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.
- ItemDevelopment of an Abbe error minimization concept for coordinate measurement machines.(Stellenbosch : Stellenbosch University, 2024-02) Nagel, M; Schreve, K.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Coordinate metrology is an expensive field and the benefit to be gained by making it available to a larger part of the engineering industry should be substantial. Coordinate measurement machines (CMMs) form a large cost point in this field as they are specialised pieces of equipment that require well-trained personnel to operate, and controlled environments to achieve high accuracy. A large hurdle to low-cost CMM design is the accuracy required to manufacture them to avoid errors. Abbe error is one of these inaccuracies, also known as cosine error, and it can be described as a misalignment of the measurement axis and the scale used to take a distance measurement. The CMM concept developed in this project shows the potential of such a system to be further developed into a viable tool. This was achieved through the development of a spherical parallel mechanism which has primarily been used as a manipulator. This mechanism has been used as part of the measurement system to minimize the Abbe error in the first system prototype. A kinematic error model was created to aid in the development of the physical concept. A series of physical tests were carried out and compared to simulated results from the error model. This comparison was used to validate the understanding of the system and the prevalent error sources. The preliminary design and construction of the CMM have been shown to outperform the manufacturing and assembly processes used by achieving confident levels of accuracy. The parallel mechanism greatly decreases the effect of individual component errors. In conclusion, the system shows a promising future for new coordinate measurement machines by using non-conventional means to minimize error.
- 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.
- ItemA study of the longitudinal open-water performance of an ice-class ship.(Stellenbosch : Stellenbosch University, 2024-02) Steyn, Barend Johannes; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: The hull and propeller of vessels engaged in operations in open water and ice are exposed to the encumbering effects of marine biofouling and the abrasive scouring of ice, both affecting ship resistance and performance. This thesis investigates the long term performance implications of such an operational profile, characterised by extensive open-water operations interspersed with ice navigation through a longitudinal study of the open-water performance of the Polar Supply and Research Vessel, the SA Agulhas II, with a specific focus on the hull and propeller condition. This study is enabled by a repository of measurement data and complementary information on the SA Agulhas II, spanning an equivalent period of ten years, the outcome of an extensive full-scale measurement campaign initiated in 2012. Key voyages within this period are selected for which the open-water performance is determined before, after, and intermittently during ice navigation. A tailored ship performance analysis method is formulated for the SA Agulhas II, utilising the available data to quantify the performance impact arising from the condition of the hull and propeller. Within the analysis method, three constituent elements are developed. First, a performance correction method, to differentiate between the effects of the degraded hull and propeller from those of environmental and operational disturbances, achieved through a constructed deterministic ship performance model. Second, a performance quantification method, to evaluate the performance losses, and third, a data conditioning method, to compile and filter the dataset to reduce uncertainty in the results. The efficacy of the formulated analysis method to exhibit the performance losses due to hull and propeller degradation is assessed through the review of four qualitative and quantitative measures, including an uncertainty analysis. The performance analysis reveals a cyclic pattern in the ship’s hull and propeller conditions, marked by progressive deterioration and subsequent near-baseline performance for the pre- and post-ice periods with each voyage. This cyclicality is attributed to the resurgence of biofouling growth between voyages, subsequently removed by ice scouring during ice navigation. Protracted docking periods in a temperate port contribute to biofouling growth, further exacerbated by anti-fouling coating degradation due to ice-scouring. Consequently, pre-ice operational penalties manifest, resulting in speed losses of up to 19% or power increases of 121%, driven by complete anti-fouling coating loss. Ecologically, the open-water performance results, recorded during operation in intermittent open-water passages after initial ice contact, indicate a gradual and near complete removal of the nonnative biofouling within a 200 km stretch into the marginal ice zone.