Masters Degrees (Mechanical and Mechatronic Engineering)

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https://scholar.sun.ac.za/handle/10019.1/781

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    Pose 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.
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    Improvement 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.
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    Techno-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.
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    Simulation and testing of centrifugal pump cavitation.
    (Stellenbosch : Stellenbosch University, 2024-02) Van der Spuy, SJ; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Cavitation, the formation of vapour filled bubbles in areas of low pressure, can be deleterious to centrifugal pump operation. Cavitating flow may cause efficiency loss, damage to impeller surfaces, and excessive vibration in pump systems. Some cavitation is unavoidable and even harmless, however, preventing cavitation will in general enhance pump reliability, and efficiency. In this research question, computational fluid dynamics was used to simulate cavitation inception using single‑phase, steady‑state flow, in a centrifugal pump. The pump was a low specific speed radial flow centrifugal pump that is used for the conveyance of water or other products. Simulations were performed using Cadence (NUMECA) Fine Turbo 16.1 and AutoGrid 5 meshing software. The simulated performance characteristics were compared to experimental performance measurements. The cavitation model determined the net positive suction head (NPSH) of cavitation inception (NPSHi) in the post‑processing stage of the simulation. The cavitation model is based solely on the inlet pressure and minimum static pressure in the impeller to determine cavitation inception. The simulated NPSHi values were 0.903 m, 1.53 m, and 2.33 m, at shaft speeds of 800 RPM, 1000 RPM, and 1200 RPM respectively. This was compared against scaled NPSH3 values of 0.281 m, 0.475 m, and 0.722 m respectively. As expected, the simulated NPSHi values were consistently higher than NPSH3 values. Vibration sensors were employed to measure cavitation inception in the pump, but due to stall occurring in the impeller, the point of cavitation inception could not be distinguished above the noise caused by backflow vibration. Broadband excitation was measured on the pump, which was consistent with other test setups where backflow was present. Backflow was also confirmed by the simulations. Experimental performance measurements showed that for accurate performance simulation, a model containing only the impeller and diffuser was insufficient. Adherence to the predicted NPSHi will prevent operating pumps under damaging cavitating conditions, however, the correspondence of these values with true cavitation inception is tenuous.
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    Upgrading the compressor stage of a solar-hybrid twin-shaft micro gas turbine.
    (Stellenbosch : Stellenbosch University, 2024-02) Fivaz, Michael Arthur; Van der Spuy, SJ; Van Eck, H.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Using a solar-hybrid gas turbine system for generating electricity combines the continuous high output power of a micro gas turbine (MGT) with the environmental benefits of a concentrating solar power (CSP) plant. An MGT's performance can be improved in a variety of options for solar-hybrid applications, with the compressor stage receiving particular focus. A centrifugal compressor, which is favoured over axial compressors due to higher per stage pressure ratios obtained, is used in the compression stage. An existing design methodology exists to assist in developing and testing a new centrifugal compressor for an MGT engine. The operational solar-hybrid MGT testbench operates with a very low engine efficiency and generates a low amount of output power. Therefore, the aim of this study is to upgrade the compressor stage of the solar-hybrid MGT through a proposed centrifugal compressor redesign to improve overall engine performance. After measuring the geometry to get an exact replica of the existing compressor impeller to establish its baseline performance, a new design is developed using a one-dimensional (1D) mean-line code. The redesigned compressor is subjected to a Computational Fluid Dynamics (CFD) simulation to produce performance charts that are imported into a thermodynamic software model of the engine for performance improvement evaluations. The new compressor design increases the MGT’s compressor stage’s compression ratio by 4.59% from the existing replica compressor of 1.48 to 1.55. Similar to the compression ratio, the efficiency of the compressor stage is improved from 78.3% of the existing replica compressor to 84.2% by the new compressor design. As a result, the MGT's output power increases by 22.7% from 18.1 kW to 22.2 kW, further improving overall engine efficiency. The improvement in performance enables the engine to be developed further, such as converting the output shaft power into electricity. The development of this MGT will ultimately assist in progressing the field of solar-hybrid gas turbine energy generation.