Parametric Wave Excitation Model for Floating Wind Turbines

This paper presents a parametric wave disturbance model for an improved representation of the overall system dynamics of a floating wind turbine (FOWT). Hydrodynamic panel codes calculate the frequency-dependent first-order wave excitation force coefficient on rigid floating bodies. This transfer function from wave height to the forces and moments on the body is approximated in this work by a linear time-invariant model. With a causal problem definition the fit to an impulse response shows a good agreement in frequency and time domain for spar-type and semi-submersible-type platforms of floating wind turbines. The disturbance model was coupled to a linear structural FOWT model and the effect of the wave height on the tower-top displacement was compared to the nonlinear model with good agreement. Applications of this parametric model are the inclusion of disturbance dynamics in model-based controller design as well as feedforward control for fatigue load reduction.