DYNAMIC RESPONSE OF A TAUT-MOORED FLOATING OSCILLATING WATER COLUMN WAVE ENERGY CONVERTER IN EXTREME WAVES

This paper presents the results of an experimental investigation into the dynamic characteristics of a 1:36 scaled Oscillating Water Column (OWC) Wave Energy Converter (WEC). Two mooring configurations were tested, namely a vertical taut mooring (i.e., tension leg) and a taut mooring with 45 degrees tendons. The tested sea state was based on conditions that were observed during Tropical Cyclone Oma in 2019 and was re-generated in the physical wave tank with NewWave theory. The orifice used to model the OWC's power take-off system during operational sea states was closed to simulate the WEC in the shut-down condition. Detailed analysis included the OWC WEC's rigid body motions (i.e., heave, surge and pitch), OWC chamber pressures, and mooring/tendon tensions. The model with both mooring configurations was found to exhibit similar heave motions, however the tension leg mooring demonstrated a larger surge response whereas the 45 degrees taut configuration demonstrated substantially larger pitch rotations. Mooring lines/tendons in both mooring configurations experienced similar maximum tensions, however the occurrence of peak loads relative to the mooring configuration tested could take place in the forward or aft moorings. For instance, the forward moorings of the 45 degrees taut configuration produced an average peak tension of 79.640 N, whereas the aft tendons for the tension leg configuration produced an average tension of 80.725 N. The load distribution between the forward and aft moorings for the tension leg configuration was similar and showed a difference of 8.3%. However, a much larger variation was observed with the 45 degrees taut configuration where a 39.7% reduction was observed between the forward and aft moorings. Finally, a very high-frequency response was observed in the time history (during and post wave impact) of both the forward and aft tendons of the tension leg mooring configuration. Interestingly, the high frequency response was not observed in the 45 degrees taut configuration.