Wayne Metcalf", "degree": "PhD", "year": "1966", "title": "An Experimental Investigation of Dynamic Crack Propagation in Plastic and Metals", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262005-152806", "creators": [ { "name": { "family": "Beebe", "given": "Wayne Metcalf" }, "id": "Beebe-Wayne-Metcalf", "display_name": "Beebe, Wayne Metcalf" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PC0B-4P13", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nCrack propagation experiments were conducted in polyester resin sheets containing a central crack. Uniaxial tension loading at several loading rates was applied perpendicular to the crack direction. Two types of experiments were conducted: (1) High loading rate tests at 24\u00b0C and -45\u00b0C, with a constant loading rate to study the acceleration characteristics of cracks running in a glassy material, and (2) high temperature-low loading rate tests to study slow crack propagation when appreciable viscous dissipation could occur.\r\n\r\nDuring crack propagation, full frame photographs were taken of the photoviscoelastic isochromatic patterns and crack tip position at framing rates from 250 to 100,000 frames per second. The principal conclusions were as follows:\r\n\r\n1. Even at loading rates exceeding [...] psi per sec, isochromatic patterns prior to crack propagation compare closely with static patterns.\r\n\r\n2. Constant crack velocities were achieved in the high loading rate tests and it was found that the isochromatic patterns compare closely with the theoretical solution of Broberg.\r\n\r\n3. During the crack acceleration period, the experimental data could not be represented adequately by the Berry elastic theory.\r\n\r\n4. For the early phase of the slow (viscous) crack growth period, the crack length could be predicted using a simple theory proposed by Schapery and Williams.\r\n\r\nSeveral tests were conducted on silicon-iron metal sheets; it was concluded that the same testing technique can be applied to the study of crack growth in metals." }, { "name": "Behrens, Hermann Wilhelm", "degree": "PhD", "year": "1966", "title": "Flow Field and Stability of the Far Wake Behind Cylinders at Hypersonic Speeds", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172010-151639253", "creators": [ { "name": { "family": "Behrens", "given": "Hermann Wilhelm" }, "id": "Behrens-Hermann-Wilhelm", "display_name": "Behrens, Hermann Wilhelm" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K0KH-9W58", "abstract": "An experimental study of the mean wake flow field and its stability has been carried out in the far wake of circular cylinders at a Mach number of 6. The Reynolds numbers ranged from 200 to 4000 with a few measurements at higher Reynolds number. Pitot pressure, static pressure and mean flow hot wire measurements were done at many axial stations behind cylinders up to (x/d) = 2400.
\r\n\r\nThe inner wake formed from the cylinder boundary layers is laminar and loses its identity within the first 60 diameters or less depending on the Reynolds numbers so that only the outer wake, caused by the bow shock, has to be considered. Within a certain region the experimental results compare well with linear laminar theory, but the wake profiles are not similar up to the farthest downstream station (x/d = 2400). At four Reynolds numbers strong deviations from steady laminar behavior were observed far behind the cylinder, indicating breakdown of the flow because of non-linear instability effects.
\r\n\r\nIn the instability study hot wire fluctuation measurements were made over the whole frequency range (f = 1 - 320 KC) and also at particular frequencies in a band width of 1 KC up to x/d = 12000 at the lowest Reynolds number. Two instability regions were found and investigated: the linear growth region and the non-linear region. In the linear region there is quite a close correspondence with linear stability theory. The onset of non-linearity is characterized by the simultaneous strong deviation of the mean flow from laminar steady behavior, the increase of the fundamental frequency fluctuation component on the wake axis and the sudden rise of the first harmonic frequency component. The non-linear region is compared with the non-linear wake region at low speeds behind a flat plate. On the basis of these measurements a tentative picture is given of the onset of non-linearity and/or transition in the inner and outer wake behind blunt bodies at hypersonic speeds.
\r\n" }, { "name": "Bowman, Robert Marcus", "degree": "PhD", "year": "1966", "title": "Investigation of Shock Front Topography in Shock Tubes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-105038", "creators": [ { "name": { "family": "Bowman", "given": "Robert Marcus" }, "id": "Bowman-Robert-Marcus", "display_name": "Bowman, Robert Marcus" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XPM1-ZZ53", "abstract": "An experimental investigation of the shape of shock waves in a circular shock tube is conducted. It is found that there are three distinct regimes governed, in a given tube, by the initial pressure in the test section.
\r\n\r\nAt very low pressures, where the shock thickness is greater than about half the tube radius, the axial extent (deviation from a plane) of the shock is roughly constant and dominated by the viscous interaction between the \"shock\", the boundary layer, and the driving piston of gas. This range of pressures is called the viscosity-dominated regime.
\r\n\r\nAt intermediate pressures, the shape of the shock is very nearly that predicted by the theory of de Boer, the shock curvature being produced by the boundary layer and the axial extent being roughly inversely proportional to the square root of the initial pressure. This is the boundary layer regime. de Boer's work is extended and the shock shapes for both the two-dimensional and axisymmetric cases are computed and plotted.
\r\n\r\nAt high pressures, the shape of the shock is complex and varies periodically down the tube. This shape is determined by transverse waves produced at the diaphragm (or other upstream disturbance) and reflecting back and forth across the tube, decaying with the square root of the distance down the tube. In this transverse wave regime, the axial extent of the shock is essentially independent of initial pressure and is much greater than had been expected.
\r\n\r\nThe square root decay of the transverse wave disturbances is in contrast to the 3/2 power decay predicted by Freeman and apparently verified by Lapworth. The experimental data of Lapworth is re-plotted and it is shown that if this data is analyzed in a slightly different manner it appears to exhibit square root decay.
\r\n\r\nIt is shown that the shock perturbations which exist in the transverse wave regime are absent at lower pressures. The transition region where these disturbances suddenly disappear seems to correspond approximately to the initial pressure at which the boundary layer (appropriately defined) at the disturbance fills the tube.
\r\n\r\nA rule of thumb is developed from which it should be possible to predict the transition initial pressure (which separates the transverse wave and boundary layer regimes) in any given shock tube. This pressure occurs when the quantity L/p1R2 is of order one, the tube dimensions being in millimeters and the initial pressure in millimeters of mercury. This rule of thumb is used to analyze the results of several shock tube experiments published by other researchers.
\r\n\r\nUsing this rule of thumb as an important constraint, a low pressure shock tube design chart is developed, from which, given the type of experiments contemplated and the nature of the instrumentation available, the proper shock tube dimensions and operating pressures may be determined.
\r\n\r\nFinally, avenues of future research are suggested, wherein it may be possible to design a new type of \"hi-fi\" shock tube, capable of producing more nearly plane shock fronts for use in shock structure and relaxation time studies, especially where methods such as integrated schlieren, optical reflectivity, or electron beam scattering are to be used.
\r\n" }, { "name": "Crow, Steven Collins", "degree": "PhD", "year": "1966", "title": "1. The Spanwise Perturbation of Two-Dimensional Boundary Layers. 2. The Turbulent Rayleigh Problem. 3. The Propagation of Free Turbulence in a Mean Shear Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11172005-144841", "creators": [ { "name": { "family": "Crow", "given": "Steven Collins" }, "id": "Crow-Steven-Collins", "display_name": "Crow, Steven Collins" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/75J2-GM72", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n1. The Spanwise Perturbation of Two-Dimensional Boundary Layers.\r\n\r\nLarge spanwise variations of boundary-layer thickness have recently been found in wind tunnels designed to maintain two-dimensional flow. Bradshaw argues that these variations are caused by minute deflections of the free-stream flow rather than an intrinsic boundary-layer instability. The effect of a small, periodic transverse flow on a flat-plate boundary layer is studied in this chapter. The transverse flow is found to produce spanwise thickness variations whose amplitude increases linearly with distance downstream.\r\n\r\n2. The Turbulent Rayleigh Problem.\r\n\r\nRayleigh flow is the non-steady motion of fluid above a flat plate accelerated suddenly into motion. Laminar Rayleigh flow is closely analogous to laminar boundary-layer flow but does not involve the analytical difficulty of non-linear convection. In this chapter, turbulent Rayleigh flow is studied to illuminate physical ideas used recently in boundary-layer theory. Boundary layers have nearly similar profiles for certain rates of pressure change. The Rayleigh problem is shown to have a class of exactly similar solutions. Townsend's energy balance argument for the wall layer and Clauser's constant eddy viscosity assumption for the outer layer are adapted to the Rayleigh problem to fix the relation between shear and stress. The resulting non-linear, ordinary differential equation of motion is solved exactly for constant wall stress, analogous to zero pressure gradient in the boundary-layer problem, and for zero wall stress, analogous to continuously separating flow. Finally, the boundary-layer equations are expanded in powers of the skin friction parameter [...], and the zeroth order problem is shown to be identical to the Rayleigh problem. The turbulent Rayleigh problem is not merely an analogy, but is a rational approximation to the turbulent boundary-layer problem.\r\n\r\n3. The Propagation of Free Turbulence in a Mean Shear Flow\r\n\r\nThis chapter begins with the assumption that the propagation of turbulence through a rapidly shearing flow depends primarily on random stretching of mean vorticity. The Reynolds stress [...] acting on a mean flow [...] in the x direction is computed from the linearized equations of motion. Turbulence homogeneous in x, z and concentrated near y = 0 was expected to catalyze the growth of turbulence further out by stretching mean vorticity, but [...] is found to become steady as [...]. As far as Reynolds stress is a measure of turbulent intensity, random stretching of mean vorticity alone cannot yield steadily propagating turbulence.\r\n\r\nThe problem is simplified by assuming that all flow properties are independent of x. Eddy motion in the y, z plane is then independent of the x momentum it transports, and the mean speed U(y,t) is diffused passively. The equations of motion are partially linearized by neglecting convection of eddies in the y, z plane, and wave equations for [...] and U(y,t) are derived. The solutions are worthless, however, for large times. Turbulence artificially steady in the y, z plane forces the mean speed gradient steadily to zero. In a real flow the eddies disperse as fast as U diffuses.\r\n\r\nNumerical experiments are designed to find how quickly concentrated vortex columns parallel to x disperse over the y, z plane and how effectively they diffuse U. It is shown that unless a lower limit on the distance between any two vortices is imposed, computational errors can dominate the solution no matter how small a time increment is used. Vortices which approach closely must be united. Uniting vortices during the computations is justified by finding a capture cross section for two vortices interacting in a strain field. The experiments confirm the result that columnar eddies disperse as fast as they transport momentum." }, { "name": "Grange, Jean-Marie Fran\u00e7ois", "degree": "Engineering Degree", "year": "1966", "title": "Laminar Boundary Layer Separation and Near Wake Flow for a Smooth Blunt Body at Supersonic and Hypersonic Speeds", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112005-152028", "creators": [ { "name": { "family": "Grange", "given": "Jean-Marie Fran\u00e7ois" }, "id": "Grange-Jean-Marie-Fran\u00e7ois", "display_name": "Grange, Jean-Marie Fran\u00e7ois" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3ZN7-BC18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAt supersonic and hypersonic speeds the location of the boundary layer separation point on the surface of a smooth, blunt body is not fixed a priori, but is determined by the pressure rise communicated upstream through the subcritical base flow. By utilizing the integral or moment method of Reeves and Lees the separation-interaction region is joined smoothly to the near-wake interaction region passing through a \"throat\" downstream of the rear stagnation point. One interesting feature of this problem is that the viscous flow over the blunt body \"overexpands\" and goes supercritical. This flow is joined to the near-wake by means of a supercritical-subcritical \"jump\" upstream of separation, and the jump location is determined by the matching conditions.\r\n\r\nDownstream of the jump the viscous flow separates in response to the pressure rise, and forms a constant pressure mixing region leading into the near wake. As an illustrative example the method is applied to an adiabatic circular cylinder at [...] = 6, and the results are compared with the experimental measurements of Dewey and McCarthy. This method can be extended to non-adiabatic bodies, and to slender bodies with smooth bases, provided that the radius of curvature is large compared to the boundary layer thickness." }, { "name": "Krane, Stanley Garson", "degree": "PhD", "year": "1966", "title": "Studies on the Biosynthesis of Studies of \u00d8X174 Coat Protein", "advisor": "Sinsheimer, Robert L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-131251", "creators": [ { "name": { "family": "Krane", "given": "Stanley Garson" }, "id": "Krane-Stanley-Garson", "display_name": "Krane, Stanley Garson" } ], "advisors": [ { "name": { "family": "Sinsheimer", "given": "Robert L." }, "id": "Sinsheimer-R-L", "role": "advisor", "display_name": "Sinsheimer, Robert L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "bioch" ], "doi": "10.7907/1MXF-6632", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA serum blocking power (SBP) assay for [phi]X174 coat protein, which depends on the ability of whole phage or certain phage components to combine with antiphage serum, was developed. This assay registers complete [phi]X, both viable and nonviable, and 70S particles, but not chemically prepared 5S subunits.\r\n\r\nStudies on the growth of wild type [phi]X, at 37[degrees], showed that SBP synthesis begins at about 5 min, under conditions such that the eclipse ends at 6 to 8 min. Although the curves for SBP and intracellular phage growth have the same shape, the titer of SBP phage equivalents exceeds that of infectious progeny particles at all times. The excess SBP is found in the form of 70S particles, complete but noninfectious phage, and subunits that sediment at about 15S.\r\n\r\nChloramphenicol, 5-fluorouracil deoxyriboside, and phleomycin when present at the time of infection each produce essentially complete inhibition of SBP synthesis. These results suggest that at least one complete RF molecule (the double stranded form of [phi]X DNA) must be made in order for SBP synthesis to occur.\r\n\r\nSeveral temperature sensitive [...] mutants were studied for their ability to produce SBP at 40[degrees]C (nonpermissive conditions for production of infectious phage). Most of the twenty-six mutants examined did make SBP at 40[degrees]C; however, mutant [...] 79 definitely did not.\r\n\r\nStudies were made on the physical state of the SBP synthesized, at 40[degrees]C, by the mutants [...] Y, 9, and [...] 4 by the technique of sucrose gradient velocity centrifugation. The results showed that [...] Y, and [...] 9 make their SBP principally in the form of subunits that sediment at approximately 15S. The mutant [...] 4 makes its SBP principally in the form of particles that sediment at 71S. The [...] 4 71S particles may contain both DNA and protein." }, { "name": "Lee, Jen-shih", "degree": "PhD", "year": "1966", "title": "Application of Finite Elastic Theory to the Deformation of Cylindrical Tubes", "advisor": "Fung, Yuan-cheng; Frasher, Wallace G.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-150440", "creators": [ { "name": { "family": "Lee", "given": "Jen-shih" }, "id": "Lee-Jen-shih", "display_name": "Lee, Jen-shih" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Frasher", "given": "Wallace G." }, "id": "Frasher-W-G", "role": "advisor", "display_name": "Frasher, Wallace G." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HM2E-AX28", "abstract": "In Part I three types of symmetrical deformations of thin cylindrical rubber tubes are discussed. In the first type a rubber tube is deformed into another circular cylindrical tube of different length and diameter by simultaneous inflation and extension of the tube. This deformation is useful in determining the mechanical properties of tube-like material and it was found that Rivlin-Saunder form of strain-energy fitted a particular latex rubber used in our experiments. The second and third types of deformation are a tube deformed by a longitudinal stretching or an increase in internal pressure to a curved surface of revolution. A number of numerical examples were worked out with a view toward designing experiments to determine mechanical properties of short cylindrical tubes.
\r\n\r\nIn Part II experimental studies on the overall mechanical properties of large blood vessels are presented. Two Lagrangian stresses and two extension ratios are used to describe the stress and strain states of the vessels subjected to symmetrical deformations. The interested deformation range is about ten to twenty percent in the neighborhood of the natural state.
\r\n\r\nTests consisted of (1) a longitudinal stretching while the diameter of the vessels was maintained, (2) a lateral distension with the length of the vessels unchanged, and (3) repeated stretching of the vessels at low frequency.
\r\n\r\nThe first two tests show that the stress-strain law of the vessels tested is highly nonlinear and the vessels behave more rigidly in the longitudinal direction than in the lateral direction. The last test shows that the vessels are more likely to behave as a plastic elastic metal and a higher tangential modulus was observed for the vessels stretched at a smaller oscillation amplitude.
" }, { "name": "Letcher, John Seymour", "degree": "PhD", "year": "1966", "title": "Transverse Hydrodynamic Forces on Slender Bodies in Free-Surface Flows at Low Speed", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112005-154228", "creators": [ { "name": { "family": "Letcher", "given": "John Seymour" }, "id": "Letcher-John-Seymour", "display_name": "Letcher, John Seymour" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M8NJ-KC21", "abstract": "The forces and moments on a moving body partially immersed in the surface of a deep ocean of heavy fluid are considered in the limit of small Froude number, F. Asymptotic expressions for velocity potential and free surface elevation are developed. The choice of the first terms of the asymptotic sequence is indicated by the behavior, at small F, of the classical results of \"small disturbance theory\" - analysis starting from the linearized free-surface boundary conditions. It is found that the leading terms depend on the local disturbance, which can be expanded as a power series in F. The wave pattern contributes higher-order terms which are not analytic about F = 0; only estimates of the order of these terms are obtained. Consequently the present work does not estimate drag but is confined to consideration of transverse forces and moments.\r\n\r\nOnce the asymptotic sequence is assumed, perturbation of the exact equations and boundary conditions about F = 0 is straightforward. The zero-order potential is that of the \"reflection-plane\" model of Davidson. For a restricted class of shapes, the slender body theory is applied to the zero-order and first-order problems. A general method is developed using conformal mapping to solve the first order problem for sufficiently slender shapes of arbitrary cross-section. This method is applied to two particular shapes, viz. a wing of zero thickness and a half-submerged body of revolution, both in sideslip. The correction to the reflection plane model is found to be generally quite small in the range of F for which this theory is expected to apply." }, { "name": "Lindsey, Gerald Herbert", "degree": "PhD", "year": "1966", "title": "Hydrostatic Tensile Fracture of a Polyurethane Elastomer", "advisor": "Williams, Max L.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11232005-113650", "creators": [ { "name": { "family": "Lindsey", "given": "Gerald Herbert" }, "id": "Lindsey-Gerald-Herbert", "display_name": "Lindsey, Gerald Herbert" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K12J-X907", "abstract": "The investigation of fracture of polymeric materials in hydrostatic tensile fields constitutes an avenue of approach to the study of fracture in more general three-dimensional environments. The advantages created by the symmetry of the stress field are considerable and, in one of the cases studied, facilitates a theoretical treatment that includes large deformations, which are characteristic of this class of materials.\r\n\r\nThe analysis is developed through the concept of fracture originating from a flaw, which in this instance is taken to be a spherical cavity. Through the application of energy principles, a theoretical prediction of ultimate strength is made for hydrostatic tensile fields.\r\n\r\nExperiments were conducted to demonstrate the existence of such flaws and to evaluate the theory. Results of the tests on specimens containing both residual flaws and artificially inserted ones indicate a fundamental difference in behavior as contrasted with cracks.\r\n\r\nAn explanation is given linking experimental results and theoretical predictions. It is based on the concept that a flaw \"grows\" in the material under load using the cavity as a nucleating point. Upon this hypothesis is built a theory of rupture in which planar cracks grow radially from the center of the cavity in the form of Saturn-ring cracks." }, { "name": "Lissaman, Peter Barry Stuart", "degree": "PhD", "year": "1966", "title": "A Linear Solution for the Jet Flap in Ground Effect", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302002-123622", "creators": [ { "name": { "family": "Lissaman", "given": "Peter Barry Stuart" }, "id": "Lissaman-Peter-Barry-Stuart", "display_name": "Lissaman, Peter Barry Stuart" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "co-advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PWFF-E933", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe paper presents the solution of the problem of the Jet Flap airfoil in a plane inviscid flow in the presence of the ground.\r\n\r\nThe basic flow equations are derived and the non-linearity of the boundary conditions are discussed. The problem is then linearized as in thin airfoil theory. By a conformal transformation the flow field is mapped into one having very simple geometry. The singularities of the mapping are identified and the asymptotic character of the flow fields derived. The basic integro-differential equation is developed; this has singular Hilbert type kernels and discontinuous boundary conditions.\r\n\r\nBy considerations of the second order effects, significant relationships between the lift slopes with angle of attack, with jet angle and jet coefficient are developed. These are further simplified by introduction of a new geometrical parameter developed from the mapping.\r\n\r\nThe lift coefficient of the airfoil is expressed in three parts, of which two may be evaluated in simple closed form. The remaining part depends on the solution of the integro-differential equation. This equation is then solved at N points by assuming a piecewise smooth velocity distribution and generating an N x N matrix: numerical results are obtained from an IBM 7094 computer. It is proved that this approximation converges to the exact solution.\r\n\r\nThe limiting cases, when the height to chord ratio, h/c, or jet coefficient, C[subscript J], approach zero or infinity are developed, exploiting the decomposition of the lifting components; and an asymptotic result for small C[subscript J] is presented.\r\n\r\nA linearized theory for wake blockage is given, which also gives an indication of the restrictions on the various parameters implied by the basic linear approach.\r\n\r\nThe results for [...] correlate excellently with Spence's solution for [...]. For low values of h/c the results agree quite well with the limited applicable test data." }, { "name": "Murthy, K. R. Ananda", "degree": "PhD", "year": "1966", "title": "A Possible Analytical Explanation for the Micrometeorite Concentration near the Earth", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-144237", "creators": [ { "name": { "family": "Murthy", "given": "K. R. Ananda" }, "id": "Murthy-K-R-Ananda", "display_name": "Murthy, K. R. Ananda" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D8XP-4Q06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe Keplerian motion of a single particle in a dissipating medium, such as air, is analysed and a theory of micrometeorite capture and resulting orbital lifetime is developed. The equations of motion are derived for a planar, two-dimensional model, and all orbital variables are assumed to be perturbed slightly from their Keplerian values. The equations are then linearized and solved. Then a statistical model of the interplanetary micrometeorite flux is developed in which the distribution of velocities at infinity relative to the earth and masses of the particles are taken into account. The velocity distribution is taken to be [...]. The distribution of the masses is taken as a constant number of particle flux M(m) at infinity. Finally, this statistical model is combined with the theory of capture and lifetime to furnish a possible explanation for the micrometeorite concentration near the earth." }, { "name": "Olson, Mervyn Daniel", "degree": "PhD", "year": "1966", "title": "Supersonic Flutter of Circular Cylindrical Shells", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022005-075701", "creators": [ { "name": { "family": "Olson", "given": "Mervyn Daniel" }, "id": "Olson-Mervyn-Daniel", "display_name": "Olson, Mervyn Daniel" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/32AP-C463", "abstract": "Various experimental and theoretical studies on the supersonic flutter of circular cylindrical shells are discussed.
\r\n\r\nResults of experiments in the Mach number range 2.5 - 3.5 are presented. Three shells with radius-to-thickness ratios of 2,000 were subjected to radial external pressure loadings and to combinations of axial compressive loading and internal pressurization while in the presence of an external axially-directed supersonic flow.
\r\n\r\nSmall amounts of internal pressurization were very stabilizing with respect to flutter, but moderate amounts reduced stability to the unpressurized level. However, high internal pressures completely stabilized the shells. The axial compressive loading was slightly destabilizing for moderate amounts of internal pressurization.
\r\n\r\nThe flutter modes (which were standing waves in the axial direction with zero, one or two circumferential nodal lines) contained many waves around the circumference (of the order of 20) that travelled in the circumferential direction. This circumferentially travelling wave phenomenon possibly results from the nonlinear nature of cylindrical shells.
\r\n\r\nModel integrity was not threatened by even the most violent flutter which occurred just prior to buckling under radial external pressure loading and just after buckling under axial compressive loading. Buckled portions of a shell did not flutter. It appears that the large local curvatures encountered in the buckling of a cylindrical shell tend to stabilize the shell locally. However, it also appears that the localized buckling usually encountered in practice reduces the stability of any unbuckled regions of the shell.
\r\n\r\nThe experimental flutter boundaries are compared with various theoretical predictions. Following Voss a modal analysis which satisfies the so-called freely supported shell boundary conditions is used in conjunction with different aerodynamic approximations - namely piston theory and the potential theory of Leonard and Hedgepeth. It was found that the pressurized cylindrical shells fluttered at a lower level of free stream energy than predicted by the theory. Of the two results, that using piston theory appears to correspond closest to the experiment both in stability boundary and in critical values of circumferential wave number. Both predictions yield a larger stabilizing influence of the shell internal pressure than observed in the experiment.
\r\n\r\nAn analysis is presented for calculating the final limiting amplitudes of flutter based on a two-mode, piston theory approximation. A Galerkin procedure is used to reduce the nonlinear shallow shell equations of Marguerre to two coupled nonlinear ordinary differential equations for the modal amplitudes. An approximate limit cycle solution to these equations is obtained by the method of Krylov and Bogoliubov. The results indicate that for practical purposes cylindrical shell flutter does not occur below the stability boundary for infinitesimal disturbances. The limit cycle amplitudes predicted by this analysis seem to agree very well with the experimental ones. The results further indicate that the flutter amplitude, frequency and mode shape should change discontinuously (or jump) as the aerodynamic pressure is increased beyond the value for first flutter.
" }, { "name": "Puhl, Andreas", "degree": "Engineering Degree", "year": "1966", "title": "Hypersonic Boundary Layer Flow Around a Sharp Corner", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11182005-111451", "creators": [ { "name": { "family": "Puhl", "given": "Andreas" }, "id": "Puhl-Andreas", "display_name": "Puhl, Andreas" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2TPX-DD83", "abstract": "An experimental investigation was conducted in the GALCIT Mach 8 hypersonic wind tunnel, in order to study the behavior of an axisymmetric hypersonic, laminar boundary layer flow undergoing a rapid expansion at the juncture of a cone-cylinder body of revolution at zero angle of yaw. Major emphasis was placed on the acquisition of detailed data near the corner where extreme changes in the flow properties were expected. All tests were carried out for two different reservoir pressures but equal total temperature. The basic measurements consist of the model surface pressure and the pitot pressure covering the entire flow field of interest. These informations with certain assumptions were sufficient to construct the flow field.\r\n\r\nThe surface pressure distribution is in total disagreement with the potential theory from three boundary layer thicknesses upstream of the corner to about fifteen boundary layer thicknesses downstream. The expansion is not concentrated near the corner but extended over the above-mentioned region which is about one and a half cylinder radii long. The pressure immediately downstream of the corner is about seven-tenths of the pressure on the cone, in construct to the two-tenths as predicted by the potential theory." }, { "name": "Sorrell, Furman Yates, Jr.", "degree": "PhD", "year": "1966", "title": "On the Generation of Shock Waves in an Inverse Pinch", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-155713", "creators": [ { "name": { "family": "Sorrell", "given": "Furman Yates, Jr." }, "id": "Sorrell-Furman-Yates", "display_name": "Sorrell, Furman Yates, Jr." } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZCDM-SF32", "abstract": "A problem inherent in magnetic shock tubes is the difficulty of achieving separation of the driving current sheet and the shock wave. If such devices are to be applied to produce shock waves for experimentation, then separation will usually be a necessary requirement. In the present experiments in an inverse pinch shock tube, preliminary measurements showed that not only was separation not achieved, but under certain conditions the shock was actually found to be located far behind the front of the current sheet. This appeared to be a paradoxical case of the shock wave pushing the piston. Moreover, measurements of the current sheet velocity indicated that the interaction of the current sheet with the gas should be strong enough to sweep up all the gas encountered by the current sheet and thus to produce a shock wave moving ahead of it. In order to find explanations for the absence of separation and for some other puzzling aspects of these early experiments, further measurements were made to study in more detail the processes taking place in the device. These included measurements of the radial electric field with electrostatic probes and of the ionization levels by the technique of spectral line broadening. The results of these measurements show that the degree of ionization is surprisingly low and that the amount of gas leaking through the current sheet is significantly high in some cases. The conclusion is then reached that although the so-called \"snowplow model\" is successful in predicting the current sheet velocity, it does not lead to the correct picture of the physical processes taking place. Finally, conditions for which separation may be achievable are inferred from the experiments." }, { "name": "Tong, Pin", "degree": "PhD", "year": "1966", "title": "Liquid Sloshing in an Elastic Container", "advisor": "Fung, Yuan-cheng; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-092311496", "creators": [ { "name": { "family": "Tong", "given": "Pin" }, "id": "Tong-Pin", "display_name": "Tong, Pin" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WYZD-Q384", "abstract": "The motion of a liquid in a flexible container is important for rocket structural dynamics. The purpose of this paper is to study the dynamic response of the liquid, the sloshing frequencies and the stability of the free surface of the liquid in an elastic container.
\r\n\r\nThe variational principle for the problem of an incompressible, inviscid fluid in an elastic container is presented by considering the pressure energy of the fluid, the surface energy, and the Lagrangian of the elastic thin shell. The corresponding linearized equations are studied in terms of eigenvalues and eigenfunctions.
\r\n\r\nThe effects of the gravitation, the surface tension, the rigidity of the container, the free surface contact angle and its dynamic variation, on the natural frequencies and the stability of the free surface are discussed.
\r\n\r\nIt is found that the flexibility of the container always lowers the natural frequencies and also induces a mean oscillatory motion of the liquid that creates an oscillatory force on the container in the vertical direction. The equilibrium contact angle and its dynamic variation have an important effect on the limit of stability.
\r\n\r\nThe motion of a liquid in a circular cylindrical container with a flat flexible bottom is worked out in detail analytically by means of eigenfunctions. Some results are presented graphically. A numerical scheme using finite elements method is developed for an arbitrary container. Methods for improving the solution systematically are indicated.
\r\n" }, { "name": "Williams, Richard R.", "degree": "PhD", "year": "1966", "title": "Application of the Two Variable Expansion Procedure to the Commensurable Planar Restricted Three-Body Problem", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-082219", "creators": [ { "name": { "family": "Williams", "given": "Richard R." }, "id": "Williams-Richard-R", "display_name": "Williams, Richard R." } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PYNV-5723", "abstract": "The nearly commensurable case of the planar restricted three-body problem is treated by application of the two variable expansion procedure. The polar angle of the infinitesimal body, rather than the time, is taken as the independent variable. A set of four coupled first order differential equations, which govern the long-period behavior of the orbital elements, is obtained by imposing the requirement that the assumed form of the expansions must be self-consistent. The independent variable in these equations is the \"slow variable\". It is then found that the short-period perturbations of the motion of the infinitesimal body do not contain small divisors or secular terms.\r\n\r\nApproximate solutions for the orbital elements are given, for two different cases. Both libratory and non-libratory solutions are found, depending upon the initial conditions. Numerical results are calculated from these solutions, and are compared to numerical computations recently reported in the literature." }, { "name": "Ahmed, Nazeer", "degree": "Engineering Degree", "year": "1965", "title": "Work Hardening During Pyramidal Slip in Zinc", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062002-155405", "creators": [ { "name": { "family": "Ahmed", "given": "Nazeer" }, "id": "Ahmed-Nazeer", "display_name": "Ahmed, Nazeer" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/92AW-H890", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe elastic stress field and energy associated with an infinite straight edge dislocation in a hexagonal crystal parallel to the line of intersection of the (0001) and the [...] planes with its Burger's Vector in the [...] plane and the [...] direction is determined taking into account the anisotropy of the crystal. The nature of the solution is found to depend on the relative numerical values of the five independent elastic constants. All possible solutions are investigated and the solution for an isotropic crystal determined as a limiting case.\r\n\r\nThe interaction force between two edge dislocations of opposite sign gliding on consecutive glide planes is studied. Expressions for the total energy of such a dislocation dipole are developed. Numerical results are given at three temperatures,-77[degrees]C, 31[degrees]C and 139[degrees]C.\r\n\r\nThese results are used to develop a quantitative theory of strain hardening in a single zinc crystal subjected to uniaxial tension or compression in the direction of its crystallographic axis. It is proposed that such strain hardening is produced by the dislocation dipoles that are formed on dislocations which are moving on any one of the six [...] pyramidal planes when they intersect similar dislocations which are moving on other planes of the same type. The density of such dislocation dipoles as a function of the uniaxial strain along the crystallographic axis is determined and possible future avenues of research that could utilize these results indicated.\r\n" }, { "name": "Lau, Jark Chong", "degree": "Engineering Degree", "year": "1965", "title": "Experimental Study of the Reattachment Pressure Rise at Subsonic Speeds", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04172003-084523", "creators": [ { "name": { "family": "Lau", "given": "Jark Chong" }, "id": "Lau-Jark-Chong", "display_name": "Lau, Jark Chong" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P8AX-3102", "abstract": "An experimental study was made of the problem of separated flow with reattachment at subsonic speeds in various geometrical configurations. It was found that when the boundary layer thickness at separation was small, the values of the reattachment pressure rise coefficient agreed with those from the Korst-Chapman theory. The importance of the relative positions of the transition and reattachment was investigated. In the free shear layer, transition occurred at Reynolds numbers as low as 3 x 10[superscript 3], based on distance from the separation point." }, { "name": "Peck, Jerry Clifford", "degree": "PhD", "year": "1965", "title": "Plane-Strain Diffraction of Transient Elastic Waves by a Circular Cavity", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-144633", "creators": [ { "name": { "family": "Peck", "given": "Jerry Clifford" }, "id": "Peck-Jerry-Clifford", "display_name": "Peck, Jerry Clifford" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GDNE-E586", "abstract": "The plane-strain problem of the diffraction of a transient plane dilatation wave by a circular cavity in an elastic medium is treated. The method used determines the (total) solution only in the shadow zone, i.e., those points which cannot be connected to the source of disturbance by straight-line rays. Numerical results are obtained for the velocities and displacements on the \"back\" surface of the cavity caused by a step-stress incident wave.\r\n\r\nThe analysis is based on a method devised by Friedlander (see his book Sound Pulses, Cambridge, 1958) for the analogous acoustic diffraction problem. This method converges most rapidly at short time, in contrast to Fourier series methods. The Friedlander method essentially employs integral transforms on both time and [Theta], the circumferential coordinate. In the shadow zone, the [Theta]-inversion can be performed by residue theory, the residues resulting from poles at the roots of a \"frequency equation.\" The roots are infinite in number, and may be regarded as forming a dispersion spectrum relating the frequencies and angular wave numbers of a series of circumferential propagation modes. The time-transform inversion is carried out by contour integration and subsequent numerical evaluation.\r\n\r\nThe transient response results are found to compare well with the Fourier-series solutions at moderate to long times, but at short time the differences are marked, as would be expected. The fact that the present technique yields good long-time results suggests it is even more powerful than might be expected. The major limitation of the numerical method is its restriction to the shadow zone." }, { "name": "Spitzer, Robert Edward", "degree": "Engineering Degree", "year": "1965", "title": "Measurements of Unsteady Pressures and Wake Fluctuations for Flow Over a Cylinder at Supercritical Reynolds Number", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-093919", "creators": [ { "name": { "family": "Spitzer", "given": "Robert Edward" }, "id": "Spitzer-Robert-Edward", "display_name": "Spitzer, Robert Edward" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WT4K-6337", "abstract": "A test was conducted to measure and map the unsteady pressure fluctuations over the surface of a smooth, cantilevered, circular cylinder in the supercritical Reynolds number range from 2.5 x 105 to 7.5 x 105. Lift fluctuations were measured, hot-wire wake surveys were made, and the effects of boundary-layer tripping were investigated. Power spectral densities were computed from recordings of the fluctuations, and cross-correlation coefficients were determined.
\r\n\r\nPressure fluctuations were found to be small in magnitude but with relatively high axial correlation except at the points of flow separation. Definite evidence of periodicity was found in the pressure fluctuations excluding those in the region of flow separation. Fluctuating lift was found to be random in nature in the supercritical regime. Power spectra of wake velocity fluctuations after transition showed largely turbulent patterns with perhaps some dominance at Strouhal number near 0.4 seen on occasion. Localized boundary-layer tripping caused earlier flow separation, significant increases in pressure and lift fluctuations, a greater degree of axial correlation, and a shift in the power spectra to indicate periodic effects.
" }, { "name": "Swedlow, Jerold Lindsay", "degree": "PhD", "year": "1965", "title": "The Thickness Effect and Plastic Flow in Cracked Plates", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-100109", "creators": [ { "name": { "family": "Swedlow", "given": "Jerold Lindsay" }, "id": "Swedlow-Jerold-Lindsay", "display_name": "Swedlow, Jerold Lindsay" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0WVE-W364", "abstract": "Over a range of plate thickness, it is well known that the fracture behavior of flat plates is substantially different from that predicted by classical fracture analyses. Finiteness of the plate thickness causes a variety of failure mechanisms to occur, and qualitative features of the associated stress and strain fields may be deduced. It is indicated that both the three-dimensional nature of the stress field and the plastic deformations will be needed for an accurate prediction of the thickness effect.\r\n\r\nAs a contribution to the three-dimensional analysis, an appropriate elastic boundary value problem is given limited consideration. It is observed that the three in-plane stresses can be singular, in accord with the two-dimensional results, but the transverse components appear to be bounded at the crack tip.\r\n\r\nEquations which include plastic behavior are outlined, and a plane stress problem is solved using numerical methods. Comparison with analytical and experimental results is made and found to be satisfactory. One important result indicates that, compared to the elastic solution, the intensity of stress at the crack point decreases with load, while that for strain increases.\r\n\r\nThe results do not include determination of a fracture stress, as this further step requires the development of an elastoplastic fracture criterion. Comments on this extension are included, together with other aspects of future work." }, { "name": "Van Atta, Charles William", "degree": "PhD", "year": "1965", "title": "Spiral Turbulence in Circular Couette Flow", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262004-102054", "creators": [ { "name": { "family": "Van Atta", "given": "Charles William" }, "id": "Van-Atta-Charles-William", "display_name": "Van Atta, Charles William" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73GQ-A629", "abstract": "Under certain conditions, the fluid motion between counter-rotating concentric cylinders is made up of alternate helical stripes of laminar and turbulent flow. The present experiments show that, over a large range of cylinder Reynolds numbers, this helical pattern of turbulence rotates steadily at very nearly the mean angular velocity of the two cylinders. When the speed of the outer cylinder is held fixed and the speed of the inner cylinder increases from rest in the opposite direction, spiral turbulence follows a catastrophic breakdown of the toroidal vortices arising from Taylor instability.\r\n\r\nThe ultimate objective of the present experiments is to measure the local rate of energy transfer between the turbulence and the mean motion in a typical spiral turbulent flow. The working fluid is air, and the instrumentation consists of hot-wire anemometers together with a variety of devices for operating on the resulting signals. Each cycle of the mixed laminar-turbulent flow (as observed by a probe mounted on one or the other cylinder) is treated as a member of an ensemble of realizations. The energy transfer (in a coordinate system rotating with the mean velocity of the turbulence) can be determined by averaging over a large number of instantaneous velocity samples taken at corresponding points in successive cycles of the turbulence.\r\n\r\nAfter some exploratory measurements, particular flow was selected for which the laminar-turbulent interfaces were sharply delineated across the entire annular gap and for which the dispersion in interface location was a minimum. This flow is about half laminar and half turbulent: it is characterized by a nose of turbulence associated with the leading interface and projecting into the laminar region near the outer cylinder, while a corresponding tail near the inner cylinder is associated with the trailing interface. The helical pattern is lefthanded and makes an angle of about 62 degrees with the axis of the cylinders.\r\n\r\nFor the flow in question, analog voltage signals from a calibrated array of four hot wires were first recorded on magnetic tape. Several thousand cycles of turbulence were recorded at each of 17 different radial positions. Sampled values from these signals were then obtained and stored in digital form on magnetic tape, and were finally processed by a large electronic computer to restore the voltage data to the original laboratory units. The total amount of didital information available to describe the turbulence is roughly 180,000,000 bits. The amount of noise introduced into the individual sampled voltages by the recording, playback, digitizing, and processing operations so far carried out is believed to be no more than 3 parts in 10,000.\r\n" }, { "name": "Wu, Jain-Ming", "degree": "PhD", "year": "1965", "title": "A Satellite Theory and its Applications", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-104844", "creators": [ { "name": { "family": "Wu", "given": "Jain-Ming" }, "id": "Wu-Jain-Ming", "display_name": "Wu, Jain-Ming" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2XH7-1828", "abstract": "A theory of an Earth satellite has been developed by considering the Earth's bulge, atmospheric drag and the rotation of the atmosphere simultaneously. The equations of motion have been set up on a tilted equatorial plane coordinate system. All of the orbital variables have been expanded in a series in terms of a perturbative force parameter based on the Keplerian orbit. These equations have been linearized and then solved. By means of geometrical arguments, all of the above solutions have been expressed in the form of conventional orbital elements. In the limiting case, these solutions agree with the classical values. One previously neglected effect, the rotation of the line of apsides by drag, is identified and evaluated. The results have been used to show the correction due to the effect of the above-mentioned forces on the Earth's gravitational potential." }, { "name": "Arenz, Robert James", "degree": "PhD", "year": "1964", "title": "Theoretical and Experimental Studies of Wave Propagation in Viscoelastic Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09072002-150755", "creators": [ { "name": { "family": "Arenz", "given": "Robert James" }, "id": "Arenz-Robert-James", "display_name": "Arenz, Robert James" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E8KM-6M98", "abstract": "The phenomenon of wave propagation in viscoelastic materials is investigated both theoretically and experimentally, with attention directed to two areas. First, analytical methods of solution are developed for certain wave propagation problems in one and two dimensions utilizing realistic material properties. This is accomplished by use of time-dependent material property characterization through a Dirichlet series representation to overcome the limitations of the widely-used simple spring and dashpot models involving two or three elements. The Laplace transformed solutions are then inverted by an extension of the Schapery collocation method to dynamic situations.\r\nThe second topic deals with dynamic photoelasticity applied to viscoelastic materials. It is shown that the relationships between stress optic and strain optic coefficients for linearly viscoelastic materials can be formulated. Then the time-dependent birefringence characteristics of a typical low modulus polymer material are determined from constant strain rate tests for a full range of dynamic loading rates by taking advantage of the time-temperature shift phenomenon. Much recent work in dynamic photoviscoelasticity has been based on static calibrations only. Hence to put the technique on a firm foundation and indicate the general necessity of including the time dependency in treatment of material properties, a comparison is made of predicted fringe patterns with experimental results for both one- and two-dimensional situations. The cases considered are the rod and semi-infinite plate geometries under quasistep pressure inputs, for which viscoelastic solutions are obtained from the wave propagation analysis in the first part of the thesis. The results indicate the feasibility of quantitative photoviscoelasticity for dynamic stress analysis." }, { "name": "Baganoff, Donald", "degree": "PhD", "year": "1964", "title": "Experiments on the Wall-Pressure History in Shock Reflection Processes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-083236", "creators": [ { "name": { "family": "Baganoff", "given": "Donald" }, "id": "Baganoff-Donald", "display_name": "Baganoff, Donald" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XK5D-HZ55", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe normal reflection of a plane shock from a plane wall is investigated experimentally using a pressure gauge which has a risetime of 0.1 [....] and no overshoot. Pressure histories of 5 [.....] duration can be obtained with this gauge. The experiments were conducted on the end wall of the GALCIT 17-in.-diameter shock tube.\r\n\r\nExperimental results for three aspects of the reflection process are discussed: (1) profile for the reflected shock front, (2) effect of a cold wall, and (3) effect of a real gas.\r\n\r\nIt is concluded that the effect of a cold wall must play a comparatively minor role in the reflection process since the thickness of the recorded profile is comparable to the thickness of the incident shock, and the pressure jump across the profile is about 85 per cent of the ideal value. Also, the pressure history immediately behind the reflected shock can be approximated by boundary layer theory. The effect of a real gas was studied in carbon dioxide and it is shown that the relaxation process behind the incident shock produces a large effect on the recorded pressure history which provides a method of measuring the vibrational relaxation time in carbon dioxide for high temperatures." }, { "name": "Burden, Harvey Worth", "degree": "Engineering Degree", "year": "1964", "title": "Some Effects of Secondary Injection of Gases into a Supersonic Flow", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102002-141125", "creators": [ { "name": { "family": "Burden", "given": "Harvey Worth" }, "id": "Burden-Harvey-Worth", "display_name": "Burden, Harvey Worth" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DRZK-W405", "abstract": "An experimental investigation was conducted in order to determine some of the effects of injection of a secondary stream of gas into a supersonic primary airstream. The flow fields behind an orifice producing essential two-dimensional flow and behind that producing full three-dimensional flow were studied. The resulting shock patterns, wall static pressure profiles, and flow field characteristics are described,and use is made of a theoretical injectant penetration height to non-dimensionalize the results as much as possible. It has been possible to draw some conclusions concerning the nature of the flow field and pressure field disturbances caused by secondary injection." }, { "name": "Bush, William B.", "degree": "PhD", "year": "1964", "title": "On the Viscous Hypersonic Blunt-Body Problem", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102002-143008", "creators": [ { "name": { "family": "Bush", "given": "William B." }, "id": "Bush-William-B", "display_name": "Bush, William B." } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QCBK-ZD50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe viscous hypersonic flow past an axisyrnmetric blunt-body is analyzed based upon the Navier-Stokes equations for a perfect gas having constant specific heats, a constant Prandtl number, P, whose numerical value is of order one, and a viscosity varying as a power, [...], of the absolute temperature, as the free-stream Mach number, M, and the freestream Reynolds number based on the body nose radius, R, go to infinity, and [...] (where [gamma] is the ratio of the specific heats) and [...] go to zero.\r\n\r\nThrough the use of strict asymptotic expansions, the behavior of the flow in the three distinct regions that comprise the interior of the \"shock structure\" is found, as well as for the one, two, or three regions that make up the \"shock layer\" depending on whether the quantity [...] is equal to [...], equal to [...], or greater than [...], respectively." }, { "name": "Evensen, David Arthur", "degree": "PhD", "year": "1964", "title": "Non-Linear Flexural Vibrations of Thin Circular Rings", "advisor": "Sechler, Ernest Edwin; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-165232", "creators": [ { "name": { "family": "Evensen", "given": "David Arthur" }, "id": "Evensen-David-Arthur", "display_name": "Evensen, David Arthur" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7D5J-3C40", "abstract": "The non-linear flexural vibrations of thin circular rings are analyzed by means of the appropriate \"shallow shell\" equations. These partial differential equations are reduced to non-linear ordinary differential equations by assuming vibration modes and applying Galerkin's procedure. Vibrations involving primarily a single bending mode are investigated for three distinct cases, and the results indicate that the basic features of the problem are exhibited by an inextensional analysis.\r\n\r\nThis information is then applied to simplify the analysis of vibrations in which several modes participate. A study of \"self-coupled\" bending modes shows that the single mode solution is valid only for certain combinations of amplitude and frequency: when the single mode exceeds a \"critical amplitude\", its companion mode is parametrically excited and participates in the motion.\r\n\r\nThe general inextensional case (involving an infinite number of modes) is examined for two important sets of forces, and possible solutions are shown to be the excitation of primarily one or two bending modes. Stability analyses of these solutions indicate that when certain restrictions are met, all other bending modes play only a minor part in the vibration.\r\n\r\nAn experimental study of the problem was also conducted. Theory and experiment both indicate a non-linearity of the softening type, the presence of ultraharmonic responses, and the appearance of the companion mode. Measurements of the steady-state response are in good agreement with the calculated values, and the experimentally determined mode shapes agree with the form of the assumed deflection.\r\n\r\nThe analytical and experimental results exhibit several features that are common to the non-linear vibration of axisymmetric systems in general and to circular cylindrical shells in particular." }, { "name": "Grimes, Charles Kenneth", "degree": "PhD", "year": "1964", "title": "Studies on the Propagation of Elastic Waves in Solid Media", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192002-160252", "creators": [ { "name": { "family": "Grimes", "given": "Charles Kenneth" }, "id": "Grimes-Charles Kenneth", "display_name": "Grimes, Charles Kenneth" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EW57-KB61", "abstract": "Several aspects of three basic problems concerned with the propagation of elastic waves in solid media are explored.\r\n\r\nStress and displacement correction terms resulting from application of a subsonically moving point load to the free surface of the infinite half-space are obtained using Fourier transform techniques (the load moves subsonically with respect to the longitudinal and transverse wave speeds). It is shown, for the supersonically travelling point load, that the solution is given, in the limit as the load velocity becomes large, by the well known solution of Sauter for the impulsive point load.\r\n\r\nAnalytic function theory is used to predict the existence of Rayleigh waves on the free surface of the infinite halfspace and Stoneley waves along the welded interface between two dissimilar solid media. A brief analysis shows that free-running waves are also possible on the interior surface of an infinitely long cylindrical cavity. These waves are dispersive, however, because of the introduction of a characteristic length.\r\n\r\nThe early and long time approximations for the hoop stress generated through scattering of a plane dilatational wave by a cylindrical cavity in an infinite medium are developed. Use is made of Friedlandler's Riemann surface representation (early time) and expansion in Fourier series (long time)." }, { "name": "Hegemier, Gilbert Arthur", "degree": "PhD", "year": "1964", "title": "Stability of Thin Cylindrical Shells Subjected to a Class of Axially Symmetric Moving Loads", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112002-121702", "creators": [ { "name": { "family": "Hegemier", "given": "Gilbert Arthur" }, "id": "Hegemier-Gilbert-Arthur", "display_name": "Hegemier, Gilbert Arthur" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4P8K-YN54", "abstract": "The stability of an infinite-length cylindrical shell subjected to a broad class of axially symmetric moving loads with constant velocity is studied by utilizing a large deflection Donnell theory. Special cases of the general loading function include the moving ring, step and decayed step loads.\r\n\r\nStability is defined on the basis of the boundedness or divergence of an infinitesimal nonsymmetric disturbed motion about an initial nonlinear steady-state symmetric response. Following the determination of the symmetric response, under this concept of stability, the analysis is reduced to a study of a system of linear partial differential equations or so-called variational equations; these are analyzed by use of a double Laplace transform technique and the original stability problem is replaced by a simpler one of determining the location of the poles of a certain function. A scheme for accomplishing this task is outlined. Extension of the method to include more exact equations of motion and to a class of static problems involving finite length shells is discussed.\r\n\r\nA related problem concerning a moving concentrated load on a nonlinear elastic cylindrical membrane (nonlinearity in both geometric and constitutive relations) and a string on a nonlinear foundation is discussed in an appendix to the text. Interesting analogies in both analysis and physical behavior of the string and shell systems are found." }, { "name": "Herzog, Robert Theodore", "degree": "Engineering Degree", "year": "1964", "title": "Nitrogen Injection into the Base Region of a Hypersonic Wake", "advisor": "Lees, Lester; Kubota, Toshi; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182002-115940", "creators": [ { "name": { "family": "Herzog", "given": "Robert Theodore" }, "id": "Herzog-Robert-Theodore", "display_name": "Herzog, Robert Theodore" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J4XP-F867", "abstract": "An experimental investigation was made of the changes occurring in the near wake of a cylinder at M = 6.0 when nitrogen was injected into the base region. The free stream Reynolds number based on cylinder diameter was 30,000 and the rate of injection was varied from zero to 3 percent of the frontal area free stream mass flow. Pitot pressure profiles across the wake, Schlieren photographs and measurement of the boundary layer separation point on the cylinder were used to define the changes in wake geometry. Static pressure and temperature surveys were made along the wake centerline starting at the base of the cylinder and continuing downstream to X/D = 6.0. The injection reduced the recompression in the neck region and left only a slight isentropic compression in place of the strong wake shock. The recirculation of mass in the base region was eliminated with approximately 1.5 percent injection.\r\n\r\nAn automated hot wire recording system which produced data suitable for computer reduction was developed and used to measure temperature. In order to reduce the measured wire temperature to total temperature an attempt was made to use a previously developed computer program. Deficiencies in this program are discussed with suggestions for improvements." }, { "name": "Levinson, Mark", "degree": "PhD", "year": "1964", "title": "Variational Principles and Applications in Finite Elastic Strain Theory", "advisor": "Blatz, Paul J.; Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-145537", "creators": [ { "name": { "family": "Levinson", "given": "Mark" }, "id": "Levinson-Mark", "display_name": "Levinson, Mark" } ], "advisors": [ { "name": { "family": "Blatz", "given": "Paul J." }, "id": "Blatz-P-J", "role": "advisor", "display_name": "Blatz, Paul J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PK58-HQ71", "abstract": "The variational principles of finite elastostatic strain theory are presented in a unified manner for both compressible and incompressible bodies. Whereas the principle of stationary potential energy, a restricted case of the general principle of Hu and Washizu, is valid for any elastic deformation, it is found that the principle of stationary complementary energy is valid only for infinitesimal elastic strains. Consequently, Reissner's Theorem is the appropriate stationary principle to use in finite elastic strain theory when the complementary strain energy density is to be the argument function.\r\n\r\nThe potential energy principle is applied to several problems dealing with the finite straining of a neo-Hookean material. All but one of these problems are concerned with plane strain deformations; the one other problem, in a spherical geometry, involves an unusual stability question. Approximate solutions are obtained for some mixed boundary value problems which are not amenable to the semi-inverse methods of solution frequently used in finite elastic strain theory.\r\n\r\nAnother plane strain problem, requiring more detailed stress information than can be obtained from the potential energy principle, is studied approximately by means of Reissner's Theorem." }, { "name": "Liu, Joseph Tsu Chieh", "degree": "PhD", "year": "1964", "title": "Problems in Particle-Fluid Mechanics", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172002-122957", "creators": [ { "name": { "family": "Liu", "given": "Joseph Tsu Chieh" }, "id": "Liu-Joseph-Tsu-Chieh", "display_name": "Liu, Joseph Tsu Chieh" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/11Y4-2H39", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe continuum equations describing the motion of a fluid containing small solid particles are discussed and stated. The examples considered fall into two categories: (1) when the fluid is incompressible and viscous, with simultaneous occurrence of particle-fluid momentum relaxation and fluid viscous diffusion; and (2) when the fluid can be considered as \"inviscid\" but compressible, with simultaneous occurrence of coupled particle-fluid momentum and thermal relaxations and fluid compressibility.\r\n\r\nUnder (1), the low Mach-number Rayleigh problem is studied. Many of the physical features of the non-linear steady (constant pressure) laminar boundary-layer problem are recovered from appropriate expansions from this exact solution. One obtains answers to questions about the modifications on the boundary layer growth and skin friction; particularly their transition from the \"frozen\" value near the leading edge, where the viscous layer is \"thin\" and the fluid viscous diffusion behaves as if in the absence of particles with the ordinary fluid kinematic viscosity,[.....], to the ultimate \"equilibrium\" value far downstream where the mixture then behaves as a single heavier fluid and viscous diffusion takes place with the \"equilibrium\" kinematic viscosity augmented by the particle density [.....].The uncoupled thermal Rayleigh problem (small relative temperature differences) is directly inferred, and this answers questions about the modifications on the surface heat-transfer rates and particularly about the possibility of similarity with the velocity boundary layer. Similarity of the two boundary layers is possible when, in addition to lateral diffusion effects being similar as indicated by Prandtl number unity, the streamwise relaxation processes must also be similar. The infinite flat plate oscillating in its own plane is studied, and appropriate expansions from the exact solutions point out how approximate treatment of periodic boundary layers in the absence of a mean flow may be made.\r\n\r\nUnder (2), the first-order small perturbation theory is discussed, leading from the equation for acoustic propagation to that for linearized supersonic flow. The two-dimensional steady case, or the Ackeret problem, is considered in detail. The Mach wave structure induced by a thin obstacle is deduced and shows a rapid damping of the disturbance along the \"frozen\" Mach wave (based on the sound speed of a gas in the absence of particles), both damping and diffusiveness along an intermediary Mach wave, and diffusiveness along the \"equilibrium\" Mach wave (based on the sound speed of an equilibrium mixture of gas and particles) and along which the bulk of the disturbance is carried to regions far from the obstacle. An exact form of the pressure coefficient is obtained for any surface shape (consistent with the linear theory), and involves a convolution integral of two Bessel functions with imaginary argument which is analytically evaluated. When the particle-fluid density ratio is small, the \"frozen\" and \"equilibrium\" Mach waves are very closely clustered together. A \"boundary layer technique\", based on the fact that changes across the Mach waves are rapid compared to changes along Mach waves, is then applied to obtain a simplified version of the linearized equation that describes Mach waves inclined toward the downstream direction only. While the Mach wave structure is consistent with the exact treatment, the pressure coefficient takes on the much simpler form of decreasing exponentials. The transition is, again, from the \"frozen\" value at the leading edge towards the \"equilibrium\" value in the downstream direction insofar as the surface shape permits.\r\n" }, { "name": "Mantle, Peter John", "degree": "Engineering Degree", "year": "1964", "title": "Spinning Symmetric Missiles in a Nonlinear Aerodynamic Field", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-102742", "creators": [ { "name": { "family": "Mantle", "given": "Peter John" }, "id": "Mantle-Peter-John", "display_name": "Mantle, Peter John" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YXWV-VV41", "abstract": "The case of a spinning symmetric body flying at a constant speed where the aerodynamic restoring moment is an arbitrary function of the angle of attack is examined. The analysis is twofold: first, the general problem is discussed, in suitable nondimensional form, to establish the generalized stability boundaries and, second, the attention is directed to the inverse problem whereby the pertinent aerodynamic parameters are extracted from a given bounded solution, suitable for use in data reduction. The general case of non-planar motion is examined and shown to be analogous to the classical orbital problems, differing only in the form of the governing potential function. The general solution is obtained in integral form and the special cases of linear aerodynamics and cubic restoring moments have been integrated and studied to reveal all the pertinent characteristics. The various combinations of potential, initial conditions and angular momentum (including that due to the impressed spin rate) are shown to determine whether or not the motion is planar, circular, elliptic or non-conic; stable or unstable and the various cases are categorized to aid the prediction of the motion of spinning symmetrical bodies acting under non-linear aerodynamic restoring moments." }, { "name": "Philippou, Demetrius", "degree": "Engineering Degree", "year": "1964", "title": "Near Minimum Energy Trajectories in the Two Fixed Force-Center Problem", "advisor": "Kevorkian, Jirair", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092002-154746", "creators": [ { "name": { "family": "Philippou", "given": "Demetrius" }, "id": "Philippou-Demetrius", "display_name": "Philippou, Demetrius" } ], "advisors": [ { "name": { "family": "Kevorkian", "given": "Jirair" }, "id": "Kevorkian-Jirair", "role": "advisor", "display_name": "Kevorkian, Jirair" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZXGH-NV43", "abstract": "The class of symmetric orbits with near minimum energy which originate very close to the earth and pass very close to a fixed moon of small mass are studied using asymptotic methods. An exact solution for the orbit is found using Bonnet's Theorem. This is an ellipse with the force centers as foci. Results obtained from the approximate solution are seen to agree exactly with the predictions of Bonnet's Theorem. The solutions thus obtained are the periodic solutions. A one dimensional study is undertaken as a guide to the planar problem." }, { "name": "Smithey, William John Henry", "degree": "Engineering Degree", "year": "1964", "title": "Optimum Thrust Programming for Low Thrust Devices", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102002-083146", "creators": [ { "name": { "family": "Smithey", "given": "William John Henry" }, "id": "Smithey-William-John-Henry", "display_name": "Smithey, William John Henry" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FGHG-HF41", "abstract": "The use of low thrust devices with continuous and discontinuous thrust programs is investigated to determine whether or not a discontinuous thrust program will provide a greater payload and structure mass fraction, where the program must impart a specified amount of energy to the satellite in a specified total time, starting from a circular parking orbit. A discontinuous thrust program is developed, based on the elliptic orbit, using a perturbation analysis, and a series solution is obtained which permits investigation of this program up to angles of one radian either side of the perigee of the elliptic orbit. These results are compared with a continuous thrust program which gave a spiral orbit. Under certain conditions, where storage batteries must be carried as part of the payload but are available for use during the thrust program, the discontinuous thrust program is found to provide a greater payload and structure mass fraction. Further investigation at angles greater than one radian either side of perigee appears to be warranted." }, { "name": "Tracy, Richard Ripley", "degree": "PhD", "year": "1964", "title": "Hypersonic Flow Over a Yawed Circular Cone", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-161203", "creators": [ { "name": { "family": "Tracy", "given": "Richard Ripley" }, "id": "Tracy-Richard-Ripley", "display_name": "Tracy, Richard Ripley" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RMWT-TH67", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA 10[degree] semi-apex, circular cone is tested in air at Mach 8 and at yaw angles to 24[degrees]; surface pressure, heat transfer, and pitot-pressure throughout the flow field are presented. The nominal surface temperature is 40% of the free stream stagnation temperature, and the Reynolds number, based on cone generator length, is varied from 0.5 x 10[^5] to 4.2 x 10[^5]. Heat transfer is measured at higher surface temperature ratios (up to 56%) and Reynolds numbers (up to 7.3 x 10[^5]) by reducing the free stream stagnation temperature. All raw data consist of continuous circumferential distributions of each quantity and are included in a supplement.\r\n\r\nThe surface pressure data are compared with the theories of Stone-Kopal and Cheng; Reshotko's theory of heat transfer to the windward generator is compared with experiment. The probe data delineate the boundary between viscous and inviscid flow and determine the shape of the outer shock wave as well as the secondary shocks which appear in the flow field at large yaw. The probe data are sufficient to determine the flow field in the plane of symmetry and permit an approximate representation of the Mach number profiles of the separated viscous flow in the leeward meridian plane beyond a moderate yaw angle." }, { "name": "Ahlstrom, Harlow Garth", "degree": "PhD", "year": "1963", "title": "Experiments on the Upstream Wake in Magneto-Fluid Dynamics", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-111323", "creators": [ { "name": { "family": "Ahlstrom", "given": "Harlow Garth" }, "id": "Ahlstrom-Harlow-Garth", "display_name": "Ahlstrom, Harlow Garth" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Lauritsen", "given": "Thomas" }, "id": "Lauritsen-T", "role": "member", "display_name": "Lauritsen, Thomas" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NAR6-M485", "abstract": "Measurements have been made of the perturbation magnetic field in front of a semi-infinite Rankine body moving parallel to a uniform impressed magnetic field in a conducting fluid. The purpose of these experiments was to investigate the so-called upstream wake effect which has been predicted by theory. It is believed that these are the first experiments in which the upstream wake was observed. Although the wake was found to exist as predicted when the Alfv\u00e9n number is greater than one, its decay behavior was remarkably different from that which was predicted. The solutions for infinite medium predicted that in the wake the perturbations should decay inversely as the distance from the body. However the experiments showed that the perturbations decayed exponentially. It was finally shown that this change in the decay behavior was an effect of the walls and the conducting material surrounding the fluid.
\r\n" }, { "name": "Anderson, William Judson", "degree": "PhD", "year": "1963", "title": "Studies in Panel Flutter at Higher Mach Numbers: I. Flat and Slightly Curved Panels at Mach Number 2.81. II. Cylindrical Shells with Boundary Layer", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152005-081824", "creators": [ { "name": { "family": "Anderson", "given": "William Judson" }, "id": "Anderson-William-Judson", "display_name": "Anderson, William Judson" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E3ZX-JG81", "abstract": "Part I.
\r\n\r\nTwo series of panel flutter tests were carried out in the Jet Propulsion Laboratory's 12 inch supersonic wind tunnel. Flat and slightly curved panels were tested at Mach number 2.81.
\r\n\r\nThe flat, rectangular panels were designed to study two-dimensional flutter. They were clamped at front and rear with free sides which extended into the boundary layer at the sides of the tunnel. These panels fluttered in a two-dimensional mode which occurred at a thickness ratio approximately 15 per cent different from the predictions of existing theory. One of the panels exhibited a three-dimensional \"rocking\" flutter which has not been observed or discussed before. A theory is developed for this type of flutter.
\r\n\r\nThe slightly curved panels were shallow circular cylindrical shells with the generators perpendicular to the flow direction. These panels were all of aspect ratio one. It was found that the effect of curvature was destabilizing and that the effect of internal pressurization was stabilizing.
\r\n\r\nPart II.
\r\n\r\nThe effect of a boundary layer on the flutter of a cylindrical shell is studied. The aerodynamic forces are developed for a shell of infinite length. The boundary layer is idealized as an annular region of uniform subsonic flow surrounding the shell. This boundary layer is of constant thickness along the shell and has a constant velocity distribution through its thickness. The external supersonic flow is also taken to be of uniform velocity, resulting in a \"stepped\" velocity profile through the boundary layer. Small perturbation theory is used in the boundary layer region and linear piston theory is used for the supersonic flow.
\r\n\r\nIn order to replace a physical boundary layer with an idealization for calculations, a procedure is developed for choosing the boundary layer parameters of velocity, pressure, etc. in a consistent way.
\r\n\r\nThe forces which are found through this boundary layer theory are compared with those obtained using piston theory directly. It is found that the forces on a mode with many circumferential waves are much smaller than the forces given by piston theory - - a reduction in amplitude of 95 per cent is possible. Phase changes also occur. The effect of the boundary layer on axisymmetric modes is not so great.
\r\n\r\nFlutter boundaries are obtained for axisymmetric flutter under several conditions and illustrate the effect of boundary layer thickness and structural damping.
\r\n" }, { "name": "Blackiston, Harry Spencer", "degree": "Engineering Degree", "year": "1963", "title": "Tip Effects on Fluctuating Lift and Drag Forces Acting on a Circular Cylinder Perpendicular to an Air Flow", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-135116", "creators": [ { "name": { "family": "Blackiston", "given": "Harry Spencer" }, "id": "Blackiston-Harry-Spencer", "display_name": "Blackiston, Harry Spencer" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TV46-TR33", "abstract": "Tests were conducted to evaluate the tip effects on the local air loads that act on a circular cylinder normal to a flow at Reynolds numbers, based on cylinder diameter, of 0.38 x 106, 0.53 x 106, 0.65 x 106 and 0.75 x 106 (corresponding to wind tunnel dynamic pressures of 10, 20, 30, and 40 psf, respectively). Tip configurations consisted of a blunt-end (or smokestack), a hemisphere, a 15 degree half-angle cone, and an ellipsoid with semi-major axis of 1.5 cylinder diameters. Localized boundary layer tripping facilitated controlled disturbances near the tip.
\r\n\r\nUnsteady lift and drag were significantly altered by the hemispherical and ellipsoidal ends as compared with the blunt-end. In contrast, the conical tip showed much smaller changes. Local lift and drag coefficients, as well as cross-correlation coefficients, vary rapidly along the cylinder axis near the tip.
\r\n\r\nThe importance of boundary layer characteristics on the fluctuating forces was demonstrated by boundary layer tripping with air blowing out through suitably located orifices in the cylinder.
" }, { "name": "Dewey, Clarence Forbes", "degree": "PhD", "year": "1963", "title": "Measurements in Highly Dissipative Regions of Hypersonic Flows. Part I. Hot-Wire Measurements in Low Reynolds Number Hypersonic Flows. Part II. The Near Wake of a Blunt Body at Hypers0nic Speeds", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-083759", "creators": [ { "name": { "family": "Dewey", "given": "Clarence Forbes" }, "id": "Dewey-Clarence-Forbes", "display_name": "Dewey, Clarence Forbes" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XG0Q-ZA42", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I:\r\n\r\nMeasurements were made of the heat loss and recovery temperature of a fine hot-wire at a nominal Mach number of 5.8. Data were obtained over an eight-fold range of Reynolds numbers in the transitional regime between continuum and free-molecule flow. At high Reynolds numbers, the heat transfer data agree well with the results of Laufer and McClellan, which were obtained at lower Mach numbers. At lower Reynolds numbers, the results indicate a monotonic transition between continuum and free molecule heat transfer laws. The slope of the heat transfer correlation also appears to vary monotonically, with Nu [...] at high Reynolds numbers and Nu ~ Re for Re< < 1.\r\n\r\nData on the wire recovery temperature (corresponding to zero net heat transfer) were obtained for free-stream Knudsen numbers between 0.4 and 3.0. Comparison with previous supersonic data suggests that for Mach numbers greater than about two the normalized variation of recovery temperature in the transitional regime is a unique function of the free-stream Knudsen number. The recent data of Vrebalovich (33) suggests that the relation between the normalized recovery temperature and Knudsen number found in this investigation also applies to subsonic and transonic flow.\r\n\r\nThe steady-state hot-wire may be used to obtain two thermodynamic measurements: the rate of heat transfer from the wire and the wire recovery temperature. An illustrative experiment was performed in the wake of a transverse cylinder, using both hot-wire and pressure instruments in a redundant system of measurements. It was shown that good accuracy may be obtained with a hot-wire even when the Reynolds number based on wire diameter is small.\r\n\r\nPart II:\r\n\r\nA theoretical model of the near wake is derived following the ideas of Chapman. This model is based on the postulates of mass conservation in the base flow region, thin viscous shear layers, and a recompression process which is independent of Reynolds number. The analysis, which includes the effects of initial shear layer thickness and base flow temperature, shows that the characteristics of the near wake (base pressure, shear layer angle, etc.) are independent of Reynolds number, and that the shear layer and initial wake thicknesses are proportional to Re[...].\r\n\r\nA series of experiments are presented which show that the postulate of thin shear layers is invalid for Reynolds numbers less than about [...]. At higher Reynolds numbers, the theory is qualitatively incorrect if the Mach number [...] external to the shear layer is large. Detailed measurements with a steady-state hot-wire in the near wake of a two-dimensional circular cylinder indicate that the compression process at the neck is not isentropic, and that the maximum pressure rise occurs downstream of the stagnation point formed by the merging shear layers. Comparison between the experimental and theoretical results points out the importance of the base flow temperature and the initial shear layer profile in determining the observable characteristics of the near wake." }, { "name": "Fourney, Michael Eugene", "degree": "PhD", "year": "1963", "title": "I. On the Application of a Laser to High Speed Photography. II. Torsional Magnetoelastic Waves in a Circular Cylinder", "advisor": "Ellis, Albert T.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-131705", "creators": [ { "name": { "family": "Fourney", "given": "Michael Eugene" }, "id": "Fourney-Michael-Eugene", "display_name": "Fourney, Michael Eugene" } ], "advisors": [ { "name": { "family": "Ellis", "given": "Albert T." }, "id": "Ellis-A-T", "role": "advisor", "display_name": "Ellis, Albert T." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6M9E-V056", "abstract": "The first part of this thesis deals with the application of a ruby laser to high speed photography. The light that is emitted from a ruby laser is monochromatic, collimated, coherent, linearly polarized, and highly intense. It has been demonstrated that these properties make the laser a very useful tool for research in areas involving photographic techniques.\r\n\r\nA method has been devised by which the output of the laser is controlled and is emitted in the form of a series of light pulses. The rate at which these pulses are generated can be controlled and repetition rates of over 1.6 Mc/sec have been achieved. The 30 nsec duration of an individual pulse represents the exposure time for a high speed laser camera which has been developed. Pictures have been taken at rates of over 1.2 million frames per second. This exposure time represents a reduction of an order of magnitude over that previously possible, with an increase of three orders of magnitude in intensity. In applications where a particular characteristic of the laser light is required, such as the monochromatic nature desired in photoelasticity, this improvement of four orders of magnitude is further increased.\r\n\r\nWhen a series of light pulses is generated in the manner described above it is found that the amplitude of the pulse train becomes stable above a certain critical frequency. This critical frequency is determined to be a function of the laser cavity length. The amplitude of the stabilized pulse train is a function of the repetition rate and the cavity length. The nature of this variation is established and a mechanistic explanation of the phenomena involved is presented." }, { "name": "Gold, Harris", "degree": "PhD", "year": "1963", "title": "Stability of Laminar Wakes", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-152513", "creators": [ { "name": { "family": "Gold", "given": "Harris" }, "id": "Gold-Harris", "display_name": "Gold, Harris" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X1TJ-MG72", "abstract": "This investigation deals with the effects of compressibility on the hydrodynamic stability of wake flows. It is found that the effect of temperature is two-fold: (1), as the wake core temperature increases, the range of Mach numbers over which neutral and self-excited subsonic disturbances can exist also increases; (2) as long as the relative Mach number is below the critical Mach number the neutral inviscid wave number will decrease with increasing core temperature, implying that a hot wake will be more stable than a cool one.\r\n\r\nThe analysis of Batchelor and Gill for the inviscid stability of axi-symmetric incompressible jets has been extended to the more general problem of compressible wakes and jets. It is shown that the results are directly analogous to those obtained for the two-dimensional problem. The sinuous (n = 1) mode is the most unstable allowable mode. This unstable mode is observed in a hypersonic wake." }, { "name": "Harwell, Kenneth Edwin", "degree": "PhD", "year": "1963", "title": "Initial Ionization Rates in Shock-Heated Argon, Krypton, and Xenon", "advisor": "Jahn, Robert G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-144544", "creators": [ { "name": { "family": "Harwell", "given": "Kenneth Edwin" }, "id": "Harwell-Kenneth-Edwin", "display_name": "Harwell, Kenneth Edwin" } ], "advisors": [ { "name": { "family": "Jahn", "given": "Robert G." }, "id": "Jahn-R-G", "role": "advisor", "display_name": "Jahn, Robert G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW2S-MW55", "abstract": "The rates of ionization behind strong shock waves in argon, krypton, and xenon are observed by a transverse microwave probe over a range of electron densities low enough that atom-atom inelastic collisions are the rate determining mechanism. Shocks of Mach number 7.0 to 10.0 propagate down a 5 cm square aluminum shock tube into ambient gases at pressures of 3 to 17 mm Hg, heating them abruptly to atomic temperatures of 5500\u00b0K to 9600\u00b0K. The subsequent relaxation toward ionization equilibrium is examined in its early stages by the reflection, transmission, and phase shifts of a 24.0 Kmc (1.25 cm) transverse microwave beam propagating between two rectangular horns abreast a glass test section. The data yield effective activation energies of 11.9 +/- 0.5 ev for argon, 10.4 +/- 0.5 ev for krypton, and 8.6 +/- 0.6 ev for xenon. These coincide, within experimental error, with the first excitation potentials, rather than the ionization potentials of the gases, indicating that in this range, ionization proceeds via a two-step process involving the first excited electronic state. Within experimental error, the pressure dependence is found to be proportional to the number density squared." }, { "name": "Knauss, Wolfgang Gustav", "degree": "PhD", "year": "1963", "title": "Rupture Phenomena in Viscoelastic Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052003-091542", "creators": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-Wolfgang-Gustav", "display_name": "Knauss, Wolfgang Gustav" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZSV-0Y32", "abstract": "A failure theory for high polymers is developed from the hypothesis that weak regions exist in the material. Defects nucleate in these regions through bond rupture until the defects reach a size which is critical for the applied boundary loading. This critical condition is based on energy balance considerations.\r\n\r\nBy considering the relaxation of the polymer chain in terms of the phenomenological stress-strain behavior and the rupture of chemical bonds in terms of an Arrhenius type rate law, the theory is able to accommodate an arbitrary stress or strain history, and shows reasonably good agreement with experiments which cover a large range of conditions.\r\n\r\nIn addition the stress analysis of a special crack geometry is presented. The geometry consists of a thin infinite strip containing a semi-infinite crack. For a uniform separation of the infinite boundaries an infinitesimal elasticity solution is obtained with the help of the Fourier transform and Wiener-Hopf techniques. The effect of large strains on the stresses near the crack tip is studied experimentally and a surprising correlation with the infinitesimal elasticity solution is found." }, { "name": "Ko, William L.", "degree": "PhD", "year": "1963", "title": "Application of Finite Elastic Theory to the Behavior of Rubber-Like Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012004-143718", "creators": [ { "name": { "family": "Ko", "given": "William L." }, "id": "Ko-William-L", "display_name": "Ko, William L." } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WMS4-A521", "abstract": "In Part I, methods for determining the strain energy function and the associated constitutive stress-deformation law for rubber-like materials is undertaken and the mechanics of data reduction needed to determine some parameters of the theory are displayed. Experiments were performed in four different stress fields on a foamed polyurethane rubber (dilatable rubber) and on several kinds of continuum rubbers. A new strain energy function and the associated stress-deformation law for a foamed rubber are generated which correlate most of the data to a high degree of accuracy. A parameter appearing in the functional expression for a foam rubber has the same significance as Poisson's ratio in infinitesimal elastic theory. For continuum rubbers, the isotropic Neo-Hookean representations of quasi-static behavior is found to be sufficient over most of the whole range of extension.\r\n\r\nIn Part II, geometrical representations of an isotropic failure surface based on various criteria are depicted both in principal stress and principal stretch spaces for elastic materials. The experimental data are compared with all criteria and the results are discussed.\r\n\t\r\nIn Part III, finite elastic theory is used to determine the stress and deformation fields around the base of a radial crack in an infinitely long rubber log opened by a facially bonded rigid wedge-shaped bellow.\r\n\t\r\nIn the last Part, the topology of interstices idealized as closest packed spherical holes (idealized foam structure) is investigated. Equivalent elastic constants are calculated for rubbery interstices of both hexagonal and face-centered cubic closest packings under small displacement." }, { "name": "Li\u00f1\u00e1n-Mart\u00ednez, Amable", "degree": "Engineering Degree", "year": "1963", "title": "On the Structure of Laminar Diffusion Flames", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-134536", "creators": [ { "name": { "family": "Li\u00f1\u00e1n-Mart\u00ednez", "given": "Amable" }, "id": "Li\u00f1\u00e1n-Mart\u00ednez-Amable", "display_name": "Li\u00f1\u00e1n-Mart\u00ednez, Amable" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JHTK-CA51", "abstract": "The structure of laminar diffusion flames is analyzed in the limiting case of large, although finite, reaction rates.\r\n\r\nIt is shown that the the chemical reaction takes place only in a very thin region or \"chemical boundary layer\" where convection effects may be neglected. Then the temperature and mass fraction distributions within the reaction zone are obtained analytically.\r\n\r\nThe flame position, rates of fuel consumption, and temperature and concentration distributions outside the reaction zone may be obtained by using the assumption of infinite reaction rates.\r\n\r\nFor large Reynolds numbers mixing and combustion take place in boundary layers and free mixing layers. And again analytical solutions are obtained for the temperature and mass fraction distributions outside of the reaction zone." }, { "name": "Mauldin, James Howard", "degree": "Engineering Degree", "year": "1963", "title": "Part I. Analysis of a Multi-Stage Axial Compressor with High Reaction Blading. Part II. A Design Study of a Multi-Stage Axial Compressor with Blading of High Aspect Ratio", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-142501", "creators": [ { "name": { "family": "Mauldin", "given": "James Howard" }, "id": "Mauldin-James-Howard", "display_name": "Mauldin, James Howard" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BBZZ-TE94", "abstract": "PART I:\r\n \r\nAn analysis of a multi-stage axial compressor with high reaction blading is carried out. The usual methods of linearizing the equations for flow through the compressor fail for this type of blading. A numerical-solution of the non-linear equations is worked through for off-design operation. Flow velocities through the first six stages are calculated for the off-design flow rates in order to insure that the flow does indeed come to a steady state repeating pattern. Entering flow angles for both rotor and stator are calculated for this repeating flow condition. The off-design incidence angles for the stators at low flow rates indicate a possible deterioration of efficiency.\r\n\r\nPART II:\r\n\r\nA method for designing blades of high aspect ratio in a multi-stage axial compressor is investigated. This method requires a calculation of the flow induced by all blade rows. The method is illustrated for the limiting condition of hub ratio equal to unity and then is carried out for the more realistic case of finite hub ratio.\r\n\r\nAn example of a blade design for a particular flow is carried out. The results are compared with those of a previous design for the same flow conditions but based on a theory applicable for blading of low aspect ratio." }, { "name": "Parks, Richard Earl", "degree": "Engineering Degree", "year": "1963", "title": "An Analysis of Turbulent Flame Spreading in a Rectangular Duct", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-133735", "creators": [ { "name": { "family": "Parks", "given": "Richard Earl" }, "id": "Parks-Richard-Earl", "display_name": "Parks, Richard Earl" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WDJR-AY43", "abstract": "The parametric equations for gas velocities and pressure, in terms of the density ratio and wake width, for a flame spreading in a rectangular duct from a point flameholder, are reviewed. A series solution for the cold gas velocity is proposed, evaluated, and its applicability to parametric values shown.\r\n\r\nAn attempt is made to determine the axial wake spreading rate, through a fluid mechanics approach utilizing the momentum equation and later the moment of the momentum equation. Both attempts are unsuccessful, for undetermined reasons.\r\n\r\nThe axial wake spreading rate is then approached, after defining an effective turbulent flame velocity, by equating the rate of disappearance of mass from cold stream with the rate of consumption of mass by the flame. Comparison is then made with a few of the conclusions that have been derived from experimental results." }, { "name": "Petty, James Sibley", "degree": "PhD", "year": "1963", "title": "Linearized Transonic Flow About Non-Lifting, Thin Symmetric Airfoils", "advisor": "Royce, Winston W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-135856", "creators": [ { "name": { "family": "Petty", "given": "James Sibley" }, "id": "Petty-James-Sibley", "display_name": "Petty, James Sibley" } ], "advisors": [ { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "advisor", "display_name": "Royce, Winston W." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "member", "display_name": "Royce, Winston W." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "member", "display_name": "Cole, Julian D." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3ZC0-7Y26", "abstract": "Transonic flow about symmetric, non-lifting airfoils is treated by solving an approximate linear differential equation of mixed type in place of the exact small-perturbation equations. The pressure distribution and drag coefficient are obtained in closed form for power series airfoils. The technique of local linearization is also applied to improve the accuracy of the results, particularly near the leading edge where the linearizing approximation is found to be invalid. Numerical results are obtained for the parabolic arc and single wedge airfoils and are found to compare favorably with experimental data and with previous theoretical results.\r\n" }, { "name": "Rupert, Viviane Claude", "degree": "Engineering Degree", "year": "1963", "title": "Influence of Radiative Dissipation on the Shock Wave Structure", "advisor": "Whitham, Gerald Beresford; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-111721", "creators": [ { "name": { "family": "Rupert", "given": "Viviane Claude" }, "id": "Rupert-Viviane-Claude", "display_name": "Rupert, Viviane Claude" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/41E3-T691", "abstract": "The influence of radiation on a steady, one dimensional flow is considered. Only radiative heat transfer is taken into account; viscosity, heat conduction and mass diffusion are neglected. It is further assumed that the radiative heat transfer is adequately described by the quasi equilibrium theory relative to a grey gas.\r\n\r\nUnder these conditions, the velocity of the fluid satisfies an integral equation which has been investigated by various methods. It is shown that under certain conditions the influence of radiation alone is not sufficient to smooth out the shock profile and a discontinuity in velocity still appears; mass diffusion processes are dominant in these cases." }, { "name": "Schmidt, Louis Vincent", "degree": "PhD", "year": "1963", "title": "Measurements of Fluctuating Air Loads on a Circular Cylinder", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102008-110237", "creators": [ { "name": { "family": "Schmidt", "given": "Louis Vincent" }, "id": "Schmidt-Louis-Vincent", "display_name": "Schmidt, Louis Vincent" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8714-PJ73", "abstract": "Measurements were made of the unsteady air loads, both lift and drag, developed on a circular cylinder when exposed to flow in the supercritical Reynolds number range from 0.38 x 106 to 0.75 x 106. The three dimensional nature of the flow, which is a consequence of the flow separation effects, is recognized. The statistical character of spatially varying random type fluctuating air loads is presented in the form of cross-spectral densities and cross-correlation coefficients. Information of this type has application to the problem of determining the response of a cylindrical structure when exposed to air loads.
\r\n\r\nThe extreme sensitivity of the flow to surface irregularities in the supercritical Reynolds number region is reported including the effects upon the local and spatial character of the fluctuating loads. Local values of steady state lift could be induced by suitably orienting surface disturbances on the forward portion of the cylinder.
\r\n" }, { "name": "Shi, Yun-Yuan", "degree": "PhD", "year": "1963", "title": "Low Reynolds Number Flow Past Finite Cylinders of Large Aspect Ratio", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-152936", "creators": [ { "name": { "family": "Shi", "given": "Yun-Yuan" }, "id": "Shi-Yun-Yuan", "display_name": "Shi, Yun-Yuan" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JA8T-4N67", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLow Reynolds number flow past finite cylinders of large aspect ratio is considered in this thesis. The first cylinder under consideration consists of a finite cylinder of constant radius [...] with two hemispherical caps attached to each end. The axis of the cylinder is perpendicular to uniform flow at infinity and the half length of the cylinder is L. Therefore, two Reynolds numbers can be formed in the present study, namely, Re=[...] and, [...] . The low Reynolds number flow is studied in the limit [...] for [...] fixed. This clearly shows that the body is of large aspect ratio.\r\n\r\nThe other cylinder under consideration is an ellipsoid of revolution whose half-axis parallel to the flow is [...] and whose half-axis perpendicular to the flow is L. The same limiting case as that for the first finite cylinder is studied.\r\n\r\nAsymptotic expansions of the solution valid for the limiting case [...] are obtained by applying singular perturbation procedures with proper use of the idea of the intermediate solution. The nature of the end source variation and the order of magnitude of various effects are clarified in the present study. In addition, certain general remarks have been made about the difference between the end effects for \"tapered\" and \"untapered\" bodies. It is found that the \"taper\" at the ends plays an essential role." }, { "name": "Slachmuylders, Erik Jaak", "degree": "Engineering Degree", "year": "1963", "title": "Measurements of the Acceleration of Reflected Shock Waves by Means of a New Heat Transfer Gauge", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-093601", "creators": [ { "name": { "family": "Slachmuylders", "given": "Erik Jaak" }, "id": "Slachmuylders-Erik-Jaak", "display_name": "Slachmuylders, Erik Jaak" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5G88-B054", "abstract": "A small heat transfer probe, operating in the free molecule tow regime, was developed with the purpose of obtaining accurate x, t diagrams of a reflected shock wave close to the end wall of the GALCIT 17-inch shock tube.\r\n\r\nThe sensitive element of the probe consists of a .005\" diameter filament of non-conducting material coated with a thin metallic film. The sensitivities of a filament probe and a conventional cold wire are compared analytically and it is found that the filament probe has favorable characteristics for measurement times of the order of a few microseconds. This is confirmed by the experiments.\r\n\r\nThe probe was mounted in the end wall of the 17-inch shock tube and x, t diagrams of reflected shock waves were measured at three levels of the initial pressure. The initial motion of the reflected shock is governed by heat loss to the reflecting wall; the wave velocity approaches its ideal value only asymptotically. The asymptotic approach agrees closely with the results of a boundary layer theory. The measurements indicate that the trajectory of the reflected shock close to the end wall is characterized by three different regions; the region in which boundary layer theory is valid, a region closer to the wall in which deviations from boundary layer theory are observed, and a non-continuum region adjacent to the wall in which the reflected shock is formed. The reflected shock wave is found to leave the formation region with a velocity which is approximately 20 per cent below the ideal velocity. It then accelerates toward this ideal velocity, approaching within 3 per cent at distances from the end wall of about 1000 mean free paths. The boundary layer approximation is found to be valid for distances greater than about 70 mean free paths. Accordingly, a non-uniform temperature profile is to be expected in a layer of approximately 100 mean free paths from the end wall." }, { "name": "Stebbins, Charles Fleming", "degree": "Engineering Degree", "year": "1963", "title": "Measurements of Heat Transfer Rates Within a Plane Shock Wave Using Very Fine Cold Wires", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-140351", "creators": [ { "name": { "family": "Stebbins", "given": "Charles Fleming" }, "id": "Stebbins-Charles-Fleming", "display_name": "Stebbins, Charles Fleming" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VDFV-DG16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPreliminary results of measurements of thermal shock structure are presented. Cold wire probes, of the type developed by W. H. Christiansen (Ref. 2), were constructed utilizing wires of .00001\" and .00005\" diameters. Heat transfer measurements were obtained at [...] and 7.5 in the GALCIT 17-inch shock tube over a range of initial pressures from 25 to 200 [...], producing thicknesses on the order of one centimeter.\r\n\r\nThe heat transfer data obtained are compared with predictions based on the Navier-Stokes theory and the recent Liepmann-Narasimha-Chahine theory (Ref. 3) for shock profiles and the free molecule heat-transfer theory of Stalder, et al. (Ref. 1)." }, { "name": "Stuart, Floyd Ronald", "degree": "Engineering Degree", "year": "1963", "title": "The Buckling of Thin Walled Circular Cylindrical Shells Under Combined Axial Compression and Bending", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-131305", "creators": [ { "name": { "family": "Stuart", "given": "Floyd Ronald" }, "id": "Stuart-Floyd-Ronald", "display_name": "Stuart, Floyd Ronald" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0SEM-H188", "abstract": "An experimental investigation of the interaction of combined axial compression and bending stresses on the buckling of cylindrical shells of similar geometry was carried out.\r\n\r\nThe shells tested were manufactured by a copper electro-forming process. This method of fabrication produced thin shells to close geometric tolerances without the usual seams.\r\n\r\nA total of 16 buckling tests were conducted. The resulting experimental interaction curve indicates that the critical buckling stress increases with increased bending moments." }, { "name": "Thompson, Thomas Ross", "degree": "Engineering Degree", "year": "1963", "title": "The Gray Gas in Hypersonic Flow", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-082033", "creators": [ { "name": { "family": "Thompson", "given": "Thomas Ross" }, "id": "Thompson-Thomas-Ross", "display_name": "Thompson, Thomas Ross" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9865-C310", "abstract": "The assumption that the spectral absorption coefficient is independent of frequency in problems involving radiant energy transfer in hot gases is examined. A particular case, that of the hypersonic wake, is treated in some detail, and a non-gray transfer equation involving two mean coefficients is developed. One mean absorption coefficient is related to emission, and the other to absorption.\r\n\r\nThe problems arising from lack of chemical equilibrium are discussed, and a modification of the equations used for prediction of the spectral absorption coefficient (for diatomic species) is suggested, wherein two distinct temperatures are utilized. Sample calculations for one nitrogen band have been made and the results presented graphically." }, { "name": "Vlases, George Charpentier", "degree": "PhD", "year": "1963", "title": "Experiments in a Cylindrical Magnetic Shock Tube", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:10092012-110749746", "creators": [ { "name": { "family": "Vlases", "given": "George Charpentier" }, "id": "Vlases-George-Charpentier", "display_name": "Vlases, George Charpentier" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1EHZ-AZ30", "abstract": "An investigation has been conducted with the two-fold purpose\r\nof producing very high Mach number shock waves and studying their\r\ninteraction with an external magnetic field parallel to the shock front.\r\nBy means of the technique of electromagnetic driving, stable reproducible, outward-going cylindrical shock waves in the Mach number\r\nrange from 20 to 100 have been produced and studied.
\r\n\r\nTheory predicts fundamental differences between the interaction\r\nof a magnetic field with a shock moving into a highly conducting\r\nfluid and the interaction of a field with a strong gas-ionizing shock.\r\nIn the former case a true mhd shock is produced. In the latter the\r\nfield interacts directly only with the piston and the shock remains\r\nan ordinary one. The effect of a conducting wall surrounding the\r\nchamber also differs substantially in the two cases.
\r\n\r\nDetailed experiments have been carried out on gas-ionizing\r\nshocks. While the overall motion is very nearly that predicted by the\r\ntheory, anomalies have arisen in the details of the flow and are\r\nexplained in a qualitative manner.
\r\n\r\nMethods of producing sufficient initial conductivity to obtain a\r\nthin magnetohydrodynamic shock are discussed, together with some\r\npreliminary experiments along these lines.
" }, { "name": "Wu, Ying-Chu Lin Susan", "degree": "PhD", "year": "1963", "title": "Flow Generated by Suddenly Heated Flat Plate", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052004-163535", "creators": [ { "name": { "family": "Wu", "given": "Ying-Chu Lin Susan" }, "id": "Wu-Ying-Chu-Lin-Susan", "display_name": "Wu, Ying-Chu Lin Susan" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "member", "display_name": "Plesset, Milton S." }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "member", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Lauritsen", "given": "Thomas" }, "id": "Lauritsen-T", "role": "member", "display_name": "Lauritsen, Thomas" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CPQD-RQ29", "abstract": "By employing the two-sided Maxwellian in Maxwell's moment method a kinetic theory description is obtained of the flow generated by a step-function increase in the temperature of an infinite flat plate. Four moments are employed in order to satisfy the three conservation equations, plus one additional equation involving the heat flux in the direction normal to the plate. For a small temperature rise the equations are linearized, and closed-form solutions are obtained for small and large time in terms of the average collision time.
\r\n\r\nInitially the disturbances propagate along two distinct characteristics, but the discontinuities across these waves damp out as time increases. At large time the main disturbance propagates with the isentropic sound speed. Solutions for mean normal velocity and temperature show the transition from the nearly collision-free regime to the Navier-Stokes-Fourier regime, which is characterized by a boundary layer near the plate surface merging into a diffuse \"wave\". The classical continuum equations, plus a temperature jump boundary condition, seem to be perfectly adequate to describe the flow beyond a few collision times, provided one accounts properly for the interaction between the inner thermal layer and the outer diffuse wave.
" }, { "name": "Babcock, Charles Dwight", "degree": "PhD", "year": "1962", "title": "The Buckling of Cylindrical Shells with an Initial Imperfection Under Axial Compression Loading", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242004-151013", "creators": [ { "name": { "family": "Babcock", "given": "Charles Dwight" }, "id": "Babcock-Charles-Dwight", "display_name": "Babcock, Charles Dwight" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0P4A-SA39", "abstract": "An experimental and theoretical investigation of the effect of a specific type of initial imperfection on the buckling load of a circular cylindrical shell under axial compression loading was carried out. The imperfection studied was axially symmetric in shape and had the form of a half sine wave in the length direction. Both inward and outward bowing imperfections were considered.\r\n\r\nThe experiments were carried out with shells fabricated by a copper electroforming process. The shells had no longitudinal seams and had unintended imperfections of the order of the wall thickness. The buckling stress for the intended imperfection studied was only slightly influenced over a considerable range of imperfection amplitudes.\r\n\r\nThe theoretical solution located the bifurcation points of the prebuckled axially symmetric state. The solution showed that outward bowing shells should have the same buckling stress as a perfect cylindrical shell and inward bowing shells should have a lower buckling stress than the perfect cylinder." }, { "name": "Casey, John Carl", "degree": "Engineering Degree", "year": "1962", "title": "A Theoretical Investigation of Using N Low Thrust Impulses to Escape from a Circular Satellite Orbit", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-142051", "creators": [ { "name": { "family": "Casey", "given": "John Carl" }, "id": "Casey-John-Carl", "display_name": "Casey, John Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/58PH-YA67", "abstract": "An investigation was made into the advantages of using a discontinuous thrust program to escape from a cricular satellite orbit when using a low thrust propulsion unit. To make maximum use of the applied thrust, the perigee distance was chosen at a point where the atmospheric drag was negligible and this distance was held constant throughout the escape maneuver. A numerical integration was made of this method and the spiralling method. The appendixes show a comparison of these two methods." }, { "name": "Cummings, Benjamin Edgar", "degree": "PhD", "year": "1962", "title": "Some Nonlinear Vibration and Response Problems of Cylindrical Panels and Shells", "advisor": "Fung, Yuan-cheng; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-115144", "creators": [ { "name": { "family": "Cummings", "given": "Benjamin Edgar" }, "id": "Cummings-Benjamin-Edgar", "display_name": "Cummings, Benjamin Edgar" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AXC2-6P94", "abstract": "Large amplitude vibrations and forced responses of curved panels and shells are studied by the application of the shallow shell equation. The Galerkin procedure is used to reduce the nonlinear partial differential equations to ordinary nonlinear equations. Marked differences are found between the behavior of curved panels and cylindrical shells. Relations for the dependence of the free vibration period on amplitude are given. A two mode analysis of the cylindrical shell problem is included.
\r\n\r\nThe curved panel is found to exhibit a buckling phenomenon for the simple \"breathing modes\". Shock response methods are used to predict dynamic buckling of the curved panel and the predictions are verified by numerical integration.
\r\n\r\nThe cylindrical shell vibrations and responses are found to be governed by Duffing's equation and certain of the well-known properties of Duffing's equation are applied to the cylindrical shell dynamics.
\r\n\r\nThe two mode analysis of the cylindrical shell is shown to exhibit weak coupling, allowing the separate excitation of the coupled modes.
\r\n\r\nSome numerical results are given.
" }, { "name": "Hoult, David Parks", "degree": "PhD", "year": "1962", "title": "Magnetohydrodynamic Surface Waves", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-082838", "creators": [ { "name": { "family": "Hoult", "given": "David Parks" }, "id": "Hoult-David- Parks", "display_name": "Hoult, David Parks" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RVM0-1T80", "abstract": "This is an experimental and theoretical study of deep water gravity-like waves which are induced in a liquid metal by a changing magnetic field. The dominant feature of such waves is the emission of Alfven waves from the free surface. A linearized theory is derived and compared with experiments." }, { "name": "Johnson, Douglas Stoddard", "degree": "Engineering Degree", "year": "1962", "title": "I. Design and Application of Piezoceramic Transducers to Transient Pressure Measurements. II. Some Measurements of Curvature and Thickness of Reflecting Normal Shocks at Low Initial Pressures", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-102730", "creators": [ { "name": { "family": "Johnson", "given": "Douglas Stoddard" }, "id": "Johnson-Douglas-Stoddard", "display_name": "Johnson, Douglas Stoddard" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJ82-FM97", "abstract": "A small pressure transducer, using the piezoelectric properties of a manufactured ceramic, was designed, constructed and installed in the end plate of the GALCIT 17-inch shock tube to obtain high-speed measurements of the pressure field behind a reflecting shock.\r\n\r\nThe design problem for piezoceramic pressure transducers and some possible solutions are discussed in detail. Results of transducer calibration and recommendations for improvement of the instrument are presented.\r\n\r\nAn initial program to determine the curvature of a shock at low initial pressures was run concurrently with calibration of five of the above pressure transducers. The results of this program are described in as much detail as the data obtained to date will permit.\r\n\r\nAt an initial pressure of 30 microns in the GALCIT 17-inch tube, the shock obtained at a Mach number of about 7.5 in argon is observed to have a total curvature of approximately 10 millimeters, or approximately two per cent of the tube diameter. The shock thickness observed under these conditions is approximately 5 millimeters. These results indicate that it may be entirely possible to obtain good optical measurements inside the shock, but that it may be necessary to resort to special techniques to avoid optical distortion caused by curvature." }, { "name": "Johnson, Grant Reed", "degree": "Engineering Degree", "year": "1962", "title": "A Theoretical Investigation of Particle Trajectories Through a Prandtl-Meyer Expansion Fan", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-145547", "creators": [ { "name": { "family": "Johnson", "given": "Grant Reed" }, "id": "Johnson-Grant-Reed", "display_name": "Johnson, Grant Reed" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FTNK-N998", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe equations of motion are developed and solved numerically for the trajectory of a spherical particle passing through a Prandtl-Meyer expansion fan. The effect of a change in [...] and n is shown, where [...] is the ratio of specific heats of the gas, and n/2 is the exponent in [...], the assumed viscosity temperature relationship.\r\n\r\nIt is demonstrated that for particles the order of a micron in diameter, slip flow will exist, and a proposed correction to the drag to account for this discontinuous nature of the flow is investigated.\r\n\r\nThe results are plotted showing particle trajectory profiles and the components of the relative velocity or slippage velocity of the particle for flow deflection angles up to 70 degrees." }, { "name": "Liu, Chung-Yen", "degree": "PhD", "year": "1962", "title": "Part I. Kinetic Theory Description of Plane, Compressible Couette Flow. Part II. Kinetic Theory Description of Conductive Heat Transfer from a Fine Wire", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-133941", "creators": [ { "name": { "family": "Liu", "given": "Chung-Yen" }, "id": "Liu-Chung-Yen", "display_name": "Liu, Chung-Yen" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q16R-JR92", "abstract": "PART I: \r\n \r\nBy utilizing the two-stream Maxwellian in Maxwell's integral equations of transfer we are able to find a closed-form solution of the problem of compressible plane Couette flow over the whole range of gas density from free molecule flow to atmospheric. The ratio of shear stress to the product of ordinary viscosity and velocity gradient, which is unity for a Newtonian fluid, here depends also on the gas density, the plate temperatures and the plate spacing. For example, this ratio decreases rapidly with increasing plate Mach number when the plate temperatures are fixed. On the other hand, at a fixed Mach number based on the temperature of one plate, this ratio approaches unity as the temperature of the other plate increases. Similar remarks can be made for the ratio of heat flux to the product of ordinary heat conduction coefficient and temperature gradient.\r\n\r\nThe effect of gas density on the skin friction and heat transfer coefficients is described in terms of a single rarefaction parameter, which amounts to evaluating gas properties at a certain \"kinetic temperature\" defined in terms of plate Mach number and plate temperature ratio. One interesting result is the effect of plate temperature on velocity \"slip\". In the Navier-Stokes regime most of the gas follows the hot plate, because the gas viscosity is larger there. As the gas density decreases the situation is reversed, because the velocity slip is larger at the hot plate than at the cold plate. In the limiting case of a highly rarefied gas most of the gas follows the cold plate.\r\n\r\nLimitations of the present six-moment approximation at high plate Mach numbers are discussed and it is concluded that an eight-moment approximation would eliminate these difficulties. The results obtained in this simple geometry suggest certain conclusions about hypersonic flow over solid bodies when the surface temperature is much lower than the kinetic temperature.\r\n\r\nPART II:\r\n\r\nThe Maxwell moment method utilizing the two-sided Maxwellian distribution function is applied to the problem of conductive heat transfer between two concentric clylinders at rest. Analytical solutions are obtained for small temperature differences between the cylinders. The predicted heat transfer agrees very well with experiments performed by Bomelburg, Schafer-Rating and Eucken. Comparison with results given by the Grad's thirteen moment equations, and with those given by Fourier's \"law\" plus Maxwell-Smoluchowski temperature-jump boundary condition shows that the two-sided character in the distribution function is a crucial factor in problems involving surface curvature." }, { "name": "Malmuth, Norman David", "degree": "PhD", "year": "1962", "title": "Perturbations on Hypersonic Wedge Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152005-133232", "creators": [ { "name": { "family": "Malmuth", "given": "Norman David" }, "id": "Malmuth-Norman-David", "display_name": "Malmuth, Norman David" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KE9Q-XN81", "abstract": "The hypersonic inviscid flow over a configuration representing a small perturbation about a two-dimensional wedge is analyzed. Equations and boundary conditions are obtained for a class of general perturbations within the framework of Hypersonic Small Disturbance Theory.\tA specialization of this formulation is made to the case where the resultant perturbation consists of semi-infinite flat plates of slightly different incidence to the freestream. The flow over such a shape is divided into an outlying uniform region and a central conefield. Here, the outlying, uniform region solution is found to be trivial. The determination of the conefield gives rise to an elliptic boundary value problem which is solved with the aid of the Tschaplygin transformation and other conformal mappings.\r\n\r\nCalculations are presented using the Fourier series solution for the perturbation pressure indicating the surface loads associated with the perturbation as well as the shock distortion function. Integral representations are obtained for the downwash and sidewash perturbations using the pressure solution.\r\n\r\nThe results are compared qualitatively with an analogous linear supersonic flow.\r\n\r\nFinally, a solution for more general profiles is obtained under the further restriction that the specific heat ratio [gamma] is close to one. This solution is specialized to the case considered previously and a qualitative evaluation of the physical significance of the results is made." }, { "name": "Marlotte, Gary Lynn", "degree": "PhD", "year": "1962", "title": "An Experimental Investigation of the Effect of a Transverse Hypersonic Flow Velocity upon a Low-Density D.C. Electrical Discharge in Air", "advisor": "Demetriades, Anthony; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132005-105051", "creators": [ { "name": { "family": "Marlotte", "given": "Gary Lynn" }, "id": "Marlotte-Gary-Lynn", "display_name": "Marlotte, Gary Lynn" } ], "advisors": [ { "name": { "family": "Demetriades", "given": "Anthony" }, "id": "Demetriades-A", "role": "advisor", "display_name": "Demetriades, Anthony" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3BR3-ZT02", "abstract": "The low-density D.C. electrical discharge in a uniform gas stationary with respect to the electrodes has been studied extensively. However, when the gas moves at a hypersonic speed transverse to the electrodes, several completely new effects are introduced. Experiments were carried out with air in the GALCIT 5-inch by 5-inch hypersonic wind tunnel with a nominal Mach number of 5.8. D.C. breakdown voltages and steady-state sub-normal glow voltages were measured across a channel formed by two sharp-edged insulating flat plates in which flat-plate \"Rogowski\" electrodes were embedded. Segmented electrodes were then used in the normal glow regime to measure current distributions at each electrode for various electrode segment combinations, total currents, and densities.\r\n\r\nSome important results of the present study are the following. For the characteristic dimensions and speeds involved, the explicit dependence of electrical breakdown upon the velocity of the stream is small compared to the effect of boundary layer density defects. A theoretical treatment of breakdown is given and qualitative agreement with experiments is obtained. In the normal glow regime using segmented electrodes, an unmistakable explicit flow velocity effect was observed, with the discharge current paths being displaced downstream compared to static bell-jar tests at equivalent densities." }, { "name": "McCarthy, John Francis", "degree": "PhD", "year": "1962", "title": "Hypersonic Wakes", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-092458", "creators": [ { "name": { "family": "McCarthy", "given": "John Francis" }, "id": "McCarthy-John-Francis", "display_name": "McCarthy, John Francis" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/63NK-AG38", "abstract": "An experimental investigation was made of the flow field behind a two-dimensional circular cylinder at a nominal Mach number of 5.7. The free-stream Reynolds number based on the cylinder diameter was varied over a range from 4300 to 66, 500 by changing both the diameter of the cylinder and the stagnation pressure of the wind tunnel. Pitot-pressure, static-pressure, and total-temperature measurements were made at various distances behind the cylindrical rod in order to determine the state properties in the wake. Base-pressure measurements were also taken at various Reynolds numbers.\r\n\r\nFrom these measurements, the transition from laminar to turbulent flow in the wake was determined and successfully correlated with other data. A transition Reynolds number based on local conditions and the length of laminar run was determined. Extensive comparison of the experimental data with Kubota's theory for laminar flow was then made. A satisfactory comparison was made between theory and experiment. Because of the nature of the tests conducted, only a qualitative comparison was made with the theory of Lees and Hromas for turbulent flow." }, { "name": "Preukschat, A. Werner", "degree": "Engineering Degree", "year": "1962", "title": "Measurements of Drag Coefficients for Falling and Rising Spheres in Free Motion", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192005-145326", "creators": [ { "name": { "family": "Preukschat", "given": "A. Werner" }, "id": "Preukschat-A-Werner", "display_name": "Preukschat, A. Werner" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/94MG-ZS76", "abstract": "The purpose of this thesis is to investigate the drag coefficient of spheres in free motion, falling and rising, in water.\r\n\r\nFollowing the introduction the test set-up, sphere release mechanism, spheres and timing device and recorder are described.\r\n\r\nSection 3 gives the results of the drag coefficient measurements for free falling spheres which show good agreement with the known measurements, quoted, for instance, in the Handbuch der Experimentalphysik.\r\n\r\nSection 4 deals with the measurement of drag coefficients of free-rising spheres. It was found that the freely rising spheres move in an oscillatory path of which wavelength and amplitude depend on the ratio of sphere density and water density.\r\n\r\nThe local drag coefficient of the spheres was measured to be the same as for falling spheres. It was found to be independent of the sphere motion.\r\n\r\nNo critical Reynolds number was found for the onset of the oscillatory motion of the sphere. The oscillatory motion appeared to be independent of initial disturbances of the sphere motion.\r\n\r\nFrom photographs of the sphere paths Strouhal numbers were formed which are about one third the value given for circular cylinders in the same Reynolds number range.\r\n\r\nA theoretical oscillatory force coefficient, based on a force balance on the sphere, was obtained. It was found to be of the same order of magnitude as the correspondent, actually measured oscillatory force coefficient on a circular cylinder.\r\n\r\nThe Strouhal number based on the main theoretical frequency was found to be four times as high as the one calculated from the frequency of the sphere path. It could be, dependent on the sphere density, as high as twice the Strouhal number found for circular cylinders in the same Reynolds number range." }, { "name": "Radey, Kendrick", "degree": "Engineering Degree", "year": "1962", "title": "A Time-Optimal Control Problem in Dynamics with Sampled Data", "advisor": "Mullin, Francis J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-132505", "creators": [ { "name": { "family": "Radey", "given": "Kendrick" }, "id": "Radey-Kendrick", "display_name": "Radey, Kendrick" } ], "advisors": [ { "name": { "family": "Mullin", "given": "Francis J." }, "id": "Mullin-F-J", "role": "advisor", "display_name": "Mullin, Francis J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CXDE-J137", "abstract": "A two-degree-of-freedom dynamical system has been analyzed to determine an optimum control sequence which will drive the dynamical system from an arbitrary initial position and velocity to one of a prescribed set of terminal position and velocity's in minimum time. The basic complexities are:
\r\n\r\n(1) that the forcing function can change only at discrete intervals of time, and
\r\n\r\n(2) that the prescribed terminal states allow a multiplicity of solutions to prevail.
A novel but not unique force program which is dependent upon the initial state of the system has been determined. This program consists essentially of the continuous application of a force of the proper sense and maximum allowable amplitude followed by a time during which no force is applied. This is followed by a time interval in which the forcing function has a maximum amplitude but is of the opposite sign to that used in the first part of the program.
" }, { "name": "Renard, Marc L.", "degree": "Engineering Degree", "year": "1962", "title": "Experimental Investigation of an Arc Heater", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192005-132228", "creators": [ { "name": { "family": "Renard", "given": "Marc L." }, "id": "Renard-Marc-L", "display_name": "Renard, Marc L." } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "member", "display_name": "Lees, Lester" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SVWJ-NB92", "abstract": "An electric arc heater, intended to provide a steady flow of high stagnation temperature gas (up to 10,000\u00b0K) into a convergent-divergent nozzle, was designed at the GALCIT Hypersonic Laboratory.\r\n\r\nSection 2 first gives a few preliminary calculations which have been made for the arc heater-nozzle combination, using argon, at stagnation pressures of 1 and 2 atm., and assuming equilibrium flow. In particular, the Mach number in the test section of a fixed nozzle will depend on the thermodynamic properties at the reservoir.\r\n\r\nIn the heater, the direct-current arc is axially constricted by a channel parallel to the gas flow. A description of the design and instrumentation is given in Sections 2 and 3.\r\n\r\nFor two series of experiments, using argon, the central electrode was either the cathode, as in the conventional arrangement, or the anode: both configurations were thoroughly investigated. Provided a sharp edge exists at the end of the flow constricting channel, the configuration with anode in the center was found to give, generally, a more stable functioning, with a voltage drop about twice as large, higher efficiency and thus higher average temperature for the same mass flow of gas, as compared to the case where the cathode is in the center. In the ranges of power (up to 13 Kw) and mass flow (up to 6.00 gr/sec) investigated, it was found that the best efficiency is obtained for a swirl close to the central electrode and large gas mass flows. When the anode is in the center, a long and narrow constricting channel leads to the optimal conditions. With the reversed polarities, the geometry of the downstream channel is not very important.\r\n\r\nFinally, a tentative explanation of the results is given, emphasizing in particular that the \"anode in the center\" case corresponds to a \"long\" arc, and the \"cathode in the center\" to a \"short\" one with poorer transfer of energy from the arc to the gas." }, { "name": "Savage, Stuart Blackton", "degree": "Engineering Degree", "year": "1962", "title": "The Effect of Heat Transfer on Separation of Laminar Compressible Boundary Layers", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-143749", "creators": [ { "name": { "family": "Savage", "given": "Stuart Blackton" }, "id": "Savage-Stuart-Blackton", "display_name": "Savage, Stuart Blackton" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XCR8-Y474", "abstract": "Tani's integral method is extended to treat laminar two-dimensional compressible boundary layers with heat transfer and arbitrary pressure gradient for both attached and separated flows. A carefully chosen one-parameter family for the velocity profiles and a \"universal\" stagnation enthalpy profile are assumed for attached flows. The accuracy of the method is examined by comparing the results with several \"exact\" numerical solutions and satisfactory agreement is obtained. For separated flows one-parameter families are assumed for both the velocity and stagnation enthalpy profiles. In this case the accuracy of the method is poor; however, suggestions are made as to how it might be improved within the present framework.\r\n" }, { "name": "Schapery, Richard Allan", "degree": "PhD", "year": "1962", "title": "Irreversible Thermodynamics and Variational Principles with Applications to Viscoelasticity", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08092011-111909246", "creators": [ { "name": { "family": "Schapery", "given": "Richard Allan" }, "id": "Schapery-Richard-Allan", "display_name": "Schapery, Richard Allan" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QEB0-N308", "abstract": "A unified theory of the thermo-mechanical behavior of\r\nviscoelastic media is developed from studying the thermodynamics of irreversible processes, and includes discussions of the general equations of motion, crack propagation, variational principles, and approximate methods of stress analysis.\r\n\r\nThe equations of motion in terms of generalized coordinates\r\nand forces are derived for systems in the neighborhood of a stable equilibrium state. They represent a modification of Biot's theory in that they contain explicit temperature dependence, and a thermodynamically consistent inclusion of the time-temperature superposition principle for treating media with temperature-dependent viscosity coefficients. The stress-strain-temperature and energy equations for viscoelastic solids follow immediately from the general\r\nequations and, along with equilibrium and strain-displacement relations, they form a complete set for the description of the thermomechanical behavior of media with temperature-dependent viscosity. In addition, an energy equation for crack propagation is derived and examined briefly for its essential features by applying it to a specific problem.\r\n\r\nThe thermodynamic equations of motion are then used to\r\ndeduce new variational principles for generalized coordinates and forces, employing convolution-type functionals. Anticipating various engineering applications, the formulation is phrased alternately in terms of mechanical displacement, stresses, entropy displacement, and temperature in thermally and mechanically linear solids. Some special variational principles are also suggested for applications wherein the nonlinear thermal effects of temperature dependent viscosity and dissipation may be important. \r\n\r\nBuilding upon the basic variational formulation, it is next\r\nshown that when these convolution functionals are Laplace-transformed with respect to time, some convenient minimum principles result which can be employed for the approximate calculation of transformed, viscoelastic responses. The characteristic time dependence of exact and approximate solutions is then derived and used in relating error\r\nin approximate viscoelastic solutions to error in the associated elastic solutions.\r\n\r\nThe dissertation is concluded with a study of some approximate methods of viscoelastic analysis. First, the important problem of inverting complicated Laplace transforms to physical time-dependent solutions is resolved by advancing two easily applied, approximate methods of transform inversion. These inversion methods and\r\nvariational principles are then used in some illustrative, numerical, examples of stress and heat conduction analysis.\r\n" }, { "name": "Seymour, Ernest Richard", "degree": "Engineering Degree", "year": "1962", "title": "Some Investigations of Heterogeneous Flow in a Rocket Nozzle", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-133112", "creators": [ { "name": { "family": "Seymour", "given": "Ernest Richard" }, "id": "Seymour-E-R", "display_name": "Seymour, Ernest Richard" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/01GY-2E21", "abstract": "In the heterogeneous flow of finely divided particles and gas in a rocket nozzle, the assumptions that the flow enters the nozzle with no lags, that the radiative transport of energy between particles is negligible, and that there are no temperature gradients within the particles, are commonly made. In this paper, each of these assumptions is investigated in detail, and they are shown to be reasonable for typical rocket nozzles." }, { "name": "Simmons, Jerry Lee", "degree": "Engineering Degree", "year": "1962", "title": "Applications of the Two-Variable Expansion Procedure to Problems in Celestial Mechanics", "advisor": "Royce, Winston W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-110043", "creators": [ { "name": { "family": "Simmons", "given": "Jerry Lee" }, "id": "Simmons-Jerry-Lee", "display_name": "Simmons, Jerry Lee" } ], "advisors": [ { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "advisor", "display_name": "Royce, Winston W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E66T-1A37", "abstract": "This work illustrates the application of the two-variable expansion procedure of reference 1 to the solution of two representative problems in celestial mechanics.\r\n\r\nThe expansion procedure is applied first to the problem of aerodynamic perturbations of a satellite orbit. The case of planar motion is considered with both lift and drag perturbations acting on the satellite. A simplified model of the earth is used, but the motion is expected to exhibit a similar qualitative behavior in the more general case. It is found that the effect of drag causes the satellite to spiral toward the center of attraction while the orbit is tending to become circular. The effect of lift, to the order computed, is felt only by a slow advance of the apse.\r\n\r\nThe second application of the expansion procedure is to the problem of third-body perturbations of a satellite orbit. A special case of the restricted three-body problem is used in which the plane of the satellite's orbit is coincident with the orbital plane of the two larger bodies. The two-variable expansion is applied to approximate equations which are valid for satellite orbits close to the smaller of the two large bodies. The results are in exact agreement with those of reference 2 and DePontecoulant's lunar theory. The solution of this problem is to serve as a preliminary step in establishing the choice of variables for the more general case in which the satellite's orbit has a high inclination to the orbital plane of the two larger bodies." }, { "name": "Watts, George Arthur", "degree": "Engineering Degree", "year": "1962", "title": "Vibration and Damping of Thin-Walled Cylinders", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-132350", "creators": [ { "name": { "family": "Watts", "given": "George Arthur" }, "id": "Watts-George-Arthur", "display_name": "Watts, George Arthur" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XPER-7Q77", "abstract": "The frequencies of normal modes of free vibration of three cylinders of different thickness were found experimentally. For some of the modes damping was also found. The modes excited were of a single axial half wave and multiple circumferential waves.
\r\n\r\nThe shells were geometrically similar except for thickness and were made by electroplating copper on accurately machined wax mandrels. Melting the wax produced shells of very uniform thickness without seams.
\r\n\r\nThe modes and frequencies agreed to within 10% of the theoretical values for cylinders with fixed ends, except at small numbers of waves where they agreed more closely with the theoretical values for freely supported ends. The damping factors tended toward a small constant value with increasing numbers of waves above the mode with fundamental frequency, but increased rapidly as the numbers of waves decreased below the fundamental.
\r\n" }, { "name": "Zukerman, Abraham", "degree": "PhD", "year": "1962", "title": "Analytical Approximations to the Solutions of the Equations of Motion in the Earth-Moon Space", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-091409", "creators": [ { "name": { "family": "Zukerman", "given": "Abraham" }, "id": "Zukerman-Abraham", "display_name": "Zukerman, Abraham" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZFV9-4018", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\t\r\nTwo methods of obtaining approximate solutions of the equations of motion in the Earth-Moon space are derived. The first method - asymptotic expansions of the solutions of the equations of motion - is a power series expansion of the solutions in powers of the inverse maximum velocity [...]. A comparison of the results of numerical integration with the asymptotic expansions is presented, which shows the range of applicability of this method.\r\n\r\nThe second method is similar to the small perturbation approach. In this method the zeroth order solution is a Keplerian orbit about the Earth (the Moon's effect being neglected). The first order solution corrects for the lunar gravity effects on the zeroth order trajectory. To demonstrate the computational difficulties involved in the application of this method, a straight line Keplerian trajectory was used as the zeroth order solution. Several applications of the solutions are discussed." }, { "name": "Ai, Daniel Kwoh-i", "degree": "PhD", "year": "1961", "title": "Part I. Cylindrical Couette Flow in a Rarefied Gas According to Grad's Equation. Part II. Small Perturbations in the Unsteady Flow of a Rarefied Gas Based on Grad's Thirteen Moment Approximation", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-131707", "creators": [ { "name": { "family": "Ai", "given": "Daniel Kwoh-i" }, "id": "Ai-Daniel-Kwoh-i", "display_name": "Ai, Daniel Kwoh-i" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Goetz", "given": "Alexander" }, "id": "Goetz-Alexander", "role": "member", "display_name": "Goetz, Alexander" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "member", "display_name": "Royce, Winston W." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9P2N-HF23", "abstract": "Part I
\r\n\r\nGrad's thirteen moment method is applied to the problem of the shear flow and heat conduction between two concentric, rotating cylinders of infinite length. In order to concentrate on the effects of curvature the problem is linearized by requiring that the Mach number is small compared with unity, and that the temperature difference between the two cylinders is small compared with the mean temperature. The solutions of the linearized Grad equations show a qualitatively correct transition of the cylinder drag from free-molecule flow to the classical Navier-Stokes regime. However the magnitude of the curvature effect on the drag in rarefied flow is not given correctly, because Grad's distribution function ignores the wedge-like domains of influence of the two cylinders.
\r\n\r\nThe solution obtained for the heat transfer rate is physically unrealistic in the free-molecule flow limit, and this result is produced by a cross-coupling between the normal stresses and the radial heat flux imposed by Grad's distribution function. In this simple problem the difficulty can be eliminated by taking the normal stresses to be identically zero and employing a truncated moment method. However, in general this device cannot be utilized in problems involving curved solid boundaries, or when dissipation is considered. One concludes that the choice of the distribution function to be employed in Maxwell's moment equations is dictated by the requirements imposed in the limiting case of highly rarefied gas flows, as well as in the Navier-Stokes regime.
\r\n\r\nPart II
\r\n\r\nIn this paper, the unsteady one-dimensional flow of a compressible, viscous and heat conducting fluid is treated, based on linearized Grad's thirteen moment equations. The fluid, initially at rest, is set into motion by some small external disturbances. Our interest is to examine the nature of all the responses. The fluid field extends to infinity in both directions; thus no length is involved, and also there is no solid wall boundary existing in the problem. The nature of the external disturbances is restricted to having a unit impulse in the momentum equation and a unit heat addition in the energy equation. The disturbances are located on an infinite plane normal to the flow direction; and the responses induced correspond to fundamental solutions of the problem. The method of Laplace transforms is applied, and the inverse transforms of all quantities are obtained in integral form. Because of the complicated expressions of the integrands involved, we consider only certain limiting cases which correspond to small and large times from the start of the motion, compared to the average time between molecular collisions. In order to study these limiting cases, it is essential to understand the behavior of the integrand in the complex plane; hence all singularities and branch points are obtained.
\r\n\r\nWhen t is small, the integrand is expanded in powers of t to obtain a wave front approximation. All discontinuities are propagated along the characteristics of the linearized system, and a damping term also appears.
\r\n\r\nAt large values of time, the integrand gets its main contribution around the branch points, and these solutions are identical to those obtained from the Navier-Stokes equation. The fundamental solution of the one-dimensional unsteady flow, idealized as it seems to be, offers itself as a tool to understand other related problems. The piston problem, as well as the normal quantities in Rayleigh's problem (e.g., normal velocity, normal stress, and thermodynamical quantities), are governed by the same set of equations. Hence, certain parts of the fundamental solutions can be applied directly to these problems. The limiting forms of the normal quantities in Rayleigh's problem are expected to be worked out in another paper in the near future.
" }, { "name": "Cann, Gordon Lawrence", "degree": "PhD", "year": "1961", "title": "Energy Transfer Processes in a Partially Ionized Gas", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202005-133300", "creators": [ { "name": { "family": "Cann", "given": "Gordon Lawrence" }, "id": "Cann-Gordon-Lawrence", "display_name": "Cann, Gordon Lawrence" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XV8R-MM73", "abstract": "The following paper is divided into three more or less separate sections. The first section (Chapters II - VI) deals with an analysis of the transport properties of a partially ionized gas subject to the constraint that the average random energy of all constituent particles is exactly equal (equipartition of energy). This constraint is necessary so that the formal Chapman-Enskog solution of Boltzman's equation can be used to evaluate the various transport coefficients. Subject to this constraint, a set of tractable equations describing the mass and energy diffusion in a partially ionized gas is obtained that includes all terms correct to the order of the square root of the ratio of the electron to atom mass compared to one. The transport coefficients are evaluated for helium and argon over the complete range of partial ionization assuming that the species particle densities are quite close to their equilibrium values.\r\n\r\nThe analysis indicates that the electron and ion diffusion velocities are more closely coupled than the equations of Chapman and Cowling show. The added coupling implicitly applies the constraint of zero mass velocity to the gas locally. Because of this constraint a current in the direction of (E x B) x B occurs in addition to the direct and Hall currents.\r\n\r\nIt is shown that the only part of the thermal conductivity that can be influenced by a magnetic field is that part of the energy carried by the diffusion of the charged particles. For this reason, magnetic fields, in general, cannot be nearly as effective in reducing heat transfer rates as was previously thought, e. g., a magnetic field will have no influence on the thermal conductivity in a fully ionized gas, except through its influence on the current density and the thermal diffusion.\r\n\r\nChapters VII - IX comprise the second section of this paper and deal with the development of a similarity solution for axially symmetric electric discharges. A number of parameters are obtained and discussed. The solution is evaluated for a discharge in argon gas at one atmosphere pressure in which the temperature on the axis of the discharge varies from 6,000\u00b0K to 19,000\u00b0K. The current-voltage characteristic obtained from this solution is compared with an experimentally determined curve of H. Maecker.\r\n\r\nThe third section of this paper (Chapters X - XIII) is concerned with the mechanisms of energy transfer in arc jet devices. Use is made of the previous sections of the paper to determine the relative magnitude of the amount of energy that is transferred to the gas in the various parts of the electric discharge. The various possible electrode configurations are discussed in detail and compared. The design and performance of an annular electrode arc heater with a rotating arc is next described and discussed. Because of a number of undesirable performance characteristics of this type of electrode configuration, a modified heater was constructed with the cathode emission occurring along the axis of the applied magnetic field. Details of the unexpectedly good performance of this configuration are given. It is shown that the arc potential drop depends primarily on the strength of the applied magnetic field and the gas enthalpy downstream of the arc. The dependence of the arc potential drop on the arc current and the ambient pressure is shown to be weak over the ranges tested, e. g., 50 to 300 amperes for the current and 1 to 4 atmospheres for the pressure. Some heat transfer measurements taken with this equipment are presented.\r\n\r\nAppendix I is concerned with the evaluation of the transport coefficients in a partially ionized gas. Formulae are developed for determining the viscosity, thermal conductivity, and electric conductivity of the plasma. These coefficients are computed for argon and helium at one atmosphere pressure and over the temperature range of partial ionization." }, { "name": "Chen, William S.", "degree": "Engineering Degree", "year": "1961", "title": "Measurements of Aerodynamic Noise on a Flat Plate in Supersonic Flow", "advisor": "Liepmann, Hans Wolfgang; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-07052006-084242", "creators": [ { "name": { "family": "Chen", "given": "William S." }, "id": "Chen-William-S", "display_name": "Chen, William S." } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SEEW-5974", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nMeasurements of aerodynamic noise, in the form of pressure fluctuations in a turbulent boundary layer, were made on a smooth flat plate in the 12- and 20-in. supersonic wind tunnels at the Jet Propulsion Laboratory. The noise was measured with small piezoelectric pressure transducers (0.015-0.03 in. diameter) constructed of barium titanate crystals which were flush-mounted in the flat plate.\r\n\r\nSpectral-energy distributions of the pressure fluctuations are obtained up to a frequency of 0.5 mc at freestream Mach numbers from 2.0 to 5.0, and Reynolds numbers based an bound layer-displacement thickness from 5 x 10(3) to 5 x 10(4). By grouping the test variables into the proper nondimensional forms and correcting for the finite transducer size, the energy spectra are found to be similar and uniquely related to both Mach number and Reynolds number. The total, or integrated, level of noise at the plate surface, in terms of root-mean-square values of the pressure fluctuations, is a constant equal to about 10 times the shear stress [...] the wall. The intensity, [...], is directly proportional to the fourth power of the freestream Mach number.\r\n\r\nCorrelation measurements in time and in the streamwise direction in space show that the noise at the plate surface to convected downstream with a characteristic velocity equal to 75% of the freestream velocity. The correlation dies off rapidly with spacing between pickup points, and the convection velocity shows no dependence on either Mach number or Reynolds number." }, { "name": "Childress, William Stephen", "degree": "PhD", "year": "1961", "title": "Asymptotic Expansion of Navier-Stokes Solutions in Three Dimensions for Large Distances", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-113027", "creators": [ { "name": { "family": "Childress", "given": "William Stephen" }, "id": "Childress-William-Stephen", "display_name": "Childress, William Stephen" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A77G-P071", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis studies the stationary flow field at large distances from a finite obstacle moving uniformly in a viscous, incompressible fluid. The principal results consist of asymptotic expansions, uniformly valid for large distance, of the velocity and the pressure of the flow field.\r\n\r\nThe expansion procedure employed is based upon the introduction of a small, extraneous parameter; the construction is thus recast as a perturbation for small values of the parameter. Owing to the presence of a viscous wake, the perturbation is in general a singular one, and is treated accordingly, using methods developed for related hydrodynamical problems.\r\n\r\nThe calculated results include the following: for the case of axially-symmetric flow, a uniformly valid expansion of the velocity to order [...] inclusive, and of the pressure to order [...] inclusive, r being the distance from the obstacle; for the general case, an expansion of the velocity to order [...] and of the pressure to order [...], inclusive." }, { "name": "Christiansen, Walter Henry", "degree": "PhD", "year": "1961", "title": "Development and Calibration of a Cold Wire Probe for Use in Shock Tubes", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12142005-124939", "creators": [ { "name": { "family": "Christiansen", "given": "Walter Henry" }, "id": "Christiansen-Walter-Henry", "display_name": "Christiansen, Walter Henry" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QGS9-WZ66", "abstract": "The use of a fine unheated wire for making shock tube flow measurements is investigated. The operation of the instrument depends on the transient nature of the shock tube flow. The wire is referred to here as a cold wire; it operates in a non-steady manner which is completely different from the usual hot wire operation. This report describes the construction and calibration of the cold wire.\r\n\r\nThe experimental law for the rate of gain of heat to the wire in air is determined over a range of Mach numbers from 0.4 to 1.9 and a range of Reynolds numbers from 0.035 to 3,500 based on the wire diameter and the conditions in the hot flow following the initial shock wave. Similar measurements are reported for argon. The heat transfer measurements cover the continuum region, the slip and transitional regions, and extend into the free-molecule flow region. The dimensionless results are compared with hot wire measurements obtained in wind tunnels and are found to differ slightly. A difference exists because the cold wire gains heat from the fluid while the hot wire loses heat to the fluid. The measurements are very repeatable and self-consistent, and they indicate that the wire can be used to give an accurate flow measurement in the shock tube.\r\n\r\nSome potential applications of the wire for the study of shocktube flows are presented. It is concluded that the fine unheated wire is a versatile tool that can be used to great advantage in the shock tube." }, { "name": "Copper, John Alan", "degree": "Engineering Degree", "year": "1961", "title": "An Experimental Investigation of the Equilibrium Interface Technique", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-080829", "creators": [ { "name": { "family": "Copper", "given": "John Alan" }, "id": "Copper-John-Alan", "display_name": "Copper, John Alan" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XC3A-2540", "abstract": "The equilibrium interface technique has been suggested as a possible shock tunnel driver method. If this technique is workable, reservoir enthalpy levels can be increased substantially over those obtainable with the tailored interface technique without any physical modification of the shock tube. In order to determine the feasibility of the equilibrium interface technique as a shock tunnel driver method, experiments were performed in a shock tube, utilizing a cold helium driver, over the shock Mach number range 3.29 to 7.26.\r\n\r\nPressure histories were measured at the end of the driven tube; this pressure was found to reach an equilibrium condition for the complete shock Mach number range investigated. From the pressure histories the equilibrium pressure, time to reach equilibrium, and test time were determined. Measured equilibrium pressures were compared with an exact theory and two approximate theories. From the measured equilibrium pressure, the equilibrium enthalpy level was computed. The maximum equilibrium enthalpy was more than six times the reservoir enthalpy produced using the tailored interface technique." }, { "name": "Jacobs, Delbert Harold", "degree": "Engineering Degree", "year": "1961", "title": "The Conduct of Basic Research in the Aerospace Industry", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-092206", "creators": [ { "name": { "family": "Jacobs", "given": "Delbert Harold" }, "id": "Jacobs-Delbert-Harold", "display_name": "Jacobs, Delbert Harold" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RVZX-EQ72", "abstract": "An analysis of basic research activities in the Aerospace industry is presented. A detailed study of Boeing, Convair, Lockheed, and Douglas indicates extensive and widely varying approaches to basic research in these companies.\r\n\r\nThe establishment of a successful basic research organization in any environment is a sequential process subject to many problems and setbacks. The airframe companies, though making promising progress toward this goal, still have a long way to go. The inherent hazards associated with the aerospace business threaten the fledgling basic research organizations, and I believe it will be the exception and not the rule that sound basic research activity will result." }, { "name": "Kevorkian, Jirair Kevork", "degree": "PhD", "year": "1961", "title": "The Uniformly Valid Asymptotic Approximations to the Solutions of Certain Non-Linear Ordinary Differential Equations", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-092728", "creators": [ { "name": { "family": "Kevorkian", "given": "Jirair Kevork" }, "id": "Kevorkian-Jirair-Kevork", "display_name": "Kevorkian, Jirair Kevork" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K8NE-5X16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis work deals with the application of an expansion procedure in terms of two independent time variables for the uniform asymptotic representation of solutions representing certain mechanical systems.\r\n\r\nThe method is first applied to systems governed by the equation [...] where [...] is a small parameter, and f has the character of a damping (i. e. y is a bounded function of t for all t [...] 0).\r\n\r\nIt is shown that the physical problems which can be brought to the above non-dimensional form possess two characteristic time scales, one associated with the oscillatory behavior of the solution, while the other measures the time interval in which the effects of the non-linear term become apparent.\r\n\r\nThe dependence of the solution on these time scales is not simple, in the sense that an asymptotic representation of the exact solution which is valid for large times cannot be obtained by a limit process in which a non-dimensional time variable is held fixed. This fact has motivated the introduction of an expansion procedure in functions of two time variables, and it is shown that with the use of certain simple boundedness criteria a uniform asymptotic representation can be derived.\r\n\r\nIn addition to the above mentioned class of problems a variety of examples possessing certain boundedness properties is studied by this method, including, for example, the Mathieu equation.\r\n\r\nThe main emphasis of this paper is on the constructive rather than general approach to the solutions of specific examples. These examples are introduced in turn to illustrate the underlying ideas of the method, whose main advantage is its simplicity especially for computing the higher approximations." }, { "name": "Kingsland, Louis", "degree": "Engineering Degree", "year": "1961", "title": "Experimental Study of Helium and Argon Diffusion in the Wake of a Circular Cylinder at M = 5.8", "advisor": "Lees, Lester; Kubota, Toshi; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-081550", "creators": [ { "name": { "family": "Kingsland", "given": "Louis" }, "id": "Kingsland-Louis", "display_name": "Kingsland, Louis" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1FDZ-JX04", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperimental measurements of the diffusion of helium and argon in the wake of a porous cylinder were made in the GALCIT hypersonic wind tunnel at Mach number 5.8. The cylinder was mounted perpendicular to the flow and small quantities of tracer gas were pumped through the model walls into the flow. The thermal conductivity method of gas analysis was used to determine the concentration of sample gases extracted from points in the wake.\r\n\r\nThe transverse and axial distribution of concentration appeared to follow theoretical estimates of \"similarity behavior\". Injection of tracer gas was found to have a measurable effect on stagnation pressure and this effect was taken into account during computations. Numerical values of diffusion coefficients along the wake centerline were computed from the experimental data and then compared with theoretical values for laminar flow. Close agreement between experimental and theoretical values at [...] = 18,000 verified that the inner wake was laminar as far downstream as measurements could be made (15 diameters). At [...] = 72,000, the data showed that mixing processes were 3 times more rapid for helium, and 10 times more rapid for argon, than those expected in laminar flow. This result confirmed the presence of turbulence at this flow condition." }, { "name": "Lock, Malcolm Harvey", "degree": "PhD", "year": "1961", "title": "A Study of Two-Dimensional Panel Flutter", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12142005-124410", "creators": [ { "name": { "family": "Lock", "given": "Malcolm Harvey" }, "id": "Lock-Malcolm-Harvey", "display_name": "Lock, Malcolm Harvey" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NZ2V-H267", "abstract": "An investigation of the problem of the flutter of two-dimensional flat panels is undertaken. The research is largely devoted to investigating the adequacy of the ideal flutter theory that has been employed to predict flutter boundaries for such panels. A series of panel flutter experiments carried out in the GALCIT 4\u201d x 10\u201d transonic wind tunnel at Mach numbers up to 1.5 are described in detail. Before the results of these experiments are compared with the predictions of the theory some further analytical studies of the flutter problem are presented that enable a more critical comparison of theory and experiment to be made. These analyses treat some aspects of the problems of transonic and supersonic panel flutter. The nature of the energy exchange at flutter is also considered. This latter study throws considerable light upon the flutter process as described by the ideal theory and also clarifies the breakdown of certain approximate unsteady aerodynamic theories in the low supersonic flow region (1 < M < 1.5). Comparison of theory and experiment reveals considerable differences between the theoretical and experimental flutter boundaries at the lower supersonic Mach numbers. The agreement between theory and experiment improves at Mach numbers above about 1.4. The possible sources of the apparent inadequacy of the theory at the lower supersonic Mach numbers are discussed." }, { "name": "Lynn, Yen-Mow", "degree": "PhD", "year": "1961", "title": "Isentropic Plane Waves in Magnetohydrodynamics", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-134709", "creators": [ { "name": { "family": "Lynn", "given": "Yen-Mow" }, "id": "Lynn-Yen-Mow", "display_name": "Lynn, Yen-Mow" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K49C-2N76", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPlane waves propagating in a perfectly electrically conducting polytropic gas of otherwise uniform state in the presence of an arbitrarily oriented uniform magnetic field are studied; they correspond to plane simple waves in magnetohydrodynamics. Riemann invariants across finite amplitude waves in ordinary gasdynamics are generalized herein to take into account all possible magnetohydrodynamics effects. There exist totally seven types of waves, namely, contact surfaces, forward and backward facing transverse simple waves and forward and backward facing coupled (fast and slow) simple waves. But of these only coupled waves are genuinely nonlinear and receive most of our attention. The mathematical theory of simple waves is discussed first to give a general picture of the underlying structure of solutions. Contact surfaces and transverse simple wave solutions are given next with particular emphasis on the case of the contact surface adjacent to a vacuum, region. An exact analytical solution of coupled waves for gases of arbitrary value of [...] is obtained in terms of generalized Riemann invariants; some of these invariants are expressed in terms of definite integrals of a parameter [...]. The invariant relations among several physical quantities are thus expressed in a parametric form. An alternative method of solving coupled waves by graphical means is proposed and some detailed calculations are presented. General properties of physical variables across coupled waves are mentioned. For the special case of gas in a purely transverse magnetic field, a scheme of solving arbitrary flow problems is discussed briefly. The corresponding case of coupled wave solutions is given in terms of a hypergeometric function. Finally, some examples are shown to illustrate the application of the solutions to actual physical problems." }, { "name": "Narasimha, Roddam", "degree": "PhD", "year": "1961", "title": "Some Flow Problems in Rarefied Gas Dynamics", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11042003-095050", "creators": [ { "name": { "family": "Narasimha", "given": "Roddam" }, "id": "Narasimha-Roddam", "display_name": "Narasimha, Roddam" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1S8T-QA38", "abstract": "This thesis discusses three rather loosely connected problems in free molecule and nearly free molecule flow. First the expansion of a gas cloud into perfect vacuum is considered on the basis of the collision-less Boltzmann equation, and it is shown that if the initial distribution is an isothermal Maxwellian, the density obeys a diffusion equation with a diffusion coefficient proportional to the time. This leads to the description of the free expansion of symmetric clouds in terms of a thick 'diffusion front' traveling at the initial isothermal speed of sound. The expansion of asymmetric clouds and the flow due to sources and jets are also studied.\r\n\r\nSecond, a method of iteration proposed by Willis for calculating nearly free molecular flow is extended to general unsteady flows; it is then applied to the flow through an orifice to show that the correction to the mass flow is of the first order in the inverse Knudsen number. The coefficient, estimated by making some reasonable assumptions about the three-dimensional nature of the flow, is found to agree quite well with Liepmann's measurements.\r\n\r\nFinally a physical basis is suggested for Krook's collision model used in the above calculations. Several consequences of the model are then derived, including the important one that, in the Navier-Stokes limit, the model implies a Stokesian gas with a Prandtl number of unity. The value to be given to the parameter in the model is also discussed at some length." }, { "name": "Rice, James Orville", "degree": "Engineering Degree", "year": "1961", "title": "A Theoretical Investigation of Particle Motion in an Oscillating Gas", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-154740", "creators": [ { "name": { "family": "Rice", "given": "James Orville" }, "id": "Rice-James-Orville", "display_name": "Rice, James Orville" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ECN5-NV36", "abstract": "An investigation is made of the drift motion of small particles under the influence of acoustic oscillations. The investigation is made to determine if the motion has a magnitude great enough to produce significant changes on the fuel distribution in the chamber of a liquid propellant rocket motor. The calculations are made for the motion in both a rectangular and a cylindrical chamber.\r\n\r\nIn the rectangular chamber the gas oscillation is restricted to the fundamental transverse mode and motion in only one dimension is considered. The particle drift velocity, that is the non-oscillating, non-damped term in the expression for the particle velocity is found in the solution of the second order equation.\r\n\r\nFor particle motion in the cylindrical enclosure, only gas oscillations in the first transverse or sloshing mode is considered and motion is restricted to a transverse plane of the cylinder. The particle drift velocity, again a second order term, is determined.\r\n\r\nThe magnitude of the drift velocity is calculated using conditions found in a liquid propellant rocket combustion chamber. Distances a typical fuel droplet would move during its average life time are calculated. The distances are small compared to the size of most rocket combustion chambers." }, { "name": "Russell, David Allison", "degree": "PhD", "year": "1961", "title": "Studies of the Effects of Cross-Sectional Area Change and Boundary-Layer Growth on the Motion of a Shock Wave", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-155010", "creators": [ { "name": { "family": "Russell", "given": "David Allison" }, "id": "Russell-David-Allison", "display_name": "Russell, David Allison" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HXQP-VQ30", "abstract": "Three problems concerned with the motion of a shock wave are discussed. The first is an analytical and experimental study of the performance of a shock tube with area change near the diaphragm. Interesting results of this section are the development of a simple shock-speed control through the use of area change, and the fact that a spread-out dissipation region was shown to exist for a configuration where a non-stationary secondary shock wave was originally expected. A general discussion of the use of this type of area change is also included.\r\n\r\nThe second problem is a study of the effects of boundary-layer growth on the motion of a shock wave. A simple theory for predicting the attenuation of a shock wave on entering an upstream-facing tube is developed from the analysis of Spence and Woods. When simple laminar boundary-layer approximations are applied, the theory shows good agreement with measurements.\r\n\r\nThe final problem is an experimental study of the motion of a shock wave downstream of a finite-length area contraction. Normalized results are presented which show that the shock wave emerges from the area change at a speed close to the \"linearized\" theory value, and is then attenuated by second-order disturbances until it reaches the speed predicted for the steady-state configuration. The results are presented in a form which is shown to be insensitive to both the incident shock Mach number and the amount of the area reduction." }, { "name": "Stearman, Ronald Oran", "degree": "PhD", "year": "1961", "title": "Part I. The Stability of a Membrane in a Subsonic Flow. Part II. The Stability of a Grid of Panels in a Supersonic Flow", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-160627", "creators": [ { "name": { "family": "Stearman", "given": "Ronald Oran" }, "id": "Stearman-Ronald-Oran", "display_name": "Stearman, Ronald Oran" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TE64-4652", "abstract": "Part I.
\r\n\r\nAn experimental investigation has been made on the stability of small aspect ratio rectangular membranes in a subsonic flow. The leading and trailing edges of the membrane were attached to rigid streamlined supports while the two streamwise edges were free. Both surfaces of the membrane were exposed to the airstream, and the membrane tension was applied through the trailing edge.
\r\n\r\nThe results of the test show that two types of flutter (instability) occur. The first to appear as the wind speed was increased from zero, with a fixed tension level in the membrane, was a small amplitude flutter which has a shallow wave like motion traveling in the streamwise direction. At higher wind speeds this motion was damped out. A narrow equilibrium zone or boundary existed which separated the first type of flutter from a second type of motion having a traveling wave of larger amplitude and greater speed. This second type of flutter had no tendency to damp out, but became more violent as the wind speed was increased.
\r\n\r\nThe span of the slender membrane is the physical parameter that uniquely determines and controls the first flutter boundary; its mass plays no part here, but does affect the equilibrium zones.
\r\n\r\nAppendix A contains an obvious formulation of the slender membrane flutter problem.
\r\n\r\nPart II.
\r\n\r\nA theoretical investigation has been made on the stability of a grid of panels in a supersonic flow. The problem is formulated by considering this structure as a limiting case of a more general configuration composed of a ring of panels (i.e. an axially stiffened cylindrical shell) whose outer surface is exposed to a supersonic flow parallel to its axis. It is shown that the stability analysis of this more general configuration can be reduced to the analysis of an \"equivalent\" single panel using the circulant matrix idea. The reduction procedure, applicable to most cyclic configurations, allows for all types of inter-element (panel) coupling and is subject to the sole restriction that the dynamic phenomenon be satisfactorily described by linear theory.
\r\n\r\nIt is shown that at least five different multi-panel configurations can be obtained from this general problem by taking the appropriate limiting process. The stability (flutter) analysis of one of these limiting cases is discussed for high Mach number flows where only an elastic coupling exists between neighboring panels.
" }, { "name": "Sullivan, Timothy Lay", "degree": "Engineering Degree", "year": "1961", "title": "The Effect of Floating Rings on the Stability of Longitudinally Stiffened Cylinders in Axial Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-135322", "creators": [ { "name": { "family": "Sullivan", "given": "Timothy Lay" }, "id": "Sullivan-Timothy-Lay", "display_name": "Sullivan, Timothy Lay" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3MBR-S755", "abstract": "An experimental investigation was conducted to determine the effect of floating rings on the stability of longitudinally stiffened, thin-walled cylinders in axial compression. Mylar and Plexiglas were used as the skin and stiffening materials, respectively. The primary objectives of the investigation were: (1) to determine the increase in buckling stress that could be obtained by the addition of floating rings; (2) to determine the ring stiffness required for the maximum cylinder strength; (3) to determine what effect the number of longitudinal stiffeners had on the ability of the rings to increase the buckling stress; and (4) to examine the mechanism of buckling in the various ring-stringer combinations. A strength-weight analysis was also made.\r\n\r\nThe addition of rings was found to be very effective in increasing the cylinder buckling load when 24 longitudinal stiffeners were used. The addition of three rings to a cylinder with 24 longitudinal stiffeners increased the buckling load 123 per cent with only a 20 per cent increase in weight. The ring stiffness beyond which there was no more increase in cylinder buckling strength was determined for the 24 stringer, two and three ring configurations. The ability of a ring to increase the buckling stress was markedly decreased when the number of longitudinal stiffeners was decreased from 24 to 12. The mechanism of buckling was also affected by the number of rings and longitudinal stiffeners.\r\n\r\nIn the light of the experimental results, two analytical methods are suggested for predicting the buckling stress of floating ring stiffened cylinders." }, { "name": "Wong, Howard", "degree": "Engineering Degree", "year": "1961", "title": "Preliminary Study of the Rate and Degree of Thermal Ionization of Argon Behind Shock Waves", "advisor": "Jahn, Robert G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-102142", "creators": [ { "name": { "family": "Wong", "given": "Howard" }, "id": "Wong-Howard", "display_name": "Wong, Howard" } ], "advisors": [ { "name": { "family": "Jahn", "given": "Robert G." }, "id": "Jahn-R-G", "role": "advisor", "display_name": "Jahn, Robert G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SDGQ-VZ93", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA microwave system (K-band, 24KMC) was designed and assembled to study the degree of ionization in argon as a function of time or distance behind shock waves in a shock tube. The relaxation time for ionization and the attenuation and reflection of the microwave at equilibrium were measured for Mach numbers from 6.19 to 7.74 at [...] of 5mm and 10mm Hg to determine the influence of temperature, density, collision cross-section and impurities. These measurements were complemented with theoretical calculation of microwave absorption and electron density at equilibrium for a Mach number range of 6 to 8 with initial pressures [...] of 1 mm to 10mm Hg. (Sections II, III, IV)" }, { "name": "Anderson, David Ellsworth", "degree": "Engineering Degree", "year": "1960", "title": "Investigation of Ablation of Ice Bodies in Hypersonic Flows", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-140201", "creators": [ { "name": { "family": "Anderson", "given": "David Ellsworth" }, "id": "Anderson-David-Ellsworth", "display_name": "Anderson, David Ellsworth" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CD24-6081", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe physical characteristics of the ablation process are described. A theoretical approach to calculate the heat transfer to the wall of an ablating body under flow conditions encountered in the GALCIT hypersonic tunnels is outlined. Simplification is achieved by assuming the vapor pressure next to the subliming body is at its equilibrium value. The GALCIT hypersonic test facilities are described briefly. Methods of manufacture are given for [...], [...], and [...] models. Techniques and special test equipment used in obtaining experiments results with [...] and [...] (camphor) are described. An illustration of the computational technique used to determine the heat transfer rates to the wall and the wall temperature distributions is included. Figures to show the agreement between theory and experiment are presented and reasonable results are obtained for temperature distribution, but heat-transfer rates (ablation rates) are greater for theory than for experiment." }, { "name": "Fleming, Edward Richard", "degree": "PhD", "year": "1960", "title": "Non-Linear Flutter", "advisor": "Fung, Yuan-cheng; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-133349", "creators": [ { "name": { "family": "Fleming", "given": "Edward Richard" }, "id": "Fleming-Edward-Richard", "display_name": "Fleming, Edward Richard" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CSNK-SA02", "abstract": "The problem of two degree of freedom flutter in the presence of structural non-linearities is investigated. The specific problem chosen for investigation is that of bending-torsion flutter of a two-dimensional airfoil in a supersonic flow. The Kryloff-Bogoliuboff assumption of nearly sinusoidal response with slowly varying amplitude and phase is made and aerodynamic piston theory is used throughout the analysis.
\r\n\r\nFormulas for flutter limit cycles are developed in terms of general structural non-linearities. Necessary and sufficient conditions are developed for the existence of stable flutter limit cycles in the case of an airfoil with torsional stiffness. Several numerical examples of this case are given including a case which exhibits flutter for large disturbances but is stable at all airspeeds for small disturbances.
\r\n\r\nAn analog computer investigation of flutter dependence on initial conditions is given.
\r\n" }, { "name": "Glick, Herbert Seymour", "degree": "PhD", "year": "1960", "title": "Modified Crocco-Lees Mixing Theory for Supersonic Separated and Reattaching Flows", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-132722", "creators": [ { "name": { "family": "Glick", "given": "Herbert Seymour" }, "id": "Glick-Herbert-Seymour", "display_name": "Glick, Herbert Seymour" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0V7K-QS61", "abstract": "Re-examination of the Crocco-Lees method has shown that the previous quantitative disagreement between theory and experiment in the region of flow up to separation was caused primarily by the improper C(K) relation assumed. A new C(K) correlation, based on low-speed theoretical and experimental data and on supersonic experimental results, has been developed and found to be satisfactory for accurate calculation of two-dimensional laminar supersonic flows up to separation.\r\n\r\nA study of separated and reattaching regions of flow has led to a physical model which incorporates the concept of the \"dividing\" streamline and the results of experiment. According to this physical model, viscous momentum transport is the essential mechanism in the zone between separation and the beginning of reattachment, while the reattachment process is, on the contrary, an essentially inviscid process. This physical model has been translated into Crocco-Lees language using a semi-empirical approach, and approximate C(K) and F(K) relations have been determined for the separated and reattaching regions. The results of this analysis have been applied to the problem of shock wave-laminar boundary layer interaction, and satisfactory quantitative agreement with experiment has been achieved." }, { "name": "Gorecki, Jacek Piotr", "degree": "PhD", "year": "1960", "title": "An Investigation of Temperature Fluctuations on Bluff Bodies", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242006-083641", "creators": [ { "name": { "family": "Gorecki", "given": "Jacek Piotr" }, "id": "Gorecki-Jacek-Piotr", "display_name": "Gorecki, Jacek Piotr" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KV3S-CJ64", "abstract": "Temperature fluctuations and recovery temperatures on the surface of a circular cylinder (with axis normal to a subsonic compressible flow) and the field of flow about the cylinder, particularly the wake area, are investigated experimentally in range between M = 0.35, Re = 117,000 and M = 0.70, Re = 201,000.\r\n\r\nSpectral analysis of fluctuations on body surface and other evidence indicate that formation of discrete vortex cores from the separated shear layers is initially an impulsive random process (of the generalized \"shot effect\" type), although the wake farther downstream from the model has a definitely periodic structure.\r\n\r\nImpulsive formation of vortex cores can be enhanced by wind tunnel resonance or by a high turbulence level in the free stream and is accompanied by abnormal cooling of the model surface in the separated area - the mechanism of these effects is also investigated." }, { "name": "Hunter, Herbert Erwin", "degree": "PhD", "year": "1960", "title": "Application of Asymptotic Expansion Procedures to Low Reynolds Number Flows about Infinite Bodies", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-134820", "creators": [ { "name": { "family": "Hunter", "given": "Herbert Erwin" }, "id": "Hunter-Herbert-Erwin", "display_name": "Hunter, Herbert Erwin" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5PBX-0J36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSeveral limiting cases for viscous incompressible flow are considered for two examples. The first example considered is that of the flow past an expanding infinite cylinder at an angle of attack. The time dependence of the radius of the cylinder is given by the power law R = [...]. The second example considered is the flow past a semi-infinite power law body of revolution (i. e. R = [...]) at zero angle of attack. Both examples are considered for the limiting case of small Reynolds number. The Reynolds number is based on a characteristic length obtained from the parameters in the expression for the radius. The second example is also considered for the limiting case of the flow far down stream.\r\n\r\nAsymptotic expansions of the solution valid for the limiting cases considered (i. e, low Reynolds number or flow far down stream) are obtained by applying singular perturbation procedures. These expansions are obtained for 0 <= n < 1 for the first example and for 0 <= n <= 1/2 for the second example. For the second example the terms in the low Reynolds number expansion are not obtained in closed form, except for n = 1/2. For n < 1/2 the low Reynolds number expansion of the Navier-Stokes equations is expressed in terms of the solution of the corresponding Stokes flow problem. The expansions obtained for the flow far down stream on the power law body of revolution have the character of a very viscous flow although they are valid for any fixed Reynolds number." }, { "name": "Lindquist, David Max Wadsworth", "degree": "Engineering Degree", "year": "1960", "title": "Exact and Approximate Solutions to the Pressure-Loaded Plate Strip with Temperature Distribution", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-131831", "creators": [ { "name": { "family": "Lindquist", "given": "David Max Wadsworth" }, "id": "Lindquist-David-Max-Wadsworth", "display_name": "Lindquist, David Max Wadsworth" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G7PZ-8898", "abstract": "The large deflection analysis for a plate strip under uniform pressure and temperature loading is extended to include spanwise variation of temperature. An exact temperature distribution is derived and stress and deflection equations are developed for the fundamental mode thereof. A parabolic approximation to the fundamental mode is shown to be reasonably accurate. Using this approximation, a direct analogy to the case of uniform temperature distribution can be demonstrated in terms of \"effective\" pressure, temperature moment, and average temperature. The equilibrium equations are formally identical, permitting the use of design charts based on spanwise constant loadings." }, { "name": "MacGillivray, Dean", "degree": "PhD", "year": "1960", "title": "Motion of a Current Element Through a Fluid of Low Electrical Conductivity", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-131316", "creators": [ { "name": { "family": "MacGillivray", "given": "Dean" }, "id": "MacGillivray-Dean", "display_name": "MacGillivray, Dean" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B0AW-TR02", "abstract": "Two-dimensional flow of an incompressible, viscous, electrically conducting fluid past a current element is studied. A solution in the form of an asymptotic development is obtained, valid as a certain dimensionless parameter (essentially the product of the electrical conductivity and the current) tends to zero. An expression for the drag on the current element is computed, and is found to be independent of viscosity." }, { "name": "Mohlenhoff, William", "degree": "Engineering Degree", "year": "1960", "title": "Experimental Study of Helium Diffusion in the Wake of a Circular Cylinder at M=5.8", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-131025", "creators": [ { "name": { "family": "Mohlenhoff", "given": "William" }, "id": "Mohlenhoff-William", "display_name": "Mohlenhoff, William" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QH2Z-TC50", "abstract": "An experimental study of the diffusion of helium in the wake of a circular cylinder was conducted in the GALCIT hypersonic wind tunnel at a Mach number of 5.8. The cylinder was constructed of material having random porosity and was mounted with its axis perpendicular to the stream. The light gas was injected in small amounts and the thermal conductivity method was utilized to detect the concentration of helium in the air at points downstream. Problems in the utilization of the thermal conductivity method for low sample densities were overcome by suitable calibration.\r\n\r\nFlow in the wake of the cylinder was found to display characteristically similar behavior at a few diameters downstream, with respect to decay and spread of the concentration. Reynolds number similarity was established in the laminar case, but turbulent Reynolds number similarity may require reference to momentum thickness, which was not possible with the present data.\r\n\r\nProfile data was somewhat marred by a tunnel pressure perturbation, but many of the important conclusions were not affected. The profiles appear to follow the theoretical Gaussian distribution in the similar region.\r\n\r\nThe thermal conductivity method is quite promising as a means of tracing the diffusion of one binary gas constituent in another, as applied to hypersonic wind tunnel experiment. It will also serve in the analysis of transition and turbulence, and of the lateral spreading of the turbulent fluid into the rest of the wake region behind the bow shock." }, { "name": "Reshotko, Eli", "degree": "PhD", "year": "1960", "title": "Stability of the Compressible Laminar Boundary Layer", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042006-141741", "creators": [ { "name": { "family": "Reshotko", "given": "Eli" }, "id": "Reshotko-Eli", "display_name": "Reshotko, Eli" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M6HG-WW29", "abstract": "In previous theoretical treatments of the stability of the compressible laminar boundary layer the effect of the temperature fluctuations on the \"viscous\" (rapidly varying) disturbances is either ignored (Lees-Lin), or is accounted for incompletely (Dunn-Lin). A thorough reexamination of this problem shows that temperature fluctuations have a profound influence on both the \"inviscid\" (slowly varying) and viscous disturbances above a Mach number of about 2.0. The present analysis includes the effect of temperature fluctuations on the viscosity and thermal conductivity, and also introduces the viscous dissipation term that was dropped in the earlier theoretical treatments.\r\n\r\nSome important results of the present study are: (1), the rate of conversion of energy from the mean flow to the disturbance flow through the action of viscosity in the vicinity of the wall increases with Mach number; (2), instead of being nearly constant across the boundary layer, the amplitude of inviscid pressure fluctuations for Mach numbers greater than 3 decreases markedly with distance outward from the plate surface. This behavior means that the jump in magnitude of the Reynolds stress in the neighborhood of the critical layer is greatly reduced; (3), at Mach numbers less than about 2 dissipation effects are minor, but they become extremely important at higher Mach numbers since for neutral disturbances they must compensate for the generally destabilizing effects of items (1) and (2).\r\n\r\nNumerical examples illustrating the effects of compressibility (including neutral stability characteristics) are obtained and are compared with the experimental results of Laufer and Vrebalovich at M = 2.2, and of Demetriades at M = 5.8." }, { "name": "Sarosdy, Louis Robert", "degree": "Engineering Degree", "year": "1960", "title": "Cavitation Similarity Studies with Water and Freon-113", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-155203", "creators": [ { "name": { "family": "Sarosdy", "given": "Louis Robert" }, "id": "Sarosdy-Louis-Robert", "display_name": "Sarosdy, Louis Robert" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CZWP-PB71", "abstract": "The development of cavitation behind a disc in water and Freon-113 was investigated in a cavitation tunnel designed for this purpose. Measurements of pressure within the cavities formed in water indicated that the vapor pressure within the cavity was less than the vapor pressure of the fluid at the bulk temperature. Observations of the cavities formed in the two liquids showed qualitative differences, and some possible reasons for this behavior are discussed." }, { "name": "Sturtevant, Bradford", "degree": "PhD", "year": "1960", "title": "The Effusion of Charged Particles from a Shock Heated Gas", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12302004-145356", "creators": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-Bradford", "display_name": "Sturtevant, Bradford" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PCNN-DW03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental and theoretical investigation is made of the application of a molecular beam type sampling device for studying low density shock tube flows to the case of slowly ionizing argon behind a reflected shock wave. The flux of charged particles from a gas heated to about 10,OOO[degrees]K and 20 mm. Hg. through a small orifice in the shock tube end wall is measured. The processes determining this flux are the initial stages of ionization in argon and the diffusion of charged particles to a cold metallic wall. Providing the diffusion process is understood, the measurements constitute a direct observation of incipient ionization ([...]).\r\n\r\nThe transient charge diffusion mechanism is studied in detail theoretically, avoiding the assumption of ambipolar diffusion. It is concluded that the major problem lies in the understanding of the wall-gas interaction as represented by boundary conditions at the wall. An approximate relation for charge effusion is derived.\r\n\r\nIt is concluded from the experimental results that the initial ionization can not be due to a single step, electron-atom collision process but must result from a series of several atom-atom collisions resulting in the ionization of argon atoms." }, { "name": "Utterback, Paul Wilson", "degree": "Engineering Degree", "year": "1960", "title": "An Experimental Investigation of Flow Conditions Behind a Bluff Body Flameholder", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-151405", "creators": [ { "name": { "family": "Utterback", "given": "Paul Wilson" }, "id": "Utterback-Paul-Wilson", "display_name": "Utterback, Paul Wilson" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YHR8-6948", "abstract": "Carbon-containing combustion products were analyzed behind a bluff body flameholder in a two-dimensional duct. Molar concentrations of carbon monoxide, carbon dioxide, and unburned hydrocarbon fuel were obtained at various positions vertically across the duct 34 1/8 inches behind the flameholder by means of an Infra Red Anaylzer. A carbon balance was conducted across the duct, and parameters such as combustion efficiency, temperature, pressure, sampling rate, density, and velocity of the gas mixture were determined.\r\n\r\nThe data indicate that the methods of sampling and measurement and the use of the analyzer were satisfactory in this type of investigation. Division of the flame into three distinct zones (unburned, reaction, and burned) is shown to be a reasonable approximation. The carbon balance across the duct was found to be in good agreement with theoretical predictions, provided that the water vapor in the gas samples was properly evaluated. Flame spreading behind the flameholder is a slow process, and this fact was verified by evaluation of the combustion efficiency and by determination of the limits of the burned zone." }, { "name": "Williams, Allen Dean", "degree": "Engineering Degree", "year": "1960", "title": "The Effect of Tip Clearance Flows on Performance of Axial Flow Compressors", "advisor": "Rannie, W. Duncan; Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-163445", "creators": [ { "name": { "family": "Williams", "given": "Allen Dean" }, "id": "Williams-Allen-Dean", "display_name": "Williams, Allen Dean" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7T14-SP07", "abstract": "The change in rotor performance with tip clearance of an axial flow compressor over a wide range of flow rates above stall was investigated to gain more understanding of the effect of the tip flow mechanism on rotor performance.\r\n\r\nThe experimental results were compared with a flow model proposed previously and found to be in reasonable agreement." }, { "name": "Bauer, Andrew Burkhard", "degree": "Engineering Degree", "year": "1959", "title": "Vortex Formation and Shedding from a Two-Dimensional, Thin, Flat Plate Parallel to the Free Stream", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-130544", "creators": [ { "name": { "family": "Bauer", "given": "Andrew Burkhard" }, "id": "Bauer-Andrew-Burkhard", "display_name": "Bauer, Andrew Burkhard" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K0ZD-XY10", "abstract": "Vortex formation and shedding from the trailing edge of a two-dimensional, thin, flat plate parallel to the free stream is studied experimentally for the case of incompressible flow. Consideration of the classical boundary layer theory, the Karman vortex-street theory, the formation of the vortex centers, and some annihilation of vorticity in the free shear layers leads to an estimate of Strouhal number. This estimate is in reasonable agreement with experiment. The flow phenomena of a splitter plate mounted aft of the main plate and of a NACA 0012 airfoil are also observed experimentally and are found to be in essential agreement with applicable portions of the theory." }, { "name": "Chang, I-Dee", "degree": "PhD", "year": "1959", "title": "Navier-Stokes Solutions at Large Distances from a Finite Object", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062006-083016", "creators": [ { "name": { "family": "Chang", "given": "I-Dee" }, "id": "Chang-I-Dee", "display_name": "Chang, I-Dee" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SMPS-TA29", "abstract": "The asymptotic expansion of the Navier-Stokes solutions at fixed Reynolds numbers and large distances from a finite object for an incompressible, stationary and two-dimensional flow is studied. The expansion is a coordinate-type expansion and differs in many mathematical aspects from the more familiar parameter-type expansions for large and small Reynolds number flows. These differences are noted and discussed in some detail. The technique chosen for dealing with the problem is that of the use of an artificial parameter. This is one possible method for using some of the techniques of parameter-type expansions. In particular, at large distances from the object one may distinguish a viscous wake region and a potential (\"outer\") flow region. The relation between these regions is very similar to the relation between the viscous boundary layer and the potential flow region for flow at large Reynolds numbers.\r\n\r\nSeveral terms of the expansion are computed. However, the main emphasis is placed on discussing the methods for deriving these terms. The special features of expansions in artificial parameters are discussed in detail. The role of various properties of Navier-Stokes solutions, such as validity of integral theorems and rapid decay of vorticity is also brought out.\r\n\r\nThe original motivation of the study was an attempt to understand the Filon's paradox which historically was an error in evaluating the momentum, integral of the asymptotic flow field. The present study, however, deals with the general problem of the flow at large distances from a finite object, and, more generally, with expansion techniques for similar problems. The author's explanation of Filon's paradox is only an incidental result." }, { "name": "Chapkis, Robert Lynn", "degree": "Engineering Degree", "year": "1959", "title": "Hypersonic Flow Over an Elliptic Cone: Theory and Experiment", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01032006-130909", "creators": [ { "name": { "family": "Chapkis", "given": "Robert Lynn" }, "id": "Chapkis-Robert-Lynn", "display_name": "Chapkis, Robert Lynn" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/35S5-3H33", "abstract": "By applying hypersonic approximations to Ferri's linearized characteristics method simple results were obtained for the shock shape and surface pressure distribution for an unyawed conical body of arbitrary cross-section. Calculations were carried out for an elliptic cone having a ratio of major to minor axis of 2:1, and a semi-vertex angle of about 12\u00b0 in the meridian plane containing the major axis. An experimental investigation of the flow over this body conducted at a Mach number of 5.8 in the GALCIT hypersonic wind tunnel showed that the surface pressure distribution at zero angle of attack agreed quite closely with the theoretical prediction. On the other hand the simple Newtonian approximation predicts pressures that are too low.\r\n\r\nSurface pressure distributions and schlieren photographs of the shock shape were also obtained at angles of attack up to 14\u00b0 at zero yaw, and at angles of yaw up to 10\u00b0, at zero pitch. At the higher angles of attack the Newtonian approximation for the surface pressures is quite accurate." }, { "name": "Dawson, Thomas Emmett", "degree": "Engineering Degree", "year": "1959", "title": "An Experimental Investigation of a Fully Cavitating Two-Dimensional Flat Plate Hydrofoil Near a Free Surface", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272006-130656", "creators": [ { "name": { "family": "Dawson", "given": "Thomas Emmett" }, "id": "Dawson-Thomas-Emmett", "display_name": "Dawson, Thomas Emmett" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y3SP-XX86", "abstract": "A fully cavitating two-dimensional flat plate hydrofoil at and below a free surface was investigated. The effects of proximity to the free surface, angle of attack, cavitation number and Froude number or gravity on the normal force, the moment about the leading edge, the center of pressure location, the cavity length and the air flow rate into the cavity are discussed. Comparisons to other experiments and theories also are made." }, { "name": "Doering, Eugene Richard", "degree": "Engineering Degree", "year": "1959", "title": "Experiments on the Flow at the Nose of a Thin Airfoil", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192006-081801", "creators": [ { "name": { "family": "Doering", "given": "Eugene Richard" }, "id": "Doering-Eugene-Richard", "display_name": "Doering, Eugene Richard" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6NZA-Q027", "abstract": "An investigation of a family of two-dimensional airfoils was conducted in the Merrill Wind Tunnel at California Institute of Technology, to determine experimentally the effect of camber on an airfoil that stalls at the nose, and to compare the results with a simplified thin airfoil theory, which requires that flow conditions at the nose be similar.\r\n\r\nThe nine percent thick models had cambers of zero, three, and six percent, and a fourth model with six percent camber had a rear slot at about 70 percent chord.\r\n\r\nTests conducted at Reynolds Numbers of 640,000 and 840,000 showed that the addition of camber to a nose-stalling airfoil tended to make it a trailing-edge staller or partially so, but that by use of the slot, the stall was shifted back to the nose.\r\n\r\nGood agreement was obtained in the theoretical and experimental determination of maximum lift for the slotted airfoil, but not for the angle at which this occurred." }, { "name": "Hemmingway, Richard Earl", "degree": "Engineering Degree", "year": "1959", "title": "Turbulent Flow in a Nuclear Heat-Exchanger", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-144119", "creators": [ { "name": { "family": "Hemmingway", "given": "Richard Earl" }, "id": "Hemmingway-Richard-Earl", "display_name": "Hemmingway, Richard Earl" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0QX0-8Y04", "abstract": "A gas-cooled, cylindrical, nuclear reactor is used as the basis in the theoretical derivation of the coolant's enthalpy increase and pressure loss across the reactor. Turbulent flow is assumed in the coolant passages of the reactor, and the Reynolds analogy is used as the basis for correlating the heat transfer coefficient and the friction coefficient.\r\n\r\nThe general equations are derived and two examples, a nuclear-hydrogen rocket and a ramjet, are given to demonstrate applications of the general results." }, { "name": "Monroe, Louis L.", "degree": "Engineering Degree", "year": "1959", "title": "Investigation of the Transmission of a Shock Wave Through an Orifice", "advisor": "Roshko, Anatol; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-134039", "creators": [ { "name": { "family": "Monroe", "given": "Louis L." }, "id": "Monroe-Louis-L", "display_name": "Monroe, Louis L." } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y42Q-9F44", "abstract": "A shock wave propagating in air in a shock tube was reflected from an orifice plate, and the strength or Mach number of the transmitted wave was measured for a range of incident shock Mach numbers from 3 to 9 for several types of orifices. Also schlieren photographs of the starting flow pattern were made for some of the orifices investigated.\r\n\r\nThe measured values of transmitted shock strength are compared with predicted values based on a theoretical one-dimensional flow model for both an ideal gas and a real gas. The agreement between the measured values of transmitted wave Mach number and the theoretically predicted values is extremely good in the Mach number range investigated for a wedge type orifice at an ambient shock tube pressure of 5.0 mm Hg, and also for a conical type orifice at an ambient shock tube pressure of 2.5 mm Hg. For both orifices the ratio of outlet area to inlet area is 7.67.\r\n\r\nThe data also indicate that for a wedge type orifice of area ratio of 23.0 and for a plate (free expansion) type orifice of area ratio 23.0 possible boundary layer and shock wave interactions downstream of the orifice result in measured values of transmitted wave Mach number somewhat greater than that predicted by the one-dimensional flow model.\r\n\r\nInvestigation of the conical orifice with an area ratio 7.67 at a low ambient pressure in the shock tube (0.4 mm Hg) also yields measured values of transmitted wave Mach number greater than that predicted by the one-dimensional flow model, indicating the probable development of a thick boundary layer behind the transmitted wave downstream of the orifice." }, { "name": "Peck, Jerry Clifford", "degree": "Engineering Degree", "year": "1959", "title": "Bending-Torsion Flutter of an Airfoil with Nonlinear Structural Characteristics", "advisor": "Sechler, Ernest Edwin; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132006-152832", "creators": [ { "name": { "family": "Peck", "given": "Jerry Clifford" }, "id": "Peck-Jerry-Clifford", "display_name": "Peck, Jerry Clifford" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P0DS-PX18", "abstract": "A theoretical analysis of the incompressible bending-torsion flutter of a two-dimensional airfoil with nonlinear structural characteristics is presented. The Method of Slowly Varying Parameters of Kryloff and Bogoliuboff is applied, and the steady-state oscillations are found. The stability of the steady-state oscillation is analyzed through the use of perturbation equations. A quasi-steady aerodynamic approximation is used, and closed-form solutions for the steady-state oscillations are found for the case of elastic torsional nonlinearities. A numerical example of a soft-hard stiffness characteristic is treated, and the steady-state and stability results given." }, { "name": "Royce, Winston Walker", "degree": "PhD", "year": "1959", "title": "Transonic Flow Over a Non-Lifting Slender Body of Revolution", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-153522", "creators": [ { "name": { "family": "Royce", "given": "Winston Walker" }, "id": "Royce-Winston-Walker", "display_name": "Royce, Winston Walker" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NFVH-YH92", "abstract": "Sonic flow past a non-lifting, slender body of revolution is investigated by the use of small disturbance theory. An approximation for the local Mach number distribution is used to linearize the transonic potential equation. Solutions for the velocity components, pressure distribution, and drag are obtained in terms of simple integrals involving the body geometry. An extension to other Mach numbers in the transonic range is given. The theoretical pressure distribution and drag are found to give good agreement with experimental data." }, { "name": "Satre, Robert Scott", "degree": "Engineering Degree", "year": "1959", "title": "An Experimental Investigation of Flame Propagation Downstream of a Cylindrical Flameholder", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01052006-153127", "creators": [ { "name": { "family": "Satre", "given": "Robert Scott" }, "id": "Satre-Robert-Scott", "display_name": "Satre, Robert Scott" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6BCM-YC54", "abstract": "Flame propagation downstream of a 1/8 inch circular cylindric flameholder was studied experimentally. The effects on flame spreading of the fuel-air mixture velocity and such chemical parameters as fuel-air ratio, mixture temperature, and fuel composition were determined. Combustion wake widths were determined from measurement of spark Schlieren photographs.\r\n\r\nThe data indicate that flow was laminar up to a critical velocity corresponding to a Reynolds number of 0.9 x 10^4, and turbulent for super critical velocities. The experiments were restricted to the turbulent flow regime. In this regime, the wake width was velocity independent and fuel-air ratio had only a slight effect. There was a small, and nearly linear, decrease in wake width as the temperature was increased. The effect substitution of hydrogen gas for hydrocarbon fuel revealed that turbulent wake spreading was independent of fuel composition.\r\n\r\nComparison of the experimental results with theoretical treatments of flame spreading showed that none of the existing theories was satisfactory." }, { "name": "Smith, Homer Leroy", "degree": "Engineering Degree", "year": "1959", "title": "The Study of a Lifting Air Breathing Boost for Satellite Launch", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-094057", "creators": [ { "name": { "family": "Smith", "given": "Homer Leroy" }, "id": "Smith-Homer-Leroy", "display_name": "Smith, Homer Leroy" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q47F-X275", "abstract": "The effect on performance of variations in power plant, aircraft, and rocket parameters was calculated for a lifting air breathing boost system for launching satellites. A limited variation in aircraft flight plan was considered also. In addition, comparisons were made between the air breathing boost system and a three stage all rocket system. For the air breathing boost computations were made for launch Mach numbers ranging from two to five.\r\n\r\nThe air breathing boost was assumed to be a turbojet or dual cycle engine powered aircraft. The rocket used in conjunction with the boost had two stages. In computing aircraft performance thrust and engine specific fuel consumption were taken as constants. The lift to drag ratio was also considered constant for each portion of the flight profile which consisted of a take off and acceleration to climb speed, a two step climb, and a pull up to the maximum angle attainable for rocket launch.\r\n\r\nIn computing rocket performance burning times, effective exhaust velocities, payload weight ratios, and structural weight ratios were assumed to be the same for each stage. Drag was neglected in rocket calculations, and the acceleration of gravity was assumed constant. The calculations were made by computing the kinetic and potential energies for a sounding rocket and equating them to the energy required for orbit." }, { "name": "Stockmair, Wilfried", "degree": "Engineering Degree", "year": "1959", "title": "Problems in Effusion", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.; Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072006-131514", "creators": [ { "name": { "family": "Stockmair", "given": "Wilfried" }, "id": "Stockmair-Wilfried", "display_name": "Stockmair, Wilfried" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." }, { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KH55-XN11", "abstract": "The flow of rarefied gases from a vessel through an orifice into vacuum is studied here. Special conditions of this study are that the mean free path of the molecules is of the same order of magnitude as the hole diameter; furthermore the thickness of the wall is neglected. Knudsen [1,2] investigated this effusion problem for constant conditions throughout the gas, assuming Maxwellian velocity distribution and very large mean free paths. In the present study the influence of a one-dimensional temperature gradient extending from the wall upstream into the gas is investigated. Formulae for the massflux and the spatial intensity distribution of the outflowing molecules are calculated for steady flow conditions. Finally the behavior corresponding to a nonstationary temperature gradient (according to suddenly heated or cooled wall) is studied." }, { "name": "Weyers, Paul Frederik Robert", "degree": "PhD", "year": "1959", "title": "The Vibration and Acoustic Radiation of Thin-Walled Cylinders Caused by Internal Turbulent Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062006-134627", "creators": [ { "name": { "family": "Weyers", "given": "Paul Frederik Robert" }, "id": "Weyers-Paul-Frederick-Robert", "display_name": "Weyers, Paul Frederik Robert" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QTM4-9Z19", "abstract": "The investigation concerned noise produced by turbulent flow adjacent to a flexible wall. Measurements of the spectrum and intensity of the pressure field outside thin-walled Mylar cylinders containing turbulent pipe flow have been made. The resulting spectra could be interpreted in relation to the elastic properties of the cylinders and the character of the turbulent fluctuations inside the flow. The eigen frequencies of the cylinders could be identified and similarity parameters for the spectra were established. The effect of cylinder wall thickness on the spectrum and intensity of the pressure fluctuations was investigated. It was found that the intensity of the external pressure field scaled with the fifth power of the velocity at the center of the pipe.
\r\n\r\nFor one particular case the spectrum and intensity of the pressure fluctuations exerted by the turbulent flow on the wall were measured. The intensity of the pressure fluctuations at the wall scaled with the fourth power of the velocity as expected. The ratio of the root-mean-square wall pressure to the dynamic pressure was found to be independent of Mach number and equal to a constant (0.0078). Similarity laws for the spectra of the wall pressure fluctuations were also confirmed.
" }, { "name": "Wood, Richard Donald", "degree": "Engineering Degree", "year": "1959", "title": "An Experimental Investigation of Hypersonic Stagnation Temperature Probes", "advisor": "Lees, Lester; Kendall, James M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082006-130736", "creators": [ { "name": { "family": "Wood", "given": "Richard Donald" }, "id": "Wood-Richard-Donald", "display_name": "Wood, Richard Donald" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kendall", "given": "James M." }, "id": "Kendall-James-Madison", "role": "advisor", "display_name": "Kendall, James M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KXK1-JQ18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of single-shielded hypersonic stagnation temperature probes was conducted in the GALCIT Leg No.1 hypersonic wind tunnel and in the Jet Propulsion Laboratory 12-inch supersonic wind tunnel.\r\n\r\nBy the combined use of both shield and base heating, a probe recovery factor of r = 1.0 was obtained over a range of Reynolds numbers at M [...] = 5.75. By using the experimental data and simple heat balance equations, the probe losses, for the conditions investigated, were found to be in the proportion: shield conduction loss - 15; base conduction loss - 3; thermocouple conduction loss - 1; thermocouple radiation loss - 3/100. The typical decrease in probe recovery factor observed for decreasing Reynolds number appears to be related to a decrease in the base temperature and not to the wire conduction loss as commonly assumed.\r\n\r\nAn optimum probe vent to entrance area ratio of [...] was found and is shown to be a function of the number of vent holes used in the shield.\r\n\r\nNo single calibration parameter was found that could relate the experimental recovery factors under all conditions." }, { "name": "Ang, Dang Dinh", "degree": "PhD", "year": "1958", "title": "Some Radiation Problems in Elastodynamics", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-092112", "creators": [ { "name": { "family": "Ang", "given": "Dang Dinh" }, "id": "Ang-Dang-Dinh", "display_name": "Ang, Dang Dinh" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TF74-2977", "abstract": "Three elastodynamic problems are studied. The first deals with waves generated by instantaneous and uniform closure of a semi-infinite crack, while in the second, a semi-infinite crack is suddenly initiated in a continuous medium initially subjected to uniform tension. The last of the three deals with a force moving at uniform velocity along a semi-infinite crack, starting from the edge. The problems are solved by means of the Wiener-Hopf integral methods. The characteristic wave patterns and stress singularities are discussed." }, { "name": "Bell, Richard William", "degree": "PhD", "year": "1958", "title": "The Elastic Instability of Thin Cantilever Struts on Elastic Supports with Axial and Transverse Loads at the Free End", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-093255", "creators": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-Richard-William", "display_name": "Bell, Richard William" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5FEX-RT33", "abstract": "An analysis is made of the elastic instability of thin, tapered cantilever struts subjected to a general concentrated load acting in the plane of the strut at its tip. The strut is supported at its root on a structure permitting elastic rotations of the root section in the buckled mode. The influence of the support on the minimum buckling load is one of the main points of interest. It is shown that the general linearized problem can be formulated in one second order differential equation with variable coefficients, and two associated boundary conditions. This homogeneous eigenvalue system constitutes a simplified statement of the problem which permits the easy extension of exact linear theory to a wide class of taper functions, including the effect of elastic supports. The solution emerges in terms of a generalized deflection parameter, rather than of either the torsional or the bending components of the coupled buckling mode, which are governed respectively by third and fourth order differential equations.\r\n\r\nSpecific solutions are derived for some \"natural\" taper forms of the strut. The general solutions for the deflection mode are power series, which are rapidly convergent for certain limiting geometries. The problems of convergence of the series, some singular physical aspects associated with pointed tips, and the increasing numerical difficulty for large taper ratio are correlated with the behavior of the singular points of the equation. Numerical results showing the effects of the elastic supports on minimum buckling loads are presented for the uniform strut and for a simple case of the tapered strut. The series solutions for more general cases are given in a form which can be applied to digital computers.\r\n" }, { "name": "Demetriades, Anthony", "degree": "PhD", "year": "1958", "title": "An Experimental Investigation of the Stability of the Hypersonic Laminar Boundary Layer", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232004-093013", "creators": [ { "name": { "family": "Demetriades", "given": "Anthony" }, "id": "Demetriades-Anthony", "display_name": "Demetriades, Anthony" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7SR9-9M59", "abstract": "NOTE: text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the stability of the hypersonic laminar boundary layer was carried out for the case of a flat insulated surface at zero angle of attack. The stream-wise amplitude variation of both \"natural\" disturbances (i.e., flow fluctuations existing naturally in the boundary layer) and of disturbances artificially excited with a \"siren\" mechanism was studied with the aid of a hot-wire anemometer. In both cases it was found that such small fluctuations amplify for certain ranges of the fluctuation frequency and the Reynolds number [...], and damp for others. The demarcation boundaries for the amplification (instability) zone were found to resemble the corresponding boundaries of boundary layer instability at lower speeds. A \"line of maximum amplification\" of disturbances was also found. The amplification rates and hence the degree of \"selectivity\" of the hypersonic layer were found, however, to be considerably lower than those at the lower speeds. The disturbances selected by the layer for maximum amplification have a wavelength estimated at about twenty times the boundary-layer thickness [...], which is appreciably longer than the corresponding wave-lengths for low-speed boundary-layer flow." }, { "name": "Fabula, Andrew George", "degree": "Engineering Degree", "year": "1958", "title": "Some Experiments in Cavitation Bubble Dynamics", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222004-134550", "creators": [ { "name": { "family": "Fabula", "given": "Andrew George" }, "id": "Fabula-Andrew-George", "display_name": "Fabula, Andrew George" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/942V-N588", "abstract": "Observations of the shape distortion during collapse of individual cavitation bubbles with maximum radii of about 0.5 to 1 cm have been made for collapse times of three to fourteen milliseconds; these observations are compared with theory. The bubbles were produced in superheated water and photographed at 3000 or 5000 frames per second. Growth was triggered by electrolysis and collapse was produced by pressurization. The distortions of bubble shape from spherical were found to be fairly well predicted by the theory of M. Rattray, when his perturbation parameter was adapted in a simple manner to the conditions used. A large variation in the collapse noise, due to bubble distortion caused by translational velocity, was observed to occur over the range of conditions tested." }, { "name": "Heimer, Harry James", "degree": "PhD", "year": "1958", "title": "Balanced Flap Type Supersonic Control Surfaces", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012004-142134", "creators": [ { "name": { "family": "Heimer", "given": "Harry James" }, "id": "Heimer-Harry-James", "display_name": "Heimer, Harry James" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YVYN-ZD39", "abstract": "The purpose of this investigation is to qualitatively explain the flow phenomena which occur on a balanced flap type control surface at supersonic speeds and to find means of calculating the pressure distributions occurring. The popular and generally useful linearized flow theory, and in fact any inviscid theory, cannot be used since viscosity plays a predominant part in the determination of the flow. It is shown that the flow often involves shock induced separation and reflection of shock waves by these separated wakes. Experimental data in the form of pressure distributions and shadowgraph pictures of the flow are used to arrive at a description of the flow. By use of the empirical results given, a method of predicting the pressure distributions for this type of surface is derived. This procedure is then used to calculate several pressure distributions which are compared with those experimentally determined.\r\n\r\nThe separation effects that occur at the larger angles of attack and/or control surface deflection angles cause the control effectiveness and hinge moments to be very non-linear. It is shown that the use of a gap between the wing and control surface delays or eliminates separation depending on the size of the gap used. Data are presented for a typical control surface, in which the hinge moments were reduced by a factor of 8 or 10 by using a gap between the wing and control surface. A method is given for estimating the size gap necessary to achieve this reduction." }, { "name": "Huebner, Danny Frederick", "degree": "Engineering Degree", "year": "1958", "title": "Experimental Development of a Short Flexible Plate Nozzle Using the Influence Method", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012004-143034", "creators": [ { "name": { "family": "Huebner", "given": "Danny Frederick" }, "id": "Huebner-Danny-Frederick", "display_name": "Huebner, Danny Frederick" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YN82-P321", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe purpose of this investigation was to determine the possibility of using a semi-empirical technique, the Influence Method, to shorten the CWT supersonic flexible plate nozzle. The experiments were conducted in the CWT 8 1/2 x 11 feet flexible plate nozzle at [...] = 1.600 and [...] = 1.700.\r\n\r\nThe Influence Method and its application to shortening a flexible plate nozzle are presented and discussed. Included are comparisons of the theoretical and experimental jack influence parameters. Theoretical length estimates are presented which determine to what extent the CWT nozzle could be shortened.\r\n\r\nResults indicate that the Influence Method can be used to shorten the CWT supersonic flexible plate nozzle. The usable testing length was increased by approximately 35% at both the Mach numbers investigated. However, as the nozzle becomes shorter the undesirable Mach number variation, in the region occupied by models, increases from [plus or minus] 0.005 to [plus or minus] 0.015." }, { "name": "Matthews, Malcolm LeRoy", "degree": "Engineering Degree", "year": "1958", "title": "An Experimental Investigation of Viscous Effects on Static and Impact Pressure Probes in Hypersonic Flow", "advisor": "Kendall, James M.; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112006-091955", "creators": [ { "name": { "family": "Matthews", "given": "Malcolm LeRoy" }, "id": "Matthews-Malcolm-LeRoy", "display_name": "Matthews, Malcolm LeRoy" } ], "advisors": [ { "name": { "family": "Kendall", "given": "James M." }, "id": "Kendall-James-Madison", "role": "advisor", "display_name": "Kendall, James M." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "co-advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MQPD-A933", "abstract": "An experimental investigation of viscous effects on static and impact pressure probes was conducted in the GALCIT Leg 1 hypersonic wind tunnel.
\r\n\r\nThis investigation of the impact probes showed viscous effects to be important for free stream Reynolds numbers less than 6000 based on the probe diameter, in the Mach number range 5.4 to 5.7. For 80 < Re < 6000, the results showed the measured impact pressure to be less than the inviscid value. The maximum deviation from the inviscid impact pressure was 2.3 per cent at a Reynolds number of 200. For Re < 80 the measured impact pressure was greater than the inviscid value.
\r\n\r\nThe investigation of the static pressure probes for a Mach number 5.8 and a free stream Reynolds number of 16,000 based on the probe diameter showed a very thick and rapidly growing boundary layer over the probe surface. This boundary layer was sufficient to cause the static pressure measured by a 10 degree cone-nosed probe with its orifice 45 diameters aft of the probe tip to be 7.5 per cent greater than the free stream static pressure. The boundary layer thickness on the 10 degree cone-nosed probe was several times that of the probe radius. The boundary layer was surveyed on a hemispherical-nosed and a flat-nosed probe and showed the boundary layer thickness to be several times that of the 10 degree cone-nosed probe.
" }, { "name": "McCoy, John Carver", "degree": "Engineering Degree", "year": "1958", "title": "An Experimental Investigation of the General Instability of Ring-Stiffened, Unpressurized, Thin-Walled Cylinders Under Axial Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102006-133017", "creators": [ { "name": { "family": "McCoy", "given": "John Carver" }, "id": "McCoy-John-Carver", "display_name": "McCoy, John Carver" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TR8H-6D86", "abstract": "Eight different series of thin-walled Mylar cylinders were tested experimentally to investigate the general instability of ring-stiffened, unpressurized, thin-walled cylinders under axial compressive loading. The primary objectives for these tests were: to determine whether the bending or the torsional stiffness of the rings was the most effective stiffening parameter; to determine the relative effectiveness of ring-stiffeners around the inside and the outside of the cylinders; and to investigate the mechanism of buckling of unpressurized cylinders under axial compression.\r\n\r\nIt was found that the torsional stiffness of the ring-stiffeners was the most important parameter for stiffening the thin-walled Mylar cylinders under axial loading. Ring-stiffeners with a low torsional stiffness did not stiffen the cylinder effectively until the rings were closely spaced. Ring-stiffeners on the inside of the cylinders did not affect the maximum buckling load when they were not bonded to the cylinder walls. Ring-stiffeners on the outside of the cylinders provided effective stiffening whether they were bonded to the cylinder walls or not.\r\n\r\nThe experimental results of thin-walled cylinders under axial compression indicated that the cylinder walls expand laterally to some critical amount, at which time they become unstable and suddenly collapse into buckling. The ring-stiffeners increase the critical compressive load with their effective torsional stiffness by resisting the annular collapse of the cylinder walls into diamond shaped buckles. At an L/R ring spacing ratio of 1.0 or less, the walls tended to buckle across the ring-stiffeners." }, { "name": "McMahon, Howard Martin", "degree": "PhD", "year": "1958", "title": "An Experimental Study of the Effect of Mass Injection at the Stagnation Point of a Blunt Body", "advisor": "Lees, Lester; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262006-142812", "creators": [ { "name": { "family": "McMahon", "given": "Howard Martin" }, "id": "McMahon-Howard-Martin", "display_name": "McMahon, Howard Martin" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PWSC-6787", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study of the effect of the injection of nitrogen and helium coolant gases at the stagnation point of a blunt body was carried out in the GALCIT Hypersonic Wind Tunnel at a Mach number of 5.8. The gases were injected straight out of the stagnation point and also tangential to the body surface. The model was also fitted with flow separation spikes.\r\n\r\nThe injection of the coolant gas resulted in a marked reduction in the model equilibrium temperature, and this cooling effect persisted over the entire length of the model. For the same mass flow, helium was a better coolant than nitrogen.\r\n\r\nThe average heat transfer near the nose of the body was reduced almost to zero by injecting a mass of helium as small as 1/2 per cent of the mass flow of free-stream air contained in the \"capture\" area [...] of the spherical nose.\r\n\r\nSeparation near the spike tip was observed up to a ratio of spike length to spherical nose diameter of 1.78 and a free-stream Reynolds number based on nose diameter of 2.84 x 10(5), resulting in a value of the foredrag coefficient which was one-third the value with no spike attached." }, { "name": "Nicholson, Kenneth F.", "degree": "Engineering Degree", "year": "1958", "title": "The Effects of Blunt Leading Edges on Delta Wings at Mach 5.8", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242006-094259", "creators": [ { "name": { "family": "Nicholson", "given": "Kenneth F." }, "id": "Nicholson-Kenneth-F", "display_name": "Nicholson, Kenneth F." } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZSFZ-MN41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPressure distributions were measured on a series of four delta wings with subsonic and supersonic leading edges, both sharp and blunt. The blunt leading edge radius was about 0.5 per cent of root chord. Schlieren studies were also made to determine top and side view shock locations. The tests were conducted at a nominal Mach number of 5.8, and at Reynolds numbers between 0.335 x 10(6) and 0.901 x 10(6) based on root chord. Angular settings covered a range [...] in pitch at zero yaw (about [...]), and a range of v/V = +/- 0.125 (about +/- 7.2\u00b0) at a fixed angle of pitch of 11.5\u00b0.\r\n\r\nThe effects of bluntness were found to be small. Also, the pressures produced by shock wave interactions with the boundary layer, and the inviscid pressures generated by the blunt leading edges, were found to be small compared with the inviscid pressures producing lift on the basic wing. Spanwise pressure distributions show no similarity to those obtained by linearized theory. Centerline lower surface pressure in pitch at zero yaw is bracketed between the Newtonian value [...] and the two-dimensional exact value." }, { "name": "Prouty, Raymond Wilbur", "degree": "Engineering Degree", "year": "1958", "title": "Part I: A Second Approximation to the Induced Drag of a Helicopter Rotor in Forward Flight. Part II: The Instantaneous Induced Velocity at the Blade of a Finite-Bladed Rotor in Forward Flight", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06202005-140259", "creators": [ { "name": { "family": "Prouty", "given": "Raymond Wilbur" }, "id": "Prouty-Raymond-Wilbur", "display_name": "Prouty, Raymond Wilbur" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GZWS-7W28", "abstract": "In Part I, a method is derived for determining the induced drag of a helicopter rotor in forward flight from the distribution of circulation in the wake. Charts of the correction factor to be applied to the ordinary momentum value of induced drag are presented for ranges of flight parameters currently in use.\r\n\r\nIn Part II, the expression for the instantaneous induced velocity at a blade is developed by application of the Biot and Savart Law to a helical wake surface on which the circulation distribution varies both with radius and with azimuth in a manner corresponding to the actual lift distribution on the blade." }, { "name": "Thorman, Herman Carl", "degree": "PhD", "year": "1958", "title": "Boundary Layer Measurements on an Axisymmetric Body with Spin and Yaw", "advisor": "Stewart, Homer Joseph; Millikan, Clark Blanchard; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192006-132244", "creators": [ { "name": { "family": "Thorman", "given": "Herman Carl" }, "id": "Thorman-Herman-Carl", "display_name": "Thorman, Herman Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R54D-S906", "abstract": "A directionally-sensitive hot-wire anemometer was developed for measuring the three-dimensional boundary-layer flow on a spinning, axisymmetric body in a low-speed wind tunnel. Boundary-layer velocity profiles at numerous positions around the body are presented for several spin rates at incidence angles of zero and 3 degrees. Displacement thickness distributions, based on integration of the velocity profiles, are also included.\r\n\r\nThe asymmetries in the azimuthal distribution of the boundary layer around the spinning body at a small angle of incidence (3\u00b0) are examined by means of a Fourier analysis of the experimental data. The experimental results are compared with the results of certain theoretical analyses (BRL 870 (Revised), NAVORD 5036) which provide a method for determining Magnus force (and also normal force) due to the displacement effect of the boundary layer." }, { "name": "Thurston, Dick Wright", "degree": "Engineering Degree", "year": "1958", "title": "An Experimental Investigation of Flame Spreading from Bluff Body Flameholders", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-133229", "creators": [ { "name": { "family": "Thurston", "given": "Dick Wright" }, "id": "Thurston-Dick-Wright", "display_name": "Thurston, Dick Wright" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BR8E-T735", "abstract": "Flame spreading from 1/16 to l inch circular cylinder flame holders in two-dimensional flow was studied experimentally. Combustion wake widths were determined by use of spark Schlieren photographs at distances up to 36 inches downstream of the flame-holder in a 3 by 6 inch duct. The effect on wake width and flow parameters of several geometric and operating variables was observed.\r\n\r\nThe data show that above a critical approach gas velocity, corresponding to the transition from laminar to turbulent flow in the flame front, the wake width was independent of velocity and remained constant. Below the critical velocity the wake width was a strong function of velocity. Small but real effects were found on changing fuel-air ratios. The wake width was smallest and the wake spreading rate lowest at the stoichiometric fuel-air ratio. An eight to one variation in flameholder diameter resulted in only a 30 per cent variation in wake width at a distance of one duct height downstream. Farther downstream the variation was even less. Total and static pressure measurements showed that combustion processes fix the total pressure wake and that the losses associated with flameholder drag were not important in fixing the wake spreading rate." }, { "name": "Turcotte, Donald Lawson", "degree": "PhD", "year": "1958", "title": "An Experimental Investigation of Flame Stabilization in a Heated Turbulent Boundary Layer", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07162004-110746", "creators": [ { "name": { "family": "Turcotte", "given": "Donald Lawson" }, "id": "Turcotte-Donald-Lawson", "display_name": "Turcotte, Donald Lawson" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XT75-T174", "abstract": "For a number of years the significant parameters governing flame stabilization in moving streams have been known. In high speed applications the chemical time delay plays a fundamental role. For the low speed problems the normal flame speed and quenching distance govern stabilization. Unfortunately the transition region between the two groups of problems has not been investigated. Also the actual relation between these parameters and the properties of the combustible mixture has not been established.\r\n\r\nTo investigate these fundamental questions an experiment was set up to study flame stabilization in heated turbulent boundary layers. For wall temperatures above about 1700[degrees]F. the chemical time delay, represented by the length of the heated flame holder wall required for stabilization, was found to be a systematic and reproducible variable. A rational explanation was made for the transition from the low speed stabilization mechanism known to be applicable in unheated turbulent boundary layers and heated laminar boundary layers to the ignition mechanism applicable in heated turbulent boundary layers.\r\n\r\nAn attempt was made to relate the observed stabilization measurements to a theoretical solution based on ignition in a laminar sub-layer. The present methods of solution for such problems were found to be inadequate. A similarity solution yielded an interesting result which agreed fairly well with experiments." }, { "name": "Benenson, David Maurice", "degree": "PhD", "year": "1957", "title": "Characteristics of Propagating Stall in Axial-Flow Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082004-133942", "creators": [ { "name": { "family": "Benenson", "given": "David Maurice" }, "id": "Benenson-David-Maurice", "display_name": "Benenson, David Maurice" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q6J5-C011", "abstract": "Both small and large amplitude propagating stalls have been observed experimentally and their characteristics distinguished. The characteristics of the small amplitude propagating stall are such that the phenomenon can be described well by linearized theory. The characteristics of the large amplitude stall (which is the propagating stall phenomenon generally found in compressors) are such that the linearized theory is not adequate to describe the stall.\r\n\r\nThe propagating stall speeds determined from the small amplitude propagating stall experiments are in good agreement with those predicted by a particular formulation of the linearized theory." }, { "name": "Carpenter, Stanley Hammack", "degree": "Engineering Degree", "year": "1957", "title": "Performance of Cavitating Axial Inducers with Varying Tip Clearance and Solidity", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-115641", "creators": [ { "name": { "family": "Carpenter", "given": "Stanley Hammack" }, "id": "Carpenter-Stanley-Hammack", "display_name": "Carpenter, Stanley Hammack" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/35Z3-YN17", "abstract": "The performance of a helical axial inducer pump was investigated in non-cavitating and heavily cavitating regimes over a wide range of tip clearance and solidity. It was found that cavity length is related to the occurrence of two cavitation phenomena: a non-steady or oscillating form of cavitation occurs when the cavity length is nearly equal to the spacing between the impeller blades, and complete pump failure is imminent if the cavity is nearly as long as the blade chord. The extent of the oscillating cavitation regime was little affected by the variation of tip clearance or solidity in the range investigated. However, an increase in tip clearance or a decrease in solidity definitely impairs cavitation performance at low inlet pressures. On the basis of these experiments a cavitation number limit is proposed for safe inducer operation." }, { "name": "Cummings, Benjamin Edgar", "degree": "Engineering Degree", "year": "1957", "title": "Supersonic Flutter of a Plate Containing Many Bays in the Spanwise Direction", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082004-143419", "creators": [ { "name": { "family": "Cummings", "given": "Benjamin Edgar" }, "id": "Cummings-Benjamin-Edgar", "display_name": "Cummings, Benjamin Edgar" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M4GA-0651", "abstract": "A special problem of panel flutter is considered by the method of Galerkin. The solution to the supersonic, non-steady potential equation is obtained by the approach of Garrick and Rubinow. Plate equations of motion are obtained by use of the Lagrange equations. Numerical solutions to the flutter determinant are presented for two cases.\r\n" }, { "name": "Fraasa, Donald Gordon", "degree": "Engineering Degree", "year": "1957", "title": "An Experimental Investigation of Hypersonic Flow over Blunt-Nosed Bodies at a Mach Number 5.8", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082004-144120", "creators": [ { "name": { "family": "Fraasa", "given": "Donald Gordon" }, "id": "Fraasa-Donald-Gordon", "display_name": "Fraasa, Donald Gordon" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G6D1-N841", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation to obtain schlieren photographs of the flow over several blunt-nosed bodies and to determine the surface static pressure distribution on certain of these models was conducted in the GALCIT hypersonic wind tunnel, leg no. 1, at a nominal Mach number of 5.8 and a free stream Reynolds number per inch of 2.22 x 10[...].\r\n\r\nSchlieren photographs were made of the following blunt-nosed models, all with cylindrical afterbodies, at angles of yaw of 0, 4, and 8 degrees: a family of nine round-nosed bodies with nose radii of curvature varying from the radius of the afterbody cylinder (hemispherical nose) to infinity (flat nose), two concave-nosed bodies having nose radii of curvature equal to 0.8 and 1.6 times the afterbody diameter, and three flat-nosed cylinders with rounded shoulders whose radii of curvature were .083, .125, and .208 times the afterbody diameter.\r\n\r\nStatic pressure distributions at angles of yaw of 0, 4, and 8 degrees were determined for three of the blunt bodies: (1) the flatnosed cylinder with infinite nose radius of curvature, (2) the flatnosed cylinder with a rounded shoulder of radius equal to .208 of the afterbody diameter, and (3) a round-nosed cylinder with nose radius of curvature equal to 1.3 times the afterbody diameter.\r\n\r\nThe schlieren photographs were analyzed on a contour projector to measure shock standoff distances, to determine the sonic point on the shock, and to observe shock shape. Data derived from these studies and the pressure distributions are presented in graphical form. Comparisons are made between the experimental results and appropriate theoretical approximations for hypersonic flow." }, { "name": "Gloria, Ruben M.", "degree": "Engineering Degree", "year": "1957", "title": "The Failure of Pressurized Thin-Walled Cylinders", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292004-150847", "creators": [ { "name": { "family": "Gloria", "given": "Ruben M." }, "id": "Gloria-Ruben-M", "display_name": "Gloria, Ruben M." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VQNF-4J52", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe object of this research was to find significant parameters in the failure of thinwalled internally pressurized cylinders. The following tests were made: (a) original crack length variation; (b) crack angle variation; (c) variation of velocity of penetration and (d) shape of a penetrating object; (e) cycling of internal pressure; and (f) change of loading media. The corresponding results were as follows: 2 (a) the crack length parameter [...] was found to bear importantly on the failing pressure of prepunctured cylinders; (b) an increase in failing pressure was achieved by changing the crack angle, originally parallel to the cylinder axis, to a perpendicular position; (c) explosive pressure level increased with decreased projectile velocity; (d) nondimensional explosive level increased with increased projectile sharpness, cylinder thickness and diameter; (e) pressure cycling tests revealed relatively fast crack growth during the first part of the life, followed by stabilization, and suceeded by another fast growth and failure; (f) a change from air to water as loading media made no effect on the static failing pressure of prepunctured cylinders.\r\n\r\nThe following tests are recommended: (a) determination of a parameter more generalized than [...] involving cylinder length; (b) more crack angle tests to obtain a family of [...] curves for various crack lengths from which effective crack lengths may be obtained; (c) explosive level runs using higher velocity and true conical projectiles; (d) pressure cycling tests to find the effect of cycling stress level on crack propagation; and (e) crack propagation by vibration, using different loading media." }, { "name": "Goddard, Frank Eber", "degree": "PhD", "year": "1957", "title": "The Effect of Uniformly Distributed Roughness on Turbulent Skin Friction Drag at Supersonic Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132004-115342", "creators": [ { "name": { "family": "Goddard", "given": "Frank Eber" }, "id": "Goddard-Frank-Eber", "display_name": "Goddard, Frank Eber" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BA5G-7H43", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental program was carried out in the 18 x 20-inch supersonic wind tunnel of the Jet Propulsion Laboratory at the California Institute of Technology to determine the effect of uniformly distributed sand-grain roughness on the skin friction drag of a body of revolution for the case of a turbulent boundary layer. The Mach-number range covered was 1.98 to 4.54 and the Reynolds number varied from about [...] to [...]. Some data were also obtained at a Mach-number of 0.70.\r\n\r\nAt speeds up to a Mach number of 5 and for roughness sizes such that the quadratic resistance law holds, the compressibility effect is indirect and the skin friction drag is a function only of the roughness Reynolds number, [...], just as in the incompressible case.\r\n\r\nThe critical roughness below which the surface is hydraulically smooth is [...] and this is equal to the thickness of the laminar sublayer for a smooth surface for both compressible and incompressible flows.\r\n\r\nOver the range of roughness sizes considered here there appears to be no wave drag associated with the drag due to roughness.\r\n\r\nThe shift in the turbulent velocity profile [...] for a rough surface at supersonic speeds is a function only of the roughness Reynolds number, [...], and quantitatively follows identically the same law as in the incompressible case." }, { "name": "Harney, Donald James", "degree": "Engineering Degree", "year": "1957", "title": "An Aerodynamic Study of the \"Electric Wind\"", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012004-134019", "creators": [ { "name": { "family": "Harney", "given": "Donald James" }, "id": "Harney-Donald-James", "display_name": "Harney, Donald James" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z774-ZM53", "abstract": "The basic physical process considered is the appearance of a pressure gradient in a slightly ionized gas under the influence of an electric field. On a molecular scale this process involves the acceleration of ions in an electric field and the transfer of momentum to the main body of the fluid through collisions.\r\n\r\nA particular phenomenon involving this basic process is the pressure gradient in a point corona discharge and the resulting \"electric wind\". The experimental arrangement studied is a point to a downstream coaxial cylinder discharge in air.\r\n\r\nThe difficulity of applying boundary conditions to the mathematical description of the process requires some simplifying assumptions. A simple one-dimensional model of the physical situation is considered, the electrical field equations being approached from the consideration of a space charge limited current. The functional relations derived appear consistent with the experimental results for the limiting cases implied by the assumptions.\r\n\r\nVelocity variations encountered in the induced flow of air present questions regarding the bulk parameter which describes the molecular interchange of momentum, the ion mobility. While this experiment was not for the purpose of measuring ion mobilities, it is believed that in any applications involving the basic process in the working fluid of the aerodynamicist the time, density, temperature and humidity dependence of the ion mobility requires data which is not now available." }, { "name": "Hartwig, Frederic William", "degree": "PhD", "year": "1957", "title": "Development and Application of a Technique for Steady State Aerodynamic Heat Transfer Measurements", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132004-161800", "creators": [ { "name": { "family": "Hartwig", "given": "Frederic William" }, "id": "Hartwig-Frederic-William", "display_name": "Hartwig, Frederic William" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y2JY-A341", "abstract": "A technique was developed for measuring steady state heat transfer on a hemisphere cylinder and the results are compared with theory. The instrumentation consisted of a miniaturized thermopile of silver-constantan thermocouples approximately 1/8\" x 1/16\" x 1/100\". The repeatability of readings with this device was found to be excellent. These heat measuring devices, or heat meters, were installed in both a ceramic hemisphere cylinder and in a similar metal one. There were obtained three different heat flow rates at each of six different combinations of tunnel pressure and temperature.
\r\n\r\nThe results compared very well with a theory developed by Lester Lees based upon the assumption of local similarity.
\r\n" }, { "name": "Kubota, Toshi", "degree": "PhD", "year": "1957", "title": "Investigation of Flow Around Simple Bodies in Hypersonic Flow", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-07142004-143403", "creators": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-Toshi", "display_name": "Kubota, Toshi" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZVPP-FK96", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theoretical analysis of the flow around slender blunt-nosed bodies was made by applying the flow similarity concept to the hypersonic small-disturbance equations. The flow field around a class of bodies of the form [...] exhibits a certain similarity in the sense that the pressure, density and transverse velocity are described by relations of the form Q(x,r)/Q(R) = f(r/R), where R is the distance from the axis to the shock wave. This similarity holds when the Mach number is infinitely large, and when the exponent in the equation defining the body shape lies in the range [...] for axially-symmetric bodies and in the range [...] for two-dimensional bodies. For large but finite Mach numbers a second approximation was obtained by expanding solutions in series of powers of [...].\r\n\r\nAn experimental investigation of the flow around \"similar-flow\" bodies of revolution was conducted at Mach number 7.7 in the GALCIT hypersonic wind tunnel. The surface pressure distributions agreed closely with the theoretical predictions, after a simplified correction was made for the boundary-layer displacement effect. The results indicated that the boundary layer interaction effect needs a further investigation." }, { "name": "Messiter, Arthur Frederic", "degree": "PhD", "year": "1957", "title": "Expansion Procedures and Similarity Laws for Transonic Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07152004-091254", "creators": [ { "name": { "family": "Messiter", "given": "Arthur Frederic" }, "id": "Messiter-Arthur-Frederic", "display_name": "Messiter, Arthur Frederic" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4HK0-K279", "abstract": "The transonic flow past slender bodies and thin wings is investigated with the use of a general theory of expansion procedures. It is assumed that the solutions for the velocity components possess asymptotic expansions of a very general form, and the differential equations and boundary conditions for the first and higher approximations are obtained by applying appropriate limiting procedures to the full equations. The following cases are treated: 1) bodies of revolution at zero incidence; 2) bodies of nearly circular cross-section, at zero incidence; 3) bodies of revolution at an angle of attack; and 4) thin wings at zero incidence. Certain first-order similarity laws are derived for these problems, and the order of magnitude of the error is stated in each case." }, { "name": "Oliver, Robert Earl", "degree": "Engineering Degree", "year": "1957", "title": "Part I. The Effect of a Simple Throat Distortion on the Downstream Flow in a Hypersonic Wind Tunnel Nozzle. Part II. An Experimental Investigation of Flow over Simple Blunt Bodies at a Nominal Mach Number of 5.8", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-07152004-105812", "creators": [ { "name": { "family": "Oliver", "given": "Robert Earl" }, "id": "Oliver-Robert-Earl", "display_name": "Oliver, Robert Earl" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/462P-XC43", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPART ONE\r\n\r\nAn experimental investigation was conducted in the GALCIT 2 1/2 inch Supersonic Wind Tunnel to determine the effect of a known distortion of the throat section of a hypersonic nozzle on the flow in the region downstream from the throat. The flow in a nozzle with a rectangular throat section was compared with the flow in the same nozzle with the throat region distorted to produce a throat height which varied linearly across the throat section. The flow was investigated by means of Pitot pressure surveys in the horizontal plane of symmetry of the undistorted nozzle.\r\n\r\nThe magnitude of the effect produced by the throat distortion was observed to be approximately that predicted by one-dimensional isentropic flow relations. However, the sign of the effect was reversed in about the distance required for a curved Mach line starting at the throat to cross the channel.\r\n\r\nPART TWO\r\n\t\t\t\t\t\r\nAn experimental investigation was conducted in Leg No. 1 of the GALCIT Hypersonic Wind Tunnel to determine flow characteristics for a series of blunt bodies at a nominal Mach number of 5.80 and free stream Reynolds numbers per inch of [...], [...] and [...]. The scope of this investigation was to determine surface static pressure distributions and to obtain schlieren photographs showing the shock configurations. The seven bodies investigated were as follows: (1) 40[degree] half-angle cone; (2) 40[degree] half-angle cone with spherical nose; (3) hemisphere-cylinder; (4) cylinder transverse to the free stream flow; (5) flatnosed cylinder with its major axis parallel to the free stream flow direction; (6) 10[degree]-40[degree] half-angle double cone; and (7) 13[degree]-30[degree] half-angle double cone. All tests were conducted in one-phase flow with a tunnel stagnation temperature of 225[degrees]F and with models at zero angles of attack and yaw." }, { "name": "Rabinowicz, Josef", "degree": "PhD", "year": "1957", "title": "Aerodynamic Studies in the Shock Tube", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152004-142813", "creators": [ { "name": { "family": "Rabinowicz", "given": "Josef" }, "id": "Rabinowicz-Josef", "display_name": "Rabinowicz, Josef" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MXH9-5H80", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn order to utilize the shock tube for quantitative investigations of some aerodynamic problems a thin platinum film resistance thermometer was developed for heat transfer rate measurements. The present report describes the construction and calibration of the heat transfer gage. Since the experimental technique presents a major problem this investigation has been carried out in the straight section of the shock tube where the flow conditions are well defined and readily measured. These flow conditions were calculated utilizing the most recent NBS data on air properties at high temperatures. The flow conditions were also measured utilizing the heat transfer gage and, several independent experimental techniques, and good agreement was found with the equilibrium flow calculations after an initial period of 30 - 50 [...]sec. Measurements of the heat transfer rate at the forward stagnation point and on the circumference of a circular cylinder are reported and compared with the theoretical calculations of L. Lees. A method for deduction of surface pressure distribution from the laminar boundary-layer heat transfer data is also presented." }, { "name": "Richards, Homer Keener", "degree": "Engineering Degree", "year": "1957", "title": "An Experimental Investigation of Heat Transfer Rates on a Blunt Body in Hypersonic Flow", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172004-095231", "creators": [ { "name": { "family": "Richards", "given": "Homer Keener" }, "id": "Richards-Homer-Keener", "display_name": "Richards, Homer Keener" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C7F5-2G95", "abstract": "An experimental investigation was made in the GALCIT hypersonic wind tunnel, leg number 1, at a nominal Mach number of 5.8 to determine the heat transfer rate and temperature distributions on a water-cooled, ellipsoid-cone at angles of yaw of 0, 4 and 8 degrees, respectively. The Reynolds number per inch based on free stream conditions was [...].\r\n\r\nThe experimental means employed was a steady-state technique developed by Mr. F. W. Hartwig at GALCIT during the past several years. This technique utilizes a heat transducer or heat meter of very small size. The primary advantage of this method is that it obviates the necessity of correcting for axial temperature gradients in the model.\r\n\r\nSurface pressure distributions were also studied on a model of identical geometry for angles of yaw of 0, 4, 8 and 12 degrees, respectively. The primary interest here was to obtain data necessary for the theoretical calculation of the heat transfer rate distributions using laminar flow theory.\r\n\r\nThe investigation showed that the heat meters were very reliable. The data obtained from independent wind tunnel runs were repeatable within [plus or minus] 1.5 per cent. It was found that the local heat transfer rate and the local pressure coefficient vary linearly with angle of yaw. The agreement of the experimentally determined stagnation heat transfer rate and the theoretically calculated one was good. Further refinement of the calibration technique appears to be the logical direction of effort for subsequent investigators." }, { "name": "Richmond, Ronald LeRoy", "degree": "PhD", "year": "1957", "title": "Experimental Investigation of Thick, Axially Symmetric Boundary Layers on Cylinders at Subsonic and Hypersonic Speeds", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-08242004-093622", "creators": [ { "name": { "family": "Richmond", "given": "Ronald LeRoy" }, "id": "Richmond-Ronald-LeRoy", "display_name": "Richmond, Ronald LeRoy" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A8P6-BA17", "abstract": "An experimental investigation of the transverse curvature effect on laminar and turbulent axially symmetric boundary layers was conducted in two subsonic wind tunnels and in the GALCIT 5 x 5 inch hypersonic wind tunnel.\r\n\r\nSubsonic turbulent skin friction coefficients were estimated from velocity profiles with axial flow on a 0.024 inch diameter cylinder and a 1.00 inch diameter cylinder. A considerable increase over the flat plate skin friction coefficient at the same momentum thickness Reynolds number was found.\r\n\r\nHypersonic laminar and turbulent skin friction coefficients with axial flow on an insulated 0.250 inch diameter cylinder were measured by the floating element technique and indicated, respectively, several times and 1.5 times the laminar and turbulent flat plate skin friction coefficients at the same momentum thickness Reynolds numbers. Turbulent skin friction coefficients were estimated from pitot profiles with axial flow on a 0.064 inch diameter cylinder and on a 0.024 inch diameter cylinder at M1 = 5.8 and indicate double the value to be found for an insulated flat plate at the same momentum thickness Reynolds number." }, { "name": "Savage, Glenn Allen", "degree": "Engineering Degree", "year": "1957", "title": "An Analytical Investigation of the Ducted Propeller for Hydrodynamic Propulsion", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172004-094413", "creators": [ { "name": { "family": "Savage", "given": "Glenn Allen" }, "id": "Savage-Glenn-Allen", "display_name": "Savage, Glenn Allen" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EBDR-SN58", "abstract": "An analytical investigation was carried out to determine the design conditions, for a ducted propeller unit operating in water, providing optimum suppression of cavitation when the forward speed, depth and body drag are given. The selection charts were constructed in detail for propellers using the NACA 65 series blades. The results indicate the pumps of generally higher flow rates are more desirable than those that have been employed in the few units actually constructed." }, { "name": "Wisenbaker, Eugene Morgan", "degree": "Engineering Degree", "year": "1957", "title": "An Experimental Investigation of Flow over Simple Blunt Bodies at Mach Number of 5.8", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062004-154112", "creators": [ { "name": { "family": "Wisenbaker", "given": "Eugene Morgan" }, "id": "Wisenbaker-Eugene-Morgan", "display_name": "Wisenbaker, Eugene Morgan" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0KC4-4827", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock stand-off distances and shock shapes were measured and/or observed for a series of 14 blunt-nosed bodies at a Mach number of 5. 8 and Reynolds number per inch of [...]. Nine of these bodies had hemisphere-segment noses designed to include the entire range of possible nose radii of curvature from flat-faced to hemispherical. Two models characterized by sharp shoulders and concave hemisphere-segment noses were also tested. Three additional models representing the round-shouldered, flat-faced type completed the set of 14. All models had cylindrical afterbodies 1.50 inches in diameter, and were yawed at angles of 0, 4, and 8 degrees.\r\n\r\nStand-off distances are compared to the theoretical predictions of Hayes, Frobstein, and Heybey where applicable, and shock shape is compared to that given by Hayes for the body with infinite nose radius of curvature. Results of the stand-off distance comparisons varied from under prediction by a factor of two to over prediction by the same amount. Hayes' shock shape approximated that actually observed very closely. It was generally found that body shape in the sonic region greatly influenced the shock shape and stand-off distance.\r\n\r\nStatic pressure distributions were measured on three representative bodies selected as follows: (1) a hemisphere-segment body having a ratio of nose radius to base diameter of 1.30 and falling in the middle of the range from hemisphere to flat-nosed; (2) a flat-faced body with sharp shoulder; and (3) a flat-faced body with a rounded shoulder of 5/16 inch radius. Pressures very close to stagnation values generally were found to be present over a large area of the nose in the case of the flat-faced body. Rounding of the shoulder tended to reduce values of [...] below those observed at corresponding points on the completely flat-faced body, except in the region near the body axis The pressure distributions are compared where applicable with the modified Newtonian approximation and with Probstein's approximation to [...] for zero angle of yaw. Agreement with the modified Newtonian values was generally good near the axis, but deteriorated rapidly in the shoulder regions, except in the case of the rounded shoulder body." }, { "name": "Ames, Lionel Eugene", "degree": "Engineering Degree", "year": "1956", "title": "Interference Effects Between Multiple Bluff Body Flameholders", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182004-140703", "creators": [ { "name": { "family": "Ames", "given": "Lionel Eugene" }, "id": "Ames-Lionel-Eugene", "display_name": "Ames, Lionel Eugene" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JJVQ-3G91", "abstract": "A general program was undertaken to determine the interference effects between multiple bluff body flameholders. The flameholders used for these experiments were 1/4 inch diameter water cooled cylinders tested in a 1 by 4 inch combustion chamber. Stability limits, flame geometry, and relative combustion efficiency were determined as functions of flameholder spacing and number.\r\n\r\nThe results of the tests showed that the maximum blowoff velocity decreased as the number of flameholders increased. This reduction was primarily due to the increase in the blockage ratio. In addition, a reduction in maximum blowoff velocity occurred when the flameholders were moved from the symmetrical arrangement in the duct.\r\n\r\nA combustion instability characterized by a loud, high frequency noise occurred over well defined ranges of fuel air ratio, gas velocity, and flameholder spacing.\r\n\r\nThe recirculation zone length and flame widths were primarily functions of blockage ratio, modified slightly by flameholder separation. No large scale interaction occurred between the wakes of adjacent flameholders. Combustion efficiency increased with the number of flameholders and was little affected by flameholder separation." }, { "name": "Bennett, Eugene Newell", "degree": "Engineering Degree", "year": "1956", "title": "Carbon Formation from Acetylene in the Shock Tube", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182004-142409", "creators": [ { "name": { "family": "Bennett", "given": "Eugene Newell" }, "id": "Bennett-Eugene-Newell", "display_name": "Bennett, Eugene Newell" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GB80-GE14", "abstract": "The use of the shock tube for the study of carbon formation from acetylene has been considered theoretically and studied experimentally.\r\n\r\nIn the calculations, the state of the gas is determined behind incident and reflected shocks for a wide range of shock strengths and for various excitation models of the internal degrees of freedom. A simple mechanism has been assumed for the thermal decomposition, namely the formation of solid carbon and hydrogen. Estimates are presented for the minimum times spent by the gas in a uniform state at the elevated temperatures behind reflected shocks.\r\n\r\nThe shock strengths required to initiate decomposition of acetylene at various pressures have been investigated experimentally. Temperature estimates and shock velocity measurements suggest that the effective specific heat ratio approaches the equilibrium value. Spectroscopic studies have been carried out to determine the light emitted in a narrow wave length region during chemical decomposition behind reflected shocks. The results show that the intensity distribution follows the black-body emission law. Therefore, a two-color method may be used in future studies for determining the temperature as a function of time behind carbon forming shocks." }, { "name": "Berry, John Warren", "degree": "Engineering Degree", "year": "1956", "title": "Fatigue of Aluminum as Affected by Temperature and Intermittent Periods of Rest", "advisor": "Sechler, Ernest Edwin; Valluri, S. R.; Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182004-143645", "creators": [ { "name": { "family": "Berry", "given": "John Warren" }, "id": "Berry-John-Warren", "display_name": "Berry, John Warren" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Valluri", "given": "S. R." }, "id": "Valluri-S-R", "role": "advisor", "display_name": "Valluri, S. R." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SNTV-ZX45", "abstract": "This investigation was undertaken in an attempt to determine the behavior of high purity aluminum when subjected to fatigue stressing in rotary bending at various elevated temperatures, and also to study the effects on fatigue life when the material was given intermittent periods of rest. Two types of rest periods were given; 1) room temperature resting from fatigue cycling at elevated temperature, and 2) resting at higher temperature after stressing at ambient temperature. Because of the limited time available and the desire to apply statistical methods of analysis, testing was restricted to only a single stress level for each phase of the experiment.\r\n\r\nUp to the highest temperature tested (600[degrees]F), results for continuous stress cycling indicate a gradual reduction in fatigue life with temperature. Rest periods at room temperature contributed only negligible changes in fatigue life, but all tests with rest periods at elevated temperature disclosed a sizable increase. The increase in fatigue life was a maximum when resting was carried out at temperatures in the neighborhood of the recrystallization temperature. In addition, it is curious to note, that in the continuous cycling tests, scatter of results was a sharp minimum at recrystallization temperature." }, { "name": "Campbell, George Stuart", "degree": "PhD", "year": "1956", "title": "Turbulence in the Wake of a Thin Airfoil at Low Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192004-142218", "creators": [ { "name": { "family": "Campbell", "given": "George Stuart" }, "id": "Campbell-George-Stuart", "display_name": "Campbell, George Stuart" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T35K-QF86", "abstract": "Experiments have been made to determine the nature of turbulence in the wake of a two-dimensional airfoil at low speeds. The experiments were motivated by the need for data which can be used for analysis of the tail-buffeting problem in aircraft design. Turbulent intensity and power spectra of the velocity fluctuations were measured at a Reynolds number 1.6 x 10[superscript 5] for several angles of attack. Total-head measurements were also obtained in an attempt to relate steady and fluctuating wake properties.\r\n\r\nMean-square downwash was found to have nearly the same dependence on vertical position in the wake as that shown by total-head loss. For this particular wing, turbulent intensity, integrated across the wake, increased roughly as the 3 /2 power of the drag coefficient.\r\n\r\nPower-spectrum measurements indicated a decrease in frequency as wing angle of attack was increased. The average frequency in the wake was proportional to the ratio of mean wake velocity to wake width." }, { "name": "Dooley, Donald Allen", "degree": "PhD", "year": "1956", "title": "Combustion in Laminar Mixing Regions and Boundary Layers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03222004-162749", "creators": [ { "name": { "family": "Dooley", "given": "Donald Allen" }, "id": "Dooley-Donald-Allen", "display_name": "Dooley, Donald Allen" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MGTH-TS83", "abstract": "The governing relations for gaseous flow systems with chemical reaction are briefly discussed. A mixture of mechanically similar Maxwellian molecules is assumed and the general relations are then reduced to the simplified forms appropriate for reacting, laminar boundary layer type flow systems. One-step unopposed, \"global\" reactions following first-order, second-order, and third-order kinetics are considered.\r\n\r\nThe simplified governing relations are transformed to an equivalent constant density plane by application of the Howarth transformation. A similarity function relating the specie concentrations to the local temperature is found for the case of equal Prandtl and Schmidt numbers. The similarity function is shown to be equal to the dimensionless streamwise velocity when the Prandtl and Schmidt numbers are both equal to unity. The remaining governing relations are then transformed to the Blasius plane in which the velocity field has known solutions. The energy equation is solved by an iteration process; a general analytic solution for the N'th approximation is obtained.\r\n\r\nThe analytic techniques developed are applied to the problems of combustion within laminar mixing regions and boundary layers. Temperature and concentration profiles are calculated and the dependence of the characteristic stay time upon the parameters of the system is determined. The application of the similarity techniques to the problem of chemical reaction within a hypersonic boundary layer is briefly discussed in an Appendix." }, { "name": "Eisley, Joe Griffin", "degree": "PhD", "year": "1956", "title": "Panel Flutter in Supersonic Flow", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03222004-163442", "creators": [ { "name": { "family": "Eisley", "given": "Joe Griffin" }, "id": "Eisley-Joe-Griffin", "display_name": "Eisley, Joe Griffin" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZF04-TK14", "abstract": "The problem of panel flutter in a supersonic flow is treated in three parts. In the first the flutter of a simply supported rectangular plate is studied. Only small deflections are considered so that linear plate theory may be used. The flutter mode is described by a series expansion in terms of the normal modes of oscillation of the plate in a vacuum. Linearized aerodynamic theory is used. The exact aerodynamic solution as well as two simplifications--strip theory and quasi-steady theory--are discussed. Numerical calculations were made to determine flutter boundaries for plates of varying aspect ratio using strip theory aerodynamics for M = 2 and M = \u221a2. The flutter mode was described by considering only two or three normal modes in the calculations.
\r\n\r\nThe flutter of a two-dimensional buckled panel with clamped edges is studied both theoretically and experimentally. The flutter mode is described by a series expansion of functions which satisfy the boundary conditions for clamped edges. Quasi-steady linearized aerodynamics is used. Large deflections of the panel are considered. Numerical calculations have been made considering only the first two terms of the series expansion. The theoretical and experimental results are compared.
" }, { "name": "Foster, James Roger", "degree": "Engineering Degree", "year": "1956", "title": "Effects of Combustion Chamber Blockage on Bluff Body Flame Stabilization", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03222004-164002", "creators": [ { "name": { "family": "Foster", "given": "James Roger" }, "id": "Foster-James-Roger", "display_name": "Foster, James Roger" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T553-DA28", "abstract": "The necessity for stabilizing a flame in a high speed flow of combustible gas has led to extensive studies of the mechanism of flame stabilization by bluff bodies. As a result of these studies it has been found that the stability limits depend directly on a characteristic wake length and that under certain conditions this characteristic dimension depends on the square root of the flame holder scale.\r\n\r\nIn the present investigation the geometry of the flame in the stabilization region is examined by means of photographic and probing techniques. The results of the studies show conclusively that for a constant blockage ratio, the wake geometry scales linearly with flame holder size. The observed square root dependence of the characteristic wake length, and hence of the blowoff velocity is shown to be directly caused by blockage effects." }, { "name": "Hartlieb, Robert Joseph", "degree": "PhD", "year": "1956", "title": "The Cancellation of Random Disturbances in Automatic Control Systems", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232004-132254", "creators": [ { "name": { "family": "Hartlieb", "given": "Robert Joseph" }, "id": "Hartlieb-Robert-Joseph", "display_name": "Hartlieb, Robert Joseph" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SCBZ-3H18", "abstract": "A disturbance-cancelling feedback transfer function is proposed in a preliminary study for linear systems with constant coefficients. This idea is then experimentally demonstrated.\r\n\r\nIn the main theory for more general systems, expressions are obtained for a computer which generates a cancelling input from measurements of the disturbances. The cases where there are fewer measurements than disturbances and also noisy measurements are treated. Three schemes and a basis for comparison are given. An example is calculated." }, { "name": "Kanevsky, Joseph Norman", "degree": "Engineering Degree", "year": "1956", "title": "I. Interference During Burning of Body-Centered Cubic Arrays of Nine Fuel Droplets in Air. II. Spray Formation and Evaporation", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252004-094228", "creators": [ { "name": { "family": "Kanevsky", "given": "Joseph Norman" }, "id": "Kanevsky-Joseph-Norman", "display_name": "Kanevsky, Joseph Norman" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JHWV-HB29", "abstract": "In order to gain some understanding of interference effects during the combustion and evaporation of fuel sprays, simple three-dimensional body-centered cubic arrays of nine n-heptane or nine methyl alcohol droplets burning in air have been studied. Different cube sizes were used to vary the amount of interference obtained during combustion of the droplets. Photographic studies of the center droplet in this nine-droplet array were made in order to determine the qualitative effects of droplet spacing on the evaporation constant (K') while combustion was in progress and to determine whether the mass rate of burning was proportional to the first power of droplet diameter for a three-dimensional array of droplets.\r\n\r\nExperimental results indicate that, when the droplets are in close proximity and the flames completely merged, the evaporation constant is reduced by 40 percent below the value obtained for minimum interference. A 25 percent increase in the evaporation constant over single-droplet values for K' was noted when the droplet spacing was altered to reduce local heat losses from the flame fronts. The results obtained from studies of the center droplet substantiate Probert's assumption (Ref. 38) that the square of droplet diameter decreases linearly with time.\r\n\r\nUnsuccessful attempts to study the combustion of liquid bipropellant mixtures and to examine the \"burning\" of red fuming nitric acid in an ammonia atmosphere are described.\r\n\r\nIn Part II, a general discussion of information available on the disintegration of liquid jets, spray characteristics, mean droplet size, droplet-size distribution, and spray evaporation is presented. The use of similarity considerations in analyzing spray-nozzle performance is demonstrated. Calculation of K' for a spray from experimental spray evaporation data is described and the results of these calculations tabulated." }, { "name": "Karamcheti, Krishnamurty", "degree": "PhD", "year": "1956", "title": "Sound Radiation from Surface Cutouts in High Speed Flow", "advisor": "Roshko, Anatol; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-114458", "creators": [ { "name": { "family": "Karamcheti", "given": "Krishnamurty" }, "id": "Karamcheti-Krishnamurty", "display_name": "Karamcheti, Krishnamurty" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1CRR-9Y28", "abstract": "In an experimental investigation of subsonic and supersonic flows of air past rectangular cavities cut into a flat surface it was discovered that the cavities emit a strong acoustic radiation.\r\n\r\nThe frequency of the sound-producing oscillations measured by a hot wire in the cavity was found to be inversely proportional to the breadth for fixed depth. For fixed breadth the frequency was found to increase, though not systematically, with a decrease in depth.\r\n\r\nA non-dimensional frequency S is defined in terms of the frequency of emission, the gap breadth, and the free stream velocity. The dependence of S on the various parameters in the problem, such as Mach number, Reynolds number and ratio of the boundary layer thickness to a dimension of the cavity, is discussed in light of appropriate experiments.\r\n\r\nAn estimate of the intensity of the radiation was obtained by means of an optical interferometer of the Mach-Zehnder type. For points located at 3 to 4 cavity breadths from the cavity, intensities of the order of 100 - 150 decibels were found for sound fields from cavities 0.1\" deep and 0.1 to 0.2 inch broad at Mach numbers 0.7 to 0.85.\r\n\r\nPossible mechanisms for the sound production by the cavities are discussed." }, { "name": "Kendall, James Madison", "degree": "PhD", "year": "1956", "title": "An Experimental Investigation of Leading Edge Shock Wave-Boundary Layer Interaction at Hypersonic Speeds", "advisor": "Nagamatsu, Henry T.; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252004-153340", "creators": [ { "name": { "family": "Kendall", "given": "James Madison" }, "id": "Kendall-James-Madison", "display_name": "Kendall, James Madison" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6XVK-B331", "abstract": "The boundary layer on a slender body tends to be very thick at hypersonic speeds. It interacts with the external flow by producing larger flow deflections near the leading edge than those due to the body alone. The increased shock strength affects the boundary layer growth. The flow around the boundary layer gives rise to an induced pressure with a negative gradient which thins the boundary layer and increases the skin friction with respect to the zero pressure gradient value.
\r\n\r\nExperiments on a flat plate with a sharp leading edge (Re\u209c < 100) have been performed in the GALCIT 5 x 5 inch Mach 5.8 hypersonic wind tunnel. The induced pressure was measured by means of orifices in the plate surface. Profiles of Mach number, velocity, mass flow, pressure, and momentum deficiency were calculated from impact pressure surveys normal to the plate surface made at various distances from the leading edge.
\r\n\r\nThe results are as follows: (1) The induced pressures are 25 per cent higher than the weak interaction theory. (2) The boundary layer and the external flow are distinctly separate for Re\u2093 as low as 6000. (3) The shock wave location is in good agreement with that predicted by the Friedrichs theory for a body shape equivalent to the observed boundary layer displacement thickness. (4) Expansion waves reflected from the shock are weak. (5) The average skin friction coefficient tends toward and nearly matches the zero pressure gradient value downstream, but increases to approximately twice that value as the leading edge is approached.
" }, { "name": "Lamson, Philip", "degree": "PhD", "year": "1956", "title": "Measurements of Lift Fluctuations Due to Turbulence", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-115115", "creators": [ { "name": { "family": "Lamson", "given": "Philip" }, "id": "Lamson-Philip", "display_name": "Lamson, Philip" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2ZDV-9T79", "abstract": "The fluctuating lift of a rigid wing in turbulent flow is studied. The power spectra of the lift and of the turbulent fluctuations are measured. From these measurements the aerodynamic admittance of the wing is obtained.\r\n\r\nThe ratio of span/scale of turbulence is varied by means of movable end plates. For a distance between the end plates of the order of the scale of turbulence the aerodynamic admittance is expected to approach the computed values of Sears.\r\n\r\nThis is shown to be the case if the reduced frequencies are larger than k = 0.8. For smaller k the experimental admittance falls below Sears' values. For large ratios of span/scale of turbulence the aerodynamic admittance is decreased for all frequencies and becomes nearly independent of frequency in the investigated range 0.2 <= k <= 2.\r\n\r\nIn general the measurements support the simplifying assumptions made in the statistical approach to gust loads and buffeting initiated by Clementson and by Liepmann." }, { "name": "Lindley, Charles Alexander", "degree": "PhD", "year": "1956", "title": "Secondary Flow in Compressor Cascades", "advisor": "Rannie, W. Duncan; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-083759", "creators": [ { "name": { "family": "Lindley", "given": "Charles Alexander" }, "id": "Lindley-Charles-Alexander", "display_name": "Lindley, Charles Alexander" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2RYC-QB23", "abstract": "An experimental study was made of the secondary flow in a compressor cascade. Detailed surveys of the entire flow channel at various operating conditions are presented. The chief difference of the experimental results from those predicted by linearized theory was the presence of a turbulent separation region at the corner of the wall and the low pressure surface of the blade. While the actual losses involved were small, the effects on the succeeding stages of a turbomachine might be more severe." }, { "name": "Machell, Reginald Montague", "degree": "Engineering Degree", "year": "1956", "title": "An Experimental Investigation of Hypersonic Flow over Blunt Nosed Cones at a Mach Number of 5.8", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-145512", "creators": [ { "name": { "family": "Machell", "given": "Reginald Montague" }, "id": "Machell-Reginald-Montague", "display_name": "Machell, Reginald Montague" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SJ75-6W93", "abstract": "Six spherical nosed cone static pressure models with cone semivertex angles of 10\u00b0, 20\u00b0, and 40\u00b0 were tested in the GALCIT 5 x 5 inch hypersonic wind tunnel at a Mach number of 5.8. The static pressure distributions obtained at yaw angles of 0\u00b0, 4\u00b0, and 8\u00b0 agreed very closely with the modified Newtonian approximation, Cp = Cpmax cos2\u03b7 on the spherical portions of the models, where \u03b7 is the angle between the normal to the body surface and the free stream direction. On the conical portions of the models the pressure distributions agreed reasonably well with the theoretical results for inviscid supersonic flow over cones as tabulated by Kopal. The significant parameter which influenced the deviations from the Newtonian and the Kopal predictions was the cone semivertex angle. The flow over the 40\u00b0 spherical nosed cone models overexpanded with respect to the Kopal pressure in the region of the spherical-conical juncture, after which the pressure returned rapidly to the Kopal value. For models with smaller cone angles the region of minimum pressure occurred farther back on the conical portion of the model, and the Kopal pressure was approached more gradually. The shape of the pressure distributions as described in nondimensional coordinates was independent of the radius of the spherical nose and of the Reynolds number over the range of Reynolds number per inch between . 97 x 105 and 2.38 x 105. Integrated results for the pressure foredrag of the models at zero yaw compared very closely with the predictions of the modified Newtonian approximation, except for models with large cone angles and small nose radii." }, { "name": "Munson, Albert Gallatin", "degree": "Engineering Degree", "year": "1956", "title": "A Preliminary Experimental Investigation of the Flow over Simple Bodies of Revolution at M = 18.4 in Helium", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-06162004-141355", "creators": [ { "name": { "family": "Munson", "given": "Albert Gallatin" }, "id": "Munson-Albert-Gallatin", "display_name": "Munson, Albert Gallatin" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X3HZ-BN39", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation was conducted in the GALCIT hypersonic blow-down tunnel to determine surface pressure distributions and shock wave shapes for a series of \"sharp\" nosed and slightly blunted bodies of revolution at a nominal Mach number of 18.5 and a free stream Reynolds number of 4.75 x 10[superscript 5] per inch. The four bodies investigated were as follows: (1) 15[degree] half-angle \"sharp\" cone; (2) 15[degree] half-angle spherically-blunt cone (bluntness ratio = .24); (3) 20[degree] half-angle \"sharp\" cone; and (4) 2/3 power body.\r\n\r\nThe pressure distributions on the \"sharp\" cones agreed well with the Taylor Maccoll theory. The pressure near the nose of the blunt cone was much higher than that predicted by the theory, as is expected, but decreases monotonically to a value lower than the theoretical value, indicating that the flow has over expanded. The measured shock wave shape for the 2/3 power body was found to be proportional to x[...], and the shock wave ordinates agree very closely with those predicted by Cole." }, { "name": "Nawoj, Henry John", "degree": "Engineering Degree", "year": "1956", "title": "Cavitation Studies in Axial Inducers", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06162004-153833", "creators": [ { "name": { "family": "Nawoj", "given": "Henry John" }, "id": "Nawoj-Henry-John", "display_name": "Nawoj, Henry John" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FJCF-EC97", "abstract": "Cavitation development was investigated in axial inducers from inception to impeller breakdown using the conventional hydraulic parameters and direct visual observation. Five distinct regimes of cavitation development were observed, and the noise and vibration associated with cavitating pumps was found to occur principally in only one regime of cavitation development. Cavitation in a highly cavitating inducer was found to be adequately modeled using the cavitation similarity number introduced by Prandtl. A simple model is presented for impeller breakdown and experimental data indicate that the general requirements for impeller breakdown given by the model are exhibited in the experimental impellers. A modification to the cavitation number is suggested to accommodate the effusion of dissolved gases from the working fluid into the cavities." }, { "name": "O'Bryant, William Theral", "degree": "Engineering Degree", "year": "1956", "title": "An Experimental Investigation of Hypersonic Flow over Blunt Nosed Cones at a Mach Number of 5.8", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-06182004-111807", "creators": [ { "name": { "family": "O'Bryant", "given": "William Theral" }, "id": "O'Bryant-William-Theral", "display_name": "O'Bryant, William Theral" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/923A-XB12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock shapes were observed and static pressures were measured on spherically-blunted cones at a nominal Mach number of 5.8 over a range of Reynolds numbers per inch from 97,000 to 238,000 for angles of yaw from 0[degrees] to 8[degrees]. Six combinations of the bluntness ratios 0.4, 0.8, and 1.064 with the cone half angles 10[degrees], 20[degrees], and 40[degrees] were used in determining the significant parameters governing pressure distribution.\r\n\r\nThe pressure distribution on the spherical nose for both yawed and unyawed bodies is predicted quite accurately by the modified Newtonian theory given by [...], where [...] is the angle between the normal to a surface element and the flow direction ahead of the bow shock. On the nose-cone junction and the conical afterbody, cone half angle was found to be the significant parameter in determining the length of the transition zone. For a cone half-angle of 40[degrees], a pressure minimum exists on the skirt immediately downstream of the nose-cone junction, but this pressure minimum is located far downstream when the half-angle is 20[degrees]. The tangent cone concept at angles of yaw is useful in predicting the downstream movement of the pressure minimum. Shock detachment distance between bow shock and body surface on the axis varies linearly with nose radius. Drag coefficients for bodies at zero yaw compare very closely with those obtained by integrating the modified Newtonian approximation, except at large half-angles and low bluntnesses where drag approaches that given by the Taylor-Maccoll theory for sharp cones." }, { "name": "Rethorst, Scott Carson", "degree": "PhD", "year": "1956", "title": "Characteristics of an Airfoil Extending Through a Circular Jet", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-153000", "creators": [ { "name": { "family": "Rethorst", "given": "Scott Carson" }, "id": "Rethorst-Scott-Carson", "display_name": "Rethorst, Scott Carson" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7PS7-T859", "abstract": "A method has been derived for the determination of the downwash in the field of an airfoil extending through a circular jet. This solution has been applied particularly to the region aft of the lifting line in the plane of the airfoil, to determine the lift distribution on a wing extending through a circular jet.\r\n\r\nThe method of solution is essentially based on a division of the flow induced by the jet boundary into parts which are even and odd with respect to the direction of flow. The analysis due to the even part alone is similar to previous theories, which in effect disregarded the odd part. Such previous results based on the even part alone differ considerably from the experimental values. The results based on the total of the even and odd parts show good agreement with the experiments, illustrating the necessity of including the odd part of the flow when the segment of the wing immersed in the jet is of low aspect ratio.\r\n\r\nThe problem has been solved in parametric form, so that the results may be employed to determine the characteristics of any geometry wing-jet combination at any jet velocity ratio." }, { "name": "Rodriguez, Alexander Martin", "degree": "PhD", "year": "1956", "title": "Theorems Concerning the Reduction of Drag for Supersonic Aircraft", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302006-133358", "creators": [ { "name": { "family": "Rodriguez", "given": "Alexander Martin" }, "id": "Rodriguez-Alexander-Martin", "display_name": "Rodriguez, Alexander Martin" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R1JD-WT10", "abstract": "In this report the problem of drag reduction or minimization for aircraft in supersonic flight is investigated within the framework of linearized theory of inviscid flow for fixed flight Mach number.\r\n\r\nGeneral theorems applicable to complete aircraft configurations are developed. These theorems state defining properties of distributions of thickness and normal force restricted to a particular region of the aircraft configurations that minimize the drag of the complete aircraft under the condition that the distribution of thickness and normal force on the remainder of the aircraft is specified in advance. These optimum distributions are further required to satisfy some of the various types of constraints that are commonly specified for aircraft.\r\n\r\nThe problem of finding the optimum distribution of thickness, lift and sideforce on a slender body of revolution is also studied under the assumption that the body carries no total lift or sideforce and can be represented by placing the distributions along the body axis. The case for which the Mach envelope of the body does not include all of the remaining portion of the aircraft configuration, upon with the thickness and normal force are specified, is solved. This solution covers the previously known case for which the Mach envelope of the body includes the entire aircraft." }, { "name": "Shen, Yung-chung", "degree": "PhD", "year": "1956", "title": "Similarity Solution for Transonic Flow Past a Cone", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282004-095155", "creators": [ { "name": { "family": "Shen", "given": "Yung-chung" }, "id": "Shen-Yung-chung", "display_name": "Shen, Yung-chung" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/74PX-HS89", "abstract": "By applying a transonic expansion procedure to a conical flow field, a system of approximate transonic equations, boundary conditions, and shock relations is derived. A similarity law for the pressure coefficient on the surface of slender cones is established. The surface pressure is computed by solving the approximate equations.\r\n\r\nBy use of similarity, the second order differential equations of the first two steps of the approximation scheme are reduced to first order equations. The solution of the first step is carried out numerically in great detail for different transonic parameters; the procedure for solving the latter is explained in the Appendix.\r\n\r\nThe results are compared with the exact solution, and a highly satisfactory agreement is reached." }, { "name": "Sibulkin, Merwin", "degree": "Engineering Degree", "year": "1956", "title": "Boundary Layer Measurements at Supersonic Nozzle Throats", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182006-150720", "creators": [ { "name": { "family": "Sibulkin", "given": "Merwin" }, "id": "Sibulkin-Merwin", "display_name": "Sibulkin, Merwin" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1JZK-HZ46", "abstract": "Wall static pressure measurements and boundary layer pitot pressure surveys were made near the throat of a flexible wall supersonic wind-tunnel nozzle at three settings having throat radii of curvature from 33 to 59 inches. It is found that the longitudinal static pressure gradient at the nozzle throat calculated from one-dimensional flow theory agreed with the measured wall static pressure gradient.
\r\n\r\nThe boundary-layer velocity profiles at the nozzle throat are presented and discussed. The boundary layers were turbulent and 0.046 to 0.107 inch thick. It is found that the boundary-layer momentum thickness at the nozzle throat calculated using the momentum-integral-equation and several approximations agrees with the values determined from the measured boundary layer profiles. Finally, it is noted that in spite of the different static pressure gradients, the boundary-layer velocity profiles for the different nozzle settings are similar, and it is shown analytically that this similarity is to be expected.
" }, { "name": "Statler, Irving Carl", "degree": "PhD", "year": "1956", "title": "The Effects of Nonstationary Aerodynamics on the Rigid-Body Dynamic Stability of an Airplane", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06302004-095128", "creators": [ { "name": { "family": "Statler", "given": "Irving Carl" }, "id": "Statler-Irving-Carl", "display_name": "Statler, Irving Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1EHQ-B547", "abstract": "A first order in frequency theory is developed for the aerodynamic loads on a harmonically oscillating thin wing of finite aspect ratio in a subsonic compressible flow. The downwash in the vicinity of a horizontal tail behind such a wing is also evaluated to the same order in frequency. The results are then used to determine the stability derivatives of a conventional-type airplane and to set up the stick-free longitudinal equations of motion including the unsteady flow effects.\r\n\r\nAn important conclusion of this study is that, within the limitations of a \"lifting-strip\" theory, the airloads on the oscillating finite span wing are linear in frequency in the neighborhood of zero frequency. This is in contrast with the two-dimensional results which show a logarithmic singularity there.\r\n\r\nAs an example of a practical application, calculations are made of the frequency, damping and transient responses of the stick-free longitudinal motion of an F-80A airplane and the results compared with those obtained using quasisteady aerodynamic coefficients. The indications are that, while nonsteady flow considerations show considerable influence upon the control surface motion, they have a negligibly small effect upon the airplane motion." }, { "name": "Vermilya, Jay J.", "degree": "Engineering Degree", "year": "1956", "title": "Migration of Vacancies to Stress Centers", "advisor": "Aroeste, Henry", "url": "https://resolver.caltech.edu/CaltechETD:etd-07162004-114521", "creators": [ { "name": { "family": "Vermilya", "given": "Jay J." }, "id": "Vermilya-Jay-J", "display_name": "Vermilya, Jay J." } ], "advisors": [ { "name": { "family": "Aroeste", "given": "Henry" }, "id": "Aroeste-H", "role": "advisor", "display_name": "Aroeste, Henry" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J43D-4D95", "abstract": "The activation energy for motion of a vacancy in an edge dislocation width is considered by a modification of the method of Bartlett and Dienes. The results indicate an expected trend of motion toward the center of the width in the compressed half with a decreasing activation energy from edge to center. On the basis of the model used there is little tendency to form nonequilibrium vacancy doublets by this mechanism." }, { "name": "Baldwin, Lawrence Cloyd", "degree": "Engineering Degree", "year": "1955", "title": "Viscous Effects on Static Pressure Distribution for a Slender Cone at a Nominal Mach Number of 5.8", "advisor": "Lees, Lester; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242003-104401", "creators": [ { "name": { "family": "Baldwin", "given": "Lawrence Cloyd" }, "id": "Baldwin-Lawrence- Cloyd", "display_name": "Baldwin, Lawrence Cloyd" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XNB2-P865", "abstract": "An experimental investigation was conducted in the GALCIT Hypersonic Wind Tunnel, Leg No. 1, to determine the static pressure distribution on a cone with 5[degrees] semivertex angle at a nominal Mach number of 5.8.\r\n\r\nThis investigation was concerned with the effect of hypersonic boundary layer-shock wave interaction on the pressure at the cone surface. Pressure distributions were measured for three values of Reynolds numbers per inch and a comparison was made with theoretically calculated pressure distributions.\r\n\r\nThe influence of viscosity in hypersonic flow was demonstrated by an induced pressure rise of approximately 45% above theoretical inviscid pressure for the lowest Reynolds number tested." }, { "name": "Benton, William Curtis", "degree": "Engineering Degree", "year": "1955", "title": "The Emissivity of Hydrogen Atoms at High Ttemperatures", "advisor": "Aroeste, Henry; Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-145619", "creators": [ { "name": { "family": "Benton", "given": "William Curtis" }, "id": "Benton-William-Curtis", "display_name": "Benton, William Curtis" } ], "advisors": [ { "name": { "family": "Aroeste", "given": "Henry" }, "id": "Aroeste-H", "role": "advisor", "display_name": "Aroeste, Henry" }, { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G0S8-8Q90", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA method is described for making estimates of the total emissivity of hydrogen in the temperature and pressure ranges where hydrogen atoms predominate under equilibrium conditions. For a characteristic geometrical depth of 50 cm, and temperatures of the order of 12,500[degrees]K and higher, with pressures of the order of 100 atmos and higher, the emissivity approaches unity [...] while for temperatures of the order of 9500[degrees]K and lower, with pressures of the order of 10 atmos and lower, the emissivity approaches zero [...]. The variations of the emissivity between these approximate limits are shown graphically as functions of temperature and pressure with the geometrical depth set at 50 cm. The variation of the emissivity with geometrical depth is also shown graphically at 12,600[degrees]K and 20 atmos." }, { "name": "Berndt, Sune Bertil", "degree": "PhD", "year": "1955", "title": "On the Influence of Wall Boundary Layers in Closed Transonic Test Sections", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-143311", "creators": [ { "name": { "family": "Berndt", "given": "Sune Bertil" }, "id": "Berndt-Sune-Bertil", "display_name": "Berndt, Sune Bertil" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T014-DR86", "abstract": "The boundary layers at the test section walls of a transonic wind tunnel are known to reduce the wall interference. In the present paper this effect is studied by means of small perturbation theory, assuming viscosity to be negligible when perturbing a turbulent boundary layer. An approximation for thin boundary layers leads to a modified boundary condition at the wall of the test section, expressing the normal streamline slope induced by changes in mass flow density and crossflow within the boundary layer. This boundary condition is applied to the linearized equations of subsonic flow and to the non-linear transonic equations at choking, the cases of plane and circular test sections only being treated in detail.\r\n\r\nThe results of linear theory show that all corrections except the three-dimensional angle-of-attack correction are considerably reduced by the presence of the boundary layers at Mach numbers greater than 0.9, the essential part of their influence being due to the change of mass flow density with pressure. In the case of choking the analysis indicates that the presence of boundary layers will increase the maximum model size for which the flow can be interpreted as corresponding to Mach number one in free flight. Finally, the technique of using artificial thickening of the wall boundary layers for reduction of wall interference is considered, though without reaching a definite conclusion as to its value compared to other techniques." }, { "name": "Birdwell, Carl", "degree": "Engineering Degree", "year": "1955", "title": "Investigation at Low Speed of a Six-Percent Thick Symmetrical Circular-Arc Airfoil with Leading Edge Retraction in Combination with Nose Slot", "advisor": "Stewart, Homer Joseph; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-154259", "creators": [ { "name": { "family": "Birdwell", "given": "Carl" }, "id": "Birdwell-Carl", "display_name": "Birdwell, Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B8SG-Y069", "abstract": "The effectiveness of leading-edge retraction as a possible high-lift device for thin, sharp-nosed airfoils was investigated. Experimental results are presented for a symmetrical, 6%-thick, circular-arc airfoil configuration, such that the forward 9.5% section of the chord is retractable up to a distance of 20% chord into the wing. The results include direct force measurements, limited surface pressure surveys and limited single-tuft surveys.\r\n\r\nTests were made with varying amounts of retraction in combination with variable stagger between leading edges of upper and lower surfaces and with several upper surface slot configurations. One retracted configuration was tested with a 20% chord, split-flap.\r\n\r\nThe results show that retraction is ineffective in increasing maximum lift. In general the effect on maximum lift was as follows: (1) Retracting up to approximately 9%, decreased maximum lift in proportion to the loss in wing area, (2) With exactly 9.06% retraction and with certain configurations of stagger and/or slots, the stalling angle of attack was increased 2[degrees] and the maximum lift was equal to that of the unaltered airfoil, (3) Retracting more than 9.06% resulted in a disproportionate loss of maximum lift, approximately 20% less than the unaltered airfoil." }, { "name": "Burggraf, Odus Roy", "degree": "PhD", "year": "1955", "title": "A Theory of Stall Propagation in Axial Compressors on the Basis of Airfoil Characteristics", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242003-103851", "creators": [ { "name": { "family": "Burggraf", "given": "Odus Roy" }, "id": "Burggraf-Odus-Roy", "display_name": "Burggraf, Odus Roy" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HQV0-7S12", "abstract": "The process of stall propagation in an axial flow compressor is represented by nonlinear airfoil lift and drag characteristics, with a time lag associated with the stalling mechanism. A pair of nonlinear integro-differential equations express the lift and drag as a function of time for a given airfoil in an isolated plane cascade representing an annulus with only a finite number of blades. Approximate solutions of these integro-differential equations are obtained by considering only the fundamental frequency in the Fourier series representing the blade loadings. Qualitative results are obtained for three cases: (a) only blade circulation is considered to be of importance in the mechanism of propagating stall, (b) blade drag is of predominant importance, and (c) combined effects of lift and drag are considered. Comparisons are made of the propagating speeds calculated for a finite number of blades with the values obtained by the approximation of an infinite number of blades. The magnitudes of the fluctuations in lift and drag are calculated as well as limiting angles of attack for which stall propagation can occur." }, { "name": "Chase, Robert Apperson", "degree": "PhD", "year": "1955", "title": "Pressurized Fuselage Stress Analysis", "advisor": "Williams, Max L.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-161233", "creators": [ { "name": { "family": "Chase", "given": "Robert Apperson" }, "id": "Chase-Robert-Apperson", "display_name": "Chase, Robert Apperson" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZCGR-N460", "abstract": "Theoretical methods for obtaining the complete stress analysis of a pressurized, stiffened circular cylinder of special geometry are presented. In certain limiting cases, the exact solutions are tractable, but in general the solutions lead to approximate results. There are practical cases for which none of the solutions is applicable. Accompanying the theoretical analysis is a short experimental program consisting of the strain gage instrumentation and testing of a Lucite and cellulose acetate model of typical aircraft structural geometry. The results compare favorably with the theoretical analysis." }, { "name": "Cornwell, Roy Stribling", "degree": "Engineering Degree", "year": "1955", "title": "Experiments in Nucleate Boiling Heat Transfer", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-092813", "creators": [ { "name": { "family": "Cornwell", "given": "Roy Stribling" }, "id": "Cornwell-Roy-Stribling", "display_name": "Cornwell, Roy Stribling" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PHKW-K604", "abstract": "The present series of experiments were undertaken in order to provide additional information on the effects of different heating surface materials on boiling heat transfer. Three different materials were used in conjunction with three different fluids.\r\n\r\nWires of platinum, tungsten and iron were chosen for the heating surface materials. All wires were approximately 0.010 inches in diameter and two inches long. The fluids used were methyl alcohol, carbon tetrachloride and iso-octane. Measurements of wire temperature and heat flux were made with the wire immersed in the fluid and heated electrically.\r\n\r\nThe results indicated that there was no major effect of the heating surface material on either the burnout heat flux or on the temperature of the nucleate boiling region. These findings are, of course, limited to the wire-fluid combinations tested as well as to the range of experimental conditions investigated." }, { "name": "Crowe, Thomas Huston", "degree": "Engineering Degree", "year": "1955", "title": "Correlation of Laminar Flame Velocities for Hydrocarbon-Oxygen-Inert Gas Mixtures", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-105228", "creators": [ { "name": { "family": "Crowe", "given": "Thomas Huston" }, "id": "Crowe-Thomas-Huston", "display_name": "Crowe, Thomas Huston" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/29MY-5D14", "abstract": "A thermal theory of laminar flame propagation for hydrocarbon-oxygen flames is described. The method of analysis follows the earlier work of von Karman and his collaborators. The problem is greatly simplified by the introduction of several approximations and assumptions.\r\n\r\nIn Section III the problem is formulated and approximate solutions are given for hydrocarbon-oxygen flames, assuming a second order rate-controlling step. Approximate analytic solutions have been obtained for all mixture ratios.\r\n\r\nHydrocarbon-oxygen-inert gas mixtures are considered in Section IV. A second order rate-controlling step is again assumed and solutions are given for various initial gas compositions.\r\n\r\nAn attempt is made to correlate experimentally determined burning velocity data in Section V. Reference to Section V shows that a good correlation was obtained only for lean mixtures. Absolute values for the laminar burning velocity cannot be estimated because of the lack of data concerning reaction mechanism and specific reaction rate constants." }, { "name": "Doss, Robert Franklin", "degree": "Engineering Degree", "year": "1955", "title": "Leading Edge Retraction as a High Lift Device", "advisor": "Stewart, Homer Joseph; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-110111", "creators": [ { "name": { "family": "Doss", "given": "Robert Franklin" }, "id": "Doss-Robert-Franklin", "display_name": "Doss, Robert Franklin" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PV47-6A63", "abstract": "A two-dimensional investigation was carried out in the Merril Wind Tunnel at the California Institute of Technology to determine the effect on low speed lift of retracting the leading edge of a thin, circular-arc airfoil.\r\n\r\nSeveral configurations were tried, some with a spanwise slot milled into the upper surface so that the leading edge recess formed by retraction could be utilized as an air intake to improve the flow. A comparison was made between the configurations with the leading edge retracted to various positions and the basic airfoil.\r\n\r\nThe investigation showed that leading edge retraction caused a linear loss of maximum lift proportional to the percent reduction in chord up to a critical position where lift and the stalling angle of attack increased abruptly. Thereafter, maximum lift was reduced at a rate higher than the chord reduction. The effect of the slot was negligible.\r\n\r\nThe critical position phenomenon warrants further study." }, { "name": "Fehrman, Alvin Lyone", "degree": "Engineering Degree", "year": "1955", "title": "Effect of Spin and Yaw on Boundary Layer Transition Along a Body of Revolution", "advisor": "Roshko, Anatol; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092003-160300", "creators": [ { "name": { "family": "Fehrman", "given": "Alvin Lyone" }, "id": "Fehrman-Alvin-Lyone", "display_name": "Fehrman, Alvin Lyone" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NP87-FA81", "abstract": "This report covers an experimental investigation of boundary layer transition on a body of revolution at low subsonic speeds, with emphasis placed on the effects of spin and yaw on transition.\r\n\r\nThe methods tried for detecting boundary layer transition for this particular investigation are reviewed and the technique finally adopted, the use of a hot wire anemometer, is described in detail.\r\n\r\nIt was found that at angles of yaw, the transition from laminar to turbulent flow in the boundary layer occurs at a higher Reynolds number over most of the body than at zero yaw, and that spin has a negligible effect on the transition Reynolds number. It was observed however that the effect of spin varies from the front to the rear of the body, although it was not ascertained whether this effect was a result of the influence of the nose section, the tripping device which was used to obtain transition, or a combination of both." }, { "name": "Howard, Weston Morgan", "degree": "Engineering Degree", "year": "1955", "title": "An Experimental Investigation of Pressure Gradients Due to Temperature Gradients in Small Diameter Tubes", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162003-155556", "creators": [ { "name": { "family": "Howard", "given": "Weston Morgan" }, "id": "Howard-Weston-Morgan", "display_name": "Howard, Weston Morgan" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SQF1-5002", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstraact is included in .pdf document.\r\n\r\nResults of an experimental investigation of pressure gradients due to axial temperature gradients in small diameter tubes are presented. The tests, which covered the region of Knudsen numbers (based on tube inside radius) of 0.01 to 6, indicate good correlation with theory.\r\n\r\nIt is of value to note that this correlation was obtained by using [Delta]T equal to the temperature difference between the hot and cold ends of the tubes and T[subscript ave] equal to the average of these two temperatures. In contrast, theory would dictate obtaining the temperature variation along the length of the tube and applying the formulas to small incremental [Delta]T's, then summing to get the total effect. Therefore, for normal laboratory conditions where pressure gradient corrections are to be computed, it is sufficient to record only the temperatures at the hot and cold ends rather than having to obtain a number of temperature readings along the tube.\r\n\r\nIn order to apply pressure corrections easily and rapidly, a system of correction curves is given. To simplify the procedure, the tube cold end temperature was assumed to be 80[degrees]F, and the correction curves drawn accordingly. However, for different laboratory conditions a similar system of curves could be drawn and used." }, { "name": "James, George Thomas", "degree": "Engineering Degree", "year": "1955", "title": "The Effect of Adhesive Coating on the Fatigue Properties of 2014-T and 7075-T at Normal and Elevated Temperatures", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01062004-163541", "creators": [ { "name": { "family": "James", "given": "George Thomas" }, "id": "James-George-Thomas", "display_name": "James, George Thomas" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "member", "display_name": "Lurie, Harold" }, { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "member", "display_name": "Williams, Max L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AX4T-KX34", "abstract": "A problem of current practical interest to the field of Aeronautics is whether cement coatings associated with strain gages and fatigue warning indicators have appreciable effect upon fatigue characteristics.\r\n\r\nFatigue tests in rotary bending were conducted at room temperature, 200[degrees]F and 400[degrees]F on plain specimens of 2014-T and 7075-T and specimens coated with a synthetic resin lacquer, a synthetic resin cement, and an epoxy resin cement.\r\n\r\nThe effect of these coatings was slight at room temperature, falling within the scatter band, but apparently affording a small increase in fatigue life. At 200[degrees]F there was no definite effect, but at 400[degrees]F there was a pronounced lowering of fatigue life for all the coated specimens. Parallel results were obtained in 2014-T and 7075-T." }, { "name": "Kiley, Donald Walter", "degree": "Engineering Degree", "year": "1955", "title": "On the Burning of Single Drops of Monopropellants", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-112346", "creators": [ { "name": { "family": "Kiley", "given": "Donald Walter" }, "id": "Kiley-Donald-Walter", "display_name": "Kiley, Donald Walter" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/33WQ-4M23", "abstract": "A simplified theoretical treatment has been developed for the burning of single drops of monopropellants. Evaporation constants and the ratios of flame to droplet radii have been calculated for the following monopropellants burning in an inert atmosphere: hydrogen peroxide, nitromethane, hydrazine, ethylene oxide, ozone and nitrous oxide. Compared with the results of similar calculations for fuels burning in air, much smaller flame radii were obtained, while the evaporation constants were found to fall in the same range as before.\r\n\r\nAttempts at burning single droplets of monopropellants (e.g. hydrazine and nitromethane) in a nitrogen atmosphere were unsuccessful. Monopropellant droplets burning stably in air were found to extinguish if the oxygen was removed during burning. These experimental findings probably reflect the well-known difficulties encountered in monopropellant operation, which is usually successful only if a suitable reaction catalyst is available. The applicability of calculated monopropellant burning rates to practical cases cannot be assessed at this time.\r\n\r\nSingle droplets of hydrazine and nitromethane were burnt in air and evaporation constants determined experimentally. The measured rate for nitromethane was found to be in good agreement with calculated results for heterogeneous burning of fuel droplets in air. The measured rate for hydrazine was found to be considerably higher than the value calculated for fuel droplets burning in air or for monopropellant droplets burning in an inert atmosphere. This latter result probably indicates that the assumption of a diffusion flame for the burning of hydrazine in air is not valid, i.e., the hydrazine decomposes throughout the region between the liquid surface and the \"flame surface\" rather than reacting instantaneously at the \"flame surface\"." }, { "name": "Lal, Shankar", "degree": "PhD", "year": "1955", "title": "Heat Transfer in Compressible Laminar Boundary-Layers", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-095744", "creators": [ { "name": { "family": "Lal", "given": "Shankar" }, "id": "Lal-Shankar", "display_name": "Lal, Shankar" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BRKX-WV81", "abstract": "This report is concerned with the investigation of skin-friction and heat-transfer in the two-dimensional flow of a viscous compressible fluid.
\r\n\r\nThe boundary-layer equations are first transformed by the Howarth-Stewartson transformation and then it is shown that for fluids of Prandtl Number unity, if the Chapman viscosity law be assumed to hold, then any boundary-layer problem with the free stream Mach Number different from zero can be formally reduced to a problem for which the free stream Mach Number is equal to zero.
\r\n\r\nThe momentum method is then used to solve the boundary-layer equations in the Howarth-Stewartson form, for the case when the free stream Mach Number is zero. The basic equations developed are first used to solve the case of those specific pressure gradients which lead to \"similarity flows\". Other investigators have solved the exact equation for these flows on the differential analyser. The results obtained in this report, with the aid of very simple methods, agree to within a few percent with these more exact but laborious computations.
\r\n\r\nThe use of the method for the case of arbitrary pressure gradients is then developed. Three ways of solving the resulting equations are discussed. In particular, an integral solution for the square of the momentum thickness, analogous to the one existing for incompressible fluids but with different exponents, is given. The application of the method is demonstrated by solving an illustrative example.
" }, { "name": "Larsen, Harold Cecil", "degree": "Engineering Degree", "year": "1955", "title": "Design of a Model for the Measurement of the Pressure Distribution on an Axially Symmetric Rotating Body", "advisor": "Millikan, Clark Blanchard; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-095556", "creators": [ { "name": { "family": "Larsen", "given": "Harold Cecil" }, "id": "Larsen-Harold-Cecil", "display_name": "Larsen, Harold Cecil" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TDEY-2865", "abstract": "Two simplified theories for the corrections to be applied to the measured pressure in order to determine the pressure distribution on a rotating body are presented. One is based on continuous sampling, and the other is based upon pulse sampling. The problems associated with and the design features of systems using different pressure sensing elements are reviewed. From these considerations, the system offering the simplest solution is selected. The design features and compromises of a model designed and constructed utilizing pulse sampling are discussed." }, { "name": "Magnus, Richard Jeffrey", "degree": "PhD", "year": "1955", "title": "An Experimental Investigation of the Transfer of Heat from Small Wires to a Viscous Compressible Fluid", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-100200", "creators": [ { "name": { "family": "Magnus", "given": "Richard Jeffrey" }, "id": "Magnus-Richard-Jeffrey", "display_name": "Magnus, Richard Jeffrey" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4ZYH-PF56", "abstract": "A steam tunnel, suitable for making experimental measurements of the heat transfer from fine wires to a viscous compressible fluid, was developed and constructed.\r\n\r\nMeasurements of Nusselt numbers and recovery temperatures were carried out using small-diameter (0.00038 to 0.00254 cm.) tungsten wires in steam flow with Reynolds numbers ranging from about 1 to 12 and with nominal Mach numbers of 0.5 to 1.7.\r\n\r\nConsiderable difference was found between the Nusselt numbers for wires in subsonic and supersonic flow at corresponding Reynolds numbers. The results could be fairly well represented by an available theory based on the assumption that a temperature discontinuity of the fluid existed at the wire surface; however, they did not agree very well with other available data in the same range of Mach and Reynolds numbers.\r\n\r\nIn supersonic flow, the wire recovery temperatures were found to be consistently higher than the tunnel stagnation temperature.\r\n\r\nAn experimental procedure for making end-loss corrections to the heat transfer and temperature recovery tests was used and found to give satisfactory correlation of data taken with wires ranging in aspect ratio from 220 to 3040. Some experiments were performed to check the validity of the simple linear theory which is usually used to calculate end loss corrections; the theory was found to be adequate in the experimental range covered." }, { "name": "McClellan, Robert", "degree": "Engineering Degree", "year": "1955", "title": "Equilibrium Temperature and Heat Transfer Characteristics of Hot Wires in Supersonic Flow", "advisor": "Laufer, John", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-105304", "creators": [ { "name": { "family": "McClellan", "given": "Robert" }, "id": "McClellan-Robert", "display_name": "McClellan, Robert" } ], "advisors": [ { "name": { "family": "Laufer", "given": "John" }, "id": "Laufer-John", "role": "advisor", "display_name": "Laufer, John" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AB2Y-MC42", "abstract": "An experimental investigation was made of two problems that are fundamental to the application of hot wire anemometry in a supersonic flow. First, the equilibrium temperature of a wire in supersonic flow was established as a function of the flow parameters. Second, the heat loss law for a heated wire in a supersonic flow was determined. In the latter case it was shown that the heat loss, represented by a Nusselt number, is a function of Reynolds number only, with the temperature loading as a parameter. There is no Mach number effect from M = 1.80 to M = 4.54, the range of the present experiments.\r\n\r\nThe results show that the hot wire should be a satisfactory instrument for the measurement of both mean values and fluctuations of the mass flow and the stagnation temperature." }, { "name": "Ormsbee, Allen Ives", "degree": "PhD", "year": "1955", "title": "Conical Techniques for Incompressible Non-Viscous Flow", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-093114", "creators": [ { "name": { "family": "Ormsbee", "given": "Allen Ives" }, "id": "Ormsbee-Allen-Ives", "display_name": "Ormsbee, Allen Ives" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/77MG-6Z64", "abstract": "An analytical investigation was made of incompressible potential flow fields in which the velocity components are homogeneous of order zero. Superpositions of such fields were then made and expressions were derived for the flow fields associated with constant-strength source and vortex sheets of finite extent.\r\n\r\nThe constant strength source-sheets were then applied to the construction of aerodynamic models of thin non-lifting wings of polygonal platform and airfoil section.\r\n\r\nBy use of the constant strength vortex-sheets, several approximate aerodynamic models were constructed for the determination of the pressure distribution on thin lifting wings at small angles of attack." }, { "name": "Rex, James Foster", "degree": "Engineering Degree", "year": "1955", "title": "Interference Effects During Burning in Air for Two Stationary N-Heptane Droplets", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01202004-145717", "creators": [ { "name": { "family": "Rex", "given": "James Foster" }, "id": "Rex-James-Foster", "display_name": "Rex, James Foster" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/334Z-RA03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstraact is included in .pdf document.\r\n\r\nIn order to gain some understanding of droplet interference during burning, experiments have been conducted for the determination of the evaporation constant and flame shapes of two closely spaced n-heptane droplets burning in air. Droplets of approximately the same and of different diameters were used at various distances between the droplet centers.\r\n\r\nExperimental results on flame shapes and evaporation constants for closely spaced droplets show somewhat surprising behavior. Thus the apparent flame shape changes very little during the burning of the droplet. The square of the droplet diameter decreases linearly with time for fixed spacing between droplet centers, at least within the experimental limits of accuracy. Since geometrically different conditions are produced continuously during burning, the observed independence of the slope of plots for the square of droplet diameter vs time is not obviously expected. Furthermore, for droplets of different average initial diameters [...], the frequency, [...], where [...] is the usual evaporation constant, is well represented as a universal function of the initial spacing between droplet centers ([...]) or adjacent droplet surfaces ([...]).\r\n\r\nThe evaporation constant [...] for constant [...], and the frequency [...] for arbitrary values of [...], increase at first as [...] is reduced and then decrease again. For large values of [...], [...] approaches the numerical value measured in studies on the burning of single droplets. This behavior can be understood in terms of a competition between heat losses to the outside from the flame front surrounding a single droplet, which decrease as the droplets are brought together, and oxygen-deficient atmospheres, which are more likely to occur for very small values of [...].\r\n\r\nAlthough an acceptable empirical correlation of experimental measurements has been obtained, the processes which determine interference during droplet burning are as yet not understood. In view of the possible practical importance of interference during burning in sprays, additional laboratory studies on the burning of simple geometric arrays, other than two droplets, appear to be indicated." }, { "name": "Schalin, Pehr Harald Benedictus", "degree": "Engineering Degree", "year": "1955", "title": "A Slender Body Aeroelastic Transfer Function Including the Effects of Structural Flexibility and Nonstationary Aerodynamics", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-114448", "creators": [ { "name": { "family": "Schalin", "given": "Pehr Harald Benedictus" }, "id": "Schalin-Pehr-Harald-Benedictus", "display_name": "Schalin, Pehr Harald Benedictus" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2GPJ-KV69", "abstract": "On the basis of linearized nonstationary aerodynamics and a normal mode representation of the motion, the aeroelastic transfer functions of a symmetrically oscillating slender body are derived from energy principles.\r\n\r\nIn the present analysis no structural damping or aerodynamic viscous forces are included, but they are believed not to alter the principal features of the system significantly.\r\n\r\nThe aerodynamic force expressions, obtained as a side result, turn out to be exceedingly simple in the slender body case.\r\n\r\nThe final eigenfrequency-analysis and the open loop frequency response of the system chosen in Appendix D indicate that the aerodynamic coupling is low. The eigenfrequencies therefore are accurately obtained from the simple decoupled equations. This also holds for the frequency response in a fairly wide band around each particular resonance frequency.\r\n\r\nThe magnitude of the response of the elastic coordinates in comparison with rigid body responses at resonance frequencies clearly indicates the importance of elastic effects with respect to closed loop control problems." }, { "name": "Seidman, Oscar", "degree": "Engineering Degree", "year": "1955", "title": "A Theoretical Investigation of the Effect of Upwash and Camber on Drag Due to Lift for Rectangular Wings at Supersonic Speeds", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01212004-103434", "creators": [ { "name": { "family": "Seidman", "given": "Oscar" }, "id": "Seidman-Oscar", "display_name": "Seidman, Oscar" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AMQ1-JJ66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theoretical investigation was conducted, using linearized theory, to determine the combined effects of upwash and camber on drag due to lift for rectangular wings at supersonic speeds. Both the case of body upwash and the case of a uniform upwash field were considered. Previous studies have shown that body upwash and wing camber, acting separately, each reduce the drag due to lift for a rectangular wing. In the present investigation it was found that the individual effects as measured by the criterion [...] are additive and that there is a further gain which increased with decreasing aspect ratio. For the basic wing-body configuration investigated, with wing having a reduced aspect ratio of two, the upwash effect was much larger than the camber effect. For a complete aircraft configuration with lifting nose, optimum camber reduced the drag at a given lift by a somewhat smaller percentage than it did for an isolated wing. The analysis further indicated that use of moderate negative wing incidence could reduce aircraft drag at a given lift." }, { "name": "Skinner, George Tolmie", "degree": "PhD", "year": "1955", "title": "A Time Correlator for Problems in Aerodynamics", "advisor": "Liepmann, Hans Wolfgang; Lagerstrom, Paco A.; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-092906", "creators": [ { "name": { "family": "Skinner", "given": "George Tolmie" }, "id": "Skinner-George-Tolmie", "display_name": "Skinner, George Tolmie" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6B8H-3139", "abstract": "An instrument, of fairly simple design, for measuring time correlation functions of two stationary random electrical signals is discussed. It is intended primarily for use in problems connected with aerodynamically produced acoustic fields, but has suitable properties for application to a rather wide range of aerodynamic problems involving turbulent fields. It has been designed and constructed with a view to economy, and simplicity of operation, and makes extensive use of the general statistical properties of the problems for which it is intended.\r\n\r\nA few experimentally determined auto-correlation functions are given in order to indicate the degree of accuracy achieved, and the Fourier transform of the auto-correlation function of a random input is compared with the power-spectrum of the same function.\r\n\r\nSome practical points of general interest are discussed." }, { "name": "Stalk, George", "degree": "Engineering Degree", "year": "1955", "title": "A Study of Fatigue Notch Sensitivity of 2014-T and 7075-T at Elevated Temperatures", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272004-110905", "creators": [ { "name": { "family": "Stalk", "given": "George" }, "id": "Stalk-George", "display_name": "Stalk, George" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A948-ZS36", "abstract": "This experiment was conducted to investigate the reversed-bending fatigue notch sensitivity of 2014-T and 7075-T at elevated temperatures. Tests were conducted on three configurations of specimens which had external circumferential notches, and on one configuration of un-notched specimens.\r\n\r\nIt was determined that the experimental stress concentration factor for both alloys, at room and elevated temperatures, increases with decreasing notch radius.\r\n\r\nAt room and elevated temperatures, the fatigue notch sensitivity for both 2014-T and 7075-T, generally increases with increasing notch radius.\r\n\r\nThe fatigue notch sensitivity factor and the experimental stress concentration factor for 2014-T increases with temperature, reaches a maximum in the range of 250[degrees]F to 350[degrees]F and then decreases at 400[degrees]F.\r\n\r\nThe experimental stress concentration factor for 7075-T increases almost linearly from room temperature to 400[degrees]F.\r\n\r\nThe fatigue notch sensitivity factor for 7075-T increases almost linearly from room temperature to 400[degrees]F, but only the 0.09 inch radius notch configuration shows a tendency to level off." }, { "name": "Williamson, William Jeffris", "degree": "Engineering Degree", "year": "1955", "title": "An Experimental Investigation of Heat Transfer from Fine Wires to Still Air at Low Density", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-02032004-142252", "creators": [ { "name": { "family": "Williamson", "given": "William Jeffris" }, "id": "Williamson-William-Jeffris", "display_name": "Williamson, William Jeffris" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J54H-9F64", "abstract": "Heat transfer from electrically heated wires of 0.00025 cm nominal diameter to still air at room temperature has been investigated at pressures ranging from 1 to 0.0076 atmospheres. Three wires, having ratios of length to diameter in the approximate proportion 1:5:10, were tested in the vertical position. Due to time limitations, only the shortest of these was tested in a horizontal position. A check was made to determine whether the results were influenced by the geometry of the enclosing vessel.\r\n\r\nFor pressures at which the molecular mean free path is smaller than the wire diameter, the results appear to satisfy a relation of a form derived for free-molecule heat conduction. Small departures from this behavior at the higher pressures are attributed to the effects of natural convection. The Nusselt number was found not to be uniquely related to the product of the Grashof and Prandtl numbers, as has been proposed, for values of this product below 10[^-5].\r\n\r\nIt was found that, at the lowest pressures reached, solid boundaries located at distances of the order of 3 x 10[^4] diameters from the wire cannot be considered infinitely remote." }, { "name": "Yang, Hsun-Tiao", "degree": "PhD", "year": "1955", "title": "Rayleigh's Problem at Lo\\w Mach Number According to the Kinetic Theory of Gases", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-105335", "creators": [ { "name": { "family": "Yang", "given": "Hsun-Tiao" }, "id": "Yang-Hsun-Tiao", "display_name": "Yang, Hsun-Tiao" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2VK2-FC14", "abstract": "Rayleigh's problem of an infinite flat plate set into uniform motion impulsively in its own plane is studied by using Grad's equations and boundary conditions developed from the kinetic theory of gases. For a heat insulated plate and a small impulsive velocity (low Mach number), only tangential shear stress and velocity and energy (heat) flow parallel to the plate are generated, while the pressure, density, and temperature of the gas remain unchanged. Moreover, no normal velocity, normal stress, or normal energy flow is developed. Near the start of the motion the flow behaves like a \"free-molecule flow\", and all physical quantities are analytic functions of the flow parameters and time. The results obtained for \"large time\", however, add to the growing lack of confidence in the Burnett-type series expansions in powers of mean free path. Although such expansions are obtained here, they are poorly convergent and inappropriate to the problem. To replace these unsatisfactory solutions, approximate closed-form solutions valid for all values of the time are developed, which agree with the free-molecule values for small time and the classical Rayleigh solution for large time. This technique may be useful in studying more general flow problems within the framework of the kinetic theory of gases." }, { "name": "Adams, Gaynor Jefferson", "degree": "Engineering Degree", "year": "1954", "title": "Investigations of Generalized Conical Flow Fields", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11202003-105420", "creators": [ { "name": { "family": "Adams", "given": "Gaynor Jefferson" }, "id": "Adams-Gaynor-Jefferson", "display_name": "Adams, Gaynor Jefferson" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GRS3-P551", "abstract": "The conical transformation of variables of M.D. Haskind and S. V. Falkovich is applied to the steady-state problem of thin delta wings with subsonic leading edges in a supersonic flow. It is shown that solutions may be obtained, in terms of elliptic functions, for lifting wings of zero thickness with prescribed angle-of-attack distribution, and for symmetric non-lifting where the perturbation pressure is prescribed on the wing surface (thickness case, mean-surface assumption); the wing boundary conditions are assumed to be given in terms of polynomials in the space variables in the plane of the wing. Some previously known results are obtained to illustrate the method of analysis.\r\n" }, { "name": "Adamson, Thomas Charles, Jr.", "degree": "PhD", "year": "1954", "title": "Ignition and Combustion in a Laminar Mixing Zone", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11202003-135437", "creators": [ { "name": { "family": "Adamson", "given": "Thomas Charles, Jr." }, "id": "Adamson-Thomas-Charles", "display_name": "Adamson, Thomas Charles, Jr." } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Bohnenblust", "given": "Henri Frederic" }, "id": "Bohnenblust-H-F", "role": "member", "display_name": "Bohnenblust, Henri Frederic" }, { "name": { "family": "Felberg", "given": "Fredrick H." }, "id": "Felberg-Fredrick-H", "role": "member", "display_name": "Felberg, Fredrick H." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "member", "display_name": "Penner, Stanford S." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "member", "display_name": "Tsien, Hsue Shen" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q9A7-T088", "abstract": "The equations describing combustion in a flow field are modified for use in laminar flows where the so called boundary layer approximations may be employed. These equations are transformed into a corresponding incompressible flow with the Howarth transformation.
\r\n\r\nAs an example of the use of boundary layer concepts this analysis considers the ignition and combustion in the laminar mixing zone between two parallel moving gas streams. One stream consists of a cool combustible mixture, the second is hot combustion products. The two streams come into contact at a given point and a laminar mixing process follows in which the velocity distribution is modified by viscosity, and the temperature and composition distributions by conduction, diffusion and chemical reaction. The decomposition of the combustible stream is assumed to follow first-order reaction kinetics with temperature dependence according to the Arrhenius law. For a given initial velocity, composition, and temperature distribution, the questions to be answered are: (1) Does the combustible material ignite and (2) How far downstream of the initial contact point does the flame appear and what is the detailed process of development?
\r\n\r\nSince the hot stream is of infinite extent it is found that ignition always takes place at some point of the stream. However when the temperature of the hot stream drops below a certain value, the distance required for ignition increases so enormously that it essentially does not occur in a physical apparatus of finite dimension. The complete development of the laminar flame front is computed using an approximation similar to the von Karman integral technique in boundary layer theory.
\r\n" }, { "name": "Berger, Howard Martin", "degree": "PhD", "year": "1954", "title": "A New Approach to the Analysis of Large Deflections of Plates", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-163054", "creators": [ { "name": { "family": "Berger", "given": "Howard Martin" }, "id": "Berger-Howard-Martin", "display_name": "Berger, Howard Martin" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FA0E-1X79", "abstract": "As a result of the assumption that the strain energy due to the second invariant of the middle surface strains can be neglected when deriving the differential equations for a flat plate with large deflections, simplified equations are derived that can be solved readily. Computations using the solution of these simplified equations are carried out for the deflection of uniformly loaded circular and rectangular plates with various boundary conditions. Comparisons are made with available numerical solutions of the exact equations. The deflections found by this approach are then used to obtain the stresses, and the resulting stresses are compared with existing solutions. In all the cases where comparisons could be made, the deflections and stresses agree with the exact solutions within the accuracy required for engineering purposes." }, { "name": "Charles, John Morrison", "degree": "Engineering Degree", "year": "1954", "title": "Variation of Burning Velocity of Laminar Flames with Pressure by the Burner-Area Method", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-160702", "creators": [ { "name": { "family": "Charles", "given": "John Morrison" }, "id": "Charles-John-Morrison", "display_name": "Charles, John Morrison" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PVFG-9X18", "abstract": "Because of the disagreement in the published data on the effect of pressure on the burning velocity of laminar flames a general study was undertaken at the California Institute of Technology Jet Propulsion Laboratory to determine the variation of burning velocity with pressure by the burner-area method. This report is a portion of that study.\r\n\r\nThe mixtures utilized for this investigation were ethylene-air, isobutylene-air, propylene-oxygen-nitrogen, and propylene-air. Expressing the pressure dependence of burning velocity as p[superscript n], the value found for n is ?0.13 for ethylene-air, -0.186 for isobutylene-air, -0.153 for propylene-oxygen-nitrogen, and ?0.132 for propylene-air. The results compare reasonably well with the experimental findings of Pardee (10), Cullen (6), and Culshaw and Garside (5). At atmospheric pressure the values of burning velocity of the mixtures studied in this report are in close agreement with several experimental investigators.\r\n\r\nAlso investigated was the effect on the burning velocity of a mixture of acetylene-oxygen with the addition of helium. The trend found is that the burning velocity of an acetylene-oxygen mixture increases with the addition of helium up to a maximum at a certain percentage of helium and then decreases as more helium is added." }, { "name": "Dailey, Charles Lee", "degree": "PhD", "year": "1954", "title": "Supersonic Diffuser Instability", "advisor": "Liepmann, Hans Wolfgang; Stewart, Homer Joseph; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-101604", "creators": [ { "name": { "family": "Dailey", "given": "Charles Lee" }, "id": "Dailey-Charles-Lee", "display_name": "Dailey, Charles Lee" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V9XM-W683", "abstract": "Steady operation of supersonic diffusers near critical mass flow is interrupted by a transient process known as buzz. This phenomenon consists of a random sequence of individual relaxation cycles. Mass flow entering the diffuser during steady operation is suddenly cut off by a strong interaction between the subcritical shock and boundary layer on the surface of the external compression generator, which blocks the inlet. Air in the plenum chamber, stored at high pressure, then ?blows down? until the inlet can restart. The subsequent supercritical flow entering the diffuser exceeds the flow rate at the exit and the plenum chamber is re-charged to the original condition.\r\n\r\nA distinction is drawn between this phenomenon and a high frequency wave-type resonance noticed at low mass flows and during an individual buzz cycle after the diffuser shock system has been expelled. For the large diffuser tested here, this high frequency oscillation compares well to the 8th closed-end organ pipe mode of the diffuser at low mass flows and to the 9th mode during the shock-expelled phase of the buzz cycle.\r\n\r\nIt is shown that burning almost always ceases in the presence of buzz. When burning was maintained during buzz, it was found to have no qualitative effect on the buzz cycle." }, { "name": "Diederich, Franklin Wolfgang", "degree": "PhD", "year": "1954", "title": "The Response of an Airplane to Random Atmospheric Disturbances", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-105523", "creators": [ { "name": { "family": "Diederich", "given": "Franklin Wolfgang" }, "id": "Diederich-Franklin-Wolfgang", "display_name": "Diederich, Franklin Wolfgang" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XPKW-QH24", "abstract": "The statistical approach to the gust-loads problem is extended by considering the aerodynamic forces due to the lateral and longitudinal variation of instantaneous gust intensity and using them in dynamic analyses of rigid and flexible airplanes free to move vertically, in pitch, and in roll, based on the assumptions of stationarity of the process (in the statistical sense) and of linearity of the forces involved. The effect on the wing stresses of the interaction of longitudinal, vertical and lateral gusts is considered.\r\n\r\nThe method of analyzing the rigid-body motions is similar to that used for analyses of the dynamic stability of airplanes, in that the equations of motion are referred to stability axes and expressed in terms of conventional stability derivatives. The method of analyzing the dynamic effects of structural flexibility consists of an extension of a numerical-integration approach to the static aeroelastic problem and is in a form which offers the possibility of calculating divergence and flutter speeds with relatively little additional effort.\r\n\r\nThe mean-square values, correlation functions and power spectra of some of the aerodynamic forces required in this type of analysis are calculated for certain special correlation functions of the atmospheric turbulence and certain special lift distributions. It is shown, for instance, that the mean-square lift is substantially reduced due to the difference in instantaneous intensity of the turbulent velocity along the span if the span is relatively large compared to the integral scale of turbulence, but that the mean-square pitching moment is substantially increased if the tail length is relatively large. Also, the wing stresses due to vertical, horizontal and side gusts are shown to be statistically independent under certain conditions." }, { "name": "Gates, Chester Wright", "degree": "Engineering Degree", "year": "1954", "title": "Some Experiments in Nucleate Boiling Heat Transfer", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-165828", "creators": [ { "name": { "family": "Gates", "given": "Chester Wright" }, "id": "Gates-Chester Wright", "display_name": "Gates, Chester Wright" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y7A3-1P44", "abstract": "The present series of experiments was designed to provide additional information on the mechanism of bubble formation in boiling liquids. In particular, knowing that a pre-pressurization treatment raises the boiling temperature of a body of water markedly, it was desired to determine the effect of such treatment on boiling from a metal heating surface immersed in the water.\r\n\t\r\nA 0.010\" nichrome wire was immersed in a vessel of water, the entire assembly having been cleaned, and subjected to a pressure of 15000 psi for periods of time in excess of 15 minutes. The pressure was reduced to atmospheric and the wire heated to burnout by electric current. It was concluded that the effect of the treatment on the maximum heat transfer was small and equivalent to degassing the water.\r\n\t\r\nA second series of experiments was conducted in which the temperature of the wire at the onset of boiling in pre-pressurized water was measured. These experiments indicated that the wire reached a temperature considerably in excess of normal nucleation temperatures, dropping to normal at the instant of nucleation. This effect could be explained in terms of the theory which postulates bubble formation from pre-existing gas or vapor nuclei." }, { "name": "Hakkinen, Raimo Jaakko", "degree": "PhD", "year": "1954", "title": "Measurements of Skin Friction in Turbulent Boundary Layers at Transonic Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152003-084052", "creators": [ { "name": { "family": "Hakkinen", "given": "Raimo Jaakko" }, "id": "Hakkinen-Raimo Jaakko", "display_name": "Hakkinen, Raimo Jaakko" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WAX3-QV41", "abstract": "The first part of this report describes the design and construction of a floating element skin friction balance. This instrument, which is essentially an improved version of Dhawan's balance, was applied to measurements of local skin friction in the turbulent boundary layer of a smooth flat plate at high subsonic Mach numbers and supersonic Mach numbers up to M = 1.75. The measured skin friction coefficients are consistent with the results of other investigations at subsonic and also at high supersonic speeds. The principal difficulties which exist in comparing skin friction coefficients at various Mach numbers are discussed.\r\n\r\nThe second part of this report describes the application of the Stanton tube technique to skin friction measurements near the base of a shock wave impinging upon a turbulent boundary layer. The floating element technique is inherently difficult to apply for skin friction measurements in non-uniform flow. Hence, a Stanton tube is calibrated by means of a floating element balance in a uniform flow field and then used to measure skin friction near the base of an impinging shock. Oblique shock waves were produced by two wedges of 2.5[degree] and 4.6[degree] semi-angles and a normal shock was generated by a choked channel. Skin friction and velocity profiles were obtained for these three cases at a free stream Mach number of 1.48." }, { "name": "Harkins, William Douglas", "degree": "Engineering Degree", "year": "1954", "title": "Base Pressure and Static Pressure for a Cone-Cylinder at a Nominal Mach Number of 5.8", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152003-095830", "creators": [ { "name": { "family": "Harkins", "given": "William Douglas" }, "id": "Harkins-William-Douglas", "display_name": "Harkins, William Douglas" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P0K8-XG38", "abstract": "An experimental investigation was made in the GALCIT Hypersonic Wind Tunnel Leg No. l to determine the base pressure and static pressure on a cone-cylinder at a nominal Mach number of 5.8 in both one-phase and two-phase flow.\r\n\r\nThe scope of the investigation was a determination of interference data necessary for proper evaluation of base pressure results, investigation of the effect of Reynolds number on base pressure, and a comparison of experimental and theoretical static pressure distribution on a cone-cylinder.\r\n\r\nAs has been noted by other investigators, viscous effects in hypersonic flow were quite pronounced and demonstrated the increased non-linearity of the problems in hypersonic flow." }, { "name": "Kaplan, Abner", "degree": "PhD", "year": "1954", "title": "Finite Deflections and Buckling of Slightly Curved Beams and Shallow Spherical Shells under Lateral Loads", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-110343", "creators": [ { "name": { "family": "Kaplan", "given": "Abner" }, "id": "Kaplan-Abner", "display_name": "Kaplan, Abner" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q1HV-T474", "abstract": "This research consists in the experimental and theoretical investigation of the finite deflection and buckling of two similar structures; the low arch or slightly curved beam and the shallow spherical dome, both subjected to lateral loads. These structures are of interest because the large interaction between bending and axial forces causes their load-deflection behavior to become nonlinear at very low values of the deflection. Due to the wide difference in the methods of solution of these two problems they are separated into two parts, each having its own abstract.
\r\n\r\n[Part I]
\r\n\r\nWhen a low arch (a thin curved beam of small curvature) is subjected to a lateral loading acting toward the center of curvature, the axial thrust induced by the bending of the arch may cause the arch to buckle so that the curvature becomes suddenly reversed. The critical lateral loading depends on the dimensions and rigidity of the arch, the elasticity of the the end fixation, the type of load distribution, and the initial curvature of the arch. A general solution of the problem is given in this paper, using the classical buckling criterion which is based on the stability with respect to infinitesimal displacements about the equilibrium positions.
\r\n\r\nFor a sinusoidal arch under sinusoidal loading, the critical load can be expressed exactly as a simple function of the beam dimension parameters. For other arch shapes and load distributions, approximate values of the critical load can be obtained by summing a few terms of a rapidly converging Fourier series. The effect of initial end thrust and axial and lateral elastic support are discussed.
\r\n\r\nThe buckling load based on the energy criterion of Karman and Tsien is also calculated. The results for both the classical and the energy criteria are compared with experiments made on a series of centrally loaded, pin-ended arches. For larger values of a dimensionless parameter [gamma subscript l], which is proportional to the ratio of the arch rise to the arch thickness, the experimental critical buckling loads agreed quite well with the classical criterion, but, for smaller values of [gamma subscript l], the experimental critical loads were appreciably below those calculated from the classical criterion, although they were always above those obtained from the energy criterion.
\r\n\r\n[Part II] The shallow spherical dome subjected to lateral pressure is a structure for which the deformation departs appreciably from the linear theory at very small values of the deflection amplitude. It is also. one for which the buckling process is characterized by a rapid decrease in the equilibrium load once the buckling load has been surpassed. For structures having this type of buckling characteristic, the question arises as to whether the proper buckling criterion to apply is the classical criterion, which considers equilibrium with respect to infinitesimal displacements or the finite displacement \"energy criterion\" proposed by Tsien.
\r\n\r\nIn this paper the problem of the finite displacement and buckling of a shallow spherical dome is investigated both theoretically and experimentally. In the theoretical approach the nonlinear equations are converted into a sequence of linear equations by expanding all of the variables in powers of the center deflection and then equating the coefficients of equal powers. The basic parameter for the shallow dome is proportional to the ratio of the central height of the dome, h, to its thickness, t. For small values of this ratio the expansions converge rapidly and enough terms are computed to determine the buckling load. For higher values of h/t, convergence deteriorates rapidly and the buckling, load is not computed. However, even for these higher values of h/t the deflection shapes are determined for deflection amplitudes below the amplitude at which buckling occurs. These deflection shapes are characterized by their rapid change as h/t increases and by the fact that, over most of the range of h/t studied, the maximum deflection does not occur at the center of the dome.
\r\n\r\nThe experimental program was carried out on a series of clamped-edge, eight inch base diameter shells, subjected to uniform pressure. The deflection shapes and the buckling loads agreed quite well with the values computed theoretically. It was also found that there was no significant difference between the buckling loads observed using air pressure and those observed using oil pressure. Thus it is concluded that for the shallow domes studied the classical buckling criterion holds rather than the \"energy criterion\" proposed by Tsien.
" }, { "name": "Kaplun, Saul", "degree": "PhD", "year": "1954", "title": "The Role of Coordinate Systems in Boundary Layer Theory", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-111930", "creators": [ { "name": { "family": "Kaplun", "given": "Saul" }, "id": "Kaplun-Saul", "display_name": "Kaplun, Saul" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9QZM-8W36", "abstract": "The boundary layer approximation to a given flow problem is not invariant if different coordinate systems are used in the approximation process. However, a correlation theorem (Theorem 1) is given, which states that the boundary layer solution with respect to any given system can be found, by a simple substitution, from that with respect to any other system. On the basis of this theorem, the dependence of the solution on the choice of coordinates is investigated in detail. The skin friction is invariant, but the flow field is not invariant. At large distances from the wall, the flow field given by boundary layer theory depends almost entirely on the choice of coordinates, rather than on the physical problem.\r\n\r\nThis dependence may be used to obtain a complete matching between the boundary layer solution and the external flow, in the following sense: Theorem 2 states how a coordinate system can be found such that the boundary layer solution with respect to this system is valid as an approximation for the entire flow field. It contains the external flow and the flow due to displacement thickness.\r\n\r\nThe discussion is restricted to steady, two-dimensional, incompressible flow without separation. These restrictions, however, are not essential for many of the results." }, { "name": "Knuth, Eldon Luverne", "degree": "PhD", "year": "1954", "title": "The Mechanics of Film Cooling", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-112656", "creators": [ { "name": { "family": "Knuth", "given": "Eldon Luverne" }, "id": "Knuth-Eldon-Luverne", "display_name": "Knuth, Eldon Luverne" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G4AT-5P75", "abstract": "Thin liquid wall films flowing under the influence of high-velocity turbulent gas streams were studied for the purpose of obtaining an understanding of the mechanics of film cooling. Conditions which insure liquid-film attachment to solid surfaces without loss of unevaporated liquid to the gas stream when simple radial-hole injectors are used were found; the maximum allowable coolant-flow rate for a stable coolant film was determined (a stable coolant film is obtained when no unevaporated coolant is entrained by the gas stream as the result of interfacial disturbances); and a method for calculating the evaporation rate and the surface temperature for a stable inert coolant film was found." }, { "name": "Korkegi, Robert Hani", "degree": "PhD", "year": "1954", "title": "Transition Studies and Skin Friction Measurements on an Insulated Flat Plate at a Hypersonic Mach Number", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072004-114554", "creators": [ { "name": { "family": "Korkegi", "given": "Robert Hani" }, "id": "Korkegi-Robert-Hani", "display_name": "Korkegi, Robert Hani" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X3B9-VW73", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn investigation of transition and skin friction on an insulated flat plate, 5 x 26 inches, was made in the GALCIT 5 x 5 inch Hypersonic Wind Tunnel, Leg No. 1, at a nominal Mach number of 5.8.\r\n\r\nThe phosphorescent lacquer technique was used for transition detection and was found to be in good agreement with total-head rake measurements along the plate surface and pitot boundary layer surveys. It was found that the boundary layer was laminar at Reynolds numbers of at least 5 x 10[superscript 6]. It was also observed that transverse contamination due to the turbulent boundary layer on the tunnel sidewall originated far downstream of the flat plate leading edge at Reynolds numbers of 1.5 to 2 x 10[superscript 6], and spread at a uniform angle of 5 1/2[degrees] compared with 9 1/2[degrees] in low speed flow.\r\n\r\nThe effect of two-dimensional and local disturbances was investigated. The technique of air injection into the boundary layer as a means of stimulating transition was extensively used. It was observed that, although the onset of transition occurred at Reynolds numbers down to 10[superscript 6], a fully developed turbulent boundary layer was not obtained at Reynolds numbers much below 2 x 10[superscript 6] regardless of the amount of air injected.\r\n\r\nA qualitative discussion of these results is given with emphasis on the possibility of a greater stability of the laminar boundary layer in hypersonic flow than at lower speeds.\r\n\r\nDirect skin friction measurements were made by means of the floating element technique incorporating a null system using chain loading, over a range of Reynolds numbers (based on distance from leading edge) from 10[superscript 6] to 4 x 10[superscript 6]. Without artificial tripping, the boundary layer was verified as being laminar over the complete range. With air injection, turbulent shear was obtained only for Reynolds numbers greater than 2 x 10[superscript 6] , this value being in good agreement with earlier results of this investigation. The turbulent skin friction coefficient was found to be approximately 0.40 of that for incompressible flow for a constant value of R[subscript theta], and 0.46 for an effective Reynolds number between 5 and 6 x 10[superscript 6]." }, { "name": "Lampert, Seymour", "degree": "PhD", "year": "1954", "title": "Homogeneous Flow Fields of Degree Greater than Zero", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092004-094836", "creators": [ { "name": { "family": "Lampert", "given": "Seymour" }, "id": "Lampert-Seymour", "display_name": "Lampert, Seymour" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W215-QX89", "abstract": "Solutions to the Prandtl-Glauert differential equation expressed in terms of polynomial type Lame functions can be applied to the problem of the thin delta wings with subsonic leading edges in a supersonic flow field. It is demonstrated how these functions of different species and degrees of homogeneity may be employed to obtain previously known results for certain lifting cases. For the non-lifting or thickness case which is treated in detail in this paper it is shown that a large class of thickness distributions with blunt leading edges my be obtained by systematically studying the Lame functions of the first species. In particular these functions have been investigated up to, and including, n = 5. It is further shown by the methods of this paper that the prescription of the pressure distribution in problems of this sort is not always sufficient to determine the thickness distribution uniquely." }, { "name": "Mark, Richard Muin", "degree": "PhD", "year": "1954", "title": "Laminar Boundary Layers on Slender Bodies of Revolution in Axial Flow", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-155216", "creators": [ { "name": { "family": "Mark", "given": "Richard Muin" }, "id": "Mark-Richard-Muin", "display_name": "Mark, Richard Muin" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4H6Z-K569", "abstract": "An exact similar solution of the modified boundary layer equations has been obtained for the axial incompressible flow past paraboloids of revolution. It has been shown that the usual boundary layer assumptions are justified and that the local skin friction increases as the boundary layer thickness becomes large compared with the body radius.\r\n\r\nAn approximate method for obtaining the local skin friction on arbitrary slender bodies of revolution in axial incompressible flow has been developed. A comparison of the approximate results with the exact solutions for paraboloids of revolution and circular cylinders shows good agreement.\r\n\r\nThe existence of energy integrals of the modified compressible boundary layer equations is established. Similarity of the governing equations for the axial compressible flow past paraboloids of revolution has been shown; for the same bodies, a hypersonic similarity law is deduced.\r\n\r\nAn approximate method for obtaining the local skin friction on arbitrary slender insulated bodies of revolution in axial compressible flow has been developed. The results show that compressibility counterbalances the rise in local skin friction due to curvature at high Reynolds numbers (based on a characteristic length of the body) and increases the local skin friction at sufficiently low Reynolds numbers.\r\n\r\nVelocity profiles on a slender ogive-cylinder have been obtained experimentally at a Mach number of 5.8 and at different Reynolds numbers. The results indicate a curvature effect when compared with flat plate results." }, { "name": "Marschner, Bernard Walter", "degree": "PhD", "year": "1954", "title": "The Flow over a Body in a Choked Wind Tunnel and in a Sonic Free-Jet", "advisor": "Guderley, Karl Gottfried", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-100833", "creators": [ { "name": { "family": "Marschner", "given": "Bernard Walter" }, "id": "Marschner-Bernard-Walter", "display_name": "Marschner, Bernard Walter" } ], "advisors": [ { "name": { "family": "Guderley", "given": "Karl Gottfried" }, "id": "Guderley-Karl-Gottfried", "role": "advisor", "display_name": "Guderley, Karl Gottfried" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P4DG-RV54", "abstract": "The pressure distribution over a double wedge airfoil under free flight conditions with Mach number one is compared with the pressure distribution over the same airfoil in a choked closed wind tunnel and in a sonic free-jet.\r\n\r\nThe computation is carried out as a development with respect to a parameter which indicates the deviation from free flight conditions with Mach number one. The results are of interest for the question of wind tunnel wall influences. It is found that the deviatiors of the pressure distribution for a sonic free-jet from the distribution in an infinite air flow are somewhat larger than the deviations in a closed wind tunnel under choked flow conditions. For a specific exam of a wedge of a length of 13% of the tunnel height and a thickness ratio of 10%, the deviation of the pressure distribution does not go much beyond the usual experimental scatter.\r\n\r\nThe results are quite encouraging for the application of closed throat wind tunnels in transonic testing although the axial symmetric case may not show entirely the same desirable behavior." }, { "name": "Mertz, Charles, III", "degree": "Engineering Degree", "year": "1954", "title": "A Study of the Effect of Boundary Layer Control on an Axial Flow Compressor Stage", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01152004-115145", "creators": [ { "name": { "family": "Mertz", "given": "Charles, III" }, "id": "Mertz-Charles-III", "display_name": "Mertz, Charles, III" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AG0W-5T14", "abstract": "The problem of increasing the pressure ratio per stage of an axial flow compressor is studied in part by considering the effect of boundary layer control by area suction on the three dimensional turbulent boundary layer flow on the casing in one stage of a compressor.\r\n\r\nThe effect of this boundary layer control, on the prevention of separation is investigated. Crossflow and crosswise variation of crossflow in the boundary layer are factors contributing to the tendency toward separation and the effect of boundary layer control on this phenomenon is determined. This analysis is limited to the boundary layer on the casing and does not take into consideration the possible separation taking place at the blades.\r\n\r\nThe boundary layer equations are used to obtain the momentum integral equations with suction applied at the surface. The method of small perturbations is applied to the equations in order to simplify them so that a solution may be reached with relatively little effort. Expressions are assumed for the boundary layer profiles, flow path outside the boundary layer, and shear stresses. These are in a form which closely resembles the actual conditions.\r\n\r\nIn order to show what effect boundary layer control exerts, a simplified single stage compressor is studied. The results show that crossflow can be reduced by applying suction to the boundary layer with a resultant decreased tendency toward separation of the flow, but this is reached only after a certain minimum suction velocity is attained, If the suction velocity is less than this minimum, in spite of the decrease in boundary layer thickness the crossflow will be increased over that of a solid wall and likewise the tendency toward separation will increase." }, { "name": "Mileson, Donald Francis", "degree": "Engineering Degree", "year": "1954", "title": "The Thermal Theory of Laminar Flame Propagation for Hydrogen-Bromine Mixtures", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01152004-120851", "creators": [ { "name": { "family": "Mileson", "given": "Donald Francis" }, "id": "Mileson-Donald-Francis", "display_name": "Mileson, Donald Francis" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WN9C-Q975", "abstract": "The thermal theory of laminar flame propagation for hydrogen-bromine mixtures is described. The method of analysis follows the earlier work of von Karmen and Millan and of von Karmen and Penner. The problem is materially simplified by introducing the steady-state approximation of classical chemical kinetics for the concentrations of H- and Br-atoms.\r\n\r\nThe general formulation of the problem is presented in Section II.\r\n\r\nApproximate solutions of the relevant mathematical problems, utilizing various procedures developed by von Karman and his collaborators, are given in Sections III to V for bromine-rich, stoichiometric, and hydrogen-rich mixtures, respectively.\r\n\r\nNumerical values for the physio-chemical parameters, which are required for the calculation of absolute values for the burning velocities, are considered in Section VI.\r\n\r\nThe calculated burning velocities are compared in Section VII with experimental results obtained by R. C. Anderson and his collaborators. Reference to Section VII shows that the variation of the observed burning velocities with mixture ratio is predicted correctly by the theoretical calculations. Absolute values for the laminar burning velocity cannot be estimated with certainty because of the possible existence of large errors resulting from extrapolation of low-temperature kinetics and heat conductivity data." }, { "name": "Mulligan, Hampton Emanuel", "degree": "Engineering Degree", "year": "1954", "title": "Experiments on the Relationship Between the Coefficients of Friction and Heat Transfer in Nucleate Boiling", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262004-105223", "creators": [ { "name": { "family": "Mulligan", "given": "Hampton Emanuel" }, "id": "Mulligan-Hampton-Emanuel", "display_name": "Mulligan, Hampton Emanuel" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6KN7-5864", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation was conducted to determine whether any relationship exists between the friction and the heat transfer coefficients in the region of nucleate boiling with forced convection. The tests were carried out with distilled water flowing through a 3/8 inch diameter tube. The water was heated by passing an electric current through the tube wall.\r\n\r\nMeasurements of the velocity of the water were taken at three positions along the test section by means of pitot tubes. The pitot tubes were also used to measure static pressure drops. From the experimental data the heat transfer and friction coefficients were computed. These coefficients were determined for a heat transfer range from 1.0 to 2.0 Btu/sq in-sec and for three pressure levels, 265, 115 and 65 psia.\r\n\r\nIt was found that for a constant subcooling in the nucleate boiling region the friction coefficient increases with increasing heat transfer rate, indicating that the bubbles actually do influence the momentum exchange. It was also found that the experimentally determined values of the friction and heat transfer coefficients plot about a line the equation of which is [...]. This is the relation that one would expect on the basis of Reynolds' analogy for turbulent flow either without a laminar boundary layer, or with the laminar boundary layer when the Prandtl number is unity. It appears therefore that the effect of the bubbles is a hydrodynamic one leading to an increase in heat exchange as well as in momentum exchange." }, { "name": "Penny, Harmon Charles", "degree": "Engineering Degree", "year": "1954", "title": "Vibrational Relaxation Times of Gaseous Mixtures of Diatomic Molecules and their Effect on Rocket Performance", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-094512", "creators": [ { "name": { "family": "Penny", "given": "Harmon Charles" }, "id": "Penny-Harmon-Charles", "display_name": "Penny, Harmon Charles" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y2D2-M834", "abstract": "The present methods available for the determination of the magnitudes of the vibrational relaxation times of molecules are discussed and the recently developed theory of Schwartz, Slawsky, and Herzfeld is used to compute the variation with temperature of the collisional vibrational excitation probabilities of mixtures of N2 and 02, and of H2 and HF. The results are used to estimate the extent of vibrational temperature lag in the hydrogen-fluorine rocket motor." }, { "name": "Perkins, Carlton Kay", "degree": "Engineering Degree", "year": "1954", "title": "Burning of Single Droplets of Hydrocarbon Fuels in Oxidizing Atmospheres", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-093547", "creators": [ { "name": { "family": "Perkins", "given": "Carlton Kay" }, "id": "Perkins-Carlton-Kay", "display_name": "Perkins, Carlton Kay" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DMX1-0Y63", "abstract": "Experiments have been conducted in order to determine the burning, rates of single droplets of liquid fuels in oxidizing atmospheres. N-heptane and absolute ethyl alcohol were tested in nitrogen-oxygen mixtures for oxygen weight fractions between 0.10 and 0.90. Measurements were made also for benzene and toluene; for oxygen weight fractions greater than for air, a carbon residue formed during the burning of these fuels, which made it impossible to obtain accurate data. For all nitrogen-oxygen mixtures it was found that the mass burning rate of single droplets of fuel is proportional to the first power of the drop diameter.\r\n\r\nThe theoretical analysis on the burning of single droplets of fuels in an oxidizing atmosphere by Goldsmith and Penner was used to obtain values for the evaporation constants of the fuels tested. The experimentally determined values of the evaporation constants were found to be in good agreement with the calculated values for all fuels tested which did not form carbon." }, { "name": "Quiel, Norwald Richard", "degree": "Engineering Degree", "year": "1954", "title": "Impact Pressure and Total Temperature Interpretation at Hypersonic Mach Numbers", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-095631", "creators": [ { "name": { "family": "Quiel", "given": "Norwald Richard" }, "id": "Quiel-Norwald-Richard", "display_name": "Quiel, Norwald Richard" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SMHA-4160", "abstract": "An experimental investigation was undertaken at a nominal Mach number of 5.6 in the GALCIT Hypersonic Wind Tunnel, Leg No. 1. The first phase was an investigation of the viscous effects on measured impact pressures. The second was an investigation of the temperature recovery characteristics of a singly shielded total-temperature probe.\r\n\r\nExperimental results are presented for a straight, sharp-lipped, cylindrical, impact-pressure probe and for a flattened-end probe. Impact-pressure data were obtained for a Reynolds number range from 425 to 8,000, where the Reynolds number was based on free stream conditions and the impact probe outside diameter, The data show that the Rayleigh equation requires corrections for viscous effects at Reynolds numbers less than 6,000 for the circular sharp-tipped probe and less than 4,000 for the flattened-end probe. The viscous effects increase with decreasing Remolds numbers. At a Reynolds number of 425, the measured impact pressure is approximately 2.5 per cent lower than that predicted by the Rayleigh equation. It was concluded that the viscous effects were dependent on Mach number as well as Reynolds number.\r\n\r\nTemperature recovery factors for the total-temperature probe were obtained throughout a Reynolds number range from 30,800 to 213,000, where the Reynolds number was based on the probe entrance outside diameter and the free stream conditions. An analysis of suitable parameters with which to present the data is included together with the experimental data. For a limited range of total temperatures, a single temperature recovery calibration curve was obtained when the Reynolds number was used as a parameter. The data show that the temperature recovery factor of the total temperature probe decreases with decreasing Reynolds numbers." }, { "name": "Rogers, Don Easterday", "degree": "Engineering Degree", "year": "1954", "title": "An Experimental Investigation of High Frequency Combustion Instability in a Fuel-Air Combustor", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082003-111443", "creators": [ { "name": { "family": "Rogers", "given": "Don Easterday" }, "id": "Rogers-Don-Easterday", "display_name": "Rogers, Don Easterday" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/65NM-7Q10", "abstract": "The results of an experimental investigation of high frequency combustion instability in a fuel-air combustor are described. The phenomenon is described in terms of alterations in the flame geometry and pressure changes associated with the flow field. Quantitative measurements of the pressure fluctuations are presented and the effects of various system parameters on the instability are indicated.\r\n\r\nA possible mechanism for forcing and sustaining the oscillations as indicated by the experimental data is suggested and discussed." }, { "name": "Strand, Torstein", "degree": "Engineering Degree", "year": "1954", "title": "Minimum Drag Due to Lift for a Delta Wing with Sonic Leading Edges", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-094215", "creators": [ { "name": { "family": "Strand", "given": "Torstein" }, "id": "Strand-Torstein", "display_name": "Strand, Torstein" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y3KY-N097", "abstract": "Using linearized theory a close approximation to the optimum camber and twist distribution of a Delta wing of zero thickness with sonic leading edges has been obtained.\r\n\r\nThe optimum wing has a camber line that is negative over the front quarter of the total planform area and is positive over the remaining area. A certain amount of washout is exhibited.\r\n\r\nCompared to the flat plate a saving in induced drag of slightly over 7 percent is shown. The leading edges are relieved of a considerable portion of the total lift. It is shown that this lift has been re-distributed over the central part of the wing." }, { "name": "Valluri, Sitaram Rao", "degree": "PhD", "year": "1954", "title": "Some Studies in the Fundamental Parameters of Fatigue", "advisor": "Sechler, Ernest Edwin; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-01292004-104442", "creators": [ { "name": { "family": "Valluri", "given": "Sitaram Rao" }, "id": "Valluri-Sitaram-Rao", "display_name": "Valluri, Sitaram Rao" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5Y4Z-CW45", "abstract": "A torsional fatigue testing machine of the resonant vibrator type has been designed in order to investigate the fatigue and internal friction properties of 3S-O aluminum. This machine uses an elastic restraint on an a-c motor to create resonant conditions and uses a photocell electronic system for the measurement of internal friction by the method of measuring the logarithmic decrement of free oscillations.\r\n\r\nIt has been established that for 3S-O aluminum at torsion stress levels below 112 psi, the stress history does not affect damping and that, for an annealed specimen, the material exhibits a maximum value of internal friction at 375[degrees]F. \"Temporary mobility\" aspects of the slip bands have been investigated and in addition, variation of internal friction as a function of stress amplitude in repeated torsional loading, temperature, and number of reversals has been obtained. At room temperature (75[degrees]F) the internal friction increases with the number of stress reversals in the 0 to 10[superscript 5] range. This increment in general increases with increasing amplitude of stress. At test temperatures of 225[degrees] and 525[degrees]F it was found that this increment does not show any regular variation with stress. In addition, however, it was found that at 375[degrees]F the internal friction decreases with stress reversals in the 0 to 10[superscript 5] range for all stresses. The variation of internal friction with stress history after a large number of stress reversals of the order 10[superscript 6] cycles, is quite complex, giving rise to random patterns of increase and decrease.\r\n\r\nThis work is exploratory in nature and suggestions for further work are indicated." }, { "name": "Vrebalovich, Thomas", "degree": "PhD", "year": "1954", "title": "The Development of Direct and Alternating Current Glow Discharge Anemometers for the Study of Turbulence Phenomena in Supersonic Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-111758", "creators": [ { "name": { "family": "Vrebalovich", "given": "Thomas" }, "id": "Vrebalovich-Thomas", "display_name": "Vrebalovich, Thomas" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/95XT-RN93", "abstract": "A direct current glow discharge anemometer (D.C. glow) was designed and constructed. This instrument was calibrated in low speed flow. Shock tube experiments with the D.C. glow indicated that its frequency response was greater than 50 kc. However, the shortcomings of the D.C. glow such as sputtering and asymmetric burning properties of the discharge became apparent. Therefore, a 700 kc. alternating current (A.C.) glow was designed and constructed. The time stability properties of this instrument were found to be much better than those of the D.C. glow. Since no frequency compensation circuits were used with the A.C. glow, the signal to noise ratio was much higher than that of a hot wire. This A.C. glow was used to survey the profile of the fluctuations in a turbulent boundary layer in supersonic flow at Mach numbers between 1.3 and 4. Power spectrum measurements of the fluctuations in this boundary layer were also made with the A.C. glow. These measurements indicated that there was energy in the spectrum above 100 kc. Finally, measurements of frequencies in excess of 100 kc. were made by the A.C. glow in a sound field produced by a source of single frequency ultrasonic sound waves in supersonic flow." }, { "name": "Willmarth, William Walter", "degree": "PhD", "year": "1954", "title": "The Lift of Thin Airfoils at High-Subsonic Speeds", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-114509", "creators": [ { "name": { "family": "Willmarth", "given": "William Walter" }, "id": "Willmarth-William-Walter", "display_name": "Willmarth, William Walter" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DFFC-8041", "abstract": "Experimental results are presented for the lift characteristics of thin, two-dimensional airfoils at high-subsonic speeds and small angles of attack. Symmetrical airfoils with different locations of maximum thickness were investigated using a surface pressure probe technique which should find use in other applications.\r\n\r\nThe flow fields over each airfoil are discussed and the quantitative results for the lift and location of the center of lift are compared with theory whenever possible. The effects of flow separation caused by boundary-layer shock-wave interaction are noted and discussed. In particular, the possibility of the forced oscillation of control surfaces due to boundary layer separation is mentioned." }, { "name": "Yoler, Yusuf Amon", "degree": "PhD", "year": "1954", "title": "The Hypersonic Shock Tube", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112004-115540", "creators": [ { "name": { "family": "Yoler", "given": "Yusuf Amon" }, "id": "Yoler-Yusuf-Amon", "display_name": "Yoler, Yusuf Amon" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/853G-K555", "abstract": "The feasibility of using a shock tube for quantitative investigations of hypersonic flow phenomena at temperatures simulating free flight conditions is studied theoretically and experimentally. In the theoretical part, various aspects of the hypersonic shock tube problem are treated in logical order. Methods of producing high Mach numbers, limitations on the test section Mach number, methods of generating strong shock waves, flows with variable specific heats and dissociation, types of problems amenable to study with the hypersonic shock tube are discussed.\r\n\r\nTo verify and supplement some of the theoretical results, a shock tube of a somewhat unconventional design has been built. The bulk of the experimental investigations undertaken to date have dealt with pressure studies using piezoelectric gages, and schlieren studies of the flow, The results obtained so far with flow Mach numbers in excess of six, stagnation temperatures up to 9000[degrees]R and stagnation pressures up to 200 psi, have not only contributed to a much greater understanding of this relatively new field of application of the shock tube, but have indicated a well defined course along Which future investigations will continue." }, { "name": "Zukoski, Edward Edom", "degree": "PhD", "year": "1954", "title": "Flame Stabilization on Bluff Bodies at Low and Intermediate Reynolds Numbers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-105717", "creators": [ { "name": { "family": "Zukoski", "given": "Edward Edom" }, "id": "Zukoski-Edward-Edom", "display_name": "Zukoski, Edward Edom" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E9V0-GM76", "abstract": "The problem of attaining stable combustion in ramjet power plants and in afterburners of turbojet engines has led to rather extensive studies of the processes involved in stabilizing flames on bluff bodies. One of the results of these studies was to indicate that the flame stabilization mechanism changes significantly at low Reynolds Numbers; the velocity at which flames may be stabilized drops abruptly as the Reynolds Number is decreased, and the mixture ratio for which maximum velocity of flame holding occurs shifts markedly from the stoichiometric value.\r\n\r\nThis abrupt change in the mechanism of flame stabilization is investigated through photographic studies of the flame front near the flame holder. A transition from a laminar to a turbulent surface of the flame front immediately downstream from the flame holder is shown to account for the change in flame stabilization characteristics. This transition was found to occur independently of fuel type and flame holder geometry.\r\n\r\nThe behavior of the low Reynolds Number stabilization limits is attributed to a diffusion process; in particular, the shift found for the mixture ratio corresponding to the maximum blowoff velocity is explained on the basis of the difference in the diffusion rate of fuel and oxygen. Detailed experiments including blowoff results, chemical analysis of gas taken from the flame holder wake, and measurements of wake temperatures are shown to confirm the suggested diffusion mechanism.\r\n\r\nOnce the transition phenomenon is appreciated, re-examination of high Reynolds Number blowoff data is found possible. The results of previous experiments are found to show that the blowoff velocity depends on the square root of the characteristic dimension if the transition Reynolds Number is exceeded and if the flame holder is a bluff body of small fineness ratio." }, { "name": "von Gerichten, Robert Louis", "degree": "Engineering Degree", "year": "1954", "title": "An Experimental Investigation of the Recirculation Zone of Laminar Flames Stabilized on Bluff Bodies at Low Reynolds Numbers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-171942", "creators": [ { "name": { "family": "von Gerichten", "given": "Robert Louis" }, "id": "von-Gerichten-Robert-Louis", "display_name": "von Gerichten, Robert Louis" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HHVW-Z921", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAs part of a program to explain the shift in the maximum blowoff velocity from stoichiometric mixture ratio for small flame holder sizes, laminar flame stabilization studies were made using cylindrical flame holders of 0.031 to 0.125 inches in diameter at Reynolds numbers in the range of 10[^3] to 10[^4]. Chemical samples of the gases in the recirculation region behind the flame holders were taken and analyzed to determine the composition of the burning gases at the flame front. Maximum temperature measurements were taken of this same region. It was found that at these low Reynolds numbers, the composition was different than in the unburned approach mixtures, and that this was apparently due to the difference in molecular diffusion of the fuel and air across the flame front. The variation in the composition of the burning gases appears to be a direct function of the approach fuel-air mixture ratio for each diameter and approach mixture velocity." }, { "name": "Beyer, David Dean", "degree": "Engineering Degree", "year": "1953", "title": "Economic Possibilities of Long Range Commercial Rocket Transports", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-122930", "creators": [ { "name": { "family": "Beyer", "given": "David Dean" }, "id": "Beyer-David-Dean", "display_name": "Beyer, David Dean" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4YV8-MX65", "abstract": "In recent publications the economic aspects of both subsonic and supersonic jet transports have been discussed in some detail. Though the high subsonic speed turbojet transport, with some restrictions on range, was found to be of interest economically, no reasonable economic case was found for the supersonic jet transport utilizing either turbojet or ramjet engines. These calculations were made, however, with the assumption of a conventional level flight path. The purpose of this study is to investigate the possibility of using a rocket motor for propulsion of a supersonic transport flying a ballistic trajectory, with the hope that the direct operating expense can be reduced to a value comparable to that of subsonic transports, and thus to indicate the economic feasibility of such high speed transports.\r\n\r\nIt is shown that direct operating costs of rocket motored transports can be less than those indicated for the turbojet and ramjet transports, and in some cases, even approach the cost of operating currently proposed subsonic turbojet engine powered transports. Also the operating ranges can be extended beyond those possible with the supersonic jet transports postulated.\r\n\r\nThe flight technique used is one which allows the high thrust of the rocket motor to produce sufficient kinetic energy in the vehicle to permit it to coast and glide the desired range.\r\n\r\nPerformance is calculated with consideration given to endurance to acceleration limits imposed by human occupants. It is shown that payload optimization decreases design acceleration to a point that the human endurance is not the limiting factor. Weight breakdowns for the major components of the airplane are made, and costs computed are based on Air Transportation Association formulas given for the purpose of comparing operating costs of various proposed aircraft." }, { "name": "Chuan, Raymond Lu-Po", "degree": "PhD", "year": "1953", "title": "The Development and Utilization of Some Equipment for Low Reynolds Number Supersonic Flow Research", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-103202", "creators": [ { "name": { "family": "Chuan", "given": "Raymond Lu-Po" }, "id": "Chuan-Raymond-Lu-Po", "display_name": "Chuan, Raymond Lu-Po" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B6T3-QB91", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA low Reynolds number supersonic wind tunnel is a useful tool for the investigation of viscous effects in a high-speed flow. In order to avoid some of the difficulties inherent in a conventional wind tunnel system when operating at low Reynolds numbers, a two-phase cycle is proposed. By examining the thermodynamics of the wind tunnel the relative merits of two methods of operation -- the one-phase cycle and the two-phase cycle -- are compared, indicating certain advantages the two-phase cycle possesses over the conventional one-phase cycle when the tunnel is operated at high-speed and low Reynolds number. The design, construction and operation of a small (about 5 cm.[superscript 2] test section area) supersonic (M[.....]2) wind tunnel using a two-phase cycle with water (in liquid and vapor phases) as the working medium are described.\r\n\r\nDifficulties in pressure measurement and flow visualization, due to the nature of the working medium and the low density of the flow, are encountered. Means of meeting these difficulties are proposed, including a critical analysis of the schlieren technique, from which is evolved a workable arrangement for visualizing the low Reynolds number flow.\r\n\r\nAs an example of the possible utilizations of the tunnel, the curvature, due to viscosity, of the attached shock wave on a wedge in uniform supersonic flow is investigated, using schlieren photography. The effective shape of the wedge is deduced from the shape of the shock wave, and is compared to theory with satisfactory qualitative agreement." }, { "name": "Coles, Donald Earl", "degree": "PhD", "year": "1953", "title": "Measurements in the Boundary Layer on a Smooth Flat Plate in Supersonic Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-180051", "creators": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-Donald-Earl", "display_name": "Coles, Donald Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0DDW-9S38", "abstract": "In Section I available measurements in low-speed turbulent boundary layer flow are compared with a simple analysis based on functional similarity, and the boundary layer is found to be unique within the accuracy of the experimental data. Some consequences of the mean equations of motion are obtained, including the distribution of shearing stress through the boundary layer, and an attempt is made to generalize the relationship known as the law of the wall to flows with variable density.
\r\n\r\nIn Section II some problems encountered in the development and use of the floating surface element and other instrumentation are discussed in detail.
\r\n\r\nIn Section III are presented measurements of mean and local surface friction carried out on a flat plate model in the 20-inch supersonic wind tunnel at the Jet Propulsion Laboratory. The boundary layer flow is studied for free stream Mach numbers of 2.0, 2.6, 3.7, and 4.5. The experiments, which involve nominal Reynolds numbers from 2 x 105 to 9 x 106, include a few measurements in laminar flow, but emphasize transition and the turbulent regime. The effectiveness of various tripping devices is mentioned, and the problem of defining an effective Reynolds number for the fully turbulent flow is discussed at length. Finally, turbulent boundary layer profile measurements are examined for consistency with low-speed data, with a generalized mixing length theory, and with the analysis of Section I of the present report.
" }, { "name": "Curran, Donald Charles", "degree": "Engineering Degree", "year": "1953", "title": "An Experimental Study of the Stability of Laminar Flame", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222003-101645", "creators": [ { "name": { "family": "Curran", "given": "Donald Charles" }, "id": "Curran-Donald-Charles", "display_name": "Curran, Donald Charles" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6W88-7713", "abstract": "Knowledge of laminar flame front structure is insufficient to make exact stability calculations possible. The analysis of Landau(1) indicated flame front instability under all conditions. Semi-empirical corrections to Landau's result by Markstein(2) demonstrated that a cellular flame front structure that Markstein observed experimentally might be a stable configuration. Karlovitz(3) has proposed that there is a significant additional amount of turbulence produced in turbulent flames over that found in the upstream flow. Of particular significance is the question of whether or not a flame may take on a turbulent structure in the absence of upstream turbulence.\r\n\r\nTherefore explorations concerning the conditions under which a laminar flame might become unstable were undertaken by burning premixed propane and air using a spherical flame holder.\r\n\r\nThe resulting conical flame had annular waves develop in the flame front a short distance downstream from the flame holder. This distance decreased as fuel-air ratio was decreased and as gas mixture flow velocity increased. Lean high velocity flames showed a parallel result in the amplitude of the wave formed - the wave in this case developing to a large amplitude in a short distance with a tendency to roll up.\r\n\r\nAnother result of the investigation was that a fairly uniform wavelength of 0.27 in. was observed even though mixture, flame holder size and flow rate were varied.\r\n\r\nThe introduction of a small external turbulence source upstream of the flame front disturbed the flame - the amount of disturbance increasing with Reynolds' number of the turbulence source and with fuel-air equivalence ratio." }, { "name": "Dayman, Bain", "degree": "Engineering Degree", "year": "1953", "title": "Experimental Aerodynamics of a Two-Dimensional Sail", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-113154", "creators": [ { "name": { "family": "Dayman", "given": "Bain" }, "id": "Dayman-Bain", "display_name": "Dayman, Bain" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7GWF-WA96", "abstract": "Some basic low-speed aerodynamic characteristics of a two-dimensional sail located between endplates were obtained during these investigations for two sail sizes. The effects of the amount of camber (resulting from variation of the slack in the sail) upon the lift, drag, and pitching moment of a sail constituted the major portion of these investigations. A limited study on the advantages of a sail with a jib was made for one particular jib location and camber.\r\n\r\nIdeally, the results should be independent of sail size. The results of these investigations, although not quite identical, are consistent for the two sail sizes. As the camber (measured in percent of length of the sail perpendicular to the leading edge) increased from zero to 10%, the maximum lift increased from 0.92 to a maximum of 1.7 and remained fairly constant as the camber increased to 23%, then it decreased to 1.5 as the camber further increased to 27%. The maximum ratio of lift to drag at maximum lift occurred at 7% camber. The addition of the jib did not affect the maximum lift relationship with the camber, but it did increase the lift to drag ratio at maximum lift." }, { "name": "DeLauer, Richard Daniel", "degree": "PhD", "year": "1953", "title": "Experimental Heat Transfer at Hypersonic Mach Number", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222003-111626", "creators": [ { "name": { "family": "DeLauer", "given": "Richard Daniel" }, "id": "DeLauer-Richard-Daniel", "display_name": "DeLauer, Richard Daniel" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/59SJ-TR03", "abstract": "An experimental investigation was conducted in Leg 1 of the GALCIT 5 x 5 inch Hypersonic Wind Tunnel to determine the heat transfer coefficients of the laminar boundary layer on a cooled flat plate at a nominal Mach number of 5.8. As a consequence of the investigation, flat plate recovery factors were determined and the effect of condensation on heat transfer was noted. In addition qualitative results as to the laminar boundary layer transition and separation are also presented.
\r\n\r\nThe tests were conducted with a ratio of wall temperature to free stream temperature (Tw/T\u03b4) of approximately 6.2; but under stagnation temperature conditions ranging from 200\u00b0F to 285\u00b0F. The stagnation pressure range of 60 psia to 115.5 psia provided a maximum Reynolds number of 2.1 x 106.
\r\n\r\nA flat plate temperature recovery factor of .858 \u00b1 .004 was determined, and it was concluded that the temperature recovery factor range of Mach number independence could be extended to a Mach number of 5.8. The independence of the recovery factor on Reynolds number up to the beginning of the laminar boundary layer transition was also substantiated.
\r\n\r\nThe heat transfer coefficients were obtained for a negative temperature gradient over a considerable portion of the plate. The effect of these gradients produced values considerably higher than would be expected for an isothermal surface. These results, when related the constant temperature case by a theoretical calculation, were in good agreement, with the theoretical results and the results of a friction investigation carried out at the same Mach number. The accuracy of the results was estimated to be \u00b110% from a value of Nu/Re1/2Pr1/3 - .285.
\r\n \r\nThere was no apparent effect on the heat transfer coefficient by condensation, but the adiabatic wall temperature appeared to be 2% lower than for the condensation free flow. Due to a step increase in thickness of the model at the ten inch station, the shock wave-boundary layer interaction appears to produce laminar boundary layer transition at a Reynolds number of 1.3 x 106, and upon reducing the Reynolds number further, the transition point is subjected to an adverse pressure gradient which results in a boundary layer separation.
" }, { "name": "Eimer, Manfred", "degree": "PhD", "year": "1953", "title": "Direct Measurement of Laminar Skin Friction at Hypersonic Speeds", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-112020", "creators": [ { "name": { "family": "Eimer", "given": "Manfred" }, "id": "Eimer-Manfred", "display_name": "Eimer, Manfred" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "role": "member", "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MK2E-1P76", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA direct measurement of flat plate laminar local skin friction was undertaken at M = 5.8 in the GALCIT Hypersonic Wind Tunnel, Leg No. 1. A new balance particularly suited to the requirements of hypersonic experimentation was designed.\r\n\r\nBy means of the fluorescent lacquer technique for indicating boundary layer transition, unexpectedly high natural transition Reynolds numbers were observed. The several methods of forcing transition which were used were unsuccessful in producing transition at a Reynolds number of two million.\r\n\r\nObservation of the leading edge shock wave and boundary layer by means of a schlieren system indicated that at M = 5.8 the shock wave and boundary layer are separated by appreciable distances wherever the boundary layer equations hold.\r\n \r\nSkin friction force measurements were made at five Reynolds numbers in condensation-free flow. The discrepancies between the observed low values of C[subscript f][...]Re and existing laminar boundary layer calculations are reconciled by means of a qualitative analysis.\r\n\r\nA theory describing the properties of the viscous boundary layer for flows with condensation in the free stream is presented. It is predicted that for a specified nozzle geometry and stagnation temperature, skin friction remains unchanged in the presence of moderate amounts of condensation, while heat transfer for a given wall temperature is affected by the presence of condensation which produces major changes in the adiabatic wall temperature." }, { "name": "Elliott, Benton Holford", "degree": "Engineering Degree", "year": "1953", "title": "Spectroscopic Studies of OH in Flames. I. Theoretical Investigations of Distortions Produced by Temperature Gradients, Self-Absorption and Changes in Spectral Line-Shape. II. Experimental Studies on Acetylene-Oxygen Flames Burning at Atmospheric Pressure", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-083315", "creators": [ { "name": { "family": "Elliott", "given": "Benton Holford" }, "id": "Elliott-Benton-Holford", "display_name": "Elliott, Benton Holford" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y37J-RF90", "abstract": "A theoretical investigation has been made to determine quantitatively the effects of temperature gradients, self-absorption, and spectral line-shape on the apparent rotational temperatures of OH.\r\n\r\nEmission experiments have been performed on the inner cone and on the outer cone of an oxygen-acetylene flame to determine the rotational temperature of the upper energy state of OH." }, { "name": "Fern\u00e1ndez, Raymond Caesar", "degree": "Engineering Degree", "year": "1953", "title": "Use of a Sampling Feedback System for Stabilization of Low Frequency Oscillations in Liquid Monopropellant Rocket Motors", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-090202", "creators": [ { "name": { "family": "Fern\u00e1ndez", "given": "Raymond Caesar" }, "id": "Fern\u00e1ndez-Raymond-Caesar", "display_name": "Fern\u00e1ndez, Raymond Caesar" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PZEC-N445", "abstract": "Instability in liquid monopropellant rocket motors may be corrected by the use of a feedback servomechanism. This mechanism consists essentially of a pressure pickup which senses pressure oscillations in the combustion chamber, an amplifier and a variable capacitance in the feed line. It is shown that a feedback system with an arbitrary sampling circuit which causes the capacitance in the line to complete its own cycle of variation once for every several cycles of combustion pressure oscillations can be made to stabilize the oscillations for all values of combustion time lag for a particular motor. It is believed that this system of stabilization may be applied to monopropellant motors in general." }, { "name": "Holmquist, Carl Oreal", "degree": "PhD", "year": "1953", "title": "An Approximate Method of Calculating Three-Dimensional Compressible Flow in Axial Turbomachines", "advisor": "Rannie, W. Duncan; Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-115022", "creators": [ { "name": { "family": "Holmquist", "given": "Carl Oreal" }, "id": "Holmquist-Carl-Oreal", "display_name": "Holmquist, Carl Oreal" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3FB2-G132", "abstract": "The two principal existing methods of calculating axially-symmetric compressible flow in turbomachines are: (1) a simplified one-dimensional analysis, and (2) numerical methods using the complete or linearized flow equations. The first is not satisfactory for multi-stage turbines with appreciable wall divergence; the second is very tedious and time consuming. The purpose of this investigation is to extend the approximate methods, successfully used in calculating incompressible flow in compressors with constant blade height, to the analysis of compressible flow in turbomachines with variable blade height. Assuming that the blades can be completely defined by the exit flow angle, and neglecting the influence of downstream blades, the analysis is made considering the flow between successive blade rows only. With these restrictions, subsonic and isentropic supersonic flow patterns can be determined for arbitrary boundary shapes as long as separation does not occur. Average losses can be accounted for by the use of a polytropic law, and the effect of radial variations in stagnation temperature can be included without difficulty. Examples illustrating the flexibility and practical value of the iteration method, and the rapid convergence of successive solutions are given." }, { "name": "Lindsley, Jack Nathan", "degree": "Engineering Degree", "year": "1953", "title": "The Effect of Temperature Cycling on the Physical Properties of FS-1 Magnesium Alloy Sheet Metal", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252003-081930", "creators": [ { "name": { "family": "Lindsley", "given": "Jack Nathan" }, "id": "Lindsley-Jack-Nathan", "display_name": "Lindsley, Jack Nathan" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N1M2-JG59", "abstract": "An investigation was made of the effect of different cyclic heat treatments on the \"high rate\" creep and stress-strain characteristics of FS-lh magnesium alloy and 75S-T6 aluminum alloy sheet metal. The heat treatments to which the alloys were subjected consisted of a varying series of heating and cooling cycles such that the periods at heat treating temperature totaled 60 minutes. Temperatures investigated were 250[degrees] and 550[degrees]F. Following heat treatment, both tensile and creep tests were conducted at room temperature and at the temperature of heat treatment.\r\n\r\nThis thesis encompasses the investigation of FS-lh magnesium alloy, while the investigation of 75S-T6 aluminum alloy is covered in the current thesis of the author's co-worker(1).\r\n\r\nIt was found for the range of heat treatment cycling (1-20 cycles) and temperatures investigated, that there is no effect on the physical properties as a result of changing the number of heating cycles. Cyclic heat treatment at 550[degrees]F was the only treatment to result in a reduction of physical properties, and this only when tested at room temperature.\r\n\t\r\nIt was also found that, within the time range investigated, exposure time exhibits a negligible effect on the physical properties of the material. However, elevated temperatures affect the yield and ultimate properties." }, { "name": "Mackay, Douglas Severance", "degree": "Engineering Degree", "year": "1953", "title": "Boundary Layer Temperature Recovery Factor on a Cone at Nominal Mach Number Six", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-095635", "creators": [ { "name": { "family": "Mackay", "given": "Douglas Severance" }, "id": "Mackay-Douglas-Severance", "display_name": "Mackay, Douglas Severance" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8DEC-WE68", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn investigation was conducted to determine the temperature recovery factors for laminar boundary layer on a cone at free stream Mach numbers from 5.6 to 5.9. The investigation was conducted in the GALCIT 5\" x 5? continuous-flow, closed-circuit wind tunnel (Leg No. 1). Two twenty degree cone models about three inches in length were used. One model was composed of a ceramic core with a thin (0.010? to 0.015?) steel surface, and the second was a hollow copper shell of 0.005? thickness.\r\n\r\nOne-phase and two-phase (condensation) flow conditions were investigated. Temperature recovery factors were determined from the data obtained from the tests conducted with one-phase airflows. The ratios of the temperatures recovered on the cone surface to the respective stagnation temperatures were computed from the data obtained in the two-phase airflow investigations and were compared with these ratios for the one-phase airflows.\r\n\r\nThe local temperature recovery factors for the laminar boundary layer were determined to be 0.844 ? 0.008 for Reynolds numbers from 2.1 x 10[superscript 4] to 5.4 x 10[superscript 5] . For this range of Reynolds numbers the recovery factor was found to be independent of the Reynolds number. The independence of the recovery factor on the Mach number was substantiated (by comparison with results of previous investigations at lower Mach numbers) for Mach numbers up to 5.9. The ratios of the temperature recovered on the cone to the stagnation temperature were found to be the same for one and two-phase airflows.\r\n\r\nThe square root of the Prandtl number evaluated at the mean of the temperatures of the cone surface for the various flow conditions investigated was found to be less than one per cent lower than the mean of the experimental temperature recovery factors.\r\n\r\nThe results of this investigation are in agreement with those of previous investigations at lower Mach numbers and, within the limits of experimental accuracy, verify theoretical solutions." }, { "name": "Mager, Artur", "degree": "PhD", "year": "1953", "title": "Laminar Boundary Layer Problems Associated with Flow Through Turbomachines", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-100849", "creators": [ { "name": { "family": "Mager", "given": "Artur" }, "id": "Mager-Artur", "display_name": "Mager, Artur" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/49CS-2731", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis analysis deals with three-dimensional boundary layer flows which are of particular interest in the design of turbomachinery. By assuming only small lateral pressure gradients and applying perturbation procedure to the steady, laminar boundary layer equations of motion a set of zeroth and first order equations is found. While the zeroth order equations are just the two-dimensional ones for flow over flat plate, the first order equations retain the characteristic Blasius similarity for a family of external flows expressible by [?] (where U* [and] W* are the perturbation velocities, x [and] z are the coordinates and A [and] B are arbitrary constants). For various types of such external flows (which may or may not be rotational) boundary layer velocity distributions were found by a numerical solution.\r\n\r\nThe investigation is divided into two parts, the first one dealing with boundary layer flows over plane surfaces and the second one considering such flows over surfaces with very sharply varying lateral curvature. In order to obtain solutions in the second part it was necessary to expand the appropriate equations in terms of the product of the local surface curvature and the boundary layer thickness. In addition, the effects of compressibility and rotation (of the surface) on the flows over a plane surface were quantitatively evaluated.\r\n\r\nComparison of the present results with the more exact solutions of other investigators in certain special cases, and with the visual studies of three-dimensional boundary layer flow in cascades, indicates a fair qualitative agreement." }, { "name": "Meghreblian, Robert Vartan", "degree": "PhD", "year": "1953", "title": "Thermodynamic Functions of Polyelectronic Atoms at Very High Temperatures", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252003-104736", "creators": [ { "name": { "family": "Meghreblian", "given": "Robert Vartan" }, "id": "Meghreblian-Robert-Vartan", "display_name": "Meghreblian, Robert Vartan" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/88PE-S208", "abstract": "A convergent series representation for the internal partition function of polyelectronic atoms is obtained by assuming a covolume equation of state for the gas as previously applied by Fermi and Urey to the hydrogen atom.
\r\n\r\nThe present investigation is limited to those cases wherein only extranuclear electronic excitation occurs. The contribution of these electronic states to the thermodynamic functions is obtained from an acceptable approximation to the sum of the convergent series for the partition function.
\r\n\r\nIt is shown that at relatively low temperatures (3000 degrees K), the customary method of evaluating the internal partition function (based on the assumption of an ideal gas) agrees to within a few percent with the results obtained from the covolume treatment. However, at higher temperatures the increase in size of the excited atoms, along with the appearance of charged particles produced by ionization, render the ideal gas treatment inadequate. Since the interaction potentials of charged particles are not known in general, an approximate procedure, which neglects these interactions, is suggested for analyzing a system wherein ions and free electrons constitute a small fraction of the total population. This procedure should be useful for treating gaseous mixtures to temperatures of about 10,000 degrees K.
" }, { "name": "Offtermatt, Wilbur Francis", "degree": "Engineering Degree", "year": "1953", "title": "Tables of Bond and Resonance Energies for Estimating Standard Heats of Fformation", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04282003-103959", "creators": [ { "name": { "family": "Offtermatt", "given": "Wilbur Francis" }, "id": "Offtermatt-Wilbur-Francis", "display_name": "Offtermatt, Wilbur Francis" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TZFF-RW53", "abstract": "Tables of bond and resonance energies have been redetermined by using the most recent thermochemical data available. The use of the data is illustrated for the calculations of standard heats of formation of chemical compounds, including propellants." }, { "name": "Pardee, William McKnight", "degree": "Engineering Degree", "year": "1953", "title": "Variation of Burning Velocity with Pressure", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-095800", "creators": [ { "name": { "family": "Pardee", "given": "William McKnight" }, "id": "Pardee-William-McKnight", "display_name": "Pardee, William McKnight" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C95P-BV39", "abstract": "A review of some of the recent theories of steady state flame propagation in gaseous mixtures reveals a considerable difference in their prediction of the effect of pressure on burning velocity. Furthermore, the experimental data obtained by various workers in the field indicate widely different trends. In some cases burning velocity appears to be independent of pressure whereas in other cases it appears to increase as the pressure is reduced below atmospheric. Hence, as a possible aid in discovering more about the mechanism of flame propagation, the burning velocity of several gaseous mixtures was studied over the general pressure range from 100 to 700 mm Hg absolute.\r\n\r\nThe mixtures used were acetylene-oxygen, acetylene-air, acetylene-oxygen-nitrogen, ammonia-oxygen, ammonia-oxygen-nitrogen, carbon monoxide-oxygen, carbon monoxide-air, and propane-air. Using the burner-visual cone-area method with burners of various sizes, the following results were obtained: for all the above mixtures, except propane-air, the burning velocity is independent of pressure; for propane-air mixtures, the burning velocity varies as P[superscript -.13]. These results are valid provided the burner size is large enough to nullify the effect of quenching.\r\n\r\nIt is concluded that these results definitely do not support the Tanford and Pease theory that burning velocity varies as P[superscript -.25]." }, { "name": "Ponsford, Henry Thomas", "degree": "PhD", "year": "1953", "title": "The Effects of Stiffness on the Buckling of Cylinders with Moderate Wall Thickness", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082003-160210", "creators": [ { "name": { "family": "Ponsford", "given": "Henry Thomas" }, "id": "Ponsford-Henry-Thomas", "display_name": "Ponsford, Henry Thomas" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JAYX-PF29", "abstract": "A series of 25 complete cylinders was tested experimentally to determine the effects of stiffening elements on the buckling of cylinders with moderate wall thickness, and to present a physical basis for an understanding of the mechanism of cylinder buckling.\r\n\r\nIt was found that both axial and circumferential stiffeners spaced at distances comparable to the buckle wave length of the unstiffened cylinder will raise the buckling stress, reduce the wave length, and alter the shape of the buckling waves. It was shown that for cylinders of D/t = 400, the addition of axial stiffening as little as 2% or 3% of the cylinder wall material can raise the buckling stress by 30% over the unstiffened case.\r\n\r\nThe experiments of this study lend support to a theory developed by Donnell and Wan which ascribes the reduction of the buckling stress of a real cylinder below the classical theoretical value to the initial imperfections of construction in the real cylinder. Conversely, the results cast doubt on the validity of the theory which explains the \"premature\" failure on the basis of external energy disturbances present in the testing laboratory.\r\n\r\nIt was shown that the buckling waves of a reasonably well-made cylinder develop with extreme rapidity without the necessity of a change in cylinder length, and are fully developed in their lateral dimensions throughout the buckling process. Some previous results of Kanemitsu and Nojima which exhibited an essentially different buckling mechanism were explained as the consequence of excessive initial imperfection.\r\n\r\nA brief study of the vibrations of a cylinder under axial load demonstrated an approximate correlation between the vibration and buckling modes of the cylinder." }, { "name": "Poorman, Herbert R.", "degree": "Engineering Degree", "year": "1953", "title": "Some Experimental Studies of Laminar Burning Velocity", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-091500", "creators": [ { "name": { "family": "Poorman", "given": "Herbert R." }, "id": "Poorman-Herbert-R", "display_name": "Poorman, Herbert R." } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J2N7-T584", "abstract": "One of the important physical parameters in flame propagation is the laminar burning velocity. A great many experimental measurements of the burning velocity have been made using a variety of experimental techniques. Furthermore, the problem has been studied theoretically by a number of different investigators. Extensive references to the original literature may be found in the books by Lewis and von Elbe(1) and by Jost(2).\r\n\r\nThis thesis is concerned with experimental studies of flame propagation in acetylene-oxygen systems containing the inert gases argon, carbon dioxide, helium, and nitrogen. These studies are introduced with a survey of experimental techniques for measuring the laminar burning velocity in premixed gases. Next, some new experimental measurements obtained by use of a small burner tube at atmospheric pressure are described. The new data are interpreted qualitatively by utilizing a thermal theory of laminar flame propagation." }, { "name": "Ritter, Darrell Lloyd", "degree": "Engineering Degree", "year": "1953", "title": "Activation Energies of Global Reactions in Laminar Flame Propagation", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-084313", "creators": [ { "name": { "family": "Ritter", "given": "Darrell Lloyd" }, "id": "Ritter-Darrell-Lloyd", "display_name": "Ritter, Darrell Lloyd" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8539-Z537", "abstract": "A survey of experimentally determined values for the laminar burning velocity of premixed, laminar hydrocarbon-air and hydrogen-oxygen-nitrogen flames shows considerable scatter between results obtained by different investigators. Within the limits of experimental reproducibility of burning velocities, it is possible to correlate measured burning velocities on the assumption that a single rate-controlling or global reaction exists. Correlation of experimental data by use of a global reaction has been made on the basis of two simplified relations for the laminar burning velocity.\r\n\r\nThe first relation was obtained by the use of an intuitive argument based on the idea that the laminar burning velocity is proportional to the square root of a second order reaction rate, with the rate-controlling reaction step depending on the first power of the initial fuel and oxygen concentrations. For lean mixtures the global activation energy was found to have a value of about 22 Kcals/mole, and for rich mixtures it has a value of roughly 56 Kcals/mole.\r\n\r\nThe second expression for the calculation of laminar burning velocity is based on a theoretical equation derived by Semenov for a thermal mechanism controlling flame propagation in rich hydrocarbon-air mixtures. Application of this relation leads to the conclusion that a global reaction with an activation energy of 87 Kcals/mole correlates rich hydrocarbon-air burning velocities, well within the limits of reproducibility of experimental data.\r\n\r\nA study of the effect of the concentration of N[subscript 2] in the oxidizing mixture shows an apparent dependence of the global activation energy on the amount of diluent gas. This observation suggests that although good correlation of experimental data has been obtained, by using the concept of a global activation energy, the results are not of fundamental significance but should be regarded simply as useful empirical methods for correlating experimental data. It is possible that additional theoretical work will lead to a modified expression for the laminar burning velocity, which not only permits correlation of experimental data, but also yields a global activation energy which is independent of the concentration of inert diluents." }, { "name": "Robinson, Winthrop Pratt", "degree": "Engineering Degree", "year": "1953", "title": "The Effect of Temperature Ccycling on the Physical Properties of 75S-T6 Aluminum Alloy Sheet Metal", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-121943", "creators": [ { "name": { "family": "Robinson", "given": "Winthrop Pratt" }, "id": "Robinson-Winthrop-Pratt", "display_name": "Robinson, Winthrop Pratt" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GEHN-V977", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis is a report on the results of an experimental investigation into the effects of cyclic heating and cooling prior to testing on the tensile and creep properties of aluminum alloy 75S-T6 Alclad sheet. A similar investigation concerning magnesium alloy sheet is described by J. N. Lindsley in Reference 1.\r\n\r\nSpecimens of 75S-T6 Alclad sheet were cyclically heated in an electric oven to either 250 [degrees] F or 550 [degrees] F and cooled to 100 [degrees] F. All specimens remained at elevated temperature an aggregate of 60 minutes , with the number of cycles during the hour varying from one to twenty. Tensile tests and short time creep tests (6 minutes) were performed at room temperature and at the temperature of heat treatment.\r\n\r\nIt was found that at room and elevated temperatures the modulus of elasticity and 0.2 per cent yield strength were essentially independent of the number of heating cycles, as were the minimum creep rates at room temperature and at 250 [degrees] F. The minimum creep rate at 550 [degrees] F increased exponentially with the number of cycles. Specimens heat treated at 550 [degrees] F and creep tested at room temperature showed practically no creep at any stress in six minutes.\r\n\r\nWithout regard to the cycling, the 0.2 per cent yield strength at room temperature was relatively unaffected by the 250 [degree] F heat treatment, but was reduced by a factor of four or more by the 550 [degree] F heat treatment. The modulus of elasticity at room temperature after either heat treatment remained very near the value for the untreated material at room temperature. Values from test conducted at elevated temperatures have been given in reports of previous investigations." }, { "name": "Robison, William Clay", "degree": "Engineering Degree", "year": "1953", "title": "Properties of Ethylene Oxide and Hydrazine Related to their Use as Propellants", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-093602", "creators": [ { "name": { "family": "Robison", "given": "William Clay" }, "id": "Robison-William-Clay", "display_name": "Robison, William Clay" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QHQT-NG37", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPART I. Ethylene Oxide as a Monopropellant.\r\n\r\nThermodynamic calculations to determine the theoretical performance of ethylene oxide as a monopropellant have been carried out for various possible decomposition reactions. A survey of the literature on the kinetics of the thermal decomposition of ethylene oxide is presented.\r\n\r\nPART II. Experimental Measurement of the Heats of Dissociation of Hydrazine - Water and Hydrazine - Alcohol Systems.\r\n\r\nA glass apparatus has been constructed for determining heats of dissociation at low temperatures. Published data on hydrazine-water mixtures have been checked. The heat of dissociation of N[subscript2] H[subscript 4][...]CH[subscript 3]OH has been found to be 8.62 Kcals/mole." }, { "name": "Saxon, John Solon", "degree": "Engineering Degree", "year": "1953", "title": "Feedback Servo-Stabilization of a Rocket During Take-Off", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-161730", "creators": [ { "name": { "family": "Saxon", "given": "John Solon" }, "id": "Saxon-John-Solon", "display_name": "Saxon, John Solon" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BV8Y-QT45", "abstract": "When a rocket is launched, there is a short initial period of acceleration during which the rocket is unstable. As the flight velocity increases, the aerodynamic forces acting on the fins and stabilizers become large enough to give stability. Various methods have been employed to stabilize the rocket during this launching period. Guide rails, \"zero length\" launchers, booster rockets which produce high initial acceleration, and auto-pilot controlled nozzles are typical devices that have been used.\r\n\r\nThis is an investigation of the requirements of a nozzle control which would stabilize the rocket during the launching period. The configuration investigated is unique in that the nozzle of the rocket is mounted as a compound pendulum, and the movement of the pendulum is utilized to furnish the signal for the nozzle control servo-mechanism, thereby eliminating the need for gyroscopic elements in the control system. The pendulum motion of the nozzle caused by a change in flight attitude of the rocket is introduced into a computer which produces an output signal proportional to the attitude of the rocket. This attitude signal is fed back to the nozzle control, which positions the nozzle.\r\n\r\nThe results of the analysis showed that the rocket was unstable during the take-off period when the nozzle control acted on the rocket attitude signal alone. Stability over a narrow range of feedback gains was indicated for the system using a simple lead circuit as a nozzle control, or in other words, when the nozzle control acted on both the attitude signal and the rate of change of attitude of the rocket. The damping characteristics of this system were poor. By changing the nozzle control function to include a response to the acceleration of the rocket attitude, the damping characteristics were improved and the range of feedback gains was widened." }, { "name": "Solomon, George Edward", "degree": "PhD", "year": "1953", "title": "Transonic Flow Past Cone-Cylinders", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-103200", "creators": [ { "name": { "family": "Solomon", "given": "George Edward" }, "id": "Solomon-George-Edward", "display_name": "Solomon, George Edward" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DE4W-ZJ43", "abstract": "Experimental results are presented for transonic flow past cone-cylinder, axially symmetric bodies. The drag coefficient, surface Mach number, etc. are studied as the free stream Mach number is varied and, wherever possible, the experimental results are compared with theoretical predictions. Interferometric results for several typical flow configurations are shown and an example of shock-free supersonic to subsonic compression is experimentally demonstrated.\r\n\r\nThe theoretical problem of transonic flow past finite cones is discussed briefly and an approximate solution of the axially symmetric transonic equations, valid for a semi-infinite cone, is presented." }, { "name": "Solverson, Robert Richard", "degree": "PhD", "year": "1953", "title": "Stress Concentrations in Fillets", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-105323", "creators": [ { "name": { "family": "Solverson", "given": "Robert Richard" }, "id": "Solverson-Robert-Richard", "display_name": "Solverson, Robert Richard" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M29Q-K453", "abstract": "The stress concentrations arising in the fillets of fan and turbine blades, tie down rods, and bolt heads from axially symmetric centrifugal or static force loadings are treated two dimensionally by photoelastic and theoretical methods. The effects of the fillet radius, the height of the base, the mode of application of retention forces, and the distance between the retention reactions and fillet tangencies are considered. The stress concentration factor, K, was found to increase with decreasing radius and decreasing base height and, for small radii, to decrease at first with the distance between the reaction and fillet tangency but, in general, to increase with this distance. Comparisons with other experiments and stress concentration configurations are also made.\r\n\r\nAn approximate theoretical solution is derived by selecting a convenient region from the whole base and replacing, where necessary, the exact boundary conditions with relaxed or integral conditions. The problem is formulated in terms of the classical Airy stress function. Agreement between theory and experiment is reasonable." }, { "name": "Stoolman, Leo", "degree": "PhD", "year": "1953", "title": "Investigation of an Instability Phenomena Occurring in Supersonic Diffusors", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-115303", "creators": [ { "name": { "family": "Stoolman", "given": "Leo" }, "id": "Stoolman-Leo", "display_name": "Stoolman, Leo" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EG52-8V58", "abstract": "Experimental investigations of supersonic normal shock type diffusors have shown the existence of self-excited oscillations that occur as the internal mass flow is reduced somewhat below its maximum value. There is a lower bound of free stream Mach number (of the order of 1.8) below which no instability could be observed. However, as free stream Mach number was increased above this lower bound, instability occurred at increasing values of the internal mass flow. Also, the frequency at instability was of the order of the natural frequency of the internal duct acting as organ pipe.\r\n\r\nFirst-order theoretical investigations of the above phenomena indicate that the instability may (in part) be interpreted as intrinsic, that is, independent of viscous effects at the duct inlet or within the diffusor. The fundamental cause of the instability is shown to be due to the nature of the oscillatory inlet flow conditions that occur as a consequence of the external compression from the shock wave to the inlet, and the type of reflections suffered at the shock wave by upstream traveling pressure waves." }, { "name": "Acosta, Allan James", "degree": "PhD", "year": "1952", "title": "An Experimental and Theoretical Investigation of Two-Dimensional Centrifugal Pump Impellers", "advisor": "Hollander, Aladar", "url": "https://resolver.caltech.edu/CaltechETD:etd-04072003-091659", "creators": [ { "name": { "family": "Acosta", "given": "Allan James" }, "id": "Acosta-Allan-James", "display_name": "Acosta, Allan James" } ], "advisors": [ { "name": { "family": "Hollander", "given": "Aladar" }, "id": "Hollander-Alandar", "role": "advisor", "display_name": "Hollander, Aladar" } ], "committee": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "chair", "display_name": "Plesset, Milton S." }, { "name": { "family": "Erd\u00e9lyi", "given": "Arthur" }, "id": "Erd\u00e9lyi-Arthur", "role": "member", "display_name": "Erd\u00e9lyi, Arthur" }, { "name": { "family": "Hollander", "given": "Aladar" }, "id": "Hollander-Aladar", "role": "member", "display_name": "Hollander, Aladar" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" } ], "option_major": [ "mecheng" ], "doi": "10.7907/159P-SA35", "abstract": "An experimental and theoretical investigation on a series of three centrifugal pump impellers has been made in order to determine the usefulness and validity of tyro-dimensional potential theory for the description of the flow. Computed values of the developed head and distribution of pressure on the vane surfaces are compared with measurements an two-, four-, and six- bladed impellers which have 30\u00b0 logarithmic spiral vanes and a radius ratio of about one-half.
\r\n\r\nIt is found that for operating points where the influence on the flow into the impeller by the inlet turn is least, the agreement between the observed and predicted values is reasonably good, while for other flow rates large discrepancies occur. Although the impeller efficiency is relatively high when the flow is least disturbed by the inlet, the slope of the work coefficient line is steeper than the theoretically predicted value. This deviation is attributed to boundary layers which are observed on the vane surfaces.
" }, { "name": "Arbo, Paul Edward", "degree": "Engineering Degree", "year": "1952", "title": "Burning Rate for a Solid Propellant Ramjet Developing Constant Tthrust", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-150232", "creators": [ { "name": { "family": "Arbo", "given": "Paul Edward" }, "id": "Arbo-Paul-Edward", "display_name": "Arbo, Paul Edward" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/31B3-3W28", "abstract": "An analysis of a solid propellant ramjet which carries the propellant in the combustion chamber was made, and a procedure outlined for calculating the required burning rate of such a ramjet which develops constant thrust. The two factors which influenced this development were:\r\n\r\n1) The solid propellant ramjet\u2019s combustion chamber varies in size with time due to burning of the fuel.\r\n2) The solid propellant ramjet develops constant thrust.\r\n\r\nThese factors were coordinated with the analysis of the internal flow system of the ramjet, and an expression for the required burning rate was derived." }, { "name": "Arthur, Paul David", "degree": "PhD", "year": "1952", "title": "Effects of Impurities on the Supersaturation of Nitrogen in a Hypersonic Wind Tunnel", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-152948", "creators": [ { "name": { "family": "Arthur", "given": "Paul David" }, "id": "Arthur-Paul-David", "display_name": "Arthur, Paul David" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PBSD-2V70", "abstract": "An experimental investigation was conducted to determine the effects of additives on the supersaturation of commercial bottled nitrogen expanded in a hypersonic nozzle. In particular, enough oxygen was added to duplicate air proportions. A stainless steel two-dimensional source-flow nozzle of one-inch width was used to conduct the tests.\r\n\r\nCommercially pure nitrogen, expanded from room temperature and 8-1/3 atm. pressure, was found to supersaturate by approximately 18\u00b0 K or 1.2 Mach number. The supersaturation of the nitrogen was decreased by the addition of impurities, and only a fraction of a percent of carbon dioxide or water vapor was required to eliminate completely all supersaturation. Addition of argon and oxygen was found to be much less effective in decreasing the supersaturation. For the synthetic air, the supersaturation was 16\u00b0 K or 0.9 Mach number based on air vapor pressure values.\r\n\r\nDuring the collapse of the supersaturated state, the static pressure gradually increased above the isentropic value because of the heat release of the condensing gas. As has been shown before, there was no evidence of condensation shock with nitrogen. The impact pressure was only slightly changed from the isentropic value by the presence of condensation in the flow. After the collapse of the supersaturated state, the flow approximated that of a condensation shock.\r\n\r\nFrom these tests it is concluded that condensation of nitrogen, containing slightly more impurities than present in the commercial nitrogen, and of air of the same purity principally caused by foreign impurities, not by spontaneous self-nucleation." }, { "name": "Becker, Jack Lincoln", "degree": "Engineering Degree", "year": "1952", "title": "An Experimental Investigation of Ignition and Flame Stabilization in a Turbulent Mixing Zone", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252009-114335", "creators": [ { "name": { "family": "Becker", "given": "Jack Lincoln" }, "id": "Becker-Jack-Lincoln", "display_name": "Becker, Jack Lincoln" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BFQK-V510", "abstract": "The present investigation constituted the first part of an attempt to isolate the essentials of flame stabilization behind a bluff body. It is thought by many that such a flame is initiated and stabilized by heat transfer, the diffusion of active chemical species, and the chemistry of the combustible mixture involved.\r\n\r\nThe ignition of a fresh combustible mixture by a hot stream of gas provides possibility for detailed study of flame stabilization because of heat transfer.\r\n\r\nResults indicate that the method followed herein to produce ignition resulted in the formation of two distinct types of flames. One flame seemed to be affected primarily by temperature, the other was affected by temperature, stream velocity and fuel-air ratio.\r\n\r\nThe work was carried on as part of a study of flame stabilization being conducted at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California." }, { "name": "Buhler, Rolf Dietrich", "degree": "PhD", "year": "1952", "title": "Condensation of Air Components in Hypersonic Wind Tunnels: Theoretical Calculations and Comparison with Experiment", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162007-152444", "creators": [ { "name": { "family": "Buhler", "given": "Rolf Dietrich" }, "id": "Buhler-Rolf-Dietrich", "display_name": "Buhler, Rolf Dietrich" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0J8Q-9Z82", "abstract": "The effect of condensation on the flow in hypersonic wind tunnels is bracketed by equilibrium saturated expansion and by instantaneous condensation. By calculation of shock waves with evaporation, direct comparison of theoretical and measured pressures is made possible. Satisfactory agreement between saturated expansion theory and experiment is obtained after the collapse of the supersaturated state.\r\n\r\nThe droplet growth theory (for free molecule regime) is reexamined, and a good approximate solution is obtained for the nonsteady case (i.e., rapidly changing vapor properties). Limits of validity of the quasi-steady theory are defined, and an upper limiting (zero growth) drop size given for expanding flow.\r\n\r\nA simplified method is presented for calculating the pressure time history of the collapse of the supersaturated state in nozzles. From this, most effective nucleus sizes for given total mass of impurities are calculated. Thus the earliest possible collapse in a nozzle due to impurities is estimated theoretically for low impurity concentrations. The agreement of the predicted trend with experimental results in nitrogen appears to justify the assumed mechanism of the collapse, which is condensation on existing foreign nuclei formed upstream of the collapse.\r\n" }, { "name": "Cox, Dale William", "degree": "Engineering Degree", "year": "1952", "title": "Stabilization of a Bipropellant Liquid Rocket Motor", "advisor": "Marble, Frank E.; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-154303", "creators": [ { "name": { "family": "Cox", "given": "Dale William" }, "id": "Cox-Dale-William", "display_name": "Cox, Dale William" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4SBW-M406", "abstract": "The unstable burning of a bipropellant rocket combustion chamber is investigated and a study made of the requirements for an automatic closed loop control circuit to stabilize the motor.\r\n\r\nThe bipropellant combustion chamber equations developed by Dr. L. Crocco(1) are utilised as the analytical description of the rocket motor burning phenomena. Equations similar to those developed by Dr. H. S. Taiga(2) are used for the oxidizer and fuel supply systems and the two closed loop stabilizing circuits.\r\n\r\nThe stability or instability of the system is demonstrated by the use of a special plotting diagram in the complex plane suggested by M. Satche as a means of handling systems with time lag, and developed for this use by H. S. Tsien. This involves separating the transfer function into two parts. In the complex plane the first portion of the transfer function, the exponential variable containing the time lag, plots as a unit circle as the complex variable p is made to take a contour enclosing the positive half of the p\u2014plane. If the remaining portion of the transfer function intersects this unit circle, the rocket motor can be unstable for large reduced time lag; if it does not intersect the unit circle, the system is generally stable, although the roots of the exponential coefficient in the positive half of the complex plane must be investigated. This latter requirement can be conveniently accomplished by the aid of a Nyquist Diagram.\r\n\r\nThe equations for the feedback circuit are developed and the oxidizer and fuel transfer function requirements are determined.\r\n \r\nTwo cases of stable combustion and two cases of unstable combustion are analyzed. One unstable case is stabilized by the addition of a feedback circuit." }, { "name": "Dervishyan, Aram Ohannes", "degree": "Engineering Degree", "year": "1952", "title": "Fatigue Stress Concentration Studies on Aluminum Alloys", "advisor": "Sechler, Ernest Edwin; Hudson, Donald E.; Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-161109", "creators": [ { "name": { "family": "Dervishyan", "given": "Aram Ohannes" }, "id": "Dervishyan-Aram-Ohannes", "display_name": "Dervishyan, Aram Ohannes" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." }, { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4BCE-M652", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nFatigue tests in reversed bending were conducted in 75S-T6 and 17S-T6 aluminum alloys to determine whether Neuber's theory on fatigue stress concentration factors in notches was applicable to these materials. The results of the tests indicate confirmation of the theory within engineering accuracy providing the value of [\u2026] (a material constant) is determined experimentally.\r\n\r\nMaterial size effect was investigated and found to exist. This was an unexpected result since other sources (see References 3 and 4) indicated that no size effect existed for aluminum alloys.\r\n\r\nIgnoring the correction due to size effect a value of the Neuber's constant [\u2026] of approximately 0.05\" gave reasonable checks with the experimental data for both 75S-T6 and 17S-T6 aluminum alloys. This may indicate that this value of [\u2026] is the correct material constant for aluminum alloys but additional data on other alloys is needed to confirm this conclusion." }, { "name": "Eriksen, George August", "degree": "Engineering Degree", "year": "1952", "title": "Investigation of Flame Velocities at Low Pressures", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-075003", "creators": [ { "name": { "family": "Eriksen", "given": "George August" }, "id": "Eriksen-George-August", "display_name": "Eriksen, George August" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NGNK-YA29", "abstract": "The purpose of this study is to investigate flame velocities of mixtures of oxygen and various fuel gases at low pressures. Acetylene and propane fuels were used, and flame velocities were measured by means of flat disc flames and by means of the geometry of cone-shaped flames. Flame front area was measured from the profile defined by the onset of luminosity. The pressure range from three to one hundred mm. of mercury was covered by using two burner inlet ducts of different diameters, 2.37 and 1.25 inches respectively. The equipment and characteristics of the low pressure flame limited the data in this range, so that restricted quantitative results were obtained in regard to the variation of flame velocities with pressure.\r\n\r\nQualitatively, very definite variations were noted. There is a marked decrease of flame velocity with decreasing pressures in the regime below forty mm. of mercury. The variation in flame speed for the same pressure increments becomes greater as the pressure decreases. This is attributed to the rapid increase of the quenching effect from the inlet duct rim at these low pressures and low flow velocities. It is also found that flame velocities from flat flames are consistently lower than those obtained through the geometry of the cone flames. Similarly, flame velocities measured with the smaller inlet duct are consistently lower than those measured with the larger duct for the same measuring criteria. Both these variations appear to be explained by the large quenching effect encountered." }, { "name": "Gaibler, Richard", "degree": "Engineering Degree", "year": "1952", "title": "Column Creep of 75S-T6 Aluminum Alloy", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-084055", "creators": [ { "name": { "family": "Gaibler", "given": "Richard" }, "id": "Gaibler-Richard", "display_name": "Gaibler, Richard" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DTB9-Y232", "abstract": "This thesis is a report of the results of the column phase of a three part experimental investigation of short time creep properties of light metal alloys under conditions of high loadings and elevated temperatures. The other parts of the investigation were concerned with creep properties of these alloys in tension and in compression. The former is described by R. J. Kauffman; the latter by R. C. Thatcher (Refs. 11 and 12).\r\n\r\nCreep characteristics of 75S-T6 aluminum alloy columns having various effective slenderness ratios were investigated at 450\u00b0F and 550\u00b0F. Of primary interest was the region of applied stresses near the maximum stresses which these columns would sustain. Lateral creep deflection of the column midpoint was measured. Coincident with this measurement, time to failure of the column was also measured. Columns tested at 550\u00b0F had rectangular cross sections and had effective slenderness ratios of 25.5, 39.9, 48.6 and 57.2. Columns tested at 450\u00b0F. had rectangular cross sections and had effective slenderness ratios of 25.5, 48.6 and 57.2.\r\n\r\nTesting equipment was designed and constructed for the investigation. A constant load was applied to the specimen by means of a lever arm having a ten to one mechanical advantage. The specimen was heated in an electric oven. The oven was maintained at temperature by automatic electrical control.\r\n\r\nIt was found that 75S-T6 aluminum alloy columns having effective slenderness ratios of 25.5 to 57.2 are suitable for short time (0 - 10 min.) use at 450\u00b0F and 550\u00b0F." }, { "name": "Grey, Jerry", "degree": "PhD", "year": "1952", "title": "The Effects of Air Condensation on Properties of Flow and their Measurement in Hypersonic Wind Tunnels", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-061157", "creators": [ { "name": { "family": "Grey", "given": "Jerry" }, "id": "Grey-Jerry", "display_name": "Grey, Jerry" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HFHE-HR77", "abstract": "Some of the fundamental problems encountered in the measurement of flow properties in condensing air have been discussed, and were investigated experimentally in the GALCIT 9 Hypersonic Wind Tunnel. The saturated expansion theory of flow in a condensing fluid as developed by Buhler was corroborated, and some of the unknown properties of the theory have been clarified by analysis of the wind tunnel tests. Several experimental techniques for the measurement of two-phase fluid properties were developed and the results were used to supply additional information concerning the nature of phenomena such as supersaturation and normal and oblique shock waves. No definite conclusions could be reached with regard to future application of condensed air wind tunnel data on the basis of these tests, but the subject of similarity parameters comparable to the Mach number in flow of a perfect gas has been discussed at some length." }, { "name": "Hartwig, Frederic William", "degree": "Engineering Degree", "year": "1952", "title": "The Evaporation Rate of Liquid Droplets in a Hot Gas", "advisor": "Penner, Stanford S.; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-09082004-114120", "creators": [ { "name": { "family": "Hartwig", "given": "Frederic William" }, "id": "Hartwig-Frederic-William", "display_name": "Hartwig, Frederic William" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NY38-9J57", "abstract": "Calculations have been carried out in order to determine the rate of evaporation of a liquid droplet surrounded by hot gases. The present study represents an extension of earlier work by Penner on evaporation rates for isothermal droplets. Thus, allowance was made for temperature gradients withing the droplet (a) by considering a droplet composed of an isothermal core and an isothermal shell and (b) by utilizing the actual termperature profile in the droplet as established as the result of a heat balance between thermal conduction within the droplet, convective heat transfer to the droplet, and cooling produced by evaporation at the droplet surface.\r\n\r\nThe results obtained for the shell model of the evaporating droplet were found to be in satisfactory agreement with the known data for evaporations of isothermal droplets, independently of the thickness chosen for the isothermal shells. On the other hand, the laborious conduction solution led to somewhat different results. The origin of the detailed deviations is not clear at this time and requires additional study." }, { "name": "Holm, Robert Joseph", "degree": "Engineering Degree", "year": "1952", "title": "I. Integrated Intensity Measurements for Vibration-Rotation Bands of Carbon Dioxide. II. Total Absorptivity Measurements on Carbon Dioxide at Room Temperature", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-081744", "creators": [ { "name": { "family": "Holm", "given": "Robert Joseph" }, "id": "Holm-Robert-Joseph", "display_name": "Holm, Robert Joseph" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RN61-AX46", "abstract": "I. This study contains an outline of the experimental measurements performed in order to determine integrated intensities of various vibration-rotation bands of carbon dioxide by use of standard techniques with a Perkin-Elmer spectrometer.\r\n\r\nII. Total absorptivity measurements on carbon dioxide at room temperatures were made in a pressurized gas cell provided with transparent windows." }, { "name": "Kauffman, Ralph J.", "degree": "Engineering Degree", "year": "1952", "title": "An Investigation of Creep in Light Metal Alloys", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-061536", "creators": [ { "name": { "family": "Kauffman", "given": "Ralph J." }, "id": "Kauffman-Ralph-J", "display_name": "Kauffman, Ralph J." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "member", "display_name": "Clark, Donald S." }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HB4M-3P19", "abstract": "An investigation was made of the creep characteristics of two aluminum alloys, 75S-T6 and 25S-T6, and one magnesium alloy, FS-1, under the conditions of high temperatures and high stresses. These alloys were selected as being representative of the light alloys in current use in the aircraft industry.
\r\n\r\nThis investigation was divided into three phases: (1) \"fast-rate\" deformation under tension, (2) creep of short columns in compression, and (3) lateral deflection creep of columns. This thesis encompasses only the first phase of the investigation. The other phases are covered by current theses by the author's coworkers.
\r\n\r\nIt was found that the aluminum alloys tested were superior in creep resistance to the magnesium alloy at the common temperatures used, 450\u00b0F and 500\u00b0F. However, the comparative creep resistance of the aluminum alloys was dependent upon the temperatures at which the alloys were compared: 75S-T6 being superior at 450\u00b0F, 25S-T6 at 500\u00b0F, and neither alloy superior to the other at 550\u00b0F.
\r\n\r\nThe possible use of the alloys tested for short duration under conditions of high temperatures and high stresses is noted.
\r\n\r\nThe data obtained is presented in both tabular and graphic form with various cross-plots provided for the purposes of cross comparison and to permit easy reference for obtaining given creep characteristics of the alloys tested.
\r\n" }, { "name": "MacCready, Paul Beattie", "degree": "PhD", "year": "1952", "title": "Investigation of Atmospheric Turbulence", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-104542", "creators": [ { "name": { "family": "MacCready", "given": "Paul Beattie" }, "id": "MacCready-Paul-Beattie", "display_name": "MacCready, Paul Beattie" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F8AR-VH67", "abstract": "Satisfactory measurement techniques were developed which overcame the four principal experimental problems arising in the investigation of atmospheric turbulence.\r\n\r\n1) The data are made reproducible for statistical analyses by recording them on a portable magnetic tape recorder.\r\n\r\n2) Measurements at elevations up to several hundred meters are made feasible by the use of a multi-cable tethering system for a balloon which supports the measuring devices.\r\n\r\n3) and 4) The problems of measuring wind velocity fluctuations over broad ranges (frequencies between 0 and 50 cycles per second, and magnitudes between 1/4 and 20 meters per second) are solved by using hot wire anemometers together with non-linear amplifiers.\r\n\r\nThe statistical analysis of recordings made under various meteorological conditions indicates that Kolmogoroff's similarity hypothesis, concerning the isotropy of turbulence in a certain inertial sub-range of eddy sizes, is directly applicable to eddies of sizes ranging from under 10 cm. to dimensions larger than the elevation of measurement. Over this range the \"2/3 law\" holds for the autocorrelation coefficient and the \"-5/3 law\" holds for the energy spectrum, within the accuracy of the measurements. The large eddy limit of the range of the \"2/3 law\" appears to be considerably extended by strong thermal instability. Heat flux measurements from the correlation between temperature and vertical velocity agree reasonably with the heat flux measured with heat meters. At 70 cm. under moderate wind conditions over half the heat flux is due to eddies of periods less than two seconds. Momentum flux measurements from velocity correlations were inconclusive." }, { "name": "Mueller, Gregg", "degree": "Engineering Degree", "year": "1952", "title": "Optimum Range of a Wingless Rocket About a Rotating Earth", "advisor": "Tsien, Hsue Shen; Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252009-111732", "creators": [ { "name": { "family": "Mueller", "given": "Gregg" }, "id": "Mueller-Gregg", "display_name": "Mueller, Gregg" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HHJS-QS62", "abstract": "The motion of a wingless rocket in a vacuum about a spherical non-rotating earth describes the elliptic orbit of a material point of mass in a central field of force. The corrections for the rotation of the earth are applied to this solution to determine the effects on optimum range. Since there is no simple mathematical solution for optimizing the range, it is necessary to obtain ranges for several angles of elevation at each initial velocity and then find the optimum range by using interpolation formulas. Only the case of firing at the equator is computed although the formulas and the computational procedure outlined can be applied at any latitude.\r\n\r\nFiring to the East gives the greatest range for a given initial velocity and firing to the West gives the least range. The angle of elevation is lowest firing East and highest firing West, although for low velocities the difference is not great and for the 5,000 mph. solution a constant angle of elevation gives ranges varying at most only one-tenth of a mile from the maximum for any direction of fire. However, for the 15,000 mph. solution all the factors are critical in obtaining the maximum range." }, { "name": "Nay, Harvey Orin", "degree": "Engineering Degree", "year": "1952", "title": "Low Speed Boundary Layer and Pressure Distribution Tests on a Family of Swept Back Wings", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-081125", "creators": [ { "name": { "family": "Nay", "given": "Harvey Orin" }, "id": "Nay-Harvey-Orin", "display_name": "Nay, Harvey Orin" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/29BY-XV92", "abstract": "Low-speed tests were conducted to determine boundary layer and surface pressure distribution characteristics of a systematic family of swept back wings. It is intended that the test results will have application in giving a better understanding of the viscous flow phenomena on swept back wings, particularly in relation to the stall. A general picture of the boundary layer flow and surface pressure distribution at high lift conditions, showing the effects of variations in wing planform, was determined. Several existing concepts were verified and an attempt was made to define the limits of applicability of these concepts.\r\n\r\nA localized separation of the flow perpendicular to the leading edge of the wing, hereinafter referred to as the \"normal flow\", was found to occur at lift coefficients somewhat below the stall on the wings with appreciable sweepback. The separation took the form of a vortex streak running aft and outboard from an origin near the leading edge, and it greatly affected the boundary layer structure and the surface pressure distribution.\r\n\r\nGeneralization of surface pressure distribution on the basis of the local lift coefficient and dynamic pressure for the normal flow was found to hold fairly well for the various sweepback angles.\r\n\r\nThe development of stall was determined for the various planforms in terms of boundary layer thickness and flow direction near the surface of the wing.\r\n\r\nGeneralization of the shape of the profiles of the normal boundary layer flow component in terms of a single family of shapes for all sweep-back angles, as suggested by other researchers, was shown to be possible." }, { "name": "Parkin, Blaine Raphael", "degree": "PhD", "year": "1952", "title": "Scale Effects in Cavitating Flow", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-081459", "creators": [ { "name": { "family": "Parkin", "given": "Blaine Raphael" }, "id": "Parkin-Blaine-Raphael", "display_name": "Parkin, Blaine Raphael" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DWKE-J388", "abstract": "Scale effects in cavitating flow are considered for the so-called limited cavitation flow regime. The roles of nuclei and air diffusion in ordinary water and the kinetic theory of liquids for pure water are considered as to their bearing on cavitation scale effects.\r\n\r\nThe attack on the problem is concentrated in three general areas. First, dynamic similarity considerations for individual bubble growth show that no useful scaling laws can be established from such arguments. Aside from changes due to Reynolds number, it is concluded that scale effects are dependent upon the time required for a nucleus to grow from its original microscopic size to a macroscopic size. Second, a series of experiments shows that the cavitation behaves in a systematic way as the scale of the immersed body is changed. In certain instances, the inception of cavitation depends on both model size and free stream velocity. Third, a theoretical study is made to gain insight into the relationships that must hold between the parameters which affect the inception of cavitation. A simplified theory gives only rough qualitative agreement with experiment." }, { "name": "Robinson, Martin Samuel", "degree": "Engineering Degree", "year": "1952", "title": "A Ten Channel Statistical Analyzer for Use in Turbulence Research", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-082004", "creators": [ { "name": { "family": "Robinson", "given": "Martin Samuel" }, "id": "Robinson-Martin-Samuel", "display_name": "Robinson, Martin Samuel" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3BGC-7N43", "abstract": "An experimental investigation of a stationary random process will involve the measurement of the mean values and probability distribution of a random function of time. This thesis describes an automatic ten channel \"statistical analyzer\" for measuring the probability distribution function of a continuous or discontinuous function of time that can be represented by a suitable electric voltage. The \"statistical analyzer\" is based upon a system of pulse amplitude modulation, followed by pulse height selection and pulse counting. An equation is developed by means of which the mean values can be computed from the distribution function. Finally, sample applications from the field of turbulence research are given." }, { "name": "Roshko, Anatol", "degree": "PhD", "year": "1952", "title": "On the Development of Turbulent Wakes from Vortex Streets", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-144124", "creators": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-Anatol", "display_name": "Roshko, Anatol" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WDN-9807", "abstract": "Wave development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations.\r\n\r\nThe Reynolds number range of periodic vortex \"shedding\" is divided into two distinct sub-ranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300.\r\n\r\nSpectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream.\r\n\r\nIt was found that in the stable range the vortex street has a periodic spanwise structure.\r\n\r\nThe dependence of shedding frequency on velocity was successfully used to measure flow velocity.\r\n\r\nMeasurements in the wake of a ring showed that an \"annular\" vortex street is developed." }, { "name": "Schroeder, Joseph Herman", "degree": "Engineering Degree", "year": "1952", "title": "Effect of Vibrational Excitation on the Theoretical Performance of the Stoichiometric Carbon-Oxygen Propellant System", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-082354", "creators": [ { "name": { "family": "Schroeder", "given": "Joseph Herman" }, "id": "Schroeder-Joseph-Herman", "display_name": "Schroeder, Joseph Herman" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BGFA-6E97", "abstract": "Accurate calculations to evaluate the performance of the stoichiometric carbon-oxygen propellant system have been carried out for nozzle flow with and without chemical reactions and with and without vibrational adjustment. The calculations show that, for frozen chemical flow, a lag of vibrational energy states at chamber conditions nearly doubles the reduction in Isp, as compared with flow in which complete vibrational equilibrium is maintained. On the other hand, lags in vibrational adjustment have practically no effect on the theoretical performance of hot propellant systems if chemical equilibrium is maintained during nozzle flow. The preceding conclusions are in agreement with the results on other propellant systems obtained previously by use of an approximate evaluation procedure." }, { "name": "Thatcher, Roland Churchill", "degree": "Engineering Degree", "year": "1952", "title": "Short Time Compressive Creep in 75S-T6 and 25S-T6 Aluminum Alloy Short Columns", "advisor": "Sechler, Ernest Edwin; Clark, Donald S.; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-083614", "creators": [ { "name": { "family": "Thatcher", "given": "Roland Churchill" }, "id": "Thatcher-Roland-Churchill", "display_name": "Thatcher, Roland Churchill" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DFBM-7A50", "abstract": "The creep characteristics of some of the light metal alloys at high temperature and stress were investigated when subject to; (1) Tension, (2) Short Column Compression, (3) Long Column effect. The tension and long column aspects are covered in the theses of R. I. Kauffman and R. Gaibler respectively. This thesis concerns the short-time creep of short columns of 25S-T6 and 75S-T6 aluminum alloy, subjected to large compressive loads, and temperatures of 450\u00b0, 500\u00b0, and 550\u00b0F. The columns were circular in cross section, and had an effective slenderness ratio of 25.5.
\r\n\r\nIt was found that 75S-T6 was superior to 25S-T6 at 450\u00b0F and, that at that temperature, 75S-T6 short columns could withstand a stress of 14,500 psi, however due to creep, failure occurred in approximately 45 seconds. At a temperature of 500\u00b0F, 25S-T6 was found to be superior, and withstood a stress of 11,000 psi for approximately 60 seconds before creep failure occurred. The load carrying ability of the two alloys was about the same at 550\u00b0F with both materials withstanding 8,000 psi for approximately 60 seconds.
\r\n\r\nIt is commonly believed that aluminum alloys are of little value at temperatures as high as 550\u00b0F, however contrary to this belief, this investigation shows that short columns of the two alloys tested can carry a large compression load if the time of duration is short.
\r\n" }, { "name": "Wallace, Richard Earl", "degree": "Engineering Degree", "year": "1952", "title": "Low-Speed Investigation of a Double Wedge Airfoil with a Leading-Edge Slat", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-084539", "creators": [ { "name": { "family": "Wallace", "given": "Richard Earl" }, "id": "Wallace-Richard-Earl", "display_name": "Wallace, Richard Earl" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NJPD-HF21", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nA two-dimensional investigation was undertaken in the California Institute of Technology Merrill Wind Tunnel to determine the effectiveness of using a 15% slat on a 10% double wedge airfoil. The investigation was conducted in three phases: force polars, pressure tests, and tuft pattern studies. All phases were conducted at a dynamic pressure of 40 lb/ft[superscript 2], equivalent to a Reynolds number of 0.78 x 10[superscript 6].\r\n\r\nThe high lift characteristics of the double wedge airfoil with the slat were found to be aerodynamically superior to those of the basic wedge section and the wedge equipped with a plain nose flap. Extension of the leading edge slat caused increases in maximum lift coefficients and in the angle of attack required for maximum lift. The following increments were measured.\r\n\r\n[\u2026].\r\n\r\nThe nose deflection produced larger [\u2026] max increments than the slot variations below nose angles of 25\u00b0 but for 25\u00b0 and larger angles the slot variations caused the major improvements in [\u2026]. The slot prevented occurrence of buffeting caused by upper surface intermittent or oscillatory separation experienced with the plain nose flap.\r\n\r\nIn all of the cases tested with the slat extended, the stall was more gradual than for the basic section. The stall for the optimum slot conditions was the result of trailing edge separation moving forward over the upper surface of the airfoil.\r\n" }, { "name": "Weinberg, Warren E.", "degree": "Engineering Degree", "year": "1952", "title": "Initial Motion of a Rocket Moving on a Stretched Cable", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-090703", "creators": [ { "name": { "family": "Weinberg", "given": "Warren E." }, "id": "Weinberg-Warren-E", "display_name": "Weinberg, Warren E." } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NY23-GR26", "abstract": "The practicability of using a stretched cable for a rocket launching device is dependent primarily upon the transverse movement of the rocket and the stresses involved in the system. This requires analysis of the effects of the moving rocket mass on the cable from the instant of contact, and the problem reduces to one of wave propagation.\r\n\r\nThe analysis here is restricted essentially to developing a procedure by which the initial motion of the mass can be calculated, and an expression is obtained which permits determination of the deflections. The problem is approached by first assuming that the mass exerts a constant transverse force on the cable. Admittedly, this is a simplifying assumption, and the result is not valid for the instant the mass hits the cable or for a short time thereafter because the inertia of the mass is not considered.\r\n\r\nNext, the problem is solved by taking into account the dynamics of the mass, and the solution reveals that the path of the actual mass deviates from the force path by as much as twenty percent during the initial motion but soon returns to the force path. The mass does not exert its full force on the cable at the instant of contact, but comes down on the cable with full force a short time later. Since maximum stresses on the system occur at this time, this factor is an important result of the analysis. Further, it is shown that increased velocity of the mass increases the deviation from the force path, and increased mass lengthens the time of return to the force path." }, { "name": "Woodward, Frank Arthur", "degree": "Engineering Degree", "year": "1952", "title": "An Investigation of the Effect of the Muzzle on the Motion of the Projectile in a Recoilless Gun", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-091019", "creators": [ { "name": { "family": "Woodward", "given": "Frank Arthur" }, "id": "Woodward-Frank-Arthur", "display_name": "Woodward, Frank Arthur" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/928R-MD36", "abstract": "Expressions for the position and velocity of a projectile at any time in a recoilless gun are derived. The one dimensional wave equation is assumed to be valid in describing the motion of the gas. The muzzle velocity of the projectile is calculated, and compared with that obtained for the case in which no waves are reflected back from the muzzle. It is shown that the effect of the reflected waves is to increase the muzzle velocity. In the limiting case, when the ratio of the mass of gas initially in the barrel to the mass of the projectile is infinite, the theoretical muzzle velocity of the projectile is increased to twice the value that would be obtained if the effect of the reflected waves was neglected." }, { "name": "Wu, Theodore Yao-tsu", "degree": "PhD", "year": "1952", "title": "On Problems of Heat Conduction in a Compressible Fluid", "advisor": "Lagerstrom, Paco A.; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032004-135328", "creators": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Theodore-Yao-tsu", "display_name": "Wu, Theodore Yao-tsu" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G8DW-K988", "abstract": "The present work starts with a study of heat conduction in a non-viscous compressible fluid based on a linearized theory which is similar to that used in the theory of sound. Important features of exact equations of motion and their corresponding linearized equations are studied briefly. For this linear system, which preserves many of the features of the original non-linear system, the fundamental solutions are found and discussed. The additional role played by viscosity in the heat conduction problem is then investigated. The fundamental solutions for this compressible, viscous, heat-conducting flow problem are found and compared with the non-viscous case. The problem of heat conduction in a two-dimensional stationary flow of a viscous compressible fluid is further studied by finding the fundamental solutions and discussing the result in some detail. As an example proposed to show how a superposition of these fundamental solutions can be used to solve a boundary value problem, the problem of the anemometry of a heated flat plate is solved for both large and small values of the Reynolds number. The result obtained herein is discussed and compared with some existing theories and experiments. The causes of the discrepancy resulting from this linearized theory are briefly explained." }, { "name": "Angelo, Raymond Louis", "degree": "Engineering Degree", "year": "1951", "title": "I. Experimental Determination of Selected Accommodation Coefficients. II. Experimental Determination of the Heat of Iodine", "advisor": "Farber, Milton; Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172009-085837", "creators": [ { "name": { "family": "Angelo", "given": "Raymond Louis" }, "id": "Angelo-Raymond-Louis", "display_name": "Angelo, Raymond Louis" } ], "advisors": [ { "name": { "family": "Farber", "given": "Milton" }, "id": "Farber-Milton", "role": "advisor", "display_name": "Farber, Milton" }, { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1DD6-8B60", "abstract": "In PART I the results of a study of the accommodation coefficient and its dependence on the temperature of the metal surface are described. The following systems were investigated: oxygen on platinum, carbon dioxide on platinum, nitrogen on platinum, carbon dioxide on tungsten, and carbon dioxide on nickel. All systems exhibit similar characteristics; i.e., a rapid rise to a maximum value of the accommodation coefficient in the region of low filament temperatures followed by a gradual decrease to a constant value as the filament temperature is increased, bulb temperature remaining constant.\r\n\r\n\t Maximum Constant value\r\n\r\nOxygen-platinum\t .98\t .68\r\n\t\r\nNitrogen-platinum .97\t .50\r\n\t\r\nCO2 -platinum\t .56\t .35\r\n\t\r\nCO2 -tungsten\t .93\t .80\r\n\t\r\nCO2 - nickel\t .68\t .47\r\n\r\nThis general behavior of the accommodation coefficient substantiates findings reported earlier by Oliver (13) for other gas-metal systems.\r\n\r\nThe experimentally determined values of the accommodation coefficient are applied to a theoretical relation obtained by application of the theory of absolute reaction rates (10). The theoretical expression is shown to be in semiquantitative agreement with the experimental data.\r\n\r\nIn PART II the \"hot wire\" method is used to determine the heat of dissociation of iodine. The experimentally determined value is 36.9 kcal/mole at 600\u00b0K. The presently accepted value for this temperature is 35.17 kcal/mole. Provided a wire can be found which is not corroded by fluorine, the present results suggest a useful method for determining the heat of dissociation of fluorine." }, { "name": "Bleviss, Zegmund Oscar", "degree": "PhD", "year": "1951", "title": "Interference Effects in Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182009-105100", "creators": [ { "name": { "family": "Bleviss", "given": "Zegmund Oscar" }, "id": "Bleviss-Zegmund-Oscar", "display_name": "Bleviss, Zegmund Oscar" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YDMK-MS28", "abstract": "A study is made of interference problems with emphasis on low-aspect-ratio supersonic missile configurations. The configurations are composed of slender pointed bodies with circular cross section, plane or cruciform delta wings, and tails which are not specified. For fin-fin interference (no body) general multi-fin delta wings are studied for the roll problems.\r\n\r\nThree types of interferences are studied. They are (1) fin-fin interference, (2) fin-fin and wing-body interferences combined, and (3) wing-body-tail interference. Where possible, three aerodynamic problems are studied under each of these interferences. They are (1) lift and incidence, (2) roll due to aileron deflection, and (3) damping in roll.\r\n\r\nA survey of the theoretical work on supersonic interference problems is included.\r\n\r\nLinearized theory is used throughout for all problems treated by the writer. Work by other writers which fits naturally into the scheme of the present work is summarized briefly. For most of the problems it is not possible to obtain exact linearized solutions without excessive labor. Where possible, approximations to or estimates of the exact solutions are obtained. It is hoped that these results will be useful for engineering estimates of the interference effects.\r\n\r\nTheoretical results for the roll problems--exact, approximate, and estimated--are presented for fin-fin interference for cruciform and more general multi-fin delta wings with subsonic and supersonic leading edges.\r\n\r\nFor fin-fin and wing-body interferences combined, theoretical results which bracket the exact solutions are obtained for the roll problems.\r\n\r\nFor wing-body-tail interference, the vorticity distributions, rolled-up vortex strengths, and initial vortex positions at the trailing edges are estimated for lift, incidence, aileron deflection, and damping in roll problems. Both plane and cruciform delta wing body configurations are studied.\r\n\r\nA qualitative discussion of some of the nonlinear, viscous, and gap effects is included.\r\n\r\nRecommendations for future research are made." }, { "name": "Bryson, Arthur Earl", "degree": "PhD", "year": "1951", "title": "An Experimental Investigation of Transonic Flow Past Two-Dimensional Wedge and Circular Arc Sections Using a Mach-Zehnder Interferometer", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-114932", "creators": [ { "name": { "family": "Bryson", "given": "Arthur Earl" }, "id": "Bryson-Arthur-Earl", "display_name": "Bryson, Arthur Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S45R-FG17", "abstract": "Interferometer measurements are given of the flow fields near two-dimensional wedge and circular arc sections at zero angle of attack at high subsonic and low subsonic velocities. Both subsonic flow with local supersonic zone and supersonic flow with detached shock wave have been investigated. Pressure distributions and drag coefficients as functions of Mach number have been obtained. The wedge data are compared with the theoretical work on flow past wedge sections of Guderley and Yoshihara, Vincenti and Wagoner, and Cole.
\r\n\r\nIt is shown that the local Mach number at any point on the surface of a finite three-dimensional body or an unswept two-dimensional body, moving through an infinite fluid, is a stationary value at Mach number one and, in fact, remains nearly constant for a range of speeds below and above Mach number one. On the basis of this concept and the experimental data, pressure distributions and drag coefficients for the wedge and circular arc sections are presented throughout the entire transonic range of velocities.
" }, { "name": "Dankworth, Edwin George", "degree": "Engineering Degree", "year": "1951", "title": "An Investigation of the Effects of a Sharp Velocity Gradient of the Flexure-Torsion Flutter Speed of an Airfoil", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-130943", "creators": [ { "name": { "family": "Dankworth", "given": "Edwin George" }, "id": "Dankworth-Edwin-George", "display_name": "Dankworth, Edwin George" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QBG8-G786", "abstract": "This report covers the results of an experimental investigation of the effects of a velocity gradient on the flexure-torsion flutter speed of a NACA 0006 airfoil suspended by means of springs.
\r\n\r\nThe presence of the velocity gradient produced no significant change in the speed at which the airfoil commenced normal self-excited oscillations. Oscillations of a torsional nature were found to occur at speeds considerably below the normal flutter speed. The causes of these torsional oscillations were not fully ascertained. It is reasoned however that they were due to flow conditions other than the presence of the velocity gradient.
\r\n" }, { "name": "Davidson, Harold William", "degree": "Engineering Degree", "year": "1951", "title": "Lift Increase Obtained with Boundary Layer Suction on a 10% Double Wedge Airfoil with a 20% Chord Leading and Trailing Edge Flaps", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-110707", "creators": [ { "name": { "family": "Davidson", "given": "Harold William" }, "id": "Davidson-Harold-William", "display_name": "Davidson, Harold William" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KPZ6-2V51", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this investigation a study was made of the effects of boundary layer control on a 10% thick, double-wedge airfoil located between endplates. In particular, the study centered around a \"high-lift\" investigation in order to obtain an optimum configuration for the specific airfoil. The double-wedge airfoil was used since: 1) it is a \"high speed\" airfoil, and 2) it has poor maximum lift and stalling characteristics.\r\n\r\nThe model used was equipped with a nose flap and a slotted trailing edge flap, both of 20% wing chord, and two suction slots, one aft of the nose flap (20% chord) and the other at the 70% wing chord. Five suction quantities were used on all possible configuration combinations. The maximum lift coefficient obtained was [...] = 2.149 at an angle of attack of 21\u00b0 and a suction quantity equal to C[subscript Q] = 0.0071.* For this particular configuration, the approximate value of the horsepower required to supply the necessary suction quantity was determined. In addition to the force and moment tests, tuft studies of flow of the \"optimum\" configurations were made and reported.\r\n\r\n\r\n\r\n* Configuration: Nose flap deflected 30\u00b0; trailing edge flap deflected 30\u00b0; slot [...](forward slot)" }, { "name": "Dhawan, Satish", "degree": "PhD", "year": "1951", "title": "Direct Measurements of Skin Friction", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-155504", "creators": [ { "name": { "family": "Dhawan", "given": "Satish" }, "id": "Dhawan-Satish", "display_name": "Dhawan, Satish" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1S03-8631", "abstract": "A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of a flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reluctance measuring device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin friction coefficients show excellent agreement with Blasius' and Karman's results respectively. The device was then applied to high-speed subsonic flow and the turbulent skin friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic floor were also made.
\r\n\r\nThe paper describes the design and construction of the device and the results of the measurements.
" }, { "name": "Dixon, Howard Henry", "degree": "PhD", "year": "1951", "title": "Stresses and Deflections of Unswept and Swept Thin-Walled Beams", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-093729", "creators": [ { "name": { "family": "Dixon", "given": "Howard Henry" }, "id": "Dixon-Howard-Henry", "display_name": "Dixon, Howard Henry" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7D5X-ZN05", "abstract": "A method is presented for the determination of the stresses and deflections of unswept and swept, thin-walled beams of uniform closed cross section. The cross section, loading distribution and boundary conditions are assumed to be arbitrary. The method is based on the differential equation governing the behavior of orthogonal elastic shells. The differential equation is transformed into a difference equation and the solution obtained by the relaxation technique. A comparison of the theoretical solution and experimental data for a swept back wing with a carry through bay under symmetrical bending showed good agreement.
\r\n\r\nA tapered wing may be treated by approximating the variation by a series of spanwise steps.
\r\n\r\nAs the difference equations are a system of simultaneous algebraic equations, they may be solved by automatic calculating equipment or by electric analogue computers as well as by the relaxation technique.
\r\n" }, { "name": "Hipsh, Harold Marvin", "degree": "PhD", "year": "1951", "title": "Harmonic Oscillations of a Narrow Delta Wing in Supersonic Flow", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-125900", "creators": [ { "name": { "family": "Hipsh", "given": "Harold Marvin" }, "id": "Hipsh-Harold-Marvin", "display_name": "Hipsh, Harold Marvin" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VRVK-HB35", "abstract": "A theory is presented for the calculation of the velocity potential of a harmonically oscillating delta wing having subsonic leading edges in a supersonic flow. The velocity potential is expanded in a power series in powers of the reduced frequency. Two modes of oscillation, plunging and pitching, are considered. For both modes the analysis is carried through the term linear in reduced frequency, this being generally sufficient for dynamic stability analyses. The results thus obtained for the pitching mode verify those of Miles (Ref. 9) obtained by an integral transformation of the steady-state solution. In addition, the term that is quadratic in the reduced frequency is presented for the plunging mode to illustrate the general procedure.\r\n\r\nLift and pitching moment coefficients are calculated from the velocity potential and numerical results valid for low frequency oscillations are presented." }, { "name": "Holmquist, Carl Oreal", "degree": "Engineering Degree", "year": "1951", "title": "Effect of Small Variations of Parameters in the Turboprop Cycle", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-104251", "creators": [ { "name": { "family": "Holmquist", "given": "Carl Oreal" }, "id": "Holmquist-Carl-Oreal", "display_name": "Holmquist, Carl Oreal" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B34Z-JX85", "abstract": "A cycle analysis of the turbine-propeller engine is given in terms of the parameters of the cycle and the component efficiencies of the engine with and without regeneration. By means of a Taylor expansion about the point of ideal efficiencies, total power output, specific fuel consumption, and optimum jet pressure ratio are given in terms of the ideal values plus corrections for small variations in the component efficiencies from 100%. In this way, the relative importance of component efficiencies in affecting the performance of the ideal turboprop cycle is demonstrated by means of simple analytical expressions involving the basic cycle parameters and the component efficiencies.\r\n\r\nThe analysis of the ideal turboprop cycles is given in terms of three basic parameters which are functions of the forward flight speed, the compressor pressure ratio, and the limiting combustion chamber temperature. For the ideal cycle, the jet pressure ratio for optimum division of power between propeller and jet results in the total work of the cycle being done by the propeller.\r\n\r\nOf the component efficiencies, the turbine efficiency was found to be the most important in affecting the performance criteria of the ideal turboprop cycle. Since all work is done by the propeller in the ideal cycle, the propeller efficiency was also found to be important in affecting performance. Regeneration, as considered in this analysis, decreased the total power output and decreased the specific fuel consumption of the ideal turbine-propeller engine." }, { "name": "Hughes, Richard Frank", "degree": "Engineering Degree", "year": "1951", "title": "Analytical Performance Study of Turbojet Cycle with Nearly Ideal Component Efficiencies", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-161901", "creators": [ { "name": { "family": "Hughes", "given": "Richard Frank" }, "id": "Hughes-Richard-Frank", "display_name": "Hughes, Richard Frank" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q2CP-J309", "abstract": "The performance of the turbojet engine for high component efficiency is approximated by an ideal expression (efficiencies equal unity) plus the first terms of a Taylor Series expansion for the purpose of isolating the individual effects of the components.\r\n\r\nThe analytical solution to two optimizations is presented; namely:\r\n\r\n(A) For fixed burner outlet temperature, flight Mach number, and component efficiency, what is the compressor pressure ratio corresponding to maximum jet velocity (maximum thrust per unit mass flow)?\r\n\r\n(B) For fixed flight Mach number, compressor pressure ratio and component efficiency, what is the burner outlet temperature corresponding to minimum specific fuel consumption?" }, { "name": "Jensen, Arnold Axtell", "degree": "PhD", "year": "1951", "title": "A Slender Cone Starting Impulsively", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102009-074636", "creators": [ { "name": { "family": "Jensen", "given": "Arnold Axtell" }, "id": "Jensen-Arnold-Axtell", "display_name": "Jensen, Arnold Axtell" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/19KD-1M64", "abstract": "The problem of a semi-infinite slender cone which starts impulsively from rest so that it suddenly has a constant supersonic velocity is considered. It is treated by using the acoustic wave equation for the air at rest at infinity. The problem is reduced to that of dealing with the radial velocity in two conical variables in space-time.\r\n\r\nIt is shown that there are three fundamental regions from the physical or mathematical standpoint. The boundary conditions and equations for each of these regions are developed so that a numerical solution of the problem may be obtained for a given Mach number and cone angle. From the solution of the radial velocity the potential and thence the pressure on the cone are obtained.\r\n\r\nAn approximation to the pressure far back on the cone where the curvature is small is obtained as an improvement on the piston value for zero curvature. This is done by suppressing variations in the axial direction and solving the resulting equation by Riemann's integration method.\r\n\r\nAn attempt to solve the problem by distributing sources on the axis with resulting difficulties is discussed." }, { "name": "Kaplun, Saul", "degree": "Engineering Degree", "year": "1951", "title": "Dimensional Analysis of the Inflation Process of Parachute Canopies", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:11182010-154343424", "creators": [ { "name": { "family": "Kaplun", "given": "Saul" }, "id": "Kaplun-Saul", "display_name": "Kaplun, Saul" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/25MM-HY18", "abstract": "The possibility of an experimental approach based on dimensional analysis is considered. Dimensional analysis of the filling of a parachute tied to a fixed support is given. The physical variables of the problem are discussed, and an attempt is made to retain for subsequent analysis of all those variables for which the a priori assumption of negligibility is not warranted. The variables are reduced to dimensionless form, leading to tables of model rules which must be obeyed for various purposes. The possibility of a rigorous experimental procedure and, especially, of separating the effects of the several parameters is discussed in light of the model rules." }, { "name": "Kendrick, James Benjamin", "degree": "Engineering Degree", "year": "1951", "title": "Automatic or Coupled Control Surfaces for Aircraft", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-062149", "creators": [ { "name": { "family": "Kendrick", "given": "James Benjamin" }, "id": "Kendrick-James-Benjamin", "display_name": "Kendrick, James Benjamin" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CN1Q-P992", "abstract": "An improved method of aircraft stabilization is described, with wind tunnel test results and stability criteria, and suggestions for use in aircraft design. The method utilizes a new type of control surface consisting of a mechanically coupled fin and rudder, which converts the tail surface into an automatic servo control.
\r\n\r\nTheory and wind tunnel tests show that the lift curve slope of the tail, [...]\tmay be increased by six times or more in this way, using reasonable but not extraordinary care with manufacturing methods and tolerances.
\r\n\r\nThe dynamic stability criteria are given and compared with wind tunnel tests for nine different balance conditions of two models tested on a swinging arm in the wind tunnel. Four out of the nine cases were stable, and the stability criteria give the correct indication in every case.
\r\n\r\nStability analysis is used to indicate the effect of coupled surfaces on the lateral and longitudinal notion of a conventional transport airplane. With the regular control surfaces, this airplane has a spiral divergence, \"dutch roll,\" and a poorly damped long-period longitudinal oscillation. With the coupled tail surfaces, having a very moderate increase in static stability over that of the fixed surfaces, all of the above objectionable characteristics are eliminated, and the resulting airplane modes are shown be either aperiodic or damped periodic motion of a very short period.
\r\n\r\nThe application of such control surfaces to real airplanes appears to be feasible with little change in the design procedure. Several examples are given of coupled tail designs for different kinds of aircraft. The principle is also shown to be applicable to supersonic vehicles. The economic advantages of airplanes equipped with such stabilizers, together with the success of the analysis and test work to date, suggest that this device is worthy of further development and application to aircraft.
" }, { "name": "Lo, Shih-Chun", "degree": "PhD", "year": "1951", "title": "Oscillating Airfoil in Parallel Streams Separated by an Interface", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-100524", "creators": [ { "name": { "family": "Lo", "given": "Shih-Chun" }, "id": "Lo-Shih-Chun", "display_name": "Lo, Shih-Chun" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HR3R-5994", "abstract": "A new approach to tail buffeting is made by studying the problem of a thin airfoil performing a periodic oscillation of small amplitude in the presence of an interface across which the flow undergoes a constant change in density and velocity. A general solution to the problem is found. Lift and moment for some special cases are obtained in simple forms and are plotted in Figs. 3 and 4 for the two basic modes of oscillation: bending and torsion. A typical application to flutter analysis is made and it is found that tail flutter at low speeds is possible for the tail lying in the wake of the wing." }, { "name": "Lobdell, John Henry", "degree": "Engineering Degree", "year": "1951", "title": "Determination of Temperature in a Low Pressure Flame", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-114701", "creators": [ { "name": { "family": "Lobdell", "given": "John Henry" }, "id": "Lobdell-John-Henry", "display_name": "Lobdell, John Henry" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MTQ1-K461", "abstract": "The extended dimensions of a flame zone which result from reducing the ambient pressure below 10 mm. Hg provide possibility for detailed investigation of flame chemistry and thermodynamics. The present investigation constitutes the first part of a detailed survey of the temperature distribution in an oxy\u2014acetylene flame and describes the instrumentation and development of the modified Schmidt Technique for measuring flame temperature and the measurement of the maximum temperature in the flame.\r\n\r\nThe results indicate the maximum flame temperature to be within plus or minus 30\u00b0C. of the equilibrium flame temperature at 4.3 mm. Hg. The technique developed, while laborious, may be used to determine flame temperature with a good degree of accuracy.\r\n\r\nThe work was carried on with the financial support of the U. S. Army Ordnance Corps and the U. S. Air Force Air Materiel Command as part of a study of low pressure combustion under way at the Jet Propulsion Laboratory." }, { "name": "Michelson, Irving", "degree": "PhD", "year": "1951", "title": "I. On the Dust Devils. II. Linearized Theory of Conical Turbomachines", "advisor": "Stewart, Homer Joseph; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042009-142746", "creators": [ { "name": { "family": "Michelson", "given": "Irving" }, "id": "Michelson-Irving", "display_name": "Michelson, Irving" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "co-advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PZKM-9280", "abstract": "Dust devils are small-scale atmospheric motions of instability arising from the development of large thermal stratifications in the lowest layers above the surface of the earth. A theory is proposed in Part I to describe the conditions of formation of these motions and depends on the new result that shear provides a powerful stabilizing influence even in non-viscous fluid motions in which denser fluid is situated above less dense. Those features of the flow which can be predicted by the theory and compared with observations are found to be in reasonably good agreement, and it is therefore indicated that the theory, which is based on a highly simplified model of flow, furnishes at least a qualitatively correct correlation of the basic ideas involved in the stable flow of very slightly viscous fluids containing density inversions. Applications to technically interesting flows of this type, in large-scale atmospheric motions as well as in high speed aerodynamic boundary layers, are indicated but not analyzed in detail.\r\n\r\nIn Part II the perfect fluid flow is determined for a turbomachine of conical shape and prescribed blade loading. On the basis of the assumption that the stream surfaces are conical in shape, a linear, elliptic partial differential equation of the second order is obtained. The associated boundary value problem is of the Sturm-Liouville type and is solved completely. An asymptotic representation of the solution is determined which is convenient for computational purposes." }, { "name": "Monroe, Gerald Morgan", "degree": "PhD", "year": "1951", "title": "A Study of Compressible Perfect Fluid Motion in Turbomachines with Infinitely Many Blades", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182009-151729", "creators": [ { "name": { "family": "Monroe", "given": "Gerald Morgan" }, "id": "Monroe-Gerald-Morgan", "display_name": "Monroe, Gerald Morgan" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HQD3-G406", "abstract": "A study is made of compressible perfect fluid motion in turbomachines having infinitely many blades and a general theory is developed. An underlying concept of the theory is that force fields which represent the action of infinitely many blades belong to a special class described as pseudo-conservative and can be expressed as the product of a scalar function and the gradient of a potential. The scalar function is simply the rate at which energy is imparted to the fluid by the blades, and the potential is simply the family of the equations for the blade surfaces. The introduction of these two functions to express the force field casts an entirely new light on problems of mixed-flow turbomachines having infinitely many blades of arbitrary shape.\r\n\r\nIn the formulation of the problem the non-linear action of rotationality and compressibility is regarded as a force tending to displace the streamsurfaces from their irrotational, incompressible position. It is shown that the character of the problem is determined by a governing velocity: the velocity relative to the blades where blades are present, or the meridional velocity, where blades are not present. Where the governing velocity is subsonic the problem is essentially elliptic, where supersonic, hyperbolic.\r\n\r\nThe theory and the examples lead to conclusions which are believed to explain in part the unexpected efficiencies observed for compressors having transonic governing velocities. These conclusions, which indicate that transonic compressors could perhaps be profitably developed, are as follows: The deflection of the streamsurfaces induced by a given strength of vorticity at a certain point in the flow has one sense when the governing velocity at the point is subsonic, the opposite sense when it is supersonic, and becomes zero as it becomes sonic. The deflection of the streamsurfaces brought about by a given distribution of vorticity in a region is less when the governing velocity in the region is transonic than when it is entirely subsonic or entirely supersonic.\r\n\r\nExamples of incompressible flow through a mixed flow compressor with prescribed blades, and subsonic and transonic flow through actuator disks, were solved by the method of finite differences, applying simultaneously the relaxation technique and an iteration process." }, { "name": "Morgan, Antony John Andrew", "degree": "PhD", "year": "1951", "title": "A General Similarity Theory of Partial Differential Equations and its Use in the Solution of Problems in Aeronautics", "advisor": "Michal, Aristotle D.; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-091419", "creators": [ { "name": { "family": "Morgan", "given": "Antony John Andrew" }, "id": "Morgan-Antony-John-Andrew", "display_name": "Morgan, Antony John Andrew" } ], "advisors": [ { "name": { "family": "Michal", "given": "Aristotle D." }, "id": "Michal-A-D", "role": "advisor", "display_name": "Michal, Aristotle D." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Michal", "given": "Aristotle D." }, "id": "Michal-A-D", "role": "chair", "display_name": "Michal, Aristotle D." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9142-KZ49", "abstract": "A general similarity theory of systems of partial differential equations of any order in any number of independent variables is developed with the aid of the theory of continuous one-parameter groups of transformations. The theory is illustrated by means of several known examples of similarity equations, previously given without motivation, in Hydrodynamics. With the aid of the theory two new examples of similarity equations, one in Elasticity and one in Fluid Mechanics, have been found; these are discussed in the text.\r\n" }, { "name": "Nielsen, Jack Norman", "degree": "PhD", "year": "1951", "title": "Supersonic Wing-Body Interference", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252009-150359", "creators": [ { "name": { "family": "Nielsen", "given": "Jack Norman" }, "id": "Nielsen-Jack-Norman", "display_name": "Nielsen, Jack Norman" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E6Z2-SM31", "abstract": "A method of solving wing-body problems for circular bodies employing wings with supersonic edges has been developed. The method is based on decomposing the wing-body combination into a wing alone plus a number of Fourier component wing-body combinations corresponding to the Fourier series for the normal velocity induced at the body surface by the wing alone. The problem is then solved for each component by a method based on Laplace transform theory, and the method is then shown to be equivalent to a distributed-solution method analogous to that used by Karman and Moore to solve problems of bodies of revolution at supersonic speeds. Two sets of universal functions are presented. The first set is used to obtain the strength distribution of the fundamental solutions distributed along the body axis, from which the entire interference pressure field can be obtained. The second set permits a direct determination of the pressures acting on the body.\r\n\r\nAs an example in the use of the theory, calculations are carried out for the technologically important case of a flat rectangular wing mounted at zero incidence on a body at zero angle of attack. The calculations are carried out for four Fourier components. It was found that all four components were necessary to get good accuracy in determining the pressures at some points in the field, while only one component was required to get a fair determination of the span loading of the combination. From the example much insight into the mechanism of wing-body interference was obtained. The use of the universal functions to obtain pressures due to protuberances on nearly cylindrical bodies is discussed." }, { "name": "Norris, James Caspar", "degree": "Engineering Degree", "year": "1951", "title": "An Analysis of a Compound Pendulum Rocket Suspension", "advisor": "Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162009-142423", "creators": [ { "name": { "family": "Norris", "given": "James Caspar" }, "id": "Norris-James-Caspar", "display_name": "Norris, James Caspar" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YDS1-JW02", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis is an investigation of the equations of motion and physical parameters involved in stabilizing the initial flight of a vertically launched rocket by means of a booster rocket pin-connected below the main rocket. The system is designed to stabilize the flight in its early stage before the aerodynamic control surfaces become effective. Stability of the system is dependent on the pendulum action of the booster rocket.\r\n\r\nThe equations of motion were derived from Lagrange's generalized momentum equation. The differential equations thus obtained were not solved but were tested for stability by means of Routh's stability criteria. The ratio of the mass of the main rocket, M[subscript 1], to the mass of the booster rocket, M[subscript 2], was investigated for the two values [...] = 1.5 and [...] = 7.75.\r\n\r\nThe system involving a mass ratio [...] = 7.75 was found to be unstable under all conditions. However, the system involving a mass ratio [...] 1.5 was determined to be stable in the range 1.62 < \u03b2 < 4.54 x 10[superscript 10], where \u03b2 is defined as the ratio of the distance [...] from the center of gravity of the booster M[subscript 2] to the pin connecting the strut to the main rocket M[subscript 1], divided by the radius of gyration, k[subscript 2], of the booster M[subscript 2]. In this range, for any given value of, \u03b2, stability was uniquely determined by one value of the ratio \u03b1 = [...], where [...], is the length of the strut from the main rocket M[subscript 1] to the booster rocket M[subscript 2]. Thus, for a given booster, stability is primarily a function of the ratio [...], and for any given [...], is uniquely determined.\r\n\t\t\r\nAlthough the system was found to be theoretically stable for the mass ratio [...] = 1.5 , the ratio [...] turned out to be of such great magnitude as to make the system entirely impractical for this particular mass ratio." }, { "name": "Ostrander, Max Howell", "degree": "Engineering Degree", "year": "1951", "title": "Emissivity Calculations for Carbon Monoxide", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-062500", "creators": [ { "name": { "family": "Ostrander", "given": "Max Howell" }, "id": "Ostrander-Max-Howell", "display_name": "Ostrander, Max Howell" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7DDZ-WA46", "abstract": "The purpose of this report is to utilize a sound theoretical formulation combined with the best available experimental data on integrated absorption and rotational line-width, for the calculation of emissivities of carbon monoxide at room temperatures under conditions where overlapping between rotational lines is negligibly small.\r\n\r\nThe results of the present investigation indicate that calculated emissivities of carbon monoxide at room temperature are in excellent agreement with empirically observed data published by Hottel and Ullrich. The theoretical dependence of emissivity upon optical density at low optical density and at room temperature has been shown to follow the experimental observations almost exactly. For low optical densities the calculated emissivity is found to be nearly proportional to the assumed rotational line-width, thus emphasizing the need for accurate line-width determinations at all temperatures. The calculated dependence of emissivity on rotational line-width permits the determination of emissivity not only as a function of temperature, total pressure, and optical density, but also as a function of concentration of optically inert gas. For numerical calculations of this type it is necessary to obtain experimental data for the dependence of rotational line-width on the concentration of non- emitting gases.\r\n\r\nThe present calculations supplement earlier theoretical emissivity calculations, which are valid only at elevated total pressures where extensive overlapping of rotational lines occurs. The range of pressures in which overlapping between rotational lines is neither extensive nor negligibly small has been considered only very briefly and requires further examination." }, { "name": "Oswald, Telford Wilbert", "degree": "PhD", "year": "1951", "title": "The Influence of Variable Air Density and of Nonlinear Aerodynamic Characteristics on Dynamic Behavior at Supersonic Speeds", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242006-160420", "creators": [ { "name": { "family": "Oswald", "given": "Telford Wilbert" }, "id": "Oswald-Telford-Wilbert", "display_name": "Oswald, Telford Wilbert" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VG6Q-C753", "abstract": "The effect of the variable density of the Standard Atmosphere on the dynamic stability of a missile in vertical flight is considered. The analysis is restricted to small disturbances from steady rectilinear flight. The exponential decrease of density with altitude characteristic of the Standard Stratosphere is introduced into the equations of motion and a stability criterion for the dynamic behavior immediately following a small disturbance is found. Alternatively, a hyperbolic variation of density with altitude is used to approximate the Standard Atmosphere and the identical stability criterion is obtained.\r\n\r\nThe effect of non-linear pitching moment and lift variations with angle of attack on the dynamic response to a sudden change in angle of attack is considered. An approximate solution to the non-linear equation of motion is developed. Several numerical examples are considered, and the results of the approximate solution are compared with the very accurate results of numerical integration as well as the classical linearized solution. The effect of a non-linear moment curve on the determination of stability derivatives from flight test data is discussed in the light of these examples." }, { "name": "Parkinson, Geoffrey Vernon", "degree": "PhD", "year": "1951", "title": "Unit-Step Motion of a Wide Delta-Wing", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-090936", "creators": [ { "name": { "family": "Parkinson", "given": "Geoffrey Vernon" }, "id": "Parkinson-Geoffrey-Vernon", "display_name": "Parkinson, Geoffrey Vernon" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73TW-ZE47", "abstract": "The effect on a wide delta wing in supersonic flight of the sudden imposition of a small velocity perturbation normal to the plane of the wing is considered. The resulting pressure field on the wing is found in closed form in terms of elementary functions. The corresponding solution for the infinite swept wing with supersonic edges is obtained as a by-product, and for this the terms of the transient pressure coefficient are shown to have geometric significance. The force and moment coefficients are obtained by means of a method of descent, which simplifies the calculations and shows the nature of the dependence of these coefficients on the wing planform. Because of the short duration and moderate strength of the transient effects of the unit-step motion, it is considered to be of little practical importance. However, because of the simplicity of the solutions for the motion, it is also considered to be of possible theoretical value as a basis for Duhamel integration to obtain solutions for more general time-dependent motions of the wide delta wing." }, { "name": "Pounder, Edwin", "degree": "Engineering Degree", "year": "1951", "title": "Investigation of Blockage Effects on Circular Cylinders in a Two-Dimensional Wind Tunnel", "advisor": "Bell, Richard William", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-085215", "creators": [ { "name": { "family": "Pounder", "given": "Edwin" }, "id": "Pounder-Edwin", "display_name": "Pounder, Edwin" } ], "advisors": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-R-W", "role": "advisor", "display_name": "Bell, Richard William" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1F84-BB81", "abstract": "These investigations include some experimental and theoretical studies upon blockage effects in a two-dimensional wind tunnel. The shape chosen to represent a body in the tunnel is that of a circular cylinder since such a body will eliminate circulation as a variable and will produce large blockage effects.\r\n\r\nIn experimental studies, three cylinders of different size are tested in a two-dimensional tunnel. It is found that interference effects are of such a magnitude that it is impossible to obtain two-dimensional flow with the basic models. Two-dimensional flow is obtained through the use of separation devices, but a quantitative blockage study is not attained.\r\n\r\nThe theoretical work attempts to show the blockage effects of a two-dimensional tunnel upon a circular cylinder of arbitrary size with and without a wake. The potential flow theory is used throughout, and some correlations with the experimental data are indicated." }, { "name": "Rannie, William Duncan", "degree": "PhD", "year": "1951", "title": "Heat Transfer in Turbulent Shear Flow", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172004-135406", "creators": [ { "name": { "family": "Rannie", "given": "William Duncan" }, "id": "Rannie-William-Duncan", "display_name": "Rannie, William Duncan" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9G0F-9R87", "abstract": "A new and relatively simple description is proposed for the velocity profile in turbulent flow close to a smooth wall. Heat transfer coefficients are calculated from the description and are shown to agree better with experiment than other theories. The analysis is extended to transport processes in liquids where the viscosity has a large variation close to the wall.\r\n" }, { "name": "Skinner, George Tolmie", "degree": "Engineering Degree", "year": "1951", "title": "Mean-Speed Measurements in Two-Dimensional, Incompressible, Fully-Developed Turbulent Channel Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092015-140302816", "creators": [ { "name": { "family": "Skinner", "given": "George Tolmie" }, "id": "Skinner-George-Tolmie", "display_name": "Skinner, George Tolmie" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CGEH-Q720", "abstract": "Mean velocity profiles were measured in the 5\u201d x 60\u201d wind channel of the turbulence laboratory at the GALCIT, by the use of a hot-wire anemometer. The repeatability of results was established, and the accuracy of the instrumentation estimated. Scatter of experimental results is a little, if any, beyond this limit, although some effects might be expected to arise from variations in atmospheric humidity, no account of this factor having been taken in the present work. Also, slight unsteadiness in flow conditions will be responsible for some scatter.
\r\n\r\nIrregularities of a hot-wire in close proximity to a solid boundary at low speeds were observed, as have already been found by others.
\r\n\r\nThat K\u00e1rm\u00e1n\u2019s logarithmic law holds reasonably well over the main part of a fully developed turbulent flow was checked, the equation u/ut = 6.0 + 6.25 log10 yut/v being obtained, and, as has been previously the case, the experimental points do not quite form one straight line in the region where viscosity effects are small. The values of the constants for this law for the best over-all agreement were determined and compared with those obtained by others.
\r\n\r\nThe range of Reynolds numbers used (based on half-width of channel) was from 20,000 to 60,000.
\r\n" }, { "name": "Struble, Arthur Dewey", "degree": "Engineering Degree", "year": "1951", "title": "Preliminary Design Study of a Centrifugal Jet Engine with a Supersonic Propeller", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242009-083922", "creators": [ { "name": { "family": "Struble", "given": "Arthur Dewey" }, "id": "Struble-Arthur-Dewey", "display_name": "Struble, Arthur Dewey" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SXBW-F552", "abstract": "A theoretical analysis was made of an aircraft propulsion system incorporating a centrifuga1 jet engine and a supersonic propeller. The primary aim was to increase the economy of a jet configurated engine. The design for a supersonic propeller was included, since it was necessary to use a propeller, in order to create maximum thrust for the installation.\r\n\r\nThe engine unit consists of a rotating disc with an internal combustion flow channel using essentially the ram-jet cycle, and the design configuration embodied only three basic moving parts for the entire propulsion plant. The performance of the engine was treated as an aerodynamic and thermodynamic problem. Computations were made on the internal flow system covering the effects of all the variables. Then, using these results, specific engines were analyzed introducing pertinent losses. In general, the numerical calculations showed theoretically that this type of engine would have slightly better economy than a reciprocating engine and was far superior to a turbojet at an aircraft speed range down to low subsonic values.\r\n\r\nThe ana1yis for the supersonic propeller indicated that the author's design approach, which includes three dimensional effects, could theoretically produce completely supersonic blades with efficiencies above 80%. Computations were made on a 10' diameter propeller which would produce 7,500 pounds of thrust with an efficiency of 83.5% t an aircraft speed of Mach number 1. This power absorption could easily be doubled, while at cruising powers efficiencies ranged up to 86%." }, { "name": "Stuart, Jay William", "degree": "Engineering Degree", "year": "1951", "title": "Spectra of the Velocity Fluctuations in the Wake of Stalled Airfoils", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-115101", "creators": [ { "name": { "family": "Stuart", "given": "Jay William" }, "id": "Stuart-Jay-William", "display_name": "Stuart, Jay William" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0DKR-ZG89", "abstract": "During the last twenty years a considerable amount of work has been done in order to understand buffeting and the mechanism of the separated flow that causes it. In these investigations the results have either not been clear or they contain some unknown interaction between the indicating apparatus and the flow in the wake. In the present paper one type of the formerly observed flow configurations is investigated by using a properly compensated hot wire anemometer. This technique exhibits some of the results previously obtained but with greater significance and some added phenomena." }, { "name": "Walker, Donald Petrilla", "degree": "Engineering Degree", "year": "1951", "title": "An Experimental Investigations of the Oscillations of an Airfoil Near a Sharp Velocity Gradient", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-090843", "creators": [ { "name": { "family": "Walker", "given": "Donald Petrilla" }, "id": "Walker-Donald-Petrilla", "display_name": "Walker, Donald Petrilla" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5PMF-4R60", "abstract": "The purpose of this study was to make an experimental investigation of the effect of a sharp velocity gradient on the oscillations of an airfoil. This information is pertinent to the formulation of theories for predicting tail buffeting. The test equipment was designed to provide conditions corresponding as closely as possible to those based on the assumptions of Lo in his theoretical study of an oscillating airfoil in parallel streams separated by an interface.
\r\n\r\nBecause of the viscous nature of air, the assumptions of Lo could not be simulated sufficiently closely to permit an experimental check on his findings. The simulation, however, was adequate to provide for an experimental check on his fundamental point of view as an explanation of buffeting.
\r\n\r\nThe presence of the high speed flutter predicted by theory was verified. Variations in the flutter speed and flutter frequency were noted as the position of the sharp velocity gradient relative to the airfoil was shifted, but these variations were not considered significant.
\r\n\r\nA low speed oscillation was found which the evidence available indicated was due to periodic vortices formed in the flow by the experimental set-up used to create the velocity gradient. Limitations on the minimum operating speed of the wind tunnel precluded a thorough investigation of the lower speeds in the low range.
\r\n\r\nThe evidence found in this investigation, though not conclusive, indicates that buffeting is simply the response of an elastic system to a turbulent flow. No conclusive evidence was found to indicate that a sharp velocity gradient near an airfoil has any effect on the oscillations of the airfoil.
\r\n\r\nFurther investigation of the airflow created by the experimental set-up used is recommended in order to explain precisely the oscillation phenomena encountered.
\r\n" }, { "name": "Wylly, Alexander", "degree": "PhD", "year": "1951", "title": "A Second-Order Solution for an Oscillating, Two-Dimensional, Supersonic Airfoil", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-084121", "creators": [ { "name": { "family": "Wylly", "given": "Alexander" }, "id": "Wylly-Alexander", "display_name": "Wylly, Alexander" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YA8A-4R06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nIn this paper a second-order solution, for the forces and moments produced by an oscillating two-dimensional airfoil of arbitrary cross section, has been determined. This solution was obtained by means of an iteration procedure. In the iteration procedure it was necessary to have a linearized solution of simple, closed form which was valid throughout the whole x, y plane. Existing solutions did not satisfy these requirements, thus, it was first necessary to develop a new linearized or first-order velocity potential. This potential was developed as a power series approximation, in frequency, to the exact linearized solution. Six terms of this series were developed and this sixth-order solution shown to be within a few percent of the exact linearized solution for reduced frequencies [...] less than 1.3.\r\n\r\nThe first two terms of the series approximation were then used in the iteration process to produce the second-order solution in thickness. This solution which is valid to second-order in thickness and frequency has been determined for an oscillating airfoil of general cross section.\r\n\r\nThe second-order terms were found to have a relatively strong influence on the final solution, particularly for the pitching moment. It will be seen in Section V that in many cases the second-order terms are larger in magnitude than the corresponding first order-terms and thus reverse the tendencies indicated by first-order theory. In particular, it was shown that the theoretical instability predicted by linearized theory for an airfoil of zero thickness is completely eliminated for an airfoil having a thickness ratio as small as three percent." }, { "name": "Alperin, Morton", "degree": "PhD", "year": "1950", "title": "A Study of Detached Shock Waves in Two-Dimensions", "advisor": "Stewart, Homer Joseph; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-081306", "creators": [ { "name": { "family": "Alperin", "given": "Morton" }, "id": "Alperin-Morton", "display_name": "Alperin, Morton" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NW30-HY03", "abstract": "The present report contains results of an experimental and theoretical investigation of the detached shock wave phenomenon. The experimental phase of this study was actually carried out at the Jet Propulsion Laboratory at California Institute of Technology, in a two-dimensional wind tunnel which is briefly described in Section I.
\r\n\r\nSection II contains a description of the experiments on circular cylinders. The circular cylinder was used in this series of tests primarily because of its simplicity. The investigation discussed in II-1 required a large variation of model shapes and would have required much more time had it been based on a more complicated body shape. In addition to data on the shock wave position and shape, the pressure distribution was also obtained at M=1.546 for a two-dimensional circular cylinder. From this pressure distribution, the drag was calculated.
\r\n\r\nAlthough the theoretical knowledge of flow involving detached shock waves is in a rather primitive state, a review of the existing theoretical work and comparison with experimental data is made in section III.
\r\n\r\nIn section IV a method is presented for finding the stream function or velocity potential for the subsonic region behind the detached shock wave. This method depends upon the hypothesis that the flow can be considered to be irrotational in this region without introducing a serious error. The results appear to be in good agreement with the experiments although the example carried out does not apply strictly to the circular cylinder body shape used in the experiments.
\r\n\r\nA general discussion of the existing theories and their comparison with experimental data is presented in section V.
" }, { "name": "Ashkenas, Harry Israel", "degree": "Engineering Degree", "year": "1950", "title": "The Design and Construction of a Mach-Zehnder Interferometer for Use with the GALCIT Transonic Wind Tunnel", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232008-154118", "creators": [ { "name": { "family": "Ashkenas", "given": "Harry Israel" }, "id": "Ashkenas-Harry-Israel", "display_name": "Ashkenas, Harry Israel" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D0V1-MJ80", "abstract": "A Mach-Zehnder Interferometer has been designed and constructed for use in conjunction with the GALCIT Transonic Wind Tunnel. The instrument is to be utilized in making detailed density measurements of supersonic air streams. The design of the instrument is such that, contrary to general wind tunnel practice, both light beams of the interferometer traverse the test section of the wind tunnel in an effort to minimize boundary layer corrections. A detailed description of the instrument is presented, as well as a \u201ccook-book\u201d adjustment procedure. A discussion of the limitations of the instrument is included." }, { "name": "Barish, David Theodore", "degree": "Engineering Degree", "year": "1950", "title": "Acoustical Airspeed Indicators", "advisor": "Liepmann, Hans Wolfgang; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-083911", "creators": [ { "name": { "family": "Barish", "given": "David Theodore" }, "id": "Barish-David-Theodore", "display_name": "Barish, David Theodore" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FR7P-K372", "abstract": "Some of the problems associated with the applications of acoustical devices for the determination of airstream characteristics are considered in this study. The velocity and pressure fields for both point sound sources and finite sound sources in both subsonic and supersonic flow are discussed, with a view toward using sound waves for the determination of velocity, Mach number , temperature, and other properties of a flow.\r\n\r\nThe experimental investigations included the measurement of the spectra of ultra-audio-pressure pulsations, both static and total, in the small C.I.T. supersonic tunnel and also in the C.I.T. hypersonic tunnel. A broad range of Mach numbers and a variety of operating conditions were covered. The development of a modified Hartmann sound generator is described, and measurements of the sound field from this device in supersonic flow are included." }, { "name": "Barker, William Cyrus", "degree": "Engineering Degree", "year": "1950", "title": "A Formulation of the Problem of Distributed Vorticity in the Shock Wave Boundary Layer Interaction process", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01292009-153901", "creators": [ { "name": { "family": "Barker", "given": "William Cyrus" }, "id": "Barker-William-Cyrus", "display_name": "Barker, William Cyrus" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H3PW-QF74", "abstract": "The problem of shock wave boundary layer interaction is reviewed and attention focused upon the role of vorticity in the process. In order to simplify the physical considerations the two phenomena exhibited by vorticity in the interaction process-reflection and refraction of the disturbance, and transport of the vorticity from its original distribution - are divorced from one another. The reflection and refraction process is then considered apart from the other, and it is found that a boundary value problem can be formulated for it and formally solved for small perturbations from the undisturbed flow.\r\n\r\nThe perturbation component, which is associated with the pressure variation over the bounding surface, is set up and carried through to a point involving evaluation of a contour integral. This integral is so complex that its analytical evaluation would require many months of effort, and at this point it is thought that a re-examination of the original problem would be in order.\r\n\r\nAlthough numerical results would be desirable, the effort expended would have to be weighed against their relative contribution to an understanding of the overall problem." }, { "name": "Benscoter, Stanley Urner", "degree": "PhD", "year": "1950", "title": "Secondary Stresses in Thin-Walled Beams with Closed Cross-Sections", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-084840", "creators": [ { "name": { "family": "Benscoter", "given": "Stanley Urner" }, "id": "Benscoter-Stanley-Urner", "display_name": "Benscoter, Stanley Urner" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XKAT-E346", "abstract": "An accurate method of determining secondary stresses in thin-walled, uniform beams of closed cross-section is herein presented. The cross-sections are assumed to be preserved by closely spaced rigid diaphragms. In part I the integro-differential equation governing axial displacements is formulated and solved for a beam without longitudinal stiffeners. In Part II the corresponding summation-difference equation is developed and solved for a beam with stiffeners (flanges and stringers). The cross-section, loading distribution and end conditions are assumed to be arbitrary.\r\n\r\nBy introducing generalized difference equations the mathematical analysis for the stiffened beam may be performed in a manner exactly analogous to the process used for the unstiffened beam. A separation of variables in the homogeneous equation leads to the natural stress or displacement modes for a cross-section. The solution of the non-homogeneous equation is then expressed as an expansion in terms of the natural stress modes. Particular attention is given to cross-sections with single symmetry and double symmetry." }, { "name": "Bryan, William Cleveland", "degree": "Engineering Degree", "year": "1950", "title": "Experimental Investigation of Detached Shock on a 70\u00b0 Cone at Various Angles of Attack", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042009-100038", "creators": [ { "name": { "family": "Bryan", "given": "William Cleveland" }, "id": "Bryan-William-Cleveland", "display_name": "Bryan, William Cleveland" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XAZW-8051", "abstract": "The results of an experimental investigation into the variation of the shock wave shape and the extent of the subsonic region behind the shock with varying angle of attack at various Mach numbers are summarized. All tests are made on a finite 70\u00b0 cone. The main interest is centered on those Mach numbers which are low enough to produce detached shocks or for which the possibility of detachment exists for increasing angles of attack.\r\n\r\nThe angles of attack for which the investigation is made are 0\u00b0, 3\u00b0, 6\u00b0, 9\u00b0, 12\u00b0 and 15\u00b0. The Mach numbers considered are 1.438, 1.544, 1.584, 1.857, 1.986, and 3.01.\r\n\r\nIt is found that, for increasing angles of attack at constant Mach numbers, the extent of the subsonic region increases behind the lower shock and decreases behind the upper shock. A subsonic region appears at increased angle of attack for two of the Mach numbers for which the shocks are initially attached. There is also quite definite interaction between the upper and lower portions of the shock which tends to inhibit both the appearance of a subsonic region after the shock on the one hand and the disappearance of it on the other." }, { "name": "Chang, Chieh-Chien", "degree": "PhD", "year": "1950", "title": "The Linearized Wing Theory of the Supersonic Flow with the Karman's Fourier Integral Method", "advisor": "von K\u00e1rm\u00e1n, Theodore; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042009-110100", "creators": [ { "name": { "family": "Chang", "given": "Chieh-Chien" }, "id": "Chang-Chieh-Chien", "display_name": "Chang, Chieh-Chien" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/67DX-1V06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I gives a short introduction and some physical interpretation of von armAn's Fourier integral method applied to the supersonic wing theory. A short review of other current contributions to the Linearized supersonic wing theory is also given.\r\n\r\nPart II presents the general formulation of the von [...] method from the view-point of the elementary harmonic sources and doublets. First, the disturbance potential and the velocity components of a general flat body with symmetrical airfoil are derived. Next, the disturbance potential of the lifting surface is presented. In contrast to the well-known conical flow method, the von [...] Fourier integral method can treat a complicated plan-form as a whole, without considering the detailed geometry, as long as the airfoil sections are similar.\r\n\r\nPart III applies the method to the investigation of the wave drag of the non-lifting wing in supersonic flight. A general solution of the wave drag is obtained for the wing with a diamond- shaped airfoil. This solution allows a free choice of a number of the important geometrical parameters. For instance, the wing may be swept forward or backward, tapered or reversed tapered to any ratio. A number of the limiting cases are also investigated. For the practical aerodynamic problems, two useful families of wing plan-form with the fixed taper ratios 0.2 and 0.5, any swept angle, aspect ratio and Mach number are shown in the graphs. A particular application is demonstrated.\r\n\r\nThe reversed flow theorem on wave drag as shown by von [...] and Hayes checks well with the consequence of the general solution. This method shows a certain elegance as no conical flow assumption is needed, and the mathematics is powerful enough to obtain a general solution covering all possible geometrical arrangements without detailed considerations.\r\n\r\nWhile in recent years, the direct problem of finding the lift distribution with given angle of attack on the wing has been well solved by the method of conical flow and others, the present treatment in Part IV, on the other hand, investigates the inverse problem, i.e., to find the downwash distribution in the plane of the wing with a pre- assigned lift distribution. This is particularly favorable with the present method. The general solution of the downwash of the tapered swept wings is derived for the case that a constant lift distribution on the wing is pre-assigned. Of course, the method may be applied to any lift or pressure distribution along the wing chord and span. The corresponding angle of attack on the wing and the downwash can be determined everywhere in the plane of the wing. To demonstrate the downwash distribution as given by the general solution, graphs are given to show the downwash of a number of wings including a swept-back tapered wing with supersonic trailing edge and a delta wing.\r\n" }, { "name": "Chase, Patrick Stanley", "degree": "Engineering Degree", "year": "1950", "title": "Flexible Plate Supersonic Wind Tunnel Flow Correction to Account for Plate Elastic Properties", "advisor": "Puckett, Allen E.; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242009-093505", "creators": [ { "name": { "family": "Chase", "given": "Patrick Stanley" }, "id": "Chase-Patrick-Stanley", "display_name": "Chase, Patrick Stanley" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EC0T-P917", "abstract": "A method of correcting the static pressure distribution in the working section of a supersonic wind tunnel with flexible nozzle walls is investigated, in order to account for the discrepancy between the theoretical nozzle wall shape and the actual wall shape due to its elastic properties.\r\n\r\nThe method of correction is described and an example for an existing wind tunnel is carried out. It is shown that the method of correction is not successful due to the inadequate accuracy of the data from physical measurements and due to the nature of the equations which must be solved. While the former difficulty could possibly be avoided, the latter is considered to be inherent in the method.\r\n\r\nSuggestions and criticisms are offered and some results of the investigation regarding correction of the actual wind tunnel static pressure distributions are mentioned." }, { "name": "Chuang, Feng-Kan", "degree": "PhD", "year": "1950", "title": "On the Statistical Theory of Turbulence", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-154021", "creators": [ { "name": { "family": "Chuang", "given": "Feng-Kan" }, "id": "Chuang-Feng-Kan", "display_name": "Chuang, Feng-Kan" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2TJM-BK44", "abstract": "The present work starts with a study of isotropic turbulence which was introduced by G. I. Taylor in 1935. The different notions of averages are critically examined. The notion of stochastic average is then introduced and the general transport equation is developed. After a detailed study of kinematics of turbulence, the concept of correlation and spectrum, the correspondence between the Karman-Howarth equation and the spectrum equation is made. The turbulence decay is studied. A theory for turbulence decay at large Reynolds number is proposed. In the study of turbulence spectrum, different assumptions on the transfer function are critically discussed and the solution using Heisenberg's assumption is obtained explicitly. The spectrum is further studied by trying to fit the turbulence phenomenon into a general scheme of stochastic processes. In the second part of the work, an entirely different approach to the statistical theory is made. Linearized vorticity transport theory is developed and finally the non-linear effects in turbulence are studied." }, { "name": "DeGroff, Harold Miller", "degree": "PhD", "year": "1950", "title": "Aerodynamic Forces on a Propeller in Non-Stationary Motion", "advisor": "Stewart, Homer Joseph; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-083100", "creators": [ { "name": { "family": "DeGroff", "given": "Harold Miller" }, "id": "DeGroff-Harold-Miller", "display_name": "DeGroff, Harold Miller" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "chair", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DYT6-1W82", "abstract": "The non-stationary lift and moment of an oscillating propeller blade element are determined. The solutions are obtained in the form of double definite integrals which are evaluated for one numerical example in Appendix A.
\r\n\r\nThe three-dimensional nature of the problem is accounted for by determination of the induced velocity field due to an approximate vorticity distribution in the propeller wake. The corresponding blade element circulation is calculated by means of the classical Munk integral theorem. The two dimensional results for non-stationary lift and moment, expressed in terms of the circulation, are then used to obtain the results of this paper. Derivations of the lift and moment equations are included.
\r\n\r\nThe resultant forces on the blade element are resolved into thrust and torque. Also, a qualitative discussion of the effects of compressibility is made based upon the Prandtl-Glauert transformation.
\r\n\r\nFinally, the results are compared with two dimensional theory and a discussion of the application to problems of flutter and forced oscillations of propellers is made. The discussion is illustrated by means of the numerical example.
\r\n" }, { "name": "DeLauer, Richard Daniel", "degree": "Engineering Degree", "year": "1950", "title": "Aerodynamic Characteristics of a Wedge and Cone at Hypersonic Mach Numbers", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechThesis:09292023-233404349", "creators": [ { "name": { "family": "DeLauer", "given": "Richard Daniel" }, "id": "DeLauer-Richard-Daniel", "display_name": "DeLauer, Richard Daniel" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rndh-4a17", "abstract": "The problem of predicting the aerodynamic characteristics of configurations at hypersonic Mach numbers has been unreliable due to the lack of experimental data.
\r\n\r\nBy predicting the aerodynamic characteristics of a wedge and cone at Mach numbers from 2 to 12 by four different supersonic theories, a basis for future experimental comparison was provided.
\r\n\r\nAn attempt was made to correlate the theoretical result of a 20\u00b0 wedge and cone with wind tunnel test results of the same configuration. However, due to scheduling difficulties the experimental phase was not completed in time enough to be included in this report.
\r\n\r\nThe theoretical results indicate that the hypersonic similarity solution gives close agreement with the exact solution for large Mach numbers. The linearized and second order theory deviates from the exact solution for Mach numbers greater than 3.
" }, { "name": "Frick, Leo Francis", "degree": "Engineering Degree", "year": "1950", "title": "Experimental Investigation of Detached Shock on a 70\u00b0 Cone at Various Angles of Attack", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122009-125456", "creators": [ { "name": { "family": "Frick", "given": "Leo Francis" }, "id": "Frick-Leo-Francis", "display_name": "Frick, Leo Francis" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D4TV-0W57", "abstract": "An experimental investigation was made to determine the variation of shock shape and extent of subsonic region behind the shock wave with angle of attack for a 70\u00b0 cone at various Mach numbers. The main interest was centered on those Mach numbers which produced detached shock waves or for which the possibility of detachment at angle of attack existed.\r\n\r\nThe tests were conducted in the GALCIT 2.5\" Supersonic Wind Tunnel at angles of attack of 0\u00b0, 3\u00b0, 6\u00b0, 9\u00b0, 12\u00b0, and 15\u00b0 and Mach numbers of 1.438, 1.544, 1.584, 1.857, 1.986, and 3.01.\r\n\r\nIt was found that, with increasing angle of attack and constant Mach number, the subsonic region behind the shock wave increased in the lower portion and decreased in the upper portion. With increasing Mach number the subsonic region decreased for all angles of attack. Interaction between the upper and lower portions of the shock wave affects the subsonic region behind the wave, suppressing its appearance on the upper surface, retarding its disappearance from the lower surface." }, { "name": "Froehlich, Jack Edward", "degree": "PhD", "year": "1950", "title": "Non-Stationary Motion of Purely Supersonic Wings", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122009-155907", "creators": [ { "name": { "family": "Froehlich", "given": "Jack Edward" }, "id": "Froehlich-Jack Edward", "display_name": "Froehlich, Jack Edward" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FCGZ-7P23", "abstract": "A general theory is presented for the calculation of the total forces acting on purely supersonic wings. The method applies to wings having an arbitrary downwash distribution (stationary or non-stationary) and is valid whenever all of the wing edges are supersonic. The general three-dimensional non-stationary problem is reduced to an equivalent two-dimensional problem. In the case of harmonic oscillations the aerodynamic coefficients are expressed in terms of known or tabulated functions. The specific example of an oscillating delta wing is considered and values of the aerodynamic coefficients for plunging, pitching, and rolling oscillations are calculated for two Mach numbers." }, { "name": "Geisberg, Ralph Lewis", "degree": "Engineering Degree", "year": "1950", "title": "Transient Analysis Methods for Determining the Longitudinal Stability Derivatives of a Submerged Body from Free Flight Tests", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052009-152837", "creators": [ { "name": { "family": "Geisberg", "given": "Ralph Lewis" }, "id": "Geisberg-Ralph Lewis", "display_name": "Geisberg, Ralph Lewis" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "chair", "display_name": "Williams, Max L." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H9NV-2777", "abstract": "The stability derivatives obtainable from dynamic free flight tests are determined. Methods for reducing flight test data to the form of stability derivatives using the Fourier integral and the Laplace transform are developed." }, { "name": "Kane, John Clarence", "degree": "Engineering Degree", "year": "1950", "title": "Correlation of Fatigue Data to Determine Stress Concentration Factors in 76s-T Aluminum Alloys", "advisor": "Sechler, Ernest Edwin; Hudson, Donald E.; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092009-081322", "creators": [ { "name": { "family": "Kane", "given": "John Clarence" }, "id": "Kane-John-Clarence", "display_name": "Kane, John Clarence" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FHCF-VX77", "abstract": "The purpose of this study was to determine the stress concentration factor in a shoulder under a cyclic tensile load. The test specimens were models of a propeller blade root section similar to the blade design now employed in the fans of the Cooperative Wind Tunnel. All specimens were given a 5 microinch finish and all were made of 76S-T aluminum alloy taken from an actual propeller blade forging. Two series of tests were conducted. One series consisted of a cyclic tensile load varying from zero to maximum over a nominal stress range from 21,000 psi to 28,000 psi. The other series consisted of a cyclic load, wherein the amplitude of the cyclic stress was varied from 20 to 50 percent of the maximum developed stress. These two conditions would correspond respectively to the \"start-stop\" cycle of wind tunnel operation and to constant speed tunnel operation.
\r\n\r\nIt was found that the stress concentration factor determined from the fatigue test results closely approximated the results obtained from the three dimensional static tests of the actual blade.
\r\n\r\nThis work was carried out by the authors at the Guggenheim Aeronautical Laboratory, California Institute of Technology, under the supervision of Dr. E. E. Sechler.
\r\n" }, { "name": "Li, Ting-Yi", "degree": "PhD", "year": "1950", "title": "Periodic Supersonic Motions of a Thin Wing of Finite Span", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172009-110456", "creators": [ { "name": { "family": "Li", "given": "Ting-Yi" }, "id": "Li-Ting-Yi", "display_name": "Li, Ting-Yi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZX8-E374", "abstract": "The present paper supplies some general theorems with which periodic supersonic motions of a thin wing of fairly general planform may be analyzed to yield valuable three-dimensional results. It is shown that the method developed by Evvard (Refs. 1,2) for treating the steady supersonic motion of a thin wing with subsonic leading or side edges is valid for an oscillating wing of similar planform. Illustrations of the application of these general theorems are furnished by a careful study of several types of periodic oscillations of a rectangular wing. The present report includes a complete analysis for the case of plunging oscillations. Important steps have also been taken towards solution of the cases of pitching and rolling oscillations. The essential results are presented in a number of vector diagrams giving the magnitudes and phase angles of the lift and moment. Computations are made for several aspect ratios at two Mach numbers (M=10/7,2) when the reduced frequency (k) ranges from 0 to 2.0. It is found that the lift and moment vectors acting on a rectangular wing with supersonic plunging oscillations have positive phase angles within certain ranges of Mach numbers and aspect ratios, while the corresponding vectors acting on a wing of infinite span with the same kind of motion have negative phase angles for every Mach number. This new discovery indicates strongly the necessity of revising present day wing flutter calculations.\r\n" }, { "name": "Lurie, Harold", "degree": "PhD", "year": "1950", "title": "Lateral Vibrations as Related to Structural Stability", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-131041", "creators": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-Harold", "display_name": "Lurie, Harold" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0P9M-XM21", "abstract": "The apparently different physical problems of lateral vibration and elastic stability are limiting cases of a single phenomenon, the most general expression being the mode of vibration with end thrust. The theory of straight beams and flat plates is discussed in detail, and it is shown that the square of the frequency of lateral vibration is approximately linearly related to the end load. The linear relationship is exact if the mode of free vibrations is identical to the buckling mode. In all cases, the load corresponding to zero frequency is the critical buckling load. The analysis is valid only if the boundary conditions do not change with load.\r\n\r\nExperimental tests were conducted on elastically restrained columns in the form of rigid rectangular frames. It is found that the relationship between the square of the frequency and the load is practically linear, and that the extrapolated load corresponding to zero frequency coincides with the buckling load. Determining the critical load by frequency measurements seems to have the advantage of predicting that load corresponding to the actual boundary conditions which prevail, whereas a theoretical calculation may unjustifiably assume certain conditions which are not exactly realized.\r\n\r\nIn the case of flat plates, tests showed that the linear relationship is not achieved in practice. It is shown that this is probably due to the fact that the linear plate equations are not valid due to initial curvatures in the plate.\r\n\r\nRigid-joint trusses were also tested. Due to the change of end restraint with load, in some cases the relationship between the square of the frequency and the load deviates considerably from linearity. The amount of deviation appears to depend on the section properties of the members of the truss." }, { "name": "Martin, Harold Clifford", "degree": "PhD", "year": "1950", "title": "Elastic Instability of Cantilever Struts Under Combined Axial and Transverse Forces at the Free End", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-130215", "creators": [ { "name": { "family": "Martin", "given": "Harold Clifford" }, "id": "Martin-Harold-Clifford", "display_name": "Martin, Harold Clifford" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F3YJ-3D63", "abstract": "This investigation considers the elastic instability of cantilever struts under applied axial and transverse forces at the free end. Fig.1 shows the general case of such a strut.\r\n\r\nFirst the strut of uniform depth and without sweep is studied. This is shown in Fig. 2. A derivation is given for the governing differential equation and boundary conditions. These are then solved for the minim coupled eigenvalues, which correspond to the critical load combinations. Fig. 10 is a plot of these calculated critical loadings.\r\n\r\nNext an experimental investigation, whose main purpose was to provide a check on the above theoretical calculations, is presented. Various difficulties are discussed in addition to the techniques finally adopted. Experimental values are shown to check theory within several per cent. See Fig. 16. Also Southwell\u2019s experimental procedure for determining instability loading is shown to apply to this case of coupled loading.\r\n\r\nThe theory is then extended to include the problem of the tapered strut. Equations and boundary conditions are given for the arbitrary taper case and a solution presented for the limiting strut having complete taper. These results are given in Fig. 24.\r\n\r\nIn the concluding Part some of the more important unsolved problems are discussed in detail. These include the strut with arbitrary taper, the swept strut, and the strut which buckles inelastically.\r\n\r\nThe Appendix derives the differential equation for the non-tapered strut by variational procedure." }, { "name": "Matzdorff, Roger Edward", "degree": "Engineering Degree", "year": "1950", "title": "Castable Plastics in Photoelastics Stress Analysis", "advisor": "Sechler, Ernest Edwin; Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02182009-112040", "creators": [ { "name": { "family": "Matzdorff", "given": "Roger Edward" }, "id": "Matzdorff-Roger-Edward", "display_name": "Matzdorff, Roger Edward" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1CAZ-4A36", "abstract": "An investigation was begun on the feasibility of utilizing castable, thermosetting plastics in experimental stress analysis by means of either photoelasticity or electrical strain gages imbedded in the plastic.\r\n\r\nThe first phase of the study was the development of a casting technique that would give a stress free casting suitable for photoelastic work. This was considerably complicated by the inherent shrinkage which occurs during the polymerization of the plastic. A good method was found for casting solid models, and a workable method was devised for casting hollow section models.\r\n\r\nThe second phase constituted the development and evaluation of the optimum physical properties of a resin known as Castolite. The results were encouraging with the exception that the strain creep was excessive. The rate of creep, however, is slow and it is possible to use the material for two dimensional photoelasticity with results comparable to those obtained from other photo-elastic materials. The desirable features are a very low optical creep, stress-strain and stress-fringe number curves that are linear for constant loading time, no time-edge stress effects, chemical stability under high temperatures, modulus of elasticity of 600,000 psi, and a fringe value of 175 psi per in-fringe in tension.\r\n\r\nAn additional feature is the ability to bond two or more cured plastic pieces together with the liquid plastic itself. The strength of the bonded area is equal to the rest of the structure.\r\n\r\nThree dimensional frozen stress properties were not determined, but there is evidence that the resin would be suitable." }, { "name": "Oliver, Robert Norris", "degree": "Engineering Degree", "year": "1950", "title": "Experimental Determination of Accommodation Coefficients as Functions of Temperature for Several Metals and Gases", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092009-080824", "creators": [ { "name": { "family": "Oliver", "given": "Robert Norris" }, "id": "Oliver-Robert-Norris", "display_name": "Oliver, Robert Norris" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MDBN-3R17", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe accommodation coefficients for the gases and metals tested vary rapidly in the range where the gas temperature is within approximately 50\u00b0C of the filament temperature.\r\n\r\nWhen the temperature excess becomes large, the [...] of argon, nitrogen and helium on platinum is approximately .7, .5 and .2, respectively, and on tungsten approximately .5, .35 and .15, although the actual value depends upon both filament and gas temperature.\r\n\r\nVariation in pressure up to 150 microns was found to have a negligible effect on [...].\r\n\r\nAll gases and metals tested gave smooth curves of [...] versus temperature except helium on tungsten at a gas temperature of 80\u00b0 K., which exhibited a sharp discontinuity at a filament temperature of approximately 225\u00b0 K. and a pressure of 34 microns." }, { "name": "Rasof, Bernard", "degree": "PhD", "year": "1950", "title": "Supersonic Source Flow Past Thin Air Foils", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052009-084956", "creators": [ { "name": { "family": "Rasof", "given": "Bernard" }, "id": "Rasof-Bernard", "display_name": "Rasof, Bernard" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NCKK-3A63", "abstract": "In this thesis the supersonic source flow over a thin sharp- edged airfoil is formulated as a linearized problem. A new potential equation is derived, using a system of spherical coordinates centered at the source; as a simplification only wings symmetrical about the z axis are considered, and of these only the limiting cases of ring- and annular- airfoils are treated.
\r\n\r\nAfter transforming to characteristic coordinates in the hodograph plane, the potential equation (which has variable coefficients) is shown to be approximated by two classical equations -- one holding for the ring wing and the other applying to the annular wing. The flow over a specific annular wing is computed by en application of the Riemann method to the telegraph equation, which is the appropriate approximation to the governing equation for this case.
\r\n\r\nThe linearized potential equation is also solved by the Method of Characteristics, using a numerical equivalent of the Mono, procedure for quasilinear partial differential equations. A complete set of compatibility equations is exhibited, allowing the computation of the perturbation velocity components at any point of the zone of influence of an airfoil set in the supersonic source flow. Two numerical examples are presented, illustrating the application to the computation of the flow over each of a ring- and annular- wing.
\r\n\r\nFinally in an appendix the usually powerful method of separation of variables is shown to be unsuitable as a procedure for solving the potential equation governing the present problem.
\r\n" }, { "name": "Rowney, James Victor", "degree": "Engineering Degree", "year": "1950", "title": "Application of the Ram Jet to Vertical Ascent", "advisor": "Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112009-094718", "creators": [ { "name": { "family": "Rowney", "given": "James Victor" }, "id": "Rowney-James-Victor", "display_name": "Rowney, James Victor" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DRA1-DS60", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\t\r\n\r\nThe purpose of this paper is to investigate the applicability of the ramjet to replace the first step of a two-step or multi-step rocket, with the hope of increasing the efficiency and performance of vertical ascent missiles of the present day. The ramjet is considered as a booster motor to boost the primary missile through the atmosphere. It is to be discarded from the primary missile after reaching its maximum velocity. To boost the ramjet to operating speed the second stage rocket must be operated for the first few seconds as a ducted rocket.\r\n\r\nGeneral ramjet performance is calculated graphically by using a step-by-step integration process to solve the differential equation of motion. The resulting flight velocity, fuel consumption per initial weight, and altitude are presented graphically in terms of time after launching the ramjet. It is assumed throughout the problem that gravity is constant and that the altitude necessary to start the ramjet is negligible. The acceleration of the missile is limited to 25 g's.\r\n\r\nImportant results present in this paper are: The most important factor that limits the performance of the ramjet is the air density ratio. The greatest increase in second-step launching altitude, by improved thrust and drag coefficients and increased ramjet cross-section area, is achieved at low ramjet launching velocities. The performance of the ramjet missile operating at a specific fuel consumption of .0007 [...] shows a marked increase of efficiency over a missile using a higher fuel consumption value. Missiles using a lower specific fuel consumption value, of the same order as the increased value, show negligible improvement in efficiency. When ramjet performance is compared to rocket performance; specifically, maximum velocity, altitude of maximum speed and altitude attained, the ramjet missile will burn only one third of the fuel required by a two-step rocket. Conversely, for the same fuel consumed, the ramjet missile will attain 65% more altitude than the two-step rocket." }, { "name": "Scherer, Lee Richard", "degree": "Engineering Degree", "year": "1950", "title": "Aerodynamic Characteristics of a Wedge and Cone at Hypersonic Mach Numbers", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112009-150520", "creators": [ { "name": { "family": "Scherer", "given": "Lee Richard" }, "id": "Scherer-Lee-Richard", "display_name": "Scherer, Lee Richard" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/29PE-XX71", "abstract": "Up to the present time, the reliability of the determination of aerodynamic characteristics at hypersonic Mach numbers by theoretical calculations has been unknown due to the lack of experimental data. This report is the calculations of these characteristics by four different theories of a wedge and a cone over a range of Mach numbers from 2 to 12.\r\n\r\nCorrelation of these results with wind tunnel tests was not possible due to scheduling difficulties of the hypersonic wind tunnel; therefore, this report is designed to serve as the basis for comparison of future hypersonic experiments.\r\n\r\nFrom correlation of the various theories it is found that the closest agreement to the exact theory at hypersonic speeds is given by the hypersonic similarity theory. Above Mach numbers of about 3, the first and second order theories deviate considerably from the exact theory." }, { "name": "Schmidt, Louis Vincent", "degree": "Engineering Degree", "year": "1950", "title": "Investigation of Blockage Effects from Flow About Circular Cylinders in a Two-Dimensional Wind Tunnel", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302010-144157909", "creators": [ { "name": { "family": "Schmidt", "given": "Louis Vincent" }, "id": "Schmidt-Louis-Vincent", "display_name": "Schmidt, Louis Vincent" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1NSH-2G22", "abstract": " In these investigations a study of the blockage effects encountered in wind tunnel testing was made. Emphasis was placed on obtaining perceptible values of wake blockage in order to check the reliability\r\nof approximate derivations that are based on the assumption of small wakes. A bluff body (circular cylinder) was chosen for these investigations since it develops a pronounced wake. Three cylinders of varying size were employed in order to obtain a variation in the magnitudes of the blockage effects.\r\n\r\n The combined influence of surface irregularities such as static pressure orifices and the vertical walls resulted in the flow over the cylinders exhibiting three-dimensional characteristics. An investigation of these effects was conducted in order to determine means of circumventing three-dimensional characteristics. Two-dimensional flow characteristics were realized after the point of flow separation on the aft portion of the cylinder was made uniform in the spanwise direction. This was accomplished by means of separation strips fastened to the cylinder forward of the point of maximum thickness.\r\n\r\n After the realization of two-dimensional flow characteristics in the test section, the original purpose of the test was carried out to a limited extent. Experimental measurements of wake blockage effects were compared with the predicted values that are based on approximate derivations for cases where comparison could be made." }, { "name": "Shepherd, John Tyler", "degree": "Engineering Degree", "year": "1950", "title": "Correlation of Fatigue Data to Determine Stress Concentration Factors in 76S-T Aluminum Alloys", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-03062009-160046", "creators": [ { "name": { "family": "Shepherd", "given": "John Tyler" }, "id": "Shepherd-John-Tyler", "display_name": "Shepherd, John Tyler" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XMFM-KC84", "abstract": "The basic problem of this particular investigation was to determine the stress concentration factors present at a shoulder in the root section of a model propeller blade manufactured from 76S-T aluminum alloy. The particular geometric section considered is found in the type propeller blades such as will be installed soon in the Southern California Cooperative Mind Tunnel, Pasadena, California. These blades were manufactured from forgings of 76S-T by the Hamilton Standard Propeller Division of the United Aircraft Corporation. Stress concentration factors were determined for what will be called the \"critical section\" of the blade. This section is understood to mean the cross section of minimum area which is located immediately above the stress-raising fillet at the junction of the blade itself and the root flange.\r\n\r\nA secondary purpose of the investigation was to correlate these data with two other experiments that had already been carried out for this particular blade shape. These earlier experiments determined the magnitudes of surface stresses in the critical section, one utilizing a full-scale, three-dimensional model, and the other a two-dimensional full scale model one inch thick. Both of these experiments utilized static tension loads, the loads being applied over the upper surface of the flange, exactly as they are assumed to act when the blade is rotating in the wind tunnel. Also, an attempt was made to compare the data obtained in this investigation with other fatigue tests of a more general nature.\r\n\r\nThe tests made in this present investigation were all of a fatigue nature, in which one-tenth scale models of the actual blade were used as fatigue specimens. Two types of loading were used. The first consisted of a cyclic loading between varying upper tension limits to zero stress, and the second consisted of a constant upper tension stress limit with varying minimum stresses.\r\n\r\nTests were conducted using an upper tension nominal stress limit of approximately 28,000 psi and were extended to tension stresses of lower values which gave a fatigue life of more than 15,000,000 cycles. Due to the slow rate of loading (2,500,000 per day) in the Sonntag Universal Fatigue Testing Machine, the investigation was not continued to the generally accepted value of 500,000,000 cycles which marks the upper cyclic limit of fatigue investigations.\r\n\r\nIt was found that stress concentration factors determined from this type of fatigue testing came surprisingly close to those determined from the full-scale, three-dimensional, static tests.\r\n\r\nThe selection of the type loadings used was not entirely arbitrary. The stress cycle, which varied from zero to a peak tension value and then to zero again, would closely simulate the loadings in a start-stop cycle; while the superposition of a cyclic stress upon a steady tension load would result in approximately the type of loading experienced by the blade when it was rotating at a constant angular speed under aeroelastic axial forces." }, { "name": "Staros, Basil", "degree": "Engineering Degree", "year": "1950", "title": "Investigation of Effect of Energy Dissipation Behind a Detached Shock Wave on Total Head Measurements", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-092800", "creators": [ { "name": { "family": "Staros", "given": "Basil" }, "id": "Staros-Basil", "display_name": "Staros, Basil" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TQG5-4092", "abstract": "The flow field behind a detached shock wave, created by a blunt body in a supersonic air stream, is analyzed with respect to energy dissipation through the action of viscosity in the fluid stress field near the axis of symmetry. This energy dissipation is related to the rise in entropy, and consequently to the additional drop in reservoir pressure beyond that given by the Rayleigh pilot tube formula. The method is applied to the calculations of an apparent defect in reservoir pressure, for more precise calculations of free stream Mach numbers using total head tube measurements." }, { "name": "Wechsler, Joseph Wolff", "degree": "Engineering Degree", "year": "1950", "title": "An Investigation of the Application of the Rayleigh-Ritz Method to the Deflection of a Small Aspect Ratio Swept Plate of Uniform Thickness", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-153457", "creators": [ { "name": { "family": "Wechsler", "given": "Joseph Wolff" }, "id": "Wechsler-Joseph-Wolff", "display_name": "Wechsler, Joseph Wolff" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JSWQ-0P95", "abstract": "An investigation was initiated to examine the possibility of improving the rate of convergence of a series solution for the deflection of a swept cantilever plate of uniform thickness, using the Rayleigh-Ritz method, by applying the solution to low aspect ratio plates instead of high aspect ratio plates as had been done previously. The Rayleigh-Ritz deflection functions which were used were products of vibration modes of uniform clamped-free and free-free bars.
\r\n\r\nDeflections were computed, using six terms in the series, for three different loading conditions at sweep angles of 20\u00b0, 40\u00b0, and 60\u00b0. The results, plotted against experimental data in Figures 7 to 24, show that the rate of convergence is satisfactory only for angles of sweep of 20\u00b0 or less. Since the cases of sweep of 20\u00b0 or more are of most interest in the application to swept back aircraft wings, it was concluded that the rate of convergence is not satisfactory.
\r\n\r\nThe possibility of improving the rate of convergence of the series solution by solving for the difference between the true deflections and the deflections given by some approximate formula was indicated as the next step in arriving at a satisfactory solution. It was pointed out that the experimental data mentioned above would provide a valuable guide in the formulation of such an approximate formula.
\r\n" }, { "name": "Welch, Frank", "degree": "Engineering Degree", "year": "1950", "title": "Analysis of an Inclined Thrust Axis as Applied to a Ramjet Propelled Aircraft", "advisor": "Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162009-142841", "creators": [ { "name": { "family": "Welch", "given": "Frank" }, "id": "Welch-Frank", "display_name": "Welch, Frank" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T1QH-QJ51", "abstract": "The low values of lift-drag ratio attained by supersonic wing configurations provide the opportunity for the utilization of an inclined thrust axis. The exhaust jet of a ramjet propelled aircraft is inclined in order to use some of the jet force to supply additional lift. This has the effect of augmenting the lift by the relatively large sine component of the jet force whereas the thrust in the flight direction is reduced only by the smaller change in the cosine component.\r\n\r\nIt was found that this principle offers a substantial decrease in fuel consumption over that of a normal ramjet for probable values of lift-drag ratios above Mach number 1.5. Almost all of the possible decrease can be obtained with jet inclination angles of 15\u00b0 or less." }, { "name": "Williams, Max Lea", "degree": "PhD", "year": "1950", "title": "The Plate Problem for a Cantilever Sector of Uniform Thickness", "advisor": "Sechler, Ernest Edwin; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202004-095445", "creators": [ { "name": { "family": "Williams", "given": "Max Lea" }, "id": "Williams-Max-Lea", "display_name": "Williams, Max Lea" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WFM9-RR55", "abstract": "As one approach to the problem of analyzing missile wings of approximately delta configuration for stress and deflection characteristics, a uniformly thin plate of sector planform clamped along one radial edge has been considered.\r\n\r\nIt is shown that an infinite set of deflection functions, resulting from a product solution to the double Laplacian, may be generated, but practical utility is impeded because the functions are non-orthogonal. It is believed that should the importance of the solution warrant, the deflection of a sector under normal loading may be found by using a combination of the deflection functions, the Trefftz variational method, and high speed computing machinery.\r\n\r\nAnother section of the report is devoted to a study of the stress along the clamped edge in the vicinity of the corner, and it is shown that the stress varies from zero to a mathematical infinity as the opening angle of the sector increases from zero through ninety degrees with the stress singularity becoming progressivev stronger as the opening angle is increased. Experimental data are included that show engineering agreement with the theoretical results, for the case of a delta plate of thirty degree opening angle and varying trailing edge angle.\r\n\r\nIn conclusion, some remarks are made upon the application of the sector results to swept rectangular plates by mans of a hydrodynamic analogy wherein the possibility of obtaining approximate overall stress distributions is indicated.\r\n" }, { "name": "Bacon, John William", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of Blowing as a Method of Increasing the Maximum Lift of a Double-Wedge Airfoil", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272009-155604", "creators": [ { "name": { "family": "Bacon", "given": "John William" }, "id": "Bacon-John-William", "display_name": "Bacon, John William" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NT63-HE54", "abstract": "This report presents the results of an investigation of boundary layer energization by blowing as a method of increasing the maximum lift coefficient for supersonic airfoils operating at low subsonic speeds.\r\n\r\nThe model used was a double wedged airfoil with end plates and a spanwise slot located at the 15%, 25% or 35% chord position. Air was blown back over the wing from this slot producing a considerable increase in maximum lift for most configurations. Blowing proved to be most effective in increasing the maximum lift when used with the nose flap, fairly effective with combined flaps and wing alone, but ineffective with the split flap." }, { "name": "Benezra, Joseph Nissim", "degree": "Engineering Degree", "year": "1949", "title": "Supersonic Flow in a Two-Dimensional Asymmetric Channel", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02102009-091251", "creators": [ { "name": { "family": "Benezra", "given": "Joseph Nissim" }, "id": "Benezra-Joseph-Nissim", "display_name": "Benezra, Joseph Nissim" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GYFS-PN59", "abstract": "A practical method is developed whereby the flow field in a two-dimensional asymmetric channel can easily be determined employing the method of characteristics. Some insight as to the accuracy of such a graphical solution is gained by checking against a known theoretical solution. An asymmetric channel having a simple geometric form is designed for uniform exit flow. The lower wall is then shifted various distances to achieve different mean flows at the exit thus simulating the operation of a wind tunnel. The velocity and flow inclination gradients are determined in the test section. The same analysis is performed on a similar channel but with one of the geometric parameters of the throat changed. Finally, an investigation is carried out to determine the amount that the profile of the upper wall differs from what it should be to attain uniform flow in the test section for the various configurations." }, { "name": "Benitez, Louis Eugenio", "degree": "Engineering Degree", "year": "1949", "title": "Studies of Radiant Heat Transfer from Pure Gases", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272009-135633", "creators": [ { "name": { "family": "Benitez", "given": "Louis Eugenio" }, "id": "Benitez-Louis-Eugenio", "display_name": "Benitez, Louis Eugenio" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EG68-PD69", "abstract": "This report contains an outline of some of the experimental measurements and theoretical considerations which are required for the calculation of the emissivity of nitric oxide. Because of lack of suitable apparatus, the experimental part of the program was restricted to the determination of apparent absorption coefficients for the fundamental vibration-rotation band of nitric oxide. Theoretical calculations of emissivity were originally suggested by Dr. Martin Summerfield. The present calculations were made by the use of an approximate procedure which has been developed recently at the Jet Propulsion Laboratory by S. S. Penner for the determination of the emissivity of pure diatomic gases. The results presented in this report facilitate making approximate estimates of the emissivity of nitric oxide as a function of temperature and optical density. For these emissivity calculations it is recommended to correct the experimentally determined apparent absorption coefficients by analogy with available data for carbon monoxide." }, { "name": "Bevernick, Richard Alexander", "degree": "Engineering Degree", "year": "1949", "title": "The Effect of Reynolds Number on the Flow Field About a 70\u00b0 Cone", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-104850", "creators": [ { "name": { "family": "Bevernick", "given": "Richard Alexander" }, "id": "Bevernick-Richard-Alexander", "display_name": "Bevernick, Richard Alexander" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FGSF-5183", "abstract": "This investigation has undertaken to measure the possible Reynolds number effects in the flow field about a 70\u00b0 finite cone in a supersonic flow. The principal means of observing such effects was by static pressure measurements at the surface of the cone.\r\n\r\nResults indicate that such effects do exist when the free stream Mach number is low enough to produce subsonic flow over the face of the cone, but they are slight. At very low Reynolds numbers with a detached shock, some decrease in static pressure on the surface of the cone results, apparently due to increased boundary layer. Over the entire range of Reynolds numbers investigated with either attached or detached shock, an increase in static pressure on the cone face at some distance from the apex results from increased Reynolds number, apparently due to the shoulder disturbance.\r\n\r\nThe investigation was conducted at GALCIT as the basis for a thesis in partial fulfillment for the professional degree of Aeronautical Engineer." }, { "name": "Blenkush, Philip George", "degree": "Engineering Degree", "year": "1949", "title": "A Wind Tunnel Investigation of the Aerodynamic Characteristics of High-Lift Devices on Supersonic Wings at Low Subsonic Speed", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272009-151720", "creators": [ { "name": { "family": "Blenkush", "given": "Philip George" }, "id": "Blenkush-Philip- George", "display_name": "Blenkush, Philip George" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N6XA-GR06", "abstract": "An investigation was made to determine the effects of various full- and partial-span high-lift devices on the lift, drag, and pitching moment characteristics of a straight wing and a highly sweptforward wing, both having an aspect ratio of 1.72 and a thin double wedge symmetrical airfoil section. Split, extended leading edge, and extended trailing edge flaps were tested at various deflection angles on each wing alone and also on wing-fuselage combinations. In addition, plain leading edge flaps extending over a portion of the outboard span were tested on the sweptforward wing. Tuft surveys were made on typical model configurations to determine the change in stall pattern due to variation in the angle of attack.\r\n\r\nFrom the results of the tests it was found that a given flap configuration produced approximately equal increments of maximum lift on the sweptforward wing alone and on the same wing combined with a fuselage. Comparison of the results obtained with the straight wing showed that the maximum lift increments were lower for a given flap used on wing plus fuselage than those obtained with the same flap on the basic straight wing. When considered from the maximum lift standpoint, the extended trailing edge flap was superior to either split or extended leading edge flap. Reduced span flaps were not as effective on the sweptforward wing, as the comparable full span flap. In the case of the straight wing alone, reduced span split and extended trailing edge flaps produced higher maximum lifts than did the corresponding full span configuration. This effect was also observed with the split flap tests on the straight wing combined with the fuselage.\r\n\r\nThe experimental work was performed in the Cal Tech-Merrill wind tunnel located on the Pasadena City College campus." }, { "name": "Bottenberg, William Robert", "degree": "Engineering Degree", "year": "1949", "title": "Effect of Reynolds Number on the Flow About a Finite Cone of 70 Degrees", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222009-153637", "creators": [ { "name": { "family": "Bottenberg", "given": "William Robert" }, "id": "Bottenberg-William-Robert", "display_name": "Bottenberg, William Robert" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PPKS-C120", "abstract": "An investigation was made to determine the effect of Reynolds number on the flow about a cone of 70 degrees apex angle with free stream Mach numbers close to the Mach number for shock attachment.\r\n\r\nConditions existing on the forward half of a one-half inch diameter cone were investigated at two Mach numbers, one giving a slightly detached shock and one giving a slightly attached shock, at Reynolds numbers from 150,000 to 1,300,000 based on model diameter.\r\n\r\nClose to the apex the static pressure on the surface of the cone divided by the stagnation pressure before the shock was found to be dependent upon the Reynolds number at the lowest Reynolds number when the shock was detached but not when the shock was attached. In both cases at a distance half way back on the cone there was a continuous increase in this ratio with increasing Reynolds number. All of these Reynolds number effects were small in magnitude.\r\n\r\nThe investigation was conducted in the GALCIT 2.5\u201d Supersonic Wind Tunnel." }, { "name": "Brown, John R.", "degree": "Engineering Degree", "year": "1949", "title": "A Critical Study of Spin-Up Drag Loads on Aircraft Landing Gears", "advisor": "Sechler, Ernest Edwin; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-153114", "creators": [ { "name": { "family": "Brown", "given": "John R." }, "id": "Brown-John-R", "display_name": "Brown, John R." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PDPG-ET80", "abstract": "This report attempts to analyze in detail the spin-up drag loads imposed upon an aircraft main landing gear. Other factors in the landing gear problem are ignored except insofar as they affect this one type of loading. As an instrument for study, one model of aircraft was chosen for which extensive flight test and drop test data were available.\r\n\r\nThe main parameters which enter into the spin-up drag load are the landing weight of the aircraft, the rate of descent at contact, the ground speed, the time interval from initial contact to attainment of maximum vertical load, and the coefficient of friction between the tire and the runway surface. Minor parameters which may affect the drag load are the tire pressure, moment of inertia of the rolling stock, oleo pressure, and quantity of oil in the hydraulic shock absorber.\r\n\r\nThe results of this study indicate that the maximum gear drag load is primarily a function of the time required to reach maximum vertical load, and that further study of this parameter, using drop test data for several types of aircraft, might well lead to some valuable empirical information essential to landing gear design. The value of the coefficient of friction was seen to vary widely in test landings but a maximum value of 0.55 appears to be satisfactory for limit design calculations." }, { "name": "Burke, James Donahue", "degree": "Engineering Degree", "year": "1949", "title": "Sounding Rocket Performances Analysis", "advisor": "Nagamatsu, Henry T.; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-152718", "creators": [ { "name": { "family": "Burke", "given": "James Donahue" }, "id": "Burke-James-Donahue", "display_name": "Burke, James Donahue" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XW5Q-1Y06", "abstract": "An investigation of the effects of basic design parameters on the performance of a single-stage sounding rocket was made. The tail area required for static stability at various supersonic flight Mach numbers was determined, and the drag coefficient for various configurations was calculated. The general equations of motion for flight in vacuum were integrated for several cases to show the effect of varying specific impulse of fuel, propellant weight ratio, and burning time. An approximate solution of the equations for trajectories in air was obtained by the method of stepwise numerical integration." }, { "name": "Chandler, Ralph Stewart", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of the Stresses and Deflections of Swept Plates", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10132015-085455473", "creators": [ { "name": { "family": "Chandler", "given": "Ralph Stewart" }, "id": "Chandler-Ralph-Stewart", "display_name": "Chandler, Ralph Stewart" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WSRF-6S68", "abstract": "The problem in this investigation was to determine the stress and \r\ndeflection patterns of a thick cantilever plate at various angles\r\nof sweepback.
\r\n\r\nThe plate was tested at angles of sweepback of zero, twenty, \r\nforty, and sixty degrees under uniform shear load at the tip, \r\nuniformly distributed load and torsional loading.
\r\n\r\nFor all angles of sweep and for all types of loading the area \r\nof critical stress is near the intersection of the root and trailing\r\nedge. Stresses near the leading edge at the root decreased rapidly\r\nwith increase in angle of sweep for all types of loading. In the\r\nouter portion of the plate near the trailing edge the stresses due\r\nto the uniform shear and the uniformly distributed load did not vary\r\nfor angles of sweep up to forty degrees. For the uniform shear and \r\nthe uniformly distributed loads for all angles of sweep the area in \r\nwhich end effect is pronounced extends from the root to approximately\r\nthree quarters of a chord length outboard of a line perpendicular to\r\nthe axis of the plate through the trailing edge root. In case of\r\nuniform shear and uniformly distributed loads the deflections near\r\nthe edge at seventy-five per cent semi-span decreased with increase\r\nin angle of sweep. Deflections near the trailing edge under the\r\nsame loading conditions increased with increase in angle of sweep\r\nfor small angles and then decreased at the higher angles of sweep.\r\nThe maximum deflection due to torsional loading increased with\r\nincrease in angle of sweep.
\r\n" }, { "name": "Clancy, Albert Harrison", "degree": "Engineering Degree", "year": "1949", "title": "Experimental Investigation of Pressure Drop in Helical Coils", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272009-153532", "creators": [ { "name": { "family": "Clancy", "given": "Albert Harrison" }, "id": "Clancy-Albert-Harrison", "display_name": "Clancy, Albert Harrison" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y2Z6-SG48", "abstract": "The purpose of this study was to begin an investigation of the pressure drop in flow through helical coils. In general, the procedure followed was to define the governing parameters and then to isolate the effect of each on the pressure drop. The pressure drop was assumed to depend upon the length of the tube, the inside diameter of the tube, the diameter of the helix, the roughness of the inside of the tube, and Reynolds number. Variation of the pressure drop with change in diameter of the tube was not investigated. Five different lengths of plastic tubing were tested separately on five helices of different diameters at Reynolds numbers from 3,000 to 100,000 to study the effects of length and helix diameter. Twelve steel coils of different inside roughnesses were tested over the same Reynolds number range to obtain the effect of roughness on pressure drop.\r\n\r\nThe results of the investigation indicated that pressure drop in a helical coil is linearly dependent on length, is only slightly effected by roughness, and is a function of both Reynolds number and diameter of helix as indicated in the attached curves. These conclusions, of course, hold only for the limited field covered by the investigation." }, { "name": "Cole, Julian David", "degree": "PhD", "year": "1949", "title": "Problems in Transonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-105506", "creators": [ { "name": { "family": "Cole", "given": "Julian David" }, "id": "Cole-Julian-David", "display_name": "Cole, Julian David" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "member", "display_name": "De Prima, Charles R." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QS66-WA09", "abstract": "No Abstract." }, { "name": "Cooley, James Siggins", "degree": "Engineering Degree", "year": "1949", "title": "Reversed Bending Fatigue Properties of 25 S-T, 75 S-T, and 76 S-T Aluminum Alloys", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262009-110934", "creators": [ { "name": { "family": "Cooley", "given": "James Siggins" }, "id": "Cooley-James-Siggins", "display_name": "Cooley, James Siggins" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HNFP-NB63", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe problem of this investigation was to determine the effects of surface roughness and surface stressing on the reversed bending fatigue properties of 25 S-T, 75 ST and 76 S-T aluminum alloys.\r\n\r\nTests were conducted in a stress range from 37,700 psi, to that stress giving a fatigue life of 500,000,000 cycles.\r\n\r\nSurface roughness was varied from five micro-inches to 400 micro-inches. Two different machining tools were used to obtain the various degrees of surface roughness: 1/8\" radius tool, and a sharp pointed tool.\r\n\r\nSurface stressing was obtained by shot peening with 0[...]028 diameter shot at .010/.012 A-2 intensity, and cold rolling at 100 lbs. and 200 lbs. pressure.\r\n\r\nIt was determined that fatigue life decreased as surface roughness increased in a similar manner for specimens machined with both types of tool; but that endurance limit was not affected by the sharp tool, whereas it was decreased by the 1/8\" radius tool.\r\n\r\nShot peening increased fatigue life of 25 S-T by about 500%; it had but slight effect on 76 S-T.\r\n\r\nCold rolling increased fatigue life of 25 S-T and 76 S T by about 2500%. 75 S-T was neither shot peened nor cold rolled.\r\n\r\nThis work was carried out by the author at the Guggenheim Aeronautical Laboratory, California Institute of Technology under the supervision of Dr. E. E. Sechler." }, { "name": "Densmore, James Edward", "degree": "Engineering Degree", "year": "1949", "title": "Wind Tunnel Investigation of the Aerodynamic Characteristics of High Lift Devices on Supersonic Wings at Low Subsonic Speed", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-104437", "creators": [ { "name": { "family": "Densmore", "given": "James Edward" }, "id": "Densmore-James-Edward", "display_name": "Densmore, James Edward" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z0Y9-J658", "abstract": "An investigation was made to determine the effect of various high lift devices on a highly sweptforward wing with a leading edge sweep angle of 55 degrees and on a straight wing, both wings having an aspect ratio of 1.72 and the same span.\r\n\r\nExperimental tests were made in the Cal Tech - Merrill low speed wind tunnel at Pasadena City College on both types of wing with and without fuselage. High lift devices investigated were extended leading edge flaps, plain leading edge flaps, extended trailing edge flaps, and split flaps. Both 70 per cent and full span configurations were used in each case except for the plain leading edge flaps. All force data was reduced to standard non-dimensional lift, drag, and pitching moment coefficients, and the results presented in standard graphical form. In addition, photographs of tuft surveys were made for typical configurations.\r\n\r\nThe maximum lift coefficient obtained from the basic wings was approximately the same for both, but the angle of attack for maximum lift was appreciably lower for the straight wing than for the sweptforward wing.\r\n\r\nThe addition of the fuselage increased the maximum lift coefficient of both the basic wings and of the sweptforward wing with flap configurations, but the fuselage was detrimental to the lift for the straight wing with flap configurations.\r\n\r\nStraight wing configurations gave respectively higher maximum lift coefficients and larger lift curve slopes than on the comparable sweptforward wing models. All high lift devices investigated were more effective on the straight wing than on the sweptforward wing.\r\n\r\nExtended trailing edge flaps were the most effective of the flaps investigated in increasing the maximum lift, but gave the largest negative increase in the pitching moments.\r\n\r\nOn the straight wing the 70 per cent span split and 70 per cent span extended trailing edge flaps at optimum flap deflection angles gave a higher maximum lift coefficient than the full span flaps at the optimum flap deflection. When the straight wing was mounted on the fuselage, this effect was true only for the split flaps." }, { "name": "Dhawan, Satish", "degree": "Engineering Degree", "year": "1949", "title": "On the Design and Use of a Flexible Nozzle for the GALCIT Transonic Wind Tunnel", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-110634", "creators": [ { "name": { "family": "Dhawan", "given": "Satish" }, "id": "Dhawan-Satish", "display_name": "Dhawan, Satish" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ESYY-5P20", "abstract": "Some aspects concerning the design of flexible nozzles for use in supersonic wind tunnels are discussed. Methods are investigated for matching the deflection patterns of nozzle plates and the theoretical aerodynamic shapes required for uniform, parallel, shockfree flow. Application of the design procedures to the Galcit 4\" x 10\", transonic wind tunnel is detailed. As a demonstration of a use of the tunnel, the Mach number of shock detachment from a 10\u00b0 wedge (half angle) is experimentally investigated." }, { "name": "Dwire, Oliver Scott", "degree": "Engineering Degree", "year": "1949", "title": "A Study of Pressure Drop in Helical Coils", "advisor": "Seifert, Howard S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-095750", "creators": [ { "name": { "family": "Dwire", "given": "Oliver Scott" }, "id": "Dwire-Oliver-Scott", "display_name": "Dwire, Oliver Scott" } ], "advisors": [ { "name": { "family": "Seifert", "given": "Howard S." }, "id": "Seifert-H-S", "role": "advisor", "display_name": "Seifert, Howard S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GV93-7D64", "abstract": "This study was made to investigate the increase in pressure drop through a helix over that through a straight pipe and to study the variables involved. The pressure drops in ten helices and seven straight pipes were observed over a range of Reynolds Numbers.\r\n\r\nThe results indicate that the increase in pressure drop due to the helical shape is a function of tube diameter, helix diameter, relative roughness, and possibly Reynolds Number. There is some indication that relative roughness may be the most important of these variables. However, the data obtained are insufficient to justify the formulation of an empirical equation for the curvature correction." }, { "name": "Ford, Warren Woodrow", "degree": "Engineering Degree", "year": "1949", "title": "Design of a Six Component Internal Strain Gage Balance System", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222009-132301", "creators": [ { "name": { "family": "Ford", "given": "Warren Woodrow" }, "id": "Ford-Warren-Woodrow", "display_name": "Ford, Warren Woodrow" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8DE6-1J31", "abstract": "A. Statement of the Thesis Problem: When the aerodynamic forces acting on a model are transmitted through struts, stings, etc. to the wind tunnel rigging for determination there are several corrections to be made to compensate for the various other forces which have unavoidably entered into the rigging. Among these are the tare corrections for the deflection of the model supports. These corrections were satisfactorily made in the case of slow speed aircraft in which the tare drag is small in comparison with the drag of the airplane. However, the performance of the new jet airplanes and missiles with extremely low drag and high speed, approaching the speed of sound and higher, cannot be satisfactorily evaluated using the same balance system. A balance system to give satisfactory data on the aerodynamic forces acting on these low drag high speed airplanes should measure only the forces acting on the model with every high degree of accuracy. This can best be achieved through use of an internal balance system.\r\n\r\nAmong the many advantages which can be realized through use of a balance system which can be placed inside a model are: (a) The above mentioned corrections can be eliminated, (b) The balance system can be designed for the loads acting on the model alone, thereby increasing the sensitivity and accuracy, (c) The complexity of the wind tunnel rigging can be reduced and, (d) The electrical sensing of all the measured components simultaneously permits their direct automatic recording, thereby saving time and reducing personnel requirements.\r\n\r\nIt is the purpose of this thesis to describe a small internal balance system which has been designed to measure the six aerodynamic forces and moments which act on a model being tested and thereby realizing the above mentioned advantages.\r\n\r\nB. Survey of the Field: Internal balance systems for measuring three or four of the aerodynamic forces and moments have been used for several years. These balances, in general, have been large in size thus restricting their use to large size models. Furthermore, galling of bearing surfaces and internal friction has in many cases reduced their load capacity and accuracy.\r\n\r\nDuring the past year the author has been able to visit the following activities for the purpose of becoming acquainted with the details of the balance systems being used: (a) The Cooperative Wind Tunnel at Pasadena, California, (b) Ames Laboratory of NACA at Moffett Field, California, (c) North American Aviation Inc., at Inglewood, California. The Cooperative Wind Tunnel has three internal strain gage balance systems of the beam type. Two of these balances measure lift, drag and pitching moment while the third also measures rolling moment. These balances are large in size. A fourth balance system in use at the Cooperative Wind Tunnel, while not of the internal type, is of particular interest. This is the transonic bump balance to which the half model is secured for testing. This balance is also of the beam type and measures all six aerodynamic forces and moments.\r\n\r\nAmes Laboratory 1 x 3 foot supersonic wind tunnel uses a four component beam type strain gage balance system in which all the beams are located in the sting and shielded from the airstream by a two inch diameter shield. The features of this balance are: (a) Use of ball bearings in races for transmitting the load to the beams, (b) Drag and rolling moment beams are readily interchangeable and, (c) The electrical system is set up to record all readings simultaneously by punching a single button.\r\n\r\nNorth American Aviation, Inc. has developed a small six component internal strain gage balance system for use in their new supersonic wind tunnel. This gage is being used satisfactorily. It is fully described in ref. (a).\r\n\r\nDue to the rapid lapse of time and after a conference with Mr. Bell and Mr. Gayman of the Cooperative Wind Tunnel it was decided that an internal strain gage balance system based on the North American design promised the quickest and most satisfactory solution of the design problem at hand. This met with the approval of Drs. Sechler and Klein." }, { "name": "Francis, Donald Lowell", "degree": "Engineering Degree", "year": "1949", "title": "An Experimental Investigation of Blocking in a High-Speed, Closed Wind Tunnel Using the Wall Pressure Method", "advisor": "Bell, Richard William", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-085025", "creators": [ { "name": { "family": "Francis", "given": "Donald Lowell" }, "id": "Francis-Donald-Lowell", "display_name": "Francis, Donald Lowell" } ], "advisors": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-R-W", "role": "advisor", "display_name": "Bell, Richard William" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V893-YJ92", "abstract": "The purpose of this investigation was to determine the possibility of using a semi-empirical, wall pressure method to determine wind tunnel blocking corrections in the transonic range. Included are axial distributions of velocity increments at the wall in the presence of the wing models. The main results are presented in the form of comparisons of the blockage corrections determined by the semi-empirical method with the blocking corrections obtained by direct calculation. The models used in this investigation were reflection-plane-mounted wings of various sizes and sweep angles and one two-dimensional wing. Data for wings at moderate angles of attach are included, when available.\r\n\r\nThe results indicate that the corrections obtained by the semi-empirical method agree with those obtained by direct calculation in the range of Mach numbers where agreement is expected. The semi-empirical corrections become rapidly larger than the calculated corrections as the critical Mach number of the wing is exceeded. The magnitudes of the differences in the transonic range are sufficiently large to warrant the application of the semi-empirical method to transonic wind tunnel tests." }, { "name": "Garrett, Joseph", "degree": "Engineering Degree", "year": "1949", "title": "Experimental Deflection Survey of Cantilever Sectors of Uniform Thickness", "advisor": "Sechler, Ernest Edwin; Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-143754", "creators": [ { "name": { "family": "Garrett", "given": "Joseph" }, "id": "Garrett-Joseph", "display_name": "Garrett, Joseph" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YP13-NN87", "abstract": "The purpose of this investigation was to experimentally determine deflection data for 0 to 180 degree uniform thickness cantilever sectors. The basic deflection data is presented in the form of influence coefficients that can be utilized in the determination of the deflection of sectors as caused by any regular transverse loading.\r\n\r\nOne phase of the investigation was specifically planned to achieve results that could be compared with an analytical solution of the problem.\r\n\r\nIn addition to the basic experimentation, preliminary investigation was made of the effect of thickness and boundary fixity on the stiffness of cantilever sectors.\r\n\r\nDeflection modes as calculated from the data of this investigation were in close agreement with those determined by the analytical solution. Agreement in absolute magnitude was of the order of 15 percent for three loading conditions checked.\r\n\r\nFurther investigation into the effect of thickness is considered desirable before the results of this investigation are applied to the determination of deflections for sectors of different thickness from those used in the investigation.\r\n\r\nThe investigation was carried out in the Guggenheim Aeronautical Laboratory at the California Institute of Technology, Pasadena, California.\r\n" }, { "name": "Gilkeson, Fillmore Bolling", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of the Stresses and Deflections of Swept Plates", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122025-153427283", "creators": [ { "name": { "family": "Gilkeson", "given": "Fillmore Bolling" }, "id": "Gilkeson-Fillmore-Bolling", "display_name": "Gilkeson, Fillmore Bolling" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wd99-c236", "abstract": "No abstract." }, { "name": "Goebel, Thomas Parker", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of the Deformation of a 3S-O Sheet Specimen During Tensile Failure", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222009-091511", "creators": [ { "name": { "family": "Goebel", "given": "Thomas Parker" }, "id": "Goebel-Thomas-Parker", "display_name": "Goebel, Thomas Parker" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/06BQ-R471", "abstract": "It is recognized that the \"necking down\" of a tensile specimen which occurs prior to failure is essentially a plastic flow phenomenon. Careful observation of this flow could conceivably be used to determine the plasticity properties of various metals and also to check the applicability of some of the assumptions in the theory of plasticity.\r\n\r\nThe present preliminary tests were carried out primarily for the purpose of developing an experimental technique. A motion picture camera was used to photograph a deforming grid in the neck of a sheet tensile specimen while the load was simultaneously recorded on a recording oscillograph. This technique yielded two-dimensional strain data on one surface of the specimen and the total load as functions of time. This is admittedly not all the information desired on the plastic flow, but it does allow a partial correlation of strain rate with rate of loading, and a determination of the extent of elastic and plastic deformation on one surface of the specimen." }, { "name": "Gompf, George Edward", "degree": "Engineering Degree", "year": "1949", "title": "Supersonic Nozzle Design for Viscous Fluids", "advisor": "Puckett, Allen E.; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262009-141501", "creators": [ { "name": { "family": "Gompf", "given": "George Edward" }, "id": "Gompf-George-Edward", "display_name": "Gompf, George Edward" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R422-S076", "abstract": "A method is presented for including the effects of viscosity in the design of supersonic wind tunnel nozzles, the effect being presented in the form of a modification to the non-viscous, or perfect fluid, nozzle shapes. The modification essentially consists of providing additional expansion area to compensate for the retarded flow near the wall, and is estimated from considerations of possible boundary layer growth along a heat insulated flat well with a pressure gradient, when both the velocity profile and friction coefficient are assumed.\r\n\r\nIt is shown that the modification to the perfect fluid shape becomes very pronounced for design Mach numbers above five and results in a shorter nozzle length for a given test section size than that predicted from perfect fluid theory. At a Mach number of 10, this method results in a nozzle length reduction of 50% indicating that the boundary layer occupies this percentage of the test section for the shortened nozzle.\r\n\r\nDesign curves are presented from which the modification to a specific perfect fluid nozzle shape may be computed for Mach numbers up to 10." }, { "name": "Hardy, Donald James", "degree": "Engineering Degree", "year": "1949", "title": "The Effect of Surface Roughness upon 25 ST Aluminum Alloy Subjected to Repeated Tensile Stresses Above the Proportional Limit", "advisor": "Sechler, Ernest Edwin; Clark, Donald S.; Converse, Frederick James", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272009-083535", "creators": [ { "name": { "family": "Hardy", "given": "Donald James" }, "id": "Hardy-Donald-James", "display_name": "Hardy, Donald James" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." }, { "name": { "family": "Converse", "given": "Frederick James" }, "id": "Converse-F-J", "role": "advisor", "display_name": "Converse, Frederick James" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q6A7-1796", "abstract": "Fatigue tests were conducted on 54 specimens of 25 ST aluminum alloy for the purpose of determining the effect of surface roughness on the fatigue life of the material when subjected to constant repeated tensile stresses above the proportional limit. In addition, the basic stress vs. cycle curve for 25 ST aluminum alloy was extended to include the range of cycles below 100,000.\r\n\r\nA machine capable of applying repeated pure tension loads at a rate of 52 cycles per minute, without shock but with a high rate of loading, was used to obtain this data.\r\n\r\nIt was found that the rate of build-up and the duration of the impulse created an equivalent static load equal to the peak of the impulse loading.\r\n\r\nFor the material tested, it was found that as the surface roughness increased from 5\u03bc to 200\u03bc, the life expectancy of the alloy in general was reduced. However, the experimental results revealed a larger degree of scatter in the cyclic range below 40,000 cycles as opposed to the relatively consistent data obtained at the higher cycles. Therefore, no general conclusions could be ascertained as to the effect of roughness on the fatigue life of the material in the high stress region." }, { "name": "Harmon, Leonard Edward", "degree": "Engineering Degree", "year": "1949", "title": "Stress, Distribution in Two Circular Cylinders Intersecting at Right Angles Under the Influence of Internal Pressure", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092015-164255953", "creators": [ { "name": { "family": "Harmon", "given": "Leonard Edward" }, "id": "Harmon-Leonard-Edward", "display_name": "Harmon, Leonard Edward" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RMGJ-1S84", "abstract": "This investigation is an experimental study of the stress distribution in two circular cylinders intersecting at right angles and acted on by internal pressure. Two specimens of the thick-wall category were tested to rupture and a strain gage analysis was made of critical points. The specifications of the specimens tested were so chosen that this investigation would be the logical beginning of an overall study of intersecting cylinders under the influence of internal pressure.
\r\n\r\nThe results of two tests are insufficient to indicate trends or establish facts as conclusive. The conclusions reached as a result of this investigation are, therefore, of such a nature as to require confirmation by subsequent continuation of this study. These conclusions are:
\r\n\r\n1. The maximum stresses present in specimens of the type tested are in the plans of intersection and tangent to the ellipse of intersection at a point approximately fifteen degrees from the crotch.
\r\n\r\n2. Additional resistance to the high stresses at the plans of intersection is necessary over that required in the wall of a straight pipe.
\r\n\r\n3. Bending associated with the stressing of this type of intersection by the application of internal pressure is of minor importance in specimens in the thick wall range.
\r\n\r\nAll the tests were made in collaboration with Lieutenant Commander Vernon E. Teig, U.S. Navy in the Structures Laboratory, Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California, during the school year 1948-1949.
\r\n" }, { "name": "Head, Richard Moore", "degree": "PhD", "year": "1949", "title": "Investigations of Spontaneous Condensation Phenomena", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:04212011-134533762", "creators": [ { "name": { "family": "Head", "given": "Richard Moore" }, "id": "Head-Richard-Moore", "display_name": "Head, Richard Moore" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/06R8-C778", "abstract": "The results of a systematic wind tunnel investigation into the attainment and ultimate collapse of the supersaturated state of water vapor are presented. These results, together with those of other recent investigations, are collected and compared with the theory. It is found that the deviations from the quasi-stationary conditions upon which the theory is based are very pronounced in the supersonic wind tunnel. A much higher degree of supersaturation can, therefore, be attained before condensation occurs than is predicted theoretically.\r\n\r\nMeasurements at low temperatures indicate that if the water vapor reaches a temperature of about 153 \u00b0K, without the occurrence of condensation, the vapor will not condense upon further expansion, regardless of how highly supersaturated it becomes. This observation is in agreement with some recent Wilson Cloud Chamber investigations.\r\n\r\nThe shock relations for flow-involving condensation are discussed. It is shown that two types of discontinuities can occur; the condensation shock and the shock with condensation (or vaporization). The latter solution has been disregarded in the past, but it is shown that the shock with vaporization is of importance and can result in appreciable errors in Mach number determination when droplets are present in the flow.\r\n\r\nVarious techniques of measurement of the condensation processes in supersonic flow are considered.\r\n" }, { "name": "Henry, William Earl", "degree": "Engineering Degree", "year": "1949", "title": "Experimental Deflection Survey of Cantilever Sectors of Uniform Thickness", "advisor": "Sechler, Ernest Edwin; Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-152036", "creators": [ { "name": { "family": "Henry", "given": "William Earl" }, "id": "Henry-William-Earl", "display_name": "Henry, William Earl" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A463-DC95", "abstract": "The purpose of this investigation was to study the deflection patterns of uniform thickness 24ST aluminum alloy sectors fixed on one radius and subjected to transverse loads.\r\n\r\nThis investigation consisted of obtaining deflection data in the form of influence coefficients for cantilever sectors of opening angles varying from 0 to 180 degrees.\r\n\r\nThe deflection data are presented in a form that requires only a matrix multiplication to obtain the deflection pattern of any sector of the same material constants and dimensions as those used in this investigation. For sectors of different material constants and dimensions the deflection pattern may be obtained by interpolation of the data presented in this investigation and use of elementary elastic relationships.\r\n\r\nThe comparison of the experimental and analytical solution of the deflection pattern of a 45 degree sector subjected to a shear loading and radial moments along the curved boundary showed satisfactory agreement.\r\n\r\nThis investigation was carried out at the Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California (referred to hereafter as GALCIT)." }, { "name": "Lamb, William Emerson", "degree": "Engineering Degree", "year": "1949", "title": "Fatigue Strength of Metal Sandwich Type Construction", "advisor": "Sechler, Ernest Edwin; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-095113", "creators": [ { "name": { "family": "Lamb", "given": "William Emerson" }, "id": "Lamb-William-Emerson", "display_name": "Lamb, William Emerson" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YEGJ-XT59", "abstract": "An investigation was conducted to determine the fatigue strength of a new type of all metal sandwich panel structure, designed and furnished by Western Engineering Associates of Los Angeles. This structure consisted basically of a new type of embossed core attached by spot welding to one or more smooth sheets of the same metal. Specimens tested were all of the single core, single skin type. Metal used was 24ST aluminum alloy of 0.032 inch thickness. This construction affords high structural rigidity for its weight. Two patterns of the embossed core were tested. One of the specimens had its core embossed with a triangular pattern, the other with a square pattern.\r\n\r\nThe specimens were tested by utilizing them as simply supported beams, loaded in the center by a sinusoidally varying load of constant maximum magnitude. This load was applied by means of loading bars one on the top of the specimen, the other on the bottom. These bars had flat, one inch wide surfaces, contacting the specimen. To prevent the sharp edges of the bars from causing local failures of the specimens, a layer of one-eighth inch thick koroseal was used between the bars and the specimen. Specimens tested had a length between end supports of 16.7 inches. Their width was 9 inches.\r\n\r\nThe loading obtained was a combination of bending and shear. The shear stress was of such a low magnitude, however, that it could be neglected.\r\n\r\nFailure of the specimens was deemed as occurring at the time the first crack appeared. A method was devised for crack detection that consisted of laying down a conducting strip over a thin insulating layer in a network fashion, covering all saddle points of the core in the central area, since previous testing had disclosed the fact that failure occurred at these points first. Any crack in one of these saddles caused a break in the conducting strip which changed the bias on the controlling electronic tube to a cut off value. This tube was part of an Eccles-Jordan Trigger circuit which with associated tubes allowed current flow through a thyratron relay circuit opening the starting circuit of the testing machine, causing it to stop.\r\n\r\nThe data shows that for the specimens oriented in a normal fashion, that is, with one of the sides of the square or triangle of the core parallel to the loading bar, which was the situation for most of the tests, the square pattern is vastly superior to the triangular one, as regards fatigue strength. For specimens oriented in this way the square pattern withstood a bending moment of 13.45 inch pounds per inch of width; whereas the triangular pattern withstood only 9.28. Two tests conducted with the square core having the sides of the squares at an angle of forty-five degrees to the loading bars gave results about midway between. However, the effective EI for this configuration was considerably reduced, and consequently actual failure stress was probably about equal to that for the ease where the sides were parallel to the loading bar.\r\n\r\nThe triangular pattern was actually much worse than the curve shows. At the higher loads cracks occurred with very few cycles of loading. Automatic cut-off feature was not in use for these tests. In service it is highly possible that overloads of short duration might cause small cracks which would become focal points of fatigue failure, thus reducing the fatigue strength well below the design point. This weakness of the triangular pattern arises from the fact that smooth fillets or saddles, joining depressed and elevated portions of the core, are harder to obtain in this pattern than in the square one. Wrinkles and tool marks were present in almost every one of the triangular specimens tested." }, { "name": "MacKinnon, Neil Allan", "degree": "Engineering Degree", "year": "1949", "title": "Flow Field Around a Finite Cone with Shock", "advisor": "Puckett, Allen E.; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02182009-110248", "creators": [ { "name": { "family": "MacKinnon", "given": "Neil Allan" }, "id": "MacKinnon-Neil-Allan", "display_name": "MacKinnon, Neil Allan" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XR4M-9R51", "abstract": "An experimental investigation was made to determine the characteristics of the flow over the surface of a 70\u00b0 cone and at the shock wave for values near the detachment Mach number. The purpose of this investigation was to compare the experimental results obtained with theoretical values.\r\n\r\nTests were made in the GALCIT 2.5\" Supersonic Wind Tunnel on a 70\u00b0 cone at zero angle of attack for five different free stream Mach numbers: 1.49, 1.630, 1.694, 1.86, 1.997.\r\n\r\nIt was found that theory gives close agreement with experimental results.\r\n\r\nThis investigation was conducted jointly with Mr. Vincent Muirhead at the California Institute of Technology, Pasadena, California." }, { "name": "Mandelbrot, Benoit B.", "degree": "Engineering Degree", "year": "1949", "title": "Some Potential Problems Arising in the Theory of Axial Turbomachines", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-085608", "creators": [ { "name": { "family": "Mandelbrot", "given": "Benoit B." }, "id": "Mandelbrot-Benoit-B", "display_name": "Mandelbrot, Benoit B." } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QGD5-YD25", "abstract": "Some potential problems raised by the trailing-vortex theory of axial turbomachines are solved in the cases of cylindrical semi-infinite and infinite helicoidal vortices and of trailing vortices in a cone. The analysis is carried out for the cylindrical doubly infinite case and the dynamical problems are set up.
\r\n\r\nThe results are in a form where further applications to the physical problems may be undertaken and actual computations worked out.
\r\n\r\nIt is hoped that this work will be completed in the future.
" }, { "name": "Marx, Michael Ferdinand", "degree": "Engineering Degree", "year": "1949", "title": "Low Speed Wind Tunnel Investigation of High Lift Devices on a 65\u00b0 Swept-Back Supersonic Wing of 3.44 Aspect Ratio", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122009-093718", "creators": [ { "name": { "family": "Marx", "given": "Michael Ferdinand" }, "id": "Marx-Michael-Ferdinand", "display_name": "Marx, Michael Ferdinand" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2B48-J790", "abstract": "A low speed survey was conducted on a 3.44 aspect ratio wing having a 65\u00b0 swept-back leading edge and double wedge symmetrical airfoil section to obtain information as to the effectiveness of various high-lift devices. These devices included trailing edge split and extended split flaps, leading edge split flaps, slats and combined configurations. Tests were carried out on the wing with and without the fuselage and horizontal tail surface.\r\n\r\nThe split flaps increased the lift over the lower ranges of angle of attack only. The extended split flaps increased the lift over the whole angle of attack range. Hose flaps showed practically no gain over any of the range when used by themselves. However, when combined with the trailing edge split flaps in the wing-fuselage configuration, the optimum maximum lift conditions were obtained. Addition of the fuselage and horizontal tail surfaces each produced considerable increments of lift.\r\n\r\nIn all configurations except leading edge flaps in the inboard position undesirably large negative pitching moments resulted. However, they had stabilizing tendencies except where there were irregularities in the lift curves." }, { "name": "McElligott, Richard Hardy", "degree": "Engineering Degree", "year": "1949", "title": "Investigation of Pressure Drop Through Helical Coils", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132009-131121", "creators": [ { "name": { "family": "McElligott", "given": "Richard Hardy" }, "id": "McElligott-Richard-Hardy", "display_name": "McElligott, Richard Hardy" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0S5A-NH14", "abstract": "This investigation was conducted to determine the character of the pressure drop through helically wound pipes by comparing the pressure drops of straight pipes and helically wound pipes of comparable relative roughness.\r\n\r\nThe scope of the study was limited to Reynolds Numbers below 10[superscript 5] and to flow through 3/8 and 1/2 inch stainless steel tubing of circular cross section. It was further limited by the use of water as the only working fluid and by the fact that no control was established over the exact character of the surface roughness.\r\n\r\nThe results show that the correction factor Hc' is rather insensitive to Reynold's number and that it has greater dependence upon roughness and less dependence upon curvature than was previously thought probable. In addition, it is shown that an empirical formula of the type Hc = 1 + K(r/D)[superscript a](D/Dh)[superscript b] where a >> b, is probably more realistic than the Ac = 1 + 3.5 D/Dh expressed in current literature. It is further shown that within the scope of this study, the relative roughness, r/D, as determined by the profilometer and the relative roughness \u03b5/D as used by L. F. Moody correspond, and r/D may be used to determine a friction factor from the Moody curves." }, { "name": "McKenney, John Dill", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of Flow Separation in an Overexpanded Supersonic Nozzle", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-143254", "creators": [ { "name": { "family": "McKenney", "given": "John Dill" }, "id": "McKenney-John-Dill", "display_name": "McKenney, John Dill" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G1V3-A479", "abstract": "An apparatus for the investigation of flow separation in a supersonic nozzle has been designed and constructed. Nozzle wall pressure distributions and shadowgraphs showing the associated shock wave configuration have been obtained for a range of different stagnation pressures and constant exit pressure.
\r\n\r\nThe pressure ratios were such that the theoretical nozzle exit pressure, without separation, was always less than atmospheric pressure. With the nozzle contour and pressure ratios investigated it is found that separation of flow from the nozzle walls always occurs. The separation is accompanied by a weak oblique shock wave of such strength that the flow deflection through it is approximately constant, independent of the location of the point of separation within the nozzle. The pressure adjustment from nozzle to exit does not occur through a normal shock wave.
\r\n\r\nAt pressure ratios below a certain value a definite asymmetry of flow appears in which the detached jet deflects away from the nozzle symmetry axis. At higher pressure ratios, the flow becomes stable with separation occurring at the same distance from the nozzle throat on both upper and lower walls.
" }, { "name": "Mettler, Ruben Fred", "degree": "PhD", "year": "1949", "title": "The Anemometric Application of an Electrical Glow Discharge in Transverse Air Streams", "advisor": "Lindvall, Frederick C.; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-110318", "creators": [ { "name": { "family": "Mettler", "given": "Ruben Fred" }, "id": "Mettler-Ruben-Fred", "display_name": "Mettler, Ruben Fred" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RTBA-4692", "abstract": "The possibility of using an electrical glow discharge for quantitative turbulence measurements is experimentally investigated. It is found that a glow discharge is stable in a transverse air stream throughout the subsonic velocity range, and at supersonic air velocities up to a Mach number of 1.5, with no indication that this Mach number represents an upper velocity limit. A calibration procedure is developed and used in measuring the decay of turbulence behind a grid at low subsonic velocities. Comparison with decay measurements made independently with a hot wire anemometer under similar flow conditions shows that the glow discharge data is as yet quite badly scattered and somewhat inconsistent.\r\n\r\nA quantitative theory of the dark current anemometer is presented and gives results which agree in form with reported experimental results. A qualitative theory of the mechanism of the glow discharge anemometer and the first steps of the corresponding quantitative analysis are also presented." }, { "name": "Monroe, Gerald Morgan", "degree": "Engineering Degree", "year": "1949", "title": "Higher Order Approximate Solutions for the Flow in Axial Turbomachines", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-092006", "creators": [ { "name": { "family": "Monroe", "given": "Gerald Morgan" }, "id": "Monroe-Gerald-Morgan", "display_name": "Monroe, Gerald Morgan" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8BJW-AE38", "abstract": "The theory of the three-dimensional rotational flow of an incompressible and inviscid fluid through an axial turbomachine is described and the hydrodynamical equations are simplified by considering an infinite number of blades in each row. The forces of the blades on the fluid are treated as non-conservative body forces distributed uniformly about the axis.\r\n\r\nFormulation of the mathematical problem leads to one non-linear partial differential equation and two integral equations for the three velocity components. A linearized solution of these simultaneous equations for any prescribed blade loading is based on the consideration that the vorticity generated by the blades is transported downstream by the mean axial velocity. An iteration process which leads to solutions of greater accuracy is developed by considering for each iteration that the vorticity is transported by the velocities found by the previous iteration.\r\n\r\nThe Bessel's functions which occur in the Green's function solution are replaced by their asymptotic values and the infinite series is summed to express the solution in closed form. The iteration process is then adapted to mechanical calculations by dividing the region of vorticity into small rings of rectangular cross-section and determining the influence on the velocity of a unit change of vorticity in each of these rings. Once this influence is established it is relatively easy to calculate the velocities in any axial flow machine with any prescribed blade loading." }, { "name": "Morikawa, George Kiyoshi", "degree": "PhD", "year": "1949", "title": "The Wing-Body Problem for Linearized Supersonic Flow", "advisor": "Stewart, Homer Joseph; Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-112820", "creators": [ { "name": { "family": "Morikawa", "given": "George Kiyoshi" }, "id": "Morikawa-George-Kiyoshi", "display_name": "Morikawa, George Kiyoshi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "co-advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PJZP-YG35", "abstract": "This work is concerned with one of the important problems remaining in the theory of linearized supersonic flow: the study of non-planar systems dealing with configurations which cannot be completely solved with the existing theory - in particular, the study of interaction or interference between fuselage and lifting or control surfaces in supersonic flow.\r\n\r\nIn Sections 1.2 and 1.3 the non-planar problems are classified and the problem considered to be the fundamental wing body problem for linearized supersonic flow is presented. In Part II, this and related problems are formulated in a manner suitable for Laplace transform methods and subsequently the transformed solutions are presented in a general form by the Green's function method.\r\n\r\nDue to the inherent difficulties arising in non-planar problems, related planar problems are solved in Part III. In Part IV, the fundamental wing-body problem is discussed in detail and in the light of the results of Part III an approximate solution (in terms of the pressure) in the region of greatest interest is presented; and a quantitative estimate of the increase in lift due to the interaction between wing and body is indicated." }, { "name": "Muirhead, Vincent Uriel", "degree": "Engineering Degree", "year": "1949", "title": "Flow Field Around a Finite Cone with Shock", "advisor": "Puckett, Allen E.; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-092339", "creators": [ { "name": { "family": "Muirhead", "given": "Vincent Uriel" }, "id": "Muirhead-Vincent-Uriel", "display_name": "Muirhead, Vincent Uriel" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7GMA-0V07", "abstract": "The objective of this investigation was to study the flow field in the immediate vicinity of a finite cone and to compare the results with analytical values for an infinite cone. Pressure distribution over the surface of a 70 degree cone and the general characteristics of the shock wave were investigated. The tests were conducted at five Mach numbers covering the four regimes of flow. Particular attention was given to the conditions at the apex of the cone. The locations of the intersection of the sonic line with the surface of the cone and with the shock wave were determined.\r\n\r\nIn general the tests demonstrate that at the apex of a finite cone the pressure and the shock wave angle closely approach the values predicted by analytical methods in the four regimes of flow.\r\n\r\nThe tests were conducted in the GALCIT 2.5\" Supersonic Wind Tunnel." }, { "name": "Nagamatsu, Henry Takeshi", "degree": "PhD", "year": "1949", "title": "Theoretical Investigation of Detached Shock Waves", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092009-130132", "creators": [ { "name": { "family": "Nagamatsu", "given": "Henry Takeshi" }, "id": "Nagamatsu-Henry-Takeshi", "display_name": "Nagamatsu, Henry Takeshi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW36-ZP15", "abstract": "The problems associated with the detached shock wave are considered from the analytical standpoint in this report. For considering the general case for the detached shock wave, the nonstationary isentropic differential equation is derived. In general the stationary detached shock wave is curved and thus the flow back of the shock is rotational. The effect of rotational flow upon the velocity and pressure distribution over a circular cylinder is analyzed for a parabolic velocity distribution in the disturbed region.\r\n\r\nThe basic equations for both normal and oblique shock waves are presented and the significance of these equations to the problem of detached shock is discussed. The condition for the shock wave to be detached are presented and the mathematical formulation of the Tricomi type of differential equation for the detached shock wave is given.\r\n\r\nThe first approximation to the location of the detached shock wave is derived and the analytical results are correlated with the perimental data for spheres obtained from the supersonic wind tunnel and the ballistic range. The agreement was found to be satisfactory.\r\n\r\nThe existence and uniqueness of a potential solution for an infinite wedge with normal detached shock wave moving at constant velocity is presented. It is shown that, even for an infinite wedge with normal detached shock wave the potential solution does not exist." }, { "name": "Ogilvie, Douglas Clark", "degree": "Engineering Degree", "year": "1949", "title": "Correlation of Existing Design Information on Sandwich Construction", "advisor": "Sechler, Ernest Edwin; Converse, Frederick James", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112009-154609", "creators": [ { "name": { "family": "Ogilvie", "given": "Douglas Clark" }, "id": "Ogilvie-Douglas-Clark", "display_name": "Ogilvie, Douglas Clark" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Converse", "given": "Frederick James" }, "id": "Converse-F-J", "role": "advisor", "display_name": "Converse, Frederick James" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F4C5-0536", "abstract": "The problem considered is one of survey and correlation of existing design information on sandwich construction. The subject matter deals with the types of sandwiches, advantages, buckling and stress analysis, published test data, design methods, core materials, weight comparisons, current applications and the manufacture, repair and inspection of sandwich construction.\r\n\r\nSuggestions for extensions needed are given and where obvious improvements in analysis could be seen, these modified methods were suggested.\r\n\r\nSuggested further work - Every phase of sandwich construction considered in the present thesis shows need for further development. Particularly useful fields for further work are the development of more adequate stress analysis methods for the core, more general correlation of existing formulas and the development of better means of attachment, inspection and repair." }, { "name": "Peterson, Norman Charles", "degree": "PhD", "year": "1949", "title": "Noncircular Fuselages in Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02032009-125355", "creators": [ { "name": { "family": "Peterson", "given": "Norman Charles" }, "id": "Peterson-Norman-Charles", "display_name": "Peterson, Norman Charles" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JCZX-0749", "abstract": "The applicability of linearized theory to the aerodynamic study of slender, three-dimensional bodies in supersonic flow is considered in detail, and figures are presented which show the limitations of body shape and mach number to be observed if quantitatively reliable results are to be achieved. Then methods are developed and evaluated for calculating the supersonic flow about slender noncircular bodies, other than wings.\r\n\r\nSections I and II are concerned with the velocity and pressure predictions of the linearized theory. It is shown that these quantities do not converge to the corresponding predictions of the exact solutions for vanishing disturbance, and the reason therefore is found. In Section III the inapplicability of wing theory methods and the theory of slender circular bodies to the present study is reviewed, and the problem is carried to the fundamental nonrotationally symmetrical solutions of the wave equation; the properties of the noncircular functions are developed in Section IV. Section V contains a description of the Lorentz transformation for obtaining solutions singular on a yawed line, and Section VI a simple statement of the Gothert transformation for changing the Mach number.\r\n\r\nSections VII and VIII contain an exposition of the use of the theory developed in the previous Sections. Bodies in supersonic flow are classified according to size and orientation, an appropriate methods for each are presented and evaluated.\r\n\r\nThe Appendices present tables of the functions used in the analysis, along with sample computations." }, { "name": "Pinkerton, Charles C.", "degree": "Engineering Degree", "year": "1949", "title": "Experimental Determination of the Thermal Conductivity of Porous Copper", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-130000", "creators": [ { "name": { "family": "Pinkerton", "given": "Charles C." }, "id": "Pinkerton-Charles-C", "display_name": "Pinkerton, Charles C." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T9JD-BK76", "abstract": "The techniques of powder metallurgy have produced porous variations of the metals copper, steel and nickel. The proposed application of these porous metals in the sweat-cooling of jet propulsion engines demands an exact knowledge of their thermal as well as their physical properties.\r\n\r\nThis thesis presents an experimental determination of the thermal conductivity of copper as a function of porosity, and an insight into the way this conductivity depends on temperature.\r\n\r\nThe experiments were performed on a simplified version of the apparatus used by the Bureau of Standards for solid metals. Four copper specimens varying in porosity from 22 to 42 per cent were measured. The results obtained are consistent with those predicted by other investigators from entirely different considerations.\r\n\r\nThe results are summarized in two graphs. The first shows temperature versus thermal conductivity. The second gives thermal conductivity versus porosity. It is shown that porosity largely determines thermal conductivity while temperature is distinctly a second-order influence. An analytical expression for the variation of thermal conductivity with porosity is introduced, and general agreement with the experimental results is noted." }, { "name": "Puckett, Allen Emerson", "degree": "PhD", "year": "1949", "title": "Supersonic Wave Drag of Thin Airfoils", "advisor": "von K\u00e1rm\u00e1n, Theodore; Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-141931", "creators": [ { "name": { "family": "Puckett", "given": "Allen Emerson" }, "id": "Puckett-Allen-Emerson", "display_name": "Puckett, Allen Emerson" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HYJJ-3241", "abstract": "The linearization of the equations of motion for the supersonic flow of a perfect fluid is discussed, and methods of solution using elementary source sink solutions are developed. These methods are applied to the calculation of performance of several types of three-dimensional supersonic airfoils; in particular, the drag at zero lift of a family of almost triangular, symmetrical wings is calculated. The significance of the results is discussed.\r\n" }, { "name": "Ringness, William Merritt", "degree": "Engineering Degree", "year": "1949", "title": "The Effect of Surface Roughness upon 25 ST Aluminum Alloy Subjected to Repeated Tensile Stresses Above the Proportional Limit", "advisor": "Sechler, Ernest Edwin; Clark, Donald S.; Converse, Frederick James", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-093120", "creators": [ { "name": { "family": "Ringness", "given": "William Merritt" }, "id": "Ringness-William-Merritt", "display_name": "Ringness, William Merritt" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." }, { "name": { "family": "Converse", "given": "Frederick James" }, "id": "Converse-F-J", "role": "advisor", "display_name": "Converse, Frederick James" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WH57-T868", "abstract": "Utilizing the Repeated Load Hydraulic Testing Machine at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California, the author, in collaboration with Lt. Comdr. D. J. Hardy, U. S. Navy, investigated the effects of surface roughness upon the cyclic life of 25 ST aluminum alloy when subjected to repeated constant tensile stresses in the region above the proportional limit.\r\n\r\nThe stress impulses are of such low frequency as to allow consideration of single impulses. The rate of build-up of the impulse and the duration of the impulsive load are such as to create an equivalent static load of substantially the same magnitude as the peak of the impulse loading.\r\n\r\nIt was found that surface roughness has some effect upon the cyclic life. In the lower stress regions, the greater the degree of surface roughness, the shorter the life appears to be. However, for the range of roughness investigated, 5\u03bc to 200\u03bc, the effect is not so pronounced as is usually found below the proportional limit.\r\n\r\nWhere the applied stresses reached far up into the plastic range the effect of surface roughness does not seem to follow quite as specific a pattern. Since the loading impulse featured a 0.33 second duration of maximum load, the effects of creep may well have taken over in shaping the life cycle curve with little regard for surface roughness." }, { "name": "Schurmeier, Harris McIntosh", "degree": "Engineering Degree", "year": "1949", "title": "An Investigation of the Interference Effects of a Sting Support System on the Pressure Distribution over a Body of Revolution", "advisor": "Bell, Richard William", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122007-131246", "creators": [ { "name": { "family": "Schurmeier", "given": "Harris McIntosh" }, "id": "Schurmeier-Harris-McIntosh", "display_name": "Schurmeier, Harris McIntosh" } ], "advisors": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-R-W", "role": "advisor", "display_name": "Bell, Richard William" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H9SM-CM40", "abstract": "The pressure distribution over a body of revolution was measured, both with and without a sting, or sting and simulated sting-support structure, present. The investigation was carried out in a wind tunnel at a low speed.
\r\n\r\nThe results indicated that the changes in the pressure distribution over the body were small if the sting diameter was half the base diameter and the sting made reasonably long. The effects of the sting and sting-support structure were felt only over the aft 20 percent of the body and were such as to increase the pressure in all cases investigated.
" }, { "name": "Shonerd, David Edwin", "degree": "Engineering Degree", "year": "1949", "title": "Winged Rocket Performance Analysis", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052009-092504", "creators": [ { "name": { "family": "Shonerd", "given": "David Edwin" }, "id": "Shonerd-David-Edwin", "display_name": "Shonerd, David Edwin" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/34ZH-KG02", "abstract": "A method is presented for estimating the effects of various parameters on the performance of a winged rocket. A program for studying three specific parameters, i.e., wing areas, reduced thrust cruising programs, and trajectory climb angles, and their effect on the horizontal range of a winged rocket is presented. Complete calculations are carried out for one combination of these parameters.\r\n\r\nAn analysis of the Lift, Drag and Stability characteristics of a long, slender rocket with trapezoidal fins and wings is made. The stabilizing effectiveness of delta and trapezoidal fins is compared.\r\n\r\nSimplified approximate methods of integrating the trajectory equations by step-by-step method are presented." }, { "name": "Teig, Vernon Ellwood", "degree": "Engineering Degree", "year": "1949", "title": "Stress Distribution in Two Intersecting Cylinders Under Pressure", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-160414", "creators": [ { "name": { "family": "Teig", "given": "Vernon Ellwood" }, "id": "Teig-Vernon-Ellwood", "display_name": "Teig, Vernon Ellwood" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9QC1-C818", "abstract": "The experimental studies presented here were undertaken in an effort to determine the stress distribution in two circular cylinders intersecting at right angles and under internal pressure. The investigation was limited to tests of two specimens in the thick-walled cylinder range.
\r\n\r\nThe experimental analysis led to the following conclusions:
\r\n\r\n1. The highest stress concentrations are located at an angle of about 14.5 degrees from the crotch centerline measured in the plane of the intersection.
\r\n2. The critical stress causing rupture is the tangential stress in the plane of the ellipse.
\r\n3. For the R/t ratios tested, the strength reduction as compared with a straight closed cylinder is approximately 50%.
\r\n4. It appears probable that bending effects for these thick-walled cylinders are of relatively minor importance.
An attempt is made to develop a second approximation to the solution of problems of supersonic flow which can be solved by existing first-order theory. The method of attack adopted is an iteration procedure using the linearized solution as the first step.
\r\n\r\nSeveral simple problems are studied first in order to understand the limitations of the method. These suggest certain conjectures regarding convergence. A second-order solution is found for the cone which represents a considerable improvement over the linearized result.
\r\n\r\nFor plane and axially-symmetric flows it is discovered that a particular integral of the iteration equation can be written down at once in terms of the first-order solution. This reduces the second-order problem to the form of the first-order problem, so that it is effectively solved. Comparison with solutions by the method of characteristics indicates that the method is useful for bodies of revolution which have continuous slope.
\r\n\r\nFor full three-dimensional flow, only a partial particular integral has been found. As an example of a more general problem, the solution is derived for a cone at an angle. The possibility of treating other bodies of revolution at angle of attack and three-dimensional wings is discussed briefly.
" }, { "name": "Weatherup, Robert Alexander", "degree": "Engineering Degree", "year": "1949", "title": "An Experimental Investigation of the Pressure Loss in Flow Through Helical Coils", "advisor": "Seifert, Howard S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052009-133758", "creators": [ { "name": { "family": "Weatherup", "given": "Robert Alexander" }, "id": "Weatherup-Robert-Alexander", "display_name": "Weatherup, Robert Alexander" } ], "advisors": [ { "name": { "family": "Seifert", "given": "Howard S." }, "id": "Seifert-H-S", "role": "advisor", "display_name": "Seifert, Howard S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZ8G-V819", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThis thesis is a report of an experimental investigation of pressure losses in flow through helical coils of circular cross section. The investigation aimed at the determination of a multiplying factor [...] which could be applied to the friction factor for an equivalent straight pipe in order to determine the effective friction factor for flow through a helical coil.\r\n\r\nThe following conclusions were reached:\r\n\r\n1. The multiplicative factor [...] is a function of Reynolds number and has a minimum value at a Reynolds number of approximately 8,000.\r\n\r\n2. The factor [...] is also dependent on the ratio [...]. The general effect of this ratio is to increase [...] as the ratio [...] is decreased. At Reynolds numbers above 8,000, however, [...] was found to be rather insensitive to variation in [...] over the range from [...] with a minimum at [...].\r\n\r\n3. The factor [...] was found to be independent of the ratios [...] and [...] over the ranges investigated." }, { "name": "Altseimer, John H.", "degree": "Engineering Degree", "year": "1948", "title": "An Experimental Investigation of Detached Shock Waves", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12232008-153257", "creators": [ { "name": { "family": "Altseimer", "given": "John H." }, "id": "Altseimer-John-H", "display_name": "Altseimer, John H." } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W6SF-EG14", "abstract": "Using the Galcit 2 1/2 inch Supersonic Tunnel equipment, surface pressure measurements were taken on cylindrical models with cone-shaped noses. The total included angle of the cones was 75\u00b0. The Mach number range covered was from 1.41 to 1.99 which for 75\u00b0 cones covers most of the range from detached to attached shock waves. Stagnation pressure measurements were also taken by means of blunt cylindrical models.
\r\n\r\nSchlieren pictures were taken of the 75\u00b0 cones and blunt models throughout the velocity range. Additional pictures of shock waves 45\u00b0, 60\u00b0, and 90\u00b0 cones at some of the velocities used were also obtained. From the Schlieren pictures the traces of the shock waves were obtained and plotted on graph paper. Shock wave angles vs. distance from the model centerlines are also presented as well as the distribution of \"M[subscript 2]\", the Mach number directly behind the wave.
\r\n\r\nAppendix #1 shows \"Blocking\" data for the 2 1/2 inch GALCIT Tunnel.
\r\n\r\nHand adjusted flexible nozzle walls were used for most of the work. Satisfactory flow through the tunnel was obtained with these nozzle blocks. However, design improvements are possible and Appendix #2 recapitulates the problems encountered and offers suggestions for future use.
" }, { "name": "Amster, Warren", "degree": "Engineering Degree", "year": "1948", "title": "An Investigation into the Effects of Running Propellers on the Static Longitudinal Stability of Multi-Engine Tractor-Propeller-Driven Monoplanes", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-141518", "creators": [ { "name": { "family": "Amster", "given": "Warren" }, "id": "Amster-Warren", "display_name": "Amster, Warren" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VMA6-2G04", "abstract": "This thesis has three main purposes:\r\n\r\n1. To establish an engineering computation procedure for predicting C[subscript M]( c. g.) as a function of C[subscript L] and power conditions for a multi-engine monoplane of conventional configuration with tractor propellers mounted on and forward of the wing from a given curve of C[subscript M] as a function of C[subscript L] for the power-off condition.\r\n\r\n2. To recommend aircraft configurations which will minimize destabilizing effect of power.\r\n\r\n3. To provide a physical explanation of the effect of power on stability.\r\n\r\nCalculated C[subscript M] vs. C[subscript L] curves are compared with \"matched-power\" wind tunnel model test results. The agreement is good for all-right-hand rotation of propellers but unsatisfactory for other rotation modes.\r\n" }, { "name": "Buhler, Rolf Dietrich", "degree": "Engineering Degree", "year": "1948", "title": "Supersonic Flow Through Cascades, with Application to Diffusers", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102008-131330", "creators": [ { "name": { "family": "Buhler", "given": "Rolf Dietrich" }, "id": "Buhler-Rolf-Dietrich", "display_name": "Buhler, Rolf Dietrich" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "chair", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Hollander", "given": "A." }, "id": "Hollander-A", "role": "member", "display_name": "Hollander, A." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FJEG-RM29", "abstract": "Supersonic flow through a two-dimensional cascade of airfoils is discussed from the point of view of one-dimensional gas dynamics. Two generalizations to compressible flow of the usual velocity vector diagrams are discussed, namely the Mach vector and the reduced velocity vector diagram. A relative mass flow parameter is found which represents the isentropic continuity equation on the two vector diagrams, so that for a set of given cascade inlet conditions all possible outlet velocities and directions appear on the diagrams.\r\n\r\nThe largest possible tangential velocity component and the largest possible change in tangential momentum in a cascade are obtained as functions of the mass flow parameter. From these the largest obtainable stagnation pressure ratio and power of any arrangement of moving and stationary cascades may easily be obtained.\r\n\r\nEquations are given for the ratios of relative stagnation temperatures, mass flows and Mach numbers in two systems of reference moving with respect to each other. Methods for tracing graphically on the vector diagrams the flow through a stage are presented.\r\n\r\nThe possibility of using cascades instead of shock waves for the transition from supersonic to subsonic flow in diffusers is pointed out. As an example a proposed single cascade supersonic diffuser is briefly analyzed by means of the reduced velocity vector diagram.\r\n" }, { "name": "Chapman, Dean Roden", "degree": "PhD", "year": "1948", "title": "Base Pressure at Supersonic Velocities", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122008-143236", "creators": [ { "name": { "family": "Chapman", "given": "Dean Roden" }, "id": "Chapman-Dean-Roden", "display_name": "Chapman, Dean Roden" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F2ZC-4B47", "abstract": "The existing theories of base pressure are described in detail and are shown to be unsatisfactory. An \"exact\" analysis is then made of the base pressure in an inviscid fluid, both for two-dimensional and axially-symmetric flow. It is shown that for a given body there are, in general, an infinite number of possible solutions satisfying all necessary boundary conditions. For the particular case of inviscid flow about projectile-shaped bodies only one solution is possible, but it corresponds to zero base drag. This latter result is generalized and the following conjecture made: it is impossible for a steady axially-symmetric inviscid supersonic flow to converge toward, and to meet the axis at a finite (non-zero) angle.\r\n\r\nSince the inviscid-fluid theory does not adequately describe the conditions in a real fluid, an approximate theory for base pressure in a viscous fluid is developed. This latter theory is based in part on the inviscid-flow calculations and in part on dimensional analysis. It includes the effects of Mach number, Reynolds number, body shape, and type of boundary-layer flow. A comparison of the theory with the available experimental data indicates satisfactory agreement.\r\n\r\nIt is shown that under certain conditions the airfoil contour for minimum profile drag in a viscous fluid necessarily has a blunt trailing edge. Approximate calculations indicate that very substantial reductions in profile drag are possible by designing airfoils with blunt trailing edges. Consideration is briefly given to the interference of a support rod on base pressure measurements in a supersonic wind tunnel.\r\n" }, { "name": "Chuan, Raymond Lu-Po", "degree": "Engineering Degree", "year": "1948", "title": "An Investigation of Vortex Shedding as Related to the Self-Excited Torsional Oscillation of an Airfoil", "advisor": "Dunn, Louis G.; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02102009-131702", "creators": [ { "name": { "family": "Chuan", "given": "Raymond Lu-Po" }, "id": "Chuan-Raymond-Lu-Po", "display_name": "Chuan, Raymond Lu-Po" } ], "advisors": [ { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6JQH-FS81", "abstract": "This report covers the results of the experimental investigation of the self-excited torsional oscillation of a NACA 0006 airfoil suspended elastically. The relationship between the torsional oscillation and the shedding of vortices was investigated for this airfoil.
\r\n\r\nTwo types of oscillation phenomena were found in the investigation. One type, exhibited by cases with angles of attack just above stall, persisted with increasing velocity without reaching any apparent limit within the range of velocity attainable in the present wind-tunnel. The other type, exhibited by cases with higher angles of attack, only showed self-excited oscillations in a certain range of velocity, the range decreasing with increasing angle of attack.
" }, { "name": "Davis, Thomas V.", "degree": "Engineering Degree", "year": "1948", "title": "Design of a Large Water Tunnel", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222008-143224", "creators": [ { "name": { "family": "Davis", "given": "Thomas V." }, "id": "Davis-Thomas-V", "display_name": "Davis, Thomas V." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H8HZ-D718", "abstract": "A ten-foot-diameter water tunnel is discussed as to feasibility and design, and consideration is narrowed to the working section -- nozzle, throat and diffuser. A non-cavitating nozzle shape is calculated by systematizing the method suggested by Hue-Shen Tsien.\r\n\r\nStructural design is approached on the basis of a six-hundred-foot static pressure head; and an additional half- full design loading is calculated as a Fourier expansion. The analysis of the structure is broken down into a number of elasticity problems.\r\n\r\nThe cylindrical throat is analyzed by membrane theory for the high-head condition; and stresses at and in the supporting rings are thoroughly investigated. More involved methods considering transverse shear and bending are used to check the stability of the shell when only partially full.\r\n\r\nMembrane theory is applied to the conical diffuser and to the double-curved nozzle to determine the stress state in both under the high-head condition. Shell thicknesses and member sizes have been selected throughout from this analysis.\r\n" }, { "name": "DeGroff, Harold M.", "degree": "Engineering Degree", "year": "1948", "title": "Calculation of the Optimum Pitch Distribution of a Propeller with Sweepback", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-151056", "creators": [ { "name": { "family": "DeGroff", "given": "Harold M." }, "id": "DeGroff-Harold-M", "display_name": "DeGroff, Harold M." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6PJQ-Q596", "abstract": "The principal problem dealt with is the derivation of a method for computing the optimum pitch distribution of a lightly loaded, sweptback propeller. The method is based on an extension to the work of Glauert as presented in Volume IV of the Durand series. A complete calculation is carried out for a swept propeller in which the resultant velocities along the blade vary through the transonic regime. The analytical work is simplified by the use of the calculus of variations. A survey of the German literature on this topic is included along with a complete discussion of the aerodynamic parameters to be considered in making of such a design.\r\n" }, { "name": "Fung, Yuan-cheng", "degree": "PhD", "year": "1948", "title": "Elastostatic and Aereolastic Problems Relating to Thin Wings of High Speed Airplanes", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-165709", "creators": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng-B", "display_name": "Fung, Yuan-cheng" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JK8Q-RH35", "abstract": "This report is concerned with the statics and dynamics of very thin wings of high speed airplanes. With the modern tendency towards sweepback, which is necessary for supersonic airplanes, the wing construction tend more and more to an ideal structure, hence for the static problem of this report, the wing is idealized to a thin cantilever elastic plate.
\r\n\r\nPart I gives a general formulation of the fundamental equations of deformation of thin elastic plates and the direct methods of solution. For small deflection of plates, the equations and boundary conditions are derived from the three-dimensional equations of elasticity developed in power series of the thickness of the plate. It is shown that the classical Poisson-Kirchhoff theory is coincident with the first approximation in this development. These equations are then transformed into oblique coordinates for treating problems concerning swept plates. Since the problem of the cantilever plate is very difficult to solve from the standpoint of biharmonic analysis, emphasis is laid on the direct methods of solution which lead to useful approximate solutions with desired accuracy. Section 1.21 discusses the relation between plate problems and equivalent variational problems. Section 1.22 contains a systematic review of the Rayleigh-Ritz method of relaxation of boundary conditions, including the Trefftz method as one instance.
\r\n\r\nPart II discusses the general aeroelastic problems of high speed airplanes. For airplanes accelerating or decelerating through the transonic region, the coefficients in the aeroelasticity equations are of transient nature. Such transient perturbations are new phenomena in aeronautics but are sufficiently important to warrant detailed investigation. A general mathematical treatment is given, though due to lack of aerodynamic data at present, no specific example is included. A general solution is obtained and this solution is expanded into a generalized power series which proves to be particularly useful when the transient perturbation is small. The present result includes the ordinary small perturbation theory for finite degrees of freedom as a particular case. Several results regarding small perturbations are given in section 2.6.
\r\n\r\nThe next two parts give a detailed computation on the deflection of and stresses in cantilever plates. The deflection of rectangular cantilever plates is solved both by the Rayleigh-Ritz method and the method of relaxation of boundary conditions. For swept plates the Rayleigh-Ritz method is used. A theory of stress approximation without using the intermediate deflection function is developed in Part IV, and is applied to rectangular plates.
" }, { "name": "Gasich, Welko Elton", "degree": "Engineering Degree", "year": "1948", "title": "Downwash Distribution Behind a Wing with an Angle of Attack Discontinuity at Supersonic Speeds", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-133842", "creators": [ { "name": { "family": "Gasich", "given": "Welko Elton" }, "id": "Gasich-Welko-Elton", "display_name": "Gasich, Welko Elton" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GGC8-CN80", "abstract": "Investigation of the downwash field behind a wing with an angle of attack discontinuity at supersonic speeds by use of linearized conical flow theory has shown the downwash to be of finite magnitude at all points in and behind the plane of the wing. The downwash at more than five chord lengths behind the wing was found to asymptotically approach the value of downwash calculated in the Trefftz plane. Behind the wing and within the span that is determined by the intersection of the Mach cones from the leading edge with the trailing edge, an unexplicable action of the downwash was found to exist. It was found that at the trailing edge the downwash was a 100 percent of that on the wing surface. At two chord lengths, the downwash was 83 percent. Upon moving aft, it was found that the downwash increased in magnitude and that at 10 chord lengths, it asymptotically approached the value at the Trefftz plane, namely 100 percent again.
\r\n\r\nBy considering an idealized missile configuration, it was found that roll reversal was possible. The possibility of reversal was found to be almost entirely dependent upon the location of the control lifting surfaces with respect to one another.
\r\n\r\nA brief reference to the sidewash field was made, since the values of sidewash were a natural outgrowth of the solution of the downwash field in the Trefftz plane. An elementary consideration of the sidewash field also showed a contribution to an induced rolling moment that tends to produce roll reversal.
" }, { "name": "Imster, Harry Frederick", "degree": "Engineering Degree", "year": "1948", "title": "Axially Symmetric Laminar Compressible Boundary Layers with Pressure Gradient", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-074849", "creators": [ { "name": { "family": "Imster", "given": "Harry Frederick" }, "id": "Imster-Harry-Frederick", "display_name": "Imster, Harry Frederick" }, { "name": { "family": "Lesko", "given": "James Steven" }, "id": "Lesko-James-Steven", "display_name": "Lesko, James Steven" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HFMY-CY49", "abstract": "Previous work on the subject of laminar compressible boundary layers has considered the flat plate without a pressure gradient (Karmen, Emmons and Brainerd), the flat plate with a pressure gradient (Illingworth), and the cone without pressure gradient (Hantzsche and Wendt). It is the purpose of this investigation to determine the effect of pressure gradient on the boundary layer thickness and skin friction for a figure of revolution in compressible flow.\r\n\r\nThe basic momentum, continuity, and energy equations of viscous, compressible flow are reduced to an approximate form in the neighborhood of the surface of a figure of revolution by the usual boundary layer assumptions and the particular assumptions that no heat is transferred between the figure of revolution and the fluid and that the Prandtl number is equal to unity. An integral relation is then developed for the approximate equations and is subsequently reduced to a differential equation in which the boundary layer thickness is the dependent variable. In addition to considering the case of compressible flow with a pressure gradient, three other cases are examined in order to aid in the interpretation of the results. These are: compressible flow with no pressure gradient, and incompressible flow with and without pressure gradient. The equations are then applied to a figure of revolution over which pressure distributions have been experimentally determined at two Mach numbers and two Reynolds numbers. The resulting boundary layer thickness distributions are then used to determine the skin friction drag for the various cases.\r\n\r\nThe effects of boundary layer velocity profile relation on skin friction drag coefficient are considered in some detail.\r\n\r\nThe results of the investigation indicate that the usual practice of applying flat plate laminar skin friction drag coefficients (either compressible or incompressible) to figures of revolution in supersonic flow may be unconservative by a considerable margin. It is also shown that resulting drag values are considerably dependent on the boundary conditions used to obtain the boundary layer velocity profile." }, { "name": "Jensen, Arnold Axtell", "degree": "Engineering Degree", "year": "1948", "title": "Wind Tunnel Investigation of a Supersonic Tailless Airplane at Low Subsonic Speed", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-103750", "creators": [ { "name": { "family": "Jensen", "given": "Arnold Axtell" }, "id": "Jensen-Arnold-Axtell", "display_name": "Jensen, Arnold Axtell" }, { "name": { "family": "Koerner", "given": "Warren Gottlieb" }, "id": "Koerner-Warren-Gottlieb", "display_name": "Koerner, Warren Gottlieb" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KFRK-AF65", "abstract": "An investigation was made in the Caltech-Merrill low speed wind tunnel at Pasadena City College to determine the lift and moment characteristics of a sweptback wing and a comparable delta wing, both with a 65\u00b0 sweptback leading edge and a double wedge symmetrical airfoil section. Both wings were tested with and without a fuselage. Leading edge flaps and slats, trailing edge plain flaps, split flaps, Fowler type flaps, and fillets were tried to determine their effects on these characteristics. The complete airplane was designed with the idea that it should be a tailless airplane.\r\n\t\r\nThe results showed unfavorable longitudinal static stability characteristics which could be improved but which could never be completely overcome at the stall when the wings were tested with the fuselage. A horizontal tail surface was necessary for longitudinal static stability at the stall but proved ineffective at the lower angles of attack.\r\n\r\nThe maximum lift coefficients for both wings of about 1.3 were higher than for a two dimensional double wedge airfoil section of approximately 0.8. The angles of attack at which these were reached were about twice as high as for the two dimensional section.\r\n\r\nTuft surveys showed the formation of two strong vortices from the leading edge of both wings first appearing at an angle of attack of approximately 10\u00b0. These vortices separated from the upper surface of the wing before reaching the trailing edge.\r\n\r\nComparison of results for the two wings indicated that the discontinuity of the trailing edge at the root of the sweptback wing was detrimental to the maximum lift.\r\n\r\nThere was an optimum deflection of the trailing edge split flap as a high lift device.\r\n\r\nOn the delta wing alone the plain flaps were very effective in increasing the maximum lift while the split flaps were ineffective.\r\n\r\nAilerons on the sweptback wing wore effective at all angles of attack through the stall." }, { "name": "Joga Rao, Chintakindi Venkata", "degree": "Engineering Degree", "year": "1948", "title": "Repeated Loads Above the Proportional Limit on 24st Aluminum Alloy", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-133111", "creators": [ { "name": { "family": "Joga Rao", "given": "Chintakindi Venkata" }, "id": "Joga-Rao-Chintakindi-Venkata", "display_name": "Joga Rao, Chintakindi Venkata" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V8T5-YS83", "abstract": "The purpose of this investigation is to study the effects of repeated tensile stresses above the proportional limit on 24ST Aluminum Alloy.\r\n\r\nThe investigation consisted of three parts:\r\n\r\n1. An investigation of the effects of the application of repeated tensile stress above the proportional limit for 500 cycles followed by a higher repeated tensile stress up to 5,000 cycles.\r\n\r\n2. An investigation of the effects of changing the number of cycles of pre-stress.\r\n\r\n3. An Investigation of the effects of aging.\r\n\r\nIt was found that permanent deformation caused by over-stress is not a useful factor in forecasting life expectancy.\r\n\r\nIt was also found that the effects of aging, initial cold work, and magnitude of overstresses applied all have definite influence on the ability of 24ST Aluminum Alloy to withstand further overstressing and require considerably more thorough investigation.\r\n\r\nIt is considered that this field offers attractive possibilities for further study of the behavior of aircraft materials with the objective of increased accuracy in airplane design.\r\n\r\nThe investigation was carried out in collaboration with Conrad N. Nelson, Captain, U. S. Air Force at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California." }, { "name": "Lampert, Seymour", "degree": "Engineering Degree", "year": "1948", "title": "Rolling Moment Due to Yaw of Flat Wings of Trapezoidal Planform at Supersonic Speeds", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-140210", "creators": [ { "name": { "family": "Lampert", "given": "Seymour" }, "id": "Lampert-Seymour", "display_name": "Lampert, Seymour" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HDT1-PR91", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe purpose of this thesis is to determine the effect of yaw on the rolling moment characteristics of rectangular and trapezoidal planforms of zero thickness. The method used is that of applying the superposition of solutions of linearized conical flow to the problem of the yawed wing. The solutions particularly applicable are those where W = [...] is symmetrical with respect to the plane of the wing, i.e., (lifting case). For the wings considered in this report it was necessary to determine uniquely W = W(b,[...], t) in the following regions: 1) subsonic leading edge, 2) subsonic trailing edge, 3) infinitely swept wing, 4) supersonic leading edges. The rolling moment and lift coefficients were calculated and the effect of varying the angle of side edge and yew angle of the wing in respect to these parameters can be computed. The rolling moment coefficient for a rectangular wing of different aspect ratios was computed and it was found that the variation of rolling moment with angle of yaw [...] increases almost linearly to a maximum and then falls off. There is also an increase in [...] with increasing aspect ratio." }, { "name": "Laufer, John", "degree": "PhD", "year": "1948", "title": "Investigation of Turbulent Flow in a Two-Dimensional Channel", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152005-133021", "creators": [ { "name": { "family": "Laufer", "given": "John" }, "id": "Laufer-John", "display_name": "Laufer, John" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6ZYC-HJ88", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 1.23 x 10\u2075, 3.08 x 10\u2075 and 6.16 x 10\u2075, based on the half width of the channel and the maximum velocity. A channel of 5\" width and 12:1 aspect ratio was used for the investigation.
\r\n\r\nMean speed and axial fluctuation measurements were made well within the laminar sublayer. The semi-theoretical predictions concerning the extent of the laminar sublayer were confirmed. It was found that the viscosity has a more profound influence on the fluctuations than on the mean velocity, the region of influence being approximately four times as wide.
\r\n\r\nFluctuations perpendicular to the flow direction v', w' and the correlation coefficient [...] were measured, and the turbulent shear distribution calculated. Shear calculations from independent methods using the measured velocity gradient at the wall and pressure gradient along the channel furnished a good check on the values of the shearing stress in all cases with the exception of the highest Reynolds number where \u03a4 obtained from the fluctuation measurements is approximately 25% lower. All mean fluctuating quantities were found to decrease with increasing Reynolds number. Measurements of the scales Ly, Lz and micro-scales of turbulence \u03bby, \u03bbz across the channel are presented and their variation with Reynolds number is discussed. Using a new technique, values for \u03bbx were obtained; a method for estimating Lx is also given.
\r\n\r\nThe energy balance in the turbulent flow field was calculated from the measured quantities. From this calculation it is possible to give a descriptive picture of turbulent energy diffusion in the center portion of the channel cross-section.
" }, { "name": "Magnus, Richard Jeffrey", "degree": "Engineering Degree", "year": "1948", "title": "Study of Vortex Shedding as Related to Torsional Oscillations of a Thin Airfoil", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-142937", "creators": [ { "name": { "family": "Magnus", "given": "Richard Jeffrey" }, "id": "Magnus-Richard-Jeffrey", "display_name": "Magnus, Richard Jeffrey" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NAKT-DG24", "abstract": "This report covers an experimental investigation of the relationship between the vortex shedding frequency and self excited torsional oscillation frequency for a thin airfoil. The work consisted of measurements of velocity fluctuations in the airstream in the vicinity of a wing model mounted in a wind tunnel so that it could oscillate about the wing axis. The velocity fluctuation measurements were made with the Wing restrained and with the wing oscillating at various angles of attack and wind velocities.\r\n\r\nTwo distinct types of oscillations were found. One type was self sustaining and increased in amplitude with increasing wind velocity while the other type stopped for velocities beyond some critical value." }, { "name": "Marble, Frank Earl", "degree": "PhD", "year": "1948", "title": "Some Problems Concerning the Rotational Motion of a Perfect Fluid", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-104144", "creators": [ { "name": { "family": "Marble", "given": "Frank Earl" }, "id": "Marble-Frank-Earl", "display_name": "Marble, Frank Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2JGF-0Z67", "abstract": "In an effort to obtain some understanding of the processes involved in the rotational motion of a perfect fluid several particular linearized examples of rotational flow are solved in detail. The first part discusses some types of boundary value problem which arise. The solution of the non-linear partial differential equation by a particular iteration process is considered and the process is shown to converge for an extended version of the problem when the vorticity distribution is sufficiently smooth. The first step of the iteration process may constitute a good approximation in these cases and is taken as the basis of linearized solutions studied in the remainder of the work.\r\n\r\nThe process of straightening a non-uniform velocity profile by means of an idealized screen is considered in Part II as a problem in rotational motion of an ideal fluid with the screen replaced by an appropriate non-conservative force field. The detailed solution is given for both the linearized problem and the second approximation, The complete second order correction is less than 6 percent of the local velocity given by the linear solution for a rather severe case, The corrections arising from the various physical processes involved are analyzed and found to exceed 6 percent in same cases but are inherently compensating.\r\n\r\nThe two-dimensional rotational flow about a closed body is obtained in Part III by utilizing the Green's function method of solving the inhomogeneous differential equation involved. The conformal transformation which maps the given contour into a circle is used to find the appropriate Green's function for the contour. Solutions are then written down for any body, the Riemann mapping function of which is known, The Blasius force and moment formula are extended to include the case of general rotational motion, the relations of Kuo appearing as special forms where the vorticity distribution is uniform.\r\n\r\nIn the final part the theory of the three-dimensional. flow through an axial turbomachine, associated with variation of circulation along the blade length, is described as an extension of the classical theory of finite wings and is simplified to a problem in axially symmetric rotational fluid motion by considering an infinite number of blades in each row. The linearized problem is solved for the radial, tangential, and axial velocity components induced by a single row of stationary or rotating blades with finite chord and prescribed loading. The particular case for which the blade chord approaches zero, and the tangential velocity changes discontinuously, is associated with the theory of the Prandtl lifting line for finite wings, The complete solution is given for a single stationary or rotating blade row of given loading with a hub/tip ratio of 0.6 and blade aspect ratio of 2. The corresponding discontinuous approximation is compared with the more nearly exact solution and is shown to constitute a useful approximation to the solution for a finite blade chord when the discontinuity is located appropriately. An exponential approximation for the velocity components, deduced from the analysis, allows rapid estimation of the rate at which the equilibrium velocity profiles develop ahead of and behind a blade row and, using the superposition principle, provides a simple means or approximating the velocity distribution in a multistage turbomachine and of discussing mutual interference of blade rows." }, { "name": "Marschner, Bernard Walter", "degree": "Engineering Degree", "year": "1948", "title": "An Investigation of Detached Shock Waves", "advisor": "Nagamatsu, Henry T.; Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152014-090058146", "creators": [ { "name": { "family": "Marschner", "given": "Bernard Walter" }, "id": "Marschner-Bernard-Walter", "display_name": "Marschner, Bernard Walter" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." }, { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "co-advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "abstract": "This investigation demonstrates an application of a\r\nflexible wall nozzle for testing in a supersonic wind tunnel.\r\nIt is conservative to say that the versatility of this nozzle\r\nis such that it warrants the expenditure of time to carefully\r\nengineer a nozzle and incorporate it in the wind tunnel as a\r\npermanent part of the system. The gradients in the test section\r\nwere kept within one percent of the calibrated Mach number, however, \r\nthe gradients occurring over the bodies tested were only\r\n\u00b1 0.2 percent in Mach number.
\r\n\r\nThe conditions existing on a finite cone with a vertex\r\nangle of 75\u00b0 were investigated by considering the pressure distribution\r\non the cone and the shape of the shock wave. The\r\npressure distribution on the surface of the 75\u00b0 cone when based\r\non upstream conditions does not show any discontinuities at the\r\ntheoretical attachment Mach number.
\r\n\r\nBoth the angle of the shock wave and the pressure distribution\r\nof the 75\u00b0 cone are in very close agreement with the theoretical\r\nvalues given in the Kopal report, (Ref. 3).
\r\n\r\nThe location of the intersection of the sonic line with\r\nthe surface of the cone and with the shock wave are given for the\r\ncone. The blocking characteristics of the GALCIT supersonic\r\nwind tunnel were investigated with a series of 60\u00b0 cones.
" }, { "name": "Miller, Herman", "degree": "Engineering Degree", "year": "1948", "title": "Investigation of Errors Obtained with Reflection-Plane Mounted Models Due to End Plate Tares", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-104129", "creators": [ { "name": { "family": "Miller", "given": "Herman" }, "id": "Miller-Herman", "display_name": "Miller, Herman" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V2HD-F021", "abstract": "Because of the great interest in and emphasis on high-speed wind-tunnel tests, it has become increasingly important to provide a support system which affects the tunnel flow and the flow over the model as little as possible. One type of support which is being used a great deal at the present time is the so-called reflection-plane mount. This mount derives its name from the fact that the model consists of only half of the prototype wing or airplane, mounted on its plane of symmetry. Ordinarily the model is mounted next to one of the tunnel walls, but many variations of mounting have been used. A circular end plate may or may not be mounted as a metrical portion of the installation.\r\n\r\nThe purpose of the tests, described in this report, was to determine the interference effects of the tunnel wall or end plate on the model, the interference effects of the model on the end plate, and the true forces acting on the model and end plate. It was also desired to determine the forces acting on the portion of the model in the boundary layer and to determine the effects of gaps between the wing and end plate and between the end plate and tunnel wall.\r\n" }, { "name": "Murphy, Walter Patrick", "degree": "Engineering Degree", "year": "1948", "title": "Performance Calculations of Rocket Tripropellant Systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-104643", "creators": [ { "name": { "family": "Murphy", "given": "Walter Patrick" }, "id": "Murphy-Walter-Patrick", "display_name": "Murphy, Walter Patrick" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ER6J-8M16", "abstract": "The purpose of this investigation is to determine the effect on the temperatures and the performance parameters of the addition of (1), liquid hydrogen, and (2), liquid ammonia to three bipropellant systems currently of interest. These bipropellant systems are: nitrogen tetroxide-hydrazine, hydrogen peroxide-hydrazine, and RFNA-hydrazine.\r\n\r\nFor each of the six tripropeliant systems investigated the chamber temperature, exhaust temperature, and all the important parameters were calculated. These calculations for each system were carried out for both equilibrium flow and constant composition flow assumptions. All the results are listed in tables and the more important parameters are presented in graphical form as well.\r\n\r\nOne hydrogen containing system and one ammonia containing system are discussed in detail. General results for all systems include the fact that the largest proportionate decreases are observed in the variation of the exhaust and chamber temperatures whereas the specific impulse shows slight increases or proportionate decreases of much smaller magnitude than the proportionate decreases in temperatures.\r\n\r\nSeveral new parameters are introduced in an effort to make possible the prediction of performances of a tripropellant system if the chamber temperature variation is known. These parameters may also be used in an indirect manner to illustrate the relative merit of liquid hydrogen and liquid ammonia as coolants in tripropellant systems." }, { "name": "Nelson, Conrad Nathaniel", "degree": "Engineering Degree", "year": "1948", "title": "Repeated Loads Above the Proportional Limit on 24-ST Aluminum Alloy", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-105659", "creators": [ { "name": { "family": "Nelson", "given": "Conrad Nathaniel" }, "id": "Nelson-Conrad-Nathaniel", "display_name": "Nelson, Conrad Nathaniel" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V6ZX-5G92", "abstract": "The purpose of this investigation was to study the effect of repeated tensile stresses above the proportional limit on 24ST aluminum alloy.\r\n\r\nThe investigation consisted in obtaining data on prepared specimens of 24ST aluminum alloy in a machine capable of applying a pure tension stress, repeated many times a minute, without shock but with a high rate of loading.\r\n\r\nIt was found that permanent deformation caused by overstressing is not a useful factor in forecasting the life expectancy of the specimen being tested.\r\n\r\nIt was also found that the effects of \"aging\" (elapsed time between overstresses), initial stresses, and magnitude of overstresses applied, all have a definite influence on the ability of 24ST aluminum alloy to withstand further overstressing. However, these effects are so scattered between different specimens of the same material that they cannot be determined accurately, either qualitatively or quantitatively, without a thorough statistical survey.\r\n\r\nIt is considered that this investigation merely points the way to a further study of the behavior of all aircraft materials above the proportional limit.\r\n\r\nThe investigation was carried out at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California. (referred to hereafter as GALCIT.)" }, { "name": "Pritchard, Ernest I.", "degree": "Engineering Degree", "year": "1948", "title": "Upwash and Sidewash Induced by Certain Control Surfaces in a Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-092628", "creators": [ { "name": { "family": "Pritchard", "given": "Ernest I." }, "id": "Pritchard-Ernest-I", "display_name": "Pritchard, Ernest I." } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HK5H-NH60", "abstract": "Dr. Lagerstrom's development of the conical flow theory to apply to upwash and sidewash problems (see reference 1) has been applied to the case of a deflected roll control surface. The upwash behind, and in the plane of, the deflected control surface at 0, 1, 4, and 9 chord lengths behind the wing is calculated. The whole upwash-sidewaeh field, an infinite distance downstream of the control surface, (in the Trefftz plane), is also calculated. It is shown that a rolling moment is induced on any aerodynamic surface - vertical, horizontal, or oblique - that lies in the wake of the deflected control surface. This induced rolling moment is in the reverse direction of that prescribed by the deflection of the roll control surface. One simple case is cited where the magnitude of the induced rolling moment is larger than that produced directly by the roll control surface, thus causing a reversal of the roll direction. An induced yawing moment may also be encountered if a vertical aerodynamic surface, not symmetrical with respect to the plane of the wing, is present in the wake of the deflected control surface." }, { "name": "Seager, Donald Barstow", "degree": "Engineering Degree", "year": "1948", "title": "Operational Flight Testing", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-153900", "creators": [ { "name": { "family": "Seager", "given": "Donald Barstow" }, "id": "Seager-Donald-Barstow", "display_name": "Seager, Donald Barstow" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/21B0-X909", "abstract": "Operational data are those which are used in routine flights to indicate the weight of payload and fuel that can safely be carried. Therefore, operational data consist of information on take-off, climb, cruise, descent, and landing.\r\n\r\nAirplanes which make the most use of this type of information at present are long range, propeller driven transports and bombers; the material presented on the following pages is specifically for use with this general type of aircraft.\r\n\r\nMethods of reducing take-off tests, climb tests, and of obtaining high speed cruise control are presented in the body of the thesis." }, { "name": "Sims, William Edward", "degree": "Engineering Degree", "year": "1948", "title": "Performance Calculations of Rocket Tripropellant Systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152008-110059", "creators": [ { "name": { "family": "Sims", "given": "William Edward" }, "id": "Sims-William-Edward", "display_name": "Sims, William Edward" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QT2H-WD21", "abstract": "This investigation was conducted to determine the effect on performance and temperatures of the addition of either liquid hydrogen or liquid ammonia to three bipropellant systems of current interest. These bipropellant systems are nitrogen tetroxide-hydrazine, hydrogen peroxide-hydrazine, and RFNA-hiydrazine.\r\n\r\nFor each tripropellant system all important parameters and chamber and exhaust temperatures are determined for equilibrium flow conditions and constant composition flow conditions. All the results are listed in tables and the effects on several of the more important parameters are illustrated graphically.\r\n\r\nThe results show that theoretically the effect of the addition of the third component is desirable by causing reduction in temperature and increase in performance.\r\n\r\nNew parameters are introduced for utilization in predicting performances of tripropellant systems once the chamber temperature has been calculated or estimated." }, { "name": "Slater, Mervin Otis", "degree": "Engineering Degree", "year": "1948", "title": "Calculation of Enthalpy-Entropy Diagrams for Rocket Propellant Systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12242008-124334", "creators": [ { "name": { "family": "Slater", "given": "Mervin Otis" }, "id": "Slater-Mervin-Otis", "display_name": "Slater, Mervin Otis" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J89N-WK27", "abstract": "The purpose of this thesis is to present a method and the fundamental data necessary to construct enthalpy-entropy diagrams and from these diagrams to calculate theoretical performance of rocket motor propellants. The systems investigated using this method are:\r\n\r\n(1) RFNA-Ammonia (1)\r\n(2) Ammonia (1)-Ozone (1)\r\n(3) Hydrogen (1) Ozone (1)\r\n\r\nEnthalpy-entropy diagrams for these fuels were constructed for several different mixture ratios: over oxidized, stoichiometric, and under-oxidized. Performance was calculated assuming chamber pressures of 600 psia and 300 psia and exhaust pressures of 14.7 psia, 7.35 psia, and 0.147 psia. These diagrams facilitate the investigation of the effect of varying chamber pressure on chamber temperature and performance. They also facilitate investigation of varying expansion ratio, varying mixtures ratios, etc. They are especially useful in determining the performance of step rockets where exhaust conditions may vary from sea level to vacuum.\r\n\r\nThe results of the performance calculations indicate that performance found by using enthalpy-entropy diagrams checks closely with those determined by other methods. The performance of the last two systems is such as to indicate that a more thorough study of them should be made." }, { "name": "Smith, Josiah E.", "degree": "Engineering Degree", "year": "1948", "title": "Investigations of the Aerodynamic Interactions Between Wind Tunnel Models and their Support Systems at the GALCIT Ten Foot Wind Tunnel", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112011-092002748", "creators": [ { "name": { "family": "Smith", "given": "Josiah E." }, "id": "Smith-Josiah-E", "display_name": "Smith, Josiah E." } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P2JE-8W83", "abstract": "This work is divided into two parts. Part I describes the GALCIT image system tare procedure as it is used at the present time, the techniques of operation, and the assumptions used. The tare procedure is an experimental method for obtaining the aerodynamic interference forces and moments produced on a wind tunnel model by the supporting structure which holds it fixed in the windstream. The present technique has been in use at GALCIT for over five years, during which time many small inconstancies kept recurring, indicating the need for refinement of the procedures. Part II is a report on the first phase of the investigations planned for the attack on these problems.\r\n\r\nIn Part II are given the measurements of the interactions on a simple, rectangular wing, and of the air loads on the suspension system without a model present. An attempt is made to give a physical picture of the rather elaborate flow patterns around the windshields, and of what happens to the aerodynamic characteristics of a wing when it is immersed in such a flow field. Some of the inadequacies of the present techniques are isolated and their magnitudes determined. A first try is made at measuring the tares for a yawed wing, with encouraging results. The need for further experimental work is clearly indicated, as well as for a theoretical study of the flow patterns in the tunnel throat.\r\n" }, { "name": "Srinivasan, Natesan", "degree": "Engineering Degree", "year": "1948", "title": "Higher Order Approximations for Transonic Flow Over Slender Bodies", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-132758648", "creators": [ { "name": { "family": "Srinivasan", "given": "Natesan" }, "id": "Srinivasan-Natesan", "display_name": "Srinivasan, Natesan" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8HMA-7V02", "abstract": "No abstract." }, { "name": "Trilling, Leon", "degree": "PhD", "year": "1948", "title": "Investigation into the Flow of a Viscous Heat Conducting Compressible Fluid", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12242008-101248", "creators": [ { "name": { "family": "Trilling", "given": "Leon" }, "id": "Trilling-Leon", "display_name": "Trilling, Leon" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "member", "display_name": "Cole, Julian D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/14DR-5V68", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe present investigation is concerned with the effect of a small viscosity and heat conduction coefficient on the flow of a compressible fluid. It is well known that, in the case of an incompressible fluid, such an investigation leads to the boundary layer theory.\r\n\r\nThe chief purpose of this paper is to determine whether the main result of boundary layer theory, namely, that viscosity plays a negligible part in the flow outside a very narrow region in the immediate vicinity of any solid boundary in the fluid, is still valid for a compressible fluid. To investigate that point, a very simple type of flow is selected: the flow past a semi-infinite two-dimensional flat plate parallel to the main stream direction. The problem is further simplified as follows: on the basis of experimental results, the existence of a layer influenced by viscosity is assumed, and the boundary conditions are applied near the outer edge of this layer. This allows a linearization of the equation of motion, and gives information on the interaction between the outer edge of this layer and the main field of flow.\r\n\r\nThe analysis is carried out by the methods based on the theory of the Laplace Transformation. The results are essentially, that if the flow is subsonic, the boundary layer theory developed for incompressible fluids may be extended without qualitative changes. However, in a supersonic flow, one must expect two related effects: one finds the boundary layer, which, as a first approximation, in similar to the boundary layer of an incompressible fluid, and a shock-wave along the Mach line which starts at the leading edge of the flat palate, and whose strength is given by the expression:\r\n[...] where [...] is the normal velocity across the shock, M is the free stream Mach number, [...] is the distance from the leading edge of the flat plate along the shock, [...] is the distance normal to the shock, [...] is sonic velocity of the free stream and [...] is the mean effective free stream kinematic viscosity of the fluid." }, { "name": "Wheldon, Wilbert Gayton", "degree": "Engineering Degree", "year": "1948", "title": "Method for Estimating Downwash Behind Swept Airfoils", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152008-143236", "creators": [ { "name": { "family": "Wheldon", "given": "Wilbert Gayton" }, "id": "Wheldon-Wilbert-Gayton", "display_name": "Wheldon, Wilbert Gayton" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/67D0-3C95", "abstract": "A theoretical investigation has been made relative to the adaptation of the simple Prandtl wing theory to wings with highly swept lifting lines for purposes of computing downwash. Equations have been developed relating the characteristic geometry of this type of wing to the associated vortex pattern and the Biot-Savart Equation has been integrated in such a way as to most facilitate engineering calculations. The assumption is made that the distribution of circulation about the wing has been predetermined by one of the recently developed span-loading theories.\r\n\r\nThe general method of approach as has been used by Silverstein, Katzoff and Bullivant in Reference (1) is used herein. The primary deviation from the procedure outlined by these authors is the extension of computational methods from the two dimensional plane-of-symmetry analysis to three dimensions. Though it is not always stated implicitly, some of their devices are employed unchanged and others are altered to fit different conditions.\r\n\r\nCalculations have been made (see Appendix A) for a wing for which experimental data on downwash are available. The comparison between theory and experiment is found to be relatively good. Charts and tabular forms have been presented which are expected to be of use to designers interested in tail loads on swept-winged aircraft whose landings and take-offs take place at high angles of attack." }, { "name": "White, Richard Street", "degree": "Engineering Degree", "year": "1948", "title": "Calculation of Enthalpy-Entropy Diagrams for Rocket Propellant Systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262009-141906", "creators": [ { "name": { "family": "White", "given": "Richard Street" }, "id": "White-Richard-Street", "display_name": "White, Richard Street" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PGDK-YH67", "abstract": "It is the purpose of this thesis to calculate the data required to construct enthalpy-entropy diagrams for propellant systems and to investigate their usefulness when applied to the determination of rocket motor performance parameters.\r\n\r\nDiagrams which cover a range of mixture ratios bracketing the stoichiometric value are included for the following systems:\r\n\r\n(1) Liquid Ammonia and RFNA;\r\n(2) Liquid Ammonia and Liquid Ozone;\r\n(3) Liquid Hydrogen and Liquid Ozone.\r\n\t\r\nGraphical performance parameter values obtained for the stoichiometric mixture of liquid ammonia and RFNA differed less than two tenths of one percent from the analytical values calculated by the Jet Propulsion Laboratory.\r\n\r\nPerformance values are determined for chamber pressures of 600 PSIA and 300 PSIA and for exhaust pressures of 14.7 PSIA, 7.65 PSIA, and .147 PSIA.\r\n\r\nBecause of the extensive calculations required to construct an h-s diagram, the graphical method of analysis is not economical unless a comprehensive study of a propellant is desired. However, if performance values are required over a wide range of boundary conditions, the h-s diagram permits the presentation of a large amount of data in a concise and readily useable form." }, { "name": "Williams, Max L.", "degree": "Engineering Degree", "year": "1948", "title": "Maximum Stress in a Cylindrical Bar of Double Wedge Cross Section Under Torsion", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-090841", "creators": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-Max-L", "display_name": "Williams, Max L." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/52Z6-WX56", "abstract": "A comparison of an exact calculation of maximum stress in a cylindrical rod under torsion is compared to the usual engineering approximation which takes the maximum stress as that existing on the boundary of the largest circle inscribed in the given cross section. A numerical example for a symmetrical thin double wedge cross section is calculated and essential agreement in stress magnitude found, although there was an eight degree difference in the location of the point of maximum stress." }, { "name": "Wunch, William Stuart", "degree": "Engineering Degree", "year": "1948", "title": "Studies of the Double-Wedge and Biconvex Airfoils in Hypersonic Flow", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-141322", "creators": [ { "name": { "family": "Wunch", "given": "William Stuart" }, "id": "Wunch-William-Stuart", "display_name": "Wunch, William Stuart" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BSMQ-5177", "abstract": "Through the development of the high altitude rocket interest has turned to the investigation of aerodynamic problems beyond the supersonic regime. This domain of speed has been termed hypersonic, meaning high Mach number flight in a homogeneous medium whose molecules describe negligible mean free paths with respect to a chosen characteristic dimension. The thesis presented given an extension of two-dimensional supersonic airfoil theory to attack the problem of getting aerodynamic coefficients for the double-wedge and biconvex airfoils.\r\n\r\nThe shock wave equations along with those for Prandtl-Meyer flow have been modified by making approximations based on the hypersonic Mach numbers. These equations have been used to treat the following three cases:\r\n\r\n(A) The Mach angle is much less than the deflection angle.\r\n\r\n(B) The Mach angle is much greater than the deflection angle.\r\n\r\n(C) The Mach angle is of the same order of magnitude as the deflection angle.\r\n\r\nA brief discussion is made of the assumptions involved in the development of each of these flows to show that they do not violate basic principles. The hypersonic approximations already mentioned are then applied to these equations. In case (A) formulas are derived giving a quick approximation to the lift, drag, and moment coefficients. In case (B) formulas are found to be similar to those already obtained by the small perturbation method for supersonic flow. The results of case (C) show that a singular investigation must be made of each airfoil. The results of each of these cases are presented in the section titled \"Applications to the Double-wedge and Biconvex Airfoils.\" Results for symmetrical double-wedge airfoils, whose maximum thicknesses are 10 per cent of the chord and are located at 25, 50, and 75 per cent of the chord, are plotted in the appendix." }, { "name": "Amster, Warren", "degree": "Masters", "year": "1947", "title": "Calculation of the Static Longitudinal Stability of Multi-Engine Tractor-Propeller-Driven Monoplanes", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132011-113934958", "creators": [ { "name": { "family": "Amster", "given": "Warren" }, "id": "Amster-Warren", "display_name": "Amster, Warren" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P9X7-WM80", "abstract": "This report has three main purposes:
\r\n\r\n1. To establish an engineering computation procedure for predicting CM(c.g.) as a function of CL for a multi-engine monoplane of conventional configuration with tractor propellers mounted on and forward of the wing.
\r\n\r\n2. To recommend aircraft configurations which will minimize the destabilizing effect of power.
\r\n\r\n3. To provide a physical explanation for the effect of power on stability.
" }, { "name": "Anderson, Roy Gene", "degree": "Engineering Degree", "year": "1947", "title": "Development of a Hydroduct", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-155842", "creators": [ { "name": { "family": "Anderson", "given": "Roy Gene" }, "id": "Anderson-Roy-Gene", "display_name": "Anderson, Roy Gene" }, { "name": { "family": "Rush", "given": "Charles Wesley" }, "id": "Rush-Charles-Wesley", "display_name": "Rush, Charles Wesley" }, { "name": { "family": "McClellan", "given": "Thomas Rufus" }, "id": "McClellan-Thomas-Rufus", "display_name": "McClellan, Thomas Rufus" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7PWR-0P18", "abstract": "This report presents the results of experiments on a device for producing thrust for underwater propulsion. The principle of the device is based on accelerating a large mass of water by expansion of a small mass of gas, the gas being injected continuously into the water. The investigation consisted of tests conducted on ducts of several different designs; varying the exit area of the duets, the water and gas flow, and the method of injecting and mixing the gas and water.
\r\n\r\nUsing hydrogen gas at a rate of 0.0165 lbs/sec at a water flow rate of 27.4 lbs/sec, a maximum gross thrust of 29.2 lbs was obtained. At this water flow rate the internal friction drag of the duct was 20.5 lbs, giving a net thrust of 8.7 lbs. The effective exhaust velocity for these flow rates was 56,900 ft/sec.. ThAt is equivalent to a specific impulse of 1,770 sec., whereas a good conventional rocket fuel would have a specific impulse of about 250 sec. At low gas flow rates an effective exhaust velocity of 296,000 ft/sec. was obtained. However, at this low gas rate the gross thrust was less than the internal friction drag of the duct.
\r\n\r\nEffective exhaust velocity is defined as gross thrust divided by the mass flow rate of gas, and has the dimensions of velocity.
\r\n" }, { "name": "Ballhaus, William Francis", "degree": "PhD", "year": "1947", "title": "Aerodynamic and Geometric Parameters Affecting Aircraft Weight", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-152006", "creators": [ { "name": { "family": "Ballhaus", "given": "William Francis" }, "id": "Ballhaus-William-Francis", "display_name": "Ballhaus, William Francis" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T60T-F120", "abstract": "A number of single engine conventional aircraft are studied to investigate the possibility of applying statistical methods to the problem of aircraft weight estimation. It is shown that the statistical treatment is definitely useful. It is also shown that, without proper care and judgment, such a statistical treatment leads to somewhat misleading results. The need for structural and aerodynamic training and experience together with essential weight estimating experience is evident. Such experience is requisite to arriving at proper weight estimates when basing these estimates upon the weights of aircraft which have previously been designed and built.
\r\n\r\nIt was hoped that the effects of all of the important aerodynamic and geometric parameters upon aircraft weight would be found from this study of successful single engine aircraft. It was further hoped that the results of this study would be applicable to the difficult problem of estimating the weight of new aircraft. The number of aircraft in the sample for which pertinent information was available was not large enough to permit the evaluation of the effects of all of the parameters although most of the important parameters and their essential effects have been indicated. Lack of complete information due to the restricted or confidential nature of the data was one of the most troublesome handicaps. The latter problem of obtaining weight estimating procedure has, however, been solved since satisfactory weight estimating formulas have been developed for use in basic design weight estimates.
\r\n\r\nIt is this latter result for which the entire study was made. That is, the study was initiated to offer assistance to practicing preliminary design engineers by providing usable information concerning the effects of such factors as gross weight, load factor, and wing span upon aircraft weight. Such information should be invaluable to assist in arriving at the optimum aircraft design with respect to performance, maneuverability, and utility.
\r\n\r\nAll the useful estimating formulas are summarized on page 43. Also included are the calculated probable errors of estimate.
" }, { "name": "Bowie, James Monfort", "degree": "Engineering Degree", "year": "1947", "title": "Gas Generation by Chemical Reaction for Pressurizing Liquid Rocket Propellants", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-100935", "creators": [ { "name": { "family": "Bowie", "given": "James Monfort" }, "id": "Bowie-James-Monfort", "display_name": "Bowie, James Monfort" }, { "name": { "family": "Huestis", "given": "Gerald Stephen" }, "id": "Huestis-Gerald-Stephen", "display_name": "Huestis, Gerald Stephen" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7T6E-3D20", "abstract": "This report is devoted to presenting the results of an investigation directed toward the design of a chemical gas generation system for the Wac Corporal. In this case the function of gas generation is to provide the necessary pressure to inject the propellants into the rocket motor.
\r\n\r\nThe investigation indicates that gas can be generated in the main acid tank of the Wac by injection of a controlled amount of aniline to react with the acid. This aniline is injected at the bottom of the acid tank, and is supplied from a small pressure cell contained integrally with the injector and aniline flow regulator. Tests show that this system is able to regulate the flow of aniline into the acid tank to maintain a pressure on the propellants with \u00b120 psi. of the desired value.
\r\n\r\nA proposed package unit for installation on the Wac Corporal is shown in Fig 1. This unit contains all the parts necessary for the gas generation function, and its installed weight including the aniline, is estimated to be eight lbs.
\r\n\r\nThe importance of the installation of such a unit on the Wac is seen when it is realized that the total weight of the gas generation system, including the acid used, will be approximately 25 lbs. This system will replace the 90 lb. air pressurization unit now being used to pressurize the propellants and it will represent a 65 lb. reduction in initial gross weight. Such a weight reduction will lead to greatly improved rocket performance.
\r\n\r\nThis report does not attempt to determine the range of gross weights, over which gas generation systems will prove superior to other methods of propellant pressurization. It is felt, however, that a definite upper and lower limit on missile gross weight does exist for which gas generation will be applicable.
\r\n\r\nThe Wac Corporal is a sounding rocket of 590 lbs. gross weight using red fuming nitric acid and aniline as propellants. It was designed at the California Institute of Technology Jet Propulsion Laboratory.
" }, { "name": "Bull, Edward George", "degree": "Engineering Degree", "year": "1947", "title": "Repeated Loads Above the Proportional Limit on 24ST Aluminum Alloy", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-093401", "creators": [ { "name": { "family": "Bull", "given": "Edward George" }, "id": "Bull-Edward-George", "display_name": "Bull, Edward George" }, { "name": { "family": "Mastin", "given": "Robert L." }, "id": "Mastin-Robert-L", "display_name": "Mastin, Robert L." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "member", "display_name": "Clark, Donald S." }, { "name": { "family": "Martin", "given": "Harold Clifford" }, "id": "Martin-H-C", "role": "member", "display_name": "Martin, Harold Clifford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BN3E-8T35", "abstract": "The purpose of this investigation is to study the effect of repeated tensile stresses above the proportional limit on 24ST Aluminum Alloy.
\r\n\r\nThe investigation consisted of two parts: the design and building of testing apparatus which would provide a pure tension stress capable of being repeated many times a minute without shock but with a high rate of loading, and to obtain data by means of runs on prepared samples of the metal under study.
\r\n\r\nIt was found that permanent deformation caused by overstress is not a useful factor in forecasting life expectancy.
\r\n\r\nIt was also found that the effects of \"aging\" (elapsed time between overstresses), initial cold work, and magnitude of over- stresses applied all have definite influence on the ability of 24ST Aluminum Alloy to withstand further overstressing and require more thorough investigation.
\r\n\r\nIt is considered that this field offers attractive possibilities for further study of the behavior of aircraft materials above the proportional limit with an eye toward increasing accuracy of airplane design.
\r\n\r\nThe investigation was carried out at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California.
" }, { "name": "Burger, Glenn William", "degree": "Engineering Degree", "year": "1947", "title": "Design of an Instrument for Measuring the True Vertical Velocity of an Airplane at Moment of Contact in Landing", "advisor": "Sechler, Ernest Edwin; Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-140606", "creators": [ { "name": { "family": "Burger", "given": "Glenn William" }, "id": "Burger-Glenn-William", "display_name": "Burger, Glenn William" }, { "name": { "family": "Daniels", "given": "Jerry Forest" }, "id": "Daniels-Jerry-Forest", "display_name": "Daniels, Jerry Forest" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R4C9-D634", "abstract": "In the design of the Vertical Velocity Meter a survey was first conducted of the existing methods used to measure the vertical velocity of an airplane when landing. A study was then made of these methods and of other unsuccessful attempts to design a Vertical Velocity Meter to determine just why they were not satisfactory and in what way they might be improved.
\r\n\r\nIt was decided to develop a design along an entirely different principle than any used before but yet one having basic simplicity. The one selected was based on the formula of velocity being equal to a distance divided by the time it took to travel that distance. To accomplish this a device was designed which consisted of two rods of different length which would strike the ground when the plane was landing, thus if the difference in length and the time between the striking of the two rods is known, the velocity at that moment would be determined.
\r\n\r\nSince it was impracticable to test this device on an airplane, a testing machine was constructed which would test both the strength of the rods and various timing methods. This machine consisted of a wedge mounted on the end of a whirling arm which would strike the rods and simulate the impact received during the landing of an airplane. Two timing methods were tried; a Miller Oscillograph with built in recorder, and a Cathode-Ray Oscilloscope with a camera to record the trace.
" }, { "name": "Clarke, Fredric B.", "degree": "Engineering Degree", "year": "1947", "title": "A Study of the Ignition Lag of Spontaneous Rocket Propellants", "advisor": "Altman, David", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-080723", "creators": [ { "name": { "family": "Clarke", "given": "Fredric B." }, "id": "Clarke-Fredric-B", "display_name": "Clarke, Fredric B." }, { "name": { "family": "Sappington", "given": "Merrill Homer" }, "id": "Sappington-Merrill-Homer", "display_name": "Sappington, Merrill Homer" } ], "advisors": [ { "name": { "family": "Altman", "given": "David" }, "id": "Altman-D", "role": "advisor", "display_name": "Altman, David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GV68-3M37", "abstract": "For this investigation, ignition lag, as previously defined, is a time required for a reaction to build up an arbitrary pressure of the order of two inches of water. This definition is of particular interest in the study of liquid rockets since the rate of pressure build-up from the spontaneous reaction propellant components is important in the performance of the rocket motor. It makes possible a comparison of propellant combinations to determine which would be better so far as the time lag in reaching the critical pressure ratio is concerned.
\r\n\r\nIt was found that under any one set of conditions it was possible to reproduce data consistently within ten percent. These consequently resulted in very smooth relationships which are of a nature that was generally expected in each case.
\r\n\r\nIn the investigation it was found that at temperatures near the freezing point of aniline, ignition lags were of the order of 12 to 16 milliseconds. On reaching ordinary room temperatures the lag was reduced by a factor of three or four. Beyond this range the effect of temperature change was not so pronounced, and the curve tends to straighten out (see Figure 3). A temperature increase of 80 degrees beyond 100 degrees F produces a decrease of only 14 percent in ignition lag.
\r\n\r\nFor the effect of dilution of the BPNA with water, two relationships were obtained--one by dropping acid into aniline, the other by reversing the two components. These relationships are plotted in Figure 2 and show that a small percentage of water as an impurity in acid will produce little noticeable effect on ignition. This should be of interest to those working with acid-aniline motors in the field. It is believed that the correct values of ignition lag for mixture ratios of a motor lie between the two curves plotted. For relatively pure acid and commercial grade aniline, 3 to 5 milliseconds were required to build up a pressure of two inches of water in a chamber of 2.655 liters volume.
\r\n\r\nBy using several burettes of different tip sizes, it was shown that drops having volumes of more than about 0.0475 milliliters produced approximately the same ignition lags. Two curves, one for acid into aniline and the other for aniline into acid, are plotted in Figure 1 and give the relationship between drop volume and ignition lag. There is an almost constant difference of about two milliseconds between these two curves, which seems to be characteristic of which component is dropped into the other.
" }, { "name": "Cole, Charles Willard", "degree": "Engineering Degree", "year": "1947", "title": "Design of an Instrument for Measuring the True Vertical Velocity of an Airplane at Moment of Contact in Landing", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122008-094038", "creators": [ { "name": { "family": "Cole", "given": "Charles Willard" }, "id": "Cole-Charles-Willard", "display_name": "Cole, Charles Willard" }, { "name": { "family": "Levitt", "given": "Bernard Barclay" }, "id": "Levitt-Bernard-Barclay", "display_name": "Levitt, Bernard Barclay" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/55P1-6Z07", "abstract": "A dynamic longitudinal stability analysis is made for a Canard (tail forward) type airplane in steady horizontal flight at Mach numbers of 1.7 and 1.3. Four different wing configurations (Fig. 1) are investigated:\r\n\r\nCase I. Delta wing with the Mach wave ahead of the leading edge. The planform of the delta wing is characterized by one-half the apex angle, w[subscript o]. In this case it has been taken to be 18\u00b0.\r\n\r\nCase II. Delta wing with the Mach wave ahead of the leading edge (w[subscript o] = 25\u00b0).\r\n\r\nCase III. Delta wing with the Mach wave behind the leading edge (w[subscript o] = 54\u00b0).\r\n\r\nCase IV. Rectangular, bi-convex, wing with an aspect ratio of 2.\r\n\r\nThe shell or fuselage of the airplane consists of a conical nose and cylindrical afterbody with no boat tailing at the aft end. The stabilizing surface is hi-convex and rectangular in plan form with an aspect ratio of 2. Power is assumed to be supplied by a constant thrust jet motor. Other characteristics may be found in Table I.\r\n\r\nThe design of the airplane is based on the Mach number of 1.7 at an altitude of 30,000 ft. and a gross weight of 10,000 lbs. Static stability is assumed to be the major design variable. The dynamic stability is first investigated for a static stability just sufficient to allow a four-g maneuver without exceeding a 20 degree angle of attack on the fin. Then the static stability is increased in multiples of 2, 3, and 4, to establish a trend.\r\n\r\nIt is found that the effects of compressibility have a powerful influence on some of the coefficients of the stability quartic and hence on the dynamic stability, and that dynamic instability will result in certain cases regardless of the amount of static stability provided.\r\n" }, { "name": "Cole, Julian David", "degree": "Engineering Degree", "year": "1947", "title": "On the Transonic Flow Past Thin Airfoils", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-105048", "creators": [ { "name": { "family": "Cole", "given": "Julian David" }, "id": "Cole-Julian-David", "display_name": "Cole, Julian David" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7YQN-9C32", "abstract": "No Abstract Submitted" }, { "name": "Collins, Hugh L. H.", "degree": "Engineering Degree", "year": "1947", "title": "Experimental Study of the Burning Rates of Some Solid Propellants by Using a Closed Bomb", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162008-141728", "creators": [ { "name": { "family": "Collins", "given": "Hugh L. H." }, "id": "Collins-Hugh-L-H", "display_name": "Collins, Hugh L. H." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EFSF-XG74", "abstract": "This report represents an attempt to correlate experimental data obtained with a burning rate bomb with the data obtained from the firing of rocket charges, and to obtain burning rate curves for new propellants where insufficient data exists.\r\n\r\nIt was found that very good agreement could be obtained between experimental data obtained in a burning rate bomb and data derived from test firing of rocket charges.\r\n\r\nA comparison was made among three different propellants which utilized Thiokol LP-3 for the fuel, and potassium perchlorate and ammonium perchlorate, separately or in combination, for the oxidizer. It was found that potassium perchlorate only gave the fastest burning rate, and the ammonium perchlorate only gave the slowest burning rate, while a mixture of the two gave an intermediate value.\r\n\r\nAn investigation was made on the coning of solid propellant charges. Coning is the term applied when the burning of a solid propellant charge forms a conical burning surface. Normally a flat burning surface is expected and desired. It was found that a wide deviation in the burning rates existed between the center of the propellant and the edge in the case of the mixture of the ammonium and potassium perchlorate and the pure ammonium perchlorate oxidizers. The results also showed that the difference in burning rates between the center and edge of the charge increased as the amount of ammonium perchlorate in the oxidizer was increased. The limited investigation seemed to indicate that the fundamental variation in burning rate was the only cause of coning.\r\n\r\nBest results were obtained from the use of a restricting material similar in nature to the propellant being investigated. In this case, a Thiokol restricting material gave the best results on the Thiokol propellants.\r\n" }, { "name": "Corrsin, Stanley", "degree": "PhD", "year": "1947", "title": "I. Extended Applications of the Hotwire Anemometer. II. Investigations of the Flow in Round, Turbulent Jets", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-105044", "creators": [ { "name": { "family": "Corrsin", "given": "Stanley" }, "id": "Corrsin-Stanley", "display_name": "Corrsin, Stanley" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NB53-K411", "abstract": "Part 1:\r\n\r\nTwo new fields of application of the hot-wire anemometer are proposed, and the appropriate response equations and measuring procedures are developed.\r\n\r\nThe first analysis leads to a method for the measurement of physically significant statistical quantities in a turbulent flow with heat transfer: for example the turbulence levels, the temperature fluctuation level, the turbulent heat transfer coefficient, the velocity scale, the temperature scale and some spectra.\r\n\r\nThe second analysis involves the use of the hot-wire in the turbulent isothermal mixing of two appropriately different gases. If the thermal conductivity of the mixture is known and is a monotonic function of the relative concentration, it is possible to measure the mean velocity and mean concentration at any point. If no data are available on the thermal conductivity of the mixture, this additional unknown can be determined by an additional measurement. Furthermore, it is also possible to measure the various statistical functions of the fluctuating velocities and the local concentration fluctuation, provided, again, that the thermal conductivity is a known monotonic function of the concentration.\r\n\r\nAlthough the details of the present analysis are dependent upon the accuracy of King's equation for the rate of heat loss from fine wires, the general approach is equally valid for any (possibly more accurate) equation that may be deduced.\r\n\r\nPart 2: \r\n\r\nA detailed investigation has been made of the flow in a round turbulent air jet, heated slightly to permit measurement of mean temperature.\r\n\r\nOscillograms of the velocity fluctuation plus direct measurement of the turbulent shear both show that the flow in a fully developed \"turbulent\" jet is completely turbulent only out to approximately the radius at which the extreme outer edge is in the nature of a \"laminar collar\", with predominantly radial (inward) mean velocity, and in between the turbulent core and the laminar collar is a rather wide annular transition region.\r\n\r\nA study of the downstream history of the radial distribution of turbulent velocity shows that the fully developed state of this round jet is reached between 15 and 20 diameters. This conclusion is corroborated by examination of the partition between turbulent motion and mean motion, of total kinetic energy crossing planes perpendicular to the axis in unit time.\r\n\r\nThe directly measured shear distribution is checked roughly by a computation of the same quantity from the mean velocity distribution.\r\n\r\nA measurement of the double correlation function between points symmetrical about the jet axis shows considerable similarity to the corresponding function in isotropic turbulence, and permits calculation of scale and microscale.\r\n\r\nWith the assumption of constant microscale across a section, a rough estimate is made of the energy balance distribution of production, dissipation and diffusion of turbulent energy.\r\n\r\nA comparison with momentum transfer, modified vorticity transfer and constant exchange coefficient theories show that none of them is satisfactory.\r\n\r\nA comparison of mean velocity and temperature distributions verifies Ruden's result that the lateral rate of heat transfer in turbulent shear flow is appreciably greater that the lateral rate of momentum transfer.\r\n\r\nThe use of considerably increased heating, in a second jet unit, has permitted direct measurement of the temperature fluctuation level. Velocity fluctuations were also measured in this case for comparison, and they were found to be the same order of magnitude.\r\n\r\nThe final result is the direct measurement of temperature-velocity correlation and of velocity correlation in the hot jet. This gives a direct measure of the turbulent heat transfer and momentum transfer in the jet, and directly verifies the fact that the former is appreciably greater than the latter.\r\n" }, { "name": "Deodati, Joseph Benjamin", "degree": "Engineering Degree", "year": "1947", "title": "An Investigation of the Round Jet in a Moving Air Sstream", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022008-112834", "creators": [ { "name": { "family": "Deodati", "given": "Joseph Benjamin" }, "id": "Deodati--Joseph-Benjamin", "display_name": "Deodati, Joseph Benjamin" }, { "name": { "family": "Monteath", "given": "Edward Berlendis" }, "id": "Monteath-Edward-Berlendis", "display_name": "Monteath, Edward Berlendis" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8QPZ-RY03", "abstract": "A theoretical investigation is made of a circular jet issuing from an orifice into an air stream flowing parallel to the jet axis and in the same direction as the jet. The analysis is divided into two portions:
\r\n\r\n1. The region immediately downstream of the orifice in which exists the potential cone of uniform velocity.
\r\n2. The region downstream of the end of the potential cone in which the jet is fully developed.
\r\n\r\nThe solution for these two portions are fitted together at the section at which the potential cone disappears giving a complete solution for the whole jet.
\r\n\r\nNumerical computations are made for several ratios of free stream velocity to jet velocity to determine the spread of the jet, velocity on the axis of the jet, and spread of the surface on which the velocity is one half the sum of the jet velocity and free stream velocity.
\r\n\r\nSquire and Trouncer's results are plotted as a comparison with those obtained in this analysis.
\r\n" }, { "name": "Dore, Frank John", "degree": "Engineering Degree", "year": "1947", "title": "The Design of Tailless Airplanes", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-152833", "creators": [ { "name": { "family": "Dore", "given": "Frank John" }, "id": "Dore-Frank-John", "display_name": "Dore, Frank John" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0RZ6-EV10", "abstract": "This paper reviews the various sources of information pertaining to the design of tailless airplanes. The particular topic of any report or memorandum is illustrated by its application to the problems encountered in the design of a given airplane. The subjects mentioned are the determination of the sweepback angle, aspect ratio, taper ratio, twist, dihedral, airfoil section, spanwise loading, and aerodynamic center of the wing; the control elements; and the fuselage and fillet for high speed aircraft.
\r\n\r\nTo illustrate the application of the source material the design of a tailless supersonic airplane is considered. The slow speed wind tunnel tests of the 1/12-scale model are included in the report.
" }, { "name": "Durup, Paul Christian", "degree": "Engineering Degree", "year": "1947", "title": "Lateral Stability of Thin Tapered Struts", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-152413", "creators": [ { "name": { "family": "Durup", "given": "Paul Christian" }, "id": "Durup-Paul-Christian", "display_name": "Durup, Paul Christian" }, { "name": { "family": "Weisenberg", "given": "Joseph Oscar" }, "id": "Weisenberg-Joseph-Oscar", "display_name": "Weisenberg, Joseph Oscar" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FGGF-0080", "abstract": "From the experimental investigation detailed herein it has been determined, at least for two types of struts, that there is a very close correlation between (1) the experimentally determined buckling load which a given strut will sustain and (2) the critical load determined by the use of Southwell\u2019s method, which does not entail loading the strut to its critical load. By using an initial eccentricity and loads considerably less than the original, the critical load may be derived from the results of three or four simple test readings, not requiring an elaborate or refined setup.\r\n\r\nExperimental verification of existing theory of lateral buckling is noted for the case of struts tapered to a point at the application of the loading.\r\n\r\nThe possibility of determining the eccentricity of a given loading by plots of \u03b2/p vs. \u03b2 is pointed out and the type of curve to be expected as noted. However due to lack of refinement of the experimental setup, no definite conclusions are presented.\r\n\r\nThe theoretical portion of this thesis offers the derivation of a formula for the lateral buckling of a thin linearly tapered strut of constant thickness. Due to the complexity of the problem certain simplifications were made to facilitate this derivation.\r\n\r\nComparison of the values determined by use of this formula with the values experimentally determined for four struts shows a fairly close correlation.\r\n\r\nIt is suggested that in some future work a more thorough investigation be made of the relation between the eccentricity of the loading and the load which a strut will carry, using a given deflection as a parameter.\r\n" }, { "name": "Fossier, Mike Walter", "degree": "Engineering Degree", "year": "1947", "title": "Supersonic Wind Tunnel Tests of Two Rocket Propelled Projectile Models", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-082853", "creators": [ { "name": { "family": "Fossier", "given": "Mike Walter" }, "id": "Fossier-Mike-Walter", "display_name": "Fossier, Mike Walter" }, { "name": { "family": "Small", "given": "John" }, "id": "Small-John", "display_name": "Small, John" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/71EK-W641", "abstract": "Two models of rocket propelled projectiles have been tested in the Galcit 2 1/2 inch supersonic wind tunnel at a Mach Number of 3.06, and angles of attack from 0\u00b0 to 10\u00b0. Variations of lift, drag, pitching moment, and position of center pressure with angle of attack have been obtained for each model.\r\n\r\nA strain gage balance system, which was designed to measure the forces acting on the models was found to be entirely satisfactory for this purpose.\r\n\r\nThe results were found to agree very closely with the small perturbation theory for supersonic flow.\r\n" }, { "name": "Griffing, Charles W.", "degree": "Engineering Degree", "year": "1947", "title": "An Application of the Method of Characteristics to Axially Symmetric Supersonic Flow", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-150626", "creators": [ { "name": { "family": "Griffing", "given": "Charles W." }, "id": "Griffing-Charles-W", "display_name": "Griffing, Charles W." }, { "name": { "family": "Wilburn", "given": "William Clarence" }, "id": "Wilburn-William-Clarence", "display_name": "Wilburn, William Clarence" }, { "name": { "family": "Purdon", "given": "David" }, "id": "Purdon-David", "display_name": "Purdon, David" }, { "name": { "family": "McLaughlin", "given": "Earl Wilson" }, "id": "McLaughlin-Earl-Wilson", "display_name": "McLaughlin, Earl Wilson" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GTHG-VM56", "abstract": "The method of characteristics for three dimensional axially symmetric bodies was used to determine the velocity distribution about the nose of the Corporal E rocket, a rocket projectile, for Mach numbers 2 and 4. From the velocities the pressure distribution was determined and a drag coefficient computed.\r\n\r\nFor a starting point the nose of the projectile was approximated for a short distance by a cone and the Taylor-Maccoll solution to this problem was used. This solution gave the angle of shockwave and the body. The Sauer graphical-numerical iteration method was used for the remainder of the solution.\r\n\r\nPreliminary calculations and the work for Mach number 3 were carried out by Dr. H. K. Forster to whom we are indebted for instruction and aid with this work.\r\n" }, { "name": "Hayes, Wallace Dean", "degree": "PhD", "year": "1947", "title": "Linearized Supersonic Flow", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132007-131650", "creators": [ { "name": { "family": "Hayes", "given": "Wallace Dean" }, "id": "Hayes-Wallace-Dean", "display_name": "Hayes, Wallace Dean" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "member", "display_name": "Lagerstrom, Paco A." } ], "option_major": [ "physics" ], "doi": "10.7907/D7N0-4412", "abstract": "This thesis is a presentation of the methods and concepts of the theory of linearized supersonic flow. The fundamental theory which serves as a basis for this investigation is discussed in the first two chapters. Special emphasis is placed upon the study of planar systems.\r\n\r\nA system of conical coordinates is introduced in which the method of separation of variables is applied. The resultant solutions have the Mach cone as a natural boundary and involve a family of hypergeometric functions related to the Legendre functions.\r\n\r\nBasic integral relations for planar systems are obtained between the normal velocity component and the component giving the pressure. The behavior of planar systems relative to the planform configuration is discussed and the concept of problems of the first and second kind is introduced. The lift problem is treated with particular reference to the behavior of the leading edge singularity and to the concept of the Kutta condition as applied to a planform in supersonic flow.\r\n\r\nThe nature of drag in linearized supersonic systems is investigated and the separation of the drag into types is discussed. For planar systems the drag may be divided into basic and induced parts. For general systems the basic division may be made into wave drag and vortex drag. Two fundamental reversed flow theorems are obtained which state that the drag of a system is the same as that of the system with the flow reversed in direction.\r\n\r\nThe theory of conical flow as applied to planar systems is developed and the results for a basic thickness distribution and various lifting triangles are presented.\r\n\r\nThe method of the separation of the lateral variable is investigated using Schlomilch series.\r\n\r\nThe flow about bodies of revolution is discussed and the application of the Riemann method to the problem is given." }, { "name": "Heppe, R. Richard", "degree": "Engineering Degree", "year": "1947", "title": "Investigation of a Variable Geometry Supersonic Diffuser", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-162416", "creators": [ { "name": { "family": "Heppe", "given": "R. Richard" }, "id": "Heppe-R-Richard", "display_name": "Heppe, R. Richard" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WYNA-G323", "abstract": "A flexible second throat supersonic diffuser has been tested in the GALCIT 2-1/2 inch supersonic wind tunnel at Mach numbers of 2.60 and 3.33. The theoretical minimum area relation for starting a supersonic tunnel has been checked at the two Mach numbers, and the amount by which the height of the second throat may be reduced after the tunnel has been started was determined. Minimum compression ratios for the starting and reduced second throat conditions have been determined and compared with those previously found here and theoretically estimated by Crocco. Effect of nozzle surface roughness on supersonic flow is noted, and Schlieren photographs representing the flow in a variety of conditions are presented. A series of Schlieren photographs shows the flow in the second throat at progressively greater amounts of area reduction.\r\n\r\nThe theoretical minimum second throat area relation was found to predict the second throat size for starting within 3 percent at both Mach numbers, being conservative by that amount in both cases. Only about 1/3 of the theoretically predicted reduction of second throat area after starting was realized at both Mach numbers before separation of the boundary layer broke down flow throughout the nozzle. Minimum compression ratios were reduced some 9 and 6 percent for Mach numbers 2.60 and 3.33 respectively. These decreases, though not as large as anticipated, nevertheless have the lowest compression ratios ever measured in the GALCIT tunnel, ratios less than Crocco's estimate, heretofore never realized. Transition, though not occurring by means of a normal shock wave, was found to be stable a few inches downstream of the second throat.\r\n" }, { "name": "Kirkwood, Thomas Frederick", "degree": "Engineering Degree", "year": "1947", "title": "Integral Methods Applied to a Compressible Boundary Layer on an Insulated Flat Plate Parallel to the Wind", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-082433", "creators": [ { "name": { "family": "Kirkwood", "given": "Thomas Frederick" }, "id": "Kirkwood-Thomas-Frederick", "display_name": "Kirkwood, Thomas Frederick" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ERYV-B305", "abstract": "The effect of compressibility upon the boundary layer thickness and wall shearing stress on an insulated flat plate parallel to the wind is investigated. Integral methods are used to investigate both laminar and turbulent boundary layers.\r\n\r\nIn order to simplify the calculations, only the limiting cases of small Mach numbers and very large Mach numbers are investigated in the laminar case. In the turbulent case only small Mach numbers are considered due to the present lack of understanding of supersonic turbulence.\r\n\r\nIt is found that in the subsonic laminar boundary layer, the wall shear stress is approximately independent of Mach number while the boundary layer thickness increases with Mach number. For large Mach numbers in the laminar case it is found that the wall shear stress is proportional to M[subscript o, superscript -.24] and the boundary layer thickness to M[subscript o, superscript 1.76].\r\n\r\nIn the turbulent case, where only small Mach numbers are investigated, both the shear stress end boundary layer thickness are found to decrease with Mach number.\r\n" }, { "name": "Li, Ting-Yi", "degree": "Engineering Degree", "year": "1947", "title": "Lift on Two-Dimensional Symmetrical Airfoil of Finite Thickness in Supersonic Flow", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09192025-183557362", "creators": [ { "name": { "family": "Li", "given": "Ting-Yi" }, "id": "Li-Ting-Yi", "display_name": "Li, Ting-Yi" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/zajs-cy52", "abstract": "This research consists of a study of several methods of computing the slope of lift curve for a two-dimensional symmetrical airfoil of finite thickness in completely supersonic potential flow. An \"exact\" formula is derived by considering the flow conditions over the airfoil surface\r\nincluding the effects of the oblique shock waves emitted from the leading edge of the airfoil. This \"exact\" formula is applied to two simple cases: (1) a 5% thick circular arc airfoil, and (2) a 10% thick circular arc airfoil. The computation results are compared with (1) Ackeret's linearized theory, (2) Busemann's second order theory and (3) Busemann's third order theory. It is found that the presence of shock waves at the airfoil leading edge will lead to a reversal in sign of the slope of lift curve at low Mach numbers close to 1.00, this effect is also sometimes observed experimentally. Furthermore, it has been shown that the linearized theory and the second order theory give too low dC\u2220 /do\u2112 values at high Mach numbers. The third order theory agrees with the \"exact\" theory in general tendency but is not quite so accurate in very high Mach number region and at Mach numbers close to 1.00. Thus, for accurate determination of the slope of lift curve, the \"exact\" formula may find some engineering uses. To facilitate future computations, charts for the necessary coefficients are prepared and steps in applying the formula for engineering cases are outlined and discussed in some detail." }, { "name": "Marble, Frank Earl", "degree": "Engineering Degree", "year": "1947", "title": "The Rotational Motion of an Ideal Fluid and Application to the Three-Dimensional Flow Through Axial Turbomachinery", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-141530", "creators": [ { "name": { "family": "Marble", "given": "Frank Earl" }, "id": "Marble-Frank-Earl", "display_name": "Marble, Frank Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CJJR-H730", "abstract": "The present paper discusses the principles and applications of an iteration method for solving certain problems involving rotational motion of an ideal fluid, such as occur in the presence of heat transfer, combustion, mechanical work processes, and non-uniform shock waves. The iteration process linearizes the essentially non-linear equations for rotational fluid motion by assuming a process for the vorticity transport, namely: the nth approximation is linearized by assuming the vorticity to be transported by the n-1th velocity field. In some important cases, the first order solutions seem to offer considerable accuracy.\r\n\r\nTwo applications of the procedure are discussed in some detail, namely: 1) The process of straightening a non-uniform flow in a two-dimensional parallel-wall channel by means of a screen and 2) The three-dimensional flow in a multistage axial turbomachine having an infinite number of blades in each blade row. The second of these, the three-dimensional flow through a turbomachine, is given detailed analysis bearing some analogy to the Prandtl theory of finite wings. The results for the first order solution of velocity and enthalpy distributions are given explicitly and are shown to be defined by four relatively simple integrals. The cases of rotating and stationary single blade rows are evaluated completely. The general iteration process for obtaining higher approximations, utilizing the method of Green's functions, is given in some detail.\r\n\r\nThe calculations of the flow field generated by a blade row of given geometry is illustrated by the problem of a \"vortex\" turbomachine operating off the design condition. The problem is found to be essentially non-linear in some respects, especially as to the approach to periodic solutions for a succession of similar stages." }, { "name": "Mullane, Leo Wayne", "degree": "Engineering Degree", "year": "1947", "title": "An Apparatus for the Study of the Turbulent Diffusion Flame", "advisor": "Sage, Bruce H.; Hough, Eldred W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-082034", "creators": [ { "name": { "family": "Mullane", "given": "Leo Wayne" }, "id": "Mullane-Leo-Wayne", "display_name": "Mullane, Leo Wayne" } ], "advisors": [ { "name": { "family": "Sage", "given": "Bruce H." }, "id": "Sage-B-H", "role": "advisor", "display_name": "Sage, Bruce H." }, { "name": { "family": "Hough", "given": "Eldred W." }, "id": "Hough-E-W", "role": "advisor", "display_name": "Hough, Eldred W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DW7B-DN61", "abstract": "The project to study the turbulent diffusion flame, by the Department of Chemical Engineering of the California Institute of Technology, is quite comprehensive. Only a small portion of the project was included in the scope of this thesis.\r\n\r\nA study will be made of the turbulent diffusion flame that is formed when fuel gas is introduced, through the end of a 1-inch-diameter tube, into air, flowing in a 4-inch-diameter tube, and combustion is started. The plan of investigation is divided into two parts. First, a study will be made of the mixing zone when combustion is not occurring; and secondly, a study will be made of the combustion zone when combustion is taking place.\r\n\r\nThe work accomplished in the scope of this thesis was the design and assistance in the fabrication and assembly of the equipment necessary to conduct this investigation. This was completed with the exception of the sampler to be used in obtaining samples of the burning gases. In addition, one series of tests was made at one stream velocity.\r\n\r\nThe equipment functioned very well during the series of runs. Recommendations for a few minor changes are included in this report. The incorporation of these changes should increase slightly both the speed of taking data and the accuracy of the results.\r\n\r\nThe results obtained in the series of tests indicated that the desired data can be obtained with this equipment.\r\n" }, { "name": "O'Meara, Donald John", "degree": "Engineering Degree", "year": "1947", "title": "A Study of the Temperature Gradients of Gases Flowing Through Heated Porous Metal", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-081553", "creators": [ { "name": { "family": "O'Meara", "given": "Donald John" }, "id": "O'Meara-Donald-John", "display_name": "O'Meara, Donald John" }, { "name": { "family": "Andrews", "given": "Clyde Cecil" }, "id": "Andrews-Clyde-Cecil", "display_name": "Andrews, Clyde Cecil" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WNFK-V169", "abstract": "Nitrogen and Hydrogen were passed through a pack of heated porous metal discs to obtain temperature distribution as a function of (1) mass flows and (2) temperatures at which metal was heated. An effort was made to obtain heat transfer per unit volume of porous metal as a function of (1) mass flows and (2) temperatures at which the metal was heated. By varying inlet gas pressures at various metal temperatures the effect of temperature on pressure drop was determined.\r\n\r\nThe results show that a cool gas flowing through a heated porous metal very quickly assumes the temperature of the metal. Heat transfer appears to increase linearly with mass flow up to a certain point above which the results were inconclusive. The variation of mass flow with pressure drop was determined to be linear for low pressure drop and to increase at a greater rate for higher pressure drops.\r\n" }, { "name": "Palmer, George Marshall", "degree": "Engineering Degree", "year": "1947", "title": "The Downwash Distribution Behind a Delta Wing at Supersonic Speeds", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-081222", "creators": [ { "name": { "family": "Palmer", "given": "George Marshall" }, "id": "Palmer-George-Marshall", "display_name": "Palmer, George Marshall" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3VWX-XE20", "abstract": "At the present date, very little information exists as to the downwash and sidewash in the wake of lifting surfaces for supersonic missiles and airplanes. To the author's knowledge, Reference 1 is the first paper to develop the theory and carry out numerical calculations for the downwash and sidewash behind wings of practical interest. However, the paper only contained brief indications of how to treat the very interesting triangular planform known as the delta wing.\r\n\r\nIt is the purpose of this paper to extend the basic idea for the determination of downwash as used in Reference 1, to the delta wing, and to carry out numerical calculations for a specific case. Although it is possible to develop expressions for the downwash and the sidewash at all points within the Mach cone and in the wake of the wing, see Reference 1, it was not carried out here. This paper applies only to the downwash field in the plane of the wing. Another restriction is that the delta wing half angle be less than the Mach angle." }, { "name": "Pollock, Albert David", "degree": "Engineering Degree", "year": "1947", "title": "A Study of Methods to Increase the Lift of Supersonic Airfoils at Low Speeds", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-083805", "creators": [ { "name": { "family": "Pollock", "given": "Albert David" }, "id": "Pollock-Albert-David", "display_name": "Pollock, Albert David" }, { "name": { "family": "Reck", "given": "Floyd Francis" }, "id": "Reck-Floyd-Francis", "display_name": "Reck, Floyd Francis" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J3NG-DD26", "abstract": "This thesis presents a study of the problem of improving the lift characteristics of a supersonic wing at low speeds. Trailing edge split flaps, nose flaps, and boundary layer control were investigated singularly and together using the optimum configuration of each.\r\n\r\nResults indicate that the nose flap has an appreciable effect on preventing separation and thus increasing the lift. Split flaps give an increment of lift as would be expected. The boundary layer control consisted of blowing a sheet of high velocity air back over the top surface of the wing with very definite improvements of the lift and drag characteristics.\r\n\r\nThe work on the blowing technique, it is suggested, indicates sufficient promise to warrant much further study. The relatively large increment of lift that can be attributed to the prevention of flow separation at high angles of attack suggests that such boundary layer control could be used to improve controlability and to delay the stall, particularly tip stall, of high speed aircraft with very large sweep back angles.\r\n" }, { "name": "Ponsford, Henry Thomas", "degree": "Engineering Degree", "year": "1947", "title": "A Study of Some Problems Affecting the Design of Wings for Transonic Aircraft", "advisor": "Martin, Harold Clifford; Housner, George W.; Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-085825", "creators": [ { "name": { "family": "Ponsford", "given": "Henry Thomas" }, "id": "Ponsford-Henry-Thomas", "display_name": "Ponsford, Henry Thomas" } ], "advisors": [ { "name": { "family": "Martin", "given": "Harold Clifford" }, "id": "Martin-H-C", "role": "advisor", "display_name": "Martin, Harold Clifford" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Martin", "given": "Harold Clifford" }, "id": "Martin-H-C", "role": "chair", "display_name": "Martin, Harold Clifford" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "member", "display_name": "Dunn, Louis G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3HNE-5E94", "abstract": "A survey of the literature concerning the design of wings for transonic aircraft is made. The problems investigated were 1) for the transonic wing: reduction of drag at high subsonic Mach numbers; achievement of high maximum lift coefficient and stability at low speeds; and determination of air loads in compressible subsonic flow, 2) for the supersonic wing: determination of flow fields at transonic Mach numbers; achievement of adequate low speed performance of a supersonic wing; and determination of air loads at transonic speeds, and 3) structural problems of both types of wings. The extent of present knowledge is outlined, and future fields of desirable research is indicated. A bibliography of reports pertaining to transonic wing design, accompanied by brief summaries is given. A supplementary bibliography of other reports of general interest to transonic wings is also presented." }, { "name": "Reiserer, Russell Lawrence", "degree": "Engineering Degree", "year": "1947", "title": "Design and Test of a Rocket Motor Expansion Joint", "advisor": "Sechler, Ernest Edwin; Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102008-090658", "creators": [ { "name": { "family": "Reiserer", "given": "Russell Lawrence" }, "id": "Reiserer-Russell-Lawrence", "display_name": "Reiserer, Russell Lawrence" }, { "name": { "family": "Barden", "given": "Kenneth Perrin" }, "id": "Barden-Kenneth-Perrin", "display_name": "Barden, Kenneth Perrin" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CM3Y-6453", "abstract": "The purpose of this investigation was to carry on the work of investigating stresses encountered in the design of rocket motor expansion joints. The previous work was done on a semicircular expansion joint by Commander N. J. Kleiss, U.S.N., and Lt. Comdr. S. W. Kerkering, U.S.N. in a thesis submitted to the Aeronautics Department of the California Institute of Technology.\r\n\r\nInformation was desired to make possible a more favorable design. The problem consists of continuing the investigation on a different design, thereby determining a trend for future designs.\r\n\r\nThe design chosen was a semicircular ring shell with reversed curvatures of the edges. It was felt that this configuration would eliminate most of the bending stresses found present at the weld of the semicircular design, and would make possible a more even distribution of stresses throughout the expansion joint.\r\n\r\nBecause the stresses encountered were so far beyond the elastic limit of the material, even for small total elongations of the expansion joint, no theoretical solutions of the problem were possible.\r\n\r\nAn analysis of the curves and data shows the joint to be unsatisfactory, particularly from the viewpoint of withstanding the internal pressure. Since the previous work indicated that the internal pressure was not critical for the semicircular design, it seems that a compromise of the two designs would more satisfactorily meet the requirements of withstanding both the elongation and the internal pressure.\r\n\r\nAn alternate design has been indicated which will make possible a trend of designs that should lead to a solution.\r\n" }, { "name": "Rice, Harold Egbert", "degree": "Engineering Degree", "year": "1947", "title": "Performance Calculations of New Propellant Systems", "advisor": "Altman, David", "url": "https://resolver.caltech.edu/CaltechTHESIS:12142015-150152042", "creators": [ { "name": { "family": "Rice", "given": "Harold Egbert" }, "id": "Rice-Harold-Egbert", "display_name": "Rice, Harold Egbert" } ], "advisors": [ { "name": { "family": "Altman", "given": "David" }, "id": "Altman-D", "role": "advisor", "display_name": "Altman, David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VJT1-6602", "abstract": "The purpose of this thesis is to investigate the effect on performance\r\nand chamber temperature of adding hydrogen to a propellant system. The systems\r\ninvestigated are:
\r\n\r\n(1) RFNA-Aniline
\r\n(2) Nitromethane
\r\n(3) Anhydrous hydrazene-liquid oxygen
\r\n\r\nSince a systematic investigation of the performance parameters of the\r\nRFNA-Aniline system over a wide range of mixture ratios has never been made,\r\nit was decided to make these calculations, in addition to the investigations\r\nstated above.
\r\n\r\nThe results of the calculations can best be summarized by a study of the\r\nfigures at the end of the thesis. A few generalizations can be made. The\r\neffect of adding hydrogen in small quantities to a high temperature system\r\nis to increase the performance considerably without too much change in the\r\nchamber temperature. As more hydrogen is added, the percentage increase in performance.\r\nIf hydrogen is added in large quantities, both the performance curve\r\n(effective exhaust velocity) and the chamber temperature curve flatten out.
\r\n\r\nThe behavior discussed above is characteristic of hot propellant systems\r\nsuch as RFNA-Aniline and anhydrous hydrazene. In a low temperature system,\r\nsuch as nitromethane, the effect is quite different. The addition\r\nof hydrogen in small quantities causes a rapid decrease in chamber temperature,\r\nbut the increase in performance is considerably less on a percentage basis.\r\nAs more hydrogen is added the changes in performance and chamber temperature\r\nare almost linear.
\r\n" }, { "name": "Sanders, Lewis B.", "degree": "Engineering Degree", "year": "1947", "title": "An Investigation of Inspection Criteria for Countersunk Rivets", "advisor": "Sechler, Ernest Edwin; Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-091447", "creators": [ { "name": { "family": "Sanders", "given": "Lewis B." }, "id": "Sanders-Lewis-B", "display_name": "Sanders, Lewis B." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X2ZV-8G18", "abstract": "An investigation was made of the existing flush rivet inspection criteria and inspection methods to establish a norm for commercial flush riveted joints. Studies were made of thirty-four flush riveted joint load deformation curves to obtain their general characteristics and to establish some correlation of yield load as defined in ANC-5 and as defined in Report on Flush Riveted Joint Strength by ARC Rivet and Screw Allowables Subcommittee (Airworthiness Project 12). The specimens corresponding to the load deformation curves were comprised of 18 machine countersunk joints, 12 double dimple joints and four sub-countersunk joints. Within each type of joints the specimen varied in series of sheet material and thickness, rivet material and rivet size.\r\n\r\nIt is shown that yield load, defined as load giving four percent of rivet diameter joint set, is dependent on d/t ratios, the yield load lowering at increasing d/t values. Also, there are indications that as softer rivet material is used with a given sheet material, the increasing d/t ratios have less adverse effects.\r\n\r\nThere could be made no particular correlation of yield load as defined by load at .005\" set with any of the varying parameters.\r\n\r\nIn the case of the double dimple and sub-countersunk joints, no particular conclusions could be reached as the test data was confined to a small range of d/t values.\r\n\r\nIt was concluded from the countersunk rivet data that permanent set based on rivet diameter is a more reasonable yield criterion than permanent set based on an arbitrary constant.\r\n" }, { "name": "Satterfield, Loys Malcolm", "degree": "Engineering Degree", "year": "1947", "title": "Theoretical Investigation of Acceleration of a Turbojet Engine", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102008-140328", "creators": [ { "name": { "family": "Satterfield", "given": "Loys Malcolm" }, "id": "Satterfield-Loys-Malcolm", "display_name": "Satterfield, Loys Malcolm" }, { "name": { "family": "Wheatley", "given": "John Paul" }, "id": "Wheatley-John-Paul", "display_name": "Wheatley, John Paul" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N3NM-X518", "abstract": "The failure of turbojet aircraft propulsion units to accelerate rapidly to high thrust operation when emergencies arise in slow speed flight has restricted their use in aircraft applications, and has also concentrated considerable attention upon their acceleration characteristics in an effort to produce better results. This thesis presents a method of computing the acceleration of a particular turbojet by making use of complete performance curves of the component parts of the turbojet.\r\n\r\nThe method presented here does not permit computation of the acceleration for a particular operating condition as determined by those variables usually considered independent; namely, (1) Flight conditions of velocity, density, pressure, and temperature, (2) Engine rotor speed (3) Fuel rate of flow, and (4) Tail cone area ratio. Computation using these four independent variables was originally attempted in preparation of this thesis. However, extreme complication in the computations dictated that turbine inlet temperature and air mass rate of flow, which are normally dependent variables, should be considered independent. Fuel rate of flow and tail cone area ratio are therefore considered dependent. Therefore, in order to match a particular operating condition it is necessary to make a family of computations for various turbine inlet temperatures (constant for each set) over a range of assumed air mass flows.\r\n\r\nComputations have been performed for the Westinghouse X19B axial flow turbojet to illustrate application of the method and to show qualitative and quantitative effects of variation of tail area ratio, at two different turbine inlet temperatures.\r\n" }, { "name": "Schamberg, Richard", "degree": "PhD", "year": "1947", "title": "The Fundamental Differential Equations and the Boundary Conditions for High Speed Slip-Flow, and their Application to Several Specific Problems", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12272004-161736", "creators": [ { "name": { "family": "Schamberg", "given": "Richard" }, "id": "Schamberg-Richard", "display_name": "Schamberg, Richard" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F44D-FG36", "abstract": "The differential equations of motion and the associated boundary conditions for the slip-flow regime of fluid mechanics are derived from the point of view of the kinetic theory of non-uniform gases. The slip-flow regime comprises the flow of gases whose molecular mean free path is smaller than but not negligible relative to the macroscopic dimension characterizing the gas flow.\r\n\r\nA systematic review is presented of the methods of Hilbert and Burnett for obtaining a successive approximation solution to the Boltzmann integro-differential equation. The complete second approximation to the molecular velocity distribution function is calculated for the molecular model of Maxwell. This molecular distribution function is employed for the derivation of the macroscopic differential equations of motion and the associated boundary conditions. It is shown that the same number of boundary conditions are required for slip flows as for gas-dynamical flows, although the differential equations of motion for slip flows are of higher order than those of continuum gas-dynamics. Expressions for the second approximations to the slip velocity and temperature jump are obtained.\r\n\r\nThe general equations obtained are applied to three specific problems: the propagation of sound waves in rarefied gases, high-speed Couette flow of a rarefied gas, and slip-flow between concentric cylinders in relative rotary motion. It is found that the rarefaction of a gas increases the damping of sound waves, whereas the propagation speed differs from the ordinary adiabatic sound velocity by less than two percent. The Couette flow solution indicates that the slippage of gas and the temperature discontinuity at a solid boundary may reduce the gas-dynamical friction coefficient and heat transfer, respectively, by ten percent under approximate conditions. When applied to the flight of aircraft through the rarefied atmosphere, the theory presented is applicable to an altitude range from 100,000 to 300,000 feet.\r\n" }, { "name": "Soli, Orlan Alton", "degree": "Engineering Degree", "year": "1947", "title": "A Study of the Effects of Rapidly Applied Loads and Repeated Loads on Countersunk Riveted Joints", "advisor": "Sechler, Ernest Edwin; Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192008-111017", "creators": [ { "name": { "family": "Soli", "given": "Orlan Alton" }, "id": "Soli-Orlan-Alton", "display_name": "Soli, Orlan Alton" }, { "name": { "family": "Ditch", "given": "William Earl" }, "id": "Ditch-William-Earl", "display_name": "Ditch, William Earl" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WEWA-8A78", "abstract": "A number of tests were conducted at Daniel Guggenheim Aeronautical Laboratory to determine the effects of rapid loading and repeated rapid loading on countersunk riveted joints. This investigation was conducted to indicate the importance and possibilities of future study in this field.\r\n\r\nThe rapid loading test results are compared to slow loading tests and to ANC-5 and Aircraft Industries Association of America values.\r\n\r\nA hydraulic testing machine designed for these specific tests was constructed and placed in operation. A general discussion of the testing machine and its operation is included.\r\n" }, { "name": "Tangren, Robert Fulton", "degree": "Engineering Degree", "year": "1947", "title": "Correction of Ramjet Experimental Data", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-082257", "creators": [ { "name": { "family": "Tangren", "given": "Robert Fulton" }, "id": "Tangren-Robert-Fulton", "display_name": "Tangren, Robert Fulton" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/291V-BB68", "abstract": "Heat energy can be converted into mechanical energy only by the expansion of a high temperature high pressure gas to a lower pressure thus changing the random energy, temperature, into a directed energy associated with a velocity. One of the simplest methods of achieving the necessary pressure for this expansion is by utilizing the high velocity of the airstream relative to a rapidly moving aircraft. The momentum of this airstream is converted into pressure by deceleration in a diffuser. The air is then heated and ejected as a high speed jet, producing thrust, hence the name given to this system is ramjet. Other names have also been proposed such as athodyd, which is a contraction of aero-thermodynamic duct.
\r\n\r\nThe purpose of this study is to derive a simple ramjet theory and to use this theory in setting up dimensionless parameters and methods of analysing experimental data. No attempt is made to devise experimental techniques but only to give a method by which the experimental data may be correlated.
\r\n\r\nIt is found that the performance of a ramjet at any altitude can be reduced to an equivalent sea level condition by the application of suitable correction factors. These factors are derived on the basis of constant flight Mach number, constant ramjet geometrical arrangement, and constant throttle setting. This latter parameter is most accurately described by the ratio of the combustion chamber temperature to the free air temperature. It is recommended that ramjet test data be corrected to this standard sea level condition for ease of correlation and analysis.
" }, { "name": "Trilling, Leon", "degree": "Engineering Degree", "year": "1947", "title": "A Problem in Potential Flow with a Free Surface", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102008-144858", "creators": [ { "name": { "family": "Trilling", "given": "Leon" }, "id": "Trilling-Leon", "display_name": "Trilling, Leon" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CA87-ZG47", "abstract": "The present paper concerns itself with the determination of impact pressure and force which act on a body when it hits a horizontal fluid surface at any angle at a high speed.\r\n\r\nIt is assumed that only the hydrodynamic force has any effect and also, that the impact is so short that the effect of the fluid splash is negligible. Under those conditions, it is possible to linearize the boundary condition of the flow and to divide the force and velocity vectors into vertical and horizontal components. The problem in the vertical direction then becomes identical with that of the motion of a body submerged in an infinite fluid, and is easily solved for bodies of simple shape. The problem in the horizontal direction resolves itself into a problem of potential flow with a symmetric discontinuity along the free surface, so that the free surface may be replaced by a symmetric configuration with velocity components opposite and equal to those in the actual fluid.\r\n\r\nUnder those conditions, two simple two-dimensional configurations are studied; an infinite elliptic semi-cylinder and an infinite flat plate. The analysis is carried out in terms of conformal transformations. Three simple three-dimensional problems are also solved: that of a sphere, an ellipsoid of revolution and a general ellipsoid. The method here is that of three dimensional harmonic analysis.\r\n\r\nIn conclusion, a specific example is given: the drag components on a sphere which hits the surface at 45\u00b0 are calculated; the results are compared to experimental data and show fair agreement with them.\r\n" }, { "name": "Weldon, Thomas Franklin", "degree": "Engineering Degree", "year": "1947", "title": "The Performance of a Supersonic Airplane", "advisor": "Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142005-112442", "creators": [ { "name": { "family": "Weldon", "given": "Thomas Franklin" }, "id": "Weldon-Thomas-Franklin", "display_name": "Weldon, Thomas Franklin" } ], "advisors": [ { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng", "aeronautics" ], "doi": "10.7907/T271-MK09", "abstract": "This thesis is primarily a survey of the methods of calculating drag and performance of an airplane capable of supersonic flight. As a basis of presentation of the findings of this survey the drag and performance calculations are worked out for a single place airplane which has a rocket power plant, sweptback wings and other low drag features. These calculations reveal that this airplane should be able to attain a Mach number of 2 at an altitude of 42,000 feet.\r\n" }, { "name": "Whitmore, Quentin Robert", "degree": "Masters", "year": "1947", "title": "Experimental Investigation of Temperature and Velocity Distribution About a Rocket Jet", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-140117", "creators": [ { "name": { "family": "Whitmore", "given": "Quentin Robert" }, "id": "Whitmore-Quentin-Robert", "display_name": "Whitmore, Quentin Robert" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics", "eleceng" ], "doi": "10.7907/SN1E-KS25", "abstract": "The purpose of the investigation was to determine the temperature distribution and velocity profile surrounding the wake of a 1500 pound thrust liquid rocket motor. The temperature measurements were restricted to those 500\u00b0F and below. The velocities measured were in the region in which the temperature measurements were made.\r\n\r\nThe region in which the temperatures exceeded 500\u00b0F was found to be included within a solid angle of ten degrees. The high temperature region was found to be larger than the high velocity region.\r\n\r\nThe investigation was carried out during the academic year 1946-1947 at GALCIT Jet Propulsion Laboratory under the supervision of Dr. Robert H. Boden.\r\n" }, { "name": "Browning, Frank Horace", "degree": "Engineering Degree", "year": "1946", "title": "Conditions for Choking in a Cylindrical Combustion Chamber with Eddying Pressure Losses", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112008-111809", "creators": [ { "name": { "family": "Browning", "given": "Frank Horace" }, "id": "Browning-Frank-Horace", "display_name": "Browning, Frank Horace" }, { "name": { "family": "Mcconnaughhay", "given": "]ames William" }, "id": "Mcconnaughhay-]ames-William", "display_name": "Mcconnaughhay, ]ames William" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BC2C-0A22", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nChoking occurs in a cylindrical combustion chamber when the gas reaches sonic velocity at the outlet, and no more fuel can be burned without causing unstable combustion and possibly \"blowout\" of the flame. In this analysis, the conditions for choking and the maximum possible fuel-air ratio for given inlet conditions are determined by a trial and error method, which proves to give accuracy within about 1/2 percent. Entering Fig. 13, 14, or 15 with the given inlet conditions, the fuel- air ratio for choking [(...)] is determined. From Fig. 16, 17, or 18, the temperature of the gas at the outlet is determined. Then [...] can be found from Fig. 1, 2, or 3, and the pressure and density of the gas at the outlet from equations (12) and (13).\r\n\r\nIf [...] is assumed to remain constant over the temperature range involved, and constant with respect to change in the gas composition due to combustion, then it is possible to solve algebraicly for the conditions for choking. This approximation is reasonably valid for small fuel-air ratios, but may cause errors of over ten percent when the inlet temperature is low and the fuel-air ratio is high.\r\n" }, { "name": "Charyk, Joseph Vincent", "degree": "PhD", "year": "1946", "title": "Condensation Phenomena in Supersonic Flows", "advisor": "von K\u00e1rm\u00e1n, Theodore; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-165637", "creators": [ { "name": { "family": "Charyk", "given": "Joseph Vincent" }, "id": "Charyk-Joseph-Vincent", "display_name": "Charyk, Joseph Vincent" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RSQH-W442", "abstract": "With the very rapid development of jet propulsion systems, the attainment of speeds which seemed to be well beyond reach a few years ago now appears to be at hand. The war has produced many examples of guided missiles traveling at supersonic speeds such as the famed German A-4 rocket, more commonly referred to in this country as the V-2. Today a supersonic airplane is no longer a designer's dream but practically an accomplished fact. Despite the impressive array of symbols of apparent mastery of high speed flight, there exists a large gap of fundamental knowledge that the theoretician working with the experimentalist must fill before true mastery of transonic and supersonic speeds can be said to be at hand. It was only due to the efforts of pioneers in high speed fluid mechanics like de Laval, Riemann, Hugoniot, Lord Rayleigh and Tschaplygin (see for example Ref. 1 to 4) and later the applications of such basic knowledge to the new field of high speed aerodynamics by men with foresight such as Prandtl, Ackeret, von Karman Taylor and Busemann (see for example Ref. 5 to 9) that tools for the engineer and designer were available when the need for them suddenly arose.
\r\n\r\nToday the emphasis of the aeronautical profession is on the basic problems of transonic and supersonic flows. One of the important and at first mystifying phenomena that emerged from experimental investigations in supersonic wind tunnels was the condensation shock. Later such shocks were noticed in the flow over an airfoil in experiments conducted at the California Institute of Technology by Kate Liepmann in 1941. In more recent years their appearance has been noted in actual flight at high speeds. The importance of such shocks in connection with the aerodynamic characteristics of airfoils in supercritical transonic flow has been pointed out by Tsien and Fejer (Ref. 10). Apparently, however, no detailed investigation of the phenomenon has been made with a view to studying the fundamental aspects of the condensation shock in order to develop practical methods for predicting the occurrence, location, strength and effect of such shocks. It has been the basic purpose of this research to study the detailed aspects of this problem and to endeavor to develop a means of accomplishing the aims noted. It is felt that though crude in many respects, the results of this investigation can provide practical knowledge of basic importance in understanding and treating the problems of condensation shocks when they appear and can point the way towards more refined and detailed future analyses of this problem.
\r\n\r\nIn attacking this problem, an examination of the phenomenon of the sudden collapse of the supersaturated state of the moist air is first made. The assumptions necessary for the determination of the critical stability limit of the supersaturated air are analyzed and the necessity for further investigation, especially from the kinetic point of view, is pointed out. The study reveals that the temperature of air at which this collapse occurs is approximately a function only of the amount of water contained in the air and does not depend upon the pressure. This enables an important simplification in the analysis to be made.
\r\n\r\nThe condition for collapse of the supersaturated state is then applied to the special case of normal condensation shocks. Because of this relatively small amount of water present in air, the effect of the presence of the water on the properties of the air can be neglected except at the shock where the release of the latent heat of vaporization upon condensation is of vital importance. A simple consideration of this heating process yields the interesting result that the flow after the shock must always be supersonic. An important simplification in treating the general condensation problem is an approximation to the actual saturation vapor pressure versus temperature curve by means of an exponential curve. Mathematically this means an approximate integration of the Clausius-Clapeyron equation in the sense that the specific volume of the fluid phase is neglected as compared to the specific volume of the vapor phase. This simplification enables a closed form solution to be obtained.
\r\n\r\nThe oblique condensation shock is then analyzed and its application to the flow over an airfoil or other body in a stream of moist air is treated.
\r\n\r\nThe possibility of a continuous condensation instead of an abrupt condensation of a combination of the two is discussed for the case of a one-dimensional flow. Certain interesting results emerge from such a consideration and experimentation will be required to determine whether under certain conditions such a condensation process can take place.
\r\n\r\nA considerable number of charts are provided which may be of use in making calculations in practical cases. In instances where a different range of values is necessary, additional charts can readily be constructed.
" }, { "name": "Halvorson, George Grandchamp", "degree": "Engineering Degree", "year": "1946", "title": "Studies on the Performance of a Rocket Propelled Orbiting Missile", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242008-082343", "creators": [ { "name": { "family": "Halvorson", "given": "George Grandchamp" }, "id": "Halvorson-George-Grandchamp", "display_name": "Halvorson, George Grandchamp" }, { "name": { "family": "Sledge", "given": "Edward Cress" }, "id": "Sledge-Edward-Cress", "display_name": "Sledge, Edward Cress" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z8SA-3358", "abstract": "NOTE: Text of symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThis report is a study of the performance requirements necessary to launch a rocket propelled missile into a circular orbit about the earth. Various trajectories by which a missile can be launched into such an orbit are investigated and an estimation is made of the minimum propellant-gross weight ratio required to reach stable orbital conditions at various altitudes.\r\n\r\nThe velocity of a projectile traveling about the earth in a circular orbit must be such that its weight is exactly balanced by the centrifugal force acting upon it. The expression for the required velocity, relative to a non-rotating earth, can be derived from the following figure.\r\n\r\n[...].\r\n\r\n\r\nBy the law of Conservation of Energy, such an orbit, once obtained, must remain circular unless influenced by additional forces. The action of atmospheric drag would be to cause a continual loss of energy; this loss would be made up at the expense of potential energy, causing the projectile to move in toward the earth in a contracting spiral. It can be shown (of. ref. 2) that, for altitudes greater than one hundred and twenty miles, the rate of this contraction is negligible.\r\n\r\nThe practical applications of an orbiting missile are numerous. A few are as follows:\r\n\r\na) A radio relay station for television and other high frequency communication.\r\nb) To carry instruments for continuous measurement of upper atmospheric phenomena.\r\nc) A military weapon of unlimited range, provided it can be brought back to earth at will.\r\n\r\nThe possibility of launching a vehicle into a circular orbit by means of rocket propulsion depends primarily upon the conditions of propellant consumption which are required to reach a stable orbital velocity. These conditions are:\r\n\r\na) Propellant characteristics (in particular, specific impulse).\r\nb) Rate of propellant consumption.\r\nc) Propellant-gross weight ratio.\r\n\t\r\nThe velocity necessary for a circular orbit is in the neighborhood of 26,000 ft/sec. For an unboosted rocket with an uniform burning rate the terminal velocity (neglecting drag and gravity forces) is given by [...] where [...] is assumed constant. If we take [...] to be equal to 400 sec., a representative value for a rocket fuel consisting of oxygen and hydrogen, the value of [...], the propellant-gross weight ratio, corresponding to [...] =26,000 ft/sec., is [...]=. 0.867. Thus, even with the most powerful rocket fuel, the required propellant gross weight ratio is very high, and the importance of a more careful estimation of this ratio is evident.\r\n\r\nA comprehensive analysis of the important factors which influence the performance of an orbiting rocket has been made by W. Z. Chien of GALCIT. In this analysis, Dr. Chien considered a vertical trajectory as a first approximation in obtaining estimates of the altitude of the circular orbit and of the propellant-gross weight ratio required (cf. ref. 2).\r\n\r\nThis report extends the considerations of Chien's work to oblique trajectories of various types, all of which terminate at the end of burning with the proper velocity conditions for a circular orbit. The first part of the report is a recapitulation of Chien's analysis. The second part deals with the characteristics of various oblique trajectories by which a rocket may be launched directly into a circular orbit; and the third part analyses a procedure whereby the rocket is launched into an elliptical orbit near its perihelion, is allowed to travel as a free body around the earth to the aphelion of the ellipse and then, by an additional boost of velocity, is projected into a circular orbit.\r\n" }, { "name": "Hoffman, Charles Calvin", "degree": "Engineering Degree", "year": "1946", "title": "A Study of Porous Metal Cooling", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202008-150040", "creators": [ { "name": { "family": "Hoffman", "given": "Charles Calvin" }, "id": "Hoffman-Charles-Calvin", "display_name": "Hoffman, Charles Calvin" }, { "name": { "family": "Gillette", "given": "Edmond Stephen" }, "id": "Gillette-Edmond Stephen", "display_name": "Gillette, Edmond Stephen" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PF1D-8T69", "abstract": "This investigation was conducted to study the flow rate necessary to maintain a sweat cooled metal at an equilibrium temperature when subjected to a high gas temperature. The study was limited to fundamental tests on copper, bronze, and stainless steel porous metal specimens which were the only types available at this time. Water cooling was used throughout the investigation.
\r\n\r\nConclusions of a qualitative nature were obtained which show that water flow rate is a primary factor in maintaining sweat cooled metals at equilibrium temperature, and that metal thermal conductivity has but slight effect. The feasibility of the sweat cooling technique was proven by the fact that a water flow rate of less than 0.1 cc/in.^2-sec was required to satisfactorily cool a porous metal surface subjected to a potential heat transfer of 1.0 BTU/in.^2-sec.
" }, { "name": "Kleiss, Norman Jack", "degree": "Engineering Degree", "year": "1946", "title": "Some Studies of Expansion Rings in Rocket Motors", "advisor": "Sechler, Ernest Edwin; Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12242008-094536", "creators": [ { "name": { "family": "Kleiss", "given": "Norman Jack" }, "id": "Kleiss-Norman-Jack", "display_name": "Kleiss, Norman Jack" }, { "name": { "family": "Kerkering", "given": "Stanley William" }, "id": "Kerkering-Stanley-William", "display_name": "Kerkering, Stanley William" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CD3E-ZE50", "abstract": "The purpose of this investigation was to investigate the stresses encountered for a semicircular expansion joint for a rocket motor. Information was desired to relate these stresses to the various parameters of the problem.
\r\n\r\nThe stresses involved in this design were found to approximate those indicated by the exact membrane theory. The specimen having the lesser thickness was found to agree more closely with the exact membrane theory, and gave the lowest value of stresses.
\r\n\r\nAn empirical method of membrane analysis, based on deformation profiles, was developed. This method is applicable for stresses slightly above the elastic limit and may be extrapolated for higher values.
\r\n\r\nThe design tested was found to be inherently unsatisfactory on the basis of tests and theoretical considerations.
\r\n\r\nAn alternative design was indicated which would have lower values of stress for a given value of deformation, and which could be designed strictly on the basis of theoretical calculations.
" }, { "name": "Olsen, Leslie Richard", "degree": "Engineering Degree", "year": "1946", "title": "A Theoretical Investigation of a Method of Increasing the Performance of Rocket Propellants for Use in Torpedoes by the Injection of Water", "advisor": "Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222008-142415", "creators": [ { "name": { "family": "Olsen", "given": "Leslie Richard" }, "id": "Olsen-Leslie-Richard", "display_name": "Olsen, Leslie Richard" } ], "advisors": [ { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JQ1R-6A08", "abstract": "In this report it is shown that water injection into the rocket motor of a rocket propelled torpedo increases the range at a given speed. For a 5000 lb. torpedo having a 1750 lb. warhead, the use of a hydrogen peroxide-nitromethane-water combination yields a range about 50 percent above that which would be obtained by the use of nitromethane or of acid-aniline propellants.
\r\n\r\nTheoretically, the use of water injection increases the specific thrust, i.e., thrust per unit mass rate of flow of propellant carried. The specific thrust is increases by water injection up to 18.5 percent for nitromethane and up to 89.1 percent for liquid oxygen and octane; the specific thrust for acid and aniline, at a mixture ratio of 3, is increases up to 27.1%.
\r\n\r\nData calculated from experimental work in connection with gas generation has shown that the increase of specific thrust for nitromethane is up to about 11.7% at L* = 868; the specific thrust measured in connection with gas generation work using acid and aniline, at a mixture ratio of 3, is increased 24.8%.
" }, { "name": "Parker, James Frederick", "degree": "Engineering Degree", "year": "1946", "title": "An Investigation of the Effects of the Sudden Extension of a Dive-Recovery Flap on the Aerodynamic Characteristics of a Symmetrical Airfoil in Two Dimensional Flow", "advisor": "Liepmann, Hans Wolfgang; Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022008-102010", "creators": [ { "name": { "family": "Parker", "given": "James Frederick" }, "id": "Parker-James-Frederick", "display_name": "Parker, James Frederick" }, { "name": { "family": "Anderson", "given": "John Berwick" }, "id": "Anderson-John-Berwick", "display_name": "Anderson, John Berwick" }, { "name": { "family": "Tunnell", "given": "Richard McClellan" }, "id": "Tunnell-Richard-McClellan", "display_name": "Tunnell, Richard McClellan" }, { "name": { "family": "Vincent", "given": "Harry Lansing" }, "id": "Vincent-Harry-Lansing", "display_name": "Vincent, Harry Lansing" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DJD3-KV06", "abstract": "This report presents the results of an investigation of the aerodynamic characteristics of the NACA symmetrical laminar flow 65,1-012 airfoil. The model was tested with and without a dive recovery flap. The effects obtained by suddenly extending the flap are compared to those obtained with the flap set down in position. The tests cover a range of angle of attack from zero to plus three degrees while the Mach number was varied from 0.5 to 0.8.
\r\n\r\nThe following conclusions were reached:
\r\n\r\n1. The lift curve for the airfoil with no flap is essentially a straight line.
\r\n\r\n2. A flap suddenly extended produces aerodynamic effects which are different from those produced by a flap which is set. Whenever model test results are to be used to produce design information to be incorporated in full scale aircraft, the dive recovery flaps on the model should be equivalent to those on the full scale airplane in regard to dimensional proportions and to the method and timing of operation, if a high degree of accuracy is desired.
This investigation was carried out by the authors at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the school year 1945-46.
" }, { "name": "Weitzenfeld, Daniel Kehr", "degree": "Engineering Degree", "year": "1946", "title": "The Effect of Dive Recovery Flaps on the Lift of a Two Dimensional Symmetrical Airfoil with Changes in Chordwise Location of the Flaps", "advisor": "Liepmann, Hans Wolfgang; Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11262008-112929", "creators": [ { "name": { "family": "Weitzenfeld", "given": "Daniel Kehr" }, "id": "Weitzenfeld-Daniel-Kehr", "display_name": "Weitzenfeld, Daniel Kehr" }, { "name": { "family": "Trauger", "given": "Robert James" }, "id": "Trauger-Robert-James", "display_name": "Trauger, Robert James" }, { "name": { "family": "Kronmiller", "given": "George Hannibal" }, "id": "Kronmiller-George-Hannibal", "display_name": "Kronmiller, George Hannibal" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CV3E-KC83", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIt was desired in this investigation to determine the effect of the chordwise position of dive recovery flaps on the lift of a laminar flow, low drag, two-dimensional airfoil at high subsonic Mach numbers. Schlieren pictures were taken to relate the formation, extension and strength of shock waves to the measured lift. Tests were made on a four inch chord airfoil of section 65,1-012 at Mach numbers from .50 to .83, a Reynolds number of 1,600,000 at M[subscript o] = 0.7, angles of attack from 1 to 3 degrees, and flap locations at 15%, 30%, and 45% chord; the flap is 10% of the chord.
\r\n\r\nThe investigation was carried out by the authors at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the school year 1945-1946.
\r\n\r\nIt was concluded that dive recovery flaps materially increase the lift of an airfoil, and there is an optimum flap location for maximum lift and one for maximum [\u2026]. Moreover, it was concluded that the formation and development of shock waves is directly related to the lift, but that the successive development of the shock wave pattern as a function of Mach number is independent of angle of attack or flap location; the Mach number for initial shock formation varies. Finally, in this tunnel where the thickness of the boundary layer is a large percent of the tunnel width the correction for non-uniform spanwise lift distribution must be investigated more carefully before absolute lift values can be computed.
" }, { "name": "Winson, Jonathan", "degree": "Engineering Degree", "year": "1946", "title": "Motion of an Unarticulated Helicopter Blade with Application to the Problem of Vibration of the Rigid Rotor Helicopter", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022008-113803", "creators": [ { "name": { "family": "Winson", "given": "Jonathan" }, "id": "Winson-Jonathan", "display_name": "Winson, Jonathan" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WBDG-XG02", "abstract": "The present investigation concerns itself almost completely with the derivation and solution of the equations of motion of the helicopter blade. The fluctuating aerodynamic forces which cause flapping in the hinged rotor bend the blades of the rigid rotor in a vertical plane. The effect of the bending is to cause fluctuating moments on the rotor hub. This pure bending oscillation is the most obvious cause of vibration and is treated here. Coupled motions are not considered and are effectively eliminated by the assumption that the mass center, aerodynamic center and elastic axis are at the point on each cross section of the blade and that the elastic axis is a straight line.
\r\n\r\nAlthough this work was undertaken to investigate rotor vibration, it has broader significance. It is, in effect, the essential step which makes possible the rational analysis of all rigid rotor dynamics and aerodynamics. It is directly comparable in importance to the solution of the problem of the blade flapping motion in hinged rotor work. For example, once the bending of the blade in forward flight is known such information as
\r\n\r\n1. Fatigue stresses in the blades
\r\n2. Control lag angle required
\r\n3. Maximum deflection of the blades, etc.
\r\n\r\nis immediately available.
The purpose of this work was to develop a means of increasing the thrust of a turbojet engine by burning kerosene in the tail pipe.
\r\n\r\nA combustion system was developed which gave the following results:
\r\n(l) Maximum thrust increase using a G.E. I-14 engine was 64 per cent over straight tail pipe thrust corresponding\r\nto 42 per cent increase over the normal engine thrust. This increase was accomplished at an engine rpm of 12,000.
\r\n(2) Increase of maximum thrust obtained was 51 per cent over the straight tail pipe thrust corresponding to 23 per cent\r\nover the normal engine thrust. This increase was accomplished at an engine rpm of l6,000.
\r\n(3) For the thrust increases mentioned in (1) and (2) above, increases of Specific Fuel Consumption were 66 per cent\r\nand 76 per cent respectively over normal engine SFC.
The hat section used by certain of the aircraft companies has been quite widely accepted as the most efficient compression carrying member when stiffened by a sheet. However, due to the difficulty of inspection and corrosion control, which is particularly important in naval aircraft, the Consolidated Vultee Aircraft Corporation has for some time been using open angle and zee sections formed from dural sheet. For this reason the members of the engineering staff of Consolidated Vultee became interested in the effect of lips on zee and angle sections such as are frequently used to stiffen panels occurring in the compression side of semi-monocoque structures subjected to bending loads.
\r\n\r\nThis paper is an attempt to determine experimentally the optimum amount of lip for the sections under consideration. Sufficient tests are made to locate the column curves for these sections, and from the curves the strengthening effect of the lip noted.
" }, { "name": "Kuo, Yung-Huai", "degree": "PhD", "year": "1945", "title": "Two-Dimensional Irrotational Mixed Subsonic and Supersonic Flow of a Compressible Fluid and the Upper Critical Mach Number", "advisor": "von-K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172010-111715951", "creators": [ { "name": { "family": "Kuo", "given": "Yung-Huai" }, "id": "Kuo-Yung-Huai", "display_name": "Kuo, Yung-Huai" } ], "advisors": [ { "name": { "family": "von-K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von-K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D9ME-DD61", "abstract": "No abstract." }, { "name": "Lancaster, Otis Ewing", "degree": "Engineering Degree", "year": "1945", "title": "Combustion Gas Turbine for Airplanes", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242008-110400", "creators": [ { "name": { "family": "Lancaster", "given": "Otis Ewing" }, "id": "Lancaster-Otis-Ewing", "display_name": "Lancaster, Otis Ewing" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/82FF-C054", "abstract": "This paper contains a theoretical study of various thermodynamic cycles for Gas-Turbine-propeller propulsion units for aircraft.\r\n\r\nThe object of the study was to evaluate the turbine-propeller engines as a source of power for fast, economical, long range airplanes. Hence, the consumption of fuel and the total weight of fuel and power plant were the main criterion for the evaluation. Since the weights of the particular units were not known, most of the results here are centered around the fuel consumption per horsepower, emphasizing the design criteria and throttle conditions for minimum values.\r\n\r\nIn order to emphasize the maximum possible performance, formulae for ideal engines were developed for all cases. These relations are compared with the corresponding ones involving unknown efficiencies. A summary table of these comparison formulae is given at the close of the thesis.\r\n\r\nIn the case of the cycles where there was sufficient experimental data available to estimate the performance of the component parts, the relations for power and specific fuel consumption were written in terms of three parameters which were convenient for graphical use in design purposes.\r\n" }, { "name": "Levy, Charles Nathaniel", "degree": "Engineering Degree", "year": "1945", "title": "Self-Excited Torsional Oscillations of an Arfoil", "advisor": "Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-110010", "creators": [ { "name": { "family": "Levy", "given": "Charles Nathaniel" }, "id": "Levy-Charles-Nathaniel", "display_name": "Levy, Charles Nathaniel" } ], "advisors": [ { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0HEH-TC15", "abstract": "This thesis is a report on one phase of a program on the self-excited oscillations of an airfoil. This program was sponsored by the National Advisory Committee for Aeronautics at the California Institute of Technology. This thesis covers the torsional oscillations of an elastically suspended airfoil.
\r\n\r\nThe experimental work consisted of measurements of the amplitude of torsional oscillations of a wing elastically suspended in the airstream of a wind tunnel so as to be capable of torsional oscillations only. The results show that torsional oscillations occur at all velocities above a critical velocity and increase in amplitude with velocity without reaching any apparent limit.
\r\n\r\nGlauert's theory of the forces on an oscillating airfoil do not agree with the experimental results obtained. This theory indicates that oscillations below the stall will not occur for the values of V/nb studied here, whereas the experiments indicate that oscillations do exist.
" }, { "name": "Leydon, John Koebig", "degree": "Engineering Degree", "year": "1945", "title": "An Investigation of Wind Tunnel Wall Effects at High Mach Numbers", "advisor": "Liepmann, Hans Wolfgang; Puckett, Allen E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162015-093151774", "creators": [ { "name": { "family": "Leydon", "given": "John Koebig" }, "id": "Leydon-John-Koebig", "display_name": "Leydon, John Koebig" }, { "name": { "family": "Miller", "given": "Walter Bernard" }, "id": "Miller-Walter-Bernard", "display_name": "Miller, Walter Bernard" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "advisor", "display_name": "Puckett, Allen E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HNBB-CK44", "abstract": "This paper presents the results of an investigation of \r\nwind tunnel wall interference in a two-dimensional wind tunnel\r\nat high Mach numbers. The results are presented in the form of\r\ncurves of lift coefficient versus the ratio of model chord to\r\ntunnel height, as functions of Mach number and angle of attack.\r\nThe investigation was carried out by the authors at the\r\nGuggenheim Aeronautical Laboratory of the California Institute\r\nof Technology during the school year 1944-45.
\r\n\r\nTests were carried out on the NACA low drag airfoil\r\nsection 65,1-012 at Mach numbers from .60 to .80, and angles of\r\nattack of from 1 to 3 degrees. Models were 1\", 2\", 4\" and 6\"\r\nchord, giving values of the chord to tunnel height ration of .1\r\nto .6. Schlieren photographs were made of shock waves where they\r\noccurred.
" }, { "name": "Baranowski, John J.", "degree": "Engineering Degree", "year": "1944", "title": "An Investigation of a Method of Underwater Propulsion by Direct Gas Injection", "advisor": "Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09252015-133043910", "creators": [ { "name": { "family": "Baranowski", "given": "John J." }, "id": "Baranowski-John-J", "display_name": "Baranowski, John J." }, { "name": { "family": "Seiler", "given": "Dayton A." }, "id": "Seiler-Dayton-A", "display_name": "Seiler, Dayton A." } ], "advisors": [ { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XDF1-M512", "abstract": "This report presents the results of an investigation of\r\na method of underwater propulsion. The propelling system utilizes\r\nthe energy of a small mass of expanding gas to accelerate the flow\r\nof a large mass of water through an open ended duct of proper shape\r\nand dimensions to obtain a resultant thrust. The investigation was\r\nlimited to making a large number of runs on a hydroduct of arbitrary\r\ndesign, varying between wide limits the water flow and gas flow\r\nthrough the device, and measuring the net thrust caused by the\r\nintroduction and expansion of the gas.
\r\n\r\nIn comparison with the effective exhaust velocity of about\r\n6,000 feet per second observed in rocket motors, this hydroduct model \r\nattained a maximum effective exhaust velocity of more than 27,000\r\nfeet per second, using nitrogen gas. Using hydrogen gas, effective\r\nexhaust velocities of 146,000 feet per second were obtained. Further\r\ninvestigation should prove this method of propulsion not only to be \r\npractical but very efficient.
\r\n\r\nThis investigation was conducted at Project No. 1, Guggenheim\r\nAeronautical Laboratory, California Institute of Technology,\r\nPasadena, California.
" }, { "name": "Boehnlein, Charles Thompson", "degree": "PhD", "year": "1944", "title": "Aerodynamic Theory of the Oscillating Wing-Aileron of Finite Span", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:04142011-111534450", "creators": [ { "name": { "family": "Boehnlein", "given": "Charles Thompson" }, "id": "Boehnlein-Charles-Thompson", "display_name": "Boehnlein, Charles Thompson" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KJZ7-FG07", "abstract": "No abstract." }, { "name": "Chambers, Lester S.", "degree": "Engineering Degree", "year": "1944", "title": "An Investigation of the Effects of Angle of Attack and Airfoil Model Size on the Occurrence of Shock Waves in a Two Dimensional Wind Tunnel", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-153938", "creators": [ { "name": { "family": "Chambers", "given": "Lester S." }, "id": "Chambers-Lester-S", "display_name": "Chambers, Lester S." }, { "name": { "family": "Doll", "given": "Raymond. E." }, "id": "Doll-Raymond-E", "display_name": "Doll, Raymond. E." }, { "name": { "family": "Harrell", "given": "Dewitt A." }, "id": "Harrell-Dewitt-A", "display_name": "Harrell, Dewitt A." } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Puckett", "given": "Allen E." }, "id": "Puckett-A-E", "role": "member", "display_name": "Puckett, Allen E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NFP2-EG08", "abstract": "This paper presents the results of an investigation of the flow in the vicinity of one of the newer symmetrical NACA laminar flow airfoil sections at and above the orbital speed of the section, in the form of schlieren photographs and wall pressure distributions. The investigation was carried out in a two dimensional tunnel, designed for this purpose by the authors, at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the spring of 1944.
\r\n\r\nThe formation and variation of the shock waves with angle of attack and Mach number are presented in a series of high speed photographs. An attempt is made to indicate the effect of model size in a tunnel of fixed cross sectional area by presenting photographic results of the tests on airfoils of 2\", 4\", and 6\" chord lengths.
\r\n\r\nCurves of C[subscript L] versus Mach number at constant angle of attack are presented for the three airfoils.
" }, { "name": "Denison, Frank G.", "degree": "Engineering Degree", "year": "1944", "title": "A Method of Performance Analysis for Sailing Vessels", "advisor": "Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-092219", "creators": [ { "name": { "family": "Denison", "given": "Frank G." }, "id": "Denison-Frank-G", "display_name": "Denison, Frank G." } ], "advisors": [ { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3697-3Y49", "abstract": "A general method for calculating the performance of all types of wind driven vessels has been developed. The method is of such a nature that it may be used, without specific experimental assistance, as a qualitative guide in preliminary design. To this same procedure, data from a few simple tests of the model in question may be applied to obtain good quantitative performance information.\r\n\r\nAs a result, existing yacht model testing procedure {Reference (4)} can be considerably simplified while at the same time obtaining information of much broader applicability.\r\n\r\nThe use of the principles of this method, if not the letter, should tend to rationalize the arbitrary and extremely restrictive handicapping rules for ocean racing now in existence.\r\n\r\nFurther, the owner, in possession of a performance analysis of his vessel, can be guided in his choice of course and sail setting as these are fundamental parameters of the general performance equation. The optimum sail setting for any wind speed and boat direction is of a necessity obtained in the process of the solution of this equation.\r\n\r\nThe method provides several rather surprising general conclusions. It is indicated that angle of heel, contrary to Reference (4) is not a fundamental variable, and therefore stability only enters the picture in so far as the designer has a \"gentlemen's agreement\" not to provide more sail than will heel the vessel to a certain angle in a given wind. It is found that only draft is a monotonic parameter in performance; all other form and sail variables exhibit optimums, some perhaps outside of the practical range.\r\n\r\nAlso, it is found from the experimental data of Reference (5) that yacht underbodies, despite their extremely low aspect ratio, exhibit a polar of lateral force and induced resistance with a character in agreement with the simple Prandtl theory. The interference effect of the surface, however, is found to be at variance with the result obtained from a lifting line vortex arranged to satisfy the water boundary condition.\r\n\r\nIt is found that the usual triangular yacht sail does not have as bad a downwash distribution as one might first suspect on considering the plan form and twist. The presence of the water surface has the effect of providing a corrective upwash distribution.\r\n\r\nIt is found that simple static stability calculations with the water surface assumed undisturbed, at the boat, lead to surprisingly good agreement with the righting moments obtained experimentally under dynamic conditions.\r\n" }, { "name": "Dixon, Howard Henry", "degree": "Engineering Degree", "year": "1944", "title": "Investigation of Design Criteria of Stiffened Wood Curved Panels", "advisor": "Sechler, Ernest Edwin; Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242008-145312", "creators": [ { "name": { "family": "Dixon", "given": "Howard Henry" }, "id": "Dixon-Howard-Henry", "display_name": "Dixon, Howard Henry" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HJ3Y-3F83", "abstract": "A total of 92 stiffened panel specimens of birch plywood of a nominal thickness of one-eighth inch with spruce stiffeners set parallel to the applied load were tested at California Institute of Technology to obtain the stress strain relations and the ultimate compression stress of the panels. The panels had heights of 12, 18, and 24 inches; stiffener spacings of 2, 3, 4, and 5 inches; and radii of curvature of 400, 200, 100, 50, 12, and 6 inches. The experimental data are presented as stress strain and column curves, and in tabular form.
\r\n\r\nThe principal results of the research are as follows:
\r\n\r\na) Although the scope of the tests were insufficient to formulate general design data, the results present a guide for design criteria of wood panels. Experimentally it has been shown that the effective width method of analysis is applicable to wooden panels.
\r\n\r\nb) The percent reinforcement vs. ultimate stress investigation indicates that a minimum of 50 to 60% reinforcement should be used in stiffened panel construction.
\r\n\r\nc) A decrease of the [radius of curvature divided by sheet thickness] ratio gives an increase of ultimate stress approximating a logarithmic variation.
" }, { "name": "Dunn, William C.", "degree": "Engineering Degree", "year": "1944", "title": "The Quantitative Effect of a Flexible Fuselage on the Symmetric Torsional Modes of the Wings of a Large Airplane", "advisor": "Myklestad, Nils O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192011-093121243", "creators": [ { "name": { "family": "Dunn", "given": "William C." }, "id": "Dunn-William-C", "display_name": "Dunn, William C." }, { "name": { "family": "Furer", "given": "Albert B." }, "id": "Furer-Albert-B", "display_name": "Furer, Albert B." } ], "advisors": [ { "name": { "family": "Myklestad", "given": "Nils O." }, "id": "Myklestad-Nils-O", "role": "advisor", "display_name": "Myklestad, Nils O." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H4PK-H195", "abstract": "Using Holzer's method of frequency calculation, the natural frequencies for the first two modes of torsional vibration of the wing were determined for a representative conventional airplane (B24-C) in the customary manner, the fuselage being considered as a rigid body. Next, using a method developed by N. O. Myklestad of the Guggenheim Aeronautics Laboratory at the California Institute of Technology, combined with Holzer's method, the natural frequencies for the same two modes of vibration were again determined, but with the fuselage this time being considered as flexible.
\r\n\r\nA comparison of results of the two methods indicates that in considering the fuselage as being flexible, a decrease in the natural frequency of torsional vibration may be expected. For the particular airplane selected, this decrease amounted to 6.68% for the first mode of vibration and to 39.1% for the second.
\r\n\r\nThe investigation reported in this paper was entirely theoretical and was performed during the 1943-1944 school year at the Guggenheim Aeronautics Laboratory at the California Institute of Technology, Pasadena, California under the direction and supervision of Dr. N. O. Myklestad, research associate in aeronautics at the Institute.
" }, { "name": "Hensel, Rudolph William", "degree": "Engineering Degree", "year": "1944", "title": "A Correlation of High Speed Drag Data", "advisor": "Tsien, Hsue Shen; Millikan, Clark Blanchard; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022025-223538610", "creators": [ { "name": { "family": "Hensel", "given": "Rudolph William" }, "id": "Hensel-Rudolph-William", "display_name": "Hensel, Rudolph William" }, { "name": { "family": "Heimer", "given": "Harry James" }, "id": "Heimer-Harry-James", "display_name": "Heimer, Harry James" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/dbv8-bw67", "abstract": "In fulfillment of the purpose of this investigation, a method of estimating the drag of an airplane at high Mach numbers has been derived. Two sets of curves, one for airplanes having conventional wing sections and the other for those having low drag sections, were drawn to show the percentage increase in total drag with the ratio of free stream Mach number to critical Mach number of the wing.
\r\nA method for computation of the blocking correction is presented and applied, resulting in good agreement between the wind tunnel and flight tests. Wind tunnel data corrected for the blocking effect were chiefly used to deduce the conclusions, but they were supplemented by all the flight test results available.
" }, { "name": "Lin, Chia-Chiao", "degree": "PhD", "year": "1944", "title": "On the Development of Turbulence", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-140148", "creators": [ { "name": { "family": "Lin", "given": "Chia-Chiao" }, "id": "Lin-Chia-Chiao", "display_name": "Lin, Chia-Chiao" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZF3F-AN21", "abstract": "The stability of two-dimensional parallel flows of an incompressible fluid is investigated, based upon a study of the equation of Orr and Sommerfeld along the lines initiated by Heisenberg. The theory of Heisenberg is carefully examined and further developed to obtain several general and specific results on hydrodynamic stability. Most of the disputes in the existing theories are clearly brought out and carefully settled. It is further shown that all symmetrical and all boundary-layer types of velocity distributions are unstable above a certain minimum critical Reynolds number, whose approximate value can be easily calculated from equations (12.24) and (12.25) respectively. General characteristics of the curve of neutral stability are obtained (Fig. 9). Complete numerical calculations of this curve have been carried through for the plane Poiseuille flow and the Blasius flow. In the first case, the minimum critical Reynolds number is found to be 16000, based upon the maximun velocity and the width of the channel. In the second case, the number is 400, based upon the free stream velocity and the displacement thickness of the boundary layer. Physical interpretations of the results obtained are given, based upon the conservation of vorticity in a perfect fluid and its diffusion by viscous forces. Indications are also given to connect the stability theory with Taylor's theory of transition to turbulence. It is hoped that this work may remove all the doubts of applying the theory of small oscillations to the treatment of hydrodynamic stability using Navier-Stokes equations for an incompressible fluid.\r\n" }, { "name": "Miles, John Wilder", "degree": "Engineering Degree", "year": "1944", "title": "The Analysis of Discontinuities in Cylindrical Tubes Propagating Sound Waves", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152004-114239", "creators": [ { "name": { "family": "Miles", "given": "John Wilder" }, "id": "Miles-John-Wilder", "display_name": "Miles, John Wilder" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/58H4-E268", "abstract": "The effect of a plane discontinuity on a plane wave propagated in a cylindrical tube is calculated by variational methods. In carrying out the calculations a transmission line analogy is used and the effect of the discontinuity at a distance is represented by a capacitance placed at the discontinuity.\r\n\r\nIn section 1 the equations of motion for the propagation of a small disturbance in a cylindrical tube are established, culminating in the tyro-dimensional wave equation, while the solutions to the equations are discussed in section 2. These solutions constitute an infinite set of modes, in addition to the plane wave usually treated in the literature. In section 3 the analogy between propagation of sound and an electrical transmission line is established, and it is shown that each mode requires a separate transmission line. In section 4 it is shown that the effect of the higher modes excited by a plane discontinuity may be represented by a lumped capacitance, and this capacitance is given by a variational expression which gives a systematic method of calculation yielding an upper bound to the true answer. For the case of a window, a variational principle is produced inihich gives a lower bound to the true answer. In section B this method is applied to a window in a rectangular tube in some detail, in section 7 it is applied to a change of cross section in a rectangular tube, and in section 8 it is applied to windows and changes of cross section in circular tubes. In section 9 the reflection and transmission factors are calculated, and in section 10 the resonant frequency of certain types of resonators is calculated.\r\n\r\nTo the authors's knowledge this is the first rigorous treatment of the above problems with the exception of an earlier paper calculating the reflection due to a change of cross section in a circular tube.\r\n" }, { "name": "Ours, Statton Ray", "degree": "Engineering Degree", "year": "1944", "title": "An Investigation of the Effects of Weight Geometry and Time in Repeated Tension Impact Testing", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-093713", "creators": [ { "name": { "family": "Ours", "given": "Statton Ray" }, "id": "Ours-Statton-Ray", "display_name": "Ours, Statton Ray" }, { "name": { "family": "Jackson", "given": "William Gauss" }, "id": "Jackson-William-Gauss", "display_name": "Jackson, William Gauss" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "member", "display_name": "Clark, Donald S." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "member", "display_name": "Duwez, Pol E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G8NX-JD54", "abstract": "The investigation covered in this report was conducted with the Falling-Carriage Repeated Tension Impact Machine at the Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California.
\r\n\r\nTwenty-eight aluminum alloy test specimens were subjected to a total of 7,834 impacts in the GALCIT Falling-Carriage Repeated Tension -impact Machine. Since the average number of impacts per specimen was about 280 it is believed that this investigation covered a regime different from other investigations made with this equipment.
\r\n\r\nThe effect of elapsed time between series of impacts was not established. The results obtained were contradictory, and it is believed that this was due to the energy per impact being variable and unknown.
\r\n\r\nIt is established that the geometry of the weight used in this type of test has some influence upon the elongation produced. It is shown that 17S-T duralumin is relatively sensitive to stress concentrations caused by change in cross-section and strain wave reflection, and relatively insensitive to stress concentrations due to small scribe marks.
\r\n\r\nEvidence is presented to indicate that the elongation at fracture of a specimen subjected to repeated tension impact is inversely proportional to the number of impacts required to produce fracture.
\r\n\r\nSuggestions are offered for improving the test equipment so as to obtain more nearly consistent results.
" }, { "name": "Wayne, Jay C.", "degree": "Masters", "year": "1944", "title": "Flight Testing : Report", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102025-185052730", "creators": [ { "name": { "family": "Wayne", "given": "Jay C." }, "id": "Wayne-Jay-C.", "display_name": "Wayne, Jay C." }, { "name": { "family": "Walkowicz", "given": "Teddy F." }, "id": "Walkowicz-Teddy-F.", "display_name": "Walkowicz, Teddy F." } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xez2-cg73", "abstract": "No abstract." }, { "name": "Hanger, Willard Muirhead", "degree": "Engineering Degree", "year": "1943", "title": "A Photoelastic Investigation of the Effect of Elliptical and Modified Cutouts in Flat Panels Subjected to Combined Bending and Shear", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11182008-133221", "creators": [ { "name": { "family": "Hanger", "given": "Willard Muirhead" }, "id": "Hanger-Willard-Muirhead", "display_name": "Hanger, Willard Muirhead" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6M05-2809", "abstract": "Quite frequently in an aircraft structure there are occasions when it is necessary or advantageous to make openings or cutouts in the structure. These may be lightening holes in a web or spar or they may be openings in the structure which are necessary for access or other reasons. An analytical solution of the problem of stress distribution around a cutout in a stressed member is often impossible since the analytical method is limited to problems in which the boundary conditions are simple. The purpose of this investigation was to determine by means of a photo-elastic analysis the amount of stress concentration caused by a cutout in a flat panel and how this concentration varied under different conditions of loading and with various types of cutouts. Simple photoelasticity provides a means of finding the stresses only along the cutout boundary. However since the stress concentrations are a maximen at the boundary, this is the region in which the designer is most interested. Only boundary stresses along the cutout are considered in this paper.\r\n\r\nThis research is a continuation of the work carried out by Gibbons and Dill at the California Institute of Technology in 1941-42. Their paper entitled \u201cA Photoelastic Investigation of the Effect of Elliptical and Modified Cutouts in Flat Panels Subjected to Combined Bending and Shear\u201d dealt with a similar panel with similar cutouts under much the same conditions of loading as carried out in this research. However the long axis of the cutout in this investigation was horizontal or perpendicular to the shear loading, while the long axis of the cutout in the previous investigation was at 90\u00b0 to this direction, i.e., vertical. Tyra and Hollister also did some research at the California Institute of Technology on this subject. Their thesis entitled \u201cA Photoelastic Investigation of the Effect of Cutouts in Panels Subjected to Combined Bending and Shear\" dealt with circular and modified circular cutouts. This paper considers an elliptical cutout which was modified by several steps to a rectangular opening, the ratio of the maximum length to width being 2:1.\r\n" }, { "name": "Hayes, Wallace Dean", "degree": "Engineering Degree", "year": "1943", "title": "Some Investigations in the Buckling of Thin Rods", "advisor": "Bateman, Harry", "url": "https://resolver.caltech.edu/CaltechETD:etd-11182008-135603", "creators": [ { "name": { "family": "Hayes", "given": "Wallace Dean" }, "id": "Hayes-Wallace-Dean", "display_name": "Hayes, Wallace Dean" } ], "advisors": [ { "name": { "family": "Bateman", "given": "Harry" }, "id": "Bateman-H", "role": "advisor", "display_name": "Bateman, Harry" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2G6H-SH82", "abstract": "The general case of a non-uniform, straight rod under varying axial load is investigated, and several methods of solution are indicated or described. The case of a uniform rod with constant axial load is investigated by means of its deflection curve, and the direct determination of the stability with general end restraints is made possible by the use of a graph. The correlation between the end fixities of a rod and its behavior as a beam is given.\r\n" }, { "name": "Kane, Richard Francis", "degree": "Engineering Degree", "year": "1943", "title": "The Theory, Design and Performance of a Two Dimensional High Speed, Induction Type Wind-Tunnel", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-134052", "creators": [ { "name": { "family": "Kane", "given": "Richard Francis" }, "id": "Kane-Richard-Francis", "display_name": "Kane, Richard Francis" }, { "name": { "family": "Kelley", "given": "Edward Frederick" }, "id": "Kelley-Edward-Frederick", "display_name": "Kelley, Edward Frederick" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "role": "advisor", "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S53W-ST96", "abstract": "(1) A two-dimensional wind tunnel, induction type, of rectangular working section, 2 1/2\" x 12\", has been designed and constructed for the purpose of testing aerodynamic shapes at velocities close to the speed of sound.\r\n\r\n(2) The design theory is based upon the fundamental equations of momentum, continuity, and energy with the assumptions that mixing takes place at constant area and that jet exit velocities in this supersonic range may be obtained.\r\n\r\n(3) Calibration runs, in which the maximum Mach number of 0.65 was obtained, revealed that the actual tunnel performance did not agree with the design performance curves except at high compression ratios.\r\n\r\n(4) A variation of the original theory, i.e., sonic jet exit velocities, was used to obtain a new set of design curves. These curves are in excellent agreement with actual performance data except at high compression ratios.\r\n\r\n(5) Failure of the tunnel to meet design conditions is considered to lie in the jet shape which assumes a true supersonic nozzle shape only at small jet openings (high compression ratios).\r\n" }, { "name": "Lee, Edwin Samuel", "degree": "Engineering Degree", "year": "1943", "title": "A Correlation of Repeated Tension Impact Tests with Other Tension Tests of 17ST Duralumin", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032008-153139", "creators": [ { "name": { "family": "Lee", "given": "Edwin Samuel" }, "id": "Lee-Edwin-Samuel", "display_name": "Lee, Edwin Samuel" }, { "name": { "family": "Sterling", "given": "Cedric Warren" }, "id": "Sterling-Cedric-Warren", "display_name": "Sterling, Cedric Warren" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VP8E-Q282", "abstract": "The strain distribution after repeated tension impacts along the length of several differently dimensioned specimens of 17ST Duralumin is determined for various energies per blow. An attempt is made to determine a relationship between the one energy available per blow, the dimensions of the specimen, and the number of blows required to cause failure of the specimen by repeated tension impacts. A relationship is determined between the percent total elongation and the length-to-diameter ratio. A relationship is determined between the energy per unit volume required to cause failure and the length-to-diameter ratio under static tension, dynamic tension, and repeated tension impact conditions. A \u201cModulus of Destructiveness\" is proposed for 17ST duralumin. A method is presented for predicting the number of repeated tension impact blows necessary to cause failure of a part.\r\n" }, { "name": "Sweeney, William Edward", "degree": "Engineering Degree", "year": "1943", "title": "Investigation of Design Criteria of Stiffened Wooden Panels", "advisor": "Sechler, Ernest Edwin; Dunn, Louis G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12242008-113646", "creators": [ { "name": { "family": "Sweeney", "given": "William Edward" }, "id": "Sweeney-William-Edward", "display_name": "Sweeney, William Edward" }, { "name": { "family": "Bridgland", "given": "Edgar Parsons" }, "id": "Bridgland-Edgar-Parsons", "display_name": "Bridgland, Edgar Parsons" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "advisor", "display_name": "Dunn, Louis G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4YVN-3R91", "abstract": "The aim of this research was to find design data for the stiffened plywood panels supplied by the Fletcher Aviation Company.
\r\n\r\nThe tests included stiffened panel tests, unstiffened panel tests, and short column tests to find the physical properties of the material.
\r\n\r\nThe results of these tests, show that the ultimate compression stress which the specimen will resist is a function of the percentage stiffener area compared to the total panel area, and the L/P ratio of the panel.
\r\n\r\nPredicted ultimate stresses from the curves developed show sufficiently good agreement with actual test, that they may be used for design purposes with allowance for descrepancies in material and workmanship.
" }, { "name": "Zebb, George Keirn", "degree": "Engineering Degree", "year": "1943", "title": "Technique of Measuring Transverse Components of Velocity Fluctuations in Turbulent Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242008-111753", "creators": [ { "name": { "family": "Zebb", "given": "George Keirn" }, "id": "Zebb-George-Keirn", "display_name": "Zebb, George Keirn" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H56H-BX29", "abstract": "The mean speed characteristics of several X-type v'/U-meters having widely varied dimensions were measured in order to verify assumptions usually made regarding the range of linear characteristics for meters of this type.
\r\n\r\nUsing the same meters, and other meters with intermediate sizes, values of v'/U were measured in the turbulent fields behind three grids. Comparison of the results gave a qualitative indication of the effect of meter size on turbulence measurements.
\r\n\r\nA length correction for the X-type meters used was derived and the turbulence values corrected, with the result that all meters gave approximately the same answers.
\r\n\r\nHowever, even after application of the length correction, it was found that in the turbulent field behind grids (generally assumed to be isotropic) v'/U was consistently lower than u'/U at a given distance behind the grid. This result is the same as that described by Corrsin in ref. (4) where no length correction was applied.
" }, { "name": "Corrsin, Stanley", "degree": "Engineering Degree", "year": "1942", "title": "Decay of Turbulence Behind Three Similar Grids", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04062006-141720", "creators": [ { "name": { "family": "Corrsin", "given": "Stanley" }, "id": "Corrsin-Stanley", "display_name": "Corrsin, Stanley" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GXRW-6609", "abstract": "u\u2019 and v\u2019 decay measurements were made behind three similar girds. The u\u2019 readings were corrected for wire length and the v\u2019 readings were corrected for the sensitivity of the v\u2019-meter to u\u2019. These corrected values were plotted against x/M on logarithmic cross-section paper. The slope of these lines gave the exponent in the theoretical law for the decay of isotropic turbulence.\r\n\r\nA consistent deviation was found between the average u\u2019 and v\u2019 values. A suitable length correction applied to the v\u2019 values would increase them somewhat, lessening the discrepancy, and giving a true comparison between the two components of the turbulent energy.\r\n\r\nFrom a comparison of the present u\u2019 values behind the 1\u201d grid with the u\u2019 values measured with a free stream turbulence level 10 times as great as the present one, it is concluded that the change in initial turbulence has no appreciable effect on the u\u2019 behind a grid." }, { "name": "Gibbons, Robert Martin", "degree": "Engineering Degree", "year": "1942", "title": "A Photoelastic Investigation of the Effect of Elliptical and Modified Cutouts in Flat Panels Subjected to Combined Bending and Shear", "advisor": "Millikan, Clark Blanchard; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:08242010-095944937", "creators": [ { "name": { "family": "Gibbons", "given": "Robert Martin" }, "id": "Gibbons-Robert-Martin", "display_name": "Gibbons, Robert Martin" }, { "name": { "family": "Dill", "given": "Douglas Gordon" }, "id": "Dill-Douglas-Gordon", "display_name": "Dill, Douglas Gordon" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/36WR-QZ84", "abstract": "No abstract." }, { "name": "Goode, John Edward", "degree": "Engineering Degree", "year": "1942", "title": "Maneuverability", "advisor": "Stewart, Homer Joseph; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-113423", "creators": [ { "name": { "family": "Goode", "given": "John Edward" }, "id": "Goode-John-Edward", "display_name": "Goode, John Edward" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7HP2-Q527", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA method has been developed which makes possible the determination of the time to make a horizontal turn of any number of degrees, and also the control deflections necessary to make the turn. Accelerations encountered during the maneuver are easily obtained from the calculations which are used in obtaining the maneuvering time.\r\n\r\nThe method worked out is based on the six fundamental stability equations. The major assumptions are angle of bank [...], and no sideslip during turn i.e. V = 0. Only the use of simple wind tunnel data is necessary.\r\n\r\nSeveral cases are worked out for different bank assumptions for a twin engine attack bomber. The bank assumption which gives the most reasonable control deflections and accelerations during the maneuver is one which produced a helix angle of 0.090 and maximum bank of 75\u00b0. For this particular bank assumption calculations were carried out for sea level and 15,000 ft. altitude.\r\n\r\nCalculations were also carried through for sea level and 15,000 ft. for a modified single engine airplane of same weight and horsepower as the twin engine one, using the bank assumption which gave [...] max. of 75\u00b0.\r\n\r\nA method is presented for the direct calculation of the stability derivative, M[...], from wind tunnel data.\r\n" }, { "name": "Kiergan, Nova Babb", "degree": "Engineering Degree", "year": "1942", "title": "A Study of Flutter in One Degree of Freedom", "advisor": "Biot, Maurice A.; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242008-082928", "creators": [ { "name": { "family": "Kiergan", "given": "Nova Babb" }, "id": "Kiergan-Nova-Babb", "display_name": "Kiergan, Nova Babb" }, { "name": { "family": "Tomamichel", "given": "Jack Jones" }, "id": "Tomamichel-Jack-Jones", "display_name": "Tomamichel, Jack Jones" } ], "advisors": [ { "name": { "family": "Biot", "given": "Maurice A." }, "id": "Biot-M-A", "role": "advisor", "display_name": "Biot, Maurice A." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Biot", "given": "Maurice A." }, "id": "Biot-M-A", "role": "chair", "display_name": "Biot, Maurice A." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Dunn", "given": "Louis G." }, "id": "Dunn-L-G", "role": "member", "display_name": "Dunn, Louis G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NX9K-JT57", "abstract": "The authors have attempted to develop a theoretical means of determining the amount of aerodynamic damping, positive or negative, existing on a symmetrical airfoil having freedom to oscillate only about an axis parallel to the span and on the zero camber line. Variables considered were oscillating frequency, wind speed, and hinge position (location of axis of oscillation.)\r\n\r\nHaving developed what they considered a proper theoretical criterion for determining the value of aerodynamic damping, the authors have conducted an experimental investigation of an airfoil oscillating system having one degree of freedom, in an attempt to verify the theoretical criterion.\r\n\r\nIt was concluded that for small oscillations the theoretical values of aerodynamic damping moment are correct except for hinge positions near the leading edge. Contrary to the theory, it was considered that the experimental investigation established the fact that negative damning does not occur for hinge positions at or near the leading edge.\r\n\r\nA general conclusion was made by the authors that an airfoil oscillating with only one degree of freedom will always have a positive aerodynamic damping moment provided the oscillations are small.\r\n\r\nIt was found that an airfoil restricted to one degree of freedom (rotation) and pivoted about the 0.75 chord line will flutter when deflected to an amplitude approximating the stall angle. Flutter will be self-induced when the aerodynamic forces are sufficient to deflect the airfoil to the stall angle.\r\n" }, { "name": "Olsen, Carl Baker", "degree": "Engineering Degree", "year": "1942", "title": "A Study of the Effects of Repeated Tension Impact Loads Upon Certain Metals Used in Aircraft Construction", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072008-100137", "creators": [ { "name": { "family": "Olsen", "given": "Carl Baker" }, "id": "Olsen-Carl-Baker", "display_name": "Olsen, Carl Baker" }, { "name": { "family": "Brown", "given": "Sheldon Willis" }, "id": "Brown-Sheldon-Willis", "display_name": "Brown, Sheldon Willis" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RXJQ-C567", "abstract": "The repeated tension impact properties of a manganese bronze, used in aircraft landing gear fittings, are presented in this report.
\r\n\r\nThe repeated tension impact test apparatus was adapted to take specimens in the form of sheet as well as specimens of the conventional bar type. With the modified apparatus, data on Alcoa 24 S-T and Dowmetal J-1H sheet specimens of varying thicknesses were obtained in order to present the aircraft designer with information directly applicable to the sheet materials currently in use.
\r\n\r\nAn investigation was made of the effect of service operation on the repeated tension impact properties of three 25 S-T propeller blades. For this purpose, propeller blades were used with approximately 5,314, and 788 hours of service operation.
\r\n\r\nA new machine, specifically designed for repeated tension impact testing, was placed in commission. With this machine, repeated tension impact test data on 24 S-T bar stock were extended to higher velocity ranges in an effort to determine the effect of velocity of impact.
\r\n" }, { "name": "Schwarzenbach, Jean Christophe", "degree": "Engineering Degree", "year": "1942", "title": "Calibration of the Merrill-G.A.L.C.I.T. Wind-Tunnel, and a Suggestion for a Variable Cross-Section on a Small High-Speed Wind-Tunnel", "advisor": "Merrill, Albert Adams", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-083306", "creators": [ { "name": { "family": "Schwarzenbach", "given": "Jean Christophe" }, "id": "Schwarzenbach-Jean-Christophe", "display_name": "Schwarzenbach, Jean Christophe" } ], "advisors": [ { "name": { "family": "Merrill", "given": "Albert Adams" }, "id": "Merrill-A-A", "role": "advisor", "display_name": "Merrill, Albert Adams" } ], "committee": [ { "name": { "family": "Merrill", "given": "Albert Adams" }, "id": "Merrill-A-A", "role": "chair", "display_name": "Merrill, Albert Adams" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Shevell", "given": "Richard" }, "id": "Shevell-R", "role": "member", "display_name": "Shevell, Richard" }, { "name": { "family": "Corrsin", "given": "Stanley" }, "id": "Corrsin-Stanley", "role": "member", "display_name": "Corrsin, Stanley" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PGWH-E460", "abstract": "Speed, power and flow inclination calibration tests run in the Merrill-GALCIT wind-tunnel are described and results presented. A description of the new balance-system is included. Turbulence measurements with hot-wires were made in the tunnel at various speeds and with various screen configurations.\r\n\r\nTests run in a small scale model of the projected cooperative wind-tunnel at subsonic and sonic velocities are briefly described. A suggestion for introducing variable working- section walls in the new scale model undergoing construction is discussed and presented.\r\n" }, { "name": "Shevell, Richard Shepherd", "degree": "Engineering Degree", "year": "1942", "title": "The Design and Testing of an Aerodynamic Model of a High Speed Wind Tunnel", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11192008-145939", "creators": [ { "name": { "family": "Shevell", "given": "Richard Shepherd" }, "id": "Shevell-Richard-Shepherd", "display_name": "Shevell, Richard Shepherd" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "chair", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "member", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Thiele", "given": "Carl" }, "id": "Thiele-C", "role": "member", "display_name": "Thiele, Carl" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DPNP-VP27", "abstract": "In conjunction with the design of the high speed Cooperative Wind Tunnel at the California Institute of Technology an aerodynamic model was built and tested. Methods of design of the contraction, working section, and diffuser are explained.\r\n\r\nThe model test showed that the working section of a wind tunnel operating at a Mach Number greater than 0.7 must have adjustable walls to maintain a constant velocity through the working section. The unsatisfactory design of the diffuser is demonstrated by both static pressure measurements and visual observations.\r\n\r\nA description is given of visual observations of supersonic phenomena occurring in the working section and diffuser of the model.\r\n" }, { "name": "Williams, Edgar Purell", "degree": "Engineering Degree", "year": "1942", "title": "Fuselage and Nacelle Effects on Airplanes as Determined by a Statistical Study of Data from the GALCIT 10-Foot Tunnel", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-104914", "creators": [ { "name": { "family": "Williams", "given": "Edgar Purell" }, "id": "Williams-Edgar-Purell", "display_name": "Williams, Edgar Purell" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "chair", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Marquardt", "given": "R. E." }, "id": "Marquardt-R-E", "role": "member", "display_name": "Marquardt, R. E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WY13-WD59", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nAn attempt to base fuselage drag upon wetted area showed no less scatter than [...] as a function of fineness ratio. For average values of [...] for fuselages and flying boat hulls see Figure 12.\r\n\r\nThe destabilizing effect of fuselages and flying boat hulls based on the volume of a circumscribed cylinder is given in figure 22 as a function of the c.g. position. The fuselage body appears to act somewhat analogous to an airfoil with an aerodynamic center at a point somewhere between the 0.2 and 0.3 body position.\r\n\r\nThe effect of fuselages and flying boat hulls on [...] is given by figures 23 through 29. One set of figures gives [...] as a function of the destabilizing effect and the other set as a function of the c.g. position.\r\n\r\nNo successful means of correlating nacelle data was found. Figures 30 through 33 show the magnitude of nacelle drag and moment effects.\r\n" }, { "name": "Yuan, Shao Wen", "degree": "PhD", "year": "1942", "title": "Thin Cylindrical Shells Subjected to Various Types of Concentrated Loads", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232008-152804", "creators": [ { "name": { "family": "Yuan", "given": "Shao Wen" }, "id": "Yuan-Shao-Wen", "display_name": "Yuan, Shao Wen" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QSE5-ZP85", "abstract": "The bending of thin cylinder shells based on the general theory of elasticity is of interest not only to the mathematician but also to the engineer. The general theory of the shells has recently been developed to the point that it is now being used by engineers as a basis for the design of this type of structure.\r\n" }, { "name": "Ashworth, Thomas", "degree": "Engineering Degree", "year": "1941", "title": "An Analytical Approach to the Problem of Longitudinal Stability of Flying Boats in the Planing Conditions", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11202008-130754", "creators": [ { "name": { "family": "Ashworth", "given": "Thomas" }, "id": "Ashworth-Thomas", "display_name": "Ashworth, Thomas" }, { "name": { "family": "Dilworth", "given": "John Andrew" }, "id": "Dilworth-John-Andrew", "display_name": "Dilworth, John Andrew" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AP1X-DP12", "abstract": "The subject of the longitudinal stability, or \"porpoising\", of flying boats has been the subject of investigation both in this country and abroad. In many cases, recourse to dynamically similar models has been had to determine the stability characteristics of the design in question. In general, however, the bare hull is tested in towing tanks, and the data are presented in the form of curves of resistance, moment, draft, speed, and angle of trim. Conclusions regarding \"porpoising\" of the full scale airplane cannot be drawn from these tests alone, but it is considered possible to evaluate certain of the hydrodynamic derivatives which in conjunction with aerodynamic derivatives obtained from wind tunnel tests, can be used in the stability equation to determine the behavior of the flying boat in the planing region.\r\n\r\nIn the analysis of the problem presented here, most of the derivations of the formulae have been omitted. For a more detailed derivation, reference is made to the thesis of Lieutenant George A. Hatton, U. S. N., entitled \"The Longitudinal Stability of a Flying Boat in the Planing Condition as Computed from Tank Test Data of a Hull Model.\"\r\n\r\nThroughout the analysis, the effect of a drag has been neglected. A discussion of this omission will be made in the conclusion of the paper.\r\n\r\nThe first part of the paper will be concerned with a presentation of the formulae and an example of their use with results of calculations made. The second part will cover the dynamic model tests and a discussion of the equipment used. The conclusion will cover the entire paper.\r\n\r\nIt must be noted that the analysis here is restricted to only the planing condition or that part of the take-off run past the hump, and the formulae are derived for that condition.\r\n" }, { "name": "Bell, Richard William", "degree": "Engineering Degree", "year": "1941", "title": "Some Aspects of the Effects of Propeller Operation on the Static Longitudinal Stability of an Airplane", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12012008-095536", "creators": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-Richard-William", "display_name": "Bell, Richard William" }, { "name": { "family": "Storms", "given": "Harrison Allen" }, "id": "Storms-Harrison-Allen", "display_name": "Storms, Harrison Allen" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A8D1-2071", "abstract": "This thesis is to be considered a continuation of the material presented in the paper by Dr. C. B. Millikan, \"The Influence of Running Propellers on Airplane Characteristics\", [ref. 1] and of the work done in the thesis [ref. 2] by Mr. S. E. Belsley on the same subject. In reference 1 Dr. Millikan has derived expressions for the prediction of the power-on effects, dependent upon empirical expressions for the power-on downwash at the tail, and the tail efficiency in the slipstream. In reference 2 Mr. Belsley has put these same expressions in forms which permit experimental determination of the two empirical factors dealing with downwash and tail efficiency power-on. It is in part the purpose of this thesis to present numerical results for these factors, determined empirically from tests run at the Galcit* 10' wind tunnel on five different airplanes. In addition there is presented a discussion of the effects on pitching moment of various rotational configurations for twin-engine mono-planes including the effects on the tail removed configuration. There has appeared in power model testing of multi-engined airplanes the existence of favorable rotational configurations giving better power-on stability than the other possible rotations. As a consequence two of the five airplanes were tested for three different rotational configurations. The experimental data have been reduced in a manner that demonstrates clearly the effect of rotation alone on pitching moment. Unfortunately, similar data could not be obtained on the other airplanes, due to the limited time available for research at the Galcit tunnel.\r\n\r\n*Guggenheim Aeronautics Laboratory, California Institute of Technology.\r\n" }, { "name": "Damberg, Carl Fillmore", "degree": "Engineering Degree", "year": "1941", "title": "Design Study Of Auxiliary Jet Propulsion Installation on the YO-55 (ERCOUPE) Airplane with an Analysis of Performance and Flight Characteristics", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-151905", "creators": [ { "name": { "family": "Damberg", "given": "Carl Fillmore" }, "id": "Damberg-Carl-Fillmore", "display_name": "Damberg, Carl Fillmore" }, { "name": { "family": "Dane", "given": "Paul Howard" }, "id": "Dane-Paul-Howard", "display_name": "Dane, Paul Howard" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MBAM-8X54", "abstract": "In recent years the use of high wing loadings on large high performance airplanes has emphasized the problem of take-off. In many cases the allowable gross weight is limited primarily by take-off considerations.\r\n\r\nThe most effective way to decrease the take-off distance without decreasing wing loading is to increase the available thrust during take-off run and initial climb. The use of auxiliary jet propulsion has been proposed as a means of accomplishing this and considerable interest has been aroused in its development. A program of development and research on jet reaction motors using various types of fuels has been undertaken at the California Institute of Technology during the past year. The development of a jet motor using solid fuel (powder) has reached the stage where it is practical to begin actual flight test experiments with assisted take-offs. For this purpose the U. S. Army Air Corps has made available a YO-55 (Ercoupe) Airplane for installation of auxiliary jet propulsion units and for flight testing. This report is concerned with a study of the various problems involved in the use of jet propulsion on an airplane, and the design of a practical installation on the YO-55 airplane.\r\n\r\nAfter a study of the various factors involved, it was decided to use two jet propulsion assemblies each containing three separate jet motors of approximately 25 lbs. thrust. The assemblies are mounted under the center section of the wing, one on each side just inboard of the main landing wheel fairing. The motors are so designed that in case of an excessive pressure build-up, the nozzle will fly off to the rear and the rest of the motor will be propelled forward clear of the airplane. Particular emphasis was placed on safety of the pilot and the airplane structure.\r\n" }, { "name": "Fischer, Charles Fink", "degree": "Engineering Degree", "year": "1941", "title": "The Performance of Jet Propelled Space Vehicles", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:04192011-133614556", "creators": [ { "name": { "family": "Fischer", "given": "Charles Fink" }, "id": "Fischer-Charles-Fink", "display_name": "Fischer, Charles Fink" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HFY8-KW92", "abstract": "This thesis presents an investigation of the steady state performance of space vehicles partially propelled by jets, the acceleration period required to reach the steady state, the use of jets for the assisted take off of flying boats, and the general economic aspects of jet propulsion applied to aircraft.\r\n" }, { "name": "Lapin, Ellis", "degree": "Engineering Degree", "year": "1941", "title": "The Effect of Gunfire on the Longitudinal Motion of an Airplane", "advisor": "Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062008-151722", "creators": [ { "name": { "family": "Lapin", "given": "Ellis" }, "id": "Lapin-Ellis", "display_name": "Lapin, Ellis" } ], "advisors": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "chair", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Biot", "given": "Maurice A." }, "id": "Biot-M-A", "role": "member", "display_name": "Biot, Maurice A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GQG7-6C62", "abstract": "The effect produced by the reaction forces and moments resulting from the fire of light and heavy calibre rapid fire guns on the path of motion of a modern military aircraft is discussed. This discussion is made on the basis of the \"exact\" equations of motion as developed by Bryan, Routh, and others, using the forms given in Dr. C. B. Millikan's notes on the dynamic stability of the airplane. The formal solution is made by the use of Heaviside operational calculus.\r\n\r\nFor general use there is developed a nomogram based on a series solution to the differential equations of motion. The application of this nomogram is illustrated and it is shown to give an easy and rapid approximation to the disturbance, and a sufficiently accurate one within the time ranges required. Since the exact solution requires several hours and the use of an experienced computer on a computing machine while the nomogram permits slide rule computations and results in a solution within a few minutes, its usefulness is readily apparent. The extension of the methods used in this paper to disturbed lateral motions is briefly discussed.\r\n" }, { "name": "McCoy, Howard Monroe", "degree": "Engineering Degree", "year": "1941", "title": "Discussion of Two Specialized Aircraft Propeller Problems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122008-082157", "creators": [ { "name": { "family": "McCoy", "given": "Howard Monroe" }, "id": "McCoy-Howard-Monroe", "display_name": "McCoy, Howard Monroe" }, { "name": { "family": "Longfelder", "given": "Harlowe Julius" }, "id": "Longfelder-Harlowe-Julius", "display_name": "Longfelder, Harlowe Julius" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9YND-4B66", "abstract": "Part I: Governing and Synchronization\r\nThe design and construction of an aircraft propeller governor or synchronizer is a specialized problem concerning Servo-Mechanism Theory. Search developed that adequate theory existed to cover the specific variables involved. The sources used in this report are listed in the extensive bibliography. Short descriptions are presented of the various governing and synchronizing means used to control present day propellers. In this research an airplane engine-propeller system was simulated and a single unit of a synchronizer, suitable for use as a governor for one engine, was invented and constructed. It was demonstrated to meet the United States Army Air Corps tentative specifications for propeller synchronizers. Time and unavailability of material and overworked shop facilities did not permit the construction of a model for full scale multi-motored airplane test. It is contemplated that such a model will later be constructed at the Materiel Division, United States Air Corps, Wright Field, Dayton, Ohio. A detailed description of this invention is presented in Appendix I. A discussion is presented of the general servo-mechanism theory as applied to airplane propeller governors and synchronizers. In addition, a short discussion is presented of how synchronization of propellers influences the tactical employment of military aircraft. The physiological effect on occupants of aircraft is also shortly discussed.\r\n\r\nPart II: Effect of Variable Engine Reduction Gearing on Aircraft Performance\r\nThe demand for improved performance in aircraft has led through the years to the development of more efficient propulsive systems, starting with the fixed pitch propeller directly driven from the engine and progressing to the modern geared constant speed variable pitch propeller. This development and the reasons for it are briefly described. The continued increase in performance leads to the two speed reduction gear and finally to the continuously variable reduction gear combined with the constant speed variable pitch propeller. The possible advantages of such an installation and the reasons for these advantages are described. Two examples of modern military airplanes are used to illustrate in detail the gains in performance that may be obtained. The extension to probable developments in airplanes to be built in the near future is considered. Mechanical difficulties and control problems are briefly discussed.\r\n" }, { "name": "Tyra, Thomas Donald", "degree": "Engineering Degree", "year": "1941", "title": "A Photoelastic Investigation of the Effect of Cutouts in Panels Subject to Shear and Bending", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11172008-105645", "creators": [ { "name": { "family": "Tyra", "given": "Thomas Donald" }, "id": "Tyra-Thomas-Donald", "display_name": "Tyra, Thomas Donald" }, { "name": { "family": "Hollister", "given": "William Wallace" }, "id": "Hollister-William-Wallace", "display_name": "Hollister, William Wallace" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q4B3-CJ36", "abstract": "In the design of modern aircraft many structural problems have arisen which are not subject to a simple analysis. Although the usual formulas of elasticity apply, their application becomes too cumbersome for practical use. A problem of this type is the determination of stresses around openings or cutouts. Thus, in monocoque construction there are openings for doors, windows, hatches, etc. Frames and bulkheads are pierced for the passage of conduits, ducts, or other members. In many of these cases, no formal determinations of the stresses can be made. It is well known, however, that stress concentrations do occur at reentrant corners, openings, etc. It was the purpose of this investigation to determine by photoelastic means the amount of this stress concentration, and how it varied in intensity under different conditions of loading, and with various types of openings. " }, { "name": "Belsley, Steven Eric", "degree": "Masters", "year": "1940", "title": "The Determination of Two Parameters Dealing with Power-On Stability for a Model with Right Hand Propellers", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-131655", "creators": [ { "name": { "family": "Belsley", "given": "Steven Eric" }, "id": "Belsley-Steven-Eric", "display_name": "Belsley, Steven Eric" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RPDT-VM86", "abstract": "This work presents expressions for determining the down-wash over the tail and the tail efficiency power-on and off. A method for the determination of empirical constants used by Millikan is presented. The method gives excellent agreement for the multiplicative factor Ap and good agreement for Bp. The theory checks experiment very well as Ap and Bp are nearly independent of Tc. " }, { "name": "Dunn, Louis Gerhardus", "degree": "PhD", "year": "1940", "title": "An Investigation of Sheet-Stiffener Panels Subjected to Compression Loads with Particular Reference to Torsionally Weak Stiffeners", "advisor": "Sechler, Ernest Edwin; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-154649", "creators": [ { "name": { "family": "Dunn", "given": "Louis Gerhardus" }, "id": "Dunn-Louis-Gerhardus", "display_name": "Dunn, Louis Gerhardus" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/84RM-ZH50", "abstract": "A total of 183 panel specimens of 24ST alloy with nominal thicknesses of 0.020, 0.025, and 0.040 inch with extruded bulb-angle sections of 12 shapes spaced 4 and 5 inches as stiffeners were tested to obtain the buckling stress and the amplitude of the maximum wave when buckled. Bulb angles from 3 to 27-1/2 inches long were tested as pin-end columns. The experimental data are presented as stress-strain and column curves and in tabular form. Some comparisons with theoretical results are presented.
\r\n\r\nAnalytical methods are developed that make it possible for the designer to predict with reasonable accuracy the buckling stress and the maximum-wave amplitude of the sheet in stiffened-panel combinations. The scope of the test was insufficient to formulate general design criteria but the results are presented as a guide for design and an indictaion of the type of theoretical and experimental work needed.
" }, { "name": "Fischer, Harold S.", "degree": "Masters", "year": "1940", "title": "An Application of Matrix Methods to Wing Theory", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sears, William Rees", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-094640", "creators": [ { "name": { "family": "Fischer", "given": "Harold S." }, "id": "Fischer-Harold-S", "display_name": "Fischer, Harold S." } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-W-R", "role": "advisor", "display_name": "Sears, William Rees" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-W-R", "role": "member", "display_name": "Sears, William Rees" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E1VN-SQ19", "abstract": "The calculation of spanwise lift distribution of a wing by a new method proposed by Theodore von Karman and W. R. Sears* depends on knowledge of certain \"characteristic values\" (eigenvalues) and \"characteristic functions\" (eigenfunctions) of the wing planform. These functions are solutions of a homogeneous boundary-value problem of the third kind.
\r\n\r\nIn the present paper the eigenvalues and the eigenfunctions, in series form, are calculated for a class of planforms by the method of successive multiplication of matrices.
\r\n\r\nThe class of planforms considered is that of trapezoidal wings with rounded tips. The eigenvalues and eigenfunctions are calculated for taper ratios 1:1, 2:1, 3:1, and 4:1; they are independent of aspect ratio. It is found, that for intermediate taper ratios they can be determined with reasonable accuracy by graphical interpolation.
\r\n\r\n* To be published shortly.
" }, { "name": "Fredrick, Joseph Louis", "degree": "Masters", "year": "1940", "title": "The Failure of Thin-Walled Semi-Elliptical Cylinders Under Torsion", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132008-142412", "creators": [ { "name": { "family": "Fredrick", "given": "Joseph Louis" }, "id": "Fredrick-Joseph-Louis", "display_name": "Fredrick, Joseph Louis" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/31X1-Q070", "abstract": "This paper constitutes a report on one phase of an investigation sponsored by the National Advisory Committee for Aeronautics at the California Institute of Technology, namely, the determination of the allowable loads in wing nose-sections under the action of combined loading conditions. As intimated by the title, the material presented here has been limited to the case of pure torsion only, this choice being dictated by the present state of the experimental program and the interpretation of its results.\r\n\r\nThe experimental program itself consisted of the testing of specimens made up of two semi-elliptical (or semi-circular) segments of sheet supported and clamped at the ends of the minor axis of the ellipse, thus simulating two wing nose-sections mounted to a common spar and tested as a single unit. As a result of the testing of these specimens with varying ellipticity, sheet thickness, and length, sufficient experimental data was obtained to establish rational design curves for both the buckling and ultimate failure of semi-elliptical cylinders under torsion.\r\n\r\nSince the type of specimens used only approximated the shape of an actual wing nose-section, it was necessary to devise a means of relating the two structures, in order that the criteria presented in this paper could be used for actual design practice.\r\n\r\nSince a limited amount of torsion tests on actual wing assemblies was available to this author, it was used to check the validity of both the geometric relation devised between the two types of structures as mentioned above and the actual design criteria developed from the experimental results. The agreement obtained was quite good, thus substantiating the usefulness and reliability of the results presented in this paper.\r\n\r\nIn the light of the above results, it is believed that the experimental portion of the investigation has been satisfactorily completed, with the possible exception of determining the affect of stiffeners upon the strength of the cylinders under discussion. However, since this represents an entirely different field of study, it is beyond the scope of this present investigation and must be relegated to the future.\r\n\r\nAttempts were made to develop a theoretical verification of the results obtained, but due to the complexities of the problem, they met with little success for the present. Therefore, this task also remains as one to be completed as a part of any future work which may be undertaken.\r\n" }, { "name": "Gentner, William Ellis", "degree": "Masters", "year": "1940", "title": "A Study of the Effect of Repeated Tension Impact Loads Upon Certain Metals Used in Aircraft Construction", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-080056433", "creators": [ { "name": { "family": "Gentner", "given": "William Ellis" }, "id": "Gentner-William-Ellis", "display_name": "Gentner, William Ellis" }, { "name": { "family": "Biglow", "given": "James Otis" }, "id": "Biglow-James-Otis", "display_name": "Biglow, James Otis" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/93VQ-ED36", "abstract": "The Impact Endurance Limit is evaluated for several materials used in aircraft construction. The Impact Endurance Limit is defined as the energy per blow in tension impact below which the specimen will withstand an indefinitely large number of blows without fracture.\r\n\r\nThe effect of grain orientation on the Impact Endurance Limit is shown.\r\n\r\nEvidence is presented that the Impact Endurance Limit may be a function of the ultimate tensile strength but not of the elongation or the yield point.\r\n\r\nThe effect of service stresses on the Impact Endurance Limit is discussed.\r\n" }, { "name": "Hatton, George Anthony", "degree": "Masters", "year": "1940", "title": "The Longitudinal Stability of a Flying-Boat in the Planing Condition as Computed from Tank Test Data of a Hull Model", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-082321", "creators": [ { "name": { "family": "Hatton", "given": "George Anthony" }, "id": "Hatton-George-Anthony", "display_name": "Hatton, George Anthony" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JR58-MH75", "abstract": "The question of \u201cporpoising\u201d of flying-boats has been the subject of investigation both abroad and in the United States. In Germany and England recourse has been had to the use of dynamically similar models, duplicating in the model as closely as possible all the features of the full scale flying-boat. In the towing tanks of the United States, usually a bare hull is tested, where measurements are made of resistance, load, trimming moment, and trim angle at various speeds. The results are usually furnished in the form of curves of trimming moment and draft against speed at various loadings and trim angles. Conclusions regarding \u201cporpoising\u201d of the full scale flying-boat cannot be drawn from the behavior of the hull alone, but it is considered possible to evaluate certain hydrodynamic stability derivatives, which, in conjunction with aerodynamic derivatives obtained from wind-tunnel tests, may be used in the stability equation to determine the behavior of the flying-boat in the planning condition.\r\n\r\nIn the following discussion the aerodynamic and hydrodynamic derivatives are deduced. The aerodynamic derivatives are similar to those normally used for airplanes, but they are evaluated in terms of beam, trim angle, and other hydrodynamic terms; then the hydrodynamic derivatives are deduced, also in terms of hull dimensions and attitudes. This permits direct addition of the hydrodynamic and aerodynamic derivatives for use in the longitudinal stability equation. The criteria of stability then are applied. In addition, a factorization of the stability quartic, formulated by Dr. Millikan, is applied to determine periods of the oscillations, as well as damping factors.\r\n\r\nAn example following the procedure above outlined and devised by Dr. Millikan is presented, using tank test data of a model 36 hull for hydrodynamic quantities. The aerodynamic quantities are based on an average of many modern flying-boats. The model 36 hull is selected as being fairly representative of present day flying boats.\r\n" }, { "name": "Koch, Walter Louis", "degree": "Masters", "year": "1940", "title": "An Experimental Investigation of Wind Tunnel Wall Interference on Rolling and Yawing Moments Due to Deflected Ailerons", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-10282005-141733", "creators": [ { "name": { "family": "Koch", "given": "Walter Louis" }, "id": "Koch-Walter-Louis", "display_name": "Koch, Walter Louis" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MN6W-EB71", "abstract": "Wind tunnel tests were made on a model wing with deflected ailerons in both open- and closed-jet configurations of a small wind tunnel. Rolling and yawing moments and lift were measured at various angles of attack. The wind tunnel wall interference on rolling and yawing moments is determined by comparison of the open- and closed-jet results. An approximate comparison with available theories is included. It appears that the interference effects measured are somewhat smaller than predicted by the theories.\r\n" }, { "name": "Kybal, Dalimil", "degree": "Masters", "year": "1940", "title": "The Aileron Influence on Wing Flutter", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:08212024-205858806", "creators": [ { "name": { "family": "Kybal", "given": "Dalimil" }, "id": "Kybal-Dalimil", "display_name": "Kybal, Dalimil" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/46zn-zn97", "abstract": "No abstract." }, { "name": "Malina, Frank Joseph", "degree": "PhD", "year": "1940", "title": "Characteristics of the Rocket Motor and Flight Analyses of the Sounding Rocket", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-143142441", "creators": [ { "name": { "family": "Malina", "given": "Frank Joseph" }, "id": "Malina-Frank-Joseph", "display_name": "Malina, Frank Joseph" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MF80-9W14", "abstract": "No abstract." }, { "name": "Moyers, Frank Neff", "degree": "Masters", "year": "1940", "title": "A Comparison of Theoretical and Experimental Pressure Distributions at High Speed About the N.A.C.A. 4412 Airfoil", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152005-142724", "creators": [ { "name": { "family": "Moyers", "given": "Frank Neff" }, "id": "Moyers-Frank-Neff", "display_name": "Moyers, Frank Neff" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YTRV-NM88", "abstract": "The general problem of aerodynamics is the determination of the forces and moments imposed on a stationary body immersed in a moving fluid. The problem is soluble if a mathematical calculation of the velocity distribution throughout the fluid can be made. The application of certain restrictions facilitates the calculation. Without great loss of usefulness we may restrict the motion to a steady, uniform, and rectilinear flow from infinity. With considerable loss of usefulness but with tremendous simplification in calculation we may add the further restrictions that the fluid be non-viscous and incompressible. Upon these assumptions the problem may be solved by utilizing two physical relationships, namely, the equations of motion and continuity." }, { "name": "Nagamatsu, Henry Takeshi", "degree": "Masters", "year": "1940", "title": "Experimental Investigation of Ultimate Loads Carried by Flat, Unstiffened Panels Under Combined Shear and Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-140614", "creators": [ { "name": { "family": "Nagamatsu", "given": "Henry Takeshi" }, "id": "Nagamatsu-Henry-Takeshi", "display_name": "Nagamatsu, Henry Takeshi" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FNQF-4Q12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe behavior of flat, unstiffened panels was investigated for two length over width ratios and five thicknesses. In each case the panels were loaded until they failed. An empirical relation was developed for the variation of the ultimate combined shear and compression stress of the form [...].\r\n\t\r\nThe values of m and n were found to be: m = 1.65 and n = .9 for panels with length over width ratio equal to 2, and m = 1.4 and n = 1.3 for panels with length over width ratio equal to 1 1/3. The above equations agree very closely with the experimental results.\r\n\r\nThere was a variation in the apparent shear modulus under different combined loading conditions, but no definite result was obtained.\r\n" }, { "name": "Pai, Shih-I", "degree": "PhD", "year": "1940", "title": "On Turbulent Flow Between Rotating Cylinders", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-143245", "creators": [ { "name": { "family": "Pai", "given": "Shih-I" }, "id": "Pai-Shih-I", "display_name": "Pai, Shih-I" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6VD9-HY80", "abstract": "The present work had as its purpose the investigation of the velocity and turbulence distributions in the turbulent flow between two co-axial cylinders, the inner of which rotated. The radius of the inner cylinder was 7-7/8\". Two aspect ratios were used, one 10\" to 1-1/16\", the other 10\" to 17/32\". All velocity and turbulence measurements were made with hot-wire technique, using a special holder which reduced spindle interference to a minimum.\r\n\r\nThe circumferential velocity of the inner rotating cylinder was several hundred times the critical speed for instability of the laminar flow as given by G. I. Taylor.\r\n\r\nIt was found that velocity distributions in which the circumferential velocity of the fluid increases outward actually exist and cannot be explained by the shadow effect of the measuring instrument as G. I. Taylor suggested. Also the flow between the rotating cylinders is three-dimensional. The mean velocity distribution depends on whether the transfer of shear is carried out by turbulent fluctuations or by secondary motion. The regions, where the secondary motion is negligible, the mean velocity distribution is logarithmic which was shown by Dr. von Karman to be the distribution in Couette's case of turbulent flow.\r\n\r\nThe analysis of the measurements indicated that the secondary flow can be described by assuming ring-shaped vortices between the cylinders. It was known that such ring-shaped vortices introduce the instability of the laminar flow (see Ref. 1); but it was not known that such vortices exist at speeds as high as several hundred times the critical speed for instability, although their shapes are distorted. The sizes of the vortices and their numbers depend on the speed of the inner cylinder. The vortices can only exist in pairs, and at certain critical speeds the flow pattern may change suddenly due to the loss or gain of a pair of vortices. At high speeds the number of the vortices tends to decrease.\r\n\r\nThe two-dimensional theories for turbulent flow between rotating cylinders are discussed. They can not even be taken as a first approximation for this three dimensional vortex-ring flow." }, { "name": "Powell, Walter Brown", "degree": "Masters", "year": "1940", "title": "An Investigation of Some Problems in the Design of Tailless Airplanes", "advisor": "Millikan, Clark Blanchard; Sears, William Rees", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252008-112304", "creators": [ { "name": { "family": "Powell", "given": "Walter Brown" }, "id": "Powell-Walter-Brown", "display_name": "Powell, Walter Brown" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-W-R", "role": "advisor", "display_name": "Sears, William Rees" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PZW5-2085", "abstract": "Some problems in the design of tailless airplanes are discussed. The conditions essential to the flight of such airplanes are determined, and a survey of methods of calculating the aerodynamic characteristics of plain wings and wings with flaps and ailerons deflected is presented. The effect of adding a fuselage and ring nacelles to a wing to form a practical airplane is discussed.
\r\n\r\nConsideration is given to the problem of damping of longitudinal oscillations, and a method of calculating the damping in pitch of a sweptback wing alone is presented.
\r\n\r\nAn example is carried through to illustrate the application of all the material covered in the paper. In all respects considered, the tailless airplane is shown to be comparable to normal type airplanes.
" }, { "name": "Sparks, Brian Orville", "degree": "Masters", "year": "1940", "title": "The Effects of Vertical Gusts on an Elastic Wing", "advisor": "Sears, William Rees", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142008-144847", "creators": [ { "name": { "family": "Sparks", "given": "Brian Orville" }, "id": "Sparks-Brian-Orville", "display_name": "Sparks, Brian Orville" } ], "advisors": [ { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-W-R", "role": "advisor", "display_name": "Sears, William Rees" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/20SK-0031", "abstract": "The case of a wing flexible in bending and rigid in torsion entering a vertical gust is treated by consideration of the corresponding two-dimensional case. The bending stiffness of the wing is expressed as a spring constant, the aerodynamic forces acting are taken from the two-dimensional theory of airfoils in non-uniform motion, and the differential equation of motion of the wing is solved by operational methods.
\r\n\r\nCases of sharp-edged and exponentially graded gusts are considered, and in each case the deflection is calculated in dimensionless form for three values of a dimensionless stiffness parameter. As a numerical example these results are put into dimensional form for a wing whose elastic properties are supposed to be typical of modern airplane wings.
\r\n\r\nThe results obtained for the cases considered show only in one instance a maximum deflection greater than the steady-state value. Even in the sharp-gust case the deflection increases comparatively slowly following the entrance of the wing into the gust. The effects of grading the gust are to decrease slightly the rate of deflection and to reduce the amplitude of the oscillations produced by the gust.
" }, { "name": "Stewart, Homer Joseph", "degree": "PhD", "year": "1940", "title": "The Effect of Shear Instability on the Transverse Circulation in the Atmosphere", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-084939", "creators": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-Homer-Joseph", "display_name": "Stewart, Homer Joseph" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1FW3-YN51", "abstract": "In this paper it is shown that the shear fields on either side of the westerlies are dynamically unstable and will roll up to form discrete eddies. A study of the stable vortex systems into which these eddies might collect shows that a \"vortex street\" is stable for a certain range of the ratio of width to vortex spacing. It is also shown that a formation with vortices placed on the corners of a regular polygon is stable if the number of vortices is less than seven. This still holds if the effect of the shear field north of the westerlies is stimulated by a fixed polar cyclone. It further appears that with a strong general circulation, i.e. strong westerlies, only two or three high pressure cells should be found while the numbers, up to six, should be found with weaker circulations. This conclusion is verified by Northern Hemisphere mean pressure charts." }, { "name": "Ashkenas, Irving Louis", "degree": "Masters", "year": "1939", "title": "Wind Tunnel Model Tests to Investigate the Effects of Boundary Layer Control", "advisor": "Millikan, Clark Blanchard; Sears, William Rees", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-104409", "creators": [ { "name": { "family": "Ashkenas", "given": "Irving Louis" }, "id": "Ashkenas-Irving-Louis", "display_name": "Ashkenas, Irving Louis" }, { "name": { "family": "Smith", "given": "Robert Beaton" }, "id": "Smith-Robert-Beaton", "display_name": "Smith, Robert Beaton" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-W-R", "role": "advisor", "display_name": "Sears, William Rees" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FE14-GP68", "abstract": "This thesis presents a study of the results obtained with the Boundary Layer Removal Model of the Guggenheim Aeronautics Laboratory, California Institute of Technology (GALCIT). It is a continuation of work begun here some time past and, as such, contains very little in the way of historical review, the origin of the project, preliminary studies of the problem and experimental technique being contained in previous reports.
\r\n\r\nThe attempt, in this series of tests, to find a definite scale effect on the power required to produce a given change in airfoil characteristics has been somewhat unsuccessful because the test Reynolds Numbers unfortunately fell in the region of critical Reynolds Number. There has, however, been some success in finding the definite mechanism by which boundary layer removal is effective, a logical explanation being given for the nature and magnitude of various changes in airfoil characteristics incurred by the use of a given amount of suction.
" }, { "name": "Atsumi, John Shoichi", "degree": "PhD", "year": "1939", "title": "Correlation and Decay of Turbulence Produced by Various Grids in a Wind Tunnel", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092024-180737116", "creators": [ { "name": { "family": "Atsumi", "given": "John Shoichi" }, "id": "Atsumi- John-Shoichi", "display_name": "Atsumi, John Shoichi" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yq2d-wt47", "abstract": "No abstract." }, { "name": "Beardsley, George Francis", "degree": "Masters", "year": "1939", "title": "A Study of the Effect of Repeated Tension Impact Loads Upon Certain Metals Used in Aircraft Construction", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102006-132339", "creators": [ { "name": { "family": "Beardsley", "given": "George Francis" }, "id": "Beardsley-George-Francis", "display_name": "Beardsley, George Francis" }, { "name": { "family": "Coates", "given": "Leonidas Dixon" }, "id": "Coates-Leonidas-Dixon", "display_name": "Coates, Leonidas Dixon" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R4GM-7G81", "abstract": "A test method is developed for evaluating the Impact Endurance Limit of a material. The Impact Endurance Limit is defined as the energy per blow in tensile impact loading below which the specimen will withstand an indefinitely large number of blows without rupture, and this value is given for ALCOA 24ST and 14ST, with and across the grain, and Dowmetals X and Z-1 with the grain. Evidence is presented that this value probably does not depend directly either on the energy absorbed in breaking in one blow or on the brittleness of the material.\r\n\r\nThe ability to absorb energy in failure under static loading is shown to decrease nearly linearly with dynamic strain, while the ability to carry design static load is not adversely affected by any amount of dynamic strain short of failure.\r\n\r\nSome shortcomings of the present test methods are pointed out and a new machine is briefly described which will be used in further investigation of repeated tension impact.\r\n\r\nCo-author: L.D. Coates" }, { "name": "Fan, Hsu-Tsi", "degree": "Masters", "year": "1939", "title": "A Study of \"Shear Lag\" Phenomenon in a Stiffened Flat Panel by Photoelastic Methods", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-161537", "creators": [ { "name": { "family": "Fan", "given": "Hsu-Tsi" }, "id": "Fan-Hsu-Tsi", "display_name": "Fan, Hsu-Tsi" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WANC-TP12", "abstract": "In the construction of modern metal airplanes there are many locations where a more or less concentrated load is transferred to a large area of material. Therefore the design-engineer is frequently confronted with the problem of \u201cshear lag.\u201d This problem can be treated in a few simple cases by the mathematical theory of elasticity, especially by Airy\u2019s stress functions, but in many other cases, in order to avoid mathematical complexities, certain assumptions must be made which will simplify the analytical solution of the problem. These assumptions usually do not agree with the actual conditions therefore the results are not adequate. By the photoelastic method, however, the results obtained by the mathematical theory can be checked. It is the purpose of this experiment to check the results which have been obtained by the theoretical investigation for a few simple cases." }, { "name": "Howland, Walter Lavern", "degree": "PhD", "year": "1939", "title": "Strength of Thin-Walled Elliptical Cylinders Supported at the Minor Axis", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin; Millikan, Clark Blanchard; Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012015-161848918", "creators": [ { "name": { "family": "Howland", "given": "Walter Lavern" }, "id": "Howland-Walter-Lavern", "display_name": "Howland, Walter Lavern" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KQK7-V396", "abstract": "In this investigation it was found that the\r\ninstability failure of curved sheet is nearly\r\nindependent of the type of loading and is primarily\r\na function of the maximum stress, radius-thickness\r\nration and modulus of elasticity. A method of\r\ncorrelating the critical stress of thin sheet\r\nunder several different types of loading is given.\r\nAn explanation for the experimental critical stress\r\nof thin walled cylinders under bending being\r\ngreater than that for pure compression is given.\r\nThe strength of unstiffened thin walled circular\r\nnose sections under pure bending was found to be \r\ncontrolled by local instability of the section,\r\nrather than a large scale instability. The equation\r\nof local instability of curved sheet gives values\r\nwhich are in fair agreement with those found experimentally.
\r\n\r\nThe strength of elliptical cylinders supported\r\nat the minor axis under bending plus shear loads is\r\ngoverned primarily by the bending strength, and is\r\nlittle effected by the sheer force unless the amount\r\nof shear is quite large with respect to the moment.\r\nThe effect of increasing the amount of elliptically\r\ngreatly reduces the bending and shear strength of nose\r\nsections. Under torsional loads the stress at\r\nbuckling falls off as the ration of the major to minor \r\naxis increases but the failure stress decreases\r\nat a slower rate than the buckling stress. The\r\nlength effect of semi-circular sections under torsion\r\nis similar to that of a circular tube, and can be\r\nobtained by Donnell's theoretical equation.
\r\n" }, { "name": "Jackson, Andrew McBurney", "degree": "Masters", "year": "1939", "title": "An Investigation of Forced Flexural Torsional Oscillations of a Wing and the Phenomenon of Flutter", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252005-082813", "creators": [ { "name": { "family": "Jackson", "given": "Andrew McBurney" }, "id": "Jackson-Andrew-McBurney", "display_name": "Jackson, Andrew McBurney" }, { "name": { "family": "Parish", "given": "Elliott Walter" }, "id": "Parish-Elliott-Walter", "display_name": "Parish, Elliott Walter" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V7TP-Q228", "abstract": "In this thesis the torsional-flexural response of a two-dimensional airfoil to forced oscillations of various frequencies and at various airspeeds is investigated. The airfoil chosen has characteristics which are typical of modern American transport wings, and the speeds cover the range from zero airspeed up through the speeds for torsional-flexural flutter and torsional divergence.
\r\n\r\nIn the latter part of this thesis, curves are plotted showing the effects which changes in the assumed wing parameters have on the torsional-flexural flutter speed and the torsional divergence speed.
" }, { "name": "Kanemitsu, Sunao", "degree": "Masters", "year": "1939", "title": "Axial Compression Test of Thin Circular Cylinders. A. Length Effect. B. Visual Study of Buckling", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-105325", "creators": [ { "name": { "family": "Kanemitsu", "given": "Sunao" }, "id": "Kanemitsu-Sunao", "display_name": "Kanemitsu, Sunao" }, { "name": { "family": "Nojima", "given": "Noble M." }, "id": "Nojima-Noble-M", "display_name": "Nojima, Noble M." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HBZ9-MZ48", "abstract": "A: This portion of the report contains results obtained from compression tests on 95 thin-walled steel circular cylinder. The tested cylinders were mainly of very small L/R ratio and large R/t ratio.
\r\n\r\nThe results are compared with the existing theoretical failing stresses and are also presented in a non dimensional form, \u03b4/E. The failure stress is best given by the equation \u03b4/E = 9(t/R)1.6 + .16(T/L)1.3. This equation shall be limited for use for L/R greater than 0.1 and for L/R greater than 1.5 assume L/R = 1.5.
\r\n\r\nB: A visual study of buckle formation is presented to aid future research which may be done on compression of thin cylinders.
" }, { "name": "Knoblock, Frederick Delbridge", "degree": "PhD", "year": "1939", "title": "Investigations on the Applications of the Hot Wire Anemometer for Turbulence Measurements", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252008-094935", "creators": [ { "name": { "family": "Knoblock", "given": "Frederick Delbridge" }, "id": "Knoblock-Frederick-Delbridge", "display_name": "Knoblock, Frederick Delbridge" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DKG6-T043", "abstract": "The principle reasons for using the hot wire type of anemometer for turbulence measurements are outlined and some of the objectionable features limiting the applicability of the conventional type anemometer are pointed out. A brief historical background of the hot wire anemometer is followed by a consideration of various possibilities of improving the method of measuring the intensity of turbulence. This analysis purposes to show why such improvements can only be realized by a direct calibration of the hot wire\u2019s response to velocity fluctuations.\r\n\r\nThe consequent development of a new technique, referred to as the \u201cVibrator Method,\u201d is then explained. A general discussion of the results of a series of investigations using the Vibrator method is then presented and includes: a comparison with the orthodox method; the response of the hot wire to periodic fluctuations relative to the validity of the theory of hot wire lag; an extension of the method to correlation measurements using two hot wires, and other applications.\r\n\r\nThe paper concludes with a detailed description of various hot wire anemometer equipment which has been developed for use with the Vibrator method of measuring turbulence intensity.\r\n" }, { "name": "Lombard, Albert Eaton", "degree": "PhD", "year": "1939", "title": "An Investigation of the Conditions for the Occurrence of Flutter in Aircraft and the Development of Criteria for the Prediction and Elimination of Such Flutter", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-07182007-091133", "creators": [ { "name": { "family": "Lombard", "given": "Albert Eaton" }, "id": "Lombard-Albert-Eaton", "display_name": "Lombard, Albert Eaton" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/80H8-TB52", "abstract": "A review is presented of the work done by other investigators on the effects of inertia couplings in producing flutter in control surfaces that are not mass balanced. The conclusion is reached that for the prevention of such flutter complete dynamic balance should always maintain.\r\n\r\nFlexural-torsional flutter is investigated in considerable detail from the consideration of the dynamical equations for steady state forced oscillations of the two dimensional case. A complete set of response curves for two typical cases are included to show the types of responses that should be observed in flight with vibration pick-up equipment. The important fact is brought out that the response and behavior of the wing at its natural bending frequency has little or no correlation with the behavior of the wing at the stability limit of flutter. Curves are presented to show that, for normal airplanes, the most important parameters which determine flutter in this mode are (a) the position of the inertia axis, (b) the torsional frequency, end (c) the radius of gyration of the wing mass about the inertia axis.\r\n\r\nThe dynamical equations are set up for the cases of flexural-aileron, torsional-aileron, and flexural-torsional-aileron flutter in the two-dimensional case and an example is given of the determination of the stability limit of a specific example of the first of these modes.\r\n\r\nAn extension of the two-dimensional case to the three-dimensional case is presented with particular reference to determining the flexural-torsional flutter speed of a tail surface with vertical surfaces on the tips of the horizontals. The method of attack is outlined for the calculation of natural frequencies at zero airspeed to use in determining the flutter speed.\r\n\r\nStatistical data in a graphical form show the variations of natural frequencies of the various components of airplanes with the size of such airplanes.\r\n\r\nThe conclusion is reached that the speed of airplanes should be restricted to two-thirds of the critical speed for any mode of flutter, divergence, or aileron reversal." }, { "name": "Piper, Clark Neil", "degree": "Masters", "year": "1939", "title": "Experimental Investigation of the Profile Drag and Boundary Layer of a Wing Section During Free Flight and in the Wind Tunnel", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-142449", "creators": [ { "name": { "family": "Piper", "given": "Clark Neil" }, "id": "Piper-Clark-Neil", "display_name": "Piper, Clark Neil" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DSRZ-HZ95", "abstract": "A general report covering the method used in obtaining flight test and wind tunnel data for the investigation of profile drag and the thickness of the boundary layer with its transition point is presented, together with some of the results and conclusions reached.\r\n\r\nMethods of data reduction with the difficulties encountered are given. After final results of the profile drag for flight test are obtained, they are compared with T. N. 695.\r\n\r\nA detailed description of the apparatus with the technique used for both the flight tests and the wind tunnel is also presented.\r\n" }, { "name": "Schairer, Robert Sorg", "degree": "PhD", "year": "1939", "title": "Unsymmetrical Lift Distributions on a Stalled Monoplane Wing", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-110200", "creators": [ { "name": { "family": "Schairer", "given": "Robert Sorg" }, "id": "Schairer-Robert-Sorg", "display_name": "Schairer, Robert Sorg" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3WX9-JZ33", "abstract": "The purpose of the research was to find if it is possible to have an unsymmetrical span load distribution on a monoplane wing at the stall without a rolling velocity. The investigation is based upon the Prandtl first order wing theory. It is shown that it is possible to have an unsymmetrical lift distribution at the stall if a certain shape is assumed for the curve of section lift coefficient vs. effective angle of attack. Two methods of determining such a solution for any particular wing shape are discussed. Curves are presented showing unsymmetrical solutions for a number of different wing shapes and also showing the resulting lift and rolling moment coefficients. The important conclusions are as follows:\r\n\r\n1. An unsymmetrical lift distribution across the span of a monoplane wing at the stall is possible.\r\n\r\n2. The unsymmetrical solution produces a rolling moment of the same order of magnitude as that caused by a fully deflected aileron.\r\n\r\n3. The unsymmetrical distribution can occur only in a very small range of angles of attack after the wing begins to stall.\r\n\r\n4. The magnitude of the maximum rolling moment coefficient and the difference between the angle of attack at which the maximum rolling moment occurs and the angle of attack for first stall are nearly the same for all of the wing shapes investigated." }, { "name": "Tsien, Hsue Shen", "degree": "PhD", "year": "1939", "title": "Problems in Motion of Compressible Fluids and Reaction Propulsion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-105646", "creators": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-Hsue-Shen", "display_name": "Tsien, Hsue Shen" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2698-R671", "abstract": "none" }, { "name": "Tsubota, George Yoshio", "degree": "Masters", "year": "1939", "title": "Experimental Investigation of Ultimate Loads Carried by Flat, Unstiffened Panels Under Combined Shear and Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-104133", "creators": [ { "name": { "family": "Tsubota", "given": "George Yoshio" }, "id": "Tsubota-George-Yoshio", "display_name": "Tsubota, George Yoshio" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZDZH-Y940", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe problem of the behavior of flat, unstiffened panels under combined shear and compression load was investigated for one length over width ratio and three thicknesses. Due to the lack of data obtained in a limited amount of time, no definite conclusion was reached. Until further investigation is carried out, the ultimate failure stress relationship of [...] is recommended. The effect of shear load on the modulus of elasticity and compression load on the shear modulus was found to be nonexistent.\r\n" }, { "name": "Wang, Tsun-Kuei", "degree": "Masters", "year": "1939", "title": "A Theoretical Investigation of the Distribution of Maximum Shearing Stresses in a Stiffened Flat Panel", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04142008-083306", "creators": [ { "name": { "family": "Wang", "given": "Tsun-Kuei" }, "id": "Wang-Tsun-Kuei", "display_name": "Wang, Tsun-Kuei" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A1JY-DH94", "abstract": "No abstract submitted.\r\n" }, { "name": "Baker, Ralph Doris", "degree": "PhD", "year": "1938", "title": "The Effect of Surface Roughness on Skin Friction and Turbulence in Two Dimensional Flow", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092006-154408", "creators": [ { "name": { "family": "Baker", "given": "Ralph Doris" }, "id": "Baker-Ralph-Doris", "display_name": "Baker, Ralph Doris" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6BXC-TP03", "abstract": "This investigation is divided into two parts. Part I deals with the effect of roughness and pressure drop and skin friction, and Part II covers the effect of surface roughness and the turbulent velocity fluctuations, and the correlation between these fluctuations in the direction of the mean flow and those normal to the channel walls.
\r\n\r\nThe roughness for both investigations was the same, and consisted of corrugated paper glued to the inside walls of a channel of 4.9 cm. wide by 85 cm. (inside dimensions). The roughness was changed by removing every other one of the corrugations, as illustrated in Fig. 6.
\r\n\r\nPressure and velocity distribution measurements were made at various stations and the results compared to Karman\u2019s equation, u/v* = Ar + B log y/k for rough walls, where u is the velocity in the channel, v* is the friction velocity = \u221a\u03c4o/\u2113, y = distance from wall, \u03c5 = the kinematic viscosity, k = the roughness height.
\r\n\r\nKarman\u2019s analysis showed B to be a universal constant independent of the wall roughness. Some investigators have given slightly different values to this constant. Their results were carried out in pipes or channels of near square cross section. These results appear to fall within 3% of those of Nikuradse as far as the value of B is concerned. However, a value of B a little less than 5.75 would fit the points better.
\r\n\r\nThese experiments were undertaken to add some information to this subject with flow in deep narrow channels and with other types of rough surfaces which had not been investigated.
\r\n\r\nThe turbulence measurements were determined with a hot-wire anemometer using a vibrating wire to calibrate it with. These results show that the correlation coefficient u'v'/(u')2 increases with speed for smooth walls and varies materially with the type of roughness with no definite systematic trend as to this change.
" }, { "name": "Bell, Willard Newton", "degree": "Masters", "year": "1938", "title": "A Photoelastic Investigation of the Distribution of Shearing Stresses in a Stiffened Flat Panel", "advisor": "Sechler, Ernest Edwin; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102006-131047", "creators": [ { "name": { "family": "Bell", "given": "Willard Newton" }, "id": "Bell-Willard-Newton", "display_name": "Bell, Willard Newton" }, { "name": { "family": "Bussey", "given": "John Kenneth" }, "id": "Bussey-John-Kenneth", "display_name": "Bussey, John Kenneth" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9JFS-SF60", "abstract": "No abstract.\r\n" }, { "name": "Berler, Irving", "degree": "Masters", "year": "1938", "title": "The Elastic Properties of 17ST Aluminum Alloy Tubing Including the Effects of Prestressing", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:02272025-192811948", "creators": [ { "name": { "family": "Berler", "given": "Irving" }, "id": "Berler-Irving", "display_name": "Berler, Irving" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/cz5j-jz92", "abstract": "No abstract." }, { "name": "Bowen, William Harold", "degree": "Masters", "year": "1938", "title": "Tests of Axial Flow Fans Designed by Lattice Theory", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122007-144119", "creators": [ { "name": { "family": "Bowen", "given": "William Harold" }, "id": "Bowen-William-Harold", "display_name": "Bowen, William Harold" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M6E1-0T44", "abstract": "This paper presents the tests and calibrations which were made on three axial flow fan units of the G.A.L.C.I.T. Boundary Layer Removal Model in order that operating parameters might be developed from the data. The tests serve also as a check on the success achieved in the design of fans using the Lattice Theory. (cf. Theoretical Aerodynamics Lecture Notes of Dr. Clark B. Millikan).\r\n" }, { "name": "Butterworth, Wesley Theodore", "degree": "Masters", "year": "1938", "title": "Experimental Investigation of Ultimate Loads Carried by Flat, Unstiffened Panels Under Combined Shear and Compression", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-095455", "creators": [ { "name": { "family": "Butterworth", "given": "Wesley Theodore" }, "id": "Butterworth-Wesley-Theodore", "display_name": "Butterworth, Wesley Theodore" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C57T-2C92", "abstract": "Four series of tests were made on flat, unstiffened panels under combined shear and compression loading for two thicknesses and two length over width ratios. In each case, the panels were carried to their ultimate loads. An empirical relation was developed for the variation of shear and compressive stresses of the form: (Pc/Pco) + (Ps/Pso)4 = 1,
\r\nwhere:
\r\nPco = failure stress, pure compression,
\r\nPso = failure stress, pure shear.
\r\nThe above equation was found to hold for the entire range of thicknesses and length over width ratios investigated.
Discrepancies in the boundary layer profiles of NACA T.N. 613, * and recent work done at Cambridge University, England, on the effect of inclination on transition required the reinvestigation of the effect of curvature on boundary layer transition using a more fundamentally sound experimental technique than previously. This technique consisted in comparing velocity profiles taken at different speeds at each measuring station with the universal Blasius laminar profile; a further indication of transition was obtained by measuring the local shear coefficient with a small total head tube pressed against the surface. Agreement between the two methods was complete in all but one case. The effect of inclination was investigated by rotating the working section of the tunnel as a whole around a fixed pivot. Unfavorable inclination produced a decrease in transition Reynolds number on either side of the sheet but a neutral region was found to exist in which inclination had no effect on the transition and in which the effect of curvature alone acted. The effect of the curvature could be expressed as a function of the single variable 1000\u03b4m/rc. As to the exact nature of the (R\u03b4m)T vs 1000\u03b4m/rc curve, little as yet can be said since a sufficient range of 1000\u03b4m/rc has not been investigated as yet. The results of T.N. 613 were thus validated qualitatively but the values of transition given there were found to be too large.
\r\n\r\n* National Advisory Committee for Aeronautics Technical Note.
\r\n" }, { "name": "Dunn, Louis Gerhardus", "degree": "Masters", "year": "1938", "title": "An Experimental Investigation of the Stresses in Extruded Sections Commonly Used in Aircraft Construction", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-06242004-092300", "creators": [ { "name": { "family": "Dunn", "given": "Louis Gerhardus" }, "id": "Dunn-Louis-Gerhardus", "display_name": "Dunn, Louis Gerhardus" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9FAV-3513", "abstract": "The extensive use of reinforced duralumin sheet in aircraft construction makes it desirable to know the behaviour of such structures under load. This paper deals principally with the experimental results obtained by testing a large number of reinforced panels of various lengths under direct compression.
\r\n\r\nThe main purpose of the investigation was to determine the ultimate stresses in the reinforcing members, which in this case were bulb-angles of a size commonly used in aircraft constrution. It was, however, felt that it would be desirable to obtain as much information from the tests as possible. Consequesntly the stresses in the bulb-angles were measured at intermediate loads for a number of panels. From this data it was possible to determine that portion of the total load carried by either the skin or the bulb-angles throughout the entire range of load.
\r\n" }, { "name": "Dykes, John Christopher", "degree": "Masters", "year": "1938", "title": "Stability Derivatives of Helicopter Rotors", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-10282005-161504", "creators": [ { "name": { "family": "Dykes", "given": "John Christopher" }, "id": "Dykes-John-Christopher", "display_name": "Dykes, John Christopher" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N0GE-EA65", "abstract": "At present there are only three published papers dealing with the stability of helicopters, all based on helicopters with rigid rotors. Since all rotors are, in practice, constructed with the blades free to \"flap\", these analyses are not sufficiently general.
\r\n\r\nBelow, the blade motion equation has been written in terms of small incremental accelerations and velocities; for which an approximate solution is obtained. This is then used to calculate the actual forces and moments that are produced on the rotor; by taking suitable mean values, it has been found possible to express these forces and moments without reference to the actual position of the blades at that instant, but only as functions of the position of the whole helicopter. The aerodynamic mechanism of the rotor has therefore been expressed in a a series of equations, and the stability of the helicopter now becomes solely a dynamical problem.
\r\n\r\nIt appears that a helicopter is most likely to become unstable when hovering; this analysis is confined to this case.
\r\n\r\nCalculated values for a helicopter of the same size as the \"C.30\" autogyro, are given to show the dimensions of the various forces and moments.
" }, { "name": "Mechling, Wallace Bristol", "degree": "Masters", "year": "1938", "title": "An Evaluation of the Tension Impact Test by Correlation With the Physical Properties of Aluminum Alloys", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07192007-104706", "creators": [ { "name": { "family": "Mechling", "given": "Wallace Bristol" }, "id": "Mechling-Wallace-Bristol", "display_name": "Mechling, Wallace Bristol" }, { "name": { "family": "Jack", "given": "Samuel Sloan" }, "id": "Jack-Samuel-Sloan", "display_name": "Jack, Samuel Sloan" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "co-advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7XWB-QP81", "abstract": "No abstract.\r\n\r\n" }, { "name": "Mellinger, George Rolland", "degree": "Masters", "year": "1938", "title": "Shear Transfer of Load From Main Beams to Intermediate Corrugations in Metal Sheet Covered Box Beams", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262006-140318", "creators": [ { "name": { "family": "Mellinger", "given": "George Rolland" }, "id": "Mellinger-George-Rolland", "display_name": "Mellinger, George Rolland" }, { "name": { "family": "Kurihara", "given": "Hisayuki" }, "id": "Kurihara-Hisayuki", "display_name": "Kurihara, Hisayuki" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5751-Y722", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA program of experimental investigation for three combinations of sheet reinforced with corrugations has been carried out.
\r\n\r\nAn assumption has been made for the transverse neutral axis of such a system.
\r\n\r\nFor an open section box beam, the conventional assumption of the neutral axis on the center of gravity plane indicates an error.
\r\n\r\nAn attempt has been made to calculate the compressive stress in each corrugation due to shear transfer of load.
\r\n\r\nAn effective shear modulus for each corrugation and its share of the skin under bending loads has been found by experimental methods.
\r\n\r\nFor the combinations tested, it was found that the effective shear modulus, G/E, decreases with increasing \u03c4, which corresponds to increasing G/E with distance from the free end of the panel.
\r\n\r\nPanel curvature was found to have a marked effect on G/E, in that the curved panel had a larger value of G/E for the same \u03c4.
\r\n\r\nContour maps of \u03c4, the shearing stress, have been constructed for the three panels.
" }, { "name": "Putt, Donald Leander", "degree": "Masters", "year": "1938", "title": "Experimental Investigation of the Thickness of the Boundary Layer and the Location of the Transitional Region Along a Wing Section", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-152711", "creators": [ { "name": { "family": "Putt", "given": "Donald Leander" }, "id": "Putt-Donald-Leander", "display_name": "Putt, Donald Leander" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "member", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZZVX-7082", "abstract": "A general review of the investigation of the thickness of the boundary layer and the location of the transition point on an airplane wing in free flight that have been published to date is presented, along with some of the conclusions that have been reached from the results of the investigations.
\r\n\r\nThe development and design of apparatus for the experimental determination of the thickness of the boundary layer, and the location of the point of transition from laminar to turbulent flow in the boundary layer which can be readily attached to the surface of a metal airplane wing is described.
\r\n\r\nAlso the method and technique developed for recording the data and the interpretation of the test results are described in detail.
" }, { "name": "Scoles, Albert Buddy", "degree": "Masters", "year": "1938", "title": "Range Calculations for Airplanes With Continuously Controllable Pitch Propellers, and the Effect of Certain Geometric Parameters of the Airplane on Range", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082006-090132", "creators": [ { "name": { "family": "Scoles", "given": "Albert Buddy" }, "id": "Scoles-Albert-Buddy", "display_name": "Scoles, Albert Buddy" }, { "name": { "family": "Schoech", "given": "William Alton" }, "id": "Schoech-William Alton", "display_name": "Schoech, William Alton" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CMHQ-E314", "abstract": "This investigation was undertaken to develop a satisfactorily exact method for the calculation of range of airplane; and with such method, to determine the effect of certain geometrical parameters of the airplane on range, namely, span, aspect ratio, and wing loading.
\r\n\r\nWith satisfactory aerodynamic data from wind tunnel reports, and with satisfactory engine performance data from test stand reports, the method developed permits determination of range, optimum speeds to use, and optimum propeller rpm to use for each speed. It further permits determination of endurance.
\r\n\r\nIn general, increasing aspect ratio for constant span will increase maximum range if reasonable upper limits are placed on wing loading. The gain is but slight for aspect ratios in excess of 11. Similarly, decreasing span for constant aspect ratio will increase maximum range. Both of these variations results in increased wing loading, which can therefore be considered as the fundamental factor giving the increase. There will in general be an optimum combination of aspect ratio and span for a given wing loading which will give maximum range. Satisfactory takeoff and sea-level rate of climb will limit the wing loading; however, for wing loadings in excess of 50, the maximum gain obtainable is of the order of 5%.
\r\n" }, { "name": "Sears, William Rees", "degree": "PhD", "year": "1938", "title": "A Systematic Presentation of the Theory of Thin Airfoils in Non-Uniform Motion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252004-134954", "creators": [ { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-William-Rees", "display_name": "Sears, William Rees" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EM5X-CZ66", "abstract": "The basic conceptions of the circulation theory of airfoils are reviewed briefly, and the mechanism by which a \"wake\" of vorticity is produced by an airfoil in non-uniform motion is pointed out. After a calculation of the induction effects of a wake vortex, it is shown how the lift and moment acting upon an airfoil in the two-dimensional case may be calculated directly from simple physical considerations of momentum and moment of momentum. Formulae for the lift and moment are then obtained which are applicable to all cases of motion of a two-dimensional thin airfoil in which the wake produced is approximately flat; i.e., in which the movement of the airfoil normal to its mean path is small.
\r\n\t\r\nThe general results are applied first to the case of an oscillating airfoil, and vector diagrams giving the magnitudes and phase angles of the lift and moment are obtained. The results of a sudden change of angle of attack are then determined, and a general method for handling transient cases is set up. This method is applied to the calculation of the lift and moment acting on an airfoil entering sharp-edged and graded gusts. The case of a series of sinusoidal gusts is also considered.
\r\n\t\r\nA method of calculating the distribution of forces over the airfoil chord is then shown, and it is applied to the steady-state oscillation. The paper concludes with a discussion of the applicability of certain results to the explanation of observed phenomena beyond the stall.
\r\n" }, { "name": "Smith, Apollo Milton Olin", "degree": "Masters", "year": "1938", "title": "A Preliminary Study of the Problem of Boundary Layer Control", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052007-091749", "creators": [ { "name": { "family": "Smith", "given": "Apollo Milton Olin" }, "id": "Smith-Apollo-Milton-Olin", "display_name": "Smith, Apollo Milton Olin" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/STNT-3N37", "abstract": "This thesis presents a study of the problem of securing high lifts by means of boundary layer removal, together with first results of tests on the Boundary Layer Model of the Guggenheim Aeronautics Laboratory, California Institute of Technology (hereinafter called GALCIT). It is divided into two parts: first, a review and discussion of previous work, and second, presentation and development of methods used for carrying out tests upon the GALCIT model, together with experimental results obtained from the tests upon the model.
\r\n\r\nPrevious researches show that boundary layer removal is indeed successful in securing high lift coefficients. Study reveals also that results from one experiment may differ greatly from those of another. Consequently, previous work is of little help in predicting results to be obtained for a design different from the model tested.
\r\n\r\nResults on the GALCIT model have not been favorable, but it is believed that flow tests have found the difficulty. Consequently, the experimental work has value only for the light it sheds upon the future course of this research at the Institute.
\r\n\r\n\r\n" }, { "name": "Allardt, Frederick Hamilton", "degree": "Masters", "year": "1937", "title": "The Brinelling of Small Ball Bearings", "advisor": "Klein, Arthur Louis; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-103946", "creators": [ { "name": { "family": "Allardt", "given": "Frederick Hamilton" }, "id": "Allardt-Frederick-Hamilton", "display_name": "Allardt, Frederick Hamilton" } ], "advisors": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K872-W635", "abstract": "The brinelling of ball bearings is a subject which has had comparatively little study. Since ball bearings have found most of their applications in such things as rotating shafts, there has been little reason to study their action under static loading conditions. This research was suggested by the Fafnir Ball Bearing Company because of the increasing use of ball bearings for static loads in aircraft. In the aircraft business, the designers, because of strict weight requirements, have used ball bearings up to their rated loads. Not infrequently these bearings brinelled. (A brinelled bearing is one in which a dent has been formed in one of the races by a ball). It is therefore evident that more should be known about the brinelling of bearings." }, { "name": "Clauser, Francis Hettinger", "degree": "PhD", "year": "1937", "title": "New Methods of Solving the Equations for the Flow of a Compressible Fluid", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-175229", "creators": [ { "name": { "family": "Clauser", "given": "Francis Hettinger" }, "id": "Clauser-Francis-Hettinger", "display_name": "Clauser, Francis Hettinger" }, { "name": { "family": "Clauser", "given": "Milton Ure" }, "id": "Clauser-Milton-Ure", "display_name": "Clauser, Milton Ure" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZAWH-VK93", "abstract": "The usual equations for the flow of a compressible fluid are non-linear in character and difficult to solve. It has been found that if the components of velocity are taken as independent variables, the resulting equations are linear. These equations are developed and new forms introduced.
\r\n\r\nA new function, \u0393 is introduced and a method advanced for effecting the transformation from the plane where the velocity components are coordinates, to the physical plane where x and y are coordinates.
\r\n\r\nA new way of finding plausible solutions to investigate is given and the case of flow in a corner is worked out in detail. The flow is found to have an anomalous behavior, the reason for which is explained. This solution is applied to the flow behind a curved shock wave.
" }, { "name": "Clauser, Milton Ure", "degree": "PhD", "year": "1937", "title": "The Effect of Curvature on the Transition from Laminar to the Turbulent Boundary Layer", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Robert Andrews", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-174320", "creators": [ { "name": { "family": "Clauser", "given": "Milton Ure" }, "id": "Clauser-Milton-Ure", "display_name": "Clauser, Milton Ure" }, { "name": { "family": "Clauser", "given": "Francis Hettinger" }, "id": "Clauser-Francis-Hettinger", "display_name": "Clauser, Francis Hettinger" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Robert Andrews" }, "id": "Millikan-R-A", "role": "advisor", "display_name": "Millikan, Robert Andrews" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E5EQ-DA15", "abstract": "In the flow over the upper surface of a wing, a discrepancy between the predicted and actual point of transition from laminar to turbulent boundary layer had been found. This effect may be due to the comparatively small radius of curvature of the upper surface of the wing. The present tests were undertaken to investigate this effect.
\r\n\r\nAs no available channel was suitable for this work, a new channel with two working sections was built. One working section had a wall with a twenty inch radius of curvature and the other section had a flat wall.
\r\n\r\nThree types of measurements were made: a. Traverses were made with a total head tube to determine the character of the boundary layer at various Reynolds numbers. b. The turbulence distribution in the boundary layer was investigated by means of a hot wire and a vacuum tube amplifier. c. A similar investigation of the mean velocity distribution in the boundary layer was made by means of a hot wire anemometer.
\r\n\r\nIt was found that by using an abbreviated form of the turbulence level traverses, critical Reynolds Numbers of the transitions could be established. These critical Reynolds are plotted as a function of x/r (x being the distance of the transition from the leading edge of the plate; r being radius of curvature of the plate) for both the convex and concave side of the plate.
" }, { "name": "Losey, Robert M.", "degree": "Masters", "year": "1937", "title": "A Theoretical Investigation of the Possibilities of Internal Cooling of Aircraft Engines by Water Injection to the Cylinder", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112008-132848", "creators": [ { "name": { "family": "Losey", "given": "Robert M." }, "id": "Losey-Robert-M", "display_name": "Losey, Robert M." } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3PXW-GF19", "abstract": "No abstract." }, { "name": "Miller, Shirley Snow", "degree": "Masters", "year": "1937", "title": "Wind Tunnel Tests on a Low-Wing Monoplane With Propeller Running", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122024-214212298", "creators": [ { "name": { "family": "Miller", "given": "Shirley Snow" }, "id": "Miller-Shirley-Snow", "display_name": "Miller, Shirley Snow" }, { "name": { "family": "Albach", "given": "Walter Henry" }, "id": "Albach-Walter-Henry", "display_name": "Albach, Walter Henry" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/y5vw-2z26", "abstract": "Various tests have been conducted on airplane wind tunnel models with an operating propeller in an endeavor to furnish the industry data as an aid in design and performance predictions. At the GALCIT, these investigations have comprised the material set forth in references 1, 2 and 4.
\r\n\r\nThe tests conducted by the authors of this paper represent a continuation of the above-mentioned investigations. The purpose of the present tests was to determine l) the effect of power on static longitudinal stability (elevator free); 2)\u00b7the effect of power on hinge moments (at various tab angles); and 3) the effect of power on static directional stability with the model operating at high and low angle of attack.
" }, { "name": "Moore, Charles Kenneth", "degree": "Masters", "year": "1937", "title": "Age Hardening of Heat Treated Aluminum Alloy. An Investigation of the Fluctuation of Hardness with Time of Ageing of Heat Treated Aluminum Alloy Sheet", "advisor": "Sechler, Ernest Edwin; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212005-103521", "creators": [ { "name": { "family": "Moore", "given": "Charles Kenneth" }, "id": "Moore-Charles-Kenneth", "display_name": "Moore, Charles Kenneth" }, { "name": { "family": "Nollan", "given": "John Lloyd" }, "id": "Nollan-John-Lloyd", "display_name": "Nollan, John Lloyd" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics", "mecheng" ], "doi": "10.7907/3G1Z-F889", "abstract": "The authors have found what they believe to be a tendency for a certain Aluminum Alloy, namely 24-SO, to fluctuate in strength, and hardness, during the process of age hardening, after heat treatment.
\r\n\r\nThis variation in hardness of the material, while the ageing process is going on, is accompanied by a change in ultimate strength, and in the stress-strain relationship of the material; and in general the condition of the alloy is indicated by the hardness number.
\r\n\r\nThe limited scope of this research does not indicate that this phenomenon of fluctuation of hardening is constant in occurrence; as the number of tests made were insufficient to determine the regularity, or irregularity, of this characteristic of the material.
\r\n\r\nAll of the metal tested became stable within the commonly accepted range of ultimate strength for this alloy.
\r\n\r\nFrom these few experiments it appears that although the hardness varies with time, the alloy, if allowed to age sufficiently, will develop its rated strength.
\r\n\r\nVarious reports have been made to the effect that sheet aluminum alloy, after being heat treated, quenched, and allowed to begin normal age hardening, did not respond to ageing as might be expected, nor did it follow the theoretical hardening curve with reasonable agreement. It was found that sheet material, although apparently properly heat treated, had not hardened, or acquired its full strength, when inspected by hardness testing methods.
\r\n\r\nFrom observations it was found that the same piece, which was observed to be soft, when allowed to age for a longer period and tested again for hardness, had in some cases come up to the required standard, and in others had exceeded the inspection limits.
\r\n\r\nTo the best of the authors knowledge no systematic investigation of this phenomenon has been undertaken, and as a preliminary quest in this field of research a periodic measurement of hardness, and tensile strength, was carried out to determine the actual manner in which the selected material would harden with time, and to correlate its indicated hardness with the strength of the piece at the time of measurement.
" }, { "name": "Smith, Joe Nelson", "degree": "Masters", "year": "1937", "title": "Investigation of Extended Bulb Angle Sections Under Compression: Part One. As Euler Columns ; Part Two. As Stiffeners Attached to Sheet", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252008-093950", "creators": [ { "name": { "family": "Smith", "given": "Joe Nelson" }, "id": "Smith-Joe-Nelson", "display_name": "Smith, Joe Nelson" }, { "name": { "family": "Murphy", "given": "Joseph Nathaniel" }, "id": "Murphy-Joseph Nathaniel", "display_name": "Murphy, Joseph Nathaniel" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R62Z-6P10", "abstract": "No abstract.\r\n" }, { "name": "Young, Bradley Hobart", "degree": "Masters", "year": "1937", "title": "A Two-Parameter Wind Tunnel Rigging System", "advisor": "Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242005-100937", "creators": [ { "name": { "family": "Young", "given": "Bradley Hobart" }, "id": "Young-Bradley-Hobart", "display_name": "Young, Bradley Hobart" } ], "advisors": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "chair", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Bowen", "given": "William H." }, "id": "Bowen-W-H", "role": "member", "display_name": "Bowen, William H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CVB4-7510", "abstract": "In January of 1935, definite steps were taken in a two part program to modernize the ten-foot wind tunnel of the Guggenheim Aeronautical Laboratory at the California Institute of Technology. Part one of the program was the design and construction of a new wind tunnel rigging system based on concepts originally laid down by Dr. A. L. Klein, Associate Professor at the same institution. Part two of the program, to be carried on intensively immediately after completion of part one, will be the development of an entirely new force measuring system to replace the present modified steelyard type balances.
\r\n\r\nIn this paper the general problem of wind tunnel testing and equipment will be briefly outlined with the bulk of the discussion then given over to the problems concerning the evolution and design of a specific wind tunnel rigging system. As the system is not yet complete in its final form obviously there can be no description of the project as a finished piece of work. Also, it has been thought inadvisable to present only the system as it exists at present, therefore all the various features or principles that have been considered will be discussed and reason for their discard or adoption made clear. The result should then be a guide or at least an aid to the completion of part one of the modernizing program
\r\n\r\nIn a latter section of the paper some of the desired features of the contemplated force measuring system will be set down in the hope that they may be a skeletal set of requirements for the second part of the modernizing program.
\r\n" }, { "name": "Bollay, William", "degree": "PhD", "year": "1936", "title": "A New Theory for Wings of Small Aspect Ratio", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112006-081734", "creators": [ { "name": { "family": "Bollay", "given": "William" }, "id": "Bollay-William", "display_name": "Bollay, William" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8BV2-QH84", "abstract": "Experiments on wings have shown that a very different kind of flow takes place for very small aspect ratios than for large aspect ratios. The lift curve continues up to about 45\u00b0 before stalling occurs. During this range it has a concave curvature upward rather than downward as the lifting line or lifting surface theories predict. No theoretical explanation of this effect has yet been given since it was generally supposed to be a stalling phenomenon and thus not adaptable to perfect fluid theories. The present paper shows that this curvature effect is due to the fact that the trailing vortices leave at an angle \u03b1 to the plate. For the limiting case of a plate with finite span and infinite chord it is shown that the bound vorticity and induced downwash are constant across the span, and the trailing vortices leave the wing at the half-angle of attack, \u03b1=\u03b8/2. These results are carried over into the assumptions for the analysis of the finite rectangular flat plate of very small aspect ratio. A surface distribution of vorticity over the plate is assumed, constant across the span, and varying according to the formula \u03b3 = \u03b30\u221at/2-x/t/2+x along the chord. Straight trailing vortices are assumed leaving the plate at an undetermined angle \u03b1. The boundary condition assumed is that the mean value of the induced velocity along the center line of the span is equal to the normal component of the free-stream velocity. This determines the constant \u03b30 and thus the normal force coefficient CN as a function of \u03b8. The parameter \u03b1 is still undetermined; however, its limits are given. For very small aspect ratios \u03b1=\u03b8/2, for large aspect ratios it approaches \u03b8. Winter\u2019s experiments on a wing of aspect ratio \u03ba=1/30 are checked very closely by this theory assuming \u03b1=\u03b8/2. At larger aspect ratios up to about \u03ba=1 the experimental curves lie between the theoretically predicted curves corresponding to \u03b1=\u03b8/2 and \u03b1=\u03b8, moving toward the latter limit at \u03ba=1." }, { "name": "Bolster, Calvin Mathews", "degree": "Masters", "year": "1936", "title": "Wind Tunnel Tests on the Effect of Power on the Stability of a Low Wing Monoplane with Three Vertical Positions of Horizontal Tail Surfaces", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102006-161025", "creators": [ { "name": { "family": "Bolster", "given": "Calvin Mathews" }, "id": "Bolster-Calvin-Mathews", "display_name": "Bolster, Calvin Mathews" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QRHQ-FP49", "abstract": "A great majority of present day airplanes are of the low wing cantilever type. An investigation into the effect of power and vertical location of the horizontal tail surfaces on the longitudinal static stability of such airplanes is therefore of interest.
\r\n\r\nThe present investigation was carried out on a one-sixth scale model of a low wing single engine tractor monoplane. The results are probably most directly applicable to airplanes of this type. However, the tendencies and general effects should also be fairly indicative of what may be expected in multiple engine low wing monoplanes of conventional design.
" }, { "name": "Childers, Milford Carlson", "degree": "Masters", "year": "1936", "title": "Stresses in Metal Beams with Flat Sheet Webs of Medium Thickness", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04242008-111115", "creators": [ { "name": { "family": "Childers", "given": "Milford Carlson" }, "id": "Childers-Milford-Carlson", "display_name": "Childers, Milford Carlson" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y3QT-J764", "abstract": "This paper develops a method by which the stresses in the component parts of a solid web beam may be computed when the dimensions of the web thickness, beam height, and distance between stiffeners are such that the web does not go into the wave state immediately upon applying a small load. The stress in the web itself is calculated by a consideration of the buckling load of the web. The load in the stiffeners and flanges is computed by assuming an effective width of sheet as acting with them. This effective width is obtained by a consideration of the buckling properties of thin sheet in shear.
\r\n\r\nThe results are in the same form as the familiar Wagner beam equations except that certain terms must be modified and corrections made. The results herein obtained are not to be considered as superseding the Wagner Equations as derived in Ref. I, but supplement them to take care of cases out of the range of the Wagner assumptions.
\r\n" }, { "name": "Colman, Philip Abbey", "degree": "Masters", "year": "1936", "title": "The Oscillating Vane-Type Fan", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-145903", "creators": [ { "name": { "family": "Colman", "given": "Philip Abbey" }, "id": "Colman-Philip-Abbey", "display_name": "Colman, Philip Abbey" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0TZ7-7Q11", "abstract": "The investigation herein described was undertaken to determine the performance characteristics of the oscillating vane-type fan. The fan was the invention of Mr. Van Dorn and Mr. Cornwell, primarily for use in circulating air in railroad refrigerator cars. In the present system of railroad refrigeration for the transportation of perishable foodstuffs, the refrigerator car is a heat insulated car, with bunkers at each end for the cakes of ice. When the car is loaded and the doors shut, cooling is obtained only due to the natural circulation of air in the car, caused by the difference in temperature between the ice in the bunker and the fruit. This circulation has not been found sufficient, in that there is a large temperature difference between the top and bottom fruit (see Appendix B) and the top half is too warm, often spoiling during transportation. Also, because of this, the car cannot be filled to its volumetric capacity. Therefore the requirements which led to the invention of this type of fan were as follows:
\r\n\r\n1. To provide a sufficient volume of air, against the resistance developed in passing through the fruit, to obtain the cooling characteristics required.
\r\n\r\n2. To provide a fan which would not require major changes in the structural design of the car, or lessen the amount of fruit which could be carried.
\r\n\r\n3. To provide a fan, simple in construction and installation, and in its drive mechanism from the car axle.
The oscillating vane-type fan met conditions 2 and 3 in that it could be situated in the four and one half inch space between the floor racks and the floor of the car, through which the air naturally circulated, and in that it could be driven by a simple wheel and crank drive directly off the axle. This thesis presents the results of the investigation of the first condition.
\r\n" }, { "name": "Dunn, Louis Gerhardus", "degree": "Bachelors", "year": "1936", "title": "Analysis of Circular and Non-Circular Rings with a Varying Distributed Load", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10312023-170752804", "creators": [ { "name": { "family": "Dunn", "given": "Louis Gerhardus" }, "id": "Dunn-Louis-Gerhardus", "display_name": "Dunn, Louis Gerhardus" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/h20d-b494", "abstract": "A rather extensive treatment of the stresses in fuselage main bulkheads is given in NACA Technical Report No. 509. The Least work equations developed in the report are for the most general case. The examples given are for concentrated loads, which are in balance, and applied. at various points on a circular bulkhead.
\r\n\r\nNow the shear loads which are transmitted by the skin and stiffeners to a main ring exist in the form of a distributed load which varies around the bulkhead.
\r\n\r\nThe purpose of\u00b7 this paper is to present an analysis pf a main bulkhead in which the wing reactions a.re balanced by a varying distributed load around the bulkhead. The shear distribution although not exact because of the interaction of skin and stiffeners, seems however, closer to the actual existing conditions than would be a case in which the shear loads are treated as concentrated loads.
\r\n\r\nTo somewhat simplify the energy equations the bending and torsional shears were treated separately, the work due to the shear and axial load deformations were also neglected. The error introduced is relatively small.
\r\n\r\nIn the particular airplane to which this solution was applied 80% of the fuselage cross section area consisted of skin and the remaining 20% consisted of stiffeners. Hence the shear transferred by the skin is of major importance.
\r\n\r\nThe case chosen as an illustrative example is an unsymmetrical condition since this is the most general case.
" }, { "name": "Fleming, Morton Klyne", "degree": "Masters", "year": "1936", "title": "Experimental Investigation of the Effect Of Power Upon the Static Longitudinal Stability of a Low Winged Monoplane and a Method for its Calculation", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04152008-085638", "creators": [ { "name": { "family": "Fleming", "given": "Morton Klyne" }, "id": "Fleming-Morton-Klyne", "display_name": "Fleming, Morton Klyne" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JKVP-P690", "abstract": "To obtain the change in the longitudinal moment of a low winged monoplane caused by the addition of the propulsive unit operating at various conditions of power.
\r\n\r\nTo construct possible working charts for use in calculating this change from power off wind tunnel tests of scale models.
\r\n" }, { "name": "Howland, Walter Lavern", "degree": "Masters", "year": "1936", "title": "Effect of Rivet Spacing on Stiffened Thin Sheet Under Compression", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07182007-093403", "creators": [ { "name": { "family": "Howland", "given": "Walter Lavern" }, "id": "Howland-Walter-Lavern", "display_name": "Howland, Walter Lavern" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KCDP-9732", "abstract": "This thesis discusses an experimental investigation of the stress distribution across a stiffened thin sheet panel under compression. The effect of bending stresses and curvature of the sheet on extensometer readings is also dealt with. An attempt is made to determine a rational design criteria for rivet spacing on stiffened thin sheet under compression. Design curves of rivet spacing against thickness are developed. The effect of changing the rivet spacing or size on the ultimate load of a compression panel is discussed in view of some experiments." }, { "name": "Lovett, Benjamin Barnes Compton", "degree": "Masters", "year": "1936", "title": "Transfer of Stress from Main Beams to Intermediate Stiffeners in Metal Sheet Covered Box Beams", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272006-091759", "creators": [ { "name": { "family": "Lovett", "given": "Benjamin Barnes Compton" }, "id": "Lovett-Benjamin-Barnes-Compton", "display_name": "Lovett, Benjamin Barnes Compton" }, { "name": { "family": "Rodee", "given": "Walter Fred" }, "id": "Rodee-Walter-Fred", "display_name": "Rodee, Walter Fred" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MAAF-MM48", "abstract": "The authors have obtained by experimental methods an effective sheer modulus for the sheet in a stiffened plane sheet beam combination under bending loads. For the combinations tested it was found that the modulus decreases rapidly under light loadings from the elastic value to some asymptotic value depending upon the sheet thickness. The thick sheet combination gave higher values of the effective shear modulus than the thin sheet." }, { "name": "Malina, Frank Joseph", "degree": "Masters", "year": "1936", "title": "Characteristics of Braked, Locked and Free-Wheeling Two- and Three-Bladed Propellers", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092007-153045", "creators": [ { "name": { "family": "Malina", "given": "Frank Joseph" }, "id": "Malina-Frank-Joseph", "display_name": "Malina, Frank Joseph" }, { "name": { "family": "Jenney", "given": "William W." }, "id": "Jenney-William-W", "display_name": "Jenney, William W." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HYXB-6T51", "abstract": "The use of multi-engined aircraft has introduced the problem of aircraft performance when one or more power units have either become unusable or voluntarily shut down during cruising flight. If the use of the engine is to be discontinued because of mechanical failure, the desirable procedure is obviously to stop it altogether, so as to prevent possible destruction to the engine. This can be accomplished by locking the propeller, by a free-wheeling arrangement, or by feathering a variable pitch propeller. If the use of the engine is to be discontinued merely to reduce fuel consumption, the propeller may be allowed to turn the engine, in which case the propeller is braked by a torque equal to the friction of the engine.
\r\n\r\nAnother recent development connected with braked propellers is the fact that the variable pitch propeller now offers the possibility of using the large increment in drag at low blade angles of braked and free-wheeling propellers for reduction in landing speed or landing run of clean, highly powered, multi-engined aircraft.
\r\n\r\nIt was the purpose of the present investigation to provide information not already made available by researches listed under the references at the end of this paper. Therefore the following thesis will be concerned chiefly with the three-bladed propeller and its effect on airplane characteristics, the two-bladed propeller being used principally for comparison purposes with other available data. The tests were performed at model scale, but their acceptance as applicable to full scale is supported by the favorable comparisons made in Reference 5.
\r\n\r\n" }, { "name": "Martin, Victor John", "degree": "Masters", "year": "1936", "title": "Airplane Takeoff Performance", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-03142005-145716", "creators": [ { "name": { "family": "Martin", "given": "Victor John" }, "id": "Martin-Victor-John", "display_name": "Martin, Victor John" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JQD0-EW36", "abstract": "In this paper a general equation for calculating the takeoff performance of landplanes is developed in terms of the usual airplane parameters.
\r\n\r\nThe analysis enables the ground effect, wind and atmospheric conditions, altitude, and the use of flaps to be taken into account. A simple and rapid method is presented for the determination of the best flap angle to be used for takeoff.
\r\n\r\nVariation in takeoff performance due to changes in any of the airplane or engine-propeller characteristics is readily determined through the introduction of a new takeoff acceleration parameter.
\r\n\r\nA method for calculating the propeller speed, engine power, and thrust variation for both fixed-pitch and constant-speed propellers is included, and a new significance is given to the thrust versus square of velocity curve for takeoff computations.
\r\n\r\nExamples are included to illustrate the use of the analysis in solving the various takeoff problems.
\r\n" }, { "name": "Whelan, Thomas Murray", "degree": "Masters", "year": "1936", "title": "The Calculated Flight Path of the U.S.S. Macon", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-112942", "creators": [ { "name": { "family": "Whelan", "given": "Thomas Murray" }, "id": "Whelan-Thomas-Murray", "display_name": "Whelan, Thomas Murray" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PC07-4F03", "abstract": "These calculations are concerned with the flight path of the Macon after the loss of the upper fin and the deflation of the three after gas cells. Taking into account the actual flight conditions, the question was raised whether the ship would rise to an altitude of 4800 feet. For at this altitude, which the record shows was actually reached, the ship had exceeded pressure height by about 2000'. In going over pressure height, the ship loses approximately 3% of her lift for every 1000 feet. Hence 4800 feet corresponds to a heaviness of nearly 11 tons. It was felt that if this additional heaviness could have been avoided, the ship might have been flown safely in spite of the loss of some 20 tons of lift from the three after cells. The calculations were undertaken to determine whether the aerodynamic and aerostatic forces alone were sufficient to force the ship up to 4800 feet or whether there were external forces acting, i. e. gust forces." }, { "name": "Kitsuda, Kaname", "degree": "Masters", "year": "1935", "title": "Investigation of Stress Distribution on Thin Metal Sheet With Holes", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112005-134957", "creators": [ { "name": { "family": "Kitsuda", "given": "Kaname" }, "id": "Kitsuda-Kaname", "display_name": "Kitsuda, Kaname" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/921K-MD80", "abstract": "This paper presents the investigation of the ultimate strength of a plate under shearing stresses when the plate contains lightening holes. The optimum arrangement of holes and the most desirable size of hole has also been investigated. Stress-strain curves have been made which show the points at which the plates reach the buckling point, the elastic limit, and the point of permanent deformation.\r\n" }, { "name": "Lipp, James Everett", "degree": "PhD", "year": "1935", "title": "Strength of Thin Walled Cylinders Subjected to Combined Compression and Torsion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192006-141156", "creators": [ { "name": { "family": "Lipp", "given": "James Everett" }, "id": "Lipp-James-Everett", "display_name": "Lipp, James Everett" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6Z0W-XJ59", "abstract": "This thesis is an extension of the work which was started by Dr. Donnell and Lieutenant Bridget on the problem of thin metal cylinders under combined torsion and direct stress. An explanation of the shape of the compression vs. torsion curve is found by calculating the yield failure of an element of sheet considered as a column with both transverse and end loads. Several causes of variation in that curve shape have been brought to light, but must wait for very complete and accurate experiments or a complete theoretical treatment for verification.
\r\n\r\nExperiments have been extended to several new materials, and have given results which parallel the previous work on steel. In order to cover as wide a range of cylinders as possible, the data of reference no. 1 have been included with the present series of tests.
" }, { "name": "McNeal, Don", "degree": "Masters", "year": "1935", "title": "Ice Formation in the Atmosphere", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222008-104429", "creators": [ { "name": { "family": "McNeal", "given": "Don" }, "id": "McNeal-Don", "display_name": "McNeal, Don" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "meteor" ], "doi": "10.7907/SX19-PN27", "abstract": "No abstract.\r\n" }, { "name": "Mills, Roscoe Harlan", "degree": "PhD", "year": "1935", "title": "The Boundary Layer for Some Axial Symmetric Flows", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05022008-122728", "creators": [ { "name": { "family": "Mills", "given": "Roscoe Harlan" }, "id": "Mills-Roscoe-Harlan", "display_name": "Mills, Roscoe Harlan" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "member", "display_name": "Tollmien, Walter" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R7Q5-V769", "abstract": "The following thesis consists of two sections. Part 1. deals with \"The Boundary Layer for Some Axial Symmetric Flows\", Part 2. with \"Preliminary Experiments on the Flow between Two Circular Disks\"." }, { "name": "Parr, Warren Sherman", "degree": "Masters", "year": "1935", "title": "Investigation of Duralumin Channel Section Strut Under Compression", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-115855", "creators": [ { "name": { "family": "Parr", "given": "Warren Sherman" }, "id": "Parr-Warren-Sherman", "display_name": "Parr, Warren Sherman" }, { "name": { "family": "Beakley", "given": "Wallace Morris" }, "id": "Beakley-Wallace-Morris", "display_name": "Beakley, Wallace Morris" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9VQN-K047", "abstract": "This investigation has clearly established the fact that, for sections built up of straight line elements, theoretical calculations can be made with a degree of accuracy sufficient for practical application and will be on the conservative side." }, { "name": "Russell, James Sargent", "degree": "Masters", "year": "1935", "title": "Propeller Characteristics and Slipstream Effects on a High Wing Monoplane from Wind Tunnel Tests", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182010-095214810", "creators": [ { "name": { "family": "Russell", "given": "James Sargent" }, "id": "Russell-James-Sargent", "display_name": "Russell, James Sargent" }, { "name": { "family": "McCoy", "given": "Howard Monroe" }, "id": "McCoy-Howard-Monroe", "display_name": "McCoy, Howard Monroe" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/91VQ-DG62", "abstract": "No abstract." }, { "name": "White, Roland James", "degree": "Masters", "year": "1935", "title": "The Stress Distribution in Reinforced Plates Under Concentrated Edge Loads", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-152042", "creators": [ { "name": { "family": "White", "given": "Roland James" }, "id": "White-Roland-James", "display_name": "White, Roland James" }, { "name": { "family": "Antz", "given": "Hans Martin" }, "id": "Antz-Hans-Martin", "display_name": "Antz, Hans Martin" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1Q4M-AS93", "abstract": "As part of the investigation of the stress distribution in metal covered wings leading to the most efficient distribution of materials, experiments have been made with flat plates reinforced with stiffeners under concentrated edge loads. Two theoretical solutions have been proposed: one by means of differential equations, considering the sheet between the stiffeners as the medium of transfer and the amount of load transferred to be proportional to the differences in the deflections; the other method, using the principle of the minimum of energy, approximates the accurate solution by considering the loaded system to be composed of columns (stiffeners acting with an effective width of sheet) under compression, the sheet being under shear." }, { "name": "Wood, Carlos Claude", "degree": "Masters", "year": "1935", "title": "Axial Flow Fan Design by Lattice Theory", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-10282005-132754", "creators": [ { "name": { "family": "Wood", "given": "Carlos Claude" }, "id": "Wood-Carlos-Claude", "display_name": "Wood, Carlos Claude" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6H0T-G579", "abstract": "This thesis takes the much discussed and comparatively little used lattice theory and applies it to the design of fans. The application is made through the use of charts coming out of the theory. It is felt that by the use of the charts that the design of confined fans, that is those where end effects on the blades need not be considered, will be made considerably simpler and easier.
\r\n\r\nThe use of the lattice theory in the design of fairly complicated vane systems is discussed, and an approximate method of analysis is given. This subject requires more study in the near future.
\r\n\r\nAs yet, at the time of writing, the method has not been checked by experiment, and as a result not much may be said concerning the accuracy of the results as actually applied to design. However, the use of the lattice theory gives designs that appear to be reasonable, and it is hoped that the method will prove to be fairly accurate in actual practice. At present a fan and vane installation as shown in Fig. XIII and Fix. XV is being constructed, and it is hoped that it will be possible to present some experimental data on the design in the near future.
" }, { "name": "Bridget, Francis Joseph", "degree": "Masters", "year": "1934", "title": "Buckling of Thin Walled Cylinders under Compression of Tension and Torsion", "advisor": "Donnell, Lloyd Hamilton", "url": "https://resolver.caltech.edu/CaltechTHESIS:09182024-203332146", "creators": [ { "name": { "family": "Bridget", "given": "Francis Joseph" }, "id": "Bridget-Francis-Joseph", "display_name": "Bridget, Francis Joseph" } ], "advisors": [ { "name": { "family": "Donnell", "given": "Lloyd Hamilton" }, "id": "Donnell-Lloyd-Hamilton", "role": "advisor", "display_name": "Donnell, Lloyd Hamilton" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3nqj-9h59", "abstract": "No abstract." }, { "name": "Descamps, Alphonse Maurice", "degree": "Masters", "year": "1934", "title": "Photographic Study of Vortex Motions", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-04142008-151832", "creators": [ { "name": { "family": "Descamps", "given": "Alphonse Maurice" }, "id": "Descamps-Alphonse-Maurice", "display_name": "Descamps, Alphonse Maurice" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6QH1-R015", "abstract": "No abstract.\r\n" }, { "name": "Goldstein, Julian Richard", "degree": "Masters", "year": "1934", "title": "Investigation of Turbulence in Circular Tubes by Means of a Hot-Wire Anemometer", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04152008-111221", "creators": [ { "name": { "family": "Goldstein", "given": "Julian Richard" }, "id": "Goldstein-Julian-Richard", "display_name": "Goldstein, Julian Richard" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A5KY-WY52", "abstract": "It is the purpose of this paper to present the results of some investigation of turbulent flow in straight circular tubes, conducted at the suggestion of Dr. Th. Von Karman, and to give a detailed description of the method of using the hot-wire anemometer to measure fluctuations of the air velocity in a direction parallel to the mean flow." }, { "name": "Magden, John Leslie", "degree": "Masters", "year": "1934", "title": "A Preliminary Investigation of Rivets and Riveted Joints in Metal Airplane Construction", "advisor": "Klein, Arthur Louis; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-081411", "creators": [ { "name": { "family": "Magden", "given": "John Leslie" }, "id": "Magden-John-Leslie", "display_name": "Magden, John Leslie" } ], "advisors": [ { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MWT3-P557", "abstract": "No abstract." }, { "name": "Moore, Norton Bartlett", "degree": "PhD", "year": "1934", "title": "The Boundary Layer and Skin Friction for a Body of Revolution at Large Reynold's Numbers", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072006-152924", "creators": [ { "name": { "family": "Moore", "given": "Norton Bartlett" }, "id": "Moore-Norton-Bartlett", "display_name": "Moore, Norton Bartlett" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JZW9-JZ15", "abstract": "Clark Millikan\u2019s work on the boundary layer and skin friction for a figure of revolution is extended, with particular reference to the completely turbulent boundary layer, in two ways:
\r\n\r\na) His expressions for the completely turbulent regime are generalized so as to hold for the assumption of a one n-th power law for the velocity distribution in the boundary layer;
\r\n\r\nb) Von Karman\u2019s logarithmic velocity distribution is introduced into the analysis.
\r\n\r\nb){sic} leads to a practical method by which the drag of a full-scale dirigible can be predicted from wind tunnel tests.
\r\n\r\nComparison of the theory as gotten from b) with experiments leads to the conclusion that the present theory can be safely used to predict drags at large Reynolds\u2019 numbers, whereas drags predicted on the basis of a one seventh power law may be from 20% to 30% low.
" }, { "name": "Rassieur, William Theodore", "degree": "Masters", "year": "1934", "title": "Hinge Moments", "advisor": "von K\u00e1rm\u00e1n, Theodore; Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechETD:etd-04152008-090606", "creators": [ { "name": { "family": "Rassieur", "given": "William Theodore" }, "id": "Rassieur-William-Theodore", "display_name": "Rassieur, William Theodore" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5P3S-7022", "abstract": "The matter herein presented represents the results of an investigation on hinge moments of ailerons on a 1/12.5 scale model of a main wing airfoil of the XP3D-l Navy Patrol Boat.
\r\n\r\nThe data obtained were then employed in the calculation of stick forces due to aileron moments on the full scale airplane, the calculations covering a flying range of eighty to one hundred eighty miles per hour.
\r\n" }, { "name": "Rockefeller, William Curtis", "degree": "Masters", "year": "1934", "title": "A Study of the Selection of Flight Paths in Air Transport Operations", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10242017-090415553", "creators": [ { "name": { "family": "Rockefeller", "given": "William Curtis" }, "id": "Rockefeller-William-Curtis", "display_name": "Rockefeller, William Curtis" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2ZSP-A355", "abstract": "1. GENERAL:
\r\n\r\nWith the introduction of the modern high perfor\u00admance airplane \r\ninto the air transportation systems of the country it has become \r\nincreasingly necessary to make some study of the variables which \r\ninfluence the proper selection of flight paths for the efficient \r\noperation of the aircraft.
\r\n\r\nIn the past it has been the practice in the air transport \r\nindustry to make a very rough estimate of the ef\u00adfect of the winds \r\nand thus determine the best altitude at which to fly on the course.\t\r\nThere has been a complete neg\u00adlect of the possibilities which \r\nare presented by a considera\u00adtion of the airplane performance.
\r\n\r\nIt is the purpose of this thesis to analize the effects of all\r\nof these variables with a view to obtaining some practical\r\nknowledge which may be valuable to the air transportation industry.
\r\n\r\n2. STATEMENT OF THE PROBLEM:
\r\n\r\nThe problem in general is the following: To provide a means of \r\nquickly determining before the start of a flight the path which the \r\npilot should follow in order to fly between any two points in the \r\nminimum possible time. Thus for a given set of cruising specifications \r\nfor the air\u00adplane, this path becomes the optimum, not only for time \r\nelapsed, but also for economy of operation. The method must take into \r\naccount both aerodynamic and meteorological varia\u00adtions.
\r\n\r\nTo be of practical use in air transport operation the method\r\nprovided must have three definite qualifications.
\r\n\r\n1. It must be such as to be readily calculated for a given\r\nflight by a person completely unfamiliar with aerodynamics and\r\nairplane performance.
\r\n\r\n2. It must not require more than a few minutes to calculate for\r\na given flight.
\r\n\r\n3. It must be such that the data can be presented to the pilot\r\nin a brief and useful form.
\r\n\r\nIn addition to the above it is highly desirable to provide information \r\nwhich will be of use to the pilot in properly navigating the airplane \r\nalong the course.
\r\n\r\nAll of the above requirements have been carefully considered throughout \r\nthe analysis and the attempt has been made to incorporate them into \r\nthe resulting method to as great an extent as possible.
\r\n" }, { "name": "Root, Leonard Eugene", "degree": "Masters", "year": "1934", "title": "A Study of the Dynamic Longitudinal Stability of Airplanes with Special Application to Design", "advisor": "Millikan, Clark Blanchard; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302024-220529723", "creators": [ { "name": { "family": "Root", "given": "Leonard Eugene" }, "id": "Root-Leonard-Eugene", "display_name": "Root, Leonard Eugene" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/an7m-3j68", "abstract": "No abstract." }, { "name": "Sechler, Ernest Edwin", "degree": "PhD", "year": "1934", "title": "The Ultimate Compressive Strength of Thin Sheet Metal Panels", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212003-155534", "creators": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-Ernest-Edwin", "display_name": "Sechler, Ernest Edwin" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HX3P-3Y69", "abstract": "No abstract. " }, { "name": "Vosseller, Aurelius Bartlett", "degree": "Masters", "year": "1934", "title": "Investigation of Relation Between Euler and Flat Plate Buckling of \"L\" Section Struts", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04242008-084758", "creators": [ { "name": { "family": "Vosseller", "given": "Aurelius Bartlett" }, "id": "Vosseller-Aurelius-Bartlett", "display_name": "Vosseller, Aurelius Bartlett" }, { "name": { "family": "Jerome", "given": "Clayton Charles" }, "id": "Jerome-Clayton-Charles", "display_name": "Jerome, Clayton Charles" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6HFP-5R14", "abstract": "No abstract.\r\n\r\n" }, { "name": "Wattendorf, Frank Leslie", "degree": "PhD", "year": "1933", "title": "A Study of the Effect of Curvature on Fully Developed Turbulent Flow", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182006-154158", "creators": [ { "name": { "family": "Wattendorf", "given": "Frank Leslie" }, "id": "Wattendorf-Frank-Leslie", "display_name": "Wattendorf, Frank Leslie" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "member", "display_name": "Tollmien, Walter" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RWZE-DP61", "abstract": "In aeronautics we are especially interested in the flow of air adjacent to surfaces, such as airfoils. There are two main types of flow of real fluids, laminar and turbulent and it is turbulent flow which is of practical importance in aeronautics. We should like to be able to predict the skin friction and flow conditions for any surface of any shape. There has recently been much success with the problem of predicting flow along a flat plate parallel to the direction of flow, and the problem was attacked by investigation of fully developed turbulent flow in straight channels, and direct application of the semi-empirical laws obtained, to the flow along a flat plate. However, surfaces met with in practice are, in general, curved, so that it would be important to be able to predict the effect of curvature on turbulent flow. Most of the previous work in curved flow, however, has been with curved pipes and channels where the behavior of the flow was complicated by secondary vortices.
\r\n\r\nThe present work had the purposes of isolating as far as possible the effect of curvature on a fully developed turbulent flow, with two dimensional mean motion. The curved channels used were 5 cm. in breadth and 90 cm. in depth, and had straight entrance sections over 60 x breadth in length to produce a fully developed straight flow before subjecting it to the effect of curvature. Channel I had inner radius 45 cm. and outer radius 50 cm., while channel II had inner radius 20 cm. and outer 25 cm. In addition, measurements were made in an appratus consisting of two concentric cylinders, the inner one of radius 20 cm. and rotating, the outer of radius 25.4 cm. and fixed. The curvature was made of the same order as channel II for purpose of comparison.
\r\n\r\nMeasurements on the channels consisted of pressure drop along the channel walls at several speeds, velocity distribution at 30\u00b0 intervals around the curved portion, velocity distributions at several speeds, and for channel II, determination of the shearing stress at the walls of one of the curved sections.
\r\n\r\nMeasurements on the cylinders consisted of velocity distributions at two speeds and determination of shearing stress at the outer wall.
\r\n\r\nEvaluation of results included: calculation of resistance law, calculation of the shearing stress, distribution in radial direction across the curved portion, determination of the exponential law for the velocity distribution near the walls in the various cases, calculation of the \"mixing length\" 1, from turbulent exchange theory, and several dimensionless methods of plotting velocity distributions to show similarity between measurements in the channels and in the concentric cylinders.
\r\n\r\nAlso included are calculations of the laminar flow distribution in a curved channel, and a discussion of Rayleigh's stability criterion.
\r\n\r\nIt appears that the distribution of centrifugal force has a strong influence on the stability of the flow, and affects materially the velocity distribution. The fact that similarity can be obtained for several cases by proper dimensionless reduction based on the effective breadth of the mixing region looks hopeful, and it remains for future investigations to determine more facts about the effective breadth of the mixing region.
" }, { "name": "Biot, Maurice A.", "degree": "PhD", "year": "1932", "title": "Transient Oscillations in Elastic Systems", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252003-113841", "creators": [ { "name": { "family": "Biot", "given": "Maurice A." }, "id": "Biot-Maurice-A", "display_name": "Biot, Maurice A." } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZHSH-T443", "abstract": "No abstract." }, { "name": "Brahtz, John Henry Augustus", "degree": "PhD", "year": "1932", "title": "Stresses at Two-Dimensional Corners for Various Force Distributions", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062007-140731", "creators": [ { "name": { "family": "Brahtz", "given": "John Henry Augustus" }, "id": "Brahtz-John-Henry-Augustus", "display_name": "Brahtz, John Henry Augustus" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4QRC-A816", "abstract": "This paper deals with the stress distribution under plain strain in a corner of any angular magnitude, i.e., a plane with an angular incision or notch.
\r\n\r\nThe Introduction contains a brief statement of the method employed by Dr. Theodor von Karman in his exact treatment of a beam in bending (Aachen Abhandlungen, Heft 7, 1927).
\r\n\r\nIn Part I a generalization of this method is outlined which is applicable to the corner for any force distribution over the straight boundaries. Solutions are found in the 3/4-plane for:
\r\n1. Concentrated load at any point of the straight boundaries.
\r\n2. Uniform distribution between the vertex and a point of the boundary.
\r\n3. Linear distribution in the same region.
\r\n4. Superposition of 2 and 3.
Certain stresses are determined and plotted and shown to be infinite at the vertex for partial loadings of the boundaries.
\r\n\r\nIn Part II an alternate method is given to obtain a solution for case 1.
\r\n\r\nThe discussion points out the very interesting paradox that stresses may be finite for certain continuous loadings, but become infinite if a portion of the load is removed.
" }, { "name": "Folsom, Richard Gilman", "degree": "PhD", "year": "1932", "title": "An Experimental Investigation of the Phenomena Produced by the Highly Turbulent Flow of Water Past a Series of Sharp Obstacles", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-104603", "creators": [ { "name": { "family": "Folsom", "given": "Richard Gilman" }, "id": "Folsom-Richard-Gilman", "display_name": "Folsom, Richard Gilman" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJ70-1607", "abstract": "A knowledge of the resistance to flow of a body placed in a stream of fluid is necessary for many problems in hydraulics, aeronautics, and ventilation. A large amount of experimental and theoretical effort has been expended investigating the drag characteristics of single bodies and small groups of similar bodies. Only a small amount of incomplete data is available regarding the performance of a long series of similar obstacles. This latter material was obtained for air flowing past supporting timber sets in mines. Since the dimensions of the mine shafts varied at different sections, the results of the experiments merely indicated the possibilities of obtaining different pressure losses depending on the size, shape, and spacing of the timber sets. Therefore, more data are needed regarding the drag characteristics of long series of obstacles." }, { "name": "Oswald, W. Bailey", "degree": "PhD", "year": "1932", "title": "The Transverse Force Distribution on Ellipsoidal and Nearly Ellipsoidal Bodies Moving in an Arbitrary Potential Flow", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard; Tollmien, Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062007-141717", "creators": [ { "name": { "family": "Oswald", "given": "W. Bailey" }, "id": "Oswald-W-Bailey", "display_name": "Oswald, W. Bailey" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "advisor", "display_name": "Tollmien, Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QK4H-C181", "abstract": "The forces acting on an airship moving in a certain field of flow and the resulting path of motion are the result of numerous aerodynamic factors. These factors are principally skin friction drag, form drag, induced drag, aerodynamic transverse force distribution, lateral and longitudinal inertial and static force distribution, lift, and moments arising from all above factors. With the exception of aerodynamic transverse force distribution, lift, and induced drag, these factors are either small or may be determined by methods now available." }, { "name": "Nagashi, Masahiro Howard", "degree": "Masters", "year": "1931", "title": "A Study of Fully Developed Turbulent Flow at a Very High Reynolds Number", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-110528", "creators": [ { "name": { "family": "Nagashi", "given": "Masahiro Howard" }, "id": "Nagashi-Masahiro-Howard", "display_name": "Nagashi, Masahiro Howard" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/815A-2M78", "abstract": "The object of this experiment is to make a study of a fully developed turbulent flow at a very high Reynolds Number, using a large circular tube, through with air was drawn. In determining the behavior of the air stream, Pitot tubes were used in the present experiment. This investigation is a preliminary study of the turbulence and other characteristics of the tunnel for the subsequent experiment to be conducted by Mr. A. M. Kuethe of the California Institute of Technology. In the subsequent experiment, a direct measurement of the eddying motion and a determination of the values of mischungsweg distribution of the turbulent flow will be made at the same measuring sections in the same tunnel, using an electric anemometer and oscillograph method." }, { "name": "Zahorski, Adam Teodor", "degree": "Masters", "year": "1931", "title": "On the Torsion of Wings", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-04172008-075520", "creators": [ { "name": { "family": "Zahorski", "given": "Adam Teodor" }, "id": "Zahorski-Adam-Teodor", "display_name": "Zahorski, Adam Teodor" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E0T0-P929", "abstract": "Methods of investigation of pure torsion differ in many ways from the general method of procedure for other types of stresses. First it is very difficult to subject a body to a pure torsion without superposing bending moments; second the exact determination of twisting moment is in most cases very doubtful; third, a body subjected to torsional shearing stresses in general does not deform according to a simple law, but this deformation is usually a function of the geometry of the body." }, { "name": "Sechler, Ernest Edwin", "degree": "Masters", "year": "1930", "title": "Problems Relating to the Use of Sheet Metal in Airplane Construction", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-10142005-081946", "creators": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-Ernest-Edwin", "display_name": "Sechler, Ernest Edwin" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RP44-R311", "abstract": "Sheet metal as used in present airplane construction may have two separate and distinct functions. The first of these is merely to supplant fabric or other covering material on the airplane. The structure of the airplane is not altered and the load is completely taken by the framework. The added strength and durability of this type of covering is usually connected with an increase in weight which makes the practice uneconomical. This use of metal is not a very serious design problem since it is only used as a covering and fairing and its strength is not included in the calculated strength of the structure.
\r\n\r\nSecondly, the sheet metal can be designed so it will take part or all of the loads on the airplane. It is this use of sheet metal, and its attendant problems, that will be discusssed here. Those problems that have been solved will be mentioned first and those yet undetermined will then be outlined. To be solved the answer to a problem must be in such a form as to be available and understandable to the average airplane designer without the use of long and intricate mathematical calculations. This means that those problems are solved which could be incorporated in a handbook for designers and those which could not be so incorporated are not solved for the designer.
" }, { "name": "Kiesling, Louis", "degree": "Bachelors", "year": "1924", "title": "The Sail-Plane", "advisor": "Merrill, Albert Adams", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052004-132633", "creators": [ { "name": { "family": "Kiesling", "given": "Louis" }, "id": "Kiesling-Louis", "display_name": "Kiesling, Louis" } ], "advisors": [ { "name": { "family": "Merrill", "given": "Albert Adams" }, "id": "Merrill-A-A", "role": "advisor", "display_name": "Merrill, Albert Adams" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "aeronautics", "eng" ], "doi": "10.7907/YB5X-9C87", "abstract": "No Abstract." } ]