Response and power output of U-oscillating water column operating in variable bathymetry regions

Realistic implementation of wave energy converters (WEC) must account for the effects of the surrounding bathymetry on the WEC performance. However, most modelling tools do not introduce this element into the design process. Thus, giving rise to unrealistic predictions of the overall WEC performance. This problem is quite relevant in WECs operating in intermediate water depths, where bathymetry effects affect the whole wave hydrodynamics. In this article, the performance of breakwater integrated U-oscillating water column wave energy systems is analysed. A Boundary Element Method (BEM) model, accounting for variable bathymetry effects, is developed and combined with a nonlinear U-OWC dynamic model for estimating the hydrodynamic quantities involved. The developed models are used for determining the impact of the water depth variability on both the U-OWC response and energy performance. As demonstrative examples, the case of a system operating in the Natural Ocean Engineering Laboratory of Mediterranea University of Reggio Calabria (NOEL) and the breakwater of the port of Salerno in Italy are examined. It is shown that bathymetry effects may play a constructive role in the U-OWC dynamics, as they may lead to higher converted energies. Furthermore, they may change the power output peak frequency.