Browsing by Author "De Waal, R. J. O."

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    Data for indirect load case estimation of ice-induced moments from shaft line torque measurements
    (Elsevier, 2018) De Waal, R. J. O.; Bekker, A.; Heyns, P. S.
    ENGLISH ABSTRACT: During ice navigation, blade measurements of ice-induced moments on ship propellers, are challenged by the harsh operating environment. To overcome this problem, shaft line measurements are performed inboard, and the required propeller loads are subsequently estimated using a dynamic model and the solution of an inverse problem. The inverse problem is mathematically ill-posed and requires the determination of the ice-induced moment on the propeller blades from shaft line measurements. Full-scale torsional response data is presented as calculated from indirect strain measurements on the shaft line of a polar supply and research vessel. The vessel operated on a 68-day voyage between Cape Town and Antarctica and spent almost 11 days in sea ice with observed concentrations above 90% and a maximum thickness of 3 m. Data for five ice-induced load cases are presented, including the shaft torque from indirect measurements and the estimated ice-induced moment, which is obtained by solving an ill-posed inverse problem. The ice-induced moments on the propeller are obtained by approximating the drive-train as a viscously damped, elastic lumped mass model. The ice-induced moment is then determined through existing approaches to solving the ill-conditioned inverse problem. The lumped mass model is presented along with algorithms to solve the inverse problem, including truncated singular value decomposition, truncated generalized singular value decomposition and Tikhonov׳s method. The resulting time series data for the inversely calculated ice-induced moments is published to provide industry with load cases for ice-going propulsion design.
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    An investigation of shaft line torsional vibration during ice impacts on PSRV's
    (Stellenbosch : Stellenbosch University, 2017-03) De Waal, R. J. O.; Bekker, Annie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: In order to estimate the forces exerted on ship propellers during ice navigation, the rotational dynamics of the propulsion system need to be accurately modelled. The direct measurements of propeller loads of ships during ice navigation is challenged by the harsh operating environment. Indirect measurements are therefore performed on the shaft line of such ships to estimate propeller loads through an inverse problem. Three case studies are presented, namely open water, cavitation and ice navigation. The maximum torque loading on the shaft occurred during ice navigation and the maximum thrust case during cavitation. Ice-induced moments on the SAA II propeller were determined from shaft line measurements using inverse methods, whereby the maximum ice load was found to be 941 kNm. Estimated load profiles for navigation in the Arctic and Antarctica are presented using rainflow counting techniques. The aim of the present research was to perform data-driven modelling of the rotational dynamics of the shaft line to aid future design of ice going vessels.