Experimental investigation into 3D scour processes around a gravity based Oscillating Water Column Wave Energy Converter

Experimental investigations measuring both bed elevation changes and near-structure flow velocities were undertaken to investigate wave scour processes around a model Oscillating Water Column (OWC) Wave Energy Converter (WEC) for a range of incident wave conditions at approximately 1:20 scale. The experiment design was informed by a proposed 200 kW OWC WEC deployment site at King Island, Australia. The measurements provide the first experimental data on scour around an OWC WEC structure, and one of the most comprehensive experimental studies of wave scour around a large rectangular cross-section structure. High resolution scour erosion and deposition patterns were measured using an above-water laser-based system. For normally incident waves, scour holes were observed to develop on all four corners, and the size of the scour holes at the four corners increased with the Keulegan-Carpenter (KC) number. An additional scour hole/ trench also formed along the upstream face of the OWC WEC due to the flow in/out of the OWC WEC internal chamber. Changing the incident wave propagation angle by 20 degrees has a significant effect on the observed scour patterns, with reduced scour on the front and back corners but significant scour holes remaining on the other two corners. It is found that if the model is not sufficiently embedded into the sediment bed, scour can undermine a significant area under the structure, with quadrant shaped scour holes underneath the back corners extending to approximately 25% of the total base area, suggesting a risk of differential settlement in field conditions.