ABSTRACT

A series of experimental tests are reported which concern the viability of capturing power from regular and irregular waves by restraint of a wave radiating body oscillating in surge. The effect of hull form and mechanical properties of the restraint on power captured through damping are investigated and the relationship between these parameters and the design requirements of a power take off system are discussed. The results show that an asymmetric plate with one convex and one concave face attains good mean power capture in a range of wave fields.

INTRODUCTION

Wave energy research, in the UK in particular, has undergone significant growth during the last decade. Numerous devices have been proposed and several, including the Danish Archimedes Wave Swing (Polinder 2004) and UK Pelamis (www.oceanpd.com) are now approaching commercial viability. Despite such progress, some fundamental aspects of floating device behaviour have not been adequately accounted for in the literature. Of particular interest is the behaviour of so called point absorbers, where a device which is small compared to its wavelength is able to absorb more energy than is incident upon its width. Despite this suggestion of greater power capture, surging devices in general have received limited attention. This is partly due to the difficulty of providing a reaction to a buoyant surging device when compared to a buoyant heaving device. In the absence of a gravitational spring force the surge mode has no natural stiffness and hence cannot be tuned to a wave frequency.

Research experience at Lancaster University and elsewhere (Folley 2005) shows that these theoretical capture width predictions are hard to achieve in practice. Despite being identified as a key factor affecting economic viability of a device (Stallard 2005), the effect of form on performance in irregular seas is also poorly understood.

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