R. Chaplin – Renewable Energy, September, 2013
This paper presents an experimental study of a new resonant-in-surge wave energy converter concept that is a successor to the “Frond” and “Wraspa” WECs investigated at Lancaster University and elsewhere. The concept is of a buoyant, rigid, surface-piercing diaphragm, the edges of which are held still but whose central area moves in resonance with the swell component of an ocean wave system. The two bodies forming this diaphragm are pivoted on the arms of a Y-shaped tubular frame that is held in position by four taut mooring lines. It is proposed to move the frame compensate for tidal changes and to maintain the WECs bearing so that it always faces the principal swell direction.
Capture-widths found in the tank tests, in regular waves of 0.5 W/m, were generally around 20 cm at 1/100 scale and were greater than this in smaller waves. A method of slow tuning was demonstrated and a method of fast-tuning, previously trialled with Wraspa, is also described. In view of the likely low structural and installation costs, combined with good power, proposed future work includes mixed-wave trials on one “best” design at scales ranging from 1/170 to 1/3, the latter being a marine trial over 1 year in the Irish Sea at a point where conditions are known to closely model North Atlantic conditions. Such a trial would include measurement of structural loads in extreme seas: these are discussed below.