Abdominal aortic aneurysms (AAA) are an expansion in diameter of the abdominal aorta and their rupture is a leading cause of mortality. One of the treatments for AAA is the implantation of an endograft (also called a stent graft), a combination of fabric and metal stents, to provide a new conduit for blood and shield the aneurysm sac from direct pressurization. After implantation of the stent graft, the aneurysm may shrink, grow, or stabilize in diameter ? even in the absence of apparent flow into the sac ? in some cases resulting in graft failure through component separation, kinking, or loss of seal at its ends. Greater understanding of AAA and treated AAA could provide insight on how treatment might be modified to improve treatment methods and/or design devices to be more effective in a wider range of patients. Computational models provide a means to investigate the biomechanics of endografts treating AAA through analysis of the endografts, the AAA, and the combination of them. Axisymmetric models of endograft-treated AAA showed that peak von Mises stress within the wall varied between 533 kPa and 1200 kPa when different material properties for the endograft were used. The patient-specific models, built from time series of patient CT scans with similar patient history but different outcomes, show that wall shrinkage and stability can be related to the level of stresses within the vessel wall, with the shrinking AAA showing a greater reduction by endograft treatment and a lower final value of average von Mises stress. The reduction in pressure felt by the wall is local to the central sac region. The inclusion of thrombus is also essential to accurate stress estimation. The combination of axisymmetric and patient-specific computational models explains in further detail the biomechanics of endograft treatment. The patient-specific reconstruction models show that when effectively deployed and reducing the pressure felt in the AAA wall, the graft is under tension in the sac region and compression at its ends.

The purpose of this study is to investigate the impact effect of varied structure of golf ball. The researcher applied finite element analysis software LS-DYNA to do nonlinear impact analysis of different golf ball models. It was hoped that this study could design a better golf ball for golfer. The researcher had developed ten stress versus strain curves of two-piece golf balls (including a core and a cover) and three-piece golf balls (including a core, an inner cover and a cover) and four different thicknesses of inner cover of three-piece golf balls. The simulation also adjust the density of inner cover to analyze the impact procedure under the definite weight. With the special design of two-piece balls and three-piece balls, the impact models extract the ball velocities, and angular velocities for the calculation of the ball flight. Finally, the researcher made suggestions for some combination of material property and thickness of the core and the inner cover of the golf ball for the designer to develop a suitable golf ball.

The roles of residual stresses distribution and creep deformation in the post-weld-shifts (PWS) of a laser model packaging are investigated in this dissertation. The temperature dependent material properties are employed to calculate the distribution of the residual stresses introduced in the solidification of soldering joints and lasering joints respectively. A power law proposed by Norton is applied to the creep deformation calculation. The post-weld-shifts of fiber-solder-ferrule (FSF) introduced in the aging and temperature cycling tests are simulation. A finite element package ¡V MARC is used to module the fiber-solder-ferrule joint and laser joint respectively. Experimental results of the PWS of a FSF joint are compared with the calculated shifts. Results indicate that the redistribution of residual stresses in joint and the creep deformation under high temperature load may affect the PWS significantly. A good agreement between the simulated and the measured results indicate the proposed model is feasible in the laser module packaging analysis.

Abstract This study aims to investigate the impact effect of varied thickness of the hitting surface and different shapes of the golf club head. The researcher integrated the computer-aided design software Pro/ENGINEER and finite element analysis software LS-DYNA to do the club head design and impact analysis. The researcher had developed five different shapes and eight different thicknesses of hitting surface of the club head model to compare the ball speed and the sweet spot of the hitting surface. He found that ball speed had increased as the hitting surface is enlarged, both laterally and vertically. He also found that thicker center surface and decreasing thickness to the rim of the thickness of the hitting surface is a better design club head. Finally, he made suggestions about the scientific information of the shape and the surface thickness of the golf club head for the designer to develop a suitable club head.

In this dissertation we are concerned with the analysis of the finite element method for the time-dependent Maxwell interface problem when Nedelec and Raviart-Thomas finite elements are employed and preconditioning of the resulting linear system when implicit time schemes are used. We first investigate the finite element method proposed by Makridakis and Monk in 1995. After studying the regularity of the solution to time dependent Maxwell's problem and providing approximation estimates for the Fortin operator, we are able to give the optimal error estimate for the semi-discrete scheme for Maxwell's equations. Then we study preconditioners for linear systems arising in the finite element method for time-dependent Maxwell's equations using implicit time-stepping. Such linear systems are usually very large but sparse and can only be solved iteratively. We consider overlapping Schwarz methods and multigrid methods and extend some existing theoretical convergence results. For overlapping Schwarz methods, we provide numerical experiments to confirm the theoretical analysis.

In this thesis, we discuss the development, implementation and testing of a piecewise linear (PWL) continuous Galerkin finite element method applied to the threedimensional diffusion equation. This discretization is particularly interesting because it discretizes the diffusion equation on an arbitrary polyhedral mesh. We implemented our method in the KULL software package being developed at Lawrence Livermore National Laboratory. This code previously utilized Palmer's method as its diffusion solver, which is a finite volume method that can produce an asymmetric coefficient matrix. We show that the PWL method produces a symmetric positive definite coefficient matrix that can be solved more efficiently, while retaining the accuracy and robustness of Palmer's method. Furthermore, we show that in most cases Palmer's method is actually a non-Galerkin PWL finite element method. Because the PWL method is a Galerkin finite element method, it has a firm theoretical background to draw from. We have shown that the PWL method is a well-posed discrete problem with a second-order convergence rate. We have also performed a simple mode analysis on the PWL method and Palmer's method to compare the accuracy of each method for a certain class of problems. Finally, we have run a series of numerical tests to uncover more properties of both the PWL method and Palmer's method. These numerical results indicate that the PWL method, partially due to its symmetric matrix, is able to solve large-scale diffusion problems very efficiently.

In this dissertation we discuss the development, implementation, analysis and testing of the Piecewise Linear Discontinuous Finite Element Method (PWLD) applied to the particle transport equation in two-dimensional cylindrical (RZ) and three-dimensional Cartesian (XYZ) geometries. We have designed this method to be applicable to radiative-transfer problems in radiation-hydrodynamics systems for arbitrary polygonal and polyhedral meshes. For RZ geometry, we have implemented this method in the Capsaicin radiative-transfer code being developed at Los Alamos National Laboratory. In XYZ geometry, we have implemented the method in the Parallel Deterministic Transport code being developed at Texas A&M University. We discuss the importance of the thick diffusion limit for radiative-transfer problems, and perform a thick diffusion-limit analysis on our discretized system for both geometries. This analysis predicts that the PWLD method will perform well in this limit for many problems of physical interest with arbitrary polygonal and polyhedral cells. Finally, we run a series of test problems to determine some useful properties of the method and verify the results of our thick diffusion limit analysis. Finally, we test our method on a variety of test problems and show that it compares favorably to existing methods. With these test problems, we also show that our method performs well in the thick diffusion limit as predicted by our analysis. Based on PWLD's solid finite-element foundation, the desirable properties it shows under analysis, and the excellent performance it demonstrates on test problems even with highly distorted spatial grids, we conclude that it is an excellent candidate for radiativetransfer problems that need a robust method that performs well in thick diffusive problems or on distorted grids.

In Taiwan, a motorcycle is the most important and general transportation. It is no denying that wearing a motorcycle helmet could prevent the rider from head injuries in the accidents. However, the ventilation of helmets still has to be improved. This study aims to set several ventilation channels in the energy absorption liner. They apply the Venturi effect to increase the ventilation of helmets. But it may affect the protection performance of helmet. The purpose of this study is to estimate the protective ability of the ventilative helmet. Therefore, the various ventilative helmets are designed by the computer-aided design software SolidWorks, and simulations of the impact test of the helmet are investigated by the finite element analysis software ANSYS/LS-DYNA. In addition, the effect of using different foam material is also discussed in this study.

In the past ten years, various sewage treatment technologies have got extensive and profound studying in the field of water pollution control in Taiwan. In each unit apparatus of the sewage disposal system, a lamella separator as the sewage treatment facility, is an important link in the structure, has irreplaceable functions. This research investigated the lamella separator structure by means of the static analysis, add factors of earthquake, and typhoon. To achieve the purpose, the researcher used the computer-aided design software Solidworks to set up this structure model. After that, he used finite element analysis software, ANSYS, to analyze the structure. This research simulated in three situations. In static, earthquake, and typhoon analysis, the researcher found the stress of the original modal is over the yielding stress of materials. So, the researcher modified the support of a model to reduce the stress. Generally, the researcher hoped that this study could provide helpful references for designers¡¦ relevant studies on lamella separator structure in the future.

This research investigates the stress anslysis of a tower skirt support respectively by the earthquake and the wind pressure loading. The researcher used the computer-aided design software Solidworks to set up the tower model and he used finite element software ANSYS to analyze the structure. This study aims to analyze the safety of a tower support for different models. By the finite element analysis, this study found the largest displacement of tower, the von Mises stresses, and the safety factor for the skirt support. Among them, the butted-flared skirt support has the smallest displacement. According to the analysis result, the empty crate type design of skirt support revealed the safety factor of stress greater than two, which ensure that the equipment safety and material-savings. It is expected the study findings can provide a reference for designing or repairing a tower skirt support.