Wave- and Wind-Induced Dynamic Response of a Spar-Type Offshore Wind Turbine

Abstract

This paper addresses coupled wave and wind-induced motions of spar-type 5-MW wind turbines in harsh and operational environmental conditions. Global dynamic motion responses have been analyzed by aero-hydro-servo-elastic time-domain simulations. The aerodynamics is based on an advanced blade element momentum theory. Panel method and Morison formula accounting for the instantaneous position of the structure are applied for hydrodynamics. Hydrodynamic drag and considering geometrical updating introduce nonlinearities. Hydrodynamic nonlinearities were found to cause excitation of the natural frequencies in the low frequency range more than in the wave frequency range. Extrapolation methods are applied to estimate the maximum responses. A previous study showed that the uncertainty of such an extrapolation for the present concept is less than 2%. In this study it is found that the mean values of the dynamic responses are primarily wind induced and the standard deviations of the responses are primarily wave induced. However, the standard deviation of the nacelle surge motion under operational conditions is primarily wind induced. The maximum of the responses under operational and survival conditions are wind induced and wave induced, respectively. For the present turbine, a power of 5 MW can be achieved at a mean wind speed greater than