Influence of control strategy to FOWT hull motions by aero-elastic-control- floater-mooring coupled dynamic analysis
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More FOWTs (floating offshore wind turbines) will be installed as relevant regulations and technological hurdles are removed in the coming years. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of FOWTs in time domain including aero-loading, tower elasticity, blade-rotor dynamics and control, mooring dynamics, and platform motions so that the influence of rotor-control dynamics on the hull-mooring performance and vice versa can be assessed. The developed coupled analysis program is applied to Hywind spar design with 5MW turbine. In case of spar-type floaters, the control strategy significantly influences the hull and mooring dynamics due to the possibility of control-induced instability causing resonant hull motions. Therefore, it is important to use a control strategy without such problems at the penalty of possibly less uniform power outputs. In this regard, the results of two different control strategies - conventional and modified control strategies - are systematically compared to better understand the subtle coupling effects between the blade-pitch-angle-control and hull motions. The developed technology and numerical tool are readily applicable to any types of floating wind farms in any combinations of irregular waves, dynamic winds, and steady currents. Copyright 2011 by the International Society of Offshore and Polar Engineers (ISOPE).
