Fully-coupled time-domain simulations of the response of a floating wind turbine to non-periodic disturbances

The dynamical response of a spar-buoy-based floating wind turbine to non-periodic disturbances is studied through a coupled aero-hydro-elastic numerical model. This methodology is characterized by a fully-nonlinear algorithm of the mooring cables, an unsteady boundary-element model for wind-blade interactions, and a time-domain boundary-element model for wave-body interactions. This model is applied to study dynamics of a 5 MW floating turbine. Through relaxation tests, we demonstrate that there is relatively small damping effect in the pitch direction to dissipate vibrations caused by disturbances, even if the aerodynamic damping effects on the rotating blades are accounted for. On the other hand, when viscous damping is included the dissipation effect in pitch is significantly increased. Furthermore, by using the coupled model we examined the time-dependent responses of this 5 MW system to a wave generated by a pulsating pressure on the free surface. The wave loading, platform movements, and wave field around the system have all been investigated. The focus of the analysis was to investigate the ability of the system to recover to the equilibrium position after being disturbed.