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.
- ItemDynamic wind load effects in a photovoltaic single-axis tracker mounting rail.(Stellenbosch : Stellenbosch University, 2024-02) Koekemoer, JH; Bredell, JR; Venter, G; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Single-axis trackers are actuated structures often used in utility-scale photovoltaic (PV) installations. These installations are sensitive to dynamic wind load effects due to their lightweight, flexible support structures and large PV module area. Significant damage to single-axis trackers have been reported in literature, despite the use of modern design methods. Design codes prescribe wind loads for a representative geometry but exclude potentially aeroelastic sensitive structures. Additionally, boundary layer wind tunnel testing and computational fluid dynamics studies are often associated with significant uncertainties. This study aimed to determine wind load effects on an existing 32 m × 25 m single-axis tracking PV array using field measurements. In this way, the uncertainties associated with wind tunnel testing and computational studies could be avoided. The project focuses on a critical component of the support structure, namely the mounting rail that attaches the PV modules to the rotating torque tube. Representative mounting rails were instrumented with strain gauges to capture dynamic wind load effects over periods of up to 109 days. The strain gauge locations were determined using results from calibrated finite element analyses of the structure. Equivalent static normal forces and moments acting on the mounting rail could be calculated using strain data and load calibration. These equivalent static loads would produce similar deformations and stresses compared to the dynamic wind loads while assuming simplified load distributions. The experimentally determined wind loads were correlated with wind speed, wind direction, and tracker tilt angle. The most critical wind directions (east and west) have a larger PV module area projected normal to the oncoming wind and subsequently showed high wind loads. Higher equivalent wind loads were also observed when the PV modules were more inclined relative to the oncoming wind. An interior located rail showed lower peak loads compared to an exterior rail, likely due to shielding from the surrounding structure. Wind load coefficients were lower compared to design codes for the range of wind conditions and tracker positions seen during the measurement period. This was expected, since design codes represent a critical combination of geometrical parameters to provide conservative estimates of wind loads. Analysis of dynamic load effects revealed contribution of torsional and bending modes of the torque tube to the normal forces and moments experienced by the mounting rails. A fatigue assessment found an insignificant fatigue damage for wind speeds below 21 m/s. Measurements suggest wind speeds above 21 m/s may be expected to cause fatigue damage. Design trends in utility-scale trackers show a decrease in mounting rail length to reduce the capital cost of new installations. The calibrated finite element model was expanded to assess the impact of a reduction in mounting rail length. Significant increases in the stress in the mounting rail and PV module were seen with a reduction in rail length, assuming all other parameters remain unchanged. Increases in stress may be non-linear, depending on the position and component.