Numerical hydrodynamic and structural analysis of a floating OWC at three Irish sites

This paper outlines the process by which a wave energy converter (WEC) is matched to its deployment site, both in terms of power production and structural design. These aspects of device design are critical for the economic feasibility of a wave energy project. The WEC analysed was the backward bent duct buoy (BBDB), a type of floating oscillating water column (OWC) device, while three sites around the Irish coast were considered. Each site has different annual wave conditions, and as such implies different design parameters for both power production and structural design. Using the energy period for each site, the hull shape for the BBDB was determined. Frequency domain modelling was employed to determine the motion and hydrodynamic pressure response amplitude operators (RAO) of each device. The method of superposition was used to determine the power matrix of each device and using wave conditions with a 50 year return period for each site, the maximum loads imposed on the hull were used as the steel design criteria, while the displacement excursions and the typical catenary mooring equations were used to assess the mooring loads and chain design. Representative scatter diagrams for each site were used to assess the annual average power production. The results of the study are presented in terms of annual energy production per tonne of hull steel mass and per tonne of mooring chain mass. These outputs act as indicators for developers to continue, with the optimum site and hull design, into a detailed project economic feasibility assessment.