Modelling the loads and motions of a floating offshore wind turbine with asymmetric moorings

Abstract

Despite the improvements in wind energy conversion technology, wake effects present in wind farms still remain a challenge. In the case of floating offshore wind turbines (FOWTs), these can be mitigated by varying the mooring lengths to dynamically position the FOWTs according to the wind direction. As this introduces asymmetry in the mooring system, the stability of the FOWTs may be affected. With the aim of unlocking the full potential of floating offshore wind, this work investigates the loads and motions of a full-scale 6 MW spar-supported FOWT with four catenary moorings as its position is shifted along the crosswind direction. A hydrodynamic model developed in ANSYS® AQWATM to obtain the dynamic response of the system in four metocean conditions is presented. Results indicate that asymmetry in the mooring system has a noticeable effect on the sway and roll motions as well as the cable tensions. The wave height and irregularity only appear to influence the FOWT motions. In general, the dynamic response of the FOWT system is not expected to be jeopardized as the typical permissible limits for a spar-supported FOWT and the proof load of the cables were not exceeded.