Experimental investigation of motion response and mooring load of semi-submersible tidal stream energy turbine under wave-current interactions

Abstract

Tidal stream energy turbines, mounted on floating platforms, harness higher current velocities at the water's surface across broader marine areas, which reduces construction costs. However, the interaction between waves and currents critically influences these platforms' motion patterns. This dynamic becomes more complex with a rotating turbine, challenging power efficiency, and increasing fatigue load. This study presents physical modeling and analysis of a semi-submersible platform equipped with a vertical-axis turbine. The proposed design features a Tri-floater semi-submersible, a suspended chain mooring system, and a Vertical-Axis Tidal Turbine. This study assesses the system's behavior under varying marine conditions, including pure wave, pure current, and combined wave-current scenarios. This study focuses on investigating the effects of structural coupling wave approach angles and evaluating the system's multi-degree-of-freedom motion response and mooring loads. Findings reveal that wave-current interactions significantly affect the motion and mooring tension of a floating tidal stream energy turbine. Wave periods mainly control motion periodicity; wave height influences its extent, and current velocity sets the equilibrium motion state and angle. Additionally, the rotation of the rotor introduces a secondary effect that significantly increases mooring tension. The study also elucidates the pronounced interdependence between the platform's motion and mooring loads.