Theoretical Analysis of an Asymmetric Offshore-Stationary Oscillating Water Column Device with Bottom Plate

Abstract

To give high performance over a broader wave frequency range and enable the multipurpose utilization of marine structures, an asymmetric offshore-stationary oscillating water column device with an outstretched bottom plate is considered theoretically. Through solving boundary value problems by means of the matched eigenfunction expansion method, the effects of the geometric parameters, including drafts of the front and back walls, air chamber height and width, and length of the bottom plate, on hydrodynamic performance, such as optimum conversion efficiency (Eopt), reflection (Cr) and transmission (Ct) coefficients, radiation conductance (B~) and susceptance (C~), and diffraction flux factor (Υ~), are explored in detail. The results show that a draft of d2/h = 3/8 is favorable to improve the extraction efficiency of the system. The air compressibility (increasing the chamber height) significantly influences the extraction efficiency for the intermediate- and short-wave regimes. Moreover, the presence of the bottom plate can provide another resonance mechanism, which can be tuned to provide a wider bandwidth of high performance.