Abstract The geomemc deformalion induced by ([0 equal blast loads on uppositt sides of a thin-walled square tube ",ill weaken the siruclure. This will improve i[s energy absorbrioll charanenstics compared to a gcomccrically "perfect" square tube of the same size by reducing me crush load when cOlnpressed i11 the axial direction. Different types of impcrfcnioll can be induced depending on the Sl?e of the blast loads. Consequent to the blast loads, high temperalures ""ill also be induced by a...
Abstract The characterization and classification of liquids through instrumentation is essential in many industries. As such, measuring the characteristics of liquids is not just useful as a control parameter within an industrial process; such measurements can also be used to classify the liquid. Such a sensor is especially practical if it can be connected in-line with the liquid to be measured, thus minimally influencing flow. A piezoceramic tube was studied in an attempt to produce a senso...
ABSTRACT The efficiency of mixing processes in impeller agitated tanks depends highly on the hydrodynamics. Computational fluids dynamics (CFD) provides a method of predicting the complex tlow structures in stirred tanks. As with any approximate numerical method, CFD methods are subject to errors due to assumptions in the underlying mathematical models, as well as errors due to the numerical solution procedures. The aim of this thesis was to present a CFD method that accurately models the hy...
Abstract All real systems experience input saturation. Since the first proportional controller was implemented, systems have been susceptible to saturation. The introduction of the proportional-integral (PI) controller complicates matters further, since it reduces the steady state error to zero for zero-order setpoint tracking. This encompasses a fair portion of the implemented control strategies in the world. It is clear that saturation, by limiting the input state for the process, limits t...
ABSTRACT South Africa is possibly facing the biggest housing backlog in its history, and the backlog is growing annually. The ability and means to deliver must be improved, together with a compromise between the construction materials used and the occupants' preferences. This study seeks to examine the use of concrete block construction for the wall superstructure of low cost housing in terms of affordability and acceptability by the end-users. Three objectives of this research study, which ...
Abstract This thesis examines the use of 3D visualisation over the Internet as a tool for analysis and presentation of the Laetoli footprints. It describes the data used in the project and the methods used for checking and processing the data. Principles for creating 3D models are explained in detail. The tools used in the project are discussed, particularly VRML-based tools and how these tools integrate with the Internet. The discussion includes the design of the tools, which have been writ...
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...