Electronic Theses and Dissertations (Masters)

Permanent URI for this collectionhttps://hdl.handle.net/10539/37972

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A report on the investigation into factors that impact the replication of operational excellence programs across the global operations of a top global mining company: The Case of Rio Tinto
(University of the Witwatersrand, Johannesburg, 2024) Tsomole, Moleboheng; Sunjka, Bernadette
Achieving operational excellence in mining is fraught with challenges, including the lack of standardized procedures, misalignment with company strategy, and cultural disparities across global operations. This study investigates the strategies for efficient deployment of operational excellence programs, with a focus on Rio Tinto’s operational excellence framework, RTSPS (Rio Tinto Safe Production System). A mixed-methods approach was adopted, integrating qualitative data from semi-structured interviews with Rio Tinto managers and employees and an analysis of secondary data from company reports. This study combined deductive and inductive research approaches to provide a comprehensive exploration of operational excellence at Rio Tinto. The deductive approach involved testing specific hypotheses drawn from existing literature on operational excellence programs, such as the assumption that standardized systems like RTSPS would encounter difficulties in culturally diverse environments. Inductive reasoning complemented this by allowing themes and insights to emerge directly from empirical observations during interviews, thus offering an authentic view of the challenges and successes of RTSPS deployment. The qualitative component of the study was centered around 14 semi-structured interviews with key stakeholders across various regions, including operational excellence managers and improvement leads. These interviews were conducted virtually using platforms like Microsoft Teams and Zoom, enabling broad participation across geographically dispersed sites. The interview questions were meticulously crafted using Wengraf’s pyramid model, which starts with Critical Research Questions (CRQs) that are broken down into Theoretical Questions (TQs) and further refined into specific Interview Questions (IQs). This structured approach ensured that the interviews remained focused on uncovering detailed insights into operational challenges and strategic alignment. The questions were adapted to account for the contextual nuances of each participant's operational environment, and particular care was taken to avoid leading questions, thereby minimizing researcher bias.The analysis of data employed thematic coding, revealing key insights into behavioural adaptability, cultural diversity, and the influence of leadership on the adoption of standardized processes. Themes were generated from the qualitative data and cross-referenced with secondary data sources, including integrated annual reports that provided a broader organizational context and corroborated the findings. Secondary data analysis allowed for a deeper understanding of Rio Tinto’s strategic objectives and how these aligned or conflicted with ground-level practices. Using qualitative data from interviews with 14 participants, the research highlights key themes identified through thematic analysis, focusing on the complexities of implementing RTSPS across diverse cultural and operational landscapes. Sentiment analysis conducted via ATLAS.ti software provided additional insights into participants' attitudes and emotional responses, shaping the creation of a comprehensive codebook that guided systematic data analysis. The findings reveal that RTSPS faces significant deployment challenges, including the integration of a standardized system across culturally varied sites, a need for a more people-centric approach, and issues with communication, resource allocation, and adaptability. Participants with experience outside of Rio Tinto provided unique insights into alternative deployment strategies that could enhance replication and adaptability across different industries and operational settings. The study also identifies the foundational elements critical to RTSPS, such as standardized processes, robust training programs, and a centralized knowledge- sharing infrastructure. These components were highlighted as essential for fostering a culture of continuous improvement and ensuring successful replication across Rio Tinto’s operations. Rio Tinto's annual reports from 2018 to 2022 emphasize RTSPS's role in enhancing safety, efficiency, and sustainability, with impacts on the triple bottom line of people, planet, and profit. However, the challenges identified through this research include cultural integration, resource constraints, and the need for local adaptability, mirror broader issues documented in the literature on operational excellence in the 7 mining sector. The study concludes that while RTSPS holds significant potential, its success hinges on balancing standardization with the flexibility to accommodate local conditions and prioritizing employee engagement throughout the deployment process.
Aerodynamic Force Variation on a Trailing MotoGP Motorcycle in a Corner
(University of the Witwatersrand, Johannesburg, 2024) Shaw, Craig Byrne; Boer, Michael
Motorcycle racing is a popular form of motor racing. The MotoGP category produces exciting and competitive races due to motorcycles following each other so closely. This has led to significant aerodynamic advancements being made in the MotoGP category over the past decade. Motorcycles and riders often race within the wake of a leading motorcycle as a result of this competitive racing. Racing in the wake provides an advantage on a straight due to the reduced drag force. This allows for greater acceleration and an opportunity to overtake the leading motorcycle. The effect of the wake on a trailing motorcycle in a corner has not been explored in depth. This research was focused on the aerodynamic force variation on a trailing motorcycle in the wake of leading motorcycle. The optimal position for the trailing motorcycle to gain an advantage over the leading motorcycle was determined subsequently. This was achieved using Computational Fluid Dynamics (CFD). The geometry of the motorcycle was obtained using 3D scans of a 1/18th scale model 2018 Repsol Honda RC213V. The geometry of the rider was drawn using CAD. Initial CFD models were created simulating the motorcycle and rider in a straight line to compare to existing published data for validation. The CFD cornering methodology was developed by Queens University in association with Siemens. The method makes use of rotating reference frames. This simulates the motorcycle and rider cornering at a constant velocity around a constant radius corner. Models were created for a singular motorcycle and rider at varying lean angles between 40 and 60 degrees with matched velocities and corner radii. The aerodynamic forces of drag, lift and side force were analysed on the motorcycle and rider for each case. The trends for these forces were determined relative to the changing lean angles. The drag on the motorcycle and rider increased non-linearly as the lean angle increased with the side force following a similar trend. The lift on the motorcycle and rider also increased non-linearly as the lean angle increased. These same CFD models were recreated with a second motorcycle and rider following a leading motorcycle to determine the effect the wake had on the aerodynamic forces. The second motorcycle and rider were positioned 1 characteristic length behind the leading pair on the same racing line. The drag on the trailing motorcycle and rider decreased as the lean angle increased. The lift on the trailing motorcycle and rider followed a similar trend to the leading pair with it increasing as the lean angle increased and the side force fluctuates as the lean angle increased. This resulted in the trailing motorcycle having a negative allowable change in forward acceleration relative to the leading motorcycle at lean angles lower than 60 degrees. The optimal position for a trailing motorcycle in a corner was determined by positioning the motorcycle and rider on various racing lines and following distances behind the leading motorcycle and rider. This created a grid pattern of the tested trailing positions. Two smaller racing line radii, three larger racing line radii and three different following distances were tested. The optimal trailing position at a 50 degree lean angle was found to be 1 characteristic length behind and on a racing line 1 characteristic width larger than the leading motorcycle. This position resulted in a positive allowable change in forward acceleration relative to the leading motorcycle around a corner radius of 125.86 m at 38.36 m/s. This iii position was tested around another two corner radii of 75 m and 150 m. This resulted in a negative allowable change in forward acceleration of around the 75 m radius corner and a greatly improved positive change in forward acceleration around the 150 m radius corner. From these results it was concluded that this optimal position is only viable around larger radius corners. It was approximated that this optimal position provides the trailing motorcycle an advantage around corner with radii larger than 86.8 m.
An analysis of factors leading to the production of defective wagons in Transnet Engineering
(University of the Witwatersrand, Johannesburg, 2024) Nemakhavhani, Pfananani Thelma; Dewa, Mncedisi Trinity
Rail manufacturing industries play a crucial role in many countries by developing cost-effective transportation solutions to move freight more efficiently. To date, the industry has seen the implementation of traditional quality management practices that are critical in driving efficiencies and better-managed operations to improve the quality of their freight wagons. Despite the conventional quality management techniques, the rail industry continues to manufacture defective rolling stock due to design changes, errors and omissions, and inadequate skills. Over the past few decades, industry and academia have identified various factors contributing to rolling stock manufacturing defects. Nevertheless, which factors were predominantly responsible for the defective wagon production at the Transnet Engineering (TE) Bloemfontein factory remained unclear. Identifying the most prevalent causes of defects is essential in addressing the organisation's quality issues. The primary purpose of this study was to gain insights into the root causes of the defects and recommend strategies to minimise them. The study used an interpretive methodology to identify the root cause of defective wagons produced at TE. Data was collected using purposive sampling. Ten experienced TE employees actively engaged in freight wagon manufacturing were selected for face-to-face interviews. During the research study, the interviews were conducted with the employees using a semi-structured format that allowed for open-ended questions. Investigative techniques, such as cause-and-effect diagrams and the Five "Whys" root cause analysis tool, were used to investigate defects' root causes on the customer complaints register. Additionally, thematic analysis was applied to thoroughly analyse the interviews conducted with the employees, which allowed for a deeper understanding of the issues at hand. The findings showed that inadequate skills, human errors and omissions, a lack of quality culture, time constraints, management's failure to enforce accountability, and poor workshop maintenance/machinery all contribute to defective wagon production. The research provided recommendations, including adopting innovative technology and skills transfer programs to enhance the company's quality management practices.
An Investigation Into The Propulsive Force Generation Of Multiple Flapping Surfaces
(University of the Witwatersrand, Johannesburg, 2024) Mabvuu, Never; Ho, Weihua
The aerodynamic performance of flapping NACA0012 airfoils was analyzed through numerical simulation, focusing on the effects of stagger, gap, phase difference, and the number of airfoils. The simulation was conducted under specific conditions: 𝑈∞ = 0.2𝑚/𝑠, f=2Hz, 𝛼0=200, C=0.04m, St=0.2 and Re= 8000). The problem was modeled in ANSYS Fluent using a transient viscous approach with absolute velocity formulation, employing the pressure-based coupled solver (PBCS). PRESTO! interpolation and second-order upwind discretization were applied for pressure, momentum, intermittency, turbulent kinetic energy, and specific dissipation rate. Mesh validation and independence studies confirmed that the results were driven by the physics setup, independent of mesh configuration. It was discovered that small stagger and gap at φ=1800 is not good for thrust production as the airfoils produced thrust less than a single airfoil with ∆Ctav = -0.94. However, lift production is increased and ∆Clav =1.2. At larger spacing ∆Ct, ∆Cl and η generally become constant. One of the worst performing cases (X=1.0C;Y=0.5C; ϕ= 1800 ) was improved by making the aft airfoil lead ( φ= -450 ). This explains why insects alter φ or frequency depending on the situation and flight requirements. The most effective X-Y- ϕ were found to be the ones at which flow separation is suppressed. For the 4 airfoils cases the fore pair performed better than the aft pair for the small spacing case. When spacing was increased the aft pair performed better than the aft pair.
An Investigation of Factors Contributing to Long Waiting of Patients Collecting Repeat Medication in a Tertiary Hospital Pharmacy
(University of the Witwatersrand, Johannesburg, 2023-02) Oladipupo, Rekgopetse Victoria; Hattingh, Teresa; Sunjka, Bernadette
According to the World Health Organization (WHO) patient waiting time is identified as a key measurement to a responsive healthcare service and is an important indicator of quality of services offered by hospitals (NDoH, 2011) as it affects the patient’s responsiveness to the services received (NDoH, 2011; SA FAM PRACTICE, 2008; Tegabu, 2008; Pandit et, al. 2016). Long waiting times at healthcare facilities undermines the services rendered resulting in compromised or unfulfilled patient care (Afolabi & Erhun, 2003). This research studies the processes associated with the collection of repeat medication in a tertiary hospital pharmacy in order to identify value adding activities and non-value adding activities that could be impacting patient waiting time using the Lean thinking concept of driving out waste. A qualitative observational method was therefore employed to observe all the steps involved during the journey of the patient collecting repeat medication from the registration point until medication was issued at the pharmacy. Value stream mapping (one of Lean Thinking principle) was employed to analyze the processes that took place. Patient waiting time was also measured from the registration point to the pharmacy. On average patients had to wait a total 159 minutes before they could access services both at the registration point (67 minutes) and at pharmacy (92 minutes). The service time was 29 minutes at both registration point (11 minutes) and pharmacy (18 minutes). Of the 18 minutes pharmacy service time; eight minutes were found to be value-adding while 10 minutes were non-value-adding mainly due to prescriptions waiting on queue to be picked, waiting to be signed by the pharmacist and waiting to be issued out to the patient. Lack of a dedicated pharmacy service points exclusively for chronic repeat patients, manual dispensing, illegible doctor’s prescriptions, were found to prolong the time it takes the Pharmacist to complete a prescription. Post Basic Pharmacist Assistants performing duties that could be performed by a less qualified staff (e.g., Learner Basic Pharmacist Assistants) during peak hours was not value adding and thus decreasing productivity. The level of staff commitment in addressing issues of quality such as long waiting time was questionable. The demand / workload and capacity during the early hours of business at the registration point did not seem to match, thus resulting in bottlenecks at the patient registration point and throughout the system.
An investigation of factors contributing to long waiting of patients collecting repeat medication in a tertiary hospital pharmacy
(University of the Witwatersrand, Johannesburg, 2022) Oladipupo, Rekgopetse Victoria; Sunjka, B.
According to the World Health Organization (WHO) patient waiting time is identified as a key measurement to a responsive healthcare service and is an important indicator of quality of services offered by hospitals (NDoH, 2011) as it affects the patient’s responsiveness to the services received (NDoH, 2011; SA FAM PRACTICE, 2008; Tegabu, 2008; Pandit et, al. 2016). Long waiting times at healthcare facilities undermines the services rendered resulting in compromised or unfulfilled patient care (Afolabi & Erhun, 2003). This research studies the processes associated with the collection of repeat medication in a tertiary hospital pharmacy in order to identify value adding activities and non-value adding activities that could be impacting patient waiting time using the Lean thinking concept of driving out waste. A qualitative observational method was therefore employed to observe all the steps involved during the journey of the patient collecting repeat medication from the registration point until medication was issued at the pharmacy. Value stream mapping (one of Lean Thinking principle) was employed to analyze the processes that took place. Patient waiting time was also measured from the registration point to the pharmacy. On average patients had to wait a total 159 minutes before they could access services both at the registration point (67 minutes) and at pharmacy (92 minutes). The service time was 29 minutes at both registration point (11 minutes) and pharmacy (18 minutes). Of the 18 minutes pharmacy service time; eight minutes were found to be value-adding while 10 minutes were non-value-adding mainly due to prescriptions waiting on queue to be picked, waiting to be signed by the pharmacist and waiting to be issued out to the patient. Lack of a dedicated pharmacy service points exclusively for chronic repeat patients, manual dispensing, illegible doctor’s prescriptions, were found to prolong the time it takes the Pharmacist to complete a prescription. Post Basic Pharmacist Assistants performing duties that could be performed by a less qualified staff (e.g., Learner Basic Pharmacist Assistants) during peak hours was not value adding and thus decreasing productivity. The level of staff commitment in addressing issues of quality such as long waiting time was questionable. The demand / workload and capacity during the early hours of business at the registration point did not seem to match, thus resulting in bottlenecks at the patient registration point and throughout the system.
Assessment of Quality Management in Major Projects in the Mining Industry in Botswana
(University of the Witwatersrand, Johannesburg, 2024) Pitswe, Odirile Boniface; Sunjka, Bernadette
While project performance is generally evaluated in terms of schedule, cost and quality performance, guidelines for project quality management are lacking, (Steyn and Nicholas, 2008). The Botswana mining industry is faced with problems of engineering projects which don’t meet the expected outcomes and most of the problems emanate around quality management and quality defects. This research project involved the assessment of quality management in major engineering projects in the Botswana mining industry by evaluating the level of adoption and implementation of quality management systems in major engineering projects, identifying the major causes of project failure, and evaluating the effectiveness of quality management system as employed in major capital projects. The research was focused mainly on Debswana Diamond Mining company as the major mining house in the country, with an objective to assess the maturity level of the company’s quality management system (QMS) and identify opportunities for improvement. A mixed method approach was used which involved archival research and survey research, the results of which were triangulated to corroborate the findings and remove bias. Archival research was conducted using the company document repository to review project retrospect reports, (Lessons learnt reports) and identify problems experienced during the implementation of different projects. These were correlated with common causes of project failures as identified in the critical literature review and cross referenced against survey results to further confirm them. The results indicated that the maturity level of the Quality Management system is at level 4 (quantitatively managed), where processes are measured and controlled. Gaps were identified that if rectified would move the maturity to level 5 (optimizing), where the focus would now be on process improvement. The gaps are mainly around operationalisation, lower-level employees training on quality management, optimisation of shared resources especially subject matter experts like project engineers, key stakeholder management, involvement and participation from end users and operational teams. The study came up with the top five (5) major causes of project failure being: 1. Shared resources and subject matter experts get overstretched between different projects and end up neglecting quality assurance. 2. Poor stakeholder management. 3. Lack of stakeholder involvement and participation in the project. 4. Inexperienced project team. 5. Unclear statements of expected quality outcomes.
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.
Control of Aerial Manipulators for Contact Inspection
(University of the Witwatersrand, Johannesburg, 2023-10) Matosse, James; Kuchwa-Dube, Chioniso
Aerial manipulators are flying robotic systems that consist of a multi-rotor vehicle tailored with one or more manipulators. These systems are promising for contact inspection of chemical plants, boilers, tunnels and chimneys without human intervention. They require sophisticated control algorithms for control and stabilisation of complex varying dynamics due to the flying, manipulating and interacting with the environment. The dynamics of an aerial manipulator are treated as two subsystems, the quadrotor and the manipulator. The quadrotor dynamics are extracted through the Newton-Euler algorithm using quaternion-based orientation instead of Euler angles. The manipulator dynamics are extracted using the recursive Newton-Euler equations for purposes of handling the floating-base effect. A classic impedance control is a widely used effective control for contact force tracking but it requires the location of the environment relative to the end-effector and the environmental stiffness to be known precisely, and mostly- the desired force as a constant. In contact inspection without human intervention, the environmental properties (geometrical and mechanical) are uncertain, causing the classic impedance control method to be less effective. Presented in this study are: an adaptive variable impedance control (AVIC) for force tracking combined with the integral linear quadratic regulator (LQR) for the quadrotor and proportional-derivative (PD) for the manipulator’s navigation control. AVIC has the capability to counteract for environmental uncertainties by varying the impedance parameter (damping coefficient) on-line corresponding to the force tracking error. This control has been utilised effectively in industrial robot manipulators for a stable force tracking performance. So far in the literature, AVIC together with integral LQR and PD controllers have not been applied to aerial manipulators as a control strategy. Since the aerial manipulator is a coupled system, a linearisation process was performed on the quadrotor dynamics coupled with the manipulator to achieve a fair approximation of the non-linear model. This study has improved force tracking abilities through the implementation of AVIC that allows the aerial manipulator to achieve a desired contact force on the inspected contour while the quadrotor remains in a stable position. Finally, the developed system was simulated using MATLAB/SIMULINK program and the attained results proved the effectiveness of the strategy in comparison to the classic impedance control.
Distributed Electric Propulsion on a Joined-Wing Air-Taxi
(University of the Witwatersrand, Johannesburg, 2024) Brand, Darren Mark; Schekman, S.
Urban Air Mobility (UAM) is a form of aerial transportation within urban areas with the main intention of easing traffic congestion. Electric Vertical Take-off and Landing (EVTOL) air-taxis are currently in development, but no single configuration has been identified as superior for UAM. There is still scope for alternate designs to be explored. A major obstacle to successful UAM operations is the combination of high energy requirements for VTOL and low battery energy densities, thereby affecting operational aircraft range. Aerodynamic efficiency has been identified as a critical factor for achieving maximum flight range while electric battery technology is matured. It is proposed that an air-taxi which combines Distributed Electric Propulsion (DEP) with a joined-wing may achieve superior aerodynamic efficiency compared to other air-taxi designs. A joined-wing air-taxi capable of carrying four passengers and a pilot has been developed with four alternative DEP configurations. These aircraft are herein investigated and compared against one another. A computational approach was followed using STAR- CCM+ to evaluate the flow characteristics and forces around the aircraft for both climb and cruise conditions. It was found that a “Non-DEP” configuration with four proprotors can achieve up to 5% higher aerodynamic efficiency than a DEP variant. However, this configuration suffers with poor lifting capability at high angles of attack. The sensitivity of aerodynamic efficiency to changes in the number of proprotors and their spacing was seen to be negligible according to this investigation.
e-Commerce adoption in South African SMMEs
(University of the Witwatersrand, Johannesburg, 2024) Mathe, Barney; Sunjka, Bernadette
In this research study e-Commerce adoption in Small, Medium and Micro enterprises (SMMEs) in South Africa was studied. The purpose of this study was to determine the factors that constitute for a successful implementation of the e-Commerce strategy and compare this to the adoption of e- Commerce in SMMEs. The study evaluated frameworks/standards for successful e-Commerce implementation and with this evaluation a consolidated conceptual framework for the successful implementation of e-Commerce was developed. Through samples of both SMME and successful/most visited platforms, functionality and performance assessments of the platforms were conducted using the Jaccard similarity method, and time and method study. T-tests and ANOVA were conducted for performance assessments, to assess if there was a significant difference in performance between SMME and successful e-Commerce sites. Through these assessments it was found that there is a clear gap in adoption from both a functionality and performance perspective, 6 out of 7 of the successful sites had advanced to the last stage of adoption while only one SMME platform reached the last stage which is an external integration stage of the developed framework.
Factors influencing innovation in public healthcare in South Africa: A critical analysis
(University of the Witwatersrand, Johannesburg, 2024) Nkosi, Mbali Rosemary; Siriram, Rajenlall
Healthcare innovation has proven to reduce morbidity and mortality rates by enhancing healthcare delivery. Most of the South African population depends on the public healthcare system for health needs. The morbidity and mortality rates in South Africa are much higher compared to other middle-income countries in the world. To enhance healthcare delivery in South Africa, understanding the factors that influence innovation in public healthcare is important. Therefore, this research aims to provide a comprehensive understanding of the factors influencing innovation in public healthcare in South Africa and the potential impact of innovation on the country's healthcare system. The main objectives of this study are to determine the level of successfully implemented innovation in public healthcare and the factors influencing it. Existing literature identifies several factors that influence innovation in public healthcare, including design empathy, technological infrastructure, decision-makers, human capital, and organisational culture. This study also investigates the readiness of the public health sector to embrace innovation and the strategies in place for implementing innovation in public healthcare. A gap was identified in the existing literature. There is evidence in literature is that healthcare innovation centres in South Africa and their impact on the adoption of innovation in public healthcare were only covered marginally by existing literature. To bridge this gap, this study provides results on the status of suitable research and development hubs for testing healthcare innovation prototypes in South Africa and their impact on the adoption of innovation in public healthcare. Currently, there are limited health innovation centres in South Africa. This study posits that an increase in the number of healthcare innovation centres would increase evidence-based innovation which would increase the uptake of innovation in public healthcare. A qualitative research approach was used to acquire descriptive information on the factors that influence innovation in healthcare through interviewing participants. Semi-structured interviews were used as the primary instruments of data collection. The interviews were then subjected to a thematic analysis. One of the significant findings of this research is that the lack of funding in public healthcare hinders innovation in the public healthcare system. Also, the rigorous regulatory requirements pertaining to healthcare innovation tend to cause uncertainty and delays, which in turn reduces the funding available for innovative proje
Fatigue Crack Propagation in AlSi10Mg Additive Manufactured Aeronautical Parts Processed by Laser Shock Peening
(University of the Witwatersrand, Johannesburg, 2024) Chinyama, Joel; Polese, Claudia
Additive manufacturing (AM) offers advantages for complex aeronautical parts, but inherent defects can reduce fatigue life. Post-processing techniques such as laser shock peening (LSP) can be used to introduce beneficial compressive residual stress that hinders crack propagation. This study investigates LSP as a method to improve fatigue performance in additively manufactured AlSi10Mg aeronautical parts. It examined how varying LSP treatment laser power intensity (1.5 – 4.5 GW/cm2) affects LSP's effectiveness and identified optimal LSP residual stress profiles for peak fatigue performance. The residual stress profiles that were used in this research were adopted from previous experimental work done on AM-manufactured AlSi10Mg alloys within the Wits AM/LSP group. Previous experimental work results on wrought AA2024-T351 (untreated and LSP-treated cases) indicated that LSP-treated samples have a fatigue life of at least four times longer as compared to as-built samples. AFGROW models with similar geometry, material properties and load conditions were used to predict the fatigue life of as-built and LSP-treated cases. An improvement in fatigue life of at least 3.8 times was observed, which was within an acceptable deviation from the experimental results. These results were used to validate AFGROW models for exploring different specimens. Fracture mechanics models (AFGROW) were used to compare the fatigue life of as-built and LSP-treated AlSi10Mg samples with different LSP power intensity parameters. The results showed that LSP treatment can significantly extend fatigue life, with the optimal laser power intensity found to be 3.0 GW/cm2. This improvement is attributed to the introduction of compressive residual stresses by LSP, which suppress crack initiation and propagation. The effectiveness of LSP was further explored in the context of the Cessna 172/175 horizontal stabilizer, a part that could benefit from AM for weight reduction and structural integrity. AFGROW models were developed to predict the fatigue life of the centre lightening hole in the forward spar, a critical location for crack initiation. The models incorporated a beta correction factor to account for the specific crack geometry and stress distribution. The beta correction factor was determined by comparing the stress intensity factors from the Finite Element Analysis (FEA) and AFGROW models. The results again demonstrated a significant increase in fatigue life (of at least six times) for LSP-treated parts compared to as-built parts. AFGROW models with a beta correction factor proved valuable for predicting fatigue life in components with complex geometries. This study confirms that LSP is an effective post-processing technique for mitigating fatigue crack propagation in AlSi10Mg AM aeronautical parts.
Financial Evaluation of Implementing In-Pit Crushing and Conveying Systems for Waste on Open Pit Mines
(University of the Witwatersrand, Johannesburg, 2024) Serepa, Ikaneng; Emwanu, B.
The South African mining industry has faced mounting challenges, especially rising expenses that threaten profitability. These escalating costs, driven by various factors including operational expenses such as mining costs, are critical. The distribution of mining costs across activities within the production cycle is crucial, with hauling operations in open pit mines representing a significant portion, as noted by Paricheh et al (2017) at 49%. Due to the substantial economic impact of hauling expenses on mining expenditures, there's a strong incentive to streamline these operations to lower overall costs effectively. Current research highlights a noticeable transition in the mining sector towards embracing in-pit crushing and conveying (IPCC) systems in open pit mines, acclaimed as a cost-effective substitute for conventional truck and shovel (CTS) systems (Awuah-Offei et al, 2009). This research assessed both the integration and financial viability of implementing a waste IPCC system in the loading and hauling operations of an open pit mine. A mixed-methods approach, combining quantitative data from production records and costs with qualitative insights from expert interviews was used. The findings of this research indicate that while the IPCC system can be integrated, there remains a degree of reliance on the CTS system for material transportation from the pit to the IPCC system. For the CTS system, 55 rigid dump trucks (RDTs) are required, constituting 57% of the initial capital expenditure of R1.27 billion. Conversely, the IPCC system requires only 31 RDTs, accounting for 29% of the initial capital costs of R1.37 billion. However, despite the substantial reduction in RDTs, the IPCC system requires significant investment in a crusher and conveyor belt system for waste management, which constitutes 32% of its capital costs. Examination of the operating costs over the life of the mine indicates that there are no cost advantages associated with operating an IPCC system compared to the CTS system. Operating expenses for the IPCC system exceed those of the CTS system by 58%, predominantly driven by the operational costs of the crusher and belt system, contributing to 67% of the IPCC system's costs. The financial assessment results show a positive and acceptable net present value (NPV), internal rate of return (IRR), and payback period for both systems. Nevertheless, the CTS system exhibits superior financial performance, with a NPV of R7.45 billion, an IRR of 83.1%, and a shorter payback period of 1.2 years, and is recommended as a viable option for the mine.
Inventory Management using Artificial Intelligence
(University of the Witwatersrand, Johannesburg, 2024) Garg, Arnav; Smith, Bevan; Rich, William
Poor inventory management negatively affects a company’s profits. Too little stock limits potential sales and customer satisfaction while too much stock increases storage costs and potential damage. Company X distributes butter in a multi-echelon supply chain consisting of multiple entities such as a manufacturing plant, distribution centre and retailers before reaching the customer. For every 1% of the demand that is not met, revenue in excess of R18 million is lost per year. This study aims to use machine learning methods (supervised and reinforcement learning) for optimal decision making that maximizes profits. Supervised learning methods (random forest, recurrent neural network and support vector machines) were used to forecast the demand based on historical data. Thereafter, deep reinforcement learning (DRL) was used to train an agent to decide when and how much to order over a period of a year. Various algorithms (PPO and DDPG) and unique reward functions were tested and the performance was compared to a benchmark heuristic that stocks inventory based on a sum of the forecasted demand. The random forest algorithm performed the best at predicting the forecasted demand. The DRL model using a continuous action and state space together with the DDPG algorithm and a reward function based on a combination of the current profit, order fulfilment rate, units available and units unsatisfied performed the best. The DDPG algorithm outperformed the PPO algorithm with the DDPG model being able to provide a 21% increase in net profit over the benchmark heuristic when the production and warehouse facilities of the supply chain were merged. The DRL models were not able to provide a higher order fulfilment rate compared to the benchmark heuristic but they were able to provide better asset utilization by sending full trucks and minimizing the inventory held to maximize the profitability in the supply chain. The results suggest that RL has potential of better handling the stochastic constraints (demand and lead times) in real supply chains to automate the ordering process. It was found that increasing the order fulfilment rate does not necessarily lead to higher profits and the reward function has a significant effect on the net profit which can be further optimized in the future.
Investigating the flow of information in a surface iron ore mining operation
(University of the Witwatersrand, Johannesburg, 2024) Loeto Levious, Sekwati
As one of the most advanced iron ore mining operations Sishen Mine has many processes and systems. As an Anglo-American flagship operation, Sishen Mine has implemented many new systems and processes to improve its effectiveness and efficiency. This increased the number of resources (equipment, infrastructure and people). Over the last 10 years, Sishen Mine has doubled the number of employees and resources. The increase in resources, especially employees, processes and systems, has made it difficult for information to flow across the mine. The research aimed to determine the factors that contribute to the issue of gaps in the flow of information. A literature review was done on the current structure of information flow at Sishen Mine and some key discoveries were made. It was found that in a mining operation, there are three main core departments: engineering, mining operation and technical service. These departments depend on each other as the mine value chain is interlinked. The importance of information flow “enabling organisation structure”, communication structure and systems that will be able to enable efficient communication was emphasised. Ten participants across the mine were interviewed to get more details on the research question. The participants had many different views on the research question and as a result, a variety of ideas were discussed. Some of the ideas were linked to what was already discovered during the literature review. Unintegration of KPIs, technical and communication systems, and processes were among the highest contributors to miscommunication between individuals, sections and departments. The mine communication structure was also found not to be centralised and as a result, information flows are divergent. The lack of an integrative culture between individuals resulted in certain professionals having a silo mentality and thus being reluctant to share information. It is envisaged that the Centralised and Integrative System (CAIS) will be able to close the existing gaps in the information flow by focusing on centralising and integrating all critical systems and processes within Sishen Mine.
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.
Measurement of combustion airf low into burners in coal fired plants
(University of the Witwatersrand, Johannesburg, 2024) Manqele, Gladwell Sizwe; Schmitz, Walter
This research study is aimed at achieving accurate measurement of mass flow rates in large square industrial square ducts at Eskom’s boiler plants. For safe and efficient operation of Fossil Fuel Firing Boiler Plants, the utility has put in place the Fossil Fuel Firing Regulation Standard which requires that the Total Combustion Air flow be measured at exit from the air heaters, into the ducts. In this study, a sophisticated airflow measuring probe was acquired, herein the current study referred to the 14-hole Omniprobe. The accuracy was found to be within 5% in a free stream flow field. A Five-hole probe was calibrated in the free-stream wind tunnel. The calibration process enabled the derivation of the probe specific polynomials of Pitch, Yaw, Total Pressure, Static Pressure coefficients and velocity components. A prototype air duct was designed for the study to simulate air flow through square ducts with a 90⁰ bend as an abrupt flow disturbance. To achieve the objectives of the study, 6 planes were identified where air flow velocity profiles were generated using the equal area method. The modeling of the velocity profiles was conducted numerically, using CFD (Ansys Fluent), and experimental, using Pitot-static probe, Omniprobe, and a Five-hole probe. The mass flow rates as measured by the Pitot-static tube were found to be consistent at planes 1, 2, 5, and 6. The mass flow rate as calculated from the Pitot-static probe varied by 2.1% through the duct. This justified the selection of the Pitot-static probe as the reference for this study. The velocity profiles generated from the traverse measurements using the 14-hole Omniprobe showed an error in velocity measurements which are in the proximity of the wall. This can be attributed to the the wall effect. The mass flow rates of air calculated from the Five- hole probe measurements were found to be within 4% of the mass flow rate as calculated from the results of the reference probe in the 1st and 2nd planes upstream of the bend. After the 90⁰ flow disturbance bend, the accuracy drops to 13% at plane 5 and improved slightly at plane 6 to 11.7%. This is attributed to complex flow pattern at these planes. The study concludes that the Pitot-static tube remains the preferred instrument for use in measuring flow rates using the equal area method in large square ducts. The Five-hole probe can be applied where the flow field is not distorted in conjunction with CFD. The Omniprobe’s accuracy in measuring the velocity magnitude, and the angularity of the flow field was verified in an open stream wind tunnel. This study recommends exploring the use of an L-type 14-hole Omniprobe for application in large square industrial ducts.
Metallic Equivalent of Aircraft Landing Gear Using Composite Materials
(University of the Witwatersrand, Johannesburg, 2024) Kotze, Marius Hugo; Boer, Michael
There are two types of Light Sport Aircraft landing gear configuration. The taildragger and tricycle arrangement where the difference is specified by the position of the main landing gear. Shipment delay of the current Aluminium 7075 T6 landing gear has caused further delays in the manufacturing of the BushCat Light Sport Aircraft. Thus, a composite alternative was required which could be manufactured locally. The objective was to determine which locally available material was best suited as an alternative to the current Aluminium 7075 T6 design. This included estimation of the correct design loads acting on the BushCat aircraft main landing gear and to specify a composite alternative that could withstand these calculated design application loads. The loads that were used would be obtained from the ASTM F2245-14 regulations and EASA CS-23 amendments. The loads were validated by means of Finite Element Analysis and analytical calculations. Drop tests were also conducted by the company and image processing was used to compare the calculated deformations to the FEA results. This was used to validate the load and constraint applications in Ansys 2023 R2 software. The composite materials used for analysis were unidirectional epoxy e-glass wet layup and prepregs fibres. A coupon study was conducted on Aluminium 7075 T6 alloy and [0/90/90/0], [0/45/45/0], [0/90/45/0] layered unidirectional epoxy e-glass wet layup and prepreg coupons loaded under tension, compression, bending and torsion. The FEA results were validated using analytical calculations obtained from the Classical Lamination Theory. It was concluded that the unidirectional epoxy e-glass prepreg coupons were best suited as an alternative as better results in withstanding the applied load applications were obtained. The prepreg fibres also contained a lower void content in comparison to the wet layup fibres, thus increasing the fatigue life of the composite laminate as well as reducing the moisture absorption. The final composite landing gear was analysed using the Puck-failure criterion and it was found that after analysis and modifications were conducted, the newly designed composite landing gear could withstand the applied loads during limit load and ultimate load conditions without any fibre or inter-fibre failure in the strut of the landing gear. It was found that, failure had occurred in one of the fibre plies near the bolted regions of the axle section during ultimate (emergency) landing conditions and was thus concluded that the composite landing gear should still be inspected when attempting emergency landing at higher load conditions at an aircraft maximum take-off weight of 600 kg. The final composite landing gear design after modifications was 4.613 kg heavier than the Aluminium 7075 T6 landing gear. With regards to manufacturing the final composite landing gear a vacuum bagging process should be followed where the final vacuum bagging assembly containing the composite layup of the landing gear should be placed inside an oven or autoclave to start the curing process. Once the composite landing gear is cured, it could be machined into its final shape were non-destructive techniques such as ultrasound of thermography should be used to inspect the final composite landing gear for any air of volatile compounds withing the laminate. Static and dynamic destructive testing should also be used to validate if the final composite landing gear can withstand all landing conditions aircraft maximum weight without any fibre failure or delamination occurring.
Prediction of Water Hyacinth Coverage on Hartbeespoort Dam
(University of the Witwatersrand, Johannesburg, 2024) de Gouveia, Claudia D. Camacho; Bührmann, Doctor Joke
Water hyacinth is an invasive weed contributing to Hartbeespoort Dam’s poor water quality. Although biological control is the most effective and sustainable method of controlling water hyacinth, the dam has unfavourable conditions for agents that the weed thrives in. Literature uses mathematical models and remote sensing to theorise growth rates or estimate coverage. However, prediction could prove beneficial as planning biological control is essential to its success. Hence, a model to predict water hyacinth coverage was developed. This research simplified the complex relationships involved in water hyacinth growth to focus on the most influential factors: temperature and nutrients. Missing data were imputed using multiple k-nearest neighbours. Nutrient datasets had limited data, thus five scenarios were developed to extrapolate datasets, using Monte Carlo simulation and seasonal patterns. The features were used to build ensemble, decision tree, artificial neural network and support vector machine models. Ensemble using the bagging method was the best model resulting in a root mean square error of 4.01 for water hyacinth coverage predictions from 1 June 2018 to 1 May 2019.