4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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Characterisation, Modelling, Finite element analysis, and optimisation of hyperelastic materials for Non-Pneumatic Wheels
(University of the Witwatersrand, Johannesburg, 2024) Bhartu, Saahil; Pietra, Francesco
This abstract concludes the exploration of hyperelasticity within the context of mechanical engineering. Through this section, we have delved into the substantial elastic deformations characteristic of hyperelastic materials, their capacity for energy conservation during deformation, and their inherently non-linear behaviour. The calibration of non-linear material models has been informed by a rigorously designed experimental regimen, where preferred methodologies and necessary precautions were identified to ensure the integrity of the data obtained. Theoretical foundations for the development of constitutive models have been established, with a discussion of prevalent models frequently employed in engineering applications. Practical modelling applications introduced have provided a tangible context for the utilization of hyperelastic material models. While our focus was predominantly on nearly or fully incompressible materials, foundational concepts for compressible behaviour were also addressed, setting the stage for further investigative pursuits. Polyurethane (PU) materials exemplify hyperelastic behaviour. Through computational simulation, we assessed the deformation in a structured wheel to be 4.6mm, utilizing a 9;5 and 2 parameter Mooney-Rivlin model for the PU material. Experimental testing was conducted measuring deformation to be 4.1mm From the results, the deformation patterns, stress distributions, and contact pressures were analysed, indicating the wheel’s ability to endure a contact pressure of 7.36MPa, deformation of 4.6mm, Von-Mises stress of 3.9MPa. This investigation not only corroborates the distinctive properties of hyperelastic materials but also illustrates how analysis results can inform and optimize design iterations. It demonstrates the practical applications of hyperelastic material models in design engineering, providing a comprehensive understanding that is indispensable for the modelling and analysis of hyperelastic components.
Investigating the impact of Railway Signalling Performance on Railway Operations & Performance in South Africa
(University of the Witwatersrand, Johannesburg, 2024) Naidoo, Pranell; Sunjka, Bernadette
The South African railway was once an attractive and thriving industry, serving as a catalyst for socio-economic growth and opportunities (George, Mokoena and Rust, 2018). However, in the past decade, the South African freight rail service has become uncompetitive, unreliable, and ineffectively integrated to other modes of freight transportation (The World Bank, 2023). Railway signalling systems are a vital component of the rail network as it ensures that trains travel safely and the rail network is operating at optimal capacity (Zhang et al., 2021). This research focuses on investigating the critical factors contributing to poor railway signalling performance in South Africa, and the impact that these risk factors have on the performance of railway operations, safety and the organization. A critical literature review revealed a gap in the knowledge and understanding of the systemic factors contributing to poor signalling performance. In the effort to close this literature gap, a holistic approach was adopted to develop a conceptual framework which presented factors identified from literature which affects the performance of railway signalling systems. This research adopted a qualitative research approach to achieve the objectives of this research. Semi-structured interviews were conducted with railway signalling and operations professionals. Thematic analysis was used to identify emergent themes from the collected data. The findings identified several factors contributing to poor signalling performance, some of the major identified factors were theft and vandalism, loss of critical skills, lack of investment and budget, managerial issues, ageing infrastructure, inadequate maintenance, human factors, etc. The research findings concluded by outlining the recommendations for future research to address theft and vandalism through collaborative strategies and initiatives, obtaining investments through public-private partnerships, addressing the skills shortage through effective skills retention programs, upgrading the freight rail signalling systems, optimizing the maintenance philosophy, and expanding the research into the passenger rail network to improve railway signalling systems in South Africa.
Improving bulk water pump station policies and operations in conditions of uncertain and changing demand
(University of the Witwatersrand, Johannesburg, 2024) Mudau, Thendo David
South Africa is facing growing and complex changes in water demand; furthermore, acute water scarcity challenges due to drought and degradation of surface water resources threaten its ability to manage the demands. Industrial and power generation sectors in some regions are plagued with water shortages, requiring inter-basin transfer schemes for bulk water transfer to these regions. The complexity in the water demand is further exacerbated when the demand that bulk water transfer systems are designed to manage varies from the demand projections. This has resulted in inefficient pumping operations and unnecessary costs, which are causing great concern as a result of the current water crisis and the increasing cost of electricity in South Africa. This was an investigation to find out how the increasing energy costs and inefficiencies due to uncertainties in demand could be mitigated in bulk water transfer schemes in South Africa. This was done through determination of the impact demand changes and uncertainties have on bulk water transfer pump stations’ adherence to the operational policy, performance, and costs. Approaches to reduce costs associated with the changes in the demand and improve the operational performance of the pump station were proposed. The Jericho pump station in the Mpumalanga province, South Africa, was used as a case study to assess the impact demand changes have on the pump station’s operation and control, as well as the operational energy costs. The results of the assessment showed that all these three aspects of the pump station had been negatively affected by the variability in the demand, particularly the energy costs with operational costs due to pumping operations during peak periods contributing to 33% of the estimated energy costs during the study period. Optimal pump scheduling and a capital investment in the form of a booster pump station to assist the Jericho pumping system and changes to the pump station control policy are proposed, and it is determined that they would ensure a 17.02% saving in annual energy costs. Furthermore, it is shown that operational costs due to pumping operations during peak Time- of-Use (TOU) periods are more than three times the standard and off-peak tariffs, and as such pumping operations during peak periods should be minimized. This research report showed the significance of optimal pump scheduling and how operational policies of bulk water transfer systems should continuously be reviewed and improved if required, especially with the ever-changing demands.
Characterization of a TW R260-60E1 Pearlite Rail Steel with a Weld Gap Size of 40 mm and 50 mm
(University of the Witwatersrand, Johannesburg, 2024) Meyiwa, Lindani; Maledi, Nthabiseng
The continuous weld rails (CWR) tracks that are joined by thermite welding (TW) method are known to experience weld failures during their service life. In avoiding or mitigating these failures, a weld gap in joining two rail ends was introduced. The purpose of the weld gap was to accommodate rail expansion during elevated temperatures. Traditionally, a weld gap of 24 mm was created between two rail ends. However, these weld joints were observed to be experiencing challenges of not being able to withstand high contact loads during service life, leading to plastic deformation and eventual failures. This study was investigating the effect on microstructural characteristics, heat-affected zone (HAZ) dimensions, mechanical properties attributes, and wear resistance behaviour of TW R260-60E1 pearlitic rail steel when the weld gap was set to 40 mm and 50 mm. The results revealed that the TW R260-60E1 pearlitic rail microstructure had no martensitic, bainitic and intergranular Widmanstätten ferritic structures. Pearlitic grain sizes and interlamellar spacing on the weld zone of the web region were measured to be 3.6 % wider on the sample with 40 mm weld gap compared to those on the sample with 50 mm weld gap. Big surface area to volume ratio and fast cooling rate had an influence on the production of finer pearlite grain sizes and interlamellar spacing within the web region for both samples. The results further showed that the HAZ width was one of the attributors to the improvement on the mechanical and wear resistance properties. HAZ width varied from 29 mm – 35 mm for sample with 40 mm weld gap, and 27 mm – 33 mm for sample with 50 mm weld gap. The HAZ width on the sample with 50 mm weld gap was narrow than the HAZ width on the sample with 40 mm weld gap. Narrow HAZ width improves microstructural characteristics, mechanical properties and wear resistance behaviour compared to the wider HAZ width. The improvement on the microstructure characterisation, mechanical properties and wear resistance behaviour are expected to extend the service life of the rail and facilitate superior rail expansion capabilities. This, in turn, is projected to diminish the probabilitiy of rail-related incidents and mitigate the risks of human fatilies associated with rail transportation
Extraction of gold from tailings using environmentally friendly reagents
(University of the Witwatersrand, Johannesburg, 2024) Khuduwe, Marema Jack
The depletion of high-grade gold ores, the high production costs associated with mining at lower depths, and the high demand for gold have caused the mining industry to search for alternative sources of gold. Additionally, the conventional cyanidation process raises health and environmental concerns. The treatment of waste generated by the cyanidation process to reduce the residual cyanide content before disposal also incurs additional costs. Therefore, this study focuses on the extraction of gold from tailings using environmentally benign reagents such as 1-butyl-3-methyl-imidazolium hydrogen sulfate (BmimHSO4) ionic liquid (IL), ethaline (mixture of choline chloride and ethylene glycol) deep eutectic solvent (DES), and thiosulfate. The gold tailings used in this work were obtained from DRD Gold Ergo Mining (Pty) Ltd operations in the Witwatersrand Basin, South Africa. Mineralogical analysis by X-ray diffraction (XRD) showed that the tailings material consisted of quartz (72.13%), muscovite (7.49%), chlorite (2.65%), pyrophyllite (1.50%), clinochlore (1.30%), and other trace minerals. The gold association by mineral liberation analysis (MLA) employing the Sparse Phase Liberation-Dual Zoom (SPL-DZ) method indicated that all the gold was locked in the iron oxide (FeO) matrix. Gold grade analysis by fire assay analysis (FAA) showed that the tailings had a head grade of 0.32 g/t Au. The leaching of the gold tailings was carried out by employing the use of the design of experiments (DOE) method to identify factors that significantly influence the gold extraction process. The central composite design (CCD) technique in conjunction with response surface methodology (RSM) was used to optimize the identified significant factors to obtain optimum conditions for optimal gold extraction. The effect of particle size and the co-dissolution of Ag, Cu, Fe, and Ni with Au was investigated. Furthermore, the recovery of Au by activated carbon (AC) from leach solutions of the investigated reagents was also investigated The results from the IL studies indicated that the reagent concentration had a positive and significant influence on the gold extraction process, suggesting that to achieve optimal gold extraction, IL concentration must be kept at a high level. The interaction of temperature, concentration, and pulp density also significantly influenced the gold extraction process in the IL solution. The theoretical optimum conditions established from the statistically-based optimization model were 75 C leaching temperature, 1.0 M (25% aqueous BmimHSO4 Extraction of gold from tailings using environmentally friendly reagents Marema J Khuduwe 4 mixture ) IL concentration, and 10 %w/v pulp density, giving a maximum Au extraction of 45.3%. This low Au extraction is attributed to the inefficiency of ILs in dissolving metals from their solid oxide form, thus unable to liberate the gold for dissolution locked in the metal iron oxide. On the other hand, leaching studies focusing on the use of DES found that pulp density and leaching time had a significant and positive influence on the gold extraction process. This suggests that to achieve maximum gold extraction, pulp density and leaching time must be kept at high levels. The optimum conditions were found to be 30 %w/v pulp density and 7 hrs leaching time. A maximum Au extraction of 76.4% was achieved. This high gold extraction is attributed to the high FeO destruction observed in the study, suggesting that the gold was liberated and amenable to leaching. Lastly, thiosulfate leaching studies identified temperature, time, pulp density, the interaction of temperature and concentration, the interaction of concentration and pulp density, and the interaction of temperature and time as the parameters significantly influencing gold extraction. A maximum Au extraction of 47% was achieved. This low gold extraction is attributed to the low efficiency of thiosulfate in dissolving metal iron oxide and the reagent consumption through silica dissolution, thus reducing the amount of thiosulfate available for gold dissolution. The results of the effect of tailings particle size results revealed that the IL leaching of bulk tailings (-300 m, P80 = 75 m) gave Au extraction of 21.9% while the leaching of smaller particle size tailings (-38 m) increased Au extraction to 45.3%. The high gold extraction at smaller particle sizes is attributed to the large surface area available for interaction with the leaching agent and the presence of a thin boundary, thus resulting in improved leaching efficiency. On the other hand, DES leaching of bulk tailings resulted in Au extraction of 71.9% and the leaching of smaller particle size tailings gave 76.4% Au extraction, indicating that reduction in particle size did not have a significant impact on gold dissolution. Lastly, thiosulfate leaching of bulk tailings gave a maximum Au extraction of 24% and the leaching of smaller particle size tailings resulted in an increased Au extraction of 47%, indicating that a reduction in particle size in this system had a significant effect. The study indicated that DES was more efficient in the dissolution of gold tailings compared to the use of IL and thiosulfate. Furthermore, DES gave higher Au extraction (71.6%) compared to cyanide solutions which gave Au extraction of 46.9%. However, cyanide gave a higher Au extraction compared to IL (21.9%) and thiosulfate (24%). These results indicate that ethaline DES is more efficient compared to 1-butyl-3-methyl-imidazolium hydrogen sulfate IL Extraction of gold from tailings using environmentally friendly reagents Marema J Khuduwe 5 and thiosulfate, and thus can be used in the processing of this kind of tailings as an alternative to cyanide. Moreover, the reagents dissolved more gold compared to other metals in the tailings except for IL which dissolved more Cu (50.4%) and Ni (61.9%) compared to Au (45.3%). Finally, the recovery of gold from the leach solution of the investigated reagents using activated carbon (AC) was found to be possible with the maximum Au adsorption of 84.6% achievable from IL leach solution in 2 hours at AC amount of 60 g/l and 4 hours at AC amount of 120 g/l. The maximum Au adsorption of 75% was achieved from DES leach solution in 4 hours at an AC amount of 120 g/l. The highest Au adsorption of 46.4% was achieved from thiosulfate leach solution in 6 hours. The recovery of Au by AC from leach solutions of IL and DES was high, however, they are not comparable to the 99% gold recovery by AC from cyanide solutions in the industry. This indicates that the recovery of gold from these solutions by alternative adsorbents should form a basis for further investigation.
Policy challenges affecting the electric vehicle manufacturing sector in South Africa
(University of the Witwatersrand, Johannesburg, 2024) Mateko, Freeman Munisi
The evolution of technology has brought many changes to the automotive sector on a global scale. Different economies in the Global South and Global North are making strides to adopt modern technology, such as electric vehicles, which are more efficient than internal combustion engine vehicles. Electric vehicles have zero emission levels and this is crucial for supporting climate change action. Economies that have adopted electric vehicles succeeded due to robust policies and financial incentives for car manufacturers, among other factors. The aim of this research was to explore the extent to which the policy environment facilitates for increased adoption and manufacturing of electric vehicles (EVs) in South Africa. This research is in line with various Sustainable Development Goals (SDGs). It supports SDG 7 by encouraging the use of electric vehicles for cleaner energy, as well as SDG 9 by advocating for automotive sector innovation and infrastructural development. Furthermore, the emphasis on lowering emissions coincides with SDGs 11 and 13 by promoting sustainable urban environments and climate action. In terms of the research methodology, the study was based on qualitative research techniques. Interviews and literature review were used for data collection. Six policy documents were analyzed in this study. The target population for the study were the stakeholders in the South African car manufacturing sector. Purposive sampling was used to select a total of ten participants for the study. Data was analyzed through content and thematic analysis techniques. The results of primary study demonstrated how ambiguous South Africa's current electric vehicle policy environment is. Additionally, it was determined that some factors must be considered to guarantee a seamless switch to electromobility. Developing and executing electric vehicle policies, maintaining a steady supply of energy, lowering import taxes on EV parts, skill development, providing purchase subsidies, and providing production and technological incentives are a few of these elements. In terms of policy recommendations, it was suggested that there is need for timeous implementation of electric vehicles policy, producing battery electric vehicles, promoting research and development on electric vehicles and there is need for increased government support towards car manufacturers in South Africa.
Determinants of Adaptation and Insurance Uptake among Small-Scale Farmers in Kenya
(University of the Witwatersrand, Johannesburg, 2024) Segone, Tshepiso; Alence, Rod
Despite the costs associated with climate-related damage and loss, WII uptake remains low among small-scale, Kenyan farmers. Many of these farmers continue to opt for traditional adaptive and mitigative strategies in the wake of climate-related challenges, despite the many known benefits insurance has for climate resilience. Thus, the study seeks to understand the determinants of insurance uptake, and to measure the relationship between these determinants and agricultural output, using a binary regression model. Overall, the study underscores the complex interplay of socio-economic, cultural, and environmental factors shaping farmers’ adaptation decisions in Kenya and highlights the need for targeted interventions to enhance insurance uptake and promote effective climate strategies
Investment and Social Conflict in Extractive Industries in Africa: The Case of Cabo Delgado, Northern Mozambique
(University of the Witwatersrand, Johannesburg, 2024) Magagula, Noncedo; Eyita-Okon, Ekeminiabasi
Following the rise of an insurgency in the mid-2010s in northern Mozambique, scholars have undertaken the task of exploring the driver of the insurgency considering the different actors including the government of Mozambique and Multinational corporations amongst others. Dominant views on the insurgency have not found a single root cause for the conflict and have settled on a number of causes including the socio economic and socio-political environment in the northern provinces of the country, the discovery and exploration of natural gas by MNCs and religious cleavages. Using a qualitative research approach based on existing sources and literature, this paper investigates the role of foreign investments towards the extraction of natural gas in exacerbating the insurgency in northern Mozambique, Cabo Delgado. It finds that the MNC led developments towards natural gas extraction exacerbated conflict by shining a spotlight on the socio-economic cleavages that have dominated Cabo Delgado throughout the country’s post-independence history. The state and the consortiums neglected the brewing issues in Cabo Delgado, which were years in the making and gave the insurgents ample opportunity to grow into the insurgency that has claimed thousands of lives and halted economic activities in the province.
Navigating Governance Processes in IT Startups: A Case Study within an Original Equipment Manufacturer (OEM)
(University of the Witwatersrand, Johannesburg, 2024) Rantho, Malekgene; Sylvester, Horvey
This qualitative study explores the intricate aspects of governance procedures within agile software development teams in IT startups in Original Equipment Manufacturers (OEM’s) environment in South Africa. The research aimed to gain a comprehensive understanding of how elements such as leadership styles, organizational culture, decision-making processes, team climate, and emotional aspects of leadership influence the navigation and effectiveness of governance in agile agile software development teams. A case study of an IT startup within an OEM was used to explore the research question. To answer this question, an investigation was conducted through interviews of a qualitative nature with 20 members of agile teams in the organization selected for the case study seeking to: (i) To examine the current governance practices employed by agile teams of software development organizations within an OEM environment in South Africa; (ii) To identify the key challenges and opportunities faced by software development organizations in implementing effective governance practices; and (iii) To recommend best practices and strategies for enhancing governance practices in software development organizations, based on the findings of the case studies and an analysis of industry trends and standards. The results indicate the necessity of adaptive leadership that balances transformational, transactional, and laissez-faire styles to effectively manage governance of agile software development teams; the importance of aligning governance frameworks with organizational cultures, fostering continuous improvement, and promoting effective communication; the challenges in role clarity and the impacts of missing team members on workload, job satisfaction, and project outcomes; and that culturally sensitive governance practices, supported by regular knowledge-sharing sessions and a culture of measured risk-taking, enhance team performance and innovation. Thus the recommendations include implementing adaptive leadership training, fostering a culture of continuous feedback, and enhancing risk management practices to ensure project stability and quality. This study contributes to understanding how governance processes can be tailored to support agile methodologies in complex organizational settings.
Designing an AI-based Predictive Maintenance Framework to Improve OEE for an Automotive Manufacturer in South Africa
(University of the Witwatersrand, Johannesburg, 2023) Phenyane, Siphamandla Sifiso; Sony, Michael
This study presents a comprehensive approach to enhancing Overall Equipment Effectiveness (OEE) in an automotive manufacturing setting by integrating artificial intelligence and Internet of Things technologies with people and processes. The research applies the Design Science Research (DSR) methodology to develop, deploy, and evaluate an AI-driven predictive maintenance framework. The first phase involves a detailed exploratory data analysis to understand the current state of OEE and identify critical bottlenecks within the production line, particularly operating below OEE industry standards. The second phase builds on the insights gathered from a semi-structured survey conducted among field experts, leading to the formulation of a cohesive framework that synergises the socio-technical aspects of the manufacturing environment. The core of the study revolves around the design and development of a Bi-directional Long Short-Term Memory (Bi-LSTM) model artefact, capable of analysing sequential data to predict the Remaining Useful Life (RUL) of machinery, thereby pre-empting production halts. The model's predictive capability is rigorously tested and validated using historical IoT data, demonstrating a high degree of accuracy across different spot-welding locations. Overall, the study highlights the critical role of AI in transforming manufacturing processes, emphasising the need for continuous adaptation and improvement of predictive models to maintain operational efficiency. The proposed framework aims to serve as a strategic tool in lean manufacturing, contributing to smoother operations and improved OEE in automotive manufacturing settings

4. Electronic Theses and Dissertations (ETDs) - Faculties submissions

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