Current Search: ElAzab, Anter (x)
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 Title
 StressDriven Surface Instabilities in Epitaxial Thin Films.
 Creator

Henke, Steven F., ElAzab, Anter, Erlebacher, Gordon, Department of Scientific Computing, Florida State University
 Abstract/Description

Heteroepitaxial thin films are essential components in many technological applications including optical, electronic and other functional devices. These films are also becoming important in the coating technologies for hightemperature materials applications. Typical heteroepitaxial systems involve one or more solid phases deposited on support structure called the substrate. Often the lattice and thermal mismatch in these systems results in significant elastic strains that, under the...
Show moreHeteroepitaxial thin films are essential components in many technological applications including optical, electronic and other functional devices. These films are also becoming important in the coating technologies for hightemperature materials applications. Typical heteroepitaxial systems involve one or more solid phases deposited on support structure called the substrate. Often the lattice and thermal mismatch in these systems results in significant elastic strains that, under the appropriate temperature conditions, drive mass transport by diffusion. Surface diffusion in these systems is usually a dominant mass transport mechanism that leads to morphological evolution of the surface. This evolution is called stressdriven morphological growth, and it has received much attention by materials modelers. In the current work, the problem of stressdriven morphological evolution in strained thin films is revisited; we develop a generalized formulation of this problem in the nonlinear regime based upon a curvilinear coordinate formalism and finite element solution of the elastic subproblem. This combination of methods facilitates the analysis of the onset of the instability and the early stage temporal evolution of the film surface. We apply our numerical scheme to surface wave, dot, pit, and ring morphologies and demonstrate the effects of model parameters on the incipient instabilities.
Show less  Date Issued
 2010
 Identifier
 FSU_migr_etd4126
 Format
 Thesis
 Title
 Effect of Interfaces on the Thermal, Mechanical and Chemical Characteristics of Carbon Nanotubes.
 Creator

Shen, Guoan, Chandra, Namas, Andrei, Petru, Dommelen, Leon van, ElAzab, Anter, Shih, Chiang, Department of Mechanical Engineering, Florida State University
 Abstract/Description

The primary focus of this work is to explore the effect of interface on thermal, mechanical, and chemical properties of carbon nanotubes (CNTs) and the methods to modify the interface between CNTs and CNTs based composites. CNTs are potentially promising fibers for ultrahighstrength composites. The load transfer between the inner and outer tubes in multiwall nanotubes (MWNTs) has to be clearly understood to realize the potential of MWNTs in composites and other applications such as nano...
Show moreThe primary focus of this work is to explore the effect of interface on thermal, mechanical, and chemical properties of carbon nanotubes (CNTs) and the methods to modify the interface between CNTs and CNTs based composites. CNTs are potentially promising fibers for ultrahighstrength composites. The load transfer between the inner and outer tubes in multiwall nanotubes (MWNTs) has to be clearly understood to realize the potential of MWNTs in composites and other applications such as nanosprings, and nanobearings. This dissertation studies the load transfer between the walls of MWNTs in both tension and compression using molecular dynamics simulations. It is found that only the minimal load is transferred to the inner nanotube in tension. The load transfer of capped nanotubes in compression is much higher than in tension. The presence of a few interstitial atoms between the walls of MWNTs can significantly improve the stiffness and enhance the load transfer to the inner nanotubes in both tension and compression. The modification of the interface of CNTs is a key factor for effectively using CNTs in many applications. The use of molecular statics and dynamics helps exploring ion irradiation as a method for functionalization of CNTs. It is found that ion bombardment of single and Multiwall carbon nanotubes creates vacancies and defects, which can act as highenergy sites for further chemical reactions; furthermore, ion irradiation of CNTs embedded in polymer matrix creates chemical attachments between CNTs and polymer matrix, enhancing the compositing process. Mechanical property simulations based on tension and pullout tests indicate that the chemical links between constituents in CNT–polymer systems result in higher load transfer, and hence, better composite properties. The effect of the interface turns out to be very crucial for printing in nanolithography processes. Molecular dynamics simulation is applied to extract interface properties, such as friction and adhesion, in nanoscale; later, the properties are input into a largescale FEM model. As found, the protrusion problem is caused by many factors, such as strength of polymer at high temperature, thermal expansion properties, and depth of metal.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd0310
 Format
 Thesis
 Title
 Interfacial and Defect Structure in Nanoscale Ceria/Zirconia Superlattices.
 Creator

Dyer, Michael, ElAzab, Anter, Shih, Chiang, Kalu, Peter N., Chandra, Namas, Department of Mechanical Engineering, Florida State University
 Abstract/Description

Ceria and zirconia ceramics are well known for their ability to conduct oxygen ions, making them useful in constructing devices such as oxygen sensors and solidoxide fuel cells. Increasing the ionic conductivity of these materials is a major point of interest, because this increases the efficiency and decreases the operating temperature of such fuel cells. Recent experimental results have shown that superlattices of alternating CeO2 and ZrO2 thin films that are alloyed with Gd2O3 exhibit...
Show moreCeria and zirconia ceramics are well known for their ability to conduct oxygen ions, making them useful in constructing devices such as oxygen sensors and solidoxide fuel cells. Increasing the ionic conductivity of these materials is a major point of interest, because this increases the efficiency and decreases the operating temperature of such fuel cells. Recent experimental results have shown that superlattices of alternating CeO2 and ZrO2 thin films that are alloyed with Gd2O3 exhibit ionic conductivity that is superior to the individual monolithic materials. The enhanced ionic conductivity in these structures is attributed to the interfacial effects. Analytical modeling has shown that there are two possible mechanisms that lead to changes in the ionic conductivity: (a) an enhanced equilibrium concentration of oxygen vacancies in the layered structure arising as a part of the thermodynamic equilibrium across the interfaces, and (b) change in the defect formation energies and kinetic barriers due to interaction of defects with the epitaxial strain field in the heterogeneous system. The extent of this interaction is determined by the layer thickness and interfacial dislocation structure. Aiming to understand these mechanisms, a molecular dynamics (MD) study is performed to determine the interfacial and defect structures in pure and Gddoped CeO2/ZrO2 superlattices, and the results are compared with the recent experimental observations.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd0614
 Format
 Thesis
 Title
 Centroidal Voronoi Tessellations for Mesh Generation: from Uniform to Anisotropic Adaptive Triangulations.
 Creator

Nguyen, Hoa V., Gunzburger, Max D., ElAzab, Anter, Peterson, Janet, Wang, Xiaoming, Wang, Xiaoqiang, Department of Mathematics, Florida State University
 Abstract/Description

Mesh generation in regions in Euclidean space is a central task in computational science, especially for commonly used numerical methods for the solution of partial differential equations (PDEs), e.g., finite element and finite volume methods. Mesh generation can be classified into several categories depending on the element sizes (uniform or nonuniform) and shapes (isotropic or anisotropic). Uniform meshes have been well studied and still find application in a wide variety of problems....
Show moreMesh generation in regions in Euclidean space is a central task in computational science, especially for commonly used numerical methods for the solution of partial differential equations (PDEs), e.g., finite element and finite volume methods. Mesh generation can be classified into several categories depending on the element sizes (uniform or nonuniform) and shapes (isotropic or anisotropic). Uniform meshes have been well studied and still find application in a wide variety of problems. However, when solving certain types of partial differential equations for which the solution variations are large in some regions of the domain, nonuniform meshes result in more efficient calculations. If the solution changes more rapidly in one direction than in others, nonuniform anisotropic meshes are preferred. In this work, first we present an algorithm to construct uniform isotropic meshes and discuss several mesh quality measures. Secondly we construct an adaptive method which produces nonuniform anisotropic meshes that are well suited for numerically solving PDEs such as the convection diffusion equation. For the uniform Delaunay triangulation of planar regions, we focus on how one selects the positions of the vertices of the triangulation. We discuss a recently developed method, based on the centroidal Voronoi tessellation (CVT) concept, for effecting such triangulations and present two algorithms, including one new one, for CVTbased grid generation. We also compare several methods, including CVTbased methods, for triangulating planar domains. Furthermore, we define several quantitative measures of the quality of uniform grids. We then generate triangulations of several planar regions, including some having complexities that are representative of what one may encounter in practice. We subject the resulting grids to visual and quantitative comparisons and conclude that all the methods considered produce highquality uniform isotropic grids and that the CVTbased grids are at least as good as any of the others. For more general grid generation settings, e.g., nonuniform and/or anistropic grids, such quantitative comparisons are much more difficult, if not impossible, to either make or interpret. This motivates us to develop CVTbased adaptive nonuniform anisotropic mesh refinement in the context of solving the convectiondiffusion equation with emphasis on convectiondominated problems. The challenge in the numerical approximation of this equation is due to large variations in the solution over small regions of the physical domain. Our method not only refines the underlying grid at these regions but also stretches the elements according to the solution variation. Three main ingredients are incorporated to improve the accuracy of numerical solutions and increase the algorithm's robustness and efficiency. First, a streamline upwind Petrov Galerkin method is used to produce a stabilized solution. Second, an adapted metric tensor is computed from the approximate solution. Third, optimized anisotropic meshes are generated from the computed metric tensor. Our algorithm has been tested on a variety of 2dimensional examples. It is robust in detecting layers and efficient in resolving nonphysical oscillations in the numerical approximation.
Show less  Date Issued
 2008
 Identifier
 FSU_migr_etd2616
 Format
 Thesis
 Title
 The Effects of Variable Tin Content on the Properties of A15 Superconducting Niobium3Tin.
 Creator

Zhou, Jian, Larbalestier, David, Siegrist, Theo, Hellstrom, Eric, Van Sciver, Steven, ElAzab, Anter, Department of Mechanical Engineering, Florida State University
 Abstract/Description

Although 2011 marks the 50th anniversary of Nb3Sn as the first high field superconductor and Nb3Sn is the presently most widely used high field superconductor, there is no detailed quantitative understanding of how its properties, particularly the upper critical field (Hc2), varies with composition. Since all practical wire forms of Nb3Sn contain the full range of A15 phase compositions, generally thought to range from ~1825 at% Sn, this uncertainty of Hc2 compromises their understanding. To...
Show moreAlthough 2011 marks the 50th anniversary of Nb3Sn as the first high field superconductor and Nb3Sn is the presently most widely used high field superconductor, there is no detailed quantitative understanding of how its properties, particularly the upper critical field (Hc2), varies with composition. Since all practical wire forms of Nb3Sn contain the full range of A15 phase compositions, generally thought to range from ~1825 at% Sn, this uncertainty of Hc2 compromises their understanding. To provide this understanding and to address some recent uncertainties about the binary phase diagram, we have carefully fabricated samples of various compositions, evaluating their properties by multiple techniques such as Xray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS), superconducting quantum interference device (SQUID), specific heat and Magnetooptical technique (MO) and reversible magnetization which are sensitive to average properties and compared them to the more often applied percolative measurements such as the transport measurements of Hc2. We found that it was much easier to make homogeneous samples from reaction sintering of high Sn mixtures of Nb and Sn powders such as the nominal 25 at% and 27 at% Sn samples. Lower Sn samples could not be made homogeneous, thus forcing us to arc melt such samples. We found that Tc and Hc2 of our homogenous Sn samples fell into 2 classes, Sn rich with 23.33~24.9 at% Sn (Tc~18K and Hc2 ~29T) and Snpoor with 16.62~18.21 at% Sn (Tc ~6K and Hc2 ~8T). Multiple characterizations indicate that our samples, though not yet completely homogeneous, are almost certainly more homogeneous than samples in the literature. An unexpected and important result is that samples exhibited identical upper critical field Hc2(0.3 K) ~ 29± 0.2 T with or without undergoing the cubictotetragonal transition, a result in strong contrast to widely used multiplesource data compilations that show a strong depression of Hc2(0K) from 29 T to 21.4 T in the tetragonal state. In agreement with the literature, we did find that the highest Hc2 occurs for slightly dirtier Nb3Sn. Our results are largely consistent with the phase diagram of Charlesworth et al. for A15 phase compositions but with the correction that the line compound at the right hand side of Nb3Sn region is NbSn2 not Nb6Sn5 is preferred and verified by our homogenous bulk binary Nb3Sn samples. We found that the lattice parameters of Snrich Nb3Sn are identical over the Sn range 23.33~24.9 at% Sn. We have established the route to fabricate samples of the highest homogeneity and the techniques to evaluate their structure, homogeneity, and superconducting properties. The fabrication route and characterization technique will provide a basis for future ternary and quaternary Nb3Sn investigation. Furthermore, our homogenous binary bulk Nb3Sn results offer new and reliable benchmarks for Nb3Sn strand comparisons.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd5302
 Format
 Thesis
 Title
 Numerical Implementation of Continuum Dislocation Theory.
 Creator

Xia, Shengxu, ElAzab, Anter, Plewa, Tomasz, Wang, Xiaoqiang, Department of Scientific Computing, Florida State University
 Abstract/Description

This thesis aims at theoretical and computational modeling of the continuum dislocation theory coupled with its internal elastic field. In this continuum description, the spacetime evolution of the dislocation density is governed by a set of hyperbolic partial differential equations. These PDEs must be complemented by elastic equilibrium equations in order to obtain the velocity field that drives dislocation motion on slip planes. Simultaneously, the plastic eigenstrain tensor that serves as...
Show moreThis thesis aims at theoretical and computational modeling of the continuum dislocation theory coupled with its internal elastic field. In this continuum description, the spacetime evolution of the dislocation density is governed by a set of hyperbolic partial differential equations. These PDEs must be complemented by elastic equilibrium equations in order to obtain the velocity field that drives dislocation motion on slip planes. Simultaneously, the plastic eigenstrain tensor that serves as a known field in equilibrium equations should be updated by the motion of dislocations according to Orowan's law. Therefore, a stress dislocation coupled process is involved when a crystal undergoes elastoplastic deformation. The solutions of equilibrium equation and dislocation density evolution equation are tested by a few examples in order to make sure appropriate computational schemes are selected for each. A coupled numerical scheme is proposed, where resolved shear stress and Orowan's law are two passages that connect these two sets of PDEs. The numerical implementation of this scheme is illustrated by an example that simulates the recovery process of a dislocated cubic crystal. The simulated result demonstrates the possibility to couple macroscopic(stress) and microscopic(dislocation density tensor) physical quantity to obtain crystal mechanical response.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd5280
 Format
 Thesis
 Title
 Monte Carlo Simulation of Phonon Transport in Uranium Dioxide.
 Creator

Deskins, Walter Ryan, ElAzab, Anter, Plewa, Tomasz, Wang, Xiaoqiang, Department of Scientific Computing, Florida State University
 Abstract/Description

Heat is transfered in crystalline semiconductor materials via lattice vibrations. Lattice vibrations are treated with a waveparticle duality just like photons are quantum mechanical representations of electromagnetic waves. The quanta of energy of these lattice waves are called phonons. The Boltzmann Transport Equation (BTE) has proved to be a powerful tool in modeling the phonon heat conduction in crystalline solids. The BTE tracks the phonon number density function as it evolves according...
Show moreHeat is transfered in crystalline semiconductor materials via lattice vibrations. Lattice vibrations are treated with a waveparticle duality just like photons are quantum mechanical representations of electromagnetic waves. The quanta of energy of these lattice waves are called phonons. The Boltzmann Transport Equation (BTE) has proved to be a powerful tool in modeling the phonon heat conduction in crystalline solids. The BTE tracks the phonon number density function as it evolves according to the drift of all phonons and to the phononphonon interactions (or collisions). Unlike Fourier's law which is limited to describing diffusive energy transport, the BTE can accurately predict energy transport in both ballistic (virtually no collisions) and diffuse regimes. Motivated by the need to understand thermal transport in irradiated Uranium Dioxide at the mesoscale, this work investigates phonon transport in UO2 using Monte Carlo simulation. The simulation scheme aims to solve the Boltzmann transport equation for phonons within a relaxation time approximation. In this approximation the Boltzmann transport equation is simplified by assigning time scales to each scattering mechanism associated with phonon interactions. The Monte Carlo method is first benchmarked by comparing to similar models for silicon. Unlike most previous works on solving this equation by Monte Carlo method, the momentum and energy conservation laws for phononphonon interactions in UO2 are treated exactly; in doing so, the magnitude of possible wave vectors and frequency space are all discretized and a numerical routine is then implemented which considers all possible phononphonon interactions and chooses those interactions which obey the conservation laws. The simulation scheme accounts for the acoustic and optical branches of the dispersion relationships of UO2. The six lowest energy branches in the [001] direction are tracked within the Monte Carlo. Because of their predicted low group velocities, the three remaining, highenergy branches are simply treated as a reservoir of phonons at constant energy in Kspace. These phonons contribute to the thermal conductivity only by scattering with the six lower energy branches and not by their group velocities. Using periodic boundary conditions, this work presents results illustrating the diffusion limit of phonon transport in UO2 single crystals, and computes the thermal conductivity of the material in the diffusion limit based on the detailed phonon dynamics. The temperature effect on conductivity is predicted and the results are compared with experimental data available in the literature.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd4796
 Format
 Thesis
 Title
 Phase Field Modeling of Microstructure Evolution in Thermal Barrier Coating Systems.
 Creator

Ahmed, Karim, ElAzab, Anter, MeyerBaese, Anke, Shanbhag, Sachin, Wang, Xiaoqiang, Program in Materials Science, Florida State University
 Abstract/Description

The development of robust thermal barrier coating (TBC) systems is crucial in many hightemperature applications. The performance of a TBC system is significantly limited by microstructural evolution mechanisms, such as sintering at elevated temperatures. Sintering reduces the porosity of TBC and makes it denser which eventually increases the thermal conductivity and reduces the strain compliance of TBC. Understanding how sintering proceeds in TBC systems is thus important in improving the...
Show moreThe development of robust thermal barrier coating (TBC) systems is crucial in many hightemperature applications. The performance of a TBC system is significantly limited by microstructural evolution mechanisms, such as sintering at elevated temperatures. Sintering reduces the porosity of TBC and makes it denser which eventually increases the thermal conductivity and reduces the strain compliance of TBC. Understanding how sintering proceeds in TBC systems is thus important in improving the design of such systems. An elaborate phase field model was developed in order to understand the sintering behavior of columnar TBC structure. The model takes into account different sintering mechanisms, such as volume diffusion, grain boundary diffusion, surface diffusion, and grain boundary migration, coupled with elastic strain arising from the thermal expansion mismatch in thermal barrier coating system. Direct relations between model parameters and material properties were established. Such relations facilitate quantitative studies of the sintering process in any material of interest. The model successfully demonstrates a strong dependence of the sintering process in TBC on the initial morphology and dimensions of coatings, strain, and temperature.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd4684
 Format
 Thesis
 Title
 Computational Modeling of Elastic Fields in Dislocation Dynamics.
 Creator

Mohamed, Mamdouh, ElAzab, Anter, Van Dommelen, Leon, Erlebacher, Gordon, Ye, Ming, Wang, Xiaoqiang, Department of Scientific Computing, Florida State University
 Abstract/Description

In the present work, we investigate the internal fields generated by the dislocation structures that form during the deformation of copper single crystals. In particular, we perform computational modeling of the statistical and morphological characteristics of the dislocation structures obtained by dislocation dynamics simulation method and compare the results with Xray microscopy measurements of the same data. This comparison is performed for both the dislocation structure and their...
Show moreIn the present work, we investigate the internal fields generated by the dislocation structures that form during the deformation of copper single crystals. In particular, we perform computational modeling of the statistical and morphological characteristics of the dislocation structures obtained by dislocation dynamics simulation method and compare the results with Xray microscopy measurements of the same data. This comparison is performed for both the dislocation structure and their internal elastic fields for the cases of homogeneous deformation and indentation of copper single crystals. A direct comparison between dislocation dynamics predictions and Xray measurements plays a key role in demonstrating the fidelity of discrete dislocation dynamics as a predictive computational mechanics tool and in understanding the Xray data. For the homogeneous deformation case, dislocation dynamics simulations were performed under periodic boundary conditions and the internal fields of dislocations were computed by solving an elastic boundary value problem of manydislocation system using the finite element method. The distribution and pair correlation functions of all internal elastic fields and the dislocation density were computed. For the internal stress field, the availability of such statistical information paves the way to the development of a densitybased mobility law of dislocations in continuum dislocation dynamics models, by correlating the internalstress statistics with dislocation velocity statistics. The statistical analysis of the lattice rotation and the dislocation density fields in the deformed crystal made possible the direct comparison with Xray measurements of the same data. Indeed, a comparison between the simulation and experimental measurements has been possible, which revealed important aspects of similarity and differences between the simulation results and the experimental data. In the case of indentation, which represents a highly inhomogeneous deformation, a contact boundary value problem was solved in conjunction with a discretedislocation dynamics simulation model; the discrete dislocation dynamics simulation was thus enabled to handle finite domains under mixed traction/displacement boundary conditions. The loaddisplacement curves for indentation experiments were analyzed with regard to cross slip, indentation speed and indenter shape. The lattice distortion fields obtained by indentation simulations were directly compared with their experimental counterparts. Other indentation simulations were also carried out, giving insight into different aspects of microscale indentation deformation.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd6962
 Format
 Thesis
 Title
 SurfaceBulk Electrochemical Coupling and offStoichiometry in Uranium Dioxide.
 Creator

Hassan, AbdelRahman, ElAzab, Anter, Andrei, Petru, Kostov, Milen, Program in Materials Science, Florida State University
 Abstract/Description

Irradiation alters the local stoichiometry of oxides significantly. The resulting stoichiometric changes play a critical role in the dynamics of defects and microstructure evolution in oxides under irradiation. Stoichiometry in oxides is also sensitive to the surrounding oxygen environment. Motivated to study the equilibrium state of UO2, this thesis investigates a theoretical approach to model spatial distribution of defects and charge carriers. In general, the levels of point defects and...
Show moreIrradiation alters the local stoichiometry of oxides significantly. The resulting stoichiometric changes play a critical role in the dynamics of defects and microstructure evolution in oxides under irradiation. Stoichiometry in oxides is also sensitive to the surrounding oxygen environment. Motivated to study the equilibrium state of UO2, this thesis investigates a theoretical approach to model spatial distribution of defects and charge carriers. In general, the levels of point defects and electronic charge carriers in an oxide are sensitive to the oxygen partial pressure in contact with the oxide and temperature. The objective of this research is twofolded. First, a detailed point defect model based on density functional theory results is devised. The model takes into account multiple charge states for each defect type as well as all the dependencies of the formation thereof. Second, a spacecharge analysis is used to find the effect of surface and environment on the spatial variation of concentrations at equilibrium. A surface charge is known to form on the surface as a result of its interaction with the environment. This interaction is explained by the theory of ionosorption. The resulting effect is found by coupling bulk concentrations from the point defect model with the surface charge through solving the electrochemical sytem. The results found by the point defect model are shown to match the experimental data on UO2±x . As for the spacecharge analysis, the concentrations of individual defects showed an order of magnitude variation in the subsurface region. This implies the importance of the spacecharge effect in any kinetic study of the system since it is controlled by the defect composition at the interface.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd4896
 Format
 Thesis
 Title
 RealTime Particle Systems in the Blender Game Engine.
 Creator

Johnson, Ian, Erlebacher, Gordon, Plewa, Tomasz, ElAzab, Anter, Department of Scientific Computing, Florida State University
 Abstract/Description

Advances in computational power have lead to many developments in science and en tertainment. Powerful simulations which required expensive supercomputers can now be carried out on a consumer personal computer and many children and young adults spend countless hours playing sophisticated computer games. The focus of this research is the development of tools which can help bring the entertaining and appealing traits of video games to scientific education. Video game developers use many tools...
Show moreAdvances in computational power have lead to many developments in science and en tertainment. Powerful simulations which required expensive supercomputers can now be carried out on a consumer personal computer and many children and young adults spend countless hours playing sophisticated computer games. The focus of this research is the development of tools which can help bring the entertaining and appealing traits of video games to scientific education. Video game developers use many tools and programming languages to build their games, for example the Blender 3D content creation suite. Blender includes a Game Engine that can be used to design and develop sophisticated interactive experiences. One important tool in computer graphics and animation is the particle system, which makes simulated effects such as fire, smoke and fluids possible. The particle system available in Blender is unfortunately not available in the Blender Game Engine because it is not fast enough to run in realtime. One of the main factors contributing to the rise in computational power and the increas ing sophistication of video games is the Graphics Processing Unit (GPU). Many consumer personal computers are equipped with powerful GPUs which can be harnassed for general purpose computation. This thesis presents a particle system library is accelerated by the GPU using the OpenCL programming language. The library integrated into the Blender Game Engine providing an interactive platform for exploring fluid dynamics and creating video games with realistic water effects. The primary system implemented in this research is a fluid sim ulator using the Smoothed Particle Hydrodynamics technique for simulating incompressible fluids such as water. The library created for this thesis can simulate water using SPH at 40fps with upwards x ï¿¼ of 100,000 particles on an NVIDIA GTX480 GPU. The fluid system has interactive features such as object collision, and the ability to add and remove particles dynamically. These features as well as phsyical properties of the simulation can be controlled intuitively from the user interface of Blender.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd4931
 Format
 Thesis
 Title
 Characterization of MetalloceneCatalyzed Polyethylenes from Rheological Measurements Using a Bayesian Formulation.
 Creator

Takeh, Arsia, Shanbhag, Sachin, ElAzab, Anter, Beerli, Peter, Department of Scientific Computing, Florida State University
 Abstract/Description

Longchain branching affects the rheological properties of the polyethylenes strongly. Branching structure  density of branch points, branch length, and the locations of the branches  is complicated, therefore, without controlled branching structure it is almost impossible to study the effect of longchain branching on the rheological properties. Singlesite catalysts now make it possible to prepare samples in which the molecular weight distribution is relatively narrow and quite...
Show moreLongchain branching affects the rheological properties of the polyethylenes strongly. Branching structure  density of branch points, branch length, and the locations of the branches  is complicated, therefore, without controlled branching structure it is almost impossible to study the effect of longchain branching on the rheological properties. Singlesite catalysts now make it possible to prepare samples in which the molecular weight distribution is relatively narrow and quite reproducible. In addition, a particular type of singlesite catalyst, the constrained geometry catalyst, makes it possible to introduce low and wellcontrolled levels of long chain branching while keeping the molecular weight distribution narrow. Linear viscoelastic properties (LVE) of rheological properties contain a rich amount of data regarding molecular structure of the polymers. A computational algorithm that seeks to invert the linear viscoelastic spectrum of singlesite metallocenecatalyzed polyethylenes is presented in this work. The algorithm uses a general linear rheological model of branched polymers as its underlying engine, and is based on a Bayesian formulation that transforms the inverse problem into a sampling problem. Given experimental rheological data on unknown singlesite metallocenecatalyzed polyethylenes, it is able to quantitatively describe the range of values of weightaveraged molecular weight, MW, and average branching density, bm, consistent with the data. The algorithm uses a Markovchain Monte Carlo method to simulate the sampling problem. If, and when information about the molecular weight is available through supplementary experiments, such as chromatography or light scattering, it can easily be incorporated into the algorithm, as demonstrated.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd1729
 Format
 Thesis
 Title
 EdgeWeighted Centroidal Voronoi Tessellation Based Algorithms for Image Segmentation.
 Creator

Wang, Jie, Wang, Xiaoqiang, Wang, Xiaoming, Gunzburger, Max, Peterson, Janet, ElAzab, Anter, Department of Scientific Computing, Florida State University
 Abstract/Description

Centroidal Voronoi tessellations (CVTs) are special Voronoi tessellations whose generators are also the centers of mass (centroids) of the Voronoi regions with respect to a given density function. CVTbased algorithms have been proved very useful in the context of image processing. However when dealing with the image segmentation problems, classic CVT algorithms are sensitive to noise. In order to overcome this limitation, we develop an edgeweighted centroidal Voronoi Tessellation (EWCVT)...
Show moreCentroidal Voronoi tessellations (CVTs) are special Voronoi tessellations whose generators are also the centers of mass (centroids) of the Voronoi regions with respect to a given density function. CVTbased algorithms have been proved very useful in the context of image processing. However when dealing with the image segmentation problems, classic CVT algorithms are sensitive to noise. In order to overcome this limitation, we develop an edgeweighted centroidal Voronoi Tessellation (EWCVT) model by introducing a new energy term related to the boundary length which is called "edge energy". The incorporation of the edge energy is equivalent to add certain form of compactness constraint in the physical space. With this compactness constraint, we can effectively control the smoothness of the clusters' boundaries. We will provide some numerical examples to demonstrate the effectiveness, efficiency, flexibility and robustness of EWCVT. Because of its simplicity and flexibility, we can easily embed other mechanisms with EWCVT to tackle more sophisticated problems. Two models based on EWCVT are developed and discussed. The first one is "local variation and edgeweighted centroidal Voronoi Tessellation" (LVEWCVT) model by encoding the information of local variation of colors. For the classic CVTs or its generalizations (like EWCVT), pixels inside a cluster share the same centroid. Therefore the set of centroids can be viewed as a piecewise constant function over the computational domain. And the resulting segmentation have to be roughly the same with respect to the corresponding centroids. Inspired by this observation, we propose to calculate the centroids for each pixel separately and locally. This scheme greatly improves the algorithms' tolerance of withincluster feature variations. By extensive numerical examples and quantitative evaluations, we demonstrate the excellent performance of LVEWCVT method compared with several stateofart algorithms. LVEWCVT model is especially suitable for detection of inhomogeneous targets with distinct color distributions and textures. Based on EWCVT, we build another model for "Superpixels" which is in fact a "regularization" of highly inhomogeneous images. We call our algorithm for superpixels as "VCells" which is the abbreviation of "Voronoi cells". For a wide range of images, VCells is capable to generate roughly uniform subregions and meanwhile nicely preserves local image boundaries. The undersegmentation error is effectively limited in a controllable manner. Moreover, VCells is very efficient. The computational cost is roughly linear in image size with small constant coefficient. For megapixel sized images, VCells is able to generate very dense superpixels in a matter of seconds. We demonstrate that VCells outperforms several stateofart algorithms through extensive qualitative and quantitative results on a wide range of complex images. Another important contribution of this work is the "DetectingSegmentBreaking" (DSB) algorithm which can be used to guarantee the spatial connectedness of resulting segments generated by CVT based algorithms. Since the metric is usually defined on the color space, the resulting segments by CVT based algorithms are not necessarily spatially connected. For some applications, this feature is useful and conceptually meaningful, e.g., the foreground objects are not spatially connected. But for some other applications, like the superpixel problem, this "good" feature becomes unacceptable. By simple "extractingconnectedcomponent" and "relabeling" schemes, DSB successfully overcomes the above difficulty. Moreover, the computational cost of DSB is roughly linear in image size with a small constant coefficient. From the theoretical perspective, the innovative idea of EWCVT greatly enriches the methodology of CVTs. (The idea of EWCVT has already been used for variational curve smoothing and reconstruction problems.) For applications, this work shows the great power of EWCVT for image segmentation related problems.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd1244
 Format
 Thesis
 Title
 Peridynamic Multiscale Models for the Mechanics of Materials: Constitutive Relations, Upscaling from Atomistic Systems, and Interface Problems.
 Creator

Seleson, Pablo D, Gunzburger, Max, Rikvold, Per Arne, ElAzab, Anter, Peterson, Janet, Shanbhag, Sachin, Lehoucq, Richard B., Parks, Michael L., Department of Scientific...
Show moreSeleson, Pablo D, Gunzburger, Max, Rikvold, Per Arne, ElAzab, Anter, Peterson, Janet, Shanbhag, Sachin, Lehoucq, Richard B., Parks, Michael L., Department of Scientific Computing, Florida State University
Show less  Abstract/Description

This dissertation focuses on the non local continuum peridynamics model for the mechanics of materials, related constitutive models, its connections to molecular dynamics and classical elasticity, and its multiscale and multimodel capabilities. A more generalized role is defined for influence functions in the statebased peridynamic model which allows for the strength of non local interactions to be modulated. This enables the connection between different peridynamic constitutive models,...
Show moreThis dissertation focuses on the non local continuum peridynamics model for the mechanics of materials, related constitutive models, its connections to molecular dynamics and classical elasticity, and its multiscale and multimodel capabilities. A more generalized role is defined for influence functions in the statebased peridynamic model which allows for the strength of non local interactions to be modulated. This enables the connection between different peridynamic constitutive models, establishing a hierarchy that reveals that some models are special cases of others. Furthermore, this allows for the modulation of the strength of non local interactions, even for a fixed radius of interactions between material points in the peridynamics model. The multiscale aspect of peridynamics is demonstrated through its connections to molecular dynamics. Using higherorder gradient models, it is shown that peridynamics can be viewed as an upscaling of molecular dynamics, preserving the relevant dynamics under appropriate choices of length scales. The statebased peridynamic model is shown to be appropriate for the description of multiscale and multimodel systems. A formulation for nonlocal interface problems involving scalar fields is presented, and derivations of non local transmission conditions are derived. Specializations that describe local, non local, and local/non local transmission conditions are considered. Moreover, the convergence of the non local transmission conditions to their classical local counterparts is shown. In all cases, results are illustrated by numerical experiments.
Show less  Date Issued
 2010
 Identifier
 FSU_migr_etd0273
 Format
 Thesis
 Title
 Analysis of Two Partial Differential Equation Models in Fluid Mechanics: Nonlinear Spectral EddyViscosity Model of Turbulence and InfinitePrandtlNumber Model of Mantle Convection.
 Creator

Saka, Yuki, Gunzburger, Max D., Wang, Xiaoming, ElAzab, Anter, Peterson, Janet, Wang, Xiaoqiang, Department of Mathematics, Florida State University
 Abstract/Description

This thesis presents two problems in the mathematical and numerical analysis of partial differential equations modeling fluids. The first is related to modeling of turbulence phenomena. One of the objectives in simulating turbulence is to capture the large scale structures in the flow without explicitly resolving the small scales numerically. This is generally accomplished by adding regularization terms to the NavierStokes equations. In this thesis, we examine the spectral viscosity models...
Show moreThis thesis presents two problems in the mathematical and numerical analysis of partial differential equations modeling fluids. The first is related to modeling of turbulence phenomena. One of the objectives in simulating turbulence is to capture the large scale structures in the flow without explicitly resolving the small scales numerically. This is generally accomplished by adding regularization terms to the NavierStokes equations. In this thesis, we examine the spectral viscosity models in which only the highfrequency spectral modes are regularized. The objective is to retain the largescale dynamics while modeling the turbulent fluctuations accurately. The spectral regularization introduces a host of parameters to the model. In this thesis, we rigorously justify effective choices of parameters. The other problem is related to modeling of the mantle flow in the Earth's interior. We study a model equation derived from the Boussinesq equation where the Prandtl number is taken to infinity. This essentially models the flow under the assumption of a large viscosity limit. The novelty in our problem formulation is that the viscosity depends on the temperature field, which makes the mathematical analysis nontrivial. Compared to the constant viscosity case, variable viscosity introduces a secondorder nonlinearity which makes the mathematical question of wellposedness more challenging. Here, we prove this using tools from the regularity theory of parabolic partial differential equations.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd2108
 Format
 Thesis
 Title
 Parallel and Sequential Algorithms for the Optimization and Design of FaultTolerant Nanoscale Semiconductor Devices.
 Creator

Oniciuc, Liviu G. (Liviu Gheorghe), Andrei, Petru, ElAzab, Anter, Zheng, Jim P., Foo, Simon Y., Arora, Rajendra K., Department of Electrical and Computer Engineering, Florida...
Show moreOniciuc, Liviu G. (Liviu Gheorghe), Andrei, Petru, ElAzab, Anter, Zheng, Jim P., Foo, Simon Y., Arora, Rajendra K., Department of Electrical and Computer Engineering, Florida State University
Show less  Abstract/Description

A robust and computationally efficient technique is developed for the design of fluctuation resistant structures (faulttolerant) semiconductor devices. This technique can be applied to the computation of the doping profiles that minimize the intrinsic variations of various parameters induced by random dopant fluctuations. The technique is based on the evaluation of doping sensitivity functions, which are defined as functionals on the adjoint space of the space of square integrable functions...
Show moreA robust and computationally efficient technique is developed for the design of fluctuation resistant structures (faulttolerant) semiconductor devices. This technique can be applied to the computation of the doping profiles that minimize the intrinsic variations of various parameters induced by random dopant fluctuations. The technique is based on the evaluation of doping sensitivity functions, which are defined as functionals on the adjoint space of the space of square integrable functions generated by all possible doping variations. The optimized doping profiles are computed by minimizing the standard deviation of fluctuations of different parameters, in which constraints are taken into consideration by using the Lagrange multipliers technique. The presented technique can be applied to any semiconductor device in general, such as metaloxidesemiconductor fieldeffecttransistors (MOSFETs), silicononinsulator (SOI) devices, Fin fieldeffecttransistors (FinFETs), etc. and can be used in the framework of any transport model. We present the results for the minimization of the random dopantinduced fluctuations of threshold voltages in 25 nm, 30 nm, and 35 nm channellength MOSFETs and doublegate fullydepleted SOI devices. It is shown that by carefully designing the doping profiles, the random dopantinduced fluctuations can be suppressed between 20% and 50% in devices with channellengths of approximately 30 nm and more than one order of magnitude in longchannel devices. Analytical equations are derived for the optimum doping profiles that minimize the random dopantinduced fluctuations of the threshold voltage in longchannel MOSFETs. It is shown that, in both longchannel and shortchannel devices, the size of the undoped region should be at least ¼ of the width of the depletion region in order to suppress efficiently the effect of random dopantinduced fluctuations on threshold voltage. In the final part of the dissertation the random dopantinduced fluctuations of static noise margins (SNM) in 6T static random access memory (SRAM) cells by using the formalism of doping sensitivity functions, developed in the first part. In the case of static random access memory (SRAM) cell the doping sensitivity functions show how sensitive the SNM are to variations of the doping concentration at different locations inside the cell. The technique presented is based on a full circuit perturbation theory at the level of each device transport model. It provides important information for the design and optimization of SNM and can capture correlation effects of doping fluctuations inside the same semiconductor device and between more devices. The bias points and the magnitude of random dopantinduced fluctuations are computed by solving the Poisson, current continuity, and DensityGradient equations for all the devices selfconsistently. Simulation results for a wellscaled SRAM cell 30 nm channellength transistors show that the most sensitive regions to doping fluctuations extend for approximately 10 nm below the oxide/semiconductor interface and are located in the middle of the conduction channels for both the pchannel and nchannel transistors. It is apparent that random dopantinduced fluctuations can significantly impinge on the yield and reliability of SRAM circuits and constitute a fundamental limit for further scaling unless these devices are properly optimized.
Show less  Date Issued
 2009
 Identifier
 FSU_migr_etd2335
 Format
 Thesis
 Title
 Phasefield Modeling of Void Nucleation and Growth in Irradiated Materials.
 Creator

Rokkam, Srujan K., ElAzab, Anter, Van Dommelen, Leon, Wang, Xiaoqiang, Hellstrom, Eric, Ordonez, Juan, Department of Mechanical Engineering, Florida State University
 Abstract/Description

Irradiation induced voids and associated swelling is one of the most intriguing and technologically relevant problems in the design of structural materials for nuclear reactor components. Traditional approaches model void nucleation and growth as separate processes that are uniform in space, treating them within the framework of classical nucleation theory and chemical rate theory, respectively. However, void formation and myriad other phenomena occurring in materials exposed to irradiation...
Show moreIrradiation induced voids and associated swelling is one of the most intriguing and technologically relevant problems in the design of structural materials for nuclear reactor components. Traditional approaches model void nucleation and growth as separate processes that are uniform in space, treating them within the framework of classical nucleation theory and chemical rate theory, respectively. However, void formation and myriad other phenomena occurring in materials exposed to irradiation are sensitive to the dynamics of point defects and their interaction with other microstructural entities. Motivated by the need to develop a spatially resolved theory of irradiationinduced microstructural evolution in materials, in the present work a phasefield framework has been developed for modeling the evolution of void microstructure under irradiation. The phasefield model treats void nucleation and growth processes simultaneously in a spatially resolved fashion. Using principles of irreversible thermodynamics and gradient description of inhomogeneous systems the temporal evolution equations for field variables characterizing the material system are cast in the form of a set of coupled CahnHilliard and AllenCahn type equations. The point defect fluxes and their distributions follow a CahnHilliard type description for vacancy and interstitial concentration fields. The dynamics of void formation and growth is obtained in terms of the evolution of nonconserved void phasefield, prescribed by a phenomenological AllenCahn type equation. Irradiation induced point defects are modeled as stochastic sources in CahnHilliard equation, which introduces vacancies and interstitials in a spatially segregated fashion similar to the nature of the displacement cascade. The model accounts for mutual interactions between point defects, interactions between point defects and extended defects or sinks, cascade and thermally induced fluctuations. Illustrative results are presented using two dimensional numerical simulations that characterize: (a) void growth or shrinkage due to supersaturated vacancy or interstitial concentrations, (b) voidvoid interactions, (c) void nucleation and growth kinetics due to cascade induced defects, (d) formation of void denuded and void peak zones adjacent to grain boundaries, and (e) dynamics of concurrent swelling, nucleation and growth under irradiation. The model reproduces essential features of void formation in addition to resolving the time and space coupling between the defect field evolution and void phase dynamics. In addition, swelling studies based on the current model reveal that swelling of the material can occur prior to the nucleation of voids, through the buildup of material layers resulting from migrating interstitials reaching the surface.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd7222
 Format
 Thesis
 Title
 Verification, Validation and Optimization of Finite Element Model of Bus Structure for Rollover Test.
 Creator

Bojanowski, Cezary, Wekezer, Jerry, ElAzab, Anter, Spainhour, Lisa, Mtenga, Primus V., Department of Civil and Environmental Engineering, Florida State University
 Abstract/Description

Paratransit buses consist of a custom body mounted to a GM/Ford cutaway chassis by a secondary manufacturer called body builder. Paratransit buses form a significant segment of the bus market in the US nowadays. They are used as a complementary service for regularly scheduled routes and usually are prepared to transport disabled passengers in their wheelchairs. Their construction method and the lack of applicable national crashworthiness standards result in a wide variance of passenger...
Show moreParatransit buses consist of a custom body mounted to a GM/Ford cutaway chassis by a secondary manufacturer called body builder. Paratransit buses form a significant segment of the bus market in the US nowadays. They are used as a complementary service for regularly scheduled routes and usually are prepared to transport disabled passengers in their wheelchairs. Their construction method and the lack of applicable national crashworthiness standards result in a wide variance of passenger compartment structural strength amongst manufactures  as reported by the Florida Department of Transportation (FDOT). The primary objective of this dissertation was to develop a testing procedure with the performance rating system for paratransit buses acquired by the state of Florida. Sponsored by FDOT an assessment and improvement methodology was developed using joint computational and empirical approach. It prioritizes the strength of the structure in a rollover type accident utilizing as a basis the European Regulation ECER66. New measure of safety margin in rollover tests, a Deformation Index, was proposed. Detailed Finite Element (FE) model of selected paratransit bus was developed and used to perform explicit LSDYNA simulations of the tilt table rollover test. Experimental tests on the bus subsections were conducted for validation purposes and weak spot identification. Discrete optimization using the Successive Response Surface Methodology in LSOPT was also utilized to indentify parts of the structure critical to rollover performance. Improvements were suggested that minimize the addition of mass. Early results showed the connections between major structural components (floor/wall/roof) to be particularly weak. Proposed structural modifications increased the remaining safety margin from an initial level of 16% to 29% (In respect to the Deformation Index). The structural modifications resulting from the validation testing were incorporated in the currently produced buses. The proposed testing procedure was accepted by FDOT in August 2007 as the Crash and Safety Assessment Program. It received attention of the state and federal transportation agencies and support from the transit bus industry.
Show less  Date Issued
 2009
 Identifier
 FSU_migr_etd3610
 Format
 Thesis