Includes bibliographical references. / Many climate change studies project that occurrence of droughts (due to dry years) in Southern Africa will increase; this raises concerns over Zambia's electricity system. Currently, over 99% of Zambia's electricity is supplied by hydropower, which is vulnerable to droughts. With Zambia targeting to be a middle income industrialised country by 2030, it isimportant that the impacts of droughts on the electricity system are understood, and how the system's adaptive capacity can be improved. This is imperative if the system were to enhance economic development. The main focus of this research therefore, was to develop an understanding of how Zambia's electricity system would evolve in different economic and climatic scenarios. A comprehensive electricity model for Zambia was developed after reviewing literature on Zambia's electricity sector and energy planning in a developing country context. A Scenario planning approach was used to model and analyse the electricity system that would be required to meet demand in two climatic scenarios (average and dry year river-flows) and for different economic growth scenarios. The results showed that the supply system has to be increased in order to support economic development. In a dry year scenario, the availability of the hydro technologies reduces significantly and this leads to a considerable increase in the average generation cost of the system. The introduction of renewable energy and coal technologies into the system lessens the impacts of droughts. Carbon emitting technologies such as coal and oil are still viable supply options even with a carbon price of $50 per tonne. Only low and base-case growth scenarios need an explicit diversification policy since least cost policy in the high growth scenario (the middle income growth trajectory) leads to a diverse supply system. Implementing a diversification policy in the high growth scenario increases average generating cost without improving the system's adaptive capacity. The most cost effective way of increasing the system's adaptive capacity is by importing electricity and gradually increasing share of renewable and coal technologies in the system. Further research on how electricity trade in Southern Africa could be enhanced, should be done.

Includes bibliographical references. / Ad-hoc networks consist of a system of wireless nodes that can freely and dynamically self-organise into a working network topology. This allows people to internetwork seamlessly in areas that have no preexisting communication infrastructure. Nodes are expected to forward the traffic of other nodes in order for the packets to reach their final destination. It is envisaged that community ad-hoc networks will become widespread in the near future, as they require no administrative support. Nodes will be able to enter and leave the network as they choose. An unfortunate result is that in an open multi-agent system such as this, the role-players tend to be unreliable and self-interested.

Includes bibliographical references (leaves 122-124). / It is well established that land cover information is an essential component in the creation of spatial information systems. Lack of current land cover information constitutes a weakness in land resource management especially in developing countries like Uganda. In response to this need, the thesis reports on a case study on tropical forest mapping in Uganda. The geographic area of study is the Bwindi Impenetrable National Park located in the southwest of the country. Digital image processing techniques were applied to SPOT and Landsat Imagery using Erdas Imagine (8.4) and Arc View GIS software. A combination of original and derived bands (Principal Components, Tasseled Cap and Texture Analysis) was used for the image analysis. Both supervised and unsupervised classification approaches were used. The optimal combination of bands was selected on the basis of secondary correlation analysis of the derived as well as original bands. Further identification of the best bands was based on separability indices. With the band combination selected, four main land cover classes were identified in the forest i.e. dense evergreen forest, evergreen forest, mixed rangeland and brush land. In addition to this, three other land use types were extracted from the imagery within the neighborhood of the forest and these were subsistence farmlands, plantation farmlands (tea plantation) and woodland. The results were confirmed by post processing field inspection.

Includes abstract. / Includes bibliographical references. / Titanium and its alloys are among the most important advanced materials in use today due to attractive properties such as high strength to weight ratio and excellent corrosion resistance. However, the cost of titanium production is high, mostly due to the high cost of extraction. This has led to investigations of potentially lower cost methods such as near-net shape powder metallurgy techniques. One approach, which has the potential of producing the lowest cost powder available, involves converting titanium waste machine turnings to powder using the hydride-dehydride (HDH) process. The focus of this project is directed at this approach where a ball milling process is used to simultaneously hydrogenate and crush the titanium turnings into titanium hydride powder.

No description available.

Electric motor systems are the largest consumers of industrial electrical energy. As Variable Speed Drives continue to dominate various industrial processes, there is need for stakeholders to fully understand and quantify the converter-fed motor losses over a wide range of operating conditions. Such knowledge is crucial for both manufacturers and end-users in performing energy-efficiency optimizations for motor-drive applications. Although there is an increase in legislative activities, particularly in Europe, toward classification and improvement of energy efficiency of electric motor-drive systems, the available standards for quantifying the various losses are still in their early stages of development. None of these standards have yet passed through all the required phases for them to be considered full international standards, owing to a lack of consensus on many technical issues. Therefore, the need for researchers to provide feedback to the relevant standards committees cannot be over-emphasized. One of the most challenging issues in estimating the efficiency of converter-fed motors is the accurate determination of additional harmonic losses due to the PWM voltages and currents. Although the recently introduced IEC 60034-2-3 Technical Specification has proposed a method of determining these losses through experimental testing, the approach is still undergoing validation. Moreover, it only considers the rated motor frequency and voltage whereas induction motor drives are usually operated over a wide range of speed and torque. The main emphasis of the work presented in this dissertation was to develop a thorough understanding of various converter-fed induction motor losses, and hence efficiency, when fed from a 2-level Voltage Source Inverter. In particular, the dissertation provides a healthy questioning of some concepts in the proposed IEC method, with a view to providing useful feedback for improving the standard. Comparisons are also drawn between the related standards to identify areas for improvement. This study further attempts to explain some conflicting reports cited in literature regarding the nature of additional harmonic losses. The experimental results obtained by testing three induction motors demonstrate some of the technical issues associated with the determination of additional harmonic losses. To mitigate the adverse effect of varying technical skill and competence levels on efficiency test results, an automated testing procedure was developed and implemented on the 110kW test rig in the UCT Machines Lab. The test rig, which boasts of a Genesis 7i high-speed Data Acquisition System, also provides an energy-efficient platform for investigating the steadystate and dynamic characteristics of converter-fed motors. By utilizing the capability of the Data Acquisition System to segregate the fundamental and harmonic components of measured input electrical power, it was found that a PWM power supply can be used in place of a conventional Variac to estimate the sinusoidal supply efficiency of an induction motor. This is a welcome development for both laboratory and field efficiency testing applications.

Alkali-Silica Reaction (ASR) is a deleterious chemical reaction whose product expands in the presence of water inducing internal pressures within the concrete microstructure resulting in cracking and a reduction in elastic properties of concrete. Thus, ASR can substantially reduce serviceability and compromise the safety of concrete structures. To ensure the safe operation of these ageing structures, a sound understanding of the material deterioration and effect of ASR on the structural performance of these structures has to be developed. To this end, a number of numerical constitutive models have been developed to simulate ASR induced expansion in concrete. These models can generally be categorised as either, (i) microstructural models which aim to link the chemical process of the reaction to its impact at material level or (ii) macrostructural models which focus on the structural level assessment of affected concrete structures. Fundamental to most of these models is the assumption that ASR gets exhausted in time, which in the field, has thus far been rarely observed. In this study, a finite element model of a hydropower plant affected by ASR showing no signs of exhaustion even after 60 years of operation, was developed, validated and calibrated. From the analysis of the developed model in which a macrostructural thermo-chemo-mechanical ASR constitutive model was used to model concrete swelling, a prognostic evaluation approach to aid in determining the life expectancy of the hydropower plant was proposed.

The MiniBus Taxi (MBT) mode is poorly understood by planning and operational authorities, yet plays a big role in the economies of developing countries transporting the workforce to and from their places of employment and offering employment to thousands in the operations of these services, as well as the numerous rank-side services and amenities offered to patrons. In recent years, research focussed on mapping paratransit services, including MBTs, in cities of the developing world has contributed significantly to the understanding of the mode in terms of its spatial extent in its respective service areas. In South Africa, experience has shown that the wholesale replacement of MBTs with scheduled services is an unattainable goal. Instead, planning authorities and researchers have, more recently, shown interest in investigating feasible methods of integrating the scheduled and unscheduled services as hybrid planned-trunk and paratransit-feeder networks. The objective of this research is to present the case for simple methods of planning and carrying out onboard surveys of paratransit services to classify and to better understand the operations of individual routes, identified route classes, the network as a whole, as well as revealed passenger demand for the services and, ultimately, how this information can be wielded in the planning and implementation of hybrid routes or networks. The data central to this study consist of onboard captured MBT data, which was collected with a public transport data capturing application using GPS enabled smartphones in the City of Cape Town from April to August 2017 as part of a City of Cape Town’s Transport and Urban Development Authority (TDA) data collection project. The purpose of the project was to clarify the actual extent of MBT services within the City and to improve the representation of the MBT mode in the City of Cape Town’s travel demand model. An Android smartphone application, purpose-built for collecting operational information onboard public transport vehicles, was used to collect spatial and temporal data on the operations of a sample of active MBT routes in Cape Town. The application, which saw some functionality updates specifically for the project, was used to collect the following information per MBT trip: · Location of stops; · Time of arrival and departure at stops; · Number of passengers boarding and alighting at each stop; · The relative boarding and alighting stop of each specific passenger; · The amount paid in fare money per passenger at each stop; · The actual path travelled by the vehicle as a GPS route trace; and · The origin and destination route description of each route captured. It is estimated that there are more than 800 active and operational routes in the Cape Town. The objective of the data collection project was to survey each one of these routes for a prespecified number of trips. As the project was still underway when this research was carried out, the information listed above collected for a sample of trips for 278 routes (556 if the reverse direction is considered as a unique route designation) formed the basis of this study. During the course of this study, the analyses of these data have shown that while the operational characteristics of individual routes are relatively consistent and stable, it is possible to distinguish between different service typologies within the larger route network. From the raw data structure listed above, the operational characteristics that were calculated for each trip and aggregated at the route level included: · Trip and route distances; · Average operating speeds; · Travel times; · Number of stops per trip; · Load factors between stops along the route; and · Fare rates and trip revenues. In addition to the identification of the operational characteristics of the MBT network, service classes and routes, the outcomes of the study include providing a framework of methods for the collection, extraction, cleansing, analysis and visualisation of the data. It also includes the identification of metrics which are key in describing the difference in service types. The descriptive operational characteristics that were calculated for each trip record, inbound and outbound per route, were evaluated to establish whether they can be used to determine if different service typologies can be observed in the data. It was found that simple k-means clustering procedures may be used to classify the routes into separate, distinguishable service classes. For the purpose of this study, it was decided, nominally, that the classification should be executed for three classes. Three was subjectively considered a good value to be inclusive of traditional Trunk and Feeder or Distribution, route types as well as the possibility of the existence of a yet to be defined third type. The clustering procedures were carried out for different combinations of the operational variables for which the most consistent results were obtained for the combination distance – stop density1 – passenger turnover. Analysis of the within-class operational characteristics indicates that these three service classes clearly differ in terms of their stop frequencies, distances, speeds and their spatial network coverage. The study furthermore provides evidence that the understanding of the MBT network and sub-networks of service classes within this network, including its interaction with other public transport modes and infrastructure, provides planning and operating authorities with key information for effectively planning and implementing hybrid networks. Finally, the study demonstrates many additional insights can be garnered from these data by implementing improved statistical sampling and survey methods at the route level and by analysing aspects of the data that were not considered central to the research. These aspects include route adherence studies, origin – destination studies and methods of expanding the onboard data samples accurately by marrying it with data collected during static rank departure and arrival counts. Ultimately, the study shows that an unprecedented knowledge of the operations of MBT routes and networks may be obtained through detailed yet simple analysis of onboard data and that this knowledge may be very useful in the planning and operations of integrated public transport networks.

Fracture is the total or partial separation of an initially intact body through the propagation of one or several cracks. Computational methods for fracture mechanics are becoming increasingly important in dealing with the nucleation and propagation of these cracks. One method is the phase field approach, which approximates sharp crack discontinuities with a continuous scalar field, the so-called phase field. The latter represents the smooth transition between the intact and broken material phases. The evolution of the phase field due to external loads describes the fracture process. An original length scale is used to govern the diffusive approximation of sharp cracks. This method further employs a degradation function to account for the loss of the material stiffness during fracture by linking the phase field to the body’s bulk energy. To prevent the development of unrealistic crack patterns and interpenetration of crack faces under compression, this study uses the anisotropic split of the bulk energy, as proposed by Amor et al. [5], to model the different fracture behavior in tension, shear and compression. This research is part of a larger project aimed at the modeling of Antarctic sea ice dynamics. One aspect of this project is the modeling of the gradual break-up of the consolidated ice during spring. As a first step, this study reviews a phase field model used for dynamic brittle fracture at finite strains. Subsequently, this model is implemented into the in-house finite element software SESKA to solve the benchmark tension and shear tests on a single-edge notched block. The implementation adopts the so-called monolithic scheme, which computes the displacement and phase field solutions simultaneously, with a Newmark time integration scheme. The results of the solved problems demonstrate the capabilities of the implemented dynamic phase field model to capture the nucleation and propagation of cracks. They further confirm that the choice of length-scale and mesh size influences the solutions. In this regard, a small value of the length-scale converges to the sharp crack topology and yields a larger stress value. On the other hand, a large length-scale parameter combined with a too coarse mesh size can yield unrealistic results.

Co-channel interference between transmit and receive antennas means that simultaneous transmission and reception (STAR) of signals on the same frequency is an engineering challenge when co-locating the transmit and receive channels. Due to advancements in Radio Frequency (RF) receiver and antenna hardware, as well as electromagnetic computation software, this technology is becoming more and more realisable, with applications in the fields of radar and communications. For a STAR system to be effective, high isolation (in excess of 90 dB) between transmit and receive channels is required to avoid self-interference. A lack of isolation will result in a significant reduction in the receiver sensitivity and dynamic range, reducing its ability to adequately detect incoming signals. This study involves the design and analysis of a STAR demonstrator where the theoretical and practical viability of such a system is evaluated. High isolation is achieved through the use of a combination of passive suppression, as well as analogue and digital cancellation techniques. The design consists of three cancellation layers: passive suppression, which uses a transmit antenna array to increase the transmit-receive antenna isolation through null placement; analogue cancellation, which aims to reduce self-interference by subtracting a copy of the estimated interference signal from the received signal; and digital cancellation, which uses adaptive filtering in the digital domain to further suppress residual self-interference. The demonstrator is tested in a typical real-world environment to characterise the performance of the system. The measured isolation between transmit and receive antennas is 29.4 dB. Passive suppression increases this isolation to 51.5 dB when using a four element linear transmit array. Analogue cancellation provides up to 30 dB of additional isolation, with digital cancellation providing a further 20 dB of suppression. Together, as an integrated system, the demonstrator is capable of providing a combined 101.5 dB of self-interference suppression. This clearly demonstrates that a STAR system is viable through the use of a multi-layer cancellation scheme comprising of passive suppression, analogue cancellation and digital cancellation techniques.