Increasing power capture of a wave energy device by inertia adjustment

This paper presents results from an experimental study on the power capture of bottom-hinged pitching point absorbers in intermediate water depth subjected to both regular waves and irregular waves. Point absorber wave energy converters exhibit high power capture when the incoming wave frequency is close to the natural frequency of the device. As average wave periods usually range between 5 and 15 s during the year, a possible way to improve power capture efficiency is to modify the wave energy converter natural frequency to match the prevailing wave frequency. The purpose of the work presented in this paper is to optimize the power capture of a cylindrical bottom-hinged point absorber by modifying the inertia, which in practice could be implemented by allowing some compartment of the device to be filled with water. The results of our experiments showed that this method of inertia modification could result in an increase of capture factor by 70-100% for the larger regular waves. Irregular wave tests showed that the use of only two ballasting configurations could lead to an overall capture factor of 55% in Summer and 35% in Winter, without damping optimization. The overall benefit of inertia modification is a 15-25% increase in power capture when compared to a constant inertia configuration. (C) 2011 Elsevier Ltd. All rights reserved.