D.Ing. / In this document the research related to the development of a microprocessor based field oriented controller is presented. An overview of the state-of-the-art is presented, with specific reference to all the different aspects related to the development of variable speed induction machine drives. During the development of it is necessary to use accurate system models. Such models are most useful when incorporated in a simulation program. In chapter 2 such a simulation program is described. Included in the simulation program are accurate models for the inverter and the induction machine. Effects such as resistance variation due to heating and inductance variation due to saturation are included. Modulation of the inverter output voltage wave from by the load current caused by the snubbers is also included. The development of a rotor current estimation strategy is presented in chapter 3. During the development extensive use was made of the simulation program. A new stationary reference frame current controller is also presented in chapter 3. Finally the implementation of the proposed field oriented controller is presented in chapter 4. As part of this a dual mode speed control algorithm was developed and implemented.

M.Ing. / This dissertation provides a review of the most notable papers published with regard to the specific performance characteristics of Tunnel Boring Machines (TBM's) during the past twenty years. It is a literature study of a Bibliography of 57 publications, which were screened from an original list of 970 documents ...

No description available.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg,in partial fulfilment of the requirements for the degree of Master of Science in Engineering (Mechanical Engineering), June 2017 / This research report describes the creation of a unique experimental facility for investigating localised stresses that can develop in conveyor belting during operation. High localised stresses can cause premature failure of conveyor belts, requiring expensive replacement. A key objective of carrying out research in this field is to gain a fundamental understanding of the stress that develops in various types of conveyor belting as it crosses over idler rollers. An experimental facility was developed that will be able to measure the stress and the deformation for different types of belting, such as solid woven/PVC and ply belting, with different belt classes. Particular attention was given to the various effects at the junction point caused by different idler configurations. Idler arrangements are configurable in the 24m–long test facility for inline, offset and belt-friendly types. Belt stresses at the idler junctions of these configurations are measured by applying strain gauges and load cells. The offset distance can be varied to determine the effect this has on the developing idler junction stress. This will allow comparison of the stresses as the class of belt increases, for each type of belt. The value of doing so is to determine the effect that the weft strength or stiffness has as the belt is forced into the idler junction. The test facility that was designed and built was shown to meet the requirements of the project. The instruments were calibrated to an acceptable uncertainty. The test facility can handle the full range of planned tests in terms of the design strength and is modular enough to handle a variety of other research initiatives. This establishment of a large, specialised experimental facility constitutes the first phase of an ongoing research programme into improving the design standards for belt conveyor systems / CK2018

Vapour-compression water chilling machines of large capacity (megawatts of refrigeration) are extensively utilised for process cooling in the manufacturing, chemical and food industries, and for cooling hot mines. If these machines under-perform, not only may the costs of consequent losses in production be considerable, but products or working conditions may degrade or become unsafe. Performance monitoring instrumentation, including water flow meters, fitted to machines on site may be infrequently calibrated, though. Therefore, the apparent performance of a machine, indicated by the measurements in its water circuits, should be verified through independent, confirming measurements in its refrigerant circuit. For custom-built machines with screw compressors, though, there is a difficulty with so verifying apparent performance. The oil cooling load of screw compressors is large, and so must be taken into account in such verification. If the oil is cooled by water, it is easy to measure oil cooling load, but not if the oil is cooled by condensed liquid refrigerant in a thermosyphon ‘loop’, because of the two-phase flow of the refrigerant there. This research report describes a study done on a water chilling machine with a screw compressor, using ammonia as refrigerant, at KDC East Mine, Westonaria, South Africa. This study was of a proposed, alternative way of determining the oil cooling load – by measuring flows and properties in the oil circuit. The oil cooling load so determined could be independently verified by measurements in the water circuit of this machine’s oil-to-water cooler. The chief problem in determining oil cooing load from measurements in the oil circuit is that the ‘oil’ is not pure lubricant, but a solution of oil and refrigerant. Therefore the most accurate available methods of predicting the thermophysical properties of oil-ammonia solutions were identified and employed. The oil cooling load hence determined agreed within 0.43 per cent with that determined on the water side of the oil cooler. It was hence used to correct the coefficient of performance (COP) calculated from measurements in the machine’s refrigerant circuit. This corrected refrigerant-circuit COP, with the estimate of total mechanical power input to the machine, were then used to indirectly estimate the machine’s water chilling load. This indirectly estimated load compared very closely, within 1.12 per cent, to the apparent water chilling load determined from the measurements in the machine’s water circuits. It is concluded that in this study, oil cooling load could be determined with satisfactory accuracy from measurements in the oil circuit. Hence, this proposed technique offers promise of being a useful and practicable development, enabling apparent performance of such machines to be more conveniently verified than hitherto.

Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

This research focuses on swarm-based optimisation algorithms, specifically the Bees Algorithm. The Bees Algorithm was inspired by the foraging behaviour of honey bees in nature. It employs a combination of exploration and exploitation to find the solutions of optimisation problems. This thesis presents three improved versions of the Bees Algorithm aimed at speeding up its operation and facilitating the location of the global optimum. For the first improvement, an algorithm referred to as the Nelder and Mead Bees Algorithm (NMBA) was developed to provide a guiding direction during the neighbourhood search stage. The second improved algorithm, named the recombination-based Bees Algorithm (rBA), is a variant of the Bees Algorithm that utilises a recombination operator between the exploited and abandoned sites to produce new candidates closer to optimal solutions. The third improved Bees Algorithm, called the guided global best Bees Algorithm (gBA), introduces a new neighbourhood shrinking strategy based on the best solution so far for a more effective exploitation search and develops a new bee recruitment mechanism to reduce the number of parameters. The proposed algorithms were tested on a set of unconstrained numerical functions and constrained mechanical engineering design problems. The performance of the algorithms was compared with the standard Bees Algorithm and other swarm based algorithms. The results showed that the improved Bees Algorithms performed better than the standard Bees Algorithm and other algorithms on most of the problems tested. Furthermore, the algorithms also involve no additional parameters and a reduction on the number of parameters as well.

The general aim of this study is to develop a 3-D FE model for multi-point forming dies using ABAQUS software and use this to study the effect of process parameters related to tool geometry such as radius of curvature of deformed parts, pin size, elastic cushion thickness and coefficient of friction. Doubly curved parts will be investigated in this research. The material properties for two blanks were determined for use as required parameters for the simulation analysis. Finite element models of the doubly curved forming process were developed and validated for two materials: DC05 steel sheet and 5251-0 aluminium sheet. The mesh sensitivity, reliability of the numerical model, suitable blank holder force, effect of gap distance between punch and blank holder on the thickness distribution, and the comer defect were studied. A parametric study was carried to investigate the effect of certain parameters on the deviation from target shape, wrinkling, and thickness variation. A test rig for the experimental work was designed and manufactured. In parallel, experiments with the forming of doubly curved parts were conducted to validate the simulation results. The numerical analysis results were compared with the experimental results and good agreement was generally found. The methodology developed in this research could help to build a reliable numerical model to predict the common defects in sheet forming using the multi-point forming process.

Surface treatments by applying laser processing have gained a significant attention due to the achievable surface properties along with the selectivity that cannot be realized with other methods. The focus of this research is on investigating and developing laser-based treatment methods, i.e. laser-induced surface oxidation, laser-induced oxygen reduction, and laser-induced periodic surface structures (LIPSS), to address the requirements of specific applications in optics, aesthetics, and anti-counterfeiting, e.g. colour marking and the fabrication of optical devices and diffraction holograms. A single spot oxidation method is proposed to control the size of the oxidation area and its thickness on titanium substrates. A pixel resolution down to the beam spot size with high special control is achieved. To produce diffraction optical devices on glass substrates a direct writing another method is proposed. Especially, the method is implemented and validated for fabricating two-level phase-type FZPs with a nanosecond laser by converting a titanium film on glass substrates into titanium dioxide patterns with a thickness controlled at nano scale. The flexibility and applicability of laser-induced oxidation is extended with a method for erasing colour marks selectively by employing a laser-induced oxygen reduction. Finally, a method for producing LIPSS patterns with varying orientations is developed and then validated for fabricating diffraction gratings on metallic surface.