Oscillating water column at a coastal corner for wave power extraction

We extend the analytical theories by Martin-Rivas and Mei1 to examine a large circular oscillating water column (OWC) installed at the tip of a coastal corner. Under the assumption of irrotational flow, a linear theory is employed. The sea depth is assumed to be constant everywhere. The diffraction and radiation problems are solved by eigenfunction expansions for an arbitrary apex angle. After calculating certain hydrodynamic coefficients, the power-absorption efficiency is obtained for two special geometries: a convex and a concave corner of right angle. For an OWC of given dimensions, the optimum efficiency is first examined by assuming that the extraction parameter can be controlled for all wave frequencies. The effects of column radius and height, the size of the submerged opening and the angle of incidence are studied. Comparisons are made between the two cornered coasts and with a thin breakwater and a straight coast studied before. Finally a simpler scheme of letting the extraction parameter be piecewise constant is shown to be a practical alternative.