ABSTRACT
For oscillating wave surge converters (OWSC) the incident wave field is changed due to the movement of the flap structure. A key component influencing this motion response is the Power Take-Off (PTO) system used. This paper examines the relationship between incident waves and the perturbed fluid field near the flap using the Computational Fluid Dynamics method by using Reynolds Averaged Navier-Stokes (RANS) equations. Further, it investigates the influence of a PTO system in the energy extracted from regular waves. Whilst this wave evolution is not significant in the effective power captured by a unit device, it is of great importance when performing in arrays as neighbouring devices may influence each other.
The Oscillating Wave Surge Converter (OWSC) is one of the most promising operating devices that use Wave Energy Conversion (WEC) technology in terms of its energy absorption capabilities and hydrodynamic performance (Babarit 2015). This device consists of a surface-piercing buoyant flap rotating around a hinge fixed to the sea bottom. The pitching motion of the WEC device combined with a hydraulic Power Take-Off (PTO), which connects the flap to its base, captures the energy from nearshore ocean surface waves (Cameron et al. 2010).
The OWSC operates usually at intermediate water depth where the energy is extracted from the surge motion of the waves (Dhanak and Xiros 2016). Under the action of these incident waves the flap oscillates back and forth (see Fig. 1). This oscillatory motion is dominated by the diffraction and the radiation effects of the incident wave acting on the device. Whilst the first is related to the solid body as an obstacle encountered by the fluid flow, the latter is identified with the oscillatory motion of the flap and consequent generation of secondary wave fields. Both effects will depend on the size of the flap and its oscillation (Henry et al. 2010).