Power absorption by closely spaced point absorbers in constrained conditions

The performance of an array of closely spaced point absorbers is numerically assessed in a frequency domain model. Each point absorber is restricted to the heave mode and is assumed to have its own linear power take-off (PTO) system. Unidirectional irregular incident waves are considered, representing the wave climate at Westhinder on the Belgian Continental Shelf. The impact of slamming, stroke and force restrictions on the power absorption is evaluated and optimal PTO parameters are determined. For multiple bodies optimal control parameters (CP) are not only dependent on the incoming waves, but also on the position and behaviour of the other buoys. Applying the optimal control values for a single buoy to multiple closely spaced buoys results in a suboptimal solution for the array. Other ways to determine the PTO parameters are diagonal optimisation (DO) and individual optimisation. These methods are applied to two array layouts consisting of 12 buoys in a staggered grid and 21 buoys in an aligned grid. Compared to DO, it was found that individually optimising the CP increased the energy absorption at Westhinder with about 16-18% for the two layouts, respectively.