Finite water depth effects on the performance of a wave farm

Abstract

The present paper focuses on the numerical investigation and the assessment of finite water depth effects on the performance (hydrodynamic behavior and energy absorption) of a wave farm. The farm consists of nine, free floating, mutually interacting, heaving Wave Energy Converters (WECs), arranged in a 3 × 3 rectilinear grid. The WECs' Power Taking Off (PTO) mechanism, actuated from their heave motion, is modelled as a linear damping system. Linear frequency domain analysis is implemented under the action of head regular and irregular waves, while three different installation depths are examined. For defining the PTO's damping coefficient, the water depth effect on the heave radiation damping coefficient is considered. Moreover, in the case of irregular waves, an incident wave spectrum with finite depth spectral formulation (TMA spectrum) is deployed for taking into account limited water depth conditions. Constructive and destructive interactions among the WECs in terms of power absorption are appropriately quantified, and the water depth effects on the existence and the extent of these interactions are assessed. The results of the present study illustrate that water depth effects are pronounced in the case of irregular waves, where the water depth's decrease leads to a significant decrease in the WECs' response and the farm's absorbed power, especially for the smallest examined installation depth. However, the comparison of absorbed power losses with power resource losses demonstrates that although the farm's installation at smaller water depth results in significant power resource losses, the farm's capture efficiency is not so intensively reduced.