Dynamic Responses of the Tower and Blades on a Spar-Type Floating Wind Turbine Under Freak Waves

A floating offshore wind turbine would be subjected to various abnormal waves. Among them, the freak waves which have high energy may suddenly enlarge the stress and deformation of the upper flexible structures such as the tower and blades. The numerical model of a Spar-type floating wind turbine is established, the freak waves are numerically generated and modulated. Fluctuated freak waves and elevated freak waves are obtained based on the phase angle modulation method. The dynamic performances of the wind turbine under the freak waves are simulated in the time domain, and the internal loads of the tower and blades are analyzed. The results of the tower load responses under the different freak waves show that fluctuated freak waves have a significant effect on the shear force and torque. When fluctuation rises by 15.0 %, shear force increases by 15.0 %, and torque by 9.3 %. Elevated freak waves have slight effects on the torque. The fluctuated freak waves have an obvious effect on the blades. When fluctuation increases by 15%, shear force increases by 8.72 %, and torque by 4.09 %. The torque moment of the blade root is not significantly affected by the change of different freak waves (less than 5%).