An experimental study for improving performance of a cylindrical OWC WEC with a heave plate

This paper presents an experimental investigation to a solution on the conventional cylindrical oscillating water column (OWC) wave energy converter (WEC), with a heave plate being attached below of the cylindrical OWC. Such a simple solution could change the hydrodynamics of the cylindrical OWC device dramatically due to the significant increase of the added mass and damping coefficient to the structure motions, in particular, the natural period of the structural heave motion could be greatly increased while the natural period of the water body remains almost unchanged. As such, the enlarged difference between these two natural periods means a large relative motion between them over a wider bandwidth, hence the improved OWC could absorb wave energy more efficiently over a larger bandwidth of the wave frequencies (or periods). This is especially beneficial for the device extracting energy from ocean waves efficiently, since ocean waves inherently contain multiple periods. Meanwhile, such a solution could maintain the simplicity for the OWC structure, and a shallow draft OWC device could be possible while its energy conversion capacity is not comprised. In this work, an experimental investigation is conducted on the improved cylindrical OWC (floating), with the aims at proving the concept: with a heave plate attached to the OWC, its wave energy extraction capacity can be dramatically increased. In addition, the device motions can be effectively reduced, which is also very beneficial for the mooring and cable connections, as well as the accessibility to the device in seas, so for reducing the cost of wave energy production further.