Laboratory testing of a combined heaving-surging wave energy converter for the nearshore zone

The EDS (Energy Double System) is a combined heave-surge oscillating-body WEC (wave energy converter) designed for the nearshore zone, composed by a heaving float and a surging paddle supported by a unique structure. This paper investigates, through laboratory modelling, the behavior of EDS at various water depths along a sloping beach. The float alone, obtained by removing the paddle from the EDS, was also tested for comparison. Tests were performed with regular waves. Results shows that, as water depth decreases, the upward motion of the float and the forward motion of the paddle are more energetic and faster than their opposite motions (downward and backward, respectively). The CWRs (capture width ratios) of the float alone and the float inside the EDS are similar and they increase as water depth increases. Thanks to the presence of the paddle, the CWR of the EDS is larger than that of the float alone at all the tested water depths; it presents a maximum off the breaking point, and then decreases as water depth increases. The interpretation of the laboratory results allowed to draft a method for detecting the optimal water depth to install the EDS in a real sea site.