Performance Enhancements and Validations of the UC-Berkeley Ocean-Wave Energy Extractor

This paper evaluates two aspects of enhancements made to the UC-Berkeley ocean-wave energy extraction device first presented in [1]. First, the differences in hydrodynamic performance between flat- and hemispherical bottom floaters were investigated theoretically using UC Berkeley 2-D viscous-flow solver: FSRVM [2]. The predicted enhancement was compared with experimental results, demonstrating that an increase in motion of over 50% was realizable. Second, important modifications to the design, fabrication, and material of the rotor and stator of the permanent magnet linear generator (PMLG) were made with the aim of increasing both power output and mechanical-to-electrical conversion efficiency, η_el. Increased power extraction and efficiency were achieved, doubling what had been previously reported. The non-linear relationship between the generator damping and the magnet-coil gap width was also investigated to verify that the conditions for optimum power extraction presented in [1] were achievable with the PMLG. Experimental results, obtained from testing the coupled floater and PMLG system in the UC-Berkeley wave tank, revealed that measured capture widths were more than double those from the previous design. These results further confirmed that matching of the generator and floater damping significantly increased the global efficiency of the extraction process.