Based on the open-source software package OpenFOAM, a modified immersed boundary method (IBM) suitable for oscillating water column (OWC) is proposed in this study. The effect of wall thickness and draft of OWC on the hydrodynamics are investigated with respect to conversion efficiency, reflection coefficient, and transmission coefficient. The impact of the height and horizontal offset of the rectangular submerged breakwater on the performance of the submerged breakwater-OWC hybrid system is also studied. In addition, the L-shaped submerged breakwater-OWC hybrid system is compared with the rectangular submerged-OWC hybrid system and single OWC in terms of hydrodynamic parameters and flow field.
The results show that increasing the thickness of the back wall can extend the primary efficiency bandwidth of the OWC, while reducing the transmission coefficient and improving the wave resistance of OWC. The reflection performance is improved by increasing the height of rectangular submerged breakwater, and there is an optimal height for such a system to maximize energy output. The submerged breakwater located at the back wall of OWC can effectively improve the conversion efficiency of such a system under large wave period. The L-shaped submerged breakwater-OWC hybrid system can improve the conversion efficiency in medium and large wave periods (maximum conversion efficiency improves by 14.21%), and show good wave resistance. Through analysis and comparison, L-shaped submerged breakwater-OWC hybrid system is not only competitive in coastal protection, but also worthy of application in wave energy conversion.