Masters Degrees (Mechanical and Mechatronic Engineering)

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Browsing Masters Degrees (Mechanical and Mechatronic Engineering) by browse.metadata.advisor "Bekker, Anriette"

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    A laboratory-based verification rig for inverse models of ice-induced propeller moments on ship propulsion shafts
    (Stellenbosch : Stellenbosch University, 2023-03) Laas, Jacobus; Bekker, Anriette; Bredell, Johann; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The rise in maritime traffic in icy polar regions, create hazardous conditions for ships that may require costly and time-consuming in-port repairs. The drive towards environmentally friendly, energy-efficient ships pressure ship builders to conform to stringent design guidelines, set by classification societies. Improving efficiency and production cost is often coupled with a reduction in over-designed components. As a result, there is a critical need for openly-available, accurate, measurement data to support theoretical computations. Due to cost, installation challenges, and harsh operating conditions, there are few openly-available shaft and propeller torque measurements during ice interaction. As such, available propulsion shaft response data, along with inverse models, are used to determine propeller torsional loads. It remains to verify and validate these models in a controlled environment. Common verification methods consist of subjecting the inverse models to standardised load cases which compare the resulting inverse to the input load cases by the classification society. The use of experimental data, however, quantifies actual ice-loading responses, as opposed to ideal load cases, and prevents inverse crime when implemented in inverse models. For this purpose, a laboratory rig was developed, manufactured and commissioned that is capable of exerting a measured external torque to the end of a shaft whilst performing conventional shaft measurements. A disc brake was implemented in the place of a propeller as load device. The laboratory rig is able to simulate important phenomena observed in ship shaft measurements during propeller-ice contact. A continuous, modal superposition model was adapted to the dynamics of the rig, and the inverse brake torque was calculated from shaft measurements. It was found that the first torque peak, of the inverse solution, is within 14% of the measured torque. Subsequent torque peaks, such as those from multi-impact ice milling cases, however, are not inverted successfully, as the free-response of the shaft contaminates the torque solution. Consequently, the nature of ice-loading is not adequately described by the continuous model. Recommendations are made to improve the laboratory rig and the continuous model investigated.
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    The numerical investigation of wave slamming on a polar supply and research vessel
    (Stellenbosch : Stellenbosch University, 2023-03) Van der Westhuizen, Alexander; Bekker, Anriette; Meyer, Christiaan J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The SA Agulhas II is a polar supply and research vessel owned by the Department of Forestry, Fisheries and the Environment of South Africa. She facilitates and supports research in the Southern Ocean and Antarctica. The SA Agulhas II was designed to polar class 5 and experiences harsh seas and ice conditions during her voyages. The ship was designed with a raised transom which results in significant slamming during open water navigation. This can cause local damage to the hull as well as increased fatigue damage to the structure of the vessel. The ship was designed to manage ice passage which may be sub-optimal during open water navigation due to the increased slamming which results from the raised transom. An investigation into a monitoring scheme with the use of full-scale measurements and simulation software is instantiated to detect slamming pressures experienced by the hull of the vessel. The full-scale slam load measurement estimation is established with the use of plate theory and strain measurements on sections of the hull plating at the transom. The strain measurements are used to determine an estimate of the pressure loads experienced on the hull during slamming events. The results show promise in the technique used after some improvements in noise attenuation and error adjustment due to simplifying assumptions. A computational fluid dynamic model and simulation procedure is developed to analyse the validity of using simulation software to predict loading and vessel responses as well as inform hindsight investigations of the vessel responses to her environment. The simulation software does not capture the response of the vessel well in some seaways and hydrodynamic pressure estimates are not determined well for small sea states.