Wind shear effect induced by the platform pitch motion of a spar-type floating wind turbine

The platform pitch motion of a Floating Wind Turbine (FWT) introduces additional relative wind speed to the rotor. This additional relative wind speed distributes linearly along the vertical altitude, which is similar to the linear wind shear, thus it is addressed as the platform-pitch-induced (PPI) wind shear effect. In this paper, the PPI wind shear is investigated numerically with the Free Vortex Method (FVM). Firstly, the typical wind shear and the PPI wind shear are separately analyzed and then compared with each other. The wind profile of the typical wind shear is stationary. However, the wind profile of the PPI wind shear is time-varying, which complicates the aerodynamics of the FWT. Subsequently, the influencing factors of the PP1 wind shear are thoroughly discussed. Results show that the PPI wind shear is related to the FWTstructures, and it is increased with the increases of the platform pitch amplitude, frequency and the tip speed ratio. The PPI wind shear introduces significant fluctuations to the aerodynamic loads, which smear the power quality and result in potential fatigue damages to the FWT structures. To mitigate the adverse effects of the PPI wind shear, advanced control strategies and optimized structure designs should be developed. (C) 2018 Published by Elsevier Ltd.