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.
", "doi": "10.7907/rv8x-jm07", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17747", "collection": "thesis", "collection_id": "17747", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11032025-192332480", "primary_object_url": { "basename": "phd_thesis_submission.pdf", "content": "final", "filesize": 32786900, "license": "other", "mime_type": "application/pdf", "url": "/17747/1/phd_thesis_submission.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Leveraging Aerial Transformation for Enhanced Air\u2013Ground Robotic Mobility", "author": [ { "family_name": "Mandralis", "given_name": "Ioannis M.", "orcid": "0000-0001-5270-0672", "clpid": "Mandralis-Ioannis-M" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" } ], "thesis_committee": [ { "family_name": "Ames", "given_name": "Aaron D.", "orcid": "0000-0003-0848-3177", "clpid": "Ames-A-D" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "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.", "doi": "10.7907/srg8-sx98", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17211", "collection": "thesis", "collection_id": "17211", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05082025-223940273", "primary_object_url": { "basename": "Mohebbi_Nina_2025.pdf", "content": "final", "filesize": 9737531, "license": "other", "mime_type": "application/pdf", "url": "/17211/1/Mohebbi_Nina_2025.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Flow Induced by Collective Vertical Migration: Impact of Swimmer Distribution, Buoyancy, and Wake Interactions", "author": [ { "family_name": "Mohebbi", "given_name": "Nina", "orcid": "0000-0003-4014-6111", "clpid": "Mohebbi-Nina" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dickinson", "given_name": "Michael H.", "orcid": "0000-0002-8587-9936", "clpid": "Dickinson-M-H" }, { "family_name": "Lozano-Duran", "given_name": "Adrian", "orcid": "0000-0001-9306-0261", "clpid": "Lozano-Duran-A" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/hz5j-g795", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16729", "collection": "thesis", "collection_id": "16729", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09142024-001942971", "type": "thesis", "title": "Chasing After the Wind: Flow Structure Detection Strategies for Autonomous Mobile Flow Field Measurements", "author": [ { "family_name": "Harms", "given_name": "Tanner David", "orcid": "0009-0003-2913-7414", "clpid": "Harms-Tanner-David" } ], "thesis_advisor": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Brunton", "given_name": "Steven L.", "orcid": "0000-0002-6565-5118", "clpid": "Brunton-S-L" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "local_group": [ { "literal": "div_eng" } ], "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.", "doi": "10.7907/vjvv-vb21", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16811", "collection": "thesis", "collection_id": "16811", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10232024-033952961", "primary_object_url": { "basename": "Huang_Yuting_2025.pdf", "content": "final", "filesize": 36962804, "license": "other", "mime_type": "application/pdf", "url": "/16811/1/Huang_Yuting_2025.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Linear and Non-Linear Interactions Involving Large-Scale Structures in Turbulence", "author": [ { "family_name": "Huang", "given_name": "Yuting", "orcid": "0000-0002-9457-7964", "clpid": "Huang-Yuting" } ], "thesis_advisor": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "thesis_committee": [ { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis performs a linear resolvent analysis (McKeon and Sharma, 2010), and a novel quantitative non-linear analysis of the triadic interactions, to study the largescale structures in wall-bounded turbulence.
\r\n\r\nFirst, resolvent analysis is applied to a flow over spanwise periodic roughness, to model the large-scale counter-rotating rolls. The experimental data (Wangsawijaya et al., 2020) is utilized to examine both the predictive and data compression capabilities of the resolvent. The improvements by the inclusion of an eddy viscosity and a crude boundary geometry model are also demonstrated. Standard resolvent is able to qualitatively predict the shape of the counter-rotating rolls. The inclusion of eddy viscosity improves the quantitative predictions and combined with the boundary geometry model is able to efficiently represent the data with small differences using only a fraction of the degree of freedom.
\r\n\r\nNext, we developed a novel framework to quantitatively analyze the triadic non-linear contributions in a turbulent channel. We incorporated the linear resolvent operator to provide the missing link from energy transfer between modes to the effect on the spectral turbulent kinetic energy. The coefficients highlight the importance of interactions involving large-scale structures, for both the large and small-scale forcing and response, providing a natural connection to the modeling assumptions of the quasi-linear (QL) and generalized quasi-linear (GQL) analyses. Specifically, it is revealed that QL and GQL are efficiently capturing important triadic interactions in the flow, and the inclusion of small amounts of wavenumbers into the GQL large-scale base flow quickly captures most of the important triadic interactions.
\r\n\r\nFinally, by performing spatio-temporal analyses of the triadic contributions to a single mode, we demonstrated the spatio-temporal nature of the triadic interactions and the effect of the resolvent operator. It is shown that the energetic triadic interactions are concentrated in temporal frequencies around a plane where all three wavespeeds are the same, allowing for a truncation of the important triadic interactions. We also demonstrated the linear amplification mechanism of the resolvent, allowing certain triadic interactions to generate a stronger response even with a weak forcing, underscoring the different perspectives offered by the inclusion of the linear resolvent operator into the analyses of the non-linear triadic interactions.
", "doi": "10.7907/739k-dj72", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16811", "collection": "thesis", "collection_id": "16811", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10232024-033952961", "primary_object_url": { "basename": "Huang_Yuting_2025.pdf", "content": "final", "filesize": 36962804, "license": "other", "mime_type": "application/pdf", "url": "/16811/1/Huang_Yuting_2025.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Linear and Non-Linear Interactions Involving Large-Scale Structures in Turbulence", "author": [ { "family_name": "Huang", "given_name": "Yuting", "orcid": "0000-0002-9457-7964", "clpid": "Huang-Yuting" } ], "thesis_advisor": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "thesis_committee": [ { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis performs a linear resolvent analysis (McKeon and Sharma, 2010), and a novel quantitative non-linear analysis of the triadic interactions, to study the largescale structures in wall-bounded turbulence.
\r\n\r\nFirst, resolvent analysis is applied to a flow over spanwise periodic roughness, to model the large-scale counter-rotating rolls. The experimental data (Wangsawijaya et al., 2020) is utilized to examine both the predictive and data compression capabilities of the resolvent. The improvements by the inclusion of an eddy viscosity and a crude boundary geometry model are also demonstrated. Standard resolvent is able to qualitatively predict the shape of the counter-rotating rolls. The inclusion of eddy viscosity improves the quantitative predictions and combined with the boundary geometry model is able to efficiently represent the data with small differences using only a fraction of the degree of freedom.
\r\n\r\nNext, we developed a novel framework to quantitatively analyze the triadic non-linear contributions in a turbulent channel. We incorporated the linear resolvent operator to provide the missing link from energy transfer between modes to the effect on the spectral turbulent kinetic energy. The coefficients highlight the importance of interactions involving large-scale structures, for both the large and small-scale forcing and response, providing a natural connection to the modeling assumptions of the quasi-linear (QL) and generalized quasi-linear (GQL) analyses. Specifically, it is revealed that QL and GQL are efficiently capturing important triadic interactions in the flow, and the inclusion of small amounts of wavenumbers into the GQL large-scale base flow quickly captures most of the important triadic interactions.
\r\n\r\nFinally, by performing spatio-temporal analyses of the triadic contributions to a single mode, we demonstrated the spatio-temporal nature of the triadic interactions and the effect of the resolvent operator. It is shown that the energetic triadic interactions are concentrated in temporal frequencies around a plane where all three wavespeeds are the same, allowing for a truncation of the important triadic interactions. We also demonstrated the linear amplification mechanism of the resolvent, allowing certain triadic interactions to generate a stronger response even with a weak forcing, underscoring the different perspectives offered by the inclusion of the linear resolvent operator into the analyses of the non-linear triadic interactions.
", "doi": "10.7907/739k-dj72", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17049", "collection": "thesis", "collection_id": "17049", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03102025-172015248", "type": "thesis", "title": "Resolvent Analysis of Non-Stationary Turbulent Flows and Transient Flow Phenomena", "author": [ { "family_name": "Ballouz", "given_name": "Eric", "orcid": "0009-0003-7034-1898", "clpid": "Ballouz-Eric" } ], "thesis_advisor": [ { "family_name": "Bae", "given_name": "H. Jane", "orcid": "0000-0001-6789-6209", "clpid": "Bae-H-J" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Lozano-Duran", "given_name": "Adrian", "orcid": "0000-0001-9306-0261", "clpid": "Lozano-Duran-A" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Bae", "given_name": "H. Jane", "orcid": "0000-0001-6789-6209", "clpid": "Bae-H-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this work, we develop a wavelet-based formulation of resolvent analysis in order to extend the method to transient phenomena and non-stationary flows. We apply this method in two ways: first, to analyze systems that were not previously amenable to traditional resolvent analysis, and second, to probe the limits of the resolvent forcing modes' \"optimality\" in a nonlinear simulation as well as investigate the mechanisms that suppress their effectiveness. In wavelet-based resolvent analysis, the Navier-Stokes equations are linearized about a mean profile, Fourier-transformed in the homogeneous directions, and wavelet-transformed in time. The nonlinear terms are represented as forcing terms acting on the system, and a maximally perturbing forcing mode and the response it produces are then computed for this linear system. The wavelet formulation enables the forcing and response modes to represent transient trajectories. By windowing the wavelet-based resolvent operator, we can also compute optimal forcing modes restricted to a time-localized pulse along with their transient response.
\r\n\r\nFor the first application of the method, we use the windowing approach to study bursting in channel flow. The optimal response mode grows and decays in time scales that match turbulent data, and we show that this optimal burst exploits the Orr mechanism.\r\nWe also study channel flow subjected to a spanwise pressure gradient. The corresponding resolvent modes mirror the mean flow and gradually realign themselves according to the new flow conditions. More interestingly, they exhibit a collapse of the lift-up mechanism during this realignment, which offers an explanation to the depletion of tangential Reynolds stresses in the turbulent system.
\r\n\r\nFor the second application of the method, we inject time-localized resolvent forcing modes for the minimal flow unit into a simulation of the system, at different intensities. The principal resolvent forcing mode is much more effective than a randomly generated forcing structure at amplifying the near-wall streak. For initial times and close to the wall, the turbulent minimal flow unit matches the principal response mode well, but due to nonlinear effects, the response decays prematurely. By computing the nonlinear energy transfer to secondary scales, we find that the breakdown of the actuated mode proceeds similarly across all forcing intensities: in the near-wall region, the induced streak forks into two branches, while in the outer region, the streak breaks up in the streamwise direction. In both regions, spanwise gradients account for the dominant share of nonlinear energy transfer.
", "doi": "10.7907/t9sw-b215", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17283", "collection": "thesis", "collection_id": "17283", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282025-170616092", "type": "thesis", "title": "Buoyancy-Driven Fluid Dynamics for Enhanced Ocular Drug Delivery", "author": [ { "family_name": "O'Gara", "given_name": "Stephanie Lea", "orcid": "0009-0003-9826-6906", "clpid": "O'Gara-Stephanie-Lea" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Fu", "given_name": "Xiaojing", "orcid": "0000-0001-7120-704X", "clpid": "Fu-Xiaojing" }, { "family_name": "Koochesfahani", "given_name": "Manoochehr", "orcid": "0000-0002-7001-8455", "clpid": "Koochesfahani-Manoochehr" }, { "family_name": "Humayun", "given_name": "Mark", "orcid": "0000-0002-5830-5208", "clpid": "Humayun-M" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The CDC has identified vision loss as a growing public health concern, with eye disease prevalence on the rise. Three of the most common and vision-threatening eye diseases, wet age-related macular degeneration, proliferative diabetic retinopathy, and diabetic macular edema, are typically managed through periodic intravitreal injections. However, treatment effectiveness varies. Given that the half-life of the drug is limited, one possible cause of the ineffective treatment is inefficient delivery to the target region. This thesis investigates heat-induced convective flow in an in-vitro eye model as a method for enhancing drug delivery by accelerating fluid transport.
\r\n\r\nFirst, an optical distortion study was conducted to identify a vitreous model that matches both the viscosity of the human vitreous and the refractive index of the eye model. Next planar two-component and volumetric three-component flow visualization and measurement experiments capture the impact of thermal pad size on the resulting flow fields, with consideration given to particle trajectories for targeted delivery. Finally, a physics-informed neural network, trained on planar velocity data and tested against additional planes from volumetric measurements, demonstrates the potential for data-driven modeling to simplify future flow visualization experiments. The outcomes of this work further our fundamental understanding of fluid dynamics in the eye and encourage continued investigation into interdisciplinary approaches for improving drug delivery, and ultimately, patient outcomes.
", "doi": "10.7907/18vw-4r15", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17406", "collection": "thesis", "collection_id": "17406", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042025-002343274", "primary_object_url": { "basename": "MeredithHooper_Dissertation.pdf", "content": "final", "filesize": 84549492, "license": "other", "mime_type": "application/pdf", "url": "/17406/1/MeredithHooper_Dissertation.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Machine-Learned Propulsion Strategies: From Adaptive Damage Compensation to Advanced Aeromobility", "author": [ { "family_name": "Hooper", "given_name": "Meredith Leigh", "orcid": "0009-0004-4819-9941", "clpid": "Hooper-Meredith-Leigh" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Ames", "given_name": "Aaron D.", "orcid": "0000-0003-0848-3177", "clpid": "Ames-A-D" }, { "family_name": "Yue", "given_name": "Yisong", "orcid": "0000-0001-9127-1989", "clpid": "Yue-Yisong" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/79aa-ja50", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17425", "collection": "thesis", "collection_id": "17425", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06092025-020707222", "type": "thesis", "title": "Perception-Driven Autonomy and Learning Control for Ground Vehicles", "author": [ { "family_name": "Lupu", "given_name": "Elena Sorina", "orcid": "0000-0002-3968-2630", "clpid": "Lupu-Elena-Sorina" } ], "thesis_advisor": [ { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" } ], "thesis_committee": [ { "family_name": "Yue", "given_name": "Yisong", "orcid": "0000-0001-9127-1989", "clpid": "Yue-Yisong" }, { "family_name": "Hadaegh", "given_name": "Fred", "orcid": "0000-0002-0992-6323", "clpid": "Fred-Hadaegh" }, { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" } ], "local_group": [ { "literal": "div_eng" } ], "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.", "doi": "10.7907/79tk-eg16", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16208", "collection": "thesis", "collection_id": "16208", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10162023-141935060", "primary_object_url": { "basename": "Spratt_Thesis.pdf", "content": "final", "filesize": 28877365, "license": "other", "mime_type": "application/pdf", "url": "/16208/1/Spratt_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Numerical Simulations of Cavitating Bubbles in Elastic and Viscoelastic Materials for Biomedical Applications", "author": [ { "family_name": "Spratt", "given_name": "Jean-S\u00e9bastien Alexandre", "orcid": "0000-0002-1962-4214", "clpid": "Spratt-Jean-S\u00e9bastien-Alexandre" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Austin", "given_name": "Joanna M.", "orcid": "0000-0003-3129-5035", "clpid": "Austin-J-M" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The interactions of cavitating bubbles with elastic and viscoelastic materials play a central role in many biomedical applications. This thesis makes use of numerical modeling and data-driven approaches to characterize soft biomaterials at high strain rates via observation of bubble dynamics, and to model burst-wave lithotripsy, a focused ultrasound therapy to break kidney stones.
\r\n\r\nIn the first part of the thesis, a data assimilation framework is developed for cavitation rheometry, a technique that uses bubble dynamics to characterize soft, viscoelastic materials at high strain-rates. This framework aims to determine material properties that best fit observed cavitating bubble dynamics. We propose ensemble-based data assimilation methods to solve this inverse problem. This approach is validated with surrogate data generated by adding random noise to simulated bubble radius time histories, and we show that we can confidently and efficiently estimate parameters of interest within 5% given an iterative Kalman smoother approach and an ensemble- based 4D-Var hybrid technique. The developed framework is applied to experimental data in three distinct settings, with varying bubble nucleation methods, cavitation media, and using different material constitutive models. We demonstrate that the mechanical properties of gels used in each experiment can be estimated quickly and accurately despite experimental inconsistencies, model error, and noisy data. The framework is used to further our understanding of the underlying physics and identify limitations of our bubble dynamics model for violent bubble collapse.
\r\n\r\nIn the second part of the thesis, we simulate burst-wave lithotripsy (BWL), a non- invasive treatment for kidney stones that relies on repeated short bursts of focused ultrasound. Numerical approaches to study BWL require simulation of acoustic waves interacting with solid stones as well as bubble clouds which can nucleate ahead of the stone. We implement and validate a hypoelastic material model, which, with the addition of a continuum damage model and calibration of a spherically- focused transducer array, enables us to determine how effective various treatment strategies are with arbitrary stones. We present a preliminary investigation of the bubble dynamics occurring during treatment, and their impact on damage to the stone. Finally, we propose a strategy to reduce shielding by collapsing bubbles ahead of the stone via introduction of a secondary, low-frequency ultrasound pulse during treatment.
", "doi": "10.7907/g34e-6p65", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16239", "collection": "thesis", "collection_id": "16239", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11062023-050222447", "type": "thesis", "title": "Wearable Sweat Sensors for Disease Monitoring and Management", "author": [ { "family_name": "Tu", "given_name": "Jiaobing", "orcid": "0000-0002-7653-6640", "clpid": "Tu-Jiaobing" } ], "thesis_advisor": [ { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" } ], "thesis_committee": [ { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" }, { "family_name": "Emami", "given_name": "Azita", "orcid": "0000-0002-6945-9958", "clpid": "Emami-A" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "With the emphasis of healthcare shifting towards prevention and early detection of diseases and monitoring of chronic conditions, there is a growing need for hassle\u2010free telemedicine sensor technologies that can be seamlessly integrated into daily life. While significant progress has been made in the development of wearable sweat and salivary biosensors to meet this need for rapid, real-time collection of physiological information, the majority of current epidermal sensing systems are unable to detect trace-level disease-relevant biomarkers accurately in biofluids and cannot be mass produced. To meet this demand for low-cost, mass-producible mHealth devices for at-home settings, we developed several fully integrated laser-engraved graphene-based biosensors for the detection of low-concentration sweat and saliva analytes including hormones (cortisol) and proteins (C-reactive protein). Several graphene surface engineering strategies are investigated for the sensitive and selective detection of targets. System-level engineering and microfluidic designs are explored to achieve on-demand sweat induction and harvesting under sedentary settings and automated sweat and reagent routing and in situ signal correction and analysis for facile operation on the skin. The utility of these fully integrated flexible mHealth systems is evaluated through multiple human studies involving healthy and various patient subgroups towards stress assessment, as well as the monitoring and management of various chronic conditions including chronic obstructive pulmonary disease, heart failure, and inflammatory bowel diseases. These fully integrated mHealth devices demonstrate a technology that can be easily adapted to monitor a broad spectrum of disease-specific proteins, cytokines, and hormones, thus advancing future applications in personalized disease diagnosis, management, and prevention.", "doi": "10.7907/7jdg-z479", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16391", "collection": "thesis", "collection_id": "16391", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192024-000137690", "primary_object_url": { "basename": "KVirgil_Thesis_2023.pdf", "content": "final", "filesize": 2810434, "license": "other", "mime_type": "application/pdf", "url": "/16391/1/KVirgil_Thesis_2023.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Polarization-Resolved, Oblique Incidence Terahertz Spectroscopy of Highly Uniform 2D Hybrid Perovskite Films", "author": [ { "family_name": "Virgil", "given_name": "Kyle Allan", "clpid": "Virgil-Kyle-Allan" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis details the development and optimization of thin film THz transmission measurements to extract spectrally resolved vibrational anisotropy in high quality layered hybrid perovskite materials. After an introduction in Chapter 1, Chapter 2 details the design, construction, and characterization of a terahertz time-domain spectrometer from scratch. Generalized THz propagation models are presented which enable accurate and diverse implementation of THz analysis. In Chapter 3, hybrid perovskite materials are introduced and our efforts towards reliably synthesizing high quality thin film perovskites using spin coating techniques are discussed. We find that optimized thin films are achieved from tailored synthetic conditions which depend on perovskite composition. In Chapter 4, we present our investigation into the elusive yet highly influential THz vibrational properties of 2D hybrid perovskite systems. A novel implementation of oblique-incidence THz transmission measurements reveals previously unseen vibrational excitations which provide valuable insight into the fundamental photodynamics that govern perovskite optoelectronics. We conclude in Chapter 5. This thesis serves to enhance the accessibility of powerful THz spectroscopic techniques as well as support the realization of promising perovskite renewable energy technologies.", "doi": "10.7907/cr97-p373", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16506", "collection": "thesis", "collection_id": "16506", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052024-052757779", "primary_object_url": { "basename": "Gunnarson_Peter_2024.pdf", "content": "final", "filesize": 32177904, "license": "other", "mime_type": "application/pdf", "url": "/16506/1/Gunnarson_Peter_2024.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Autonomous Flow-Based Navigation in Unsteady Underwater Environments", "author": [ { "family_name": "Gunnarson", "given_name": "Peter John", "orcid": "0000-0002-4437-5379", "clpid": "Gunnarson-Peter-John" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Bae", "given_name": "H. Jane", "orcid": "0000-0001-6789-6209", "clpid": "Bae-H-J" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "orcid": "0000-0002-3091-540X", "clpid": "Burdick-J-W" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.", "doi": "10.7907/vnh6-3t44", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15100", "collection": "thesis", "collection_id": "15100", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02042023-015312785", "primary_object_url": { "basename": "Oshima_EK_Dissertation.pdf", "content": "final", "filesize": 77968077, "license": "other", "mime_type": "application/pdf", "url": "/15100/1/Oshima_EK_Dissertation.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Experimental Studies of Flow Control Techniques for Future Aircraft", "author": [ { "family_name": "Oshima", "given_name": "Emile Kazuo", "orcid": "0000-0002-1689-3726", "clpid": "Oshima-Emile-Kazuo" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Bae", "given_name": "H. Jane", "orcid": "0000-0001-6789-6209", "clpid": "Bae-H-J" }, { "family_name": "Wygnanski", "given_name": "Israel J.", "orcid": "0009-0001-5711-7029", "clpid": "Wygnanski-I-J" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/fpcj-w268", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15252", "collection": "thesis", "collection_id": "15252", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-001712615", "primary_object_url": { "basename": "Tamborini_Alessio_2023_redacted.pdf", "content": "final", "filesize": 14813490, "license": "other", "mime_type": "application/pdf", "url": "/15252/9/Tamborini_Alessio_2023_redacted.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "A Novel Approach to Cardiac Health Assessment Using a Redesign of the Brachial Cuff Device", "author": [ { "family_name": "Tamborini", "given_name": "Alessio", "orcid": "0000-0001-7651-3505", "clpid": "Tamborini-Alessio" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Tai", "given_name": "Yu-Chong", "orcid": "0000-0001-8529-106X", "clpid": "Tai-Yu-Chong" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Current diagnostic methodologies in cardiology face large tradeoffs between procedure invasiveness and diagnostic reliability, ultimately requiring individuals to undergo cardiac catheterization for accurate diagnosis. Given the current societal burden of cardiovascular disease, there is a need for translational medical devices that bridge the accuracy gap between invasive and non-invasive measurements in the assessment of heart health. This thesis focuses on the development and validation of a high-resolution cuff-based system for assessment of central cardiovascular health.
\r\n\r\nTraditional pressure cuffs suffer low signal resolution when applied to non-invasive pulse waveform acquisition. In the first section of this thesis, we develop a cuff-based device with a pneumatic filter for high fidelity pulse waveform acquisition. This work discusses the design and functionality of the cuff-device, and investigates the repeatability of the cuff-based measurement. Furthermore, the derived mathematical model of the pneumatic filter is shown to have an equivalent behavior to an electrical low-pass filter inclusive of a time constant and a frequency response curve.
\r\n\r\nThe accuracy and reliability of the pulse waveform features from the cuff-device are evaluated with human study data. Firstly, an IRB study is performed at Caltech on a young and healthy population showing that the cuff-device data lies within a narrow distribution indicative of the healthy nature of the population. Secondly, data from a clinical trial collecting simultaneous invasive catheter, cuff, and ECG is analyzed. The first analysis compared waveform parameters from the cuff in sSBP hold pressure with simultaneous aortic catheter, showing strong correlations between the two measurement modalities for both magnitude and fluctuations thereof.
\r\n\r\nLastly, this work investigated the relationship between cuff-based parameters and left ventricular functions. We introduced a cuff-based method for extraction of the pressure-sound waveform, a pressure based surrogate of heart sounds. The results from this analysis showed that the pressure-sound features correlate with the strength of the left ventricular isovolumetric contraction and relaxation. Other important results from this work demonstrated the correlations between the heart-lung interactions in the left ventricle and cuff parameters: breathing fluctuations proportionally affect LV pressures and cuff sSBP waveform parameters. Overall these results support the accuracy and reliability of a cuff-based device for central cardiovascular health assessments.
", "doi": "10.7907/rp22-me93", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15260", "collection": "thesis", "collection_id": "15260", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-194820518", "primary_object_url": { "basename": "Thesis-Edit.pdf", "content": "final", "filesize": 18957251, "license": "other", "mime_type": "application/pdf", "url": "/15260/1/Thesis-Edit.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Geometry and Dynamical Systems in Machine Learning and Control", "author": [ { "family_name": "Dorobantu", "given_name": "Victor David", "orcid": "0000-0002-2797-7802", "clpid": "Dorobantu-Victor-David" } ], "thesis_advisor": [ { "family_name": "Yue", "given_name": "Yisong", "orcid": "0000-0001-9127-1989", "clpid": "Yue-Yisong" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-John-O" }, { "family_name": "Schroeder", "given_name": "Peter", "orcid": "0000-0002-0323-7674", "clpid": "Schr\u00f6der-P" }, { "family_name": "Azizzadenesheli", "given_name": "Kamyar", "orcid": "0000-0001-8507-1868", "clpid": "Azizzadenesheli-Kamyar" }, { "family_name": "Yue", "given_name": "Yisong", "orcid": "0000-0001-9127-1989", "clpid": "Yue-Yisong" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "For many problems of interest in machine learning and control, we have access to rich information about underlying geometry and dynamics; we can leverage this information to build robust and performant solutions in new algorithms, optimizations, and designs. In this thesis we study four problem settings to stress this central assumption. First, we study conformal generative modeling, using computational geometry techniques to simplify and register complex 2D surfaces and enabling the use of a variety of flow-based generative models as plug-and-play subroutines. Second, we study data-driven robust optimization problems in control, modeling the precise impact of dynamics uncertainty in several control frameworks using convex geometry. Third, we study compactly-restrictable policy optimization, constraining the available states and actions in reinforcement learning and optimal control problems to be consistent with the inherent dynamics of the systems to be controlled. Finally, we study nonlinear model predictive control on Lie groups as applied to a 3D hopping robot platform, developing a control methodology compatible with nontrivial state space geometry and hybrid system dynamics.", "doi": "10.7907/x271-r088", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15270", "collection": "thesis", "collection_id": "15270", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-233342281", "primary_object_url": { "basename": "Dissertation_NJW_v2_final.pdf", "content": "final", "filesize": 28173009, "license": "other", "mime_type": "application/pdf", "url": "/15270/1/Dissertation_NJW_v2_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Dynamics and Performance of Wind-Energy Systems in Unsteady Flow Conditions", "author": [ { "family_name": "Wei", "given_name": "Nathaniel James", "orcid": "0000-0001-5846-6485", "clpid": "Wei-Nathaniel-James" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.", "doi": "10.7907/d9wh-pj98", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15112", "collection": "thesis", "collection_id": "15112", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02272023-230531120", "primary_object_url": { "basename": "Thesis_Draft___Final.pdf", "content": "final", "filesize": 20577292, "license": "other", "mime_type": "application/pdf", "url": "/15112/1/Thesis_Draft___Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Applied Machine Learning for Prediction and Control of Fluid Flows", "author": [ { "family_name": "Renn", "given_name": "Peter Ian James", "orcid": "0000-0002-5735-3873", "clpid": "Renn-Peter-Ian-James" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Bae", "given_name": "H. Jane", "orcid": "0000-0001-6789-6209", "clpid": "Bae-H-J" }, { "family_name": "Anandkumar", "given_name": "Anima", "orcid": "0000-0002-6974-6797", "clpid": "Anandkumar-Anima" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "div_eng" } ], "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.
", "doi": "10.7907/smnv-tz73", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15195", "collection": "thesis", "collection_id": "15195", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192023-015643241", "primary_object_url": { "basename": "Palmer_Emily_2023_Thesis.pdf", "content": "final", "filesize": 90569338, "license": "other", "mime_type": "application/pdf", "url": "/15195/1/Palmer_Emily_2023_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Locomotory Control Algorithms and Their Neuronal Implementation in Drosophila melanogaster", "author": [ { "family_name": "Palmer", "given_name": "Emily Hope", "orcid": "0009-0006-8370-4709", "clpid": "Palmer-Emily-Hope" } ], "thesis_advisor": [ { "family_name": "Dickinson", "given_name": "Michael H.", "orcid": "0000-0002-8587-9936", "clpid": "Dickinson-M-H" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dickinson", "given_name": "Michael H.", "orcid": "0000-0002-8587-9936", "clpid": "Dickinson-M-H" } ], "local_group": [ { "literal": "div_eng" } ], "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.
", "doi": "10.7907/yyjd-a554", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15079", "collection": "thesis", "collection_id": "15079", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12222022-065507477", "primary_object_url": { "basename": "Tang_Ellande_2023.pdf", "content": "final", "filesize": 128945946, "license": "other", "mime_type": "application/pdf", "url": "/15079/1/Tang_Ellande_2023.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Studies on Off-Nominal Rotor Aerodynamics for eVTOL Aircraft", "author": [ { "family_name": "Tang", "given_name": "Ellande", "orcid": "0000-0001-5933-4716", "clpid": "Tang-Ellande" } ], "thesis_advisor": [ { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "orcid": "0000-0002-3091-540X", "clpid": "Burdick-J-W" }, { "family_name": "Tokumaru", "given_name": "Phil", "clpid": "Tokumaru-P" }, { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "As electric Vertical Takeoff and Landing (eVTOL) aircraft become increasingly common, improved understanding of rotor aerodynamics in off-nominal conditions becomes ever more important. A better fundamental understanding of these effects can help inform vehicle design, leading to lower power consumption and improved performance. This thesis will cover a selection of topics to gain a better understanding of the expected rotor aerodynamics associated with use in this class of vehicle, as well as the development of tools to aid in the studies and an analysis of the impact of the effects.
\r\n\r\nTo consider special effects on a rotor in hover on such a vehicle, Chapter 2 is the study of obstructions in the upstream of a propeller, representing the effects of a wing or fuselage blocking a propeller\u2019s inlet. The next is the effect of forward flight on the forces produced by a rotor. Lifting rotors are often used in eVTOL aircraft as the craft transitions to forward flight, so a study of their performance in forward flight as well as a model are presented in Chapter 3. Having examined rotor-wing interactions in hover and isolated rotor performance in forward flight, the next step is to examine rotor-wing interactions in forward flight. Chapter 6 shows the design of an integrated test stand for studying the aerodynamic interactions between lifting propellers and a wing in low-speed, transitional forward flight, as well as the subsequent results.
\r\n\r\nThis thesis also describes the development and implementation of two tools to aid in the work herein. The first (Chapter 4) is a rapid, low-cost method of extracting the geometry of a propeller using photogrammetry which is subsequently used in simulations. The second (Chapter 5) is low-cost and accessible multi-axis force sensor used in the integrated test stand for propeller-wing interaction studies. To assess the impact of the findings, the experimental results and models developed are then taken into consideration by applying them to models of existing eVTOL aircraft in Chapter 7. The change in modeling of hover and transition performance is studied with and without the additional modeling.
", "doi": "10.7907/eytr-nd50", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14948", "collection": "thesis", "collection_id": "14948", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-033735914", "primary_object_url": { "basename": "Ryan_Yichuan__Song_Caltech_thesis_new_template.pdf", "content": "final", "filesize": 67838358, "license": "other", "mime_type": "application/pdf", "url": "/14948/3/Ryan_Yichuan__Song_Caltech_thesis_new_template.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Rheological Measurements in Moderate Reynolds Number Liquid-Solid Flows", "author": [ { "family_name": "Song", "given_name": "Yichuan", "orcid": "0000-0001-7276-2029", "clpid": "Yichuan-Song" } ], "thesis_advisor": [ { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" } ], "local_group": [ { "literal": "div_eng" } ], "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.
", "doi": "10.7907/5ey8-v324", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14485", "collection": "thesis", "collection_id": "14485", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01252022-055518852", "type": "thesis", "title": "Axial Descent of Multirotor Configurations -- Experimental Studies for Terrestrial and Extraterrestrial Applications", "author": [ { "family_name": "Veismann", "given_name": "Marcel", "orcid": "0000-0001-8106-6738", "clpid": "Veismann-Marcel" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "orcid": "0000-0002-3091-540X", "clpid": "Burdick-J-W" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Axial descent, specifically the vortex ring state (VRS), poses great challenges for rotorcraft operation as this flight stage is typically accompanied by severe aerodynamic losses and excessive vibrational loads due to the re-ingestion of rotor downwash. Given the hazardous nature of this flight stage, its fluid dynamic properties in regards to single, large-scale rotors have been extensively investigated since the early stages of manned helicopter flight. In light of the rapidly expanding use of small-scale multirotor systems, the field of VRS research has recently received increased interest, with a shifted focus towards small-scale rotors, as the thrust generation and stability of these aerial systems have also been shown to be adversely affected by complex descent aerodynamics. While experimental studies have started examining low Reynolds number rotor aerodynamics in steep or vertical descent, the influence of small-scale rotor geometry and aerodynamic coupling between neighboring rotors have not yet been sufficiently explored.
\r\n\r\nThe objective of this work is, therefore, to extend the current understanding of rotorcraft vortex ring state aerodynamics to low Reynolds number multirotor systems. A series of experimental studies employing various wind tunnel setups and flow visualization techniques is presented with the aim of identifying the underlying \ufb02uid-structure interactions, and quantifying rotor performance losses during multirotor axial descent. The work is divided into two fundamental experimental approaches, one utilizing statically mounted rotor systems and one utilizing free-flight testing.
\r\n\r\nThe first part of this work (Chapters 4 and 5) presents the results of wind-tunnel tested statically-mounted rotors for precise aerodynamic identification of rotor performance under simulated descent conditions. Chapter 4 covers a parametric analysis to comprehensively assess the extent to which relevant geometric parameters of a small-scale rotor influence its descent characteristic. Chapter 5 then explores the influence of separation between rotors and identifies potential rotor-rotor interactions in the VRS. The studies in this part of the thesis also make use of PIV setups for visualizing the flow field around small-scale rotors in the axial descent regime, subject to changing geometric parameters and rotor separation.
\r\n\r\nIn the second part (Chapters 6 and 7), a series of free-flight investigations is described for realistically simulated axial descent scenarios. Chapter 6 introduces the methodology for quantifying thrust generation of a multirotor in free-flight without rigid attachment to a load cell, and presents the results of exploratory axial flight studies. Chapter 7 discusses a study on axial descent of variable-pitch multirotor configurations, which was carried out to evaluate the feasibility of deploying a future Mars helicopter in mid air. Findings from this study helped to inform the entry descent and landing (EDL) strategy for JPL's future Martian rotorcraft missions.
", "doi": "10.7907/w49w-qy54", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14636", "collection": "thesis", "collection_id": "14636", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-085410375", "primary_object_url": { "basename": "DoughertyChristopher2022Thesis.pdf", "content": "final", "filesize": 123919426, "license": "other", "mime_type": "application/pdf", "url": "/14636/10/DoughertyChristopher2022Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "On the Experimental Simulation of Atmospheric-Like Disturbances Near the Surface", "author": [ { "family_name": "Dougherty", "given_name": "Christopher John", "orcid": "0000-0002-0974-5696", "clpid": "Dougherty-Christopher-John" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Brown", "given_name": "Garry L.", "clpid": "Brown-Garry-L" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/293w-ev66", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14097", "collection": "thesis", "collection_id": "14097", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03022021-005902351", "type": "thesis", "title": "Resolvent Modeling of Turbulent Jets", "author": [ { "family_name": "Pickering", "given_name": "Ethan Marcus", "orcid": "0000-0002-4485-6359", "clpid": "Pickering-Ethan-Marcus" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Blanquart", "given_name": "Guillaume", "orcid": "0000-0002-5074-9728", "clpid": "Blanquart-G" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Optimal control of turbulent flows requires a detailed prediction of the unsteady, three-dimensional turbulent structures that govern quantities of interest like noise, drag, and mixing efficiency. There is a need for physics-based, reduced-order models of turbulent structure for those cases where direct simulation of the flow would be computationally prohibitive. In this thesis, we explore resolvent analysis as a framework for such models. Based on a linearization about the turbulent mean flow field, the resolvent finds optimal (highest gain) forcing functions that give rise, through linear amplification mechanisms, to energetic coherent structures. The forcing functions represent the nonlinear interactions between the coherent structures as well as with background incoherent turbulence. While the high-gain structures capture many characteristics of the observed turbulent coherent structures in both wall-bounded and free-shear flows, closures for the forcing function are required to make these models predictive and thus utilize them for flow control.
\r\n\r\nIn the first part of this thesis, we examine a linear model for the resolvent forcing by adapting the concept of a turbulent (eddy) viscosity from classical Reynolds-Averaged Navier--Stokes (RANS) turbulence modeling. We present a data-driven approach to identify an optimal eddy-viscosity field that best matches the resolvent prediction to the most energetic coherent structure educed via spectral proper orthogonal decomposition (SPOD) of data from high-fidelity simulations. We analyze the specific case of turbulent jets spanning a range of Mach numbers from subsonic to supersonic. We find the optimal eddy-viscosity field to be effective at matching both the shape and energy distribution of structures. More importantly, we find that calibrated eddy-viscosity fields predicted using standard eddy-viscosity models (utilizing only quantities available from RANS) yield results that are close to optimal.
\r\n\r\nWe use the resulting resolvent model together with the high-fidelity data to investigate the full spectrum of amplification mechanisms and coherent structures present in turbulent jets. The addition of a turbulence model provides a clear separation between two established mechanisms in turbulent jets (Kelvin-Helmholtz and Orr) and leads to the identification of a third mechanism known as lift-up. Lift-up becomes the dominant mechanism at low-frequency limits for nonzero azimuthal wavenumbers, generating elongated, streaky structures. We find these streaks to be the most energetic structures in the jet, and that their presence has implications for altering the mean flow and controlling noise.
\r\n\r\nFinally, we extend resolvent analysis to that of an acoustic analogy that relates the near-field forcing to the far-field acoustics 100 diameters from the nozzle. We again leverage high-fidelity data to produce an ensemble of realizations of the acoustic field and find that only a few resolvent modes are necessary for reconstruction. Ultimately, we find that a resolvent model based solely upon RANS quantities can reconstruct and predict the peak acoustic field at rank-1 to within 2 decibels for both the supersonic and transonic jets.
", "doi": "10.7907/szxb-f168", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:10380", "collection": "thesis", "collection_id": "10380", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08152017-194113650", "primary_object_url": { "basename": "Lin-Caltech-FINAL-APPROVED.pdf", "content": "final", "filesize": 9828967, "license": "other", "mime_type": "application/pdf", "url": "/10380/1/Lin-Caltech-FINAL-APPROVED.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Ultrasound Speckle Image Velocimetry: Studies on System Performance and Application to Cardiovascular Fluid Dynamics", "author": [ { "family_name": "Lin", "given_name": "Ben Albert", "clpid": "Lin-Ben-Albert" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Yang", "given_name": "Changhuei", "orcid": "0000-0001-8791-0354", "clpid": "Yang-Changhuei" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Fraser", "given_name": "Scott E.", "orcid": "0000-0002-5377-0223", "clpid": "Fraser-S-E" } ], "local_group": [ { "literal": "div_bbe" } ], "abstract": "Knowledge of detailed blood flow characteristics can be extremely valuable in a variety of settings. Examples range from studying disease processes such as\r\natherosclerosis to aiding in the design of medical devices such as prosthetic cardiac valves. For in vivo and optically inaccessible in vitro flows, accurate measurements of velocity fields and shear stresses can be difficult to obtain. Doppler ultrasound and magnetic resonance imaging are the most commonly used techniques, but have important limitations. Recently, there has been increased interest in the application of particle image velocimetry principles towards tracking of ultrasound speckle patterns to determine multidimensional flow velocities with increased temporal resolution. We refer to our implementation as ultrasound speckle image velocimetry (USIV). In this research project, our first objective was to obtain a detailed characterization of the factors unique to ultrasound imaging that can influence the accuracy of velocity measurements. By conducting in vitro experiments with uniform speckle phantom translation as well as steady tube flow, we have shown that characteristics such as transducer focal depth and beam sweep speed as well as particle motion direction and velocity can all influence USIV results. Our second objective was to demonstrate the utility of USIV for analyzing in vivo blood flows. After administering ultrasound contrast agent to anesthetized\r\npigs, we were able to obtain detailed images of both left ventricular flow and\r\nabdominal aortic flow. Velocity profiles were measured during both left ventricular filling and ejection. Our most interesting finding was the presence in certain cases of highly asymmetric retrograde flow in the infrarenal aorta. The factors that lead to such flows may have relevance to the development of atherosclerosis and abdominal aneurysms. USIV is likely to be very useful for further studies both in vivo and with in vitro elastic aorta models.", "doi": "10.7907/Z998856J", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11017", "collection": "thesis", "collection_id": "11017", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-104549400", "primary_object_url": { "basename": "Self-repair_and_Sleep_in_Jellyfish.pdf", "content": "final", "filesize": 18533210, "license": "other", "mime_type": "application/pdf", "url": "/11017/1/Self-repair_and_Sleep_in_Jellyfish.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Self-Repair and Sleep in Jellyfish", "author": [ { "family_name": "Abrams", "given_name": "Michael Jacob", "orcid": "0000-0003-1864-1706", "clpid": "Abrams-Michael-Jacob" } ], "thesis_advisor": [ { "family_name": "Goentoro", "given_name": "Lea A.", "orcid": "0000-0002-3904-0195", "clpid": "Goentoro-L-A" } ], "thesis_committee": [ { "family_name": "Hay", "given_name": "Bruce A.", "orcid": "0000-0002-5486-0482", "clpid": "Hay-B-A" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Sternberg", "given_name": "Paul W.", "orcid": "0000-0002-7699-0173", "clpid": "Sternberg-P-W" }, { "family_name": "Goentoro", "given_name": "Lea A.", "orcid": "0000-0002-3904-0195", "clpid": "Goentoro-L-A" } ], "local_group": [ { "literal": "div_bbe" } ], "abstract": "Studying the cnidarian jellyfish, we have pursued basic biological questions related to self-repair mechanisms and sleep behavior. Working in Aurelia we have discovered a novel strategy of self-repair; we determined that they can undergo body reorganization after amputations that culminates in the recovery of essential radial symmetry without rebuilding lost parts. Working with Cassiopea, we have, for the first time, identified a behavioral sleep-like state in an animal without a centralized nervous system, supporting the hypothesis that sleep is ancestral in animals.
", "doi": "10.7907/69br-kb59", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10320", "collection": "thesis", "collection_id": "10320", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-183218154", "type": "thesis", "title": "Hydrodynamics of Insects. Part 1. Jetting of the Dragonfly Larvae. Part 2. Honeybee at the Air-water Interface: Surfing with the Capillary Wave", "author": [ { "family_name": "Roh", "given_name": "Chris", "orcid": "0000-0002-5681-0040", "clpid": "Roh-Chris" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Dickinson", "given_name": "Michael H.", "orcid": "0000-0002-8587-9936", "clpid": "Dickinson-M-H" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/Z97P8WFW", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9347", "collection": "thesis", "collection_id": "9347", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12232015-091951061", "primary_object_url": { "basename": "Thesis_MMW_final.pdf", "content": "final", "filesize": 100602731, "license": "other", "mime_type": "application/pdf", "url": "/9347/1/Thesis_MMW_final.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Fluid Transport by Aggregations of Small Swimming Organisms", "author": [ { "family_name": "Martinez-Ortiz", "given_name": "Monica Paola", "clpid": "Martinez-Ortiz-Monica-Paola" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Zenit Camacho", "given_name": "Jose Roberto", "orcid": "0000-0002-2717-4954", "clpid": "Zenit-Camacho-J-R" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Diel vertical migration of zooplankton has been proposed to affect global ocean circulation to a degree comparable to physical phenomena. Almost a decade after shipboard measurements showed high kinetic energy dissipation rates in the vicinity of migrating krill swarms, the hypothesis that biogenic mixing is relevant to ocean dynamics and local fluid transport has remained controversial due to the inability to directly measure the efficiency of this biological process. In situ field measurements of individual swimming jellyfish have demonstrated large-scale fluid transport via Darwinian drift, but it has remained an open question how this transport mechanism is manifested in smaller species of vertically-migrating zooplankton that are sufficient in number to be accountable in the dynamics. The goals of the present study are, first, to devise and implement experimental instruments and develop methodologies to investigate this biological process in a laboratory setting and, second, to determine whether efficient fluid transport mechanisms become available during vertical collective motion and, if so, analyze how energy is distributed within the flow. By leveraging the phototactic abilities of zooplankton, a multi-laser guidance system was developed to achieve controllable vertical migrations of A. salina concurrently with laser velocimetry of the surrounding flow. Measurements show that the hydrodynamic interactions between neighboring swimmers during vertical migration result in the development of a pronounced jet opposite to animal motion. In non-stratified fluid, this hydrodynamic feature is shown to trigger a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the individual size of the organisms. Experiments in a thermally stratified water column also display the presence of a downward jet despite the strong stable stratification. Furthermore, overturning regions larger than the size of an individual organism are observed adjacent to the migrating aggregation, suggesting an alternate energy transfer route from the small scale of individual swimmers to significantly larger scales, at which mixing can be efficient via a Rayleigh-Taylor instability. The computed velocity spectrum is consistent with these findings and displays energy input at scales larger than the body length of a single swimmer. The mixing efficiency, inferred from the spectral energy distribution with and without stratification, matches experimentally achieved mixing efficiencies via a Rayleigh-Taylor instability within a stable stratification. According to our findings, biogenic mixing does have the potential to redistribute temperature, salinity and nutrients effectively. We propose the employment of laser control to examine additional species as well as alternative oceanic environments and interrogate its effect on the efficiency of biogenic mixing.\r\n", "doi": "10.7907/Z9057CX7", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9796", "collection": "thesis", "collection_id": "9796", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-150613633", "primary_object_url": { "basename": "Hsieh-Chen_Tsai_thesis_2016_final.pdf", "content": "final", "filesize": 13168932, "license": "other", "mime_type": "application/pdf", "url": "/9796/1/Hsieh-Chen_Tsai_thesis_2016_final.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Numerical Investigation of Vertical-Axis Wind Turbines at Low Reynolds Number", "author": [ { "family_name": "Tsai", "given_name": "Hsieh-Chen", "clpid": "Tsai-Hsieh-Chen" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Blanquart", "given_name": "Guillaume", "orcid": "0000-0002-5074-9728", "clpid": "Blanquart-G" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis is aimed at numerically investigating the aerodynamics and the starting of a vertical-axis wind turbine at low Reynolds number using the immersed boundary method. The influence of the Coriolis effect on dynamic stall is isolated by comparing the rotating airfoil to one undergoing an equivalent planar motion that is composed of surging and pitching motions that produce an equivalent speed and angle of attack variation over a cycle. At lower tip-speed ratios, the Coriolis force leads to the capture of a vortex pair which results in a significant decrease in lift when the angle of attack of a rotating airfoil begins to decrease in the upwind half cycle. In the absence of the wake-capturing, the equivalent planar motion is a good approximation to a rotating blade in a vertical-axis wind turbine.
\r\n\r\nAnalysis on the starting torque shows that when the turbine solidity is lower than about 0.5, the starting torque distribution can be well-modeled by considering a single blade at different orientations, and starting torque distributions for multi-bladed turbines can be constructed by linearly combining the torques at the respective positions of the blades. Using this model, optimal configurations to start a multi-bladed low-solidity vertical-axis wind turbine is proposed.
\r\n\r\nA preliminary study is made to determine an optimal blade pitch for a single-bladed motor-driven turbine using optimal control theory. When the input power is minimized directly, the solution seems to converge to only a local minimum due to a lower input power reduction than that obtained by maximizing the mean tangential force. After a transient, both controls converge to time-invariant pitch angles of about the same magnitude but with opposite signs. The wake-capturing phenomenon observed in the uncontrolled case necessitates large input power. Under active control, the disappearance of wake-capturing and attendant changes in the flow field collectively result in a reduction of required input power.
", "doi": "10.7907/Z9SF2T5R", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9303", "collection": "thesis", "collection_id": "9303", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12022015-023535926", "primary_object_url": { "basename": "DBA_PhDthesis_final.pdf", "content": "", "filesize": 27987407, "license": "other", "mime_type": "application/pdf", "url": "/9303/1/DBA_PhDthesis_final.pdf", "version": "v1.0.0" }, "type": "thesis", "title": "Aerodynamics of Vertical-Axis Wind Turbines in Full-Scale and Laboratory-Scale Experiments", "author": [ { "family_name": "Araya", "given_name": "Daniel Borsodi", "clpid": "Araya-Daniel-Borsodi" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/Z9VD6WC2 ", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9303", "collection": "thesis", "collection_id": "9303", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12022015-023535926", "primary_object_url": { "basename": "DBA_PhDthesis_final.pdf", "content": "", "filesize": 27987407, "license": "other", "mime_type": "application/pdf", "url": "/9303/1/DBA_PhDthesis_final.pdf", "version": "v1.0.0" }, "type": "thesis", "title": "Aerodynamics of Vertical-Axis Wind Turbines in Full-Scale and Laboratory-Scale Experiments", "author": [ { "family_name": "Araya", "given_name": "Daniel Borsodi", "clpid": "Araya-Daniel-Borsodi" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/Z9VD6WC2 ", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9140", "collection": "thesis", "collection_id": "9140", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09042015-152813860", "type": "thesis", "title": "Dynamic Stall on Vertical Axis Wind Turbines", "author": [ { "family_name": "Dunne", "given_name": "Reeve", "clpid": "Dunne-Reeve" } ], "thesis_advisor": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this study the dynamics of flow over the blades of vertical axis wind turbines was investigated using a simplified periodic motion to uncover the fundamental flow physics and provide insight into the design of more efficient turbines. Time-resolved, two-dimensional velocity measurements were made with particle image velocimetry on a wing undergoing pitching and surging motion to mimic the flow on a turbine blade in a non-rotating frame. Dynamic stall prior to maximum angle of attack and a leading edge vortex development were identified in the phase-averaged flow field and captured by a simple model with five modes, including the first two harmonics of the pitch/surge frequency identified using the dynamic mode decomposition. Analysis of these modes identified vortical structures corresponding to both frequencies that led the separation and reattachment processes, while their phase relationship determined the evolution of the flow.
\r\n\r\nDetailed analysis of the leading edge vortex found multiple regimes of vortex development coupled to the time-varying flow field on the airfoil. The vortex was shown to grow on the airfoil for four convection times, before shedding and causing dynamic stall in agreement with 'optimal' vortex formation theory. Vortex shedding from the trailing edge was identified from instantaneous velocity fields prior to separation. This shedding was found to be in agreement with classical Strouhal frequency scaling and was removed by phase averaging, which indicates that it is not exactly coupled to the phase of the airfoil motion.
\r\n\r\nThe flow field over an airfoil undergoing solely pitch motion was shown to develop similarly to the pitch/surge motion; however, flow separation took place earlier, corresponding to the earlier formation of the leading edge vortex. A similar reduced-order model to the pitch/surge case was developed, with similar vortical structures leading separation and reattachment; however, the relative phase lead of the separation mode, corresponding to earlier separation, necessitated that a third frequency to be incorporated into the reattachment mode to provide a relative lag in reattachment.
\r\n\r\nFinally, the results are returned to the rotating frame and the effects of each flow phenomena on the turbine are estimated, suggesting kinematic criteria for the design of improved turbines.
", "doi": "10.7907/Z92Z13FX", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8508", "collection": "thesis", "collection_id": "8508", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06092014-120248372", "primary_object_url": { "basename": "Final_Thesis_Yu Zhao_2014_Submit_06102014.pdf", "content": "final", "filesize": 10633193, "license": "other", "mime_type": "application/pdf", "url": "/8508/1/Final_Thesis_Yu Zhao_2014_Submit_06102014.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Flexible Microimplants for In Vivo Sensing", "author": [ { "family_name": "Zhao", "given_name": "Yu", "clpid": "Zhao-Yu" } ], "thesis_advisor": [ { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" } ], "thesis_committee": [ { "family_name": "Choo", "given_name": "Hyuck", "clpid": "Choo-Hyuck" }, { "family_name": "Hsiai", "given_name": "Tzung", "clpid": "Hsiai-Tzung" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The work in this thesis develops two types of microimplants for the application of cardiovascular in vivo biomedical sensing, one for short-term diagnosis and the other for long-term monitoring.
\r\n\r\nDespite advances in diagnosis and therapy, atherosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in the Western world. Predicting metabolically active atherosclerotic plaques has remained an unmet clinical need. A stretchable impedance sensor manifested as a pair of quasi-concentric microelectrodes was developed to detect unstable intravascular. By integrating the impedance sensor with a cardiac catheter, high-resolution Electrochemical Impedance Spectroscopy (EIS) measurements can be conducted during cardiac catheterization. An inflatable silicone balloon is added to the sensor to secure a well-controlled contact with the plaque under test in vivo. By deploying the device to the explants of NZW rabbit aorta and live animals, distinct EIS measurements were observed for unstable atherosclerotic plaques that harbored active lipids and inflammatory cells.
\r\n\r\nOn the other hand, zebrafish (Danio rerio) is an emerging genetic model for heart regenerative medicine. In humans, myocardial infarction results in the irreversible loss of cardiomyocytes. Zebrafish hearts can fully regenerate after two months with 20% ventricular resection. Long-term electrocardiogram (ECG) recording can characterize the heart regeneration in a functional dimension. A flexible microelectrode membrane was developed to be percutaneously implanted onto a zebrafish heart and record epicardial ECG signals from specific regions on it. Region-specific aberrant cardiac signals were obtained from injured and regenerated hearts. Following that, in order to achieve continuous and wireless recording from non-sedated and non-restricted small animal models, a wireless ECG recording system was designed for the microelectrode membrane, prototyped on a printed circuit board and demonstrated on a one-day-old neonatal mouse. Furthermore, a flexible and compact parylene C printed circuit membrane was used as the integration platform for the wireless ECG recording electronics. A substantially miniature wireless ECG recording system was achieved.
", "doi": "10.7907/SHYA-5Y51", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:8401", "collection": "thesis", "collection_id": "8401", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272014-160129404", "primary_object_url": { "basename": "JCosse2014Thesis.pdf", "content": "final", "filesize": 17750294, "license": "other", "mime_type": "application/pdf", "url": "/8401/1/JCosse2014Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "On the Behavior of Pliable Plate Dynamics in Wind: Application to Vertical Axis Wind Turbines", "author": [ { "family_name": "Coss\u00e9", "given_name": "Julia Theresa", "clpid": "Coss\u00e9-Julia-Theresa" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Sader", "given_name": "John E.", "orcid": "0000-0002-7096-0627", "clpid": "Sader-J-E" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/X7S3-CS74", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:7665", "collection": "thesis", "collection_id": "7665", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05032013-161632237", "type": "thesis", "title": "A Dynamical Systems Analysis of Vortex Pinch-Off", "author": [ { "family_name": "O'Farrell", "given_name": "Clara", "clpid": "O'Farrell-Clara" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" }, { "family_name": "Doyle", "given_name": "John Comstock", "orcid": "0000-0002-1828-2486", "clpid": "Doyle-J-C" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/AFAA-KF43", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7338", "collection": "thesis", "collection_id": "7338", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12172012-143708325", "type": "thesis", "title": "Conceptual Framework and Physical Implementation of a Systematic Design Strategy for Tissue-Engineered Devices", "author": [ { "family_name": "Nawroth", "given_name": "Janna C.", "clpid": "Nawroth-Janna-C" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Hay", "given_name": "Bruce A.", "clpid": "Hay-B-A" }, { "family_name": "Sternberg", "given_name": "Paul W.", "clpid": "Sternberg-P-W" }, { "family_name": "Fraser", "given_name": "Scott E.", "clpid": "Fraser-S-E" } ], "local_group": [ { "literal": "div_biol" } ], "abstract": "Tissue-engineered and biologically inspired devices promise to advance medical implants, robotic devices and diagnostic tools. Ideally, biohybrid constructs combine the versatility and fine control of traditional building substrates with dynamic properties of living tissues including sensory modalities and mechanisms of repair, plasticity and self-organization. These dynamic properties also complicate the design process as they arise from, and act upon, structure-function relationships across multiple spatiotemporal scales that need to be recapitulated in the engineered tissue. Biomimetic designs merely copying the structure of native organs and organisms, however, are likely to reflect evolutionary constraints, phenotypic variability and environmental factors rather than rendering optimal engineering solutions.
\r\n\r\nThis thesis describes an alternative to biomimetic design, i.e., a systematic approach to tissue engineering based on mechanistic analysis and a focus on functional, not structural, approximation of native and engineered system. As proof of concept, the design, fabrication and evaluation of a tissue-engineered jellyfish medusa with biomimetic propulsion and feeding currents is presented with an emphasis on reasoning and strategy of the iterative design process. A range of experimental and modeling approaches accomplishes mechanistic analysis at multiple scales, control of individual and emergent cell behavior, and quantitative testing of functional performance. The main achievement of this thesis lies in presenting both conceptual framework and physical implementation of a systematic design strategy for muscular pumps and other bioinspired and tissue-engineered applications.
", "doi": "10.7907/5ZTQ-2J09", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7166", "collection": "thesis", "collection_id": "7166", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06252012-171451630", "primary_object_url": { "basename": "Thesis_Wendian.pdf", "content": "final", "filesize": 9564483, "license": "other", "mime_type": "application/pdf", "url": "/7166/1/Thesis_Wendian.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Blood Cell Count On-a-Chip", "author": [ { "family_name": "Shi", "given_name": "Wendian (Leo)", "clpid": "Shi-Wendian-Leo" } ], "thesis_advisor": [ { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" } ], "thesis_committee": [ { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" }, { "family_name": "Choo", "given_name": "Hyuck", "clpid": "Choo-Hyuck" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "White blood cell (WBC) count is one of the most frequently ordered clinical tests in hospitals. There are five types of WBCs in the circulating blood, including lymphocyte, monocyte, neutrophil, eosinophil and basophil. The WBC count test enumerates not only the total number of WBCs in per volume blood, but also the percentage of each WBC type. A portable instrument for the WBC count test is currently in demand by the NASA human spaceflight, and also by the on-earth telemedicine application. However, the commercially available tests do not meet the requirement of the portable applications, because of their large instrument size and the large reagent volume consumed per test.
\r\n\r\nThis study describes the development of a WBC count technology optimized for portable applications. First, a sheathless microfluidic cytometer is developed for WBC count. This technology consumes only a small amount of blood (5 microlitre) and a minimal volume of reagents (50 microlitre). Second, fluorescent dye assays are developed for the WBC differential count by measuring fluorescent emissions on the microfluidic cytometer. Based on this technology, a portable instrument is built with high test accuracy (maximum error less than 10%).
\r\n \r\nFurthermore, this study explores two key components for future integrating this technology into a self-contained chip. First, a microvalve actuated by thermal blood clogging is developed. This valve has a simple structure suitable for on-chip integration. Second, a micromixer is used to demonstrate the staining of blood with dye assays, and the following fluorescent detection of WBCs on the cytometer.
\r\n", "doi": "10.7907/6YF1-WR04", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7747", "collection": "thesis", "collection_id": "7747", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05232013-150116734", "primary_object_url": { "basename": "Hesham_Azizgolshani_Thesis.pdf", "content": "final", "filesize": 15952345, "license": "other", "mime_type": "application/pdf", "url": "/7747/1/Hesham_Azizgolshani_Thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Tissue Engineering Active Biological Machines: Bio-Inspired Design, Directed Self-Assembly, and Characterization of Muscular Pumps Simulating the Embryonic Heart", "author": [ { "family_name": "Azizgolshani", "given_name": "Hesham", "clpid": "Azizgolshani-Hesham" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Fraser", "given_name": "Scott E.", "orcid": "0000-0002-5377-0223", "clpid": "Fraser-S-E" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Biological machines are active devices that are comprised of cells and other biological components. These functional devices are best suited for physiological environments that support cellular function and survival. Biological machines have the potential to revolutionize the engineering of biomedical devices intended for implantation, where the human body can provide the required physiological environment. For engineering such cell-based machines, bio-inspired design can serve as a guiding platform as it provides functionally proven designs that are attainable by living cells. In the present work, a systematic approach was used to tissue engineer one such machine by exclusively using biological building blocks and by employing a bio-inspired design. Valveless impedance pumps were constructed based on the working principles of the embryonic vertebrate heart and by using cells and tissue derived from rats. The function of these tissue-engineered muscular pumps was characterized by exploring their spatiotemporal and flow behavior in order to better understand the capabilities and limitations of cells when used as the engines of biological machines.", "doi": "10.7907/2C8T-TB84", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7757", "collection": "thesis", "collection_id": "7757", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282013-114822808", "primary_object_url": { "basename": "thesisMain.pdf", "content": "final", "filesize": 25807880, "license": "other", "mime_type": "application/pdf", "url": "/7757/1/thesisMain.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Dynamics and Scaling of Self-Excited Passive Vortex Generators for Underwater Propulsion", "author": [ { "family_name": "Whittlesey", "given_name": "Robert Wells", "clpid": "Whittlesey-Robert-Wells" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/SC4M-8896", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7817", "collection": "thesis", "collection_id": "7817", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012013-192515668", "primary_object_url": { "basename": "Aria_thesis_2013.pdf", "content": "final", "filesize": 25006301, "license": "other", "mime_type": "application/pdf", "url": "/7817/1/Aria_thesis_2013.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Control of Wettability of Carbon Nanotube Array by Reversible Dry Oxidation for Superhydrophobic Coating and Supercapacitor Applications", "author": [ { "family_name": "Aria", "given_name": "Adrianus Indrat", "clpid": "Aria-Adrianus-Indrat" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Heath", "given_name": "James R.", "orcid": "0000-0001-5356-4385", "clpid": "Heath-J-R" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/B6MF-FX89", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:6636", "collection": "thesis", "collection_id": "6636", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08312011-003358925", "type": "thesis", "title": "Axel Rover Tethered Dynamics and Motion Planning on Extreme Planetary Terrain", "author": [ { "family_name": "Abad-Manterola", "given_name": "Pablo", "clpid": "Abad-Manterola-Pablo" } ], "thesis_advisor": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" } ], "thesis_committee": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Hunt", "given_name": "Melany L.", "clpid": "Hunt-M-L" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Nesnas", "given_name": "Issa A.", "clpid": "Nesnas-I-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Some of the most appealing science targets for future exploration missions in our solar system lie in terrains that are inaccessible to state-of-the-art robotic rovers such as NASA's Opportunity, thereby precluding in situ analysis of these rich opportunities. Examples of potential high-yield science areas on Mars include young gullies on sloped terrains, exposed layers of bedrock in the Victoria Crater, sources of methane gas near Martian volcanic ranges, and stepped delta formations in heavily cratered regions. In addition, a recently discovered cryovolcano on Titan and frozen water near the south pole of our own Moon could provide a wealth of knowledge to any robotic explorer capable of accessing these regions.
\r\n\r\nTo address the challenge of extreme terrain exploration, this dissertation presents the Axel rover, a two-wheeled tethered robot capable of rappelling down steep slopes and traversing rocky terrain. Axel is part of a family of reconfigurable rovers, which, when docked, form a four-wheeled vehicle nicknamed DuAxel. DuAxel provides untethered mobility to regions of extreme terrain and serves as an anchor support for a single Axel when it undocks and rappels into low-ground.
\r\n\r\nAxel's performance on extreme terrain is primarily governed by three key system components: wheel design, tether control, and intelligent planning around obstacles. Investigations in wheel design and optimizing for extreme terrain resulted in the development of grouser wheels. Experiments demonstrated that these grouser wheels were very effective at surmounting obstacles, climbing rocks up to 90% of the wheel diameter. Terramechanics models supported by experiments showed that these wheels would not sink excessively or become trapped in deformable terrain.
\r\n\r\nPredicting tether forces in different configurations is also essential to the rover's mobility. Providing power, communication, and mobility forces, the tether is Axel's lifeline while it rappels steep slopes, and a cut, abraded, or ruptured tether would result in an untimely end to the rover's mission. Understanding tether forces are therefore paramount, and this thesis both models and measures tension forces to predict and avoid high-stress scenarios.
\r\n\r\nFinally, incorporating autonomy into Axel is a unique challenge due to the complications that arise during tether management. Without intelligent planning, rappelling systems can easily become entangled around obstacles and suffer catastrophic failures. This motivates the development of a novel tethered planning algorithm, presented in this thesis, which is unique for rappelling systems.
\r\n\r\nRecent field experiments in natural extreme terrains on Earth demonstrate the Axel rover's potential as a candidate for future space operations. Both DuAxel and its rappelling counterpart are rigorously tested on a 20 meter escarpment and in the Arizona desert. Through analysis and experiments, this thesis provides the framework for a new generation of robotic explorers capable of accessing extreme planetary regions and potentially providing clues for life beyond Earth.
", "doi": "10.7907/MPHD-PC75", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:7037", "collection": "thesis", "collection_id": "7037", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05162012-131336010", "primary_object_url": { "basename": "Boettcher_P_A.pdf", "content": "final", "filesize": 627165112, "license": "other", "mime_type": "application/pdf", "url": "/7037/1/Boettcher_P_A.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Thermal Ignition", "author": [ { "family_name": "Boettcher", "given_name": "Philipp Andreas", "clpid": "Boettcher-Philipp-Andreas" } ], "thesis_advisor": [ { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" } ], "thesis_committee": [ { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Blanquart", "given_name": "Guillaume", "orcid": "0000-0002-5074-9728", "clpid": "Blanquart-G" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "Explosion Dynamics Laboratory" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/H2W9-ZK95", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6450", "collection": "thesis", "collection_id": "6450", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-111659863", "primary_object_url": { "basename": "Meier_Thesis2011_Final.pdf", "content": "final", "filesize": 3809795, "license": "other", "mime_type": "application/pdf", "url": "/6450/1/Meier_Thesis2011_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Novel Experimental Study of a Valveless Impedance Pump for Applications at Lab-On-Chip, Microfluidic, and Biomedical Device Size Scales", "author": [ { "family_name": "Meier", "given_name": "John Allen", "clpid": "Meier-John-Allen" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In 1954, Gerhart Liebau demonstrated a simple valveless pumping phenomenon utilizing the periodic compression of a compliant tube and some systematic asymmetry to pump water out of a bucket. Liebau's goal was to explain peculiarities seen in the human circulatory system. In the years that have followed, the Liebau phenomenon has been studied in a variety of open and closed loop configurations, through experimental, computational, and analytical studies.
\r\n\r\nRecent advances in microfluidic and microelectromechanical systems (MEMS) technology have enabled a wide range of small scale engineering systems. The further development of many important systems is limited by the absence of an appropriate means of fluid transport. Valveless pumps based on the Liebau phenomenon show great promise, particularly in lab-on-chip (LOC), biological, and medical applications in which biocompatibility and the ability to move sensitive molecules without damage are key design requirements.
\r\n\r\nThe purpose of this thesis is to synthesize previous studies of the Liebau phenomenon and produce the first extensive experimental study of a novel valveless pump at size scales and geometries that are relevant to lab-on-chip, microfluidic, and biomedical device applications. For the first time, detailed, dynamic pressure and flow data have been recorded during the operation of these valveless pumps for a large range of operating parameters. This dynamic data allowed us to identify new flow regimes and observe previously undocumented pump behaviors and performance. Parameters investigated include pump material properties and geometry, working fluid density and viscosity, pump excitation properties (amplitude, offset, location, and frequency), and flow loop/system properties. A critical relationship between the relative volumetric compliance of the valveless pump to the system it acts upon is identified, and the implications for practical implementation of valveless pumps at small size scales are discussed.
", "doi": "10.7907/DBKG-EJ21", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:5886", "collection": "thesis", "collection_id": "5886", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-150032204", "primary_object_url": { "basename": "jjk_thesis_final.pdf", "content": "final", "filesize": 2429194, "license": "other", "mime_type": "application/pdf", "url": "/5886/1/jjk_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Numerical Simulation of Wave Focusing and Scattering in Shock Wave Lithotripsy", "author": [ { "family_name": "Krimmel", "given_name": "Jeffrey James", "clpid": "Krimmel-Jeffrey-James" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Brennen", "given_name": "Christopher E.", "clpid": "Brennen-C-E" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this work we simulate shock wave focusing and scattering that occurs during shock wave lithotripsy, a noninvasive medical treatment for kidney stone disease. Shock waves are generated outside the body of the patient and are focused at the kidney stone with the intention of pulverizing the stone while it remains inside the patient. The patient can then ostensibly pass the debris naturally. We use a multidimensional second-order method of the Godunov type with slope limiters and shock capturing capability to solve the inviscid Euler equations. Because we begin with the fundamental statements of conservation of mass, momentum, and energy, we simulate all the relevant acoustics occurring during a typical treatment.
\r\n\r\nLithotripters, the machines that generate and focus shock waves, can be classified according to the mechanism of shock generation. In this work, we simulate three different types of lithotripters: electrohydraulic, piezoelectric, and electromagnetic. We choose one representative of each lithotripter type: the Dornier HM3, a research piezoelectric lithotripter array, and the XX-Es, respectively. We first study a model of the in vitro setting for each lithotripter, where shock waves are generated and focus in a bath of pure water. Next, we introduce different heterogeneous materials near the focus of the lithotripter to model the effect of the body of an actual patient, i.e., the in vivo condition. We use two approaches in this modeling effort. One approach is to use simple geometrical models for the body cavity and kidney that we created ourselves. The other approach is to import real anatomical data made available from the VOXEL-MAN Group.
\r\n\r\nIn studying the focal region acoustics, we specifically examine the maximum calculated pressures. These pressures represent the forces that will ultimately cause the kidney stone to break. We also study the pulse intensity integral, i.e., the energy density carried by the focusing shock wave. In addition to these pressures and energy densities, we are interested in investigating how soft tissue in the focal region may potentially be damaged by the resulting wavefields. We isolate two mechanisms that are thought to be important in soft tissue injury: shearing and cavitation. We calculate estimates for the maximum principal normal and shear strains in the focal region in addition to the corresponding strain rates and use these as metrics for the potential for damage via shearing. We study the calculated negative pressure fields in this region as a surrogate for potential damage caused by cavitation.
\r\n\r\nWe find that our simple geometrical anatomical models cause little deviation from the acoustics observed in a water bath. However, when the real anatomical data of the VOXEL-MAN Group is used, the fields of the various relevant flow quantities become more highly oscillatory and produce secondary extrema that could produce damage not predicted from the water bath case. In addition to the conclusions from our own work, we discuss how our results motivate future studies that will hopefully help elucidate specific mechanisms by which kidney stones break and soft tissue becomes damaged.
", "doi": "10.7907/XWED-RZ95", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5927", "collection": "thesis", "collection_id": "5927", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-114858790", "primary_object_url": { "basename": "thesis_Daegyoum_Kim.pdf", "content": "final", "filesize": 10569763, "license": "other", "mime_type": "application/pdf", "url": "/5927/1/thesis_Daegyoum_Kim.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Characteristics of Three-dimensional Vortex Formation and Propulsive Performance in Flapping Locomotion", "author": [ { "family_name": "Kim", "given_name": "Daegyoum", "clpid": "Kim-Daegyoum" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/8VZJ-7Z78", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5838", "collection": "thesis", "collection_id": "5838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252010-172302796", "primary_object_url": { "basename": "thesis_kakani_2010_1.pdf", "content": "final", "filesize": 8795768, "license": "other", "mime_type": "application/pdf", "url": "/5838/1/thesis_kakani_2010_1.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Effect of In Situ Animal-Fluid Interactions on Transport and Mixing", "author": [ { "family_name": "Young", "given_name": "Kakani Katija", "clpid": "Young-Kakani-Katija" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Traditional studies of animal-fluid interactions have led to the understanding of factors that affect the distribution, ecology and energetics of swimming organisms. These interactions are commonly investigated by using quantitative flow measurement techniques, which include digital particle image velocimetry. Due to limitations in quantitative flow measurements in the natural environment, animal measurements are conducted in laboratories. Laboratory measurement techniques have been shown to have an altering impact on animal behavior and resulting flow fields. Hence, it is reasonable to question conclusions made about the impact of background flows in the natural environment from measurements conducted in the laboratory. Therefore, an apparatus that will enable the quantitative measurement of flows surrounding a swimming animal in the field is needed to accurately address the effect of background flows on animal swimming and fluid transport.
\r\n\r\nWe describe the development of a self-contained underwater velocimetry apparatus that achieves the goal of real-time, quantitative field measurements of aquatic animal-fluid interactions. Using this apparatus, we obtain measurements of flow fields surrounding animals in the field and analyze the effect of background flows on swimming animals. Using a dynamical systems technique called Lagrangian coherent structures to quantitatively compare laboratory and field-generated flows, we find that background flow structures alter fluid transport by swimming jellyfish. From these studies, we define a biologically-relevant metric for animal feeding that is based entirely on the volume of fluid that interacts with the swimming animal. The ability to quantify background flows and their influence on animal-fluid interactions will allow us to broaden our concept of animal-fluid interactions to include the effects swimming animals have on their surrounding environment. This represents a paradigm shift in the analysis of animal-fluid interactions.
\r\n\r\nRecent studies have provided heated debate about whether biologically-generated (or biogenic) mixing can have an impact in the ocean. Arguments for biogenic mixing lacked an efficient mechanism for fluid transport in viscous and stratified flow environments. We present an effective mechanism for biogenic mixing called drift, which is active during swimming, and results in permanent displacement of fluid in the direction of the animal's motion (in unstratified flow). We show that unlike mechanisms that rely on turbulent mixing generated by wake structures, drift is enhanced as viscous effects are increased. While drift has been observed in jellyfish and copepods, to understand its relevance in the global ocean, the effects of stratification need to be considered. By conducting simulations of moving bodies in stratified flow, we show that at buoyancy frequencies on the order of the mean ocean, fluid transport due to drift remains a powerful mechanism through which swimming animals may provide a significant contribution to mixing in the oceans.
", "doi": "10.7907/QJAM-9228", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5857", "collection": "thesis", "collection_id": "5857", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-122004587", "primary_object_url": { "basename": "Full_Thesis.pdf", "content": "final", "filesize": 38221978, "license": "other", "mime_type": "application/pdf", "url": "/5857/1/Full_Thesis.pdf", "version": "v9.0.0" }, "type": "thesis", "title": "The Role of Unsteady Hydrodynamics in the Propulsive Performance of a Self-Propelled Bioinspired Vehicle", "author": [ { "family_name": "Ruiz", "given_name": "Lydia Ann", "clpid": "Ruiz-Lydia-Ann" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Aquatic animals differ from typical engineering systems in their method of locomotion. In general, aquatic animals propel using unsteady dynamics producing vortex rings. Researchers have long shown interest in designing devices that resemble their shape and propulsive behavior. Traditional definitions of propulsive efficiency used to model these behaviors have not taken unsteady effects into account and are typically based on steady flow through propellers or rocket motors. Measurements of aquatic animals based on these quasi-steady metrics have suggested propulsive efficiencies over 80% when utilizing certain swimming kinematics. However, the mechanical efficiency of muscle-actuated biological propulsion has been found to be much lower, typically less than 20%. It is important to take into account the total efficiency of the system, the product of the mechanical and propulsive efficiency, when designing and implementing a biologically inspired propulsive device.
\r\n\r\nThe purpose of my research is to make a direct, experimental comparison between biological and engineering propulsion systems. For this study, I designed an underwater vehicle that has the capability of producing either a steady or unsteady jet for propulsion, akin to a squid and jellyfish, while utilizing the same mechanical efficiency. I show that it is unnecessary to take an approach that mimics animal shape and kinematics to achieve the associated propulsive performance. A bioinspired, propeller-based platform that mimics animal wake dynamics can be similarly effective.
\r\n\r\nA study on how vortex dynamics plays a key role in improving the propulsive efficiency of pulsed jet propulsion was conducted. Measurements of propulsive performance resulted in superior performance for the pulsed-jet configuration in comparison to the steady jet configuration particularly at higher motor speeds. The analysis demonstrated that vortex ring formation led to the acceleration of two classes of ambient fluid, entrained and added mass, and this consequently led to an increased total fluid impulse of the jet and propulsive performance. The first source of ambient fluid acceleration investigated was entrained mass. The magnitude of the entrainment ratio was measured and found to be smaller for the steady jet mode of propulsion in comparison to the pulsed jet mode of propulsion given comparable motor speeds. The role of the added mass effect was also investigated in increasing propulsive performance. A model developed by Krueger is used to determine the fraction of the total impulse imparted to the flow that was contributed by the added mass effect. Results demonstrated that the added mass effect associated with the acceleration of ambient fluid at the initiation of a starting jet provides an increase in the total impulse and is thus a source for increased propulsive performance. Last, a model was developed to investigate how an increase in the total fluid impulse due to vortex ring formation is related to the propulsive efficiency. Results obtained using the model are in agreement, within uncertainty, with previous experimental results for the measurement of propulsive efficiency. The results support that the additional force generated from the acceleration of two classes of ambient fluid are the source of increased propulsive efficiency for the pulsed jet configuration in comparison to the steady jet configuration. This model serves as an additional metric for determining the propulsive efficiency of a system utilizing pulsed jet propulsion.
\r\n", "doi": "10.7907/7JWD-TB88", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5886", "collection": "thesis", "collection_id": "5886", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-150032204", "primary_object_url": { "basename": "jjk_thesis_final.pdf", "content": "final", "filesize": 2429194, "license": "other", "mime_type": "application/pdf", "url": "/5886/1/jjk_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Numerical Simulation of Wave Focusing and Scattering in Shock Wave Lithotripsy", "author": [ { "family_name": "Krimmel", "given_name": "Jeffrey James", "clpid": "Krimmel-Jeffrey-James" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Brennen", "given_name": "Christopher E.", "clpid": "Brennen-C-E" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this work we simulate shock wave focusing and scattering that occurs during shock wave lithotripsy, a noninvasive medical treatment for kidney stone disease. Shock waves are generated outside the body of the patient and are focused at the kidney stone with the intention of pulverizing the stone while it remains inside the patient. The patient can then ostensibly pass the debris naturally. We use a multidimensional second-order method of the Godunov type with slope limiters and shock capturing capability to solve the inviscid Euler equations. Because we begin with the fundamental statements of conservation of mass, momentum, and energy, we simulate all the relevant acoustics occurring during a typical treatment.
\r\n\r\nLithotripters, the machines that generate and focus shock waves, can be classified according to the mechanism of shock generation. In this work, we simulate three different types of lithotripters: electrohydraulic, piezoelectric, and electromagnetic. We choose one representative of each lithotripter type: the Dornier HM3, a research piezoelectric lithotripter array, and the XX-Es, respectively. We first study a model of the in vitro setting for each lithotripter, where shock waves are generated and focus in a bath of pure water. Next, we introduce different heterogeneous materials near the focus of the lithotripter to model the effect of the body of an actual patient, i.e., the in vivo condition. We use two approaches in this modeling effort. One approach is to use simple geometrical models for the body cavity and kidney that we created ourselves. The other approach is to import real anatomical data made available from the VOXEL-MAN Group.
\r\n\r\nIn studying the focal region acoustics, we specifically examine the maximum calculated pressures. These pressures represent the forces that will ultimately cause the kidney stone to break. We also study the pulse intensity integral, i.e., the energy density carried by the focusing shock wave. In addition to these pressures and energy densities, we are interested in investigating how soft tissue in the focal region may potentially be damaged by the resulting wavefields. We isolate two mechanisms that are thought to be important in soft tissue injury: shearing and cavitation. We calculate estimates for the maximum principal normal and shear strains in the focal region in addition to the corresponding strain rates and use these as metrics for the potential for damage via shearing. We study the calculated negative pressure fields in this region as a surrogate for potential damage caused by cavitation.
\r\n\r\nWe find that our simple geometrical anatomical models cause little deviation from the acoustics observed in a water bath. However, when the real anatomical data of the VOXEL-MAN Group is used, the fields of the various relevant flow quantities become more highly oscillatory and produce secondary extrema that could produce damage not predicted from the water bath case. In addition to the conclusions from our own work, we discuss how our results motivate future studies that will hopefully help elucidate specific mechanisms by which kidney stones break and soft tissue becomes damaged.
", "doi": "10.7907/XWED-RZ95", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:2962", "collection": "thesis", "collection_id": "2962", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07212009-132708", "primary_object_url": { "basename": "main.pdf", "content": "final", "filesize": 8401537, "license": "other", "mime_type": "application/pdf", "url": "/2962/1/main.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Lagrangian Approach to Transport of Momentum and Biomass in Aquatic Biological Systems", "author": [ { "family_name": "Peng", "given_name": "Jifeng", "clpid": "Peng-Jifeng" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Troian", "given_name": "Sandra M.", "orcid": "0000-0003-1224-6377", "clpid": "Troian-S-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In recent years, a Lagrangian Coherent Structures (LCS) method was developed to identify boundaries between distinct kinematic regions in unsteady flows. Many fluid transport processes can be described in terms of these kinematic boundaries in the flow. The method has since been applied to many engineering, biological, and geological fluid systems, but primarily on transport of homogenous fluid mass.
\r\n\r\nIn this thesis, with emphases on aquatic biological transport systems, the LCS analysis is further developed to study momentum transport in animal locomotion and biomass transport in animal predation. Three independent studies are included in this thesis.
\r\n\r\nIn the first study, LCS analysis is used to identify the boundary of the vortex attached to the fin in sunfish pectoral fin locomotion. A potential flow, deformable body theory is used to describe the dynamics of the vortex. The hydrodynamic forces acting on the fin are evaluated from the linear momentum of the vortex itself and its added-mass. The quantification of instantaneous locomotive forces provides necessary information for studying complicated locomotive behaviors such as motion control and maneuvers.
\r\n\r\nIn the second study, the LCS analysis is applied to a numerically simulated undulatory swimming and shows existence of 'upstream fluid structures' that are invisible in Eulerian velocity/vorticity fields. These structures indicate the exact portion of fluid that interacts with the swimmer. A mass flow rate and a momentum flux are then defined. A metric for propulsive efficiency is established using the momentum flux, which can be used to measure and compare the efficiency of other engineering and natural propulsion systems.
\r\n\r\nIn the third study, a framework is developed to study transport of zooplankton prey in the feeding currents generated by a predator jellyfish. An equation of motion is proposed to describe the dynamics of prey in the flow. Then the concept of particle Lagrangian Coherent Structures (pLCS) is introduced to separate prey encounter regions from prey escape regions. The framework provides a mechanical basis for evaluating the predatory role of medusae in marine planktonic ecosystems. It can also be used to study transport and mixing in multiphase and granular flows in general.
\r\n", "doi": "10.7907/3XEF-X568", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5293", "collection": "thesis", "collection_id": "5293", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10072009-165901284", "primary_object_url": { "basename": "philipdutoit_thesis.pdf", "content": "final", "filesize": 47249560, "license": "other", "mime_type": "application/pdf", "url": "/5293/19/philipdutoit_thesis.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Transport and Separatrices in Time-Dependent Flows", "author": [ { "family_name": "Du Toit", "given_name": "Philip Christopher", "clpid": "Du-Toit-Philip-Christopher" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The method of using Finite Time Liapunov Exponents (FTLE) to extract Lagrangian Coherent Structures (LCS) in aperiodic flows, as originally developed by Haller, is applied to geophysical flows, and flows in the phase space of second order dynamical systems. In this approach, the LCS are identified as surfaces of greatest separation that parse the flow into regions with different dynamical behavior. In this way, the LCS reveal the underlying skeleton of turbulence. The time-dependence of the LCS provides insight into the mechanisms by which fluid is transported from one region to another. Of especial interest in this study, is the utility with which the FTLE-LCS method can be used to reveal homoclinic and horseshoe dynamics in aperiodic flows.
\r\n\r\nThe FTLE-LCS method is applied to turbulent flow in hurricanes and reveals LCS that delineate sharp boundaries to a storm. Moreover, intersections of the LCS define lobes that mediate transport into and out of a storm through the action of homoclinic lobe dynamics. Using FTLE-LCS, the same homoclinic structures are seen to be a dominant transport mechanism in the Global Ocean, and provide insights into the role of mesoscale eddies in enhancing lateral mixing.
\r\n\r\nBeyond geophysical flows, we also study transport in the phase space of a coupled oscillator model for biomolecules. Before we can analyze transport in this model, we first introduce an appropriate model reduction that captures the relevant statistics of the full system. In the reduced model, we see that transport is again mediated by the process of horseshoe dynamics in a perturbed homoclinic tangle.
\r\n\r\nWe also consider some theoretical aspects of FTLE-LCS, including the relationship between LCS and stable/unstable manifolds, the invariance of LCS, and the possibility of an evolution equation describing the motion of the LCS. A parallelized software for computing FTLE is also introduced.
", "doi": "10.7907/X0Y5-N133", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5300", "collection": "thesis", "collection_id": "5300", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10162009-053129363", "primary_object_url": { "basename": "thesis_mikeliu.pdf", "content": "final", "filesize": 14346681, "license": "other", "mime_type": "application/pdf", "url": "/5300/1/thesis_mikeliu.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Integrated Microfluidic Devices for Cell Culture and Assay", "author": [ { "family_name": "Liu", "given_name": "Mike Chia-Chung", "clpid": "Liu-Mike-Chia-Chung" } ], "thesis_advisor": [ { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" } ], "thesis_committee": [ { "family_name": "Tai", "given_name": "Yu-Chong", "clpid": "Tai-Yu-Chong" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Yang", "given_name": "Changhuei", "clpid": "Yang-Changhuei" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis presents the development of three-dimensional (3-D) microfluidic devices for cellular studies, with focus on applications for high-throughput cell culture and cell-based assay. Microfluidic devices provide potential inexpensive platforms for high-throughput screening with the advantages of precise liquid handling, ability to control cell culture microenvironment, and reduced reagents and cells.
\r\n \r\nBecause a mixture of drugs or chemical compounds can often treat diseases more effectively or act synergistically in certain cellular pathways, a device capable of screening the combinatorial effects of multiple compound exposures on cells is highly desirable. To this end, a novel method to monolithically fabricate 3-D microfluidic networks was developed, and based on this fabrication technology, the first cell culture device with an integrated combinatorial mixer was constructed. The proof-of-concept chip having a three-input combinatorial mixer and eight individually isolated micro culture chambers was fabricated on silicon utilizing the surface micromachining of Parylene C (poly(chloro-p-xylylene)). Unlike other 3-D microfluidic fabrications, multilayer bonding process was favorably obviated. By incorporating several microfluidic overpass structures to allow one microfluidic channel to cross over other microfluidic channels, the combinatorial mixer generated all the combinations of the input fluidic streams. Cell culturing on-chip was successful, and the ability to simultaneously treat arrays of cells with different combinations of compounds was demonstrated.
\r\n\r\nTo facilitate cell-based assay, another combinatorial cell array device was fabricated on glass with incorporated membrane. Characterization of the combined compound concentration profile at each chamber with a fluorescence method was developed. We demonstrated functionality of the quantitative cell-based assay by screening three different compounds\u2019 ability to reduce cytotoxicity of hydrogen peroxide on neuron cells and also assaying combinatorial exposures of three chemotherapeutic agents on breast cancer cells. The 3-D microfluidic fabrication process was extended to construct multilayer microfluidic device with integrated membrane. Applications of microfluidic devices for marine microbiology were demonstrated. Based on the capabilities demonstrated in this work, devices with high-density cell array and integrated high-input combinatorial mixer can be constructed. At the same time, the technology has general applicability for building complex 3-D microfluidic devices, which can broaden the applications for current lab-on-a-chip systems.
\r\n", "doi": "10.7907/D43B-D825", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5343", "collection": "thesis", "collection_id": "5343", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11012009-234712901", "primary_object_url": { "basename": "McDowell_Thesis_Final.pdf", "content": "final", "filesize": 54950750, "license": "other", "mime_type": "application/pdf", "url": "/5343/1/McDowell_Thesis_Final.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Low Optical Signal Detection in Biological Materials: SNR Considerations and Novel Techniques", "author": [ { "family_name": "McDowell", "given_name": "Emily Jayne", "clpid": "McDowell-Emily-Jayne" } ], "thesis_advisor": [ { "family_name": "Yang", "given_name": "Changhuei", "orcid": "0000-0001-8791-0354", "clpid": "Yang-Changhuei" } ], "thesis_committee": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Yang", "given_name": "Changhuei", "orcid": "0000-0001-8791-0354", "clpid": "Yang-Changhuei" }, { "family_name": "Fraser", "given_name": "Scott E.", "orcid": "0000-0002-5377-0223", "clpid": "Fraser-S-E" }, { "family_name": "Phillips", "given_name": "Robert B.", "orcid": "0000-0003-3082-2809", "clpid": "Phillips-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Light scattering poses significant challenges for biomedical optical imaging techniques. Diffuse scattering scrambles wavefront information, confounding easy analysis of signals reflected from or transmitted through biological tissues. For optical imaging techniques that employ only unscattered light components, the penetration depth is severely limited. In this thesis, we develop and discuss two general methods for dealing with large levels of light scattering in tissue. The first involves optimization of the signal-to-noise ratio (SNR) of coherence domain optical tomography techniques. The majority of the signal measured in these techniques is singly scattered. Thus, an improvement in SNR will improve the penetration depth of the system by picking out the weak signal contribution from increasing depths that would otherwise be buried in noise. We show that the SNR can be optimized in terms of image reconstruction algorithms, and in terms of detection parameters. An important detection parameter, the integration time, determines the dominant noise source of the measurement, and can be varied to obtain the maximal SNR. A second general method that will be discussed involves the time-reversal of scattered light components in tissues through the process of optical phase conjugation (OPC). OPC has long been used to remove optical aberrations and distortions, but has never before been applied to light scattering in tissues. We show that we are capable of time reversing light scattering in both chicken tissue sections and tissue phantoms, and characterize both the amplitude and resolution trends of the process. Finally, we provide the first successful results of OPC in living tissues.", "doi": "10.7907/7Q7B-1E27", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5838", "collection": "thesis", "collection_id": "5838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252010-172302796", "primary_object_url": { "basename": "thesis_kakani_2010_1.pdf", "content": "final", "filesize": 8795768, "license": "other", "mime_type": "application/pdf", "url": "/5838/1/thesis_kakani_2010_1.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Effect of In Situ Animal-Fluid Interactions on Transport and Mixing", "author": [ { "family_name": "Young", "given_name": "Kakani Katija", "clpid": "Young-Kakani-Katija" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Traditional studies of animal-fluid interactions have led to the understanding of factors that affect the distribution, ecology and energetics of swimming organisms. These interactions are commonly investigated by using quantitative flow measurement techniques, which include digital particle image velocimetry. Due to limitations in quantitative flow measurements in the natural environment, animal measurements are conducted in laboratories. Laboratory measurement techniques have been shown to have an altering impact on animal behavior and resulting flow fields. Hence, it is reasonable to question conclusions made about the impact of background flows in the natural environment from measurements conducted in the laboratory. Therefore, an apparatus that will enable the quantitative measurement of flows surrounding a swimming animal in the field is needed to accurately address the effect of background flows on animal swimming and fluid transport.
\r\n\r\nWe describe the development of a self-contained underwater velocimetry apparatus that achieves the goal of real-time, quantitative field measurements of aquatic animal-fluid interactions. Using this apparatus, we obtain measurements of flow fields surrounding animals in the field and analyze the effect of background flows on swimming animals. Using a dynamical systems technique called Lagrangian coherent structures to quantitatively compare laboratory and field-generated flows, we find that background flow structures alter fluid transport by swimming jellyfish. From these studies, we define a biologically-relevant metric for animal feeding that is based entirely on the volume of fluid that interacts with the swimming animal. The ability to quantify background flows and their influence on animal-fluid interactions will allow us to broaden our concept of animal-fluid interactions to include the effects swimming animals have on their surrounding environment. This represents a paradigm shift in the analysis of animal-fluid interactions.
\r\n\r\nRecent studies have provided heated debate about whether biologically-generated (or biogenic) mixing can have an impact in the ocean. Arguments for biogenic mixing lacked an efficient mechanism for fluid transport in viscous and stratified flow environments. We present an effective mechanism for biogenic mixing called drift, which is active during swimming, and results in permanent displacement of fluid in the direction of the animal's motion (in unstratified flow). We show that unlike mechanisms that rely on turbulent mixing generated by wake structures, drift is enhanced as viscous effects are increased. While drift has been observed in jellyfish and copepods, to understand its relevance in the global ocean, the effects of stratification need to be considered. By conducting simulations of moving bodies in stratified flow, we show that at buoyancy frequencies on the order of the mean ocean, fluid transport due to drift remains a powerful mechanism through which swimming animals may provide a significant contribution to mixing in the oceans.
", "doi": "10.7907/QJAM-9228", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:2225", "collection": "thesis", "collection_id": "2225", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05282009-215548", "primary_object_url": { "basename": "GCard_Thesis-revised.pdf", "content": "final", "filesize": 41193781, "license": "other", "mime_type": "application/pdf", "url": "/2225/1/GCard_Thesis-revised.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Neural Control and Biomechanics of Flight Initiation in Drosophila melanogaster", "author": [ { "family_name": "Card", "given_name": "Gwyneth Megan", "orcid": "0000-0002-7679-3639", "clpid": "Card-Gwyneth-Megan" } ], "thesis_advisor": [ { "family_name": "Dickinson", "given_name": "Michael H.", "clpid": "Dickinson-M-H" } ], "thesis_committee": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Konishi", "given_name": "Masakazu", "clpid": "Konishi-M" }, { "family_name": "Dickinson", "given_name": "Michael H.", "clpid": "Dickinson-M-H" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In response to abrupt visual stimulation, the fruit fly, Drosophila melanogaster, quickly initiates flight. This rapid takeoff is believed to be a reflex coordinated by a pair of large descending interneurons (the \"giant fibers\"). However, it has been difficult to evoke escapes in wild-type flies, and thus flight initiation behavior in the unrestrained wild-type fly is poorly described. I have taken advantage of recent advances in high-speed videography to capture video sequences of Drosophila flight initiation at the temporal resolution of 6,000 frames per second. A three-dimensional kinematic analysis of takeoff sequences indicates that wing use during the jumping phase of flight initiation is essential for stabilizing flight. During voluntary takeoffs, flies raise their wings prior to leaving the ground, resulting in a stable, controlled takeoff. In contrast, during visually-elicited escapes flies pull their wings down close to their body during the takeoff jump, resulting in tumbling flights that are faster but less steady. The takeoff kinematics suggest that the power delivered by the legs is substantially greater during these escapes than during voluntary takeoffs. Thus, I show that the two types of Drosophila flight initiation result in different flight performances once the fly is airborne, and that these performances are distinguished by a trade-off between speed and stability. I also determined that flies can use visual information to plan a jump directly away from a looming threat. This is surprising, given the simple architecture of the giant fiber pathway thought to mediate escape. I found that approximately 200 ms before takeoff, flies begin a series of postural adjustments that determine the direction of their escape. These movements position their center of mass so that leg extension will push them away from the looming stimulus. These preflight movements are not the result of a simple feed-forward motor program because their magnitude and direction depend on the flies' initial postural state. Furthermore, flies plan a takeoff direction even in instances when they choose not to jump. This sophisticated motor program is evidence for a form of rapid, visually mediated motor planning in a genetically accessible model organism.\r\n", "doi": "10.7907/PR7S-Y618", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:5221", "collection": "thesis", "collection_id": "5221", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06022009-183247", "primary_object_url": { "basename": "Thesis_Franck.pdf", "content": "final", "filesize": 3520640, "license": "other", "mime_type": "application/pdf", "url": "/5221/1/Thesis_Franck.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Large-Eddy Simulation of Flow Separation and Control on a Wall-Mounted Hump", "author": [ { "family_name": "Franck", "given_name": "Jennifer Ann", "clpid": "Franck-Jennifer-Ann" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Active flow control techniques such as synthetic jets have been successful in increasing the performance of naturally separating flows on post-stall airfoils, bluff body shedding, and internal flows such as wide-angle diffusers. However, in order to implement robust control techniques there is a need for accurate computational tools capable of predicting unsteady separation and control at high Reynolds numbers. This thesis developed a compressible large-eddy simulation (LES) and validated it by simulating the turbulent flow over a wall-mounted hump. The flow is characterized by an unsteady, turbulent recirculation region along the trailing edge of the geometry, and is simulated at a Reynolds number of 500,000. Active flow control is applied just before the natural separation point via steady suction and zero-net mass flux oscillatory forcing. The addition of control is shown to be effective in decreasing the size of the separation bubble and pressure drag. LES baseline and controlled results are validated against previously performed experiments by Seifert and Pack and those performed for the NASA Langley Workshop on Turbulent Flow Separation and Control. Three test cases are explored to determine the effect of explicit filtering and the Smagorinsky subgrid scale model on the average flow and turbulent statistics. The flow physics and the control effectiveness are investigated at two Mach numbers, M=0.25 and M=0.6. Compressibility is shown to increase the separation bubble length in the baseline case, but does not significantly change the effectiveness of the control. In terms of decreasing drag on the wall-mounted hump model, steady suction is more effective than oscillatory control, but both control techniques are effective in reducing the separation bubble length. Two-dimensional direct numerical simulations (DNS) of the wall-mounted hump flow are also presented, and the results show different baseline flow features than the 3D LES. However the controlled 2D flow gives an indication of the most receptive actuation frequencies around twice that of the natural shedding frequency. Two regimes of reduced actuation frequency are also explored with the 3D LES. It is found that the low frequency actuation is successful in reducing the separation bubble length, but high frequency actuation produces an average flow comparable to the baseline case, and does not result in drag or separation bubble length reduction.\r\n", "doi": "10.7907/DH38-D592", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:5215", "collection": "thesis", "collection_id": "5215", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-115810", "primary_object_url": { "basename": "Rinderknecht_thesis.pdf", "content": "final", "filesize": 26701577, "license": "other", "mime_type": "application/pdf", "url": "/5215/16/Rinderknecht_thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Development of a Microimpedance Pump for Pulsatile Flow Transport - Part 1: Flow Characteristics of the Microimpedance Pump. Part 2: A Systematic Study of Steady and Pulsatile Transport in Microscale Cavities", "author": [ { "family_name": "Rinderknecht", "given_name": "Derek Gresham", "orcid": "0000-0001-6387-8433", "clpid": "Rinderknecht-Derek- Gresham" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Microfluidics offers an effective means to carry out a wide range of transport processes within a controlled microenvironment by drawing on the benefits imparted by increasing surface area to volume ratio at the microscale. Critical to the impact of microfluidics on integrated devices in the fields of bioengineering and biomedicine is the ability to transport fluids and biomolecules effectively particularly at the size scales involved. In this context a bio-inspired pumping mechanism, the valveless impedance pump, was explored for applications in microfluidics ranging from micro total analysis systems to microchannel cooling. Adhering to the basic principles of the impedance pump mechanism, pumps have been constructed at a variety of size scales from a few centimeters to a few hundred microns. The micro impedance pump is valveless, bidirectional, and can be constructed simply from a wide range of materials. Depending on the size of the pump flow rates range from nL/min to mL/min and pressures can be generated that exceed 20 kPa. Another benefit of the impedance pump is the pulsatile flow output which can be used in the context of microfluidic applications to enhance transport at low Reynolds numbers as well as metering in drug delivery.
\r\n\r\nPulsatile flow was therefore investigated as a method of augmenting transport in microfluidic systems. Micro PIV was used to study the affect of both steady and pulsatile flows on transport at low Reynolds number was examined in microscale rectangular cavities. Ventilation of the cavity contents was examined in terms of the residence time or average time a particle remains in the cavity region. Lagrangian coherent structures (LCS) were applied to empirical velocity fields to determine the impact of unsteadiness on time dependent boundaries to fluid transport present in the flow. Experimental results show that there are both frequencies which are beneficial and detrimental to cavity ventilation as well as certain frequencies which more evenly distribute particles originating in the cavity throughout the freestream.
\r\n", "doi": "10.7907/0K4J-0548", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:1990", "collection": "thesis", "collection_id": "1990", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05232008-124342", "primary_object_url": { "basename": "Taira_thesis.pdf", "content": "final", "filesize": 7582318, "license": "other", "mime_type": "application/pdf", "url": "/1990/3/Taira_thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Immersed Boundary Projection Method and Its Application to Simulation and Control of Flows Around Low-Aspect-Ratio Wings", "author": [ { "family_name": "Taira", "given_name": "Kunihiko (Sam)", "orcid": "0000-0002-3762-8075", "clpid": "Taira-Kunihiko-Sam" } ], "thesis_advisor": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "thesis_committee": [ { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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.
", "doi": "10.7907/VSDD-P465", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:5215", "collection": "thesis", "collection_id": "5215", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-115810", "primary_object_url": { "basename": "Rinderknecht_thesis.pdf", "content": "final", "filesize": 26701577, "license": "other", "mime_type": "application/pdf", "url": "/5215/16/Rinderknecht_thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Development of a Microimpedance Pump for Pulsatile Flow Transport - Part 1: Flow Characteristics of the Microimpedance Pump. Part 2: A Systematic Study of Steady and Pulsatile Transport in Microscale Cavities", "author": [ { "family_name": "Rinderknecht", "given_name": "Derek Gresham", "orcid": "0000-0001-6387-8433", "clpid": "Rinderknecht-Derek- Gresham" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Microfluidics offers an effective means to carry out a wide range of transport processes within a controlled microenvironment by drawing on the benefits imparted by increasing surface area to volume ratio at the microscale. Critical to the impact of microfluidics on integrated devices in the fields of bioengineering and biomedicine is the ability to transport fluids and biomolecules effectively particularly at the size scales involved. In this context a bio-inspired pumping mechanism, the valveless impedance pump, was explored for applications in microfluidics ranging from micro total analysis systems to microchannel cooling. Adhering to the basic principles of the impedance pump mechanism, pumps have been constructed at a variety of size scales from a few centimeters to a few hundred microns. The micro impedance pump is valveless, bidirectional, and can be constructed simply from a wide range of materials. Depending on the size of the pump flow rates range from nL/min to mL/min and pressures can be generated that exceed 20 kPa. Another benefit of the impedance pump is the pulsatile flow output which can be used in the context of microfluidic applications to enhance transport at low Reynolds numbers as well as metering in drug delivery.
\r\n\r\nPulsatile flow was therefore investigated as a method of augmenting transport in microfluidic systems. Micro PIV was used to study the affect of both steady and pulsatile flows on transport at low Reynolds number was examined in microscale rectangular cavities. Ventilation of the cavity contents was examined in terms of the residence time or average time a particle remains in the cavity region. Lagrangian coherent structures (LCS) were applied to empirical velocity fields to determine the impact of unsteadiness on time dependent boundaries to fluid transport present in the flow. Experimental results show that there are both frequencies which are beneficial and detrimental to cavity ventilation as well as certain frequencies which more evenly distribute particles originating in the cavity throughout the freestream.
\r\n", "doi": "10.7907/0K4J-0548", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:65", "collection": "thesis", "collection_id": "65", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-103832", "primary_object_url": { "basename": "L.Loumes-Thesis-All.pdf", "content": "final", "filesize": 4871165, "license": "other", "mime_type": "application/pdf", "url": "/65/12/L.Loumes-Thesis-All.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Multilayer Impedance Pump: A Bio-Inspired Valveless Pump with Medical Applications", "author": [ { "family_name": "Loumes", "given_name": "Laurence", "clpid": "Loumes-Laurence" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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", "doi": "10.7907/MT2J-AR81", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:3761", "collection": "thesis", "collection_id": "3761", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09252006-134742", "primary_object_url": { "basename": "FinalThesis.pdf", "content": "final", "filesize": 84036185, "license": "other", "mime_type": "application/pdf", "url": "/3761/1/FinalThesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Exploration into the Feasibility of Underwater Synthetic Jet Propulsion", "author": [ { "family_name": "Polsenberg Thomas", "given_name": "AnnMarie", "clpid": "Polsenberg-Thomas-AnnMarie" } ], "thesis_advisor": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" } ], "thesis_committee": [ { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Dabiri", "given_name": "John O.", "clpid": "Dabiri-J-O" }, { "family_name": "Brennen", "given_name": "Christopher E.", "clpid": "Brennen-C-E" }, { "family_name": "Antonsson", "given_name": "Erik K.", "clpid": "Antonsson-E-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis explores the feasibility of using synthetic jet actuators for the propulsion of small underwater vehicles. This work was inspired by the widespread use of pusatile jet propulsion by sea creatures such as squid, salp, and jellyfish. The jets created by these animals utilize vortex rings for thrust production. A method for creating similar vortex ring-based jets is the use of synthetic, or zero net mass flux, jets. These jets, which form a jet structure through the alternating sucking and blowing of fluid through a single orifice, have previously been investigated for the utility in air flow control.
\r\n\r\nThe design, construction, and testing of aquatic synthetic jet prototypes is presented. Force measurement and flow visualization experiments are performed on these jets to gain an understanding of the forces and flow structures produced. The flow visualizations confirm the outflow vortex ring observations reported previously in the literature and present the first images of vortex ring formation inside the synthetic jet chamber. A new phenomenon, that of self-induced coflow upstream of the jet orifice, is discussed. The force measurements present confirmation that a net thrust is produced by the jets and give insight to the relationship between jet forcing parameters (such as frequency) and the resulting thrust. An automated genetic algorithmic approach to optimizing the thrust for a given jet geometry is also presented and tested.
\r\n\r\nUsing the results of these experiments I propose a model for synthetic jet thrust. This model asserts that there are three force producing components to the flow: orifice inflow, orifice outflow, and a self-induced coflow. The contribution of each of these components is derived and compared with experimental results.
\r\n\r\nIncluded at the end of this thesis is a preliminary study into possible vehicle architecture for the utilization of synthetic jet thrusters.
", "doi": "10.7907/72SZ-T823", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:65", "collection": "thesis", "collection_id": "65", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-103832", "primary_object_url": { "basename": "L.Loumes-Thesis-All.pdf", "content": "final", "filesize": 4871165, "license": "other", "mime_type": "application/pdf", "url": "/65/12/L.Loumes-Thesis-All.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Multilayer Impedance Pump: A Bio-Inspired Valveless Pump with Medical Applications", "author": [ { "family_name": "Loumes", "given_name": "Laurence", "clpid": "Loumes-Laurence" } ], "thesis_advisor": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" } ], "thesis_committee": [ { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "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", "doi": "10.7907/MT2J-AR81", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:1755", "collection": "thesis", "collection_id": "1755", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05122006-083011", "primary_object_url": { "basename": "Shadden06.pdf", "content": "final", "filesize": 16601102, "license": "other", "mime_type": "application/pdf", "url": "/1755/1/Shadden06.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "A Dynamical Systems Approach to Unsteady Systems", "author": [ { "family_name": "Shadden", "given_name": "Shawn Christopher", "orcid": "0000-0001-7561-1568", "clpid": "Shadden-Shawn-Christopher" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Owhadi", "given_name": "Houman", "orcid": "0000-0002-5677-1600", "clpid": "Owhadi-H" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "For steady systems, interpreting the flow structure is typically straightforward because streamlines and trajectories coincide. Therefore the velocity field, or quantities derived from it, provide a clear description of the flow geometry. For unsteady flows, this is often not the case. A more natural choice is to understand the flow in terms of particle trajectories, i.e., the Lagrangian viewpoint. While the chaotic behavior of trajectories of unsteady systems makes direct interpretation difficult, more structured and frame-independent techniques have been developed. The method presented here uses finite-time Lyapunov exponent (FTLE) fields to locate Lagrangian Coherent Structures (LCS). LCS are co-dimension 1 separatrices that partition regions in phase space with dynamically different behavior. This method enables the detection of often non-obvious, time-dependent boundaries in complicated flows, which greatly elucidates the transport and mixing geometry.
\r\n\r\nThe first portion of this thesis deals with the theoretical development of LCS for two-, and then, n-dimensional systems, where n>2. Based on the definitions presented, some important properties of these structures are proven. It is shown that the flux across an LCS is typically very small and depends on the relative strength of the structure, the difference between the local rotation rate of the LCS with that of the Eulerian velocity field, and the integration time used to compute the FTLE field.
\r\n\r\nThe second portion of the thesis presents a series of numerical studies in which LCS are used to examine a range of interesting applications. This portion is bridged with the theoretical development presented in the first half by a brief chapter describing the numerical computation of FTLE fields and LCS. Applications presented in the second half of the thesis include the study of vortex rings in which LCS are used to define the unsteady vortex boundary to clarify the entrainment and detrainment processes; the computation of LCS in the ocean to provide mesoscale separatrices that help characterize the flow conditions and help navigate gliders or drifters used for sampling; flow over an airfoil where an LCS captures the unsteady separation profile; flow through a micro-mixing channel where LCS reveal the mechanism and geometry of chaotic mixing.
\r\n", "doi": "10.7907/BG86-YB12", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:1755", "collection": "thesis", "collection_id": "1755", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05122006-083011", "primary_object_url": { "basename": "Shadden06.pdf", "content": "final", "filesize": 16601102, "license": "other", "mime_type": "application/pdf", "url": "/1755/1/Shadden06.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "A Dynamical Systems Approach to Unsteady Systems", "author": [ { "family_name": "Shadden", "given_name": "Shawn Christopher", "orcid": "0000-0001-7561-1568", "clpid": "Shadden-Shawn-Christopher" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Owhadi", "given_name": "Houman", "orcid": "0000-0002-5677-1600", "clpid": "Owhadi-H" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "For steady systems, interpreting the flow structure is typically straightforward because streamlines and trajectories coincide. Therefore the velocity field, or quantities derived from it, provide a clear description of the flow geometry. For unsteady flows, this is often not the case. A more natural choice is to understand the flow in terms of particle trajectories, i.e., the Lagrangian viewpoint. While the chaotic behavior of trajectories of unsteady systems makes direct interpretation difficult, more structured and frame-independent techniques have been developed. The method presented here uses finite-time Lyapunov exponent (FTLE) fields to locate Lagrangian Coherent Structures (LCS). LCS are co-dimension 1 separatrices that partition regions in phase space with dynamically different behavior. This method enables the detection of often non-obvious, time-dependent boundaries in complicated flows, which greatly elucidates the transport and mixing geometry.
\r\n\r\nThe first portion of this thesis deals with the theoretical development of LCS for two-, and then, n-dimensional systems, where n>2. Based on the definitions presented, some important properties of these structures are proven. It is shown that the flux across an LCS is typically very small and depends on the relative strength of the structure, the difference between the local rotation rate of the LCS with that of the Eulerian velocity field, and the integration time used to compute the FTLE field.
\r\n\r\nThe second portion of the thesis presents a series of numerical studies in which LCS are used to examine a range of interesting applications. This portion is bridged with the theoretical development presented in the first half by a brief chapter describing the numerical computation of FTLE fields and LCS. Applications presented in the second half of the thesis include the study of vortex rings in which LCS are used to define the unsteady vortex boundary to clarify the entrainment and detrainment processes; the computation of LCS in the ocean to provide mesoscale separatrices that help characterize the flow conditions and help navigate gliders or drifters used for sampling; flow over an airfoil where an LCS captures the unsteady separation profile; flow through a micro-mixing channel where LCS reveal the mechanism and geometry of chaotic mixing.
\r\n", "doi": "10.7907/BG86-YB12", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" } ]