Comparisons Between the Typical Wind Shear and the Wind Shear Induced by Platform Pitch Motion for an Offshore Floating Wind Turbine

The pitch motion of the Offshore Floating Wind Turbine (OFWT) introduces additional wind speed to the rotor. The additional wind speed distributes linearly along the vertical altitude, which is called as the platform-pitch-induced wind shear effect in this paper. Comparisons between the typical wind shear and the platform-pitch-induced wind shear are conducted with the Free Vortex Method (FVM) for the NREL 5MW baseline wind turbine. It is found that the platform-pitch-induced wind shear is the results of the rotor rotating and platform pitching, and its wind speed profile is time-varying. At the designed point of tip speed ratio of 7, the averaged power output is reduced slightly under the typical wind shear while it is increased by 4% under the platform-pitch-induced wind shear. The aerodynamic loads of the OFWT under the platform pitch-induced wind shear experience much more considerable variations than the typical wind shear, which introduce severer fatigue damages to the OFWT components. For the sake of the safety of the OFWT, advanced control strategy and superior design should be developed to mitigate the platform pitch motion.