Experimental and Simulation Research on the Motion Response of a Floating Offshore Wind Turbine During Wet-Towing Operation

The vast potential of deep-sea wind resources has driven substantial research focus on floating offshore wind turbines (FOWTs) in recent years. The wet-towing of the FOWT is critically challenged by the harsh conditions and remote locations of deep-sea sites. This paper proposes an innovative concept of FOWT based on the in-service FOWT “Sanxia Yinling”, establishing a numerical model of wet-towing for the FOWT in AQWA. The experiments of free-decay and wet-towing resistance in still water at the towing tank are carried out to validate reliability of the numerical model-integrated viscous damping and resistance coefficient of wind and current. Then, the method is applied to evaluate the effects of sea states and wet-towing speeds for the dynamic responses of the towing system. The results show that the natural periods of the FOWT in heave, roll and pitch DOFs all exceed 25 s, which is sufficiently longer than the typical wave spectral peak. In addition, the numerical model is verified against experimental data, showing close agreement. For the established towing configuration, safe operation requires sea states to be maintained at or below level 4 (significant wave height ≤ 2.5 m) and the towing speed at or below four knots. It is also found that a slack-taut cycle in towing lines at low speeds, which is attributed to wave excitation.