Masters Degrees (Mechanical and Mechatronic Engineering)

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    Human responses to wave-induced motion, slamming and whipping.
    (Stellenbosch : Stellenbosch University, 2023-11) Engelbrecht, MC; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Ship motion is known to a ect comfort, rest and productivity. On ships, these factors could in uence fatigue-related accidents. Discomfort on cruise ships could adversely a ect customer satisfaction. The crew and passengers of vessels, live and work in this dynamic environment, often for months on end. Research regarding human comfort, as a result of impulsive wave slamming is specifically limited. Wave slamming is the random impact of waves against the ship hull leading to the phenomenon called whipping which causes vibration to propagate through the ship structure. This study investigated the effects of impulsive vibration on activity disturbance in the operational context of a slamming-prone vessel. Metrics from whole-body vibration standards were investigated as a possible means to quantify comfort. A possible threshold of the onset of discomfort was determined and compared to likely responses to whole-body vibration as documented in whole-body vibration standards, maritime standards and ship classification society documents. Subjective data was obtained from daily diary surveys conducted willingly by people on board. Additional human responses were reaped from instantaneous slam observations which were conducted from the Bridge during designated ship manoeuvres. Full-scale vibration measurements were recorded at several locations across the ship for the entire duration of the voyage and expressed in terms of metrics as provided in standards. Subjective and objective data were correlated. Subjective results show that slamming was prevalent on most days during investigated voyages. Sleeping was observed to be the activity most disturbed. Metrics such as vibration dose value and root-mean-square value had displayed positive strong correlations with the human response data. An hourly vibration dose value threshold of approximately 0.43 m/s1:75 and 0.47 m/s1:75 resulted from both the surveys and instantaneous slam ratings. This corresponds to the threshold where 50% of the sample population felt discomfort. The determined threshold for root-mean-square value of 0.03 m/s2 is much lower than guideline values provided in ISO 2631-1 for discomfort in public transport applications.
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    Using a lattice structure coupon sample for build quality monitoring in metal additive manufacturing.
    (Stellenbosch : Stellenbosch University, 2023-11) Park, M; Du Plessis, A; Venter, MP; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Additive manufacturing (AM), particularly Laser Powder Bed Fusion (L-PBF), has revolutionised the manufacturing industry by offering enhanced geometrical design freedom, part integration, and reduced production lead time. However, the presence of manufacturing defects during the L-PBF process poses challenges to the mechanical properties and build quality of the manufactured parts. Traditional quality assessment methods involve costly and time-consuming manufacturing, destructive or non-destructive analysis and mechanical testing. To address these challenges, this research proposes a novel approach for quality control using lattice coupon samples instead of solid mechanical test specimens. Lattice structures, comprising repetitive unit cells with struts and nodes, serve as effective indicators of build quality. The smaller size and volume of the lattice coupon samples result in significant cost and time savings compared to traditional test samples. The high sensitivity of lattices to parameter deviations enables their use in assessing build quality within an L-PBF system. These coupon samples provide reliable indicators of structural integrity and long-term performance of AM parts, simplifying the quality control process and optimising L-PBF manufacturing. Additionally, this research develops a Finite Element (FE) model for AM lattice structures under quasi-static compression, offering a powerful tool for the virtual testing of components, enabling the study of their mechanical behaviour without the need for costly physical prototypes. The FE model incorporates defect states of the AM lattice structures observed from computed tomography (CT) scanning. By taking input from the CT scans, the prediction of mechanical properties of lattices with a high accuracy rate of 83 % was achievable. This model represents a promising tool for developing manufacturing defect-incorporated lattice representative volume elements (RVEs) for use in the design of AM parts incorporating lattice regions. By replacing complex lattice structures with solid-infilled features in the form of RVEs in simulations, the computational expense can be significantly reduced. This approach allows for efficient exploration of the mechanical behaviour of latticed AM components while accounting for manufacturing defects, offering insights for design optimisation and material selection. Furthermore, this research aims to leverage the developed FE model and interpolation methods to predict the mechanical properties of lattice structures, reducing the reliance on physical printing and CT scanning. By utilising these computational tools, accurate estimations of the mechanical properties can be achieved, minimising the need for extensive experimental testing and CT scan. Overall, this research contributes to the advancement of quality control in AM by introducing lattice coupon samples as indicators of build quality and developing computational models for predicting their mechanical properties. These innovations lead to improved efficiency and optimisation of L-PBF manufacturing processes, benefiting industries that rely on AM technology.
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    A prototype development for a quadcopter with a novel configuration
    (Stellenbosch : Stellenbosch University, 2023-11) Wessels, W; Smit, WJ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Unmanned aerial vehicles have become increasingly important, and multirotors have played a key role in unlocking new possibilities in various applications. However, the quadcopter’s range, payload, and endurance are limited by the energy density of power sources and the ef􀏐iciency of energy transfer to the air. To overcome these challenges, a new quadcopter con􀏐iguration has been introduced that combines the mechanical simplicity of multirotors with the energy ef􀏐iciency of helicopters. This innovative design comprises a large 􀏐ixed‑pitch rotor and three smaller rotors, which promises to increase the endurance, energy transfer ef􀏐iciency, and energy density of the power source. A basic mathematical model was created that captured the most important factors that in􀏐luence the dynamics. This model was used as a design tool to size standard components such as motors and propellers. The mathematical model was then extended into a dynamic Simulink model, which allowed analysis of the gyroscopic effect of the large central diameter propeller. The design was checked against this analysis, and the control mixer was derived. The Simulink simulations indicated a high degree of coupling between the quadcopter’s roll and pitch angle responses, primarily due to the gyroscopic effects of the central propeller, offering valuable insights into the intricate quadcopter dynamics. Several practical challenges arose from the use of a petrol engine: the available torque of the petrol engine limited the propeller diameter and pitch, unburned oil ended up on the electrical motors, the restrictive exhaust system hindered the engine’s performance, and vibrations from the internal combustion engine interfered with measurements taken by the inertial measurement unit. The controller was 􀏐ine‑tuned during the test 􀏐lights to improve the 􀏐light performance. Extensive 􀏐light testing assessed control ef􀏐iciency, power consumption, and overall response, validating the effectiveness of the mathematical model and design choices. This research opens up new possibilities for quadcopters with extended endurance. The innovative design solutions, coupled with rigorous testing and analysis, present a promising trajectory for the future of quadcopter technology.
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    Error correction in 2D-digital image correlation strain measurements due to out-of-plane motion.
    (Stellenbosch : Stellenbosch University, 2023-11) Visser, C; Venter, G; Neaves, M; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Digital image correlation (DIC) can be performed as eithermulti-camera stereo-DIC or single-camera 2D-DIC. Stereo-DIC is generally preferred as it corrects for errors from out-of-plane motion, giving it superior accuracy, despite 2DDIC being both computationally and financially less expensive, and being more user-friendly. This study proposes a strain gauge-based error compensation method for the compensation of strain errors in 2D-DIC due to out-of plane motion. The method was initially developed by considering the theoretical strain errors from out-of-plane motion in 2D-DIC and was then applied in a numerical simulation as a proof-of-concept. Two sets of validation experiments were then performed on two different specimen geometries which demonstrated an improvement in the accuracy of the 2D-DIC strain data in both cases. This makes 2D-DIC a more attractive option for measuring fullfield strains, particularly in cases where stereo-DIC is not an option.
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    Development of a pilot low temperature solar thermal co-generation system for water distillation and energy production.
    (Stellenbosch : Stellenbosch University, 2023-12) Van Zyl, Jacobus Gerhardus; Owen, Michael; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: This study aimed to develop a pilot system for low temperature solar thermal combined power and clean water co-generation. The system comprised a solar thermal steam generation system (6.5 kWth external compound parabolic concentrating collector array and kettle-type boiler) coupled to a condensing steam engine (reciprocating steam expander and condenser). The system uses solar thermal energy to produce steam at ~1 atm from raw feedwater. The steam is used to drive the steam expander (both through steam work and condensation) to produce mechanical work (which can be used directly for pumping or converted to electricity). The vapor exiting the engine is condensed and collected, providing distilled water for human use. The steam expander was designed by the University of Southampton and was manufactured at Stellenbosch University. The rest of the overall system (solar steam generator and condenser) was designed and constructed as part of this work with the intent to integrate the expander. Unfortunately, the expander did not operate, and this thesis thus reports on the design of the overall system and the measured performance of the solar steam generator and condenser (including measured distilled water production). The mechanical and electrical energy generation of the system was estimated using the measured steam generation and engine thermal efficiencies from literature. Results from three day-long on-sun tests are provided and prove that the steam generation system was able to meet its performance requirements (specifically providing steam at the required flow rate and condition to the condensing engine). The system produced distillate at an average specific energy consumption (SEC) of 2125 kWh/m3 and an estimated average mechanical energy output of 0.039 kWh/m2 of collector aperture area per day. The monthly and annual distillate production and energy generation were also estimated to illustrate the longer term expected performance with an estimated annual yield of 17.1 kWh/m2 mechanical energy and 1012 L distilled water. Compared to existing low temperature energy systems (e.g. organic Rankine cycles for low-grade power generation), and various technologies for solar desalination (notably solar PV powered reverse osmosis), the investigated system proves to be infeasible based on its high SEC, low overall efficiency and relative complexity (notably in terms of the condensing engine).