POWER PERFORMANCE AND RESPONSE ANALYSIS OF A SEMI-SUBMERSIBLE WIND TURBINE WITH COMBINED FLAP TYPE AND TORUS WAVE ENERGY CONVERTERS

An integrated offshore wind and wave energy system is an attractive concept in areas with abundant wind and wave energy resources. The sharing of supporting platform and facilities, e.g., mooring systems, offers significant cost savings. This will effectively lower the levelized cost of energy (LCOE). In the present study, a conceptual design consisting of a braceless semi-submersible floating horizontal axis wind turbine (FHAWT), three flap type wave energy converters (WECs) as well as a torus (donut-shaped) point absorber-type WEC is proposed. The flap type WECs harvest wave energy through the flap motion caused by oscillating wave surge while the torus WEC absorbs wave energy generated from its heaving motion relative to the platform. The absorbed mechanical power of the power take-off (PTO) systems is calculated based on linear damping forces and the relative motions of the WECs. The effect of hydrodynamic interactions between the WECs and the platform are taken into account in the evaluation of hydrodynamic coefficients and wave excitation force transfer functions. A fully coupled aero-servohydro-elastic numerical model of the concept is constructed. The feasibility study of the concept is carried out using time domain simulations. Only operational environmental conditions are simulated based on simultaneous wind and wave hindcast data of the selected offshore site. The effect of the WECs on the wind turbine, platform motions and WEC power take-off are examined. Based on the power performance of the WECs, recommendations are also provided for optimum power absorption.