No description available.

No description available.

This thesis describes the development of a coupled finite element — boundary element program for a microcomputer. The steps outlined in the thesis include the adaptation of a mainframe—based boundary element code for use on a microcomputer, the Verification of this program with sample problems, the development of an algorithm for coupling the Finite Element Method to the Boundary Element Method, the implementation of the coupling algorithm with finite element and boundary element codes, including the development of a Constant Strain Triangular finite element, and the Verification of the coupled program with sample problems. Conclusions are drawn from the results presented, and suggestions are made for future research in this area. / Master of Science

A stress model of the filament-winding fabrication process, previously implemented in a finite element program, was improved. Pre- and post-processing codes were developed to make the program easier and more efficient to use. A program which is used to design filament wound composite rocket motor cases was modified to write a model file for the fabrication stress code in the pre-processing stage. The same code was altered to provide post-processing output in the form of graphic displays. Also, a new code was written to provide additional post-processing capability for the fabrication stress model. Verification of the model of the filament-winding process was performed by comparing experimental pressure and strain data, for the fabrication of a filament wound bottle, with results of an analytical model. The final analytical results using consecutive models of the filament wound bottle show reasonable agreement with experimental pressure and hoop strain data. The maximum difference in the analytical and experimental values in the pressure data was about 25% for the final winding stage. The difference was smaller during the winding progression. These results also show that the accuracy of the model depends heavily on the assumptions made for input parameters during modelling. The stiffness of the segmented steel mandrel, simulated by an effective modulus (degraded by segmentation), and the instantaneous laydown tension loss parameters significantly affected the results of the model. Including the effective modulus for the segmented mandrel in the model reduced the difference in the experimental and analytical pressure results by about 150%. The inclusion of instantaneous laydown tension loss in the model reduced the analytical-experimental difference by roughly 225%. These two parameters reduced the largest difference in the predicted pressure values from about 400% for the first model to around 25% for the final model. The fabrication stress model was coupled with the thermo-kinetic cure model to provide more accurate fiber motion tension loss analysis capability. The stress model was modified to use the thermo-kinetic model as a subroutine to calculate fiber motion tension loss using a two-dimensional analysis. The results of the qualitative verification show that fiber motion tension loss is more important in the later stages of winding than in the beginning stages which indicates that it may provide the needed accuracy in the final winding stages. / Master of Science

"January 14, 2004" Includes bibliographical references (leaves 201-213)

The movement of a fluid and solute through a porous medium is of great practical interest because this describes the spread of contaminants through an aquifer. Many contaminants occur at concentrations sufficient to alter the density of the fluid, in which case the physics is typically modelled mathematically by a pair of coupled, nonlinear partial differential equations. There is disagreement as to the exact form of these governing equations. Codes aiming to solve some version of the governing equations are typically tested against the Henry and Elder benchmark problems. Neither benchmark has an analytic solution, so in practice they are treated as exercises in inter code comparison. Different code developers define the boundary conditions of the Henry problem differently, and the Elder problems results are poorly understood. The Henry, Elder and some other problems are simulated on several different codes, which produce widely-varying results. The existing benchmarks are unable to distinguish which code, if any, simulates the problems correctly, illustrating the benchmarks' limitations. To determine whether these discrepancies might be due to numerical error, one popular code, SUTRA, is considered in detail. A numerical analysis of a special case reveals that SUTRA is numerically dispersive. This is confirmed using the Gauss pulse test, a benchmark that does have an analytic solution. To further explain inter code discrepancies, a testcode is developed which allows a choice of numerical methods. Some of the methods are based on SUTRA's while others are finite difference methods of varying levels of accuracy. Simulations of the Elder problem reveal that the benchmark is extremely sensitive to the choice of solution method: qualitative differences are seen in the flow patterns. Finally, the impact of numerical error on a real-world application, the simulation of saline disposals, is considered. Saline disposal basins are used to store saline water away from rivers and agricultural land in parts of Australia. Existing models of disposal basins are assessed in terms of their resemblance to real fieldsite conditions, and in terms of numerical error. This leads to the development of a new model which aims to combine verisimilitude with numerical accuracy. / Thesis (Ph.D.)--School of Mathematical Sciences (Applied Mathematics), 2004.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Structural Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

It has been hypothesized that increasing the number of active sites on a cochlear implant electrode array will enable the recipient to distinguish a higher number of pitch precepts, thus creating a more natural sound. While DSP processing strategies for cochlear implants have evolved significantly to address this, technology for the actual electrode array has remained relatively constant and limits the number of physical electrodes possible. Previous work introduced the concept of using Thin-Film Array (TFA) technology to allow for much higher site densities, although the original devices proved unreliable during surgical insertion tests. This work presents a new method of combining polyimide-based TFA's with supporting silicone insertion platforms to create assembled electrode arrays that are a more viable option for surgical insertion. The electrical and mechanical properties of these assemblies are investigated with physical deformation tests and finite element analysis in COMSOL to quantify how they will perform upon insertion into the cochlea, and the preliminary results of a surgical insertion study into human cadaveric temporal bones will be discussed.

A direct solution procedure is proposed and developed which exploits the parallelism that exists in current symmetric multiprocessing (SMP) multi-core processors. Several algorithms are proposed and developed to improve the performance of the direct solution of FE problems. A high-performance sparse direct solver is developed which allows experimentation with the newly developed and existing algorithms. The performance of the algorithms is investigated using a large set of FE problems. Furthermore, operation count estimations are developed to further assess various algorithms. An out-of-core version of the solver is developed to reduce the memory requirements for the solution. I/O is performed asynchronously without blocking the thread that makes the I/O request. Asynchronous I/O allows overlapping factorization and triangular solution computations with I/O. The performance of the developed solver is demonstrated on a large number of test problems. A problem with nearly 10 million degree of freedoms is solved on a low price desktop computer using the out-of-core version of the direct solver. Furthermore, the developed solver usually outperforms a commonly used shared memory solver.

Not available / text