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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 15:58:10 +0000Stress-Strain Characteristics of Cohesionless Granular Materials Subjected to Statically Applied Homogeneous Loads in an Open System
https://resolver.caltech.edu/CaltechETD:etd-03242003-102726
Authors: {'items': [{'id': 'Bell-James-Melvin', 'name': {'family': 'Bell', 'given': 'James Melvin'}, 'show_email': 'NO'}]}
Year: 1965
DOI: 10.7907/066B-HV20
A general stress-strain relationship in incremental and invariant form is derived for sand on the basis of experimental evidence. The resulting expression does not include the yield condition but makes allowance for the direction of loading and the state of stress. Two new modified and dimensionless invariant functions are introduced and a detailed description and classification of stress paths presented. A new first yield criterion for sand stressed to yield along one stress path is developed from experimental evidence. The friction angle in triaxial compression was minimum and 14[degrees] less than that in triaxial extension. The Mohr-Coulomb yield criterion extended to three dimensions is rejected.
Emphasis is placed on the importance of obtaining homogeneous stress in physical experiments. A new spherical compression apparatus was developed to study the behavior of sand under spherical compression. Disadvantages of former apparatuses were largely overcome by elimination of frictional loading, and a homogeneous state of stress was obtained. A new stress controlled three-dimensional compression apparatus capable of applying principal stresses to a rectangular, plate sample was developed to study the behavior of sand under a general stress state, particularly under deviatoric stress. This apparatus provided for the independent measurement of volumetric strain and allowed for the development of considerable deformation in obtaining yield.https://thesis.library.caltech.edu/id/eprint/1084Shear Flows of Granular Materials
https://resolver.caltech.edu/CaltechETD:etd-11242003-104837
Authors: {'items': [{'email': 'campbell@usc.edu', 'id': 'Campbell-Charles-Soutter', 'name': {'family': 'Campbell', 'given': 'Charles Soutter'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/QZSF-E358
<p>Many of the macroscopic and microscopic features of shearing granular materials were observed during the course of this investigation.</p>
<p>The principal results were obtained from a computer simulation of the flows in an inclined chute, and in a Couette shear cell. The simulation followed the exact trajectories of two-dimensional discs through a control volume. Properties of the flow were obtained from temporal averages of the instantaneous particle properties. Macroscopic flow characteristics such as velocity and density profiles are presented. Because the simulation follows the exact mechanics of the particles it was also possible to investigate the statistical nature of granular flows. Towards this purpose velocity distributions, collision angle distributions and pair correlation functions were measured.</p>
<p>The results of the simulation draw a picture of a flowing granular material as a self-excited gas. There appears to be a "temperature" associated with the random motions of the particles, that is a product of gradients in the mean velocity field. An equation of state is proposed, involving this temperature, to describe the behavior of the density within the flow. A phenomenon reminscent of conduction is observed. The particle velocities appear to obey a Maxwellian distribution based on this temperature.</p>
<p>Preliminary experiments were also performed to investigate the flow of glass beads down inclined chutes. It is shown that the flows may be classified as either supercritical or subcritical depending on the local value of the Froude number, and that the classification had a strong influence on the flow properties. In addition, wall friction coefficients were determined.</p>https://thesis.library.caltech.edu/id/eprint/4649Experimental Observations of the Effect of Foundation Embedment on Structural Response
https://resolver.caltech.edu/CaltechTHESIS:05162018-100416743
Authors: {'items': [{'id': 'Lin-Albert-Niu', 'name': {'family': 'Lin', 'given': 'Albert Niu'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/ksr8-pf30
<p>Ambient, ring-down, and forced vibration tests were used to determine the effect of foundation embedment on the response of a one-story model structure 10 ft square in plan and 11.4 ft high. The tests, conducted at the full-, half- and unembedded foundation conditions, led to the identification of the fundamental translatory mode in the primary (east-west) and secondary (north-south) directions, and two torsional modes. The forced vibration consisted of horizontally incident SH-waves generated at an excitation structure located 47.5 ft (center-to-center) away. During these tests, detailed measurements of the near-field ground motion and modal displacement ratios were obtained at the fundamental mode in the primary direction. The displacement ratios were used to calculate the structural and foundation-soil stiffnesses and damping coefficients for comparison to theoretical results. Foundation embedment increased the model frequencies and decreased the contribution of the foundation motion to the overall displacement of the superstructure. For the fundamental mode response, which consisted of translatory and rocking motions, the resonant frequency predicted by lumped parameter analysis was higher than that measured experimentally by 25% for the unembedded case. While the experimental and theoretical fundamental mode shapes were in close agreement, the calculated effect of embedment on the response was less than that measured. These results were consistent with the comparison of the impedances and embedment factors. Serious discrepancies between analytical and experimental results were found for the case of torsion; a simple two-degree-of-freedom model was consistent only with the first of the two measured resonant frequencies.</p>https://thesis.library.caltech.edu/id/eprint/10896Dynamic Centrifuge Testing of Cantilever Retaining Walls
https://resolver.caltech.edu/CaltechETD:etd-12132006-104119
Authors: {'items': [{'id': 'Ortiz-Louis-Alexander', 'name': {'family': 'Ortiz', 'given': 'Louis Alexander'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/vep9-1127
<p>An investigation was made into the behavior of flexible cantilever walls retaining a cohesionless soil backfill and subjected to earthquake-type dynamic excitations using the centrifuge modelling technique. The study was motivated by the abundant observations of earth retaining structure damage and failures documented in earthquake damage reports.</p>
<p>The "prototype" typical walls were designed using the traditional Mononobe-Okabe dynamic lateral earth pressure theory, were properly scaled for use in the centrifuge at 50 g's and were subjected to lateral earthquake-like motions which were considered to be of realistic levels. The walls were amply instrumented with pressure and displacement transducers, accelerometers, and strain gages. Moment, pressure, shear, and displacement distributions (static, dynamic, and residual) were obtained.</p>
<p>From the test data, some empirical curves for relating the upper bound responses of the retaining walls to the strong motion characteristics of the applied earthquakes were obtained.</p>https://thesis.library.caltech.edu/id/eprint/4982Dynamic Analyses of Fluid-Structure Systems
https://resolver.caltech.edu/CaltechTHESIS:01252019-143659174
Authors: {'items': [{'id': 'Rashed-Ahmed-Atef', 'name': {'family': 'Rashed', 'given': 'Ahmed Atef'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/1yc0-fm70
<p>Theoretical investigations of the dynamic behavior of some important fluid-structure systems are conducted to seek a better understanding of: 1) the hydrodynamic pressures generated in the fluid as a result of both the rigid body and the vibrational motions of the structure, and 2) the effects of the fluid on the dynamic properties of the structure as well as on its response to earthquake ground motions.</p>
<p>Explicit formulas are presented for the hydrodynamic pressures generated in fluid domains having boundaries which can be approximated by simple geometries. Such domains may be reservoirs behind dams, or around intake towers, water around bridge piers or liquids stored in circular cylindrical tanks. The formulas are used to calculate the hydrodynamic pressures analytically and the results are exhibited in a form showing the pressure dependence on the various parameters of the problem.</p>
<p>The fluid-structure interaction problems of long straight walls, having uniform rectangular sections, and long straight gravity dams, having uniform triangular sections, are investigated. The natural frequencies of vibration and the associated mode shapes are found in the former case, through a fully analytical approach for both the structure and the fluid domains, and in the latter, by discretizing the dam into finite elements and treating the reservoir as a continuum by boundary solution techniques. A method is presented for computing the earthquake response of both structures, based on superposition of their free vibrational modes.</p>
<p>The problems of limited length dam or wall-reservoir systems are investigated. The natural frequencies of the structure and the corresponding mode shapes are found by the Rayleigh-Ritz method. This method is also used to obtain the frequency domain response of the structure to all three components of the ground motion. The validity of the two dimensional approximation, often made in the analysis of gravity dams, and the effect of the length to height ratio on the dynamic properties and response of the structure are studied.</p>
<p>Time domain responses to arbitrary earthquake ground motions are evaluated by superposing the frequency domain responses, to individual Fourier components of the excitation, through the Fourier Integral. For efficiency of computation, a fast Fourier analysis is used for both the forward transform of the ground excitation and the inverse transform of the Fourier Integral.</p>https://thesis.library.caltech.edu/id/eprint/11363Application of Plasticity Theory to Soil Behavior: A New Sand Model
https://resolver.caltech.edu/CaltechETD:etd-12212005-143343
Authors: {'items': [{'id': 'Bardet-Jean-Pierre', 'name': {'family': 'Bardet', 'given': 'Jean-Pierre'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/Z23J-9E80
<p>The representation of rheological soil behavior by constitutive equations is a new branch of soil mechanics which has been expanding for 30 years. Based on continuum mechanics, numerical methods (finite elements) and experimental techniques, this new discipline allows practicing engineers to solve complex geotechnical problems. Although all soils are constituted of discrete mineral particles, forces and displacements within them are represented by continuous stresses and strains. Most stress-strain relationships, which describe the soil behavior, are derived from plasticity theory. Originated for metals, the conventional plasticity is presented and illustrated simultaneously with a metal and a soil model. Each plasticity concept may be criticized when applied to soil. A recent theory, called "bounding surface plasticity," generalizes the conventional plasticity and describes more accurately the cyclic responses of metals and clays. This new theory is first presented and linked with the conventional plasticity, then applied to a new material, sand. Step by step a new sand model is constructed, mainly from data analysis with an interactive computer code. In its present development, only monotonic loadings are investigated. In order to verify the model ability to describe sand responses, isotropic, drained and undrained tests on the dense Sacramento River sand are simulated numerically and compared with real test results and predictions with another model. Finally the new constitutive equation, which was formulated in the p-q space for axisymmetric loadings, is generalized in the six-dimensional stress state with the assumption of isotropy and a particular Lode's angle contribution. This new model is ready to be used in finite element codes to represent a sand behavior.</p>https://thesis.library.caltech.edu/id/eprint/5102Experimental Studies of Dynamic Response of Foundations
https://resolver.caltech.edu/CaltechETD:etd-08152006-091708
Authors: {'items': [{'email': 'ben@hushmand-associates.com', 'id': 'Hushmand-Behnam', 'name': {'family': 'Hushmand', 'given': 'Behnam'}, 'show_email': 'YES'}]}
Year: 1984
DOI: 10.7907/6TJK-6088
<p>An investigation was made into the behavior of rigid foundations and structures resting on the surface or embedded in a cohesionless soil and subjected to transient active or passive excitations and forced vibrations using the centrifuge modeling technique. The investigation was aimed at studying both low and high amplitude vibrations of foundations under machine type loadings, earthquake or wave induced vibrations, and other sources of dynamic loads. Rigid "prototype" foundations of mass and size comparable to foundations of a low rise building were simulated in the centrifuge at a centrifugal acceleration of 50g. Rigid model structures (aluminum towers) attached to foundations of different shapes, sizes, masses, and moments of inertia were tested. The effect of soil depth, boundary conditions, and depth of foundation embedment were investigated. Mainly rocking and horizontal modes of vibration were studied. The impulse rocking-horizontal excitation of the models was provided by actively perturbing the model structures using explosive energy or by passively exciting them by shaking the whole soil bucket using a hydraulic shaking system. The forced vibration was produced by a miniature air-driven counterrotating eccentric mass shaker mounted on the model structures. During the tests detailed measurements of the static and dynamic contact pressure distributions, displacement components of the model, and acceleration amplitudes at different elevations of the model structure were obtained. The acceleration ratios were used to determine the modes of vibration of the foundation systems. Natural frequencies and damping coefficients of the modes were calculated by fitting the amplitude-frequency response of a single degree of freedom mass-spring-dashpot oscillator to the experimental response curves derived from the test data. Experimental results provided information regarding the influence of different geometrical, inertial, and loading conditions on the vibrational characteristics of the soil-structure system. In particular the effect of foundation embedment was to increase the model resonant frequencies and to cause an appreciable change in contact pressure distribution underneath the footing. However, the resonant frequencies predicted by the lumped parameter analysis for a simple two-degree-of-freedom (rocking and translation) model were about 20 to 55 per cent higher than those measured experimentally. These results were consistent with the comparisons made in similar theoretical and experimental studies such as those performed by Morris in the Cambridge centrifuge and those performed on full-scale footings by Stokoe and Richart. Damping ratios of the rocking-sliding vibration did not change considerably when footing size or depth of embedment changed. The existence of rigid boundaries around the soil mass in the bucket, and an inefficient contact between soil and the foundation side walls and lower surface could account for these observations. Uplift and nonlinear large amplitude vibrations were consistently observed during the steady-state vibration tests. Uplift led to a softer vibrating system which behaved non-linearly. As a result the frequency of vibration decreased with the amount of lift-off. In transient vibration uplift reduced the intensity of higher frequency vibration. Soil around the foundation edge yielded and plastic deformations and subsequent softening of the contact soil increased the material damping while it decreased the resonant frequency of the system. It was concluded that elastic half-space theory does not satisfy the needs for analysis of foundation behavior under high amplitude vibrations and more sophisticated methods of analysis are required.</p>https://thesis.library.caltech.edu/id/eprint/3131Investigation of Local Geology Effects on Strong Earthquake Ground Motions
https://resolver.caltech.edu/CaltechTHESIS:12122018-092221333
Authors: {'items': [{'id': 'Huang-Moh-jiann', 'name': {'family': 'Huang', 'given': 'Moh-jiann'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/pm3k-w086
<p>Accelerograms recorded at four stations in the Pasadena area during the 1971 San Fernando, the 1970 Lytle Creek, the 1968 Borrego Mountain and the 1952 Kern County earthquakes are analyzed to investigate local geology effects on strong earthquake ground motions. Spatial variations of the ground motions at two nearby stations are also investigated. It is found that the ground motions in this area caused by the local geology effects depend on the 3- dimensional configuration of the local geology and the direction of arriving seismic waves. Local geology effects are less evident on the leading portions of the accelerograms than the trailing portions, indicating the effects of local geology on surface wave propagations. Comparison of the Fourier amplitudes of the motions recorded at the same station during different earthquakes shows that there are no significant spectral peaks can be identified as site periods. Hence, it is not appropriate to characterize such local sites by a site period.</p>
<p>A two-dimensional model considering inclined propagating P and S waves in a horizontal-layered structure, which is more realistic and closer to the actual seismic environment within a local geology than the one-dimensional model of vertically propagating waves, is studied. The transfer functions between the free surface and the half-space outcrop for a single incident P, SV or SH wave from the half-space at an incident angle are defined and derived by a matrix method. Two numerical examples are given to demonstrate the effects of incident angle and material damping on the transfer function. It is found that the transfer function between the free surf ace motions and the bedrock outcrop motions to multiple incident waves having different amplitudes, angles and arrival times is quite different from that for a single incident wave. Completely satisfactory results cannot be expected when using the analytical model for evaluating the local geology effects on the motions during a nearby shallow-focus earthquake for which seismic waves emitted from different parts of the fault will approach the bedrock from different directions and at different angles.</p>
<p>The analytical model for assessing local geology effects is evaluated in the light of the data recorded at stations in the Pasadena area during the 1971 San Fernando earthquake. The observed site transfer functions between the alluvial and the rock sites are obtained and compared with the computed results from a two-dimensional model with 7-layers overlying a half-space. Values of model parameters are optimally adjusted to give a best least-squares fit between computed and observed amplitude ratios. It is concluded that the analytical model oversimplifies the local geological structure in the Pasadena area and the actual seismic environment in the area during the 1971 San Fernando earthquake.</p>
<p>It is concluded from these studies that the effects of the source mechanism and the seismic wave travel paths upon the site ground motion can be comparable to the effect of the local geology. The characteristics of the source mechanism, such as type of faulting, direction of fault-slip propagation, nature of stress drop across the fault surface, orientation of fault, depth beneath ground surface, etc., can appreciably influence the ground motion at the site. Also, the travel path can have a significant effect through influencing the types of waves that reach the site, and the directions of approach of the waves. The results of this study indicate that a better understanding of the spatial variation of ground motions, of the role played by different types of waves and their contributions to an accelerogram, and of the propagation directions of the waves is needed for assessing local geology effects on earthquake ground motions. A local array is desirable to provide data for giving a reasonably complete picture of the nature of ground motions in a local area.</p>https://thesis.library.caltech.edu/id/eprint/11308A Simple Strain-Space Plasticity Model for Clays
https://resolver.caltech.edu/CaltechTHESIS:01022019-123640478
Authors: {'items': [{'id': 'Chelvakumar-Kasivisvanathan', 'name': {'family': 'Chelvakumar', 'given': 'Kasivisvanathan'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/kcgf-c188
<p>This thesis develops and demonstrates a simple strain-space constitutive model for wet clays. It has been seen that a strain-space formulation of the constitutive behavior of engineering materials facilitates the solution of boundary value problems involving these materials. Soil, because of its multi-phase granular constitution poses challenging problems in constitutive modeling. Although several stress-space plasticity models exist for soils, they are not used commonly in engineering practice due to their complexity. It is attempted herein to develop and test a simple model which could result in simplified solutions for some soil problems.</p>
<p>The model is based on the experimentally observed physical behavior of soil. Certain approaches alien to conventional plasticity. Are employed so that the material behavior is closely predicted without sacrificing the simplicity of the model.</p>
<p>The model is initially developed for triaxial load systems. Its predictions are then tested against other model predictions and experimental data. The model is then generalized. The generalization renders the model capable of handling general stress-strain states and finite deformations.</p>
<p>Finally, the generalized model is used to solve an idealization of a practical problem. The problem of a pile driven into a soil medium is idealized as an expanding cavity in a homogeneous infinite medium. The solution predicted by the strain-space model is compared with other model predictions and test results.</p>https://thesis.library.caltech.edu/id/eprint/11330Dynamic Response of a Partially Embedded Bar Under Transverse Excitations
https://resolver.caltech.edu/CaltechTHESIS:01222019-152401456
Authors: {'items': [{'id': 'Pak-Ronald-Y-S', 'name': {'family': 'Pak', 'given': 'Ronald Y.S.'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/pp2r-fc10
<p>This dissertation is concerned with the dynamic response of a finite flexible bar partially embedded in a half-space, under transverse loadings. The loadings are applied at the unembedded end of the bar and may, in general, be a combination of time-harmonic shear and moment. The problem is intended to serve as a fundamental idealization for the dynamic analysis of piles or other embedded foundations whose flexibilities are not negligible.</p>
<p>By treating the bar as a one-dimensional structure and the half-space as a three-dimensional elastic continuum, the interaction problem is formulated as a Fredholm integral equation of the second kind. The essential tool required in the formulation is a group of Green's functions which describe the response of an elastic half-space to a finite, distributed, buried source which acts in the lateral direction. By means of a technique developed for a class of three-dimensional asymmetric wave propagation problems, the Green's functions are derived as integral representations. A numerical procedure for the computation of the semi-infinite Hankel-type integrals involved is presented which is free of the basic difficulties commonly encountered in such problems. Owing to the special nature of the kernel function, a numerical scheme which contains the essence of quadrature and collocation techniques is developed for the solution of the governing integral equation. Selected results for the interaction problem are presented to illustrate various basic features of the solution. In addition to furnishing the compliance functions commonly used in soil-structure interaction studies, the solution should prove useful in providing a basis for the assessment and improvement of approximate and numerical models currently employed for such analyses.</p>https://thesis.library.caltech.edu/id/eprint/11355Flow-Induced Vibration of Long Structures
https://resolver.caltech.edu/CaltechETD:etd-11072006-091025
Authors: {'items': [{'id': 'Jones-Nicholas-Patrick', 'name': {'family': 'Jones', 'given': 'Nicholas Patrick'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/ZXWC-ZZ44
<p>When a body is exposed to a flowing fluid, oscillations can occur due to one or more of several different mechanisms. The resulting large amplitudes of motion and fatigue are potential sources of structural failure. Furthermore, the drag force on a structure can be increased due to the effectively larger cross-sectional area presented to the flow from the oscillation. A complete understanding of the nature of such vibration is essential in the design of many civil and mechanical engineering systems.</p>
<p>Previous solutions to the vortex-induced vibration problem were primarily based on modal analysis, using a one- or two-mode approximation. Use of modal analysis implies a "locked-in" condition: the vortex shedding frequency and a natural frequency of the system are coincident. Observations made on long cable systems indicate that the amplitude of response is smaller than is predicted by a conventional modal analysis. The drag forces on such structures are therefore overestimated by current design approaches.</p>
<p>In very long structures, typical of those found in ocean applications, modes are closely spaced, and it is not reasonable to assume total spanwise correlation in the fluid forces or response. The approach used herein attempts to avoid the limitations associated with the modal solution of such problems by implementing a solution based on traveling waves. The technique draws on earlier theoretical and empirical models for the complex vortex-shedding phenomenon, and incorporates these into a new method for analyzing the structural response problem.</p>
<p>The traveling wave approach can be used to model effectively spanwise variable flow environments by summing the calculated responses of adjacent active sections of cable. Until this method was developed, there was no suitable method available for modeling flow characteristics of this type. Modal analysis is effectively limited to systems with uniform flow over all or part of the system.</p>https://thesis.library.caltech.edu/id/eprint/4441Analysis of Unanchored Liquid Storage Tanks under Seismic Loads
https://resolver.caltech.edu/CaltechTHESIS:10232019-110854163
Authors: {'items': [{'id': 'Peek-Ralf', 'name': {'family': 'Peek', 'given': 'Ralf'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/w43k-hj54
<p>Because of cost, cylindrical, ground supported liquid storage tanks are often not fixed to their foundation, even in seismic areas. For such an unanchored tank made of steel, the weight of the cylindrical shell is mostly insufficient to prevent local uplift due to seismic overturning moments. Although, for properly designed connecting pipes, uplift itself is not a problem, it results in larger vertical compressive stresses in the tank wall at the base, opposite to where the uplift occurs. These compressive stresses have often caused buckling, even in earthquakes which did not cause much damage to other structures.</p>
<p>Various investigators have studied the behavior of unanchored tanks experimentally, but, due to the complexity of the problem, so far very little theoretical work has been done. Two methods of analysis for static lateral loads are presented: An approximate one in which the restraining action of the base plate is modeled by nonlinear Winkler springs, and a more comprehensive one in which the two dimensional nonlinear contact problem is solved by the finite difference energy method. The theoretical results are compared with existing experimental results and with the approach from current U.S. design standards. The theoretical peak compressive stresses are in good agreement with the experimental results, but in some cases exceed those calculated by the code method by more than 100%.</p>
<p>Finally, a new design concept, by which the tank wall is preuplifted all around its circumference by inserting a ring filler is described. It will be shown theoretically and experimentally that this preuplift method substantially improves the lateral load capacity.</p>https://thesis.library.caltech.edu/id/eprint/11848Two-Phase Soil Study: A. Finite Strain Consolidation. B. Centrifuge Scaling Considerations
https://resolver.caltech.edu/CaltechETD:etd-03082008-084249
Authors: {'items': [{'id': 'Tan-Thiam-Soon', 'name': {'family': 'Tan', 'given': 'Thiam-Soon'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/agt3-mf84
<p>Two different aspects of the behavior of soil as a two-phase medium are studied, namely, the consolidation of soil and scaling relations for soils in centrifuge testing.</p>
<p>PART A</p>
<p>First a consistent approach is presented that unifies all current theories of consolidation of soil. For one-dimensional finite strain consolidation, a Lagrangian finite element scheme is then given and tested against three different experiments and found to give consistent results. For a quick solution to a particular problem, the regular perturbation method applied to the formulation in which the dependent variable is the natural strain is shown to give the most consistent results. For the Eulerian formulation, the material derivative contains a convective term. This convective effect is then analytically studied and found not to be negligible for a final natural strain greater than 10%. A method is then introduced that can account for both the moving boundary and the convective effect. This method is tested in a finite difference scheme and found to give identical results with the Lagrangian finite element scheme for the one-dimensional case. Finally the method is used for the axisymmetric problem of consolidation by vertical drain. The solution to this case suggests that arching and subsequent load redistribution should be considered.</p>
<p>PART B</p>
<p>Conceptually, when a centrifuge is used to test models, the centrifuge is assumed to produce an equivalent ng gravitational field (as on another planet) and the behavior of the model in the ng field is then assumed to be similar to that of the prototype. For most static problems, the centrifuge does model the prototype well but for some dynamic problems, these assumptions can break down. To investigate this, the similarity requirements are examined for the case of a single particle moving in a fluid. It is found that for the post-liquefaction process and for seepage flow, unless the Reynolds number is much less than one in both model and prototype, the centrifuge is not a good simulation of the prototype situation. But, perhaps contrary to expectations, the breakdown is due to the fact that the behavior in the ng planet is not similar to the prototype ig planet, whereas the centrifuge does simulate the ng planet well. Further, it is shown that the concept of "modeling of models" can lead to misleading results. Lastly, for cratering experiments, it is concluded that the centrifuge will only model the crater shape just after an explosion and not the final crater shape.</p>https://thesis.library.caltech.edu/id/eprint/902A Physical Model of Wind-Blown Sand Transport
https://resolver.caltech.edu/CaltechETD:etd-08042008-114600
Authors: {'items': [{'id': 'Werner-Bradley-T', 'name': {'family': 'Werner', 'given': 'Bradley T.'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/6cbp-es88
<p>Eolian saltation, the transport of sand by the wind, involves a variety of physical processes. A fundamental understanding of saltation requires an analysis starting from the level of the individual sand grain. The complexity of this nonlinear dynamical system compels us to divide the problem into more easily handled decoupled components: the saltating grain-bed impact process, the force of the wind on individual grains, the determination of the wind profile from the spatially averaged force of the moving grains on the air, and the formation of small-scale bedforms: ripples.</p>
<p>The impact of a moving sand grain with a bed of sand is studied with two-dimensional dynamical computer simulations and an experiment propelling single grains onto a sand bed. We find that the result of the impact may be described in terms of the rebound of the incident particle and the ejection of bed grains. The bed grain ejections originate from a localized area around the impact point, and at steps in the surface (elevation changes of one grain diameter) which are more widely distributed; these surface steps we term brinks (downstream-facing) and anti-brinks (upstream-facing).</p>
<p>A model for steady-state saltation is proposed which incorporates both aerodynamics and the mechanics of the grain-bed impacts, and balances the losses of saltating particles on impact with the bed by gains due to impact generated bed grain ejections. This model does not require data on blowing sand. Results are obtained which qualitatively agree with existing data. Quantitative tests will require new experiments. We argue that grain-bed impacts, not fluid stresses, are the means for entraining grains in steady-state eolian saltation.</p>
<p>The development of sand surface topography is viewed as a result of surface grain transport (reptation) driven by the impact of high-energy saltating grains onto the bed. The collision and merger of small collections of sand, proto-ripples, lead to the asymptotic development of uniform ripples from an initially smoothed surface. The limiting wavelength is pictured as being determined by statistical fluctuations in the saltating impact flux and/or the shortening of the saltation shadow zone below the mean reptation length during a collision between two ripples. Field observations of developing ripple cross-sectional shapes confirm these ideas qualitatively, and rough calculations of limiting wavelengths agree with existing data.</p>
https://thesis.library.caltech.edu/id/eprint/3014Modeling and Identification in Structural Dynamics
https://resolver.caltech.edu/CaltechTHESIS:02272019-105053083
Authors: {'items': [{'id': 'Jayakumar-Paramsothy', 'name': {'family': 'Jayakumar', 'given': 'Paramsothy'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/1wwx-ca82
<p>Analytical modeling of structures subjected to ground motions is an important aspect of fully dynamic earthquake-resistant design. In general, linear models are only sufficient to represent structural responses resulting from earthquake motions of small amplitudes. However, the response of structures during strong ground motions is highly nonlinear and hysteretic.</p>
<p>System identification 1s an effective tool for developing analytical models from experimental data. Testing of full-scale prototype structures remains the most realistic and reliable source of inelastic seismic response data. Pseudo-dynamic testing is a recently developed quasi-static procedure for subjecting full-scale structures to simulated earthquake response. The present study deals with structural modeling and the determination of optimal linear and nonlinear models by applying system identification techniques to elastic and inelastic pseudo-dynamic data from a full-scale, six-story steel structure.</p>
<p>It is shown that the feedback of experimental errors during the pseudo-dynamic tests significantly affected the higher modes and led to an effective negative damping for the third mode. The contributions of these errors are accounted for and the small-amplitude modal properties of the test structure are determined. These properties are in agreement with the values obtained from a shaking table test of a 0.3 scale model.</p>
<p>The nonlinear hysteretic behavior of the structure during strong ground motions is represented by a general class of Masing models. A simple model belonging to this class is chosen. with parameters which can be estimated theoretically, thereby making this type of model potentially useful during the design stages. The above model is identified from the experimental data and then its prediction capability and application in seismic design and analysis are examined.</p>https://thesis.library.caltech.edu/id/eprint/11411Failure of Slopes
https://resolver.caltech.edu/CaltechETD:etd-03012008-132659
Authors: {'items': [{'id': 'Burridge-Paul-Brian', 'name': {'family': 'Burridge', 'given': 'Paul Brian'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/2C4G-6R71
<p>The dynamic mechanism of slope failure is studied both experimentally and analytically to establish the spatial and temporal process of failure initiation and propagation during collapse of a natural or man-made slope.</p>
<p>Model slopes, constructed of a brittle cemented sand material, are tested to collapse in a geotechnical centrifuge and the dynamics of failure recorded by motion picture film and mechanical detectors within the slope specimen. Shear failure is observed to initiate at the toe and propagate rapidly to the crest in the presence of crest tension cracking.</p>
<p>A finite difference approach is taken to numerically solve the plane strain slope stability problem under gravity, based on unstable material behavior. Using a Lagrangian differencing scheme in space and explicit integration in time with dynamic relaxation, the numerical method finds the equilibrium state of the slope as the large-time limit of a dynamic problem with artificial parameters. The solution predicts localized shear failure zones which initiate at the slope toe and propagate to the slope crest in the manner and geometry observed in the centrifuge tests. In so doing, the finite difference algorithm also demonstrates an apparent ability to predict shear failure mechanisms in solid continua in general.</p>
https://thesis.library.caltech.edu/id/eprint/825Stability of the Structure in Multicomponent Flows
https://resolver.caltech.edu/CaltechETD:etd-03262007-142052
Authors: {'items': [{'id': 'Kytömaa-Harri-Kaarlo', 'name': {'family': 'Kytömaa', 'given': 'Harri Kaarlo'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/VNYA-FE49
<p>Friction pressure drop measurements were made in vertical bubbly and particulate flows, and friction factors up to two orders of magnitude higher than pure liquid values were obtained. The two-phase friction multiplier for air-water flows was shown to attain values up to 15 times higher than the predictions given by the Lockhart and Martinelli correlations (1949). These findings exemplify the lack of detailed understanding of multi-component flow phenomena. The lack of understanding of the flow kinematics and the small amount of information available on the topic has been primarily due to the primitive stage of development of flow measuring instrumentation.</p>
<p>A shielded, temperature compensated and non-intrusive Impedance Volume Fraction Meter (IVFM) was built and shown to have good spatial and temporal resolution. The dynamic calibration of the device demonstrated that the volume fraction measuring device could also be used to measure both the dispersed medium velocity and concentration. This device enabled us to carry out measurements of small and large amplitude kinematic stability and wave propagation in two-component and three-component flows. The velocities of small amplitude kinematic waves in both air-water and solids-water flows were measured using a cross-correlation technique and these were shown to be non-dispersive. The persistence of flow structure was quantified using the coherence of the IVFM noise at two locations. The structure in solids-water flows was found to be more persistent than in air-water flows, and the most coherent wave length was measured to be of the order of .5 m, or five pipe diameters in both flows. The statistical properties in the inherent noise in the IVFM output was shown to contain valuable information on two- and three-component flow quantities and regime.</p>
<p>In this thesis, we show that much can be learned about the complex nature of multi-component flows with adequate instrumentation, and we emphasize the need for further development of critical flow measuring techniques for use not only in fundamental investigations but also in the monitoring and control of practical multiphase flow processes.</p>https://thesis.library.caltech.edu/id/eprint/1149Experimental Investigation of the Nonlinear Seismic Response of Concrete Gravity Dams
https://resolver.caltech.edu/CaltechETD:etd-05232007-074318
Authors: {'items': [{'id': 'Donlon-William-Patrick-Jr', 'name': {'family': 'Donlon', 'given': 'William Patrick, Jr.'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/4mqw-6z67
<p>The nonlinear seismic response of concrete gravity dams is investigated experimentally through the use of small-scale models. Of primary interest is crack formation, crack opening and closing, and sliding along crack planes. Also of concern is the stability of the structure after cracking. Three small-scale models (length scale - 115) of a single monolith of Pine Flat Dam are tested to determine the extent of such behavior and its effect on structural stability. The models are constructed of one polymer-based and two plaster-based materials developed for these experiments. The plaster-based materials fulfill the strength, stiffness, and density requirements established by the laws of similitude, while the polymer-based material fulfills only the stiffness and density requirements and is used only in the lower part of the dam where cracking is not expected. The excitation is a modified version of the N00E component of the 1940 Imperial Valley earthquake, applied to each model's base in the stream direction through a vibration table with high-frequency capability. Tests are performed with and without water in the reservoir. The response of each earthquake test is presented in the form of acceleration and displacement time histories, Fourier spectra, and frames taken from high-speed films of the model's response. The results of the experiments indicate that the neck region of a concrete gravity dam is most susceptible to cracking, although crack profiles can differ as a result of variations in excitation, material properties, and construction techniques. These results also indicate alternate design techniques which could improve the seismic stability of a cracked gravity dam.</p>https://thesis.library.caltech.edu/id/eprint/1982Effect of Nonuniform Seismic Input on Arch Dams
https://resolver.caltech.edu/CaltechTHESIS:06042013-091930444
Authors: {'items': [{'id': 'Nowak-Paul-Scott', 'name': {'family': 'Nowak', 'given': 'Paul Scott'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/zbd0-ty45
<p>Standard earthquake analyses of civil engineering structures use uniform ground motions even though considerable variations in both amplitude and phase can occur along the foundation interface for long-span bridges and large dams. The objective of this thesis is to quantify the effect that these nonuniformities have on the structural response.</p>
<p>The nonuniform, free-field motions of the foundation interface are assumed to be caused by incident plane body waves. The medium in which these waves travel is a linear, elastic half-space containing a canyon of uniform cross section in which the structure is placed. The solutions for the free-field motions that are due to incident SH, P and SV waves are calculated using the boundary element method.</p>
<p>An analysis of Pacoima (arch) dam located near Los Angeles, California, is performed for both uniform and nonuniform excitations. The important effect of nonuniformities in the free-field motions, sometimes leading to a decrease in the dam response and sometimes to an increase, is quantified.</p>https://thesis.library.caltech.edu/id/eprint/7830Nonlinear Earthquake Response of Concrete Gravity Dam Systems
https://resolver.caltech.edu/CaltechETD:etd-06072007-132404
Authors: {'items': [{'id': 'El-Aidi-Bahaa', 'name': {'family': 'El-Aidi', 'given': 'Bahaa'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/n2f8-rv33
<p>The earthquake response of concrete gravity dam systems is investigated with emphasis on the nonlinear behavior associated with tensile concrete cracking and water cavitation. A single dam-monolith is considered and is assumed to respond independently as a two-dimensional system under plane stress conditions. The two-dimensional assumption is also extended to model the compressible water body impounded upstream of the dam. Standard displacement-based finite element techniques are used to spatially discretize the field equations and produce a single symmetric matrix equation for the dam-water system. Energy dissipation in the reservoir, through radiation in the infinite upstream direction and absorption at the bottom, is approximately accounted for, and a set of numerical examples is presented to demonstrate the accuracy of the present formulation in modeling the linear earthquake response of infinite reservoirs. An approximate procedure to account for dam-foundation interaction is incorporated based on the response of a rigid plate attached to a three-dimensional viscoelastic half-space.</p>
<p>Water cavitation is modeled by a smeared approach which uses a bilinear pressure-strain relation. It is shown that the water response becomes dominated by spurious high frequency oscillations upon closure of cavitated regions, and improved results can be obtained by using some stiffness-proportional damping in the water reservoir. As demonstrated in an example analysis of Pine Flat Dam (linear dam), cavitation occurs in the upper part of the reservoir along the dam face, unlike other investigations which show cavitated regions at considerable distances from the dam, and both the tensile pressure cutoffs and compressive impacts have a minor effect on the dam response.</p>
<p>Tensile cracks are incorporated using the smeared crack approach, and sliding along closed cracks is allowed. Coupling effects inherent in the finite element formulation are explained, and their influence on open and closed cracks is investigated. Propagation of cracks is monitored in an interactive environment which uses an equivalent strength criterion and allows for user input; remeshing is avoided. The algorithm adopted here produces narrow cracks, unlike many other investigations which show large zones of cracking. An extensive numerical study of Pine Flat Dam demonstrates some interesting features of the nonlinear response of the system, identifies potential failure mechanisms, and reveals a number of difficulties that the analysis encounters. Although no instability of the dam occurs, the numerical difficulties will have to be overcome before definite conclusions regarding stability can be made. It is shown that cracking reduces the hydrodynamic pressures in the reservoir and, hence, reduces water cavitation.</p>https://thesis.library.caltech.edu/id/eprint/2510Soil Stress Field Around Driven Piles
https://resolver.caltech.edu/CaltechETD:etd-02212007-130942
Authors: {'items': [{'id': 'Allard-Marie-Agnès', 'name': {'family': 'Allard', 'given': 'Marie-Agnès'}, 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/GGE1-GC92
<p>The description, equipment, and results of a series of pile-driving experiments conducted in a centrifuge using a model pile driven in dry sand are presented.</p>
<p>The work was conceived on the basis of the modelling of a soil-structure system under an artificially generated gravitational field, and motivated by the need for experimental data for a better understanding of the complex phenomena involved in the pile-soil interaction during driving. The behavior of the pile itself has been the focus of more attention in the past, but few full-scale or model experimental results have been obtained to the present concerning the soil stress field during pile driving. These are necessary for comparison with analytical and theoretical work. The work presented here appears to be the first attempt to obtain dynamic response of the soil during driving. The objective was to obtain a good understanding of the physical phenomena occurring in the soil and pile during driving.</p>
<p>In order to achieve these objectives both dynamic (transient) and static responses of the soil and pile were measured by means of transducers: accelerometers and strain gages for the pile, pressure transducers for the soil. In particular, the relations between static and dynamic data were explored, which resulted in the modelling of the soil-transducer interaction with a non-linear, history-dependent, model.</p>
<p>Results were obtained regarding pile dynamics, soil dynamics, and soil stress field (radial and vertical distribution, stress contours). Both linear and soil-cell model assumptions were used, which enabled a comparison between the two, leading to an estimate that each constitutes a bound of the real stress field, with the linear giving the higher, and the non-linear the lower bound, and the true stress being closer to the lower bound.</p>
<p>The soil response during driving is obtained, filling the gap in the study of the pile-soil system, where only the pile response was known. Recommendations for further work and better experimental procedures are given.</p>https://thesis.library.caltech.edu/id/eprint/696Nonlinear seismic behaviour of steel planar moment-resisting frames
https://resolver.caltech.edu/CaltechTHESIS:10062011-075420910
Authors: {'items': [{'id': 'Challa-Venkata-Ramana-Murty', 'name': {'family': 'Challa', 'given': 'Venkata Ramana Murty'}, 'show_email': 'NO'}]}
Year: 1992
DOI: 10.7907/jk1f-2d70
<p>The nonlinear response of steel planar moment-resisting frames during strong earthquakes poses a strong need for accurately modelling inelastic behaviour and large displacements. This thesis attempts to provide realistic and efficient analytical tools to aid this study.</p>
<p>Two large-displacement small-strain beam-column models are employed to include material and geometric nonlinearities. The first model assumes lumped plasticity, and discretises an element into segments. Axial force-Bending Moment strength interaction and flexural bowing are considered. Ten characteristic segment states are identified. An efficient numerical scheme is suggested to solve the nonlinear governing equations. This model only approximately represents the strength and stiffness of beam-columns.</p>
<p>A comprehensive finite element beam-column model is developed to more accurately model the strength and stiffness. A beam-column is discretised into segments, and further, each segment into one-dimensional fibres. A uniaxial cyclic constitutive law valid under arbitrary transient loading is proposed for structural steel. This physically motivated law incorporates the initial yield plateau, and provides explicit expressions for stress in terms of strain throughout the hysteretic path. This law is used to control the hysteretic loading of fibres.</p>
<p>A simple semi-empirical model is employed to analytically describe the highly nonlinear hysteretic behaviour of flexible joint panel zones in steel planar frames. Some modelling assumptions that may be made in frame analyses are evaluated. Numerical study of a building frame with flexible joints indicates that its collapse is sensitive to the joint panel zone design in addition to the ground motion.</p>
https://thesis.library.caltech.edu/id/eprint/6707Basal mechanics and geologic record of ice streaming, West Antarctica
https://resolver.caltech.edu/CaltechETD:etd-03092004-155058
Authors: {'items': [{'email': 'tulaczyk@es.ucsc.edu', 'id': 'Tulaczyk-Slawek-M', 'name': {'family': 'Tulaczyk', 'given': 'Slawek M.'}, 'show_email': 'YES'}]}
Year: 1999
DOI: 10.7907/N04E-S040
Piston coring in boreholes drilled at the UpB camp through Ice Stream B, West Antarctica, provided the first samples of sediments ever recovered from beneath an active ice stream. Sedimentological analyses indicate that the samples come from the layer of weak, subglacial till underlying this ice stream (the UpB till). Textural properties of the till and the Tertiary diatoms found in it suggest that the UpB till is recycled from the sediments of the inferred eastern subglacial extension of the Ross Sea sedimentary basin. Geotechnical tests show that the UpB till can be modeled as a compressible, Coulomb-plastic material whose strength is practically independent of deformation rate but is determined by effective stress which also determines the water content. Simulations of the subglacial behavior of such till have successfully reproduced fundamental features of the observed, subglacial till kinematics, e.g., viscous-like vertical distribution of strain and oscillations in tilt rates. The compressible-Coulomb-plastic till model offers a framework for understanding and modeling of ice stream motion and ice-till interactions. The high porosity of the UpB till ([approximately] 0.4) suggests that effective stress is consistently very low, ca. 0.1 to 30 kPa, in the subglacial zone of Ice Stream B. These conditions are explained by the 'undrained-bed' model of sub-ice-stream hydrology that includes only local exchange of water between the water stored in the till pore space and the water stored as basal ice. In this model, there is a negative feedback effect between the basal melting rate and till strength which forces a steady-state in which the basal melting rate is zero and the till is water-rich and weak. Coupling of the undrained-bed model with an equation for the velocity of ice stream sliding yields the undrained plastic-bed model of ice streaming (the UpB model). In accordance with the existing observations, the physics of the UpB model produces two stable modes: an active 'ice-stream' mode and an 'ice-sheet' mode. The model may experience thermally-triggered switches between the two modes and it can be used to test the hypothesis that the West Antarctic Ice Sheet will become unstable in the near-future.https://thesis.library.caltech.edu/id/eprint/903Structural Design under Seismic Risk Using Multiple Performance Objectives
https://resolver.caltech.edu/CaltechThesis:05052016-115652196
Authors: {'items': [{'email': 'ayhan@alumni.caltech.edu', 'id': 'Irfanoglu-Ayhan', 'name': {'family': 'Irfanoglu', 'given': 'Ayhan'}, 'orcid': '0000-0001-8334-6717', 'show_email': 'NO'}]}
Year: 2000
DOI: 10.7907/W5WE-TD86
<p>Structural design is a decision-making process in which a wide spectrum of requirements, expectations, and concerns needs to be properly addressed. Engineering design criteria are considered together with societal and client preferences, and most of these design objectives are affected by the uncertainties surrounding a design. Therefore, realistic design frameworks must be able to handle multiple performance objectives and incorporate uncertainties from numerous sources into the process.</p>
<p>In this study, a multi-criteria based design framework for structural design under seismic risk is explored. The emphasis is on reliability-based performance objectives and their interaction with economic objectives. The framework has analysis, evaluation, and revision stages. In the probabilistic response analysis, seismic loading uncertainties as well as modeling uncertainties are incorporated. For evaluation, two approaches are suggested: one based on preference aggregation and the other based on socio-economics. Both implementations of the general framework are illustrated
with simple but informative design examples to explore the basic features of the framework.</p>
<p>The first approach uses concepts similar to those found in multi-criteria decision theory, and directly combines reliability-based objectives with others. This approach is implemented in a single-stage design procedure. In the socio-economics based approach, a two-stage design procedure is recommended in which societal preferences are treated through reliability-based engineering performance measures, but emphasis is also given to economic objectives because these are especially important to the structural designer's client. A rational net asset value formulation including losses from uncertain future earthquakes is used to assess the economic performance of a design. A recently developed assembly-based vulnerability analysis is incorporated into the loss estimation.</p>
<p>The presented performance-based design framework allows investigation of various design issues and their impact on a structural design. It is a flexible one that readily allows incorporation of new methods and concepts in seismic hazard specification, structural analysis, and loss estimation.</p>
https://thesis.library.caltech.edu/id/eprint/9702Couette Flows of Granular Materials: Mixing, Rheology, and Energy Dissipation
https://resolver.caltech.edu/CaltechETD:etd-03272007-093837
Authors: {'items': [{'email': 'annakarion@gmail.com', 'id': 'Karion-Anna', 'name': {'family': 'Karion', 'given': 'Anna'}, 'show_email': 'NO'}]}
Year: 2000
DOI: 10.7907/HX15-PC72
<p>This thesis examines the behavior of a granular material sheared in a gap between two moving boundaries. In fluid mechanics, this type of flow is known as a Couette flow. Two different kinds of granular Couette flows were studied. First, gravity-free flow between two infinite plates moving in opposite directions was investigated using computer simulations. Second, flow between a stationary outer cylinder and an inner rotating cylinder was studied using both experiments and computer simulations.</p>
<p>Two-dimensional discrete element computer simulations of infinite planar Couette flows were used to study the rheology, energy dissipation, and other flow properties in flows of particles of uniform size for three different gap widths. The energy dissipation rate was measured and a thermal analysis was conducted to determine the thermodynamic temperature rise and heat flux of such flows. Given a constant wall velocity, all of the properties in flows of identical particles were found to depend on the value of the solid fraction at the walls, which in turn depended on both the average solid fraction and the gap width. When the average solid fraction reached a critical threshold, the amount of work done on the flow drastically increased, increasing the average strain rate, granular temperature, wall stresses, and energy dissipation in the flow. This solid fraction threshold occurred after the center region of the flow had reached a dense limit and any further increase in solid fraction necessarily occurred in the wall regions. Various results from computer simulations were found to compare reasonably well with past results derived using kinetic theory.</p>
<p>Mixing and other flow properties were also investigated in planar Couette flows of two different particle sizes, as functions of the size ratio and solid fraction ratio of the two species. Larger particles were found to migrate away from the regions of high fluctuation energy near the two moving boundaries in all cases. Mixture flows were found to behave very similarly to flows of mono-sized particles at high ratios of the solid fraction of small to large particles. As the solid fraction ratio decreased and the number of large particles increased, results deviated from the corresponding flow of identical particles. Flows with large size ratios of large to small particles deviated the most from the result of mono-sized particles, because stresses and energy dissipation rates are both mass-dependent.</p>
<p>The second type of Couette flow, between two concentric cylinders, was investigated in a horizontal orientation (with the axis of rotation perpendicular to the direction of gravity) and in a vertical orientation (with the axis parallel to the direction of gravity), using both experiments and computer simulations. In the horizontal geometry, high-speed imaging was used to calculate experimental mean and fluctuation velocity profiles that were compared to results from three-dimensional discrete element simulations. Segregation of binary particle mixtures was also investigated in this geometry. Segregation in this flow was driven by a percolation mechanism acting at the free surface, causing large particles to migrate to the top. Computer simulations compared well qualitatively with experiments, successfully predicting the velocity profiles and the segregation pattern at the surface. When compared quantitatively, however, fluctuation velocities in the simulations were considerably greater than those found in the experiment, and the radial segregation observed in experiments did not occur to the same extent in simulations.</p>
<p>The vertically-oriented cylindrical Couette flow experiment was used to measure the shear stress on the outer cylinder wall as a function of different variables. The shear stress was found to be independent of the inner cylinder rotation rate, because the material was unconfined and allowed to dilate. The measured stress showed a linear dependence on the height of material in the apparatus, indicating a hydrostatic variation of the normal stress. The shear stress also varied significantly with the ratio of the gap width to the particle diameter.</p>https://thesis.library.caltech.edu/id/eprint/1171