Non-axisymmetric oscillating water column wave energy converter: A semi-analytical study

A non-axisymmetric floating oscillating water column (OWC) wave energy converter (WEC) is proposed in this paper. In contrast to the traditional bottom opening used in axisymmetric OWCs, the newly proposed OWC WEC has a submerged opening positioned on the front cylindrical wall. A semi-analytical coupled hydrodynamic–pneumatic model is developed to investigate the power extraction of the proposed OWC, where the hydrodynamic model is established using the matching eigenfunction expansions and method of separation of variables. Following the model validation against general theoretical identities, the model is first applied to a stationary offshore OWC to study the effects of the chamber breadth and submerged opening geometry on power extraction under a series of regular waves with varying wave periods and incident directions, and then to an elastically constrained floating OWC WEC with six degree-of-freedom motion under both regular and irregular waves. The numerical results show that in comparison with axisymmetric OWCs, the proposed non-axisymmetric configuration significantly broadens the effective frequency bandwidth and increases the capture width ratio by up to three times with normal incidence of both regular and irregular waves. For floating OWCs, the free-sway motion emerges as a detrimental factor, negatively affecting both power extraction and safe operation.