Wave power extraction by a nearshore oscillating water column converter with a surging lip-wall

A near-shore oscillating water column (OWC) device with a surging front-wall, which can be conveniently mounted on various cliff-like shores or coastal structures, is proposed to improve the pneumatic efficiency of wave energy extraction. Based on linear potential theory, the interaction between ocean waves and the OWC device is solved by the matched eigenfunction expansion method (MEEM). Auxiliary functions, expanded in orthogonal polynomials, are introduced to approximate the singular behaviors of fluid field in the vicinity of the salient corner. The effects of the dimensions of lip-wall and the stiffness of the spring on the hydrodynamic performances, such as the response amplitude operator (RAO), average inside free-surface elevation, phase difference between the motions of lip-wall and inside free-surface, and optimum conversion efficiency are taken into consideration. The numerical results show that the existence of a freely surging lip-wall can considerably improve the performance of the device over a wider bandwidth, especially for the intermediate and short wavelength regimes, compared with the fixed one.