Hydrodynamic response and power efficiency analysis of heaving wave energy converter integrated with breakwater

Abstract

The hydrodynamic and power capture performance of an asymmetric floating device called “Dolphin” wave energy converter (WEC) integrated with a fixed breakwater has been proposed. The operation of the floating WEC device is restricted to the vertical direction called heaving motion. In this research, the theories of heaving motion, wave energy conversion, and computational fluid dynamics (CFD) were studied. A numerical simulation of the CFD with the laminar model was conducted; namely, the effects of four different model shapes were investigated, distance effect between the WEC device and breakwater, WEC integrated with/without breakwater, and vorticity effect analysis using STAR-CCM+ software based on the viscous flow theory in the time domain. The optimal power take-off (PTO) system was considered during the numerical calculation, including the parameters of the WEC model, which were optimized to exploit a higher efficiency by analyzing the motion response in order to obtain the response amplitude operator (RAO) and capture width ratio (CWR) values. From the RAO and vortex field analysis, the RAO value of the Dolphin WEC was exhibited better than that of the other models. A vortex method was applied to verify the CFD simulation results. From the vortex simulation, it can be clearly seen that the integration of breakwater also affected the hydrodynamic performance of the WEC. The Dolphin WEC model with breakwater integration at experimental scale was built and tested in wave tank at Harbin Engineering University under various wave conditions. The breakwater was welded with the steel plate to restrict movement. The displacement sensor and linear generator were installed on top of the WEC device during the experiment. To modify the damping in the system, the heaving motion and power generation characteristics were analyzed and electrical resistance was assumed. The displacement and power in the time domain, RAO, and CWR for different wave periods and wave heights were investigated in the experiment, where the maximum motion response and power efficiency of the WEC model were 1.57 and 0.376, respectively.