Wave–structure interaction in hybrid wave farms

Hybrid wave farms, consisting of different types of Wave Energy Converters (WECs), have rarely been investigated so far. In this work we propose a hybrid wave farm consisting of Oscillating Water Columns (OWCs) and point-absorbers (PAs), and develop a semi-analytical model of the interaction between this hybrid wave farm and the incident wave field. The OWCs and PAs are modelled as truncated cylinders with and without moonpools, respectively, each with its own outer radius, inner radius, draft and mass. The hydrodynamic model solves the wave diffraction and radiation problems using linear potential flow theory and the methods of separation of variables and eigen-function matching. The independent oscillations of each WEC in any degree of freedom, including both translating and rotating modes, together with the pressure fluctuations of the air inside each OWC chamber, are all accounted for. The model is successfully validated based on numerical data, and thereupon applied to two configurations of the hybrid wave farm. We find that the excitation volume flux/forces are strongly dependent on the incident wave direction, the spacing between the WECs and, more generally, the configuration of the farm. The hydrodynamic coefficients, especially those of the PAs, are sensitive to the spacing and configuration. Notwithstanding the interest of these results in relation to the selection of the optimum configuration and WEC spacing of the hybrid wave farm for specific locations (with specific prevailing wave directions), the interest of this work lies in the semi-analytical model itself, which is found to be efficient in modelling the interaction of the hybrid wave farm and the wave field, and can be used in future wave farm projects.