Hydroelastic response of wind-tracing floating offshore structures to irregular waves and wind

Motion and hydroelastic responses of floating offshore wind turbines (FOWT) to irregular waves and wind loads are studied by use of a numerical coupling approach in frequency domain. The hydrodynamic and aerodynamic loads on the structure are obtained by linear wave diffraction theory and the steady blade element momentum method, respectively, and the structural responses are computed by finite element method. Rigid body responses of a SPAR to combined irregular waves (JONSWAP spectrum)and steady wind are computed and compared with existing laboratory measurements. Good agreement between the computed responses of the structure and existing laboratory data is observed. Next, the rigid and hydroelastic responses of a new concept of FOWT, where multiple towers are placed on the floating platform, to irregular waves and wind are studied. The FOWT consists of an equilateral triangular platform that supports three 5 MW NREL wind turbines on its corners. The FOWT is attached to the seabed with turret-bearing system that allows for the rotation of the structure in response to environmental loads, hence wind-tracing FOWT. It is found that the hydroelastic motions of the wind-tracing FOWT results in significant changes on its heave and pitch responses compared with its rigid body motions.