Estimating energy loss due to vortex shedding and pneumatic efficiency of an oscillating water column device: experiments

Monday, 15 December 2014
Zhenhua Huang and Conghao Xu, University of Hawaii at Manoa, Honolulu, HI, United States
In laboratory tests of oscillating-water-column (OWC) devices for extracting wave energy from ocean waves, an orifice is often used as the power-takeoff mechanism. Calculations of the energy loss due to vortex shedding and the pneumatic extraction efficiency of the OWC chamber are two challenging issues. Direct measurement of the energy loss due to vortex shedding is difficult. The pneumatic extraction efficiency is often calculated by using a one-point measurement method, in which one pressure senor is used to measure the air pressure variation and one wave gauge is used to measure the instantaneous surface displacement inside the OWC chamber. This method is simple, but a systematic error may be introduced, especially for shorter waves. Based on our recent laboratory and theoretical studies of a pile-supported OWC device, we present a method for estimating the energy loss due to vortex shedding and improving the accuracy in the calculation of pneumatic extraction efficiency using one-point method. The method in this study is designed for an OWC device whose chamber has a circular cross section, but can be extended to other cases where development of an analytical theory is possible.