H. Fernandez, G. Iglesias, R. Carballo, A. Castro, J.A. Fraguela, F. Taveira-Pinto, M. Sanchez – Marine Structure, December, 2012
For wave energy to become a fully-fledged renewable, efficient and reliable Wave Energy Converters (WECs) must be developed. The objectives of this article are to present WaveCat, a recently patented WEC, and its proof of concept by means of an experimental campaign in a large wave tank. WaveCat is a floating WEC whose principle of operation is oblique overtopping; designed for offshore deployment (in 50–100 m of water), it has two significant advantages: minimum (if at all) impact on the shoreline, and access to a greater resource than nearshore or shoreline WECs. It consists of two hulls, like a catamaran (hence its name); unlike a catamaran, however, these hulls are not parallel but converging. Using a single-point mooring to a CALM buoy, the bows of WaveCat are held to sea, so incident waves propagate into the space between the hulls. Eventually, wave crests overtop the inner hull sides, and overtopping water is collected in reservoirs at a level higher than the (outer) sea level. As the water is drained back to sea, it drives turbine-generator groups. The freeboard and draught, as well as the angle between the hulls, can be varied depending on the sea state. After preliminary tests with a fixed model of WaveCat in a wave flume, which constituted the first step in the development of the WaveCat patent, in this work a floating model was tested in a large wave tank. In addition to serving as a proof of concept of the WaveCat model, this experimental campaign allowed to gather data that will be used to calibrate and validate a numerical model with which to optimise the design. In addition, it was found in the tests that the overtopping rates (and, therefore, the power performance) greatly depended on the angle between hulls, so that the possibility of varying this angle (as contemplated in the patent) should indeed be incorporated into the prototype.