Hydrodynamic and power conversion performance of a hybrid raft-type WEC and breakwater system using SPH method

The present paper proposes a hybrid raft-type system which can act as wave energy converter (WEC) and breakwater. The device, anchored to the seabed with mooring lines, comprises multiple plate-like rafts equipped with power take-off (PTO) systems at their joints. Based on the Smoothed Particle Hydrodynamics (SPH) method, a two-dimensional wave tank is established to study wave interactions with this hybrid multi-raft system. To validate the proposed SPH model, a laboratory experiment is conducted to assess the hydrodynamic performance of a triple-raft structure. The SPH model is then applied to compare hydrodynamic performance between double and triple raft configurations. This study reveals the interaction and interference effects between waves and the rafts. The results indicate that, compared to the double-raft structure, the addition of a third raft significantly enhances the pitching motion of the original two rafts. The effects of the raft width, the resonance mode, and the mooring system are analyzed. The findings demonstrate that resonance dominates the wave energy extraction performance at specific frequencies. The double-point mooring mode facilitates the device's absorption of multi-period waves, while its mooring forces are significantly higher than that of the single-point mooring system. These results offer valuable insights on the design of hybrid floating WEC-breakwater system.