Abstract Fractal image compression is a comparatively new technique which has gained considerable attention in the popular technical press, and inore recently in the research literature. The most significant advantages claimed are high reconstruction quality at low coding rates, rapid decoding, and "resolution independence" in the sense that an encoded image may be decoded at a higher resolution than the original. While many of the claims published in the popular technical press are cle...
Abstract Spread Spectrum systems are found in many flavours, used in many applications and have existed since the early days of radio communications. The properties of spread spectrum do however place restrictions on the design, and often make the implementation expensive and complex. When using spread spectrum to provide a basic communications infrastructure, many factors need to be considered. These indude supplying the appropriate technology at the right cost. To achieve this a trade-off ...
Abstract This thesis deals with the damping of electromechanical oscillations using Power System Stabilizers (PSS). The thesis focuses on three problems associated with the damping of these oscillations, namely the determination of the optimal locations of the PSS, the determination of the best control structure of the PSS and the design of robust PSS. We develop two new methods for determining the optimal locations of the PSS. These two methods are based on Total Modified Coupling Factors (T...
Abstract An anisotropic damage model is proposed for the constitutive description of microcracking processes in brittle rock under a general loading path. Experimental data and micromechanical models are reviewed to quantify the effect of microcracking on the material stiffness and the mechanisms of microcrack formation in brittle rocks under compression are discussed. The sliding crack concept is adopted as the micromechanical basis of the anisotropic damage model. Undamaged material is rep...
ABSTRACT Continuum and finite element formulations ofthe static and dynamic initial-boundaryvalue evolution (elastoplastic) problems are considered in terms of both the classical and internal variable frameworks. The latter framework is employed to develop algorithms in the form of convex mathematical programming and Newton-Raphson schemes. This latter scheme is shown to be linked to the former in the sense that it expresses the conditions under which the convex non-linear function can be m...
ABSTRACT MATHEMATICAL SIMULATION OF DYNAMIC BEHAVIOUR OF SECONDARY SETTLING TANKS The main objective of this thesis was to briiig the theoretical and practical aspects of secondary settling tank developments closer together. This was achieved firstly, by evaluating and developing empirical relationships from which the flux theory constants may be derived from simpler sludge settleability measures; and secondly, by developing a computer model for the simulation of dynamic behaviour of full sca...
ABSTRACT Several theories of creep and creep rupture are reviewed. Specific attention is devoted to the brittle damage theory proposed by Kachanov. Creep, damage and life predictions for rectangular or circular cross section beams under bending and tensile loads are presented. Comparison with data for a Ni Superalloy showed life predictions could be 30X in excess of experimental values. This beam model also revealed that it is imperative that no bending moments be inadvertently applied during...
ABSTRACT Coal is one of the most importa~t energy resources in South Africa. It covers 80% of the country's energy needs and provides valuable foreign exchange and employment. The purpose of this thesis is to provide an analytical framework for the examination of the demand for coal for the generation of electricity where more than 50% of the coal produced in the country is consumed. More specifically, the aim of the thesis is to identify the factors influencing the demand for steam-coal, dis...
ABSTRACT The requirements of a standard 3-phase Induction Motor driven by a Voltage Source Inverter studied. A ful I 3-phase Variable Speed Drive and its controller have been designed, constructed and tested. Gate Turn-Off Thyristors used as the main switching elements in the Inverter stage of the Drive. The drive requirements of GTO's are studied in detai 1.
Abstract Selection of optimum machining parameters is an essential factor in process planning for efficient metal cutting operations. In this study, an artificial neural network- based tool wear predictive model and a genetic algorithm-based optimization model were developed to determine the optimum cutting parameters for turning NST 37.2 steel with uncoated carbide cutting inserts. Multi-layer, feed-forare, back -propagation network was used in predictive model, while maximum metal removal r...
ABSTRACT Crop production is influenced by on-site soil moisture availability and application of water conservation methods for dry areas. This research explored the interactive effects of spate irrigation as an application method and the soil moisture conservation techniques. The objective of this research was to analyze the effectiveness of soil moisture conservation techniques and its correlation to water productivity for sorghum production under spate irrigation. The soil water holding ca...
ABSTRACT The e-beam stimulated reaction, CdCI2(s) ---> Cd (s) + CI(g), has been studied in casmium chloride thin films between 303 and 483 K using 2-keV electrons. The dose required to make 90-nm-deep holes at 483 K is 3x10-3 C cm -2. Extrapolated dosing levels of 6x10-5 C cm -2 are expected. The use of CdCI2 as a positive-type electron resist in a new scheme is proposed. A working model, useful for considering the e-beam stimulated decomposition energetics and mechanism is briefly discussed.
Abstract Several procedures have been proposed to overcome various challenges of product-content analysis after manufacturing and downstream automatad recycling pmcesws. These procedures have been restricted by factors such as the inabiiity to determine exactly the physical state of the hidden pm of End-of-Life products. This inhibition among others has rresldted into an explosion of solutions by researchers. This paper presents the initial investigations in the development of imaging softwa...
ABSTRACT Tool wear measurement is of great concern in machining industry, as it affects the surface qualities, dimensional accuracy and production costs of the machined components. The orthodox methods of measuring tool wear are time consuming and limited in accuracy and application. In this study, machine vision system based on digital image processing was developed for measurement of tool wear. The basic components of the system are: a charge coupled device (CCD) camera, PC, Microsoft Wind...
ABSTRACT Engineering structures subjected to dynamic loading exhibit vibration motions. These vibrations induce accelerations on the structures and their component parts. The accelerations in turn generate inertia forces that propagate the vibrations and significantly affect the response of the structures and their components parts to external loading. This cyclic cause and effect situation result in randomly oriented and time-dependent displacements as the basic response criteria of s...