Abstract
Ocean renewable sources of energy are to play a large role in mitigating the damaging future effects of climate change. Though, in becoming a viable alternative, greater work must be done in driving their capital costs down towards that of non-renewable technologies. An emerging solution is to combine offshore wind and wave energy devices within the same marine space, offering the potential benefits of increased power generation and shielding of structures in lee.
This paper presents the preliminary results of a novel experimental study into the linear and non-linear wave-structure interactions on a fixed WEC co-located with an OWT. The hydrodynamic response of the WEC was investigated for a range of regular wave sets, focusing particularly the effect of increasing wave amplitude on higher order wave-structure interactions. A process of harmonic decomposition was performed to capture higher order force components at multiple integers of the peak wave frequencies. The study revealed that non-linear contributions to the surge force became significant as wave amplitude increased, showing considerable variation at half the peak loading frequency. It followed that these experimental forces were found to be the sum of linear diffraction and total non-linear force components, with the first order component of the surge force fitting the numerical curve well. Second and third order force components were found to agree well with Stokes’ theory of wave amplitude proportionality. Finally, in maximising the hydrodynamic loading, focus wave tests were performed on the isolated WEC and co-located arrangement. With the OWT in lee, the WEC experienced a reduction in maximum surge force of approximately 23.2%.