Browsing by Subject "Hydrodynamics"
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Item A model of periodic capillary flow(Texas Tech University, 1988-05) Kellogg, Denise RaeNot availableItem Analysis of Brownian dynamics and unsteady particle-motion in viscoelastic fluids(2012-05) Azese, Martin; Bhattacharya, Sukalyan; Blawzdziewicz, Jerzy; Ibragimov, Akif; Christopher, Gordon; He, ZhaomingIn recent times, micro-rheological applications involve determination of viscoelastic properties for samples that are either too precious and fragile or in a state (like inside a cell) where macroscopic experiments are impossible. In such cases, direct measurements using rheometers are not possible, because then the system can be structurally destroyed. One way to circumvent this problem is to predict fluid-rheology from the random motion of a Brownian sphere in the medium. Thus, many past attempts tried to relate viscoelastic properties to features of stochastic motion like time-dependent velocity correlation or mean square displacement. All such theories, however, invariably involve heuristic assumptions inherited from classical studies on purely viscous fluid. This is why in this thesis the classical theories of statistical mechanics for Brownian dynamics are first reevaluated and then modified to suit the new technological demand. This research first focuses on the flow-analysis which describes hydrodynamic field inside a viscoelastic medium. Accordingly, a mathematically rigorous perturbation method is developed which isolates the leading order linear contributions from higher order non-linearities due to both convective acceleration and constitutive relation. As a result, the conditions for linearized analysis are identified, and the leading order fields as well as particle-motion are determined. Then the analysis concentrates on the leading order linearized hydrodynamic equation only, and scrutinizes the relevance of classical theories of statistical mechanics for micro-rheological applications. In this context, three key conclusions are drawn revealing the errors in the earlier concepts. Firstly, the validity of fluctuation-dissipation theorem are questioned, as it requires Markovian condition only true for memory-less systems without viscoelasticity and flow-inertia. Secondly, well-known Langevin equation for Brownian dynamics is rectified by including the effect of fluid-inertia in the equation of motion of the suspended body in a density-matched liquid. Thirdly, the equipartition principle is reinterpreted to find the correct normalization for correlation of Brownian forces where energy associated with the translation of a Brownian particle is considered to have an additional contribution from the induced flow in the liquid. Thus, we discard the fluctuation-dissipation postulate, and recommend an inertia-corrected modified Langevin formulation to be used in micro-rheological problems. We use our new theory to correctly describe the stochastic dynamics of a Brownian sphere in a viscoelastic liquid by relating its time-dependent velocity correlation function and mean square displacement to fluid-rheology. Resulting conclusions differ substantially from popular beliefs while maintaining agreements under the long-time or low-frequency limit under proper conditions. Thus, our alternative formulation can be used in microrheological measurements to predict large-frequency complex viscosity for which the failure of past theories are well-documented. Moreover, we analyze the classical problem involving a Brownian sphere in a purely viscous liquid with density similar to the suspended solid. The errors in the original Langevin formulation are highlighted where the inertia of the fluid is ignored in both equation of particle-motion and equipartition principle. Our new theory with proper corrections is used to find the unsteady velocity correlation and mean square displacement of the sphere. The computed temporal variations of these quantities differ substantially from the results obtained from the classical Langevin equation. Curiously, however, the long-time diffusion coefficients in both cases exactly coincide. It seems that the earlier analysis calculates the correct diffusivity, because the error in equation of motion and misinterpretation in equipartition principle nullify each other. As long-time diffusivity is a quantity which has been experimentally verified over a century, the aforementioned agreement can be viewed as a further verification of the new theory.Item Biogeographic Patterns, Predator Identity, and Chemical Signals Influence the Occurrence and Magnitude of Non-lethal Predator Effects(2011-10-21) Large, Scott IsaacPredators can have large effects on prey populations and on the structure and function of communities. In addition to direct consumption of prey, predators often cause prey to alter their foraging behavior, habitat selection, and morphology. These non-lethal effects of predators can propagate to multiple trophic levels and often exert equal or larger effects upon communities than those of direct consumption. For non-lethal predatory effects to occur, prey must detect and respond to predation risk. While the importance of information transfer in this process has been realized, few studies explore how prey responses are influenced by predator characteristics and environmental conditions that influence the transmission of cues indicative of predation risk. In this dissertation I investigate factors that influence how a single prey species evaluates and responds to predation risk. Here, I examined: 1) the type and nature of cues prey use to evaluate predator risk; 2) how predator identity, predator diet, and the relative risk of predators influence prey response to predation risk; 3) how hydrodynamic conditions influence the delivery of predator cues; 4) how biogeographic trends in predator distribution influence prey response to predation risk; and 5) how genetic structure might vary according to prey geographic location and habitat. To address these questions, I used a common intertidal model system consisting of the rocky intertidal whelk Nucella lapillus (Linnaeus, 1758) and a suite of its predators, the native rock crab Cancer irroratus (Say, 1817), Jonah crab Cancer borealis (Stimpson, 1859), and the invasive green crab Carcinus maenas (Linnaeus, 1758). Nucella use chemical cues emanating from their most common predator (Carcinus maenas) and crushed conspecifics to evaluate predation risk. Nucella from different habitats experience different levels of predation risk, and Nucella from habitats with high levels of predation had larger antipredatory responses to predator risk cues than Nucella that experienced less predation. These chemical cues indicative of predation risk are influenced by hydrodynamic conditions, and Nucella have the strongest anti-predatory response in flow velocities of u= ~4- 8 cm s^-1. Furthermore, Nucella from geographic regions where green crabs are historically absent did not elicit anti-predatory responses, while Nucella from regions where green crabs are common frequently responded. Findings from my dissertation research demonstrate that prey detection and response to predation risk is highly dependent upon predator identity, predator diet, environmental forces, and biogeographic patterns in predator and prey distributions.Item Development of a Computer Program for Three Dimensional Frequency Domain Analysis of Zero Speed First Order Wave Body Interaction(2012-11-29) Guha, Amitava 1984-Evaluation of motion characteristics of ships and offshore structures at the early stage of design as well as during operation at the site is very important. Strip theory based programs and 3D panel method based programs are the most popular tools used in industry for vessel motion analysis. These programs use different variations of the Green?s function or Rankine sources to formulate the boundary element problem which solves the water wave radiation and diffraction problem in the frequency domain or the time domain. This study presents the development of a 3D frequency domain Green?s function method in infinite water depth for predicting hydrodynamic coefficients, wave induced forces and motions. The complete theory and its numerical implementation are discussed in detail. An in house application has been developed to verify the numerical implementation and facilitate further development of the program towards higher order methods, inclusion of forward speed effects, finite depth Green function, hydro elasticity, etc. The results were successfully compared and validated with analytical results where available and the industry standard computer program WAMIT v7.04 for simple structures such as floating hemisphere, cylinder and box barge as well as complex structures such as ship, spar and a tension leg platform.Item Dynamic wetting: hydrodynamic or molecular-kinetic?(Texas Tech University, 2004-08) Ranabothu, Srinivas ReddyThe dynamic wetting behavior of simple liquids (water, glycerin, formamide, ethylene glycol, and a mixture of water and ethylene glycol) and polydimethylsiloxane (PDMS) oils with different viscosities has been investigated. The hydrodynamic, molecular-kinetic, and combined molecular-hydrodynamic models have been applied to the experimental results to evaluate each model's adequacy. The hydrodynamic model does not explain the experimentally observed dependence of dynamic contact angles on the contact velocity of simple liquids, and the fitted parameter (Ls) value is not physically reasonable; all are in the sub-atomic dimension. The molecular-kinetic model fits reasonably well with the experimental data of simple liquids, but the fitted parameters (k and Kw) are significantly different in advancing and receding cases. Finally, for simple liquids investigated in this work, the combined molecular-hydrodynamic model is not superior when compared to the molecular-kinetic model, which contradicts the literatures. These observations lead to a conclusion that the molecular displacement (adsorption and desoprtion) process seems to be dominant for the simple liquids investigated in this work. However, the inconsistency in the advancing and receding cases question the assumption in the molecular-kinetic model that "the same amount of work is done on each site, irrespective of whether the adsorption site is occupied by the advancing phase or the receding phase." For the dependence of dynamic contact angles on the contact velocity for PDMS oils, the hydrodynamic model fits well with experimental results in terms of a linear relationship, but the fitted equilibrium contact angles are significantly different from the measured values. The molecular-kinetic model provides a relatively poor fitting to the experimental data of PDMS oils. Although the combined model fits reasonably well with the experimental data in terms of curve fitting, the fitted parameter Kw is practically less meaningful. This work provides the first, to the best of knowledge, extensive comparison of the three models with experimental data using a wide range viscosity. Remarkably, the work suggests that none of the evaluated models is sufficient to explain the dependence of dynamic contact angles of the investigated PDMS oils on contact velocity. The contact angle hysteresis of the simple fluids and PDMS oils has also been investigated. The work supports the hypothesis that the hysteresis strongly depends on the interactions between the contacting fluids and the solid substrate and reports the dependence of hysteresis on fluid viscosity for the first time.Item Experimental Study on Wave Transformation and Nearshore Circulation on a Variable Bathymetry in Wetlands(2012-10-19) Truong, Melanie Khanh PhuongHurricanes are one of the primary threats to the Texas coastal environment and economy. They generate large wave and storm surges that have caused much damage on the Texas coast in the past. Understanding both the hydrodynamic processes that damage coastal habitats and hurricane hazard and risk are critical to preserve coastal vegetation and quantify its benefits to coastal storm protection. The goal of this project is to quantify the impact of wave attenuation and wave refraction as well as the development of coherent structures in marsh fringes and the formation of a rip current system over wetlands on storm protection. The 3D Shallow Water Wave Basin at Texas A&M University hosted a series of large-scale experiments considering an idealized wetland model to pursue this goal. Study of the marsh geometry of the Texas coast was done in order to scale the experiments to the size of the Haynes Laboratory 3D-Water Wave Basin using a Froude and a Reynolds scalings. Particularly, averaged size and idealized shape of marsh segments in the area of Dalehite Cove in Galveston Bay were considered. Three sets of different wave conditions and water levels were tested to approximate different intensities of storm surge. Identical tests with both vegetated and non-vegetated marshes were run to compare the influence of the vegetation in storm conditions, and three different spacings between marsh segments were tested. In the basin, normally incident regular waves were generated at three water circulation structures. Data analysis allows the determination of the impact of discontinuous marsh segments on wave attenuation and wave refraction. Coherent structures such as rip current and the circulation pattern were analyzed to study the change in the flow field during passage of the waves. The experimental measurements were able to describe the wave transformations over the marsh segments. The influence of coastal wetlands was identified to affect the hydrodynamic process and reduce the total wave energy which is dissipated and redistributed by vegetation. The presence of the mounds induced an important decrease in the wave height, in addition to the damping of the waves by the vegetation stems. The variation in spatial coverage of the wetland model has been shown to highly affect the flow dynamics by generating offshore directed flow in the channel and onshore directed flow on the marsh mounds. This experimental approach provides a further understanding of flow dynamics by waves and surge in wetlands, at a large scale.Item Hydrodynamic instabilities of radiative blast waves(2013-12) Kim, In Tai; Ditmire, Todd R.We present the results from a series of experimental investigations into the hydrodynamic instabilities that occur in radiative blast waves. In particular, we examine the Vishniac instability in which the perturbation modes oscillate in time and, for certain mode numbers and polytropic index of the medium, can exhibit a growth in their amplitudes. Experiments were conducted on the GHOST laser laboratory in which a source of atomic clusters was irradiated by a 1J-2J, 115fs laser pulse to produce cylindrical blast waves. The thrust of this thesis falls into two categories. First, we analyze the effects radiative cooling has on the evolution of blast waves such as the lowering of the effective polytropic index and consequently the lowering of their deceleration parameter. Radiation from the blast wave surface results in a preheated ionization precursor in the upstream material and is indicated by a gradual decline in the electron density profile of the blast wave rather than a sharp jump. This mechanism, if strong enough, can also create a secondary shock wave to form ahead of the main blast wave. The second set of experiments investigates the temporal evolution of longitudinal perturbations induced on the blast waves by use of a transverse interferometric beam that modifies the cluster medium prior to the onset of the main pump beam. These perturbations are analyzed and compared to theory set forth in Vishniac's mechanism for oscillatory instabilities and their growth rate.Item Imaging particle migration with electrical impedance tomography: an investigation into the behavior and modeling of suspension flows(2004) Norman, Jay Thomas; Bonnecaze, R. T. (Roger T.)Item Multidimensional multiscale dynamics of high-energy astrophysical flows(2010-05) Couch, Sean Michael; Wheeler, J. Craig; Milosavljević, Miloš; Bromm, Volker; Hoeflich, Peter; Jaffe, Daniel; Kumar, PawanAstrophysical flows have an enormous dynamic range of relevant length scales. The physics occurring on the smallest scales often influences the physics of the largest scales, and vice versa. I present a detailed study of the multiscale and multidimensional behavior of three high-energy astrophysical flows: jet-driven supernovae, massive black hole accretion, and current-driven instabilities in gamma-ray burst external shocks. Both theory and observations of core-collapse supernovae indicate these events are not spherically-symmetric; however, the observations are often modeled assuming a spherically-symmetric explosion. I present an in-depth exploration of the effects of aspherical explosions on the observational characteristics of supernovae. This is accomplished in large part by high-resolution, multidimensional numerical simulations of jet-driven supernovae. The existence of supermassive black holes in the centers of most large galaxies is a well-established fact in observational astronomy. How such black holes came to be so massive, however, is not well established. In this work, I discuss the implications of radiative feedback and multidimensional behavior on black hole accretion. I show that the accretion rate is drastically reduced relative to the Eddington rate, making it unlikely that stellar mass black holes could grow to supermassive black holes in less than a Hubble time. Finally, I discuss a mechanism by which magnetic field strength could be enhanced behind a gamma-ray burst external shock. This mechanism relies on a current-driven instability that would cause reorganization of the pre-shock plasma into clumps. Once shocked, these clumps generate vorticity in the post-shock plasma and ultimately enhance the magnetic energy via a relativistic dynamo process.Item Non-Darcy flow through porous media(2000) Bené, James Edward; Sharp, John Malcolm, Jr., 1944-Since its introduction, Darcy's law has been implemented as a mathematical tool that allows simple calculation and prediction of low velocity subsurface flows. However, turbulence, non-isothermal conditions, as well as other factors can create conditions where Darcy's law does not accurately describe the head and velocity distributions within a given porous matrix. Darcy's law has been widely applied to analytical and numerical modeling of fluid flow through porous matrix, regardless of the hydrogeologic setting. This study attempts to quantify the error incurred by these models through simultaneous numerical modeling of the mass continuity equation using Darcy's law as well as Forchheimer's relation. To this end, results from steady-state and transient Darcy-based and Forchheimer-based numerical models are presented in this study.Item Reactive transport modeling in fractures and two-phase flow(2003) Noh, Myeong Hwan; Lake, Larry W.This study presents a mathematical model to simulate hydrodynamics and fluid-mineral reactions in a fracture within permeable media. Fluid convection, diffusion and precipitation / dissolution (PD) reactions inside a finite space are solved as a simplified representation of natural fracture mineralization. The problem involves mass transfer within the fluid accompanied by chemical reaction at the fracture surface. Mass-conservation equations for components in the fluid are solved, and these are coupled with chemical reaction at the fracture surface. The intent of this model is to show the time evolution of fracture aperture shrinkage patterns caused by the calcite cementation. We present the aperture width distribution along the fracture. In this study, we consider the precipitate as porous media and allow porosity and permeability in the cement. Therefore, the calcite cementation completely fills eventually. As a second subject, the reactive transport model of CO2 sequestration in aquifers is studied. Geologic formations are considered as a target for the sequesvi tration ofCO2 from stationary sources such as power plants or large industrial facilities. Deep saline aquifers have a large potential storage capacity for CO2 and they are ubiquitous in sedimentary formations. CO2 can be sequestered in geologic formations by three principal mechanisms: hydrodynamic trapping, solubility trapping and mineral trapping. Mineral trapping is the most stable way of CO2 sequestration in aquifers. Storage capacities of CO2 for each trapping mechanism are presented using GEM, a commercial program from Computer Modeling Group Ltd. We also present the anlaytical solutions for the miscible displacement and compare them with the numerical results. Developing methods for increasing the mineral trapping creates stable repositories of carbon dioxide and that decreases mobile hazards such as leakage of CO2 to the surface.Item Regional analysis of Residual Oil Zone potential in the Permian Basin(2014-08) West, Logan Mitchell; Tinker, Scott W. (Scott Wheeler)This study provides independent analysis of Residual Oil Zones (ROZs) in the Permian Basin from a regional perspective, focusing on the formation mechanism and present ROZ locations. Results demonstrate widespread potential for ROZs, defined here as thick volumes of reservoir rock containing near-residual saturations of predominantly immobile oil formed by natural imbibition and displacement of oil by dynamic buoyant or hydrodynamic forces. Previous work suggests hydrodynamic forces generated by regional tectonic uplift drove widespread oil remobilization and ROZ creation. To test the hypothesis, uplift and tilting are quantified and the resulting peak regional potentiometric gradient used as a physical constraint to compute and compare predicted ROZ thicknesses from hydrodynamics for several ROZ-bearing San Andres fields with known ROZ thicknesses. Late-Albian Edwards Group geologic contacts, which are interpreted to have been deposited near sea level prior to uplift, are used as a regional datum. Approximate elevations determined for the present datum show ~1800 m of differential uplift since Edwards deposition, with an average regional slope of ~0.128˚. This post-Edwards tilting increased the pre-existing regional structural gradient of the San Andres Formation to ~0.289˚. Using the calculated post-Edwards gradient results in to prediction of ROZ thicknesses from hydrodynamics that is consistent with measured ROZ thicknesses at several fields. When compared with countervailing buoyancy forces, hydrodynamics is calculated to be the more dominant driving force of oil movement for reservoirs with structural dips less than 1.5˚, which is the common dip for San Andres Formation platform deposits where ROZs have been identified. To predict the location of ROZs, ROZ-related oil field properties were identified and analyzed for over 2,800 Permian Basin reservoirs. A strong basin-wide correlation between API and crude sulfur content is consistent with the expected outcome of oil degradation driven by oil-water interaction, and supports the use of API and sulfur content as proxies for ROZ potential in the Permian Basin. Spatial analysis of sulfur data shows that the highest probability for ROZ existence exists in Leonardian through Guadalupian-age reservoirs, distributed primarily in shelf and platform areas of Permian structures. Combined, these results support the widespread potential for ROZs across the Permian Basin generated primarily by regional scale tilting and resultant hydrodynamic forces.Item Simulations of granular materials: kinetics and hydrodynamic phenomena(2003) Moon, Sung Joon; Swift, Jack B.Granular materials often exhibit fluid-like behavior in the presence of an external forcing. This dissertation deals with kinetics and hydrodynamic phenomena in granular fluids subject to two types of forcing, vertical oscillation and homogeneous bulk heating, using a molecular dynamics simulation of frictional inelastic hard spheres. The oscillated granular fluid is simulated to probe microscopic dynamics of the transition from a wave pattern to spatiotemporal chaos, and to reveal a new kind of convection, transport, and segregation mechanism that is induced by a kink (a boundary between domains oscillating out of phase by π). We also examine the role of friction in the wave pattern, and find that a pattern loses its stability without friction. Due to their dissipative nature, granular fluids are always far from equilibrium, and the velocity distributions deviate from the Maxwellian. The single particle distribution functions both in homogeneously heated and vertically oscillated granular gases are studied. High energy tails of the distributions are described by stretched exponentials ∼ exp(−Av α ), and the exponent α depends on the system and material parameters. Precollisional velocities are strongly correlated (up to 15% of the granular temperature), and the correlations decay algebraically with the distance from a grain (∼ r −(1+δ) , where 0.2 < δ < 0.3) in a three-dimensional system. The normal shock wave in vertically oscillated layers of frictionless inelastic hard spheres are studied, and the results are compared with a continuum model; the agreement is shown to be remarkably good, even with the failure of the molecular chaos assumption and mean-field approximation that are used in the derivation of the model. Continuum equations for realistic granular fluids might include friction and a velocity-dependent coefficient of restitution, and the derivation of the equations accounting for such properties is still far from complete. We show that the coarse-grained integration/bifurcation method can be successfully applied to granular fluids. This method enables the accomplishment of some of the tasks traditionally performed only by use of continuum equations, even without the knowledge of the equations.Item Simulations of high-energy astrophysical phenomena(2014-12) Lindner, Christopher Carl; Milosavljević, MilošSupercomputer technology has revolutionized our studies of the most energetic astrophysical phenomena. Here, I present my simulations of energetic outbursts of gamma rays and the explosions of massive stars, and my efforts to further the computational astrophysics frontier with the development of a radiation hydrodynamics code. First, I present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst (GRB) progenitor star, a "collapsar," onto the central compact object, which we assume is a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB [gamma]-ray and X-ray light curve, which lends support to the proposal by Kumar et al. (2008a,b) that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of ~ 0.2 [solar mass] s⁻¹. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied by a sudden and rapid power-law decline in the central accretion rate [mathematical formula], which resembles the L [subscript x] [is proportional to] t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows, which is potentially suggestive of the "plateau"' phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase will be ~ 20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt [gamma]-ray emission should have more slowly rotating envelopes. Observational evidence suggests a link between long GRBs and Type Ic supernovae. I propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. I present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies ~ 5 x 10⁵⁰ ergs, velocities ~ 3000 km s⁻¹, and unbound material masses > 5 [solar mass] are possible in a rapidly rotating 16 [solar mass] main sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications. In many high-energy astrophysical phenomena, the force of radiation pressure will have a direct effect on the hydrodynamics. Observing radiation is also the primary way we investigate our universe. With this in mind, I present my expansion of the FLASH hydrodynamics code, where I have implemented a gray, flux-limited diffusion (FLD) radiation hydrodynamics (RHD) solver. My solver utilizes the FLASH's diffusion packages that are powered by HYPRE. I have written a new, efficient radiation-matter coupling solver, which exactly integrates the equations for radiation-matter coupling and operates without any time step restrictions. I have also rewritten the unsplit hydrodynamics solver in FLASH to incorporate the changes in PPM characteristic tracing and the Riemann solver required to properly capture the radiation pressure force in regions that are not entirely optically thick. This has required the addition of a new Riemann solver to FLASH, similar to the Riemann solver in the CASTRO RHD code. I then present my validation tests of the code. This code will be made publicly available.Item Stokesian dynamic simulations and analyses of interfacial and bulk colloidal fluids(Texas A&M University, 2006-10-30) Anekal, Samartha GuhaUnderstanding dynamics of colloidal dispersions is important for several applications ranging from coatings such as paints to growing colloidal crystals for photonic bandgap materials. The research outlined in this dissertation describes the use of Monte Carlo and Stokesian Dynamic simulations to model colloidal dispersions, and the development of theoretical expressions to quantify and predict dynamics of colloidal dispersions. The emphasis is on accurately modeling conservative, Brownian, and hydrodynamic forces to model dynamics of colloidal dispersions. In addition, we develop theoretical expressions for quantifying self-diffusion in colloids interacting via different particle-particle and particle-wall potentials. Specifically, we have used simulations to quantitatively explain the observation of anomalous attraction between like-charged colloids, develop a new criterion for percolation in attractive colloidal fluids, and validate the use of analytical expressions for quantifying diffusion in interfacial colloidal fluids. The results of this work contribute to understanding dynamics in interfacial and bulk colloidal fluids.Item Superluminous supernovae : theory and observations(2013-05) Chatzopoulos, Emmanouil; Wheeler, J. CraigThe discovery of superluminous supernovae in the past decade challenged our understanding of explosive stellar death. Subsequent extensive observations of superluminous supernova light curves and spectra has provided some insight for the nature of these events. We present observations of one of the most luminous self-interacting supernovae ever observed, the hydrogen-rich SN 2008am discovered by the Robotic Optical Transient Search Experiment Supernova Verification Project with the ROTSE-IIIb telescope located in the McDonald Observatory. We provide theoretical modeling of superluminous supernova light curves and fit the models to a number of observed events and similar transients in order to understand the mechanism that is responsible for the vast amounts of energy emitted by these explosions. The models we investigate include deposition of energy due to the radioactive decays of massive amounts of nickel-56, interaction of supernova ejecta with a dense circumstellar medium and magnetar spin-down. To probe the nature of superluminous supernovae progenitor stars we study the evolution of massive stars, including important effects such as rotation and magnetic fields, and perform multi-dimensional hydrodynamics simulations of the resulting explosions. The effects of rotational mixing are also studied in solar-type secondary stars in cataclysmic variable binary star systems in order to provide an explanation for some carbon-depleted examples of this class. We find that most superluminous supernovae can be explained by violent interaction of the SN ejecta with >1 Msun dense circumstellar shells ejected by the progenitor stars in the decades preceding the SN explosion.Item Vertically Loaded Anchor: Drag Coefficient, Fall Velocity, and Penetration Depth using Laboratory Measurements(2011-08-08) Cenac, WilliamThe offshore oilfield industry is continuously developing unique and break-through technologies and systems to extract hydrocarbons from ever increasing ocean depths. Due to the extreme depths being explored presently, large anchors are being utilized to secure temporary and permanent facilities over their respective drilling/production site. A vertically loaded, torpedo-style, deepwater mooring anchor developed by Delmar Systems, Inc. is one of these anchors. The OMNI-Max anchor is an efficient, cost-effective alternative for use as a mooring system anchor intended for floating facilities. The OMNI-Max is designed to free-fall towards the ocean bottom and uses its kinetic energy for self-embedment into the soil, providing a mooring system anchor point. Values such as drag coefficient and terminal velocity are vital in predicting embedment depth to obtain the mooring capacity required by the floating facility. Two scaled models of the Mark I OMNI-Max anchor were subjected to a series of tests in the Haynes Coastal Engineering Laboratory at Texas A & M University to evaluate the overall drag coefficient and penetration depth. The 1/24 scale model was tested by measuring the amount of penetration into an artificial mud mixture. The 1/15 scale model was attached to a tow carriage and towed through a water-filled tank to measure the drag forces and evaluate the drag coefficient. The anchor terminal velocity was measured using underwater cameras to track the free fall of the model anchor through 15 ft of water inside the tow tank. The 1/24 scale model penetrated the mud an average of 22 inches from the leading tip of the anchor to the mud surface, approximately 1.5 anchor lengths. The penetration depth increased as impact velocity increased, while the penetration depth decreased as the fins were retracted. The 1/15 scale anchor was towed at 6 different velocities producing a varied total drag coefficient between 0.70 and 1.12 for Reynolds number flows between 3.08E 05 and 1.17E 06. The drag coefficient increased as the fins were retracted and when the mooring rope was attached. The 1/15 scale anchor was allowed to free-fall in the tow tank and obtained an average terminal velocity of and 14.6 feet per second. The drag coefficients ranged from 0.46 to 0.83, which increased as the fins were retracted. When using the results to estimate prototype sized anchor drag coefficient, the average value was estimated to be 0.75.