ABSTRACT

The analysis of floating oscillating water column (OWC) wave energy conversion (WEC) devices involves the coupled dynamics of the water column and the floating structure. In the present study, a mechanical oscillator model was used to examine this relationship for the heave motion of a floating wave energy conversion device. Optimal power take-off damping of the system was determined and the effects on maximum power capture examined. The influence of relative OWC and floating structure natural frequencies on OWC WEC device optimisation was also investigated.

INTRODUCTION

Oscillating water column (OWC) wave energy conversion devices consist of a partially submerged chamber open to wave forces at the base (see Fig. 1). The wave forces cause the water column within the chamber to rise and fall, driving the air in and out (inhalation and exhalation) of the chamber typically through a Wells or variable pitch type air turbine. An electrical generator is then utilised to convert the oscillatory airflow established into electrical energy. The pneumatic gearing provided by the air coupling allows the conversion of low frequency wave power into high frequency electrical power. (figure 1 shown in paper). Oscillating water column type wave energy conversion devices can be located near-shore as a fixed structure or offshore in a floating mooredstructure configuration. Much analytical, numerical and experimental work has been undertaken on fixed (e.g. Morris-Thomas & Irvin, 2007) and floating (e.g. Chudley, Mrina, Ming & Johnson (2002)) oscillating water column wave energy conversion. A number of concepts have been demonstrated at scale prototype including the Limpet (Boake, Whittaker, Folley & Ellen 2002), Oceanlinx's near-shore OWC (Gray, 2007) and the Pico plant (Brito-Melo, Neuman & Sarmento, 2008). The analysis of floating oscillating water column wave energy conversion devices involves the coupled dynamics of the water column and the floating structure.

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