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,..

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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. "

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Thesis. 1976. Ph.D. cn--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. Vita. / Includes bibliographical references. / by Per I. Johansson. / Ph.D.cn

Chan Kit Hung. / "August 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 132-152). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Thin-walled structures are often used as kinetic energy absorbers in vehicular systems and infrastructure designs. In such applications, high specific energy absorption is usually desirable, because it is beneficial for weight reduction. The dimpling cold-roll metal forming process introduces dimpled geometry and increases the strength of sheet metal. This thesis aims to investigate the energy absorption characteristics of the dimpled thin-walled structures. A finite element (FE) modelling analysis was performed using ANSYS Explicit Dynamics solver, to predict the response of dimpled structures to dynamic and quasi-static loads. A series of experimental tests were conducted and the FE method was validated through comparing the numerical and experimental results. To understand the response of the dimpled structural components to axial crushing loads, numerical simulations were performed. A parametric study on a key cold-roll forming parameter “forming depth” was carried out to evaluate its effects on the dimpled geometry and material properties. Through the parametric study, manufacturing parameters for the cold-roll forming process were suggested to improve yield strength and energy absorption performance of dimpled steel components. It was shown that the specific energy absorption can be increased by up to 16% after optimizing the forming depth. To take the most advantage of the dimpled geometry, multi-layer dimpled thin-walled columns were analysed. The interlocking mechanism of dimpled plates were investigated and an empirical model was proposed to describe the interaction between dimpled plates. It was shown that a considerable amount of energy can be absorbed through the interaction between dimpled walls. The behaviour of dimpled columns under lateral impact loads was also investigated. It was revealed that the introduced dimpled geometry contributes to reducing the peak impact force without sacrificing the energy absorption capacity. However, this is only valid when at least one end of the dimpled thin-walled column is fully restrained.