Masters Degrees (Mechanical and Mechatronic Engineering)
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- ItemPose estimation through two non-overlapping orthogonally mounted cameras for fiducial markers.(Stellenbosch : Stellenbosch University, 2024-02) Olivier, Paul; Smit, WJ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: This thesis explores the use of ArUco markers for precise pose estimation in Concentrated Solar Power (CSP) plants, aiming to enhance the accuracy and functionality of Unmanned Aerial Vehicles (UAVs) within these environments. The study is structured around three main objectives: assessing and implementing the Gazebo simulation engine’s applicability to real-world scenarios to create a tested for the next two objectives, creating a framework for selecting optimal markers, and evaluating different camera setups for improved system performance. Key findings include the successful validation of the Gazebo engine for simulating UAV operations. The research further delves into marker selection criteria, addressing aspects such as accuracy, focal length, resolution, and the impact of motion blur as well as giving insights into the operating distance and angle for different camera-marker configurations. Additionally, the comparative analysis of monocular, stereo, and orthogonal camera configurations reveals no significant performance disparity, suggesting that resolution adjustments for a monocular camera could mitigate the benefits of more complex setups. Although ArUco markers show promise for CSP applications, the study acknowledges potential limitations related to UAV operational distances and marker scalability. The conclusions drawn show the importance of tailored technological solutions, suggesting the incorporation of advanced sensor fusion and filtering strategies for enhanced system precision. Recommendations for future work include improving Gazebo’s simulation accuracy by adding motion blur effects and expanding the analysis to cover a wider range of focal lengths and marker sizes, aiming for a closer approximation to real-world conditions.
- ItemFeasibility analysis of a bacterial isolation technology.(Stellenbosch : Stellenbosch University, 2024-02) Wessels, FJ; Nieuwoudt, MJ; Hoffmann, JE; Grobbelaar, M; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Currently it is highly challenging to use whole genome sequencing on expectorated sputum samples for the detection and analysis of Mycobacterium tuberculosis. This is due, in large part, to the lack of a suitable sample preparation process that can take expectorated sputum as input and output highly purified Mycobacterium tuberculosis genomic material. This thesis proposes a new strategy for combining existing methods in the literature into such a sputum sample preparation process. To initiate this new strategy, the project selects and tests the feasibility of a cell isolation technology for the final stage in the sample preparation process. Through a comparison of candidate cell isolation technologies in terms of the stakeholder requirements for the sample preparation process, the deterministic lateral displacement method was identified as the most promising technology for the application. More specifically, the approach involved employing two sequential deterministic lateral displacement arrays that use cylindrical and I-shaped obstacles to evaluate the Mycobacterium tuberculosis rod-shaped cells based on their diameter and length, respectively. This would, in theory, allow the Mycobacterium tuberculosis rods to be separated from a first group of cells that are larger than the diameter of the rods and a second group of cells that are smaller than the length of the rods. Then, if the lower limit of the first group of cells overlapped with the upper limit of the second group of cells, only purified Mycobacterium tuberculosis cells would remain at the end of the two arrays. To investigate the feasibility of using this method for the final stage in the sample preparation process, Computational Fluid Dynamics flow simulations were used to design a 2000:1 scale model of the proposed geometry. The experiments on this upscaled model provided an enhanced perspective of the problem on two fronts, which should be of value to future work on this topic. Firstly, the upscaled experiments generated high resolution footage of the particle behaviour, which is difficult to do at the microscale. This footage allowed for the identification and analysis of behavioural patterns in the model Mycobacterium tuberculosis cells. Most notably, this showed that motion occurs predominantly in the xy-plane, that rotating rocking motion punctuated by periodic flipping dominates the contactless flow, and that various particle-to-obstacle interactions occur in a rigid hierarchy. Secondly, the upscaled device allowed for a detailed quantification of the flow field, which is next to impossible at the microscale. These flow measurements show that the I-shaped obstacles pose a 38.6% higher fluidic resistance than the cylindrical obstacles at a column slant angle of 1.59°. These upscaled results provide an ideal foundation for future numerical investigations, as they provide both high-quality qualitative data of the particle behaviour and high-quality quantitative data of the flow field. This data may be used as validation benchmarks for future simulations that continue the investigation started here.
- ItemExperimental testing and simulation of a nutating grinding mill.(Stellenbosch : Stellenbosch University, 2024-02) Van Tonder, JJ; Bredell, JR; Coetzee, CJ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Mined materials are comminuted for valuable mineral extraction, often using a nutating grinding machine. The HICOM mill is known for efficient grinding but faces operational challenges, primarily due to fatigue at kinematic joints. This study investigates nutating mill dynamics, focusing on force responses at key kinematic joints. The NuMILL, an experimental model representing the HICOM, was designed for data collection. In addition to the experimental investigation, two simulation methods were used: Multi-Body Dynamics (MBD) and Discrete Element Method (DEM), where MBD deals with internal mechanical loads and DEM with loads acting on the chamber as a result of material contact. The critical load path was identified as the crankpin joint of the torque arm, which experiences high cyclic loads. The MBD and DEM simulations had limitations when used independently. The combined DEM and MBD model, accounting for both structural and charge material loads, was evaluated against experimental measurements. Its accuracy in predicting crankpin resultant forces varied with rotational speed, showing errors of 19 %, 6 %, and 1% at 100 RPM, 400 RPM, and 700 RPM, respectively. This combined simulation method demonstrated its potential for real-world application in predicting kinematic joint forces, as illustrated through its application to the HICOM mill.
- ItemImprovement of vineyard spraying equipment by recirculation of overspray through air flow modification.(Stellenbosch : Stellenbosch University, 2024-02) Le Roux, Anri; Coetzee, CJ; Hoffmann, JE; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: The South African wine producer’s profitability has been under enormous pressure over the past few years due to rising input costs. For this reason, a method was developed to save on crop protection costs by minimising losses due to overspray from multi-row air-assisted sprayers. The performance of a recently developed collection chamber which is attached to a standard sprayer to recirculate the air flow over the canopy, was analysed. Experiments were carried out to obtain the flow characteristics for vine canopies during the growing season. These experiments included the development of a mobile wind tunnel that was calibrated and then transported to the Farm Pokkraal, in the Breedekloof Valley near Rawsonville, where field tests were conducted. Field tests were conducted with the wind tunnel orientated in two directions, inline and perpendicular to the vineyard row and the pressure loss over the leaf canopy was measured as a function of the air volume flow rate through the test section. Results indicated important differences in canopy density and flow characteristics for different vineyards as the growing season progressed. The results from these experiments were used to set up a qualitative computational fluid dynamic (CFD) model of the airflow inside the collection chamber around a vineyard canopy. The CFD model results were validated with high-speed camera footage of the airflow inside the collection chamber. The airflow patterns inside the chamber were analysed to determine whether the current design of the collection chamber would induce the self-recirculation of overspray to reduce potential overspray. The CFD models showed that the air flow inside the chamber interacted with the walls of the collection chamber and that the flow in the mid-region, where the canopy is located, experienced little variation. This supports the objectives of this research that the collection chamber induces self-recirculation and that overspray, which would otherwise be lost to the environment, is contained and directed back onto the intended target area. This limits the harmful effect of overspray to the environment, tractor operators and nontarget areas. This project has the potential for further studies in this field regarding modifications to the existing collection chamber prototype as well as the development of an improved CFD model towards a better understanding of what is taking place inside the collection chamber.
- ItemTechno-economic analysis of solid oxide electrolysis using concentrated solar energy for green hydrogen production in South Africa.(Stellenbosch : Stellenbosch University, 2024-02) Janse van Vuuren, Martin; McGregor, Craig; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: RRising global awareness about climate change, depletion of fossil reserves, and economic pressure are propelling many countries to decarbonise their energy sectors. Green hydrogen, which is produced by the electrolysis of water, may play a vital role in decarbonising the ‘hard to abate’ sectors. Solid oxide electrolysis cells (SOECs), currently the most electrically efficient electrolysis technology, operate with high-temperature steam between 700-1000°C, which leads to a reduction in the electrical requirement for electrolysis but introduces a thermal energy demand. Concentrated solar thermal (CST) energy with thermal energy storage (TES) is a potential candidate for providing dispatchable renewable high-temperature heat for an SOEC system. This thesis presents a techno-economic analysis and optimisation of a 100 MW hypothetical SOEC plant with heat integration from CST+TES in the Northern Cape of South Africa for green hydrogen export. The primary objective was to perform a direct economic comparison between a hybrid system that sources thermal energy integration from CST+TES, and a reference system that uses thermal energy from electric heating. Both the hybrid and reference systems rely on electricity generated by dedicated photovoltaic (PV) and wind turbine plants. The capacities of the CST, TES, PV and wind turbine plant models for both systems were optimised to achieve the minimum levelised cost of hydrogen (LCOH) produced by the SOEC. Results from the SOEC plant model showed that up to 16.6 % of the electricity demand of the SOEC plant can be replaced by integrating CST+TES to augment the thermal demand of the electric boiler for steam production. For the hybrid system, a parabolic trough CST plant with a twotank direct oil storage was modelled which delivered 92 % of the annual thermal demands of the hybrid system. The hybrid system with CST exhibited an LCOH of 5.88 $/kg compared to the reference system’s 6.13 $/kg. A sensitivity analysis showed that the hybrid system maintains its economic competitiveness over the reference system over a wide range of CST, TES, PV and wind turbine capacities. In conclusion, this thesis demonstrated the economic advantages of integrating CST+TES into a SOEC plant which is powered by PV and wind turbines, leading to a 4.1 % reduction in LCOH. However, this integration introduces complexity and associated operational and financial risks, which will influence investment decisions.