Experimental Investigation of Dynamic Characteristics of OC-3 SPAR Platform Subjected to Aero-Hydrodynamic Loading

Abstract

Abstract. This study presents insights gained from wave flume experiments conducted to investigate the hydrodynamic responses of a SPAR floating offshore wind turbine (FOWT) platform supporting a 5 MW wind turbine under combined wind and wave loading conditions. The significance of this work lays in the methodology in which a FOWT model was subjected to regular and irregular waves under aerodynamic loading introduced as rotor thrust force for below-rated and rated wind speeds to determine platform-level dynamics. First, free decay tests were conducted to obtain the natural periods and damping ratios of the SPAR FOWT system. Furthermore, the wave elevations, displacements, rotations, and rotor thrust were measured under the influence of varying regular, irregular waves, and thrust forces. Response amplitude operators (RAOs), statistical and spectral analyses, were carried out to determine the response behavior of the SPAR FOWT under aero-hydrodynamic loading. It could be noted that the surge was affected by the rotor thrust force. A coupled surge–pitch phenomenon was observed during the wind–wave interaction on the platform, especially for higher wave periods. The rotor thrust influence on heave was negligible. However, the aerodynamic damping resulted in reduced pitch responses. The rotor thrust exhibited noticeable fluctuations under wave conditions, highlighting the clear coupling between platform motions and aerodynamic loading and became more pronounced with increasing wave heights, primarily due to the amplified platform responses under larger waves. These observations highlight the importance of including aerodynamic loading effects in understanding the dynamics of FOWT and suggest that the proposed aero-hydrodynamic framework could be a robust design approach for effective FOWT analysis.