A new model of viscous dissipation for an oscillating wave surge converter

A mathematical model of an oscillating wave surge converter is developed to study the effect that viscous dissipation has on the behaviour of the device. Recent theoretical and experimental testing have suggested that the standard treatment of viscous drag (e.g. Morison's equation) may not be suitable when the effects of diffraction dominate the wave torque on the device. In this paper, a new model of viscous dissipation is presented and explored within the framework of linear potential flow theory, and application of Green's theorem yields a hypersingular integral equation for the velocity potential in the fluid domain. The hydrodynamic coefficients in the device's equation of motion are then calculated, and used to examine the effect of dissipation on the device's performance. A Haskind relationship, expressing the link between the scattering- and radiation-potential problems is derived, and its connection to existing Haskind relations is explored. A sensitivity study of the device's power capture to the magnitude of the dissipation present in the system is carried out for a selection of device widths. The results of the sensitivity study are explained with reference to existing experimental and numerical data. A special focus is given to the effects of dissipation on the performance of a device whose pitching motion is tuned to resonate with the incoming waves.