Wave power extraction by an oscillating water column array embedded in comb-type breakwaters: Performance analysis and hydrodynamic mechanism

Cost-sharing, space-sharing, and multi-function can be achieved through integrating wave energy converters into coastal defense facilities. In this paper, we consider a periodical array of oscillating water columns (OWCs) embedded in the coast-based comb-type breakwater in the presence of the step bottom. Based on the linear potential flow theory and matched eigenfunction expansion method, a semi-analytical model for solving the diffraction and radiation problems of the periodic OWC array is developed. The mathematical model is verified using Haskind relations and energy conservation law. Parametrical studies are carried out to illustrate the hydrodynamic characteristics of the OWC array embedded in the comb-type breakwater. This study also reveals the constructive and destructive interference effects between the breakwater and OWCs. It is found that the wave amplification caused by the projecting caisson produces a constructive effect on the wave power extraction. However, the inherent strong wave reflection caused by the caisson array weakens the wave power extraction, particularly in the sensitive frequency range (i.e., 2 < kh₁ < 5.5 in the present investigations).