Design considerations for a hybrid wind-wave platform under energy-maximising control

The environmental impact of emissions of fossil fuels and their rising prices, together with countries’ commitment to mitigate the effect of the alarming and rapid climate changes, have been a crucial thrust to investigate new solutions to exploit renewable energies for efficient and effective energy supply. Offshore wind-wave hybrid platforms have been proposed to produce higherquality power at a lower cost, by exploiting the existing synergies between these two technologies. The aim of this study is to investigate the effects of structural (geometric) design changes on the dynamics of a hybrid wind-wave platform under energy-maximising control for the wave conversion system. In particular, the device considered is a semi-submersible platform with an incorporated flaptype WEC, analysed both from a closed-loop and open-loop perspectives with a control system designed to maximise the energy produced by the WEC. Design changes on the wind-wave conversion platform are performed in terms of flap dimensions, starting from a suitably defined nominal geometry. The corresponding dynamical analysis is conducted by both increasing and decreasing the flap draft with respect to the nominal case, to investigate the effect of different structures on the interactions between WEC and platform. A frequency-domain analysis of the overall input/output (velocity) system is presented, highlighting the situations that can enhance the potential of both devices and exploit their synergies.