Department of Mechanical and Mechatronic Engineering

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Browsing Department of Mechanical and Mechatronic Engineering by browse.metadata.advisor "Bredell, Johann"

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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.