Hydrodynamic analysis of one-way energy capture by an oscillating water column wave energy device

This work evaluates the hydrodynamic performance of an oscillating water column wave energy converter, with a focus on comparing conventional two-way energy capture to one-way energy capture where only the up- or down-stroke is used drive the turbine. Small-scale model test experiments are performed, and numerical calculations are made using weakly-nonlinear potential flow theory. The air turbine is represented experimentally by an orifice plate with a flow area equal to about 1% of the internal-chamber water-plane area. One-way energy capture by the experimental model is realized by incorporating a passive, low-inertia, non-return valve which vents the air inside the chamber on one half-cycle of the internal water-column oscillation. In the numerical calculations, there is little difference between the two venting configurations, due to the simplified weakly non-linear model. However, the experimental results show that up-stroke venting generally yields a higher power absorption than down-stroke venting and the two-way energy capture generally yields a higher power absorption compared to the one-way energy capture. The calculations agree well with the experiments for two-way absorption, but substantially over-predict the absorbed power in the one-way configuration. This is mainly attributed to the imperfect venting system in the physical model, but further tests and/or CFD calculations are needed to confirm this conclusion.