School of Mechanical, Industrial and Aeronautical Engineering (ETDs)
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Item Acceleration Effects on 3-D Aerodynamics of Slender Bodies(University of the Witwatersrand, Johannesburg, 2025) Mahomed, Irshaad; Skews, B.W.Transient fluid dynamic effects in the transonic regime generate unique fluid behaviour during rapid acceleration when compared to a steady analysis. There is a change in the pressure load- ing upon the aerodynamic body during rapid acceleration (or deceleration) where well-known steady prediction methods for aerodynamic coefficients may not be accurate. Knowledge of changes in aerodynamic loads is valuable in obtaining increased agility and manoeuvrability. This study investigated the effect of acceleration and deceleration for a cone-cylinder at four angles of incidence, α=0◦, 5◦, 10◦, 15◦. The aerodynamic coefficients for acceleration and deceleration were compared with constant velocity to identify acceleration effects. The effects at the shoulder were tested for α=0◦, by using three cone half-angles: 10◦, 20◦ and 30◦. The computational model was three dimensional symmetric for α>0◦ and axisymmetric for α=0◦. The acceleration magnitude was constant 100g for α=0◦, and 400g for α>0◦, with straight and level flight. The Moving Reference Frame acceleration technique for one-dimensional flight was implemented in ANSYS Fluent® V.19 series and validated against Schlieren data from a free-flight ballistic range. The effects of significant axial acceleration and deceleration on an axisymmetric body was investigated in order to understand the development of the unsteady flow field and its influ- ence on drag in the transonic region. Wave and separation behaviour differed substantially between acceleration and deceleration cases. Acceleration to higher speeds was dominated by the developments of the bow, terminal, and wake shocks, which appear at higher Mach numbers than in the equivalent steady flow; due to the lag acceleration effect. Acceleration caused a shift in the transonic drag rise to higher Mach numbers with reduced maximum drag. The flow field for an accelerating cone-cylinder at incidence in the transonic Mach regime is described by downstream wave propagation and gradual wave development. The axial force coefficient for acceleration at incidence is characterized by a gradual slope in the subsonic iii Mach regime until a flight Mach number of M (t) near 1. There occurred no transonic peak and the maximum axial force was delayed to M (t)=1.1. The normal force coefficient for acceleration at incidence is characterized by a subsonic step- jump at the onset of acceleration. This is maintained until the transonic rise near M (t)=1 with an α-dependent behaviour in the supersonic Mach regime. There is an offset in the position of the primary body vortex core between acceleration and constant velocity, when measured from the cylinder surface. The position of the primary vortex core was closer to the cylinder surface during acceleration. The rear-foot of the lambda shock was classified as a weak shock, this shock was initially aft of the shoulder and propagates downstream towards the cylinder-base vertex, as the cone-cylinder accelerates from subsonic to supersonic speed. The foot of this shock locally disrupts the vortex lift, and as this shock leaves the cylinder- base vertex, the full vortex lift is then applied to the cylinder surface. This produces a step-disturbance in the normal force coefficient. The flow field for a decelerating cone-cylinder at incidence in the transonic Mach regime is characterised by upstream wave propagation and wave-surface interaction. The axial force coefficient for deceleration is characterized by a gradual reduction through M (t)=1, followed by wave-surface interactions. The cause is associated with upstream propagation of the asymmetric bow shock. The strength of this shock, the post shock pressure, and its proximity to the cone-apex modify the cone-surface pressure load in the axial direction. This gradual reduction of the axial force coefficient is maintained until the foot of the terminal and wake shocks are incident on the cone surface, the occurrence of which generates a sharp increase of the axial force coefficient. The normal force coefficient for deceleration at incidence is characterised by vortex lift flow history for deceleration through M (t)=1, from supersonic flight. The body vortices developed at supersonic flight remain in the flow field, as the cone-cylinder decelerates from supersonic to subsonic speeds. This leads to an increase in vortex lift during the subsonic Mach re- gime, compared to the constant velocity case. The elevated vortex lift during deceleration is maintained until the wake shock interacts with the body vortices at the cylinder’s aft-end. This significantly disrupts the vortex lift reducing the normal force coefficient. The upstream propagation of the terminal and wake shocks leads to shock wave boundary layer separation aft of the shoulder-vertex and with development of spiral vortex pairs around the leeward periphery of the shoulder. This raises the vortex lift, creating a temporal and sharp rise in the normal force coefficient while the terminal and wake shocks are located aft of the shoulder- vertex. This effect dissipates when the terminal and wake shocks propagate upstream and away from the shoulder vertex.Item Optimising the Throughput of a Complex Multimodal Freight Network(University of the Witwatersrand, Johannesburg, 2025) Reddy, DeneshThis research, situated within the logistic domain, extends its relevance to global supply chains. In a context where revenues are constrained, customer demand for capacity expansion is rising, the commodity mix is evolving, and time sensitivity is critical, relying solely on critical infrastructure expansion for capacity development is neither sustainable nor desirable. Consequently, this study focuses on unlocking latent capacity within existing infrastructure and facilities. Initially, a strategic area for growth was identified, enabling railways to increase their market share in the container sector. The transition of goods from road to rail is a significant economic lever, particularly as the global shift away from fossil fuels continues and railways remain an efficient mode of transport. While bulk commodities are predominantly transported by rail, the Fourth Industrial Revolution presents substantial opportunities in other sectors, notably in the increasing volume of goods suitable for containerization. To address these challenges, a mathematical model was developed to serve as a theoretical foundation for an intermodal hub-and-spoke system, offering a framework for approaching the optimal solution proposed in this thesis. This work makes a novel contribution by addressing the hub network problem with considerations for train lengths and departure decisions. The research investigates whether cost optimisation can be achieved by optimising train lengths. Although the proposed mathematical model is general, it has been specifically applied to a South African context. The optimisation process was carried out using the MATLAB® programming language, and customizing solutions for the specific problem, thereby representing another novel contribution to the field. iv In conjunction, a Simulink® model of a conceptual hub-and-spoke system was developed as a further independent contribution, incorporating key elements to facilitate the study of operations and the impact of varying train lengths. The integration of MATLAB® and Simulink® allowed for solution techniques to be developed using built in optimisation toolboxes, separate from the solution technique developed for the mathematical model. Simulation scenarios were designed to cover a range of operational environments, including considerations for double-stacked container trains. While double stacking is not feasible on narrow-gauge tracks, it provides insight into the potential benefits of transitioning to wider gauges. Results for the South African corridor problem indicate that train lengths can be optimised to achieve lower unit costs, for both the mathematical model and the simulation.Item Investigation of Wake Redirection Techniques for Wind Farms(University of the Witwatersrand, Johannesburg, 2025) Surujhlal, Kayla; Hua Ho, WeiA world-wide increase in wind energy has seen an increase in the need for optimisation of wind farms. In a wind farm, an upstream turbine has several negative effects on the downstream turbine. The upstream turbine extracts a lot of the energy from the freestream, leaving little energy remaining in the wake to be extracted by the downstream turbine. There is also a significantly higher turbulence intensity in the wake leading to uneven loads being exerted. This all results in reduced power outputs of the wind farm as a whole. Wake redirection techniques, and specifically yaw misalignment, could reduce these negative effects and improve the overall power output of a wind farm. The first aim of this study is to investigate the ability of a surrogate model to predict the flow field when the upstream turbine is at different yaw angles. This could assist with real-time wake analysis and optimisation of a wind farm, without the need for running high-fidelity simulations to predict the wake when the yaw angle of the turbine is changed. The second aim is to investigate the physical effect of the upstream turbine yaw on the wake, as well as the interaction between the wake and the downstream turbine. A surrogate model is a combination of a Reduced Order Model (ROM) and a Machine Learning (ML) algorithm. A ROM was created using an existing, open-source dataset that conducted Large Eddy Simulations (LES) on a two-turbine array using the Simulator for Wind Farm Applications (SOWFA) software. The Dynamic Mode Decomposition (DMD) modes generated during this process were grouped according to the physical property of the wake that they represent. These modes were used to train the ML model to predict the development of individual modes at different yaw angles, which were then reconstructed in groups or combinations of groups to predict the entire flow field at the different yaw angles. It was found that the mode group related to the mean flow is essential to reconstruction and it alone results in the most accurate reconstructions with an average error of 7% and a reduction in computational resources by a factor of approximately 300 compared to LES. Smoke visualisation, hot-wire measurements and force tests were conducted to further investigate the physical properties of the wake. A difference of 8.1% was recorded between the experimentally measured maximum angle of deflection and the maximum generated from the surrogate model. It was found that the larger the yaw angle of the upstream turbine, the greater the wake deflection. This relationship is hypothesised to be linear until the tested yaw angle of 45°, however it is expected to plateau after it reaches its stall condition. As yaw increases, both the force in the horizontal direction (Fy) and the side toppling moment (Mx) decrease linearly with the yaw angle, suggesting that a larger yaw angle also helps reduce the structural loads on the downstream turbine.Item A data science framework for mineral resource exploration and estimation using remote sensing and machine learning(University of the Witwatersrand, Johannesburg, 2024) Mahboob, Muhammad Ahsan; Genc, BekirExploring mineral resources and transforming them into ore reserves is imperative for sustainable economic growth, particularly in low income developing economy countries. Limited exploration budgets, inaccessible areas, and long data processing times necessitate the use of advanced multidisciplinary technologies for minerals exploration and resource estimation. The conventional methods used for mineral resources exploration require expertise, understanding and knowledge of the spatial statistics, resource modelling, geology, mining engineering and clean validated data to build accurate estimations. In the past few years, data science has become increasingly important in the field of minerals exploration and estimation. This study is a step forward in this field of data science and its integration with minerals exploration and estimation. The research has been conducted to develop a state-of-the-art data science framework that can effectively use limited field data with remotely sensed satellite data for efficient mineral exploration and estimation, which was validated through case studies. Satellite remote sensing has emerged as a powerful modern technology for mineral resources exploration and estimation. This technology has been used to map and identify minerals, geological features, and lithology. Using digital image processing techniques (band ratios, spectral band combinations, spectral angle mapper and principal component analysis), the hydrothermal alteration of potential mineralization was mapped and analysed. Advanced machine learning and geostatistical models have been used to evaluate and predict the mineralization using field based geochemical samples, drillholes samples, and multispectral satellite remote sensing based hydrothermal alteration information. Several machine learning models were applied including the Convolutional Neural Networks (CNN), Random Forest (RF), Support Vector Machine (SVM), Support Vector Regression (SVR), Generalized Linear Model (GLM), and Decision Tree (DT). The geostatistical models used include the Inverse Distance Weighting (IDW) and Kriging with different semivariogram models. IDW was used to interpolate data points to make a prediction on mineralization, while Kriging used the spatial autocorrelation to make predictions. iv In order to assess the performance of machine learning and geostatistical models, a variety of predictive accuracy metrics such as confusion matrix, a receiver operating characteristic (ROC) curve, and a success-rate curve were used. In addition, Mean Absolute Error, Mean Square Error, and root mean square prediction error were also used. The results obtained based on the 10 m spatial resolution show that Zn is best predicted with RF with significant R2 values of 0.74 (p < 0.01) and 0.7 (p < 0.01) during training and testing. However, for Pb, the best prediction is made by SVR with significant R2 values of 0.72 (p < 0.01) and 0.64 (p < 0.01) for training and testing, respectively. Overall, the performance of SVR and RF outperforms the other machine learning models with the highest testing R2 values. The experimental results also showed that there is no single method that can be used independently to predict the spatial distribution of geochemical elements in streams. Instead, a combinatory approach of IDW and kriging is advised to generate more accurate predictions. For the case study of copper prediction, the results showed that the RF model exhibited the highest predictive accuracy, consistency and interpretability among the three ML models evaluated in this study. RF model also achieved the highest predictive efficiency in capturing known copper (Cu) deposits within a small prospective area. In comparison to the SVM and CNN models, the RF model outperformed them in terms of predictive accuracy and interpretability. The evaluation results have showed that the data science framework is able to deliver highly accurate results in minerals exploration and estimation. The results of the research were published through several peer reviewed journal and conference articles. The innovative aspect of the research is the use of machine learning models to both satellite remote sensing and field data, which allows for the identification of highly prospective mineral deposits. The framework developed in this study is cost-effective and time-saving and can be applied to inaccessible and/or new areas with limited ground-based knowledge to obtain reliable and up- to-date mineral information.Item Internal Cooling at the Trailing-Edge of a High- Pressure Gas Turbine Blade(University of the Witwatersrand, Johannesburg, 2024) Schekman, Sjouke W.The efficiency of a gas turbine engine tends to be increased when its turbine blades are operated at higher temperatures. In turn, this requires the adequate cooling of these turbine blades (for both rotors and stators, collectively termed “airfoils”). Of specific concern in this study is the cooling at the trailing- edge of the airfoils. However, there exists limited space for cooling due to a requirement for a thin trailing-edge. A combination of perforated blockage plates and a pin-fin array (a “blockage pin-fin” configuration) is particularly focused on here. Such a configuration has been previously discounted due to a presumed poor thermal performance ( hTP < 1.0). This thesis demonstrates that the thermal performance has been misrepresented in part due to a misunderstanding of flow behaviours present in the configuration. To this end, a series of experimental tests are undertaken using particle image velocimetry, oil-dye flow visualization, and thermochromic liquid crystal paints. The new results show that a thermal performance greater than one (i.e., hTP > 1.0) can be achieved for a blockage pin-fin configuration. Despite previous studies concluding otherwise there may be merit in the use of a blockage pin-fin configuration for internally cooling the trailing-edge of a turbine blade. Further, a unique flow topology, present in a blockage pin-fin configuration was revealed. Such a flow, termed as a “jet-pin” flow, and its interactions has been previously unidentified or misinterpreted.Item Modelling the badminton jump smash for injury prevention and performance enhancement(University of the Witwatersrand, Johannesburg, 2023) Chohan, Raees Ghalib; Mangera, TaahirahBadminton is considered the fastest competitive racket sport. To gain a competitive edge, athletes commonly execute a forward jump smash to return the shuttlecock with high speeds and steep angles. Research has shown that common injuries in badminton, resulting from incorrect landing during the execution of the jump smash, include rupture of the Achilles tendon and Anterior Cruciate Ligament (ACL). There is a need to identify safe landing techniques to minimise risk of injury while preserving the performance of the manoeuvre. This study involved assessing four different landing techniques. The techniques involved varying the initial contact with the ground upon landing. The landing techniques assessed were the Normal Landing Technique (NLT), Toe-First (TF) technique, Flat Foot (FF) technique and the Heel First (HF) technique. Data was obtained using an Xsens motion capture suit which uses inertial sensors placed on body segments to capture kinematic and kinetic data. Sixteen athletes from the South African Badminton team participated, however, only data from ten athletes were considered due to the experimental obstacles identified during the analysis of the data. Kinematic data, Newton- Euler equations and inverse kinematics were used to model the ground reaction forces and moments at the foot, ankle, knee and hip joints. The ground reaction forces were validated alongside data collected from a Bertec Force Plate. By use of the Stretch-Shortening Cycle, the force vs time profile of each landing technique was assessed to classify if a landing technique was “good,” “moderate” or “poor.” The angular velocity of body segments was also assessed at various phases of the jump smash to determine the effect on performance. The study found that there are no statistical differences in the ground reaction forces when varying the landing technique. When analysing the force vs time profiles during landing, the Normal Landing Technique (NLT), which typically involves landing on the ball of the foot, and the Toe- First (TF) technique exhibited spring like characteristics and were therefore classified as good landing techniques. The Flat Foot (FF) and Heel First (HF) techniques displayed impact peaks and were therefore considered poor landing techniques. The Heel First and Flat Foot techniques produced the largest reaction moment at the floor and in all lower limb joints, therefore contributing to a higher risk of injury. There were no statistical differences in segment angular velocity when varying the landing technique. Further analysis on differences in biomechanical responses between male and female athletes is advised.Item Magnetically Enhanced Vacuum Arc Thruster for Nanosatellites(University of the Witwatersrand, Johannesburg, 2024) Rencken, Tristan MarkThis dissertation describes the development and testing of a magnetically-enhance Vacuum Arc Thruster (VAT) with various cathode materials and magnetic field strengths. The thruster uses a Power Processing Unit (PPU) used to generate a high-voltage spike to initiate and maintain a high current arc discharge. A multi-layer solenoid coil is placed around the arc discharge to investigate the effects of pulsed magnetic fields on the ion density distribution. The VAT produces consistent arc discharges with a peak arc current of IApk ≈ 270 A with a pulse length of tp ≈ 3.5 ms for three cathode materials, Fe (iron), Al (aluminium), and Cu (copper). The magnetic field generator uses a separate capacitive discharge circuit which produces field strengths between⃗ B = 0 - 250 mT along the center line of the thruster. Research was conducted to determine the effects of applied magnetic fields to the ion density distribution of ions with the VAT plasma plume. Ion-to-arc current ratios were normalised to a baseline VAT to directly compare qualitative distributions for the various materials and magnetic field strengths. The application of a magnetic field results in the increase in peak ion-to-arc current ratios with a decrease in ion-to-arc ratios at higher angles from the center line. The increased peak and narrowing of the ion distribution suggests that the magnetic field causes ion collimation within the plasma plume. For 0 <⃗ B < 250mT, performance increase over the non-magnetic case is observed with the best percentage increase in thrust factor of 16.4% for Al, 10.8% for Cu, and 6.3% for Fe, obtained at⃗ B ≈ 150 mT. For⃗ B > 150 mT, the ion distribution is shown to result in higher ion-to-arc ratios at higher angles perpendicular to the center line resulting in greater momentum loss. The greatest thrust factor increase of Al was found to be as a result of the mass-to-charge ratio of the Al ion which is subjected to greater accelerations due to Lorentz forces. The application of an axial magnetic field was found to increase the thrust factor and result in improved VAT thrust performances.Item Uncontrolled aerobatic tumble manoeuvre mechanics(University of the Witwatersrand, Johannesburg, 2024) Piccolo, Stefano FabrizioDespite advancements in aerobatic aircraft, the issues concerning aerobatic flight safety remain largely unresolved with incidents occurring at airshows, during training and during private flights, even with stable, predictable and reliable aircraft. The likelihood of aerobatic incidents has increased as aircraft are now capable of being flown in even more dangerous, low energy scenarios. Spins or tumble manoeuvres are typically the origin of loss-of-control accidents. Such scenarios occur generally in manoeuvres that result in low energy states. This dissertation aims to understand the mechanics behind a low energy aerobatic manoeuvre. The positive 𝑔 tumble manoeuvre was selected as the manoeuvre to analyse, as it is one of the most difficult aerobatic manoeuvres to recover from. The Extra 330SC was selected as the model aircraft as it is one of the most popular aerobatic aircraft across all pilot skill levels. Additionally, the Extra Aircraft Corporation provided more information about the aircraft than any other aerobatic aircraft manufacturer. Methods to develop mass, inertial and aerodynamic data were explored. The aerodynamic data was extended to high angles of attack. Aerodynamic models for the wing, fuselage, horizontal stabiliser and propeller were considered. Generated mass and inertial data were compared to reference data and demonstrated good correlation. Static aerodynamic data was compared to published experimental data (where possible). Good agreement was shown between the generated data and test data. Considerations for surfaces exposed to propeller slipstream and rotational dynamics were considered. No literature was available for direct comparison of these considerations. A non-linear three degree of freedom model was developed to simulate the tumble manoeuvre. This was achieved by simplifying the equations of motion in the velocity axes. The velocity axes were appropriate in determining the flight path of the manoeuvre along with all affiliated parameters. The aircraft body axes were utilised in determining the rotational parameters during the tumble manoeuvre. Force components at high angles of attack were modelled in both the velocity and body axes. The current model does not include any lateral-directional forces or moments, assuming the manoeuvre is purely in the longitudinal plane. A tumble manoeuvre is possible for a very specific aircraft configuration. An upgraded engine and propeller slipstream effects are essential in performing the tumble manoeuvre. It was shown the entire manoeuvre could be completed in a horizontal distance of ≈ 50 m and a vertical distance of ≈ 15 m for manoeuvre entry velocities of 25 m/s, 30 m/s, 35 m/s and 40 m/s. Each of the minimum radius tumble manoeuvres occurred at the most rearward centre of mass location. An entry velocity of 30 m/s provided the smallest possible radius tumble. The entry to the manoeuvre requires large decelerations and normal forces that were beyond the lift limits of the wing. Both these requirements were met by orientating the aircraft at large pitch angles and subsequently large angles of attack. The large angles of attack resulted in large decelerating forces and orientated various aircraft force components, other than iii the wing, in the lift direction. Significant energy loses are seen through the manoeuvre resulting in large losses in airspeed and ultimately altitude. The risks associated with a tumble manoeuvre could be minimised by adjusting the normal forces and moments acting on the aircraft. By altering the propeller blade pitch angle, the normal forces and subsequently the moments from the propeller could be changed, altering the overall normal forces and moments acting on the aircraft. This resulted in a slightly larger overall manoeuvre but illustrated increased velocity values throughout the manoeuvre. A form of validation of the results was performed by comparing model results of tumble manoeuvres that were generated through a patchwork of images compiled from video footage of the manoeuvre. Good correlation was shown between the model data and video footage.Item Water Management Practices of South African Electricity Power Plants(University of the Witwatersrand, Johannesburg, 2024) Mkhize, Zama; Sunjka, BernadetteSouth African (SA) power plants are experiencing several challenges when managing water usage and containing it within their clean and dirty water dams (leading to water wastage and pollution). Numerous reasons have been provided to explain the increased water usage. However, the key issue is understanding the causes of high-water use that leads to dam overflows and pollution of the natural water streams/rivers and groundwater system. The main aim of this research, thus, sought to establish the causes of high-water usage in thermal power plants in South Africa. The objective to identify where and how water wastage occurs in the system, any variations from the power plants' standard operating procedures (SOPs) contributing to water wastage and finally, recommend solutions to address the gaps. Qualitative research was conducted through semi-structured interviews at two power plants (namely Power Plant 1 and Power Plant 2) to provide an understanding and detailed information on water use at thermal power plants in South Africa. The standard operating procedures and policies that govern and control water processes were analysed. As a result, the study showed that the most significant cause that came out of the interviews was leadership, followed by financial constraints, negligence (of the plant and water) and lastly, maintenance. Water management is failing and needs to be improved, with the primary challenges being maintenance and a lack of leadership decision-making. Further research on the remaining power plants will be required to determine the generalisability of the findings.Item Supply Chain Risk Management in Manufacturing Small and Medium Enterprises: A Systematic Literature Review(University of the Witwatersrand, Johannesburg, 2024) Pungula, Vusumuzi; Sunjka, B.Background: Small and Medium Enterprises (SMEs) are becoming major actors in the manufacturing sector due to the rising complexity of global supply chains. However, they still face enormous risks from supply chain disruptions and market dynamics, which can have costly effects. SMEs sometimes lack the means and expertise to execute comprehensive risk management plans intended for larger businesses, despite their significance. Research on Supply Chain Risk Management (SCRM) specifically for small and medium-sized enterprises (SMEs) is noticeably lacking, especially in the manufacturing sector. Purpose: The aim of the study was to systematically review how SCRM has been developing in manufacturing SMEs globally over the past two decades, and provide insights for policymakers, industry associations, and SMEs themselves. Method: A Systematic Literature Review (SLR) was conducted by utilizing a qualitative research approach. Seven key phrases were formulated to guide the search for relevant articles published between 2000 and 2023. A thorough screening process was employed to select 38 articles that met inclusion criteria, and data analysis was performed using NVivo software on these articles. Following this, thematic analysis and textual narrative synthesis methods were employed for data analysis and synthesis. The discussion of the identified themes provides comprehensive insights to policymakers, industry associations, and SMEs into the current status of SCRM research in manufacturing SMEs globally. It highlights the importance of effectively addressing risk variables, developing tailored SCRM approaches, and striking a balance between risk reduction efforts and strategic opportunities within supply chains to enhance resilience and ensure operational continuity. Results: The review revealed a significant increase in SCRM research pertaining to manufacturing SMEs over the past decade. Trends analysis indicated a growing emphasis on SCRM in various disciplines, highlighting its increasing significance. Thematic analysis identified eight key themes, including the current status of SCRM research and factors influencing SCRM strategies in manufacturing SMEs. Conclusion: Based on the comprehensive review of literature, several key conclusions can be drawn. There is prevalent recognition of the importance of SCRM within SMEs, emphasizing the need for proactive risk mitigation strategies tailored to the SME context. While formal risk management approaches are increasingly adopted, the context-specific nature of risk management practices highlights the importance of tailored approaches. Technological advancements play a significant role in enhancing SCRM strategies, alongside the integration of green supply chain management practices.