Study of the effect of water depth on potential flow solution of the OC4 Semisubmersible Floating Offshore Wind Turbine

This work aims at assessing the influence of water depth on the potential flow solution for a semisubersible floating offshore wind turbine. More specifically, the OC4 (International Energy Agency IEA - Taks 30) was considered for this paper. This work has been inspired by previous studies concerning the effect of shallow water on Liquified Natural Gas Carriers (LNGC). The influence of water depth on the hydrodynamics of such systems is evident from measurements as well as from simulations, specifically when secondary effects in the wave and flow modelling are addressed. Starting From this scenario a comparative study for the Floating Wind Turbine considered was carried out, also taking into account second order hydrodynamics (Quadratic Transfer Functions, QTF) as well as low frequency contribution in the incoming wave, due to shallow water (Setdown effect). The simulations were conducted relying on the codes DIFFRAC and aNySIM, developed at Maritime Research Institute of Netherlands (MARIN) and the results are presented for a range of water depths between the nominal value of 200 m and the extreme shallow water of 30 m.