Numerical investigation on the wave power extraction for a 3D dual-chamber oscillating water column system composed of two closely connected circular sub-units

The key to promote the development of wave energy device industry lies in economy, which ensures the benefit output is greater than the input cost. To extract wave power over a much broader range of wave frequencies, an offshore dual-chamber oscilating water colum (OWC) system composed of two closely connected 3D circular sub-units, aligned in the direction of wave propagation is proposed and investigated under the framework of CFD toolbox OpenFOAM. Wave conditions with a variety of periods are considered and the power take-off system for each individual chamber is modelled by a top orifice. Different methods used in estimating the wave energy capture width ratio are compared and the effects from the variation of the front and rear chamber breadth ratio, the shape angle of the supporting structure existing in the front chamber, on the wave power extraction are examined and discussed. The results show that the marginal non-uniformity in the vertical air flow velocity through the orifice makes the method based on the air pressure and air flow velocity more reasonable for estimating the capture width ratio. A system with the front and rear chamber breath ratio equal to 2/3 is more desirable as remarkable improvement can be identified from the total capture width ratio when it is operated near the resonant period condition of the front chamber. In addition, the optimal shape angle is identified when designed as a value of 180∘ as more wave power entering into the front chamber and less wave power reflected by the lip-wall can be guaranteed simultaneously.