No description available.

No description available.

A thesis submitted in candidacy for the Degree of Doctor of Technology: Electrical Engineering, Technikon Natal, 2001. / This thesis details a study conducted to investigate the dynamic stability of an existing active control model (ACFl) of a composite structure embedded with a piezoelectric sensor and actuator for the purpose of vibration measurement and control. Criteria for stability are established based on the second method of Lyapunov which considers the energy of the system. Results show that ACFl is asymptotically stable although piezoelectric control effects persist when the feedback gain is set to zero. Meanwhile, it is required that there should be no control effects occurring through the piezoelectric actuator when the gain is set to zero. In this study, a new active control model (ACF2) is developed to satisfy the stability criteria, which satisfies the requirement of no piezoelectric control effects when the gain is set to zero. In ACF2 - as well as ACFl - the displacement and potential fields are discretised using the finite element method. In light of the locking phenomena associated with discrete displacements - which is expected to be pronounced in the case of discrete potentials due to their element geometry, ACF2-mixed is developed. ACF2 and ACF2-mixed control methodologies are similar except that in ACF2 both the displacement and potential field are discretised whereas in ACF2-mixed, only the displacement field is discretised and the potential field is continuous. Consequent to ACF2 and ACF2-mixed, stability analysis of the resulting time integration scheme is investigated as well. The results show that the damping forces due to the piezoelectric effect do not add energy to the structure. Hence, asymptotic stability is achieved. The time integration scheme yielded a small error, consistent with the literature. Numerical results revealed that ACFl exhibits a high degree of locking which is relaxed in ACF2 whereas ACF2-mixed exhibits envisaged results when compared with the other two models. Therefore, the ACF2 and ACF2-mixed will provide engineers with an alternative simulation model to solve actively controlled vibration problems hitherto. / D

M.Ing. / High frequency magnetic components have significant advantages related to cost and physical size compared to their low frequency counterparts. The advent of high frequency power switch technology made the transformer frequency a variable and recent advances in this field have been ever pushing the switching frequency of higher power converters. Although high frequency inductors and transformers have been used and applied extensively to an increasingly broad range of applications over recent decades, analysis and design of these devices involves certain difficulties, related to extra losses due to eddy currents as well as smaller cooling surfaces,..

M.Ing. / To investigate the effect of plastic anisotropy in 1200H14 Aluminium sheet, simulations of the Swift Cupping Test were carried out using the finite element program ABAQUS. Anisotropy was built into all simulations based on the plastic strain ratio which was calculated from tensile tests on specimen cut in three directions in the plane of the sheet. Deep drawing tests were carried out using a punch and die sub-assembly as described by the Swift Cupping Test. Holder loads were kept constant while the punch load and displacement were recorded. Punch force-punch displacement curve and the formation of ears were compared with experimental results.

Approved for public release; distribution is unlimited. / The objective of this study was to develop an analytical model of the basic hierarchical structure of the human bone. The model computed the stiffness of composite collagen fibers comprised of collagen fibrils and hydroxyapatite mineral crystals. Next, the stiffness of the concentric lamella was computed utilizing the stiffness of the collagen fibers and layer information. Finally, the effective stiffness of the bone was estimated. In order to determine the stiffness of the collagen fiber, a three-dimensional finite element model was developed and a simple analytical model was derived. The simple analytical model was validated using the finite element results. The lamination theory of unidirectional fibrous composites was used to calculate the stiffness of the lamella and eventually the bone stiffness. A series of parametric studies were conducted to understand what parameter(s) affected the stiffness of the bone most significantly. This information will be useful when an artificial bone structure is designed. / http://hdl.handle.net/10945/1123 / Lieutenant, United States Navy

No description available.

Chung Tsz Shun Eric. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 102-104). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Applications of Maxwell's equations --- p.1 / Chapter 1.2 --- Introduction to Maxwell's equations --- p.2 / Chapter 1.3 --- Historical outline of numerical methods --- p.4 / Chapter 1.4 --- A new approach --- p.5 / Chapter 2 --- Mathematical Backgrounds --- p.7 / Chapter 2.1 --- Sobolev spaces --- p.7 / Chapter 2.2 --- Tools from functional analysis --- p.8 / Chapter 3 --- Discretization of Vector Fields --- p.10 / Chapter 3.1 --- Domain triangulation --- p.10 / Chapter 3.2 --- Mesh dependent norms --- p.11 / Chapter 3.3 --- Discrete circulation operators --- p.13 / Chapter 3.4 --- Discrete flux operators --- p.20 / Chapter 4 --- Spatial Discretization of the Maxwell's Equations --- p.23 / Chapter 4.1 --- Derivation --- p.23 / Chapter 4.2 --- Consistency theory --- p.29 / Chapter 4.3 --- Convergence theory --- p.33 / Chapter 4.3.1 --- Polyhedral domain --- p.33 / Chapter 4.3.2 --- Rectangular domain --- p.38 / Chapter 5 --- Fully Discretization of the Maxwell's Equations --- p.63 / Chapter 5.1 --- Derivation --- p.63 / Chapter 5.2 --- Consistency theory --- p.65 / Chapter 5.3 --- Convergence theory --- p.69 / Chapter 5.3.1 --- Polyhedral domain --- p.69 / Chapter 5.3.2 --- Rectangular domain --- p.77 / Chapter 6 --- Numerical Tests --- p.97 / Chapter 6.1 --- Convergence test --- p.97 / Chapter 6.2 --- Electromagnetic scattering --- p.99 / Bibliography --- p.102

Chan Ming-Ho Gordon. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 104-105). / Abstracts in English and Chinese. / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- BACKGROUND ON MICRO POWER SUPPLY --- p.1 / Chapter 1.1.1 --- Brief Introduction --- p.1 / Chapter 1.1.2 --- Proposed Applications of Micro Power Supplies --- p.3 / Chapter 1.1.3 --- Comparison Among Different Power Sources --- p.4 / Chapter 1.2 --- LITERATURE SURVEY --- p.8 / Chapter CHAPTER 2 --- MICRO POWER GENERATOR WITH COPPER SPRINGS --- p.10 / Chapter 2.1 --- POWER PRODUCTION FROM MECHANICAL VIBRATIONS: SYSTEM ANALYSIS --- p.10 / Chapter 2.2 --- DESIGN OF MICRO RESONATING SPRING --- p.16 / Chapter 2.2.1 --- Design Objective --- p.16 / Chapter 2.2.2 --- Material Selection --- p.18 / Chapter 2.2.2.1 --- Mechanical Resonating Structure --- p.18 / Chapter 2.2.2.2 --- Electromagnetic Structure --- p.23 / Chapter 2.3 --- LASER MICROMACHINING OF SPRING STRUCTURE --- p.26 / Chapter 2.3.1 --- Si Bulk Micromachining --- p.26 / Chapter 2.3.2 --- Laser Micromachining --- p.28 / Chapter CHAPTER 3 --- COMPUTER SIMULATION --- p.31 / Chapter 3.1 --- TRANSIENT VOLTAGE AND POWER OUTPUT --- p.31 / Chapter 3.2 --- SYSTEM RESPONSE WITH VARYING PARAMETERS --- p.35 / Chapter CHAPTER 4 --- FINITE ELEMENT ANALYSIS --- p.39 / Chapter 4.1 --- STRUCTURAL STATIC ANALYSIS --- p.41 / Chapter 4.1.1 --- Building a Model --- p.41 / Chapter 4.1.2 --- "Material, Loading And Boundary Condition" --- p.45 / Chapter 4.1.3 --- Comparison Between Generator Designs --- p.46 / Chapter 4.2 --- MODAL ANALYSIS AND HARMONIC RESPONSE ANALYSIS --- p.51 / Chapter 4.3 --- NONLINEARITY --- p.52 / Chapter CHAPTER 5 --- COMPARISON OF MODELING AND EXPERIMENTAL RESULTS --- p.55 / Chapter 5.1 --- EXPERIMENT SETUP --- p.55 / Chapter 5.1.1 --- Generator System --- p.55 / Chapter 5.1.2 --- Vibration and Measurement --- p.60 / Chapter 5.2 --- MODELING AND EXPERIMENTAL COMPARISON --- p.62 / Chapter 5.2.1 --- Voltage and Power Comparison --- p.64 / Chapter 5.2.2 --- Mechanical Response --- p.66 / Chapter CHAPTER 6 --- SUGGESTIONS FOR POWER GENERATOR WITH RESONATING FREQUENCY BELOW 10HZ --- p.77 / Chapter CHAPTER 7 --- CONCLUSION --- p.80 / BIBLIOGRAPHY --- p.104

"A numerical description of the extraordinary optoconductance (EOC) effect is presented using two separate models. Extraordinary optoconductance is part of a general class of EXX geometric effects involving the external perturbation of the properties of a 2D electron gas in a macroscopic semiconductor or metal-semiconductor hybrid structure. The addition of metallic inclusions, has been shown to increase the sensitivity of devices relying on EXX effects. Following the discovery of the first EXX effect, extraordinary magneto-resistance (EMR), an optical equivalent was suggested. Unlike EMR, where the external perturbation is an applied magnetic field, EOC results from the modification of the local charge density in the semiconductor by a focused laser. The first model assumes Gaussian charge densities for the photo-generated electron-hole pairs while the second model directly solves the semiconductor drift-diffusion equations using the finite element method (FEM). Results from both models are shown to agree with experimental EOC data, both as a function of the laser spot position and temperature. The FEM model has the ability to describe EOC in more complex geometries making it useful in designing EOC devices geared for particular applications. "