WEC shape effect on the motion response and power performance of a combined wind-wave energy converter

Abstract

As offshore wind and wave energy technologies are attracting larger attention, various energy devices have been proposed to extract larger amount of energy from oceans. In the present work, a combined concept consisting of a 5-MW braceless semisubmersible floating offshore wind turbine (FOWT) and a torus-type wave energy converter (WEC) is proposed and investigated for four different examined WEC shapes. The hydrodynamic performance of the concept has been compared in frequency domain, in terms of hydrodynamic coefficients (e.g. added mass, radiation damping) and dynamic responses (e.g. relative motion, produced power by WEC). Also, analysis is performed for both operational and extreme conditions in time domain. Moreover, a survival mode has been proposed and studied for the examined extreme condition. In addition, motion suppression of the structural responses is achieved through the adjustment of the interface stiffness and damping coefficient between WEC and semisubmersible floater. The use of the concave-shape WEC results to a better dynamic responses of the combined concept and larger power production. For the specific combined structure, the wave direction has large effect on its dynamic responses.