Wave energy extraction from a semi-circular oscillating water column attached to a straight breakwater

Attaching wave energy converters (WECs) to coastal structures, rather than embedding them, reduces construction costs, prevents damage to the coastal structures and ensures the integrity of OWC-breakwater structures. This paper presents an analytical model, based on linear potential flow theory, to evaluate the hydrodynamic performance of a semi-circular oscillating water column (OWC) attached to a straight breakwater. The wave motion is represented by regionally-defined complex velocity potentials. The eigenfunction matching method is employed to solve the unknown coefficients in the velocity potentials. In addition to the straightforward method, an indirect method using reciprocity relations is derived to evaluate wave excitation volume flux and hydrodynamic coefficients. The maximum wave force acting on the OWC chamber over a period is also evaluated. Following convergence analysis and model verification, the analytical model is employed to investigate the influence of OWC geometry (radius, wall thickness, draught), air chamber volume and incident wave direction on wave power absorption of the semi-circular OWC and the wave forces acting on the OWC chamber. Results indicate that the excitation and power absorption of the OWC are independent of incident wave direction, akin to a circular offshore OWC. However, the peak frequency response of the maximum resultant wave force acting on the OWC chamber attenuates with increasing wave angle, reaching a minimum when the incident waves approach perpendicular to the breakwater.