Abstract: Floating offshore wind turbines (FOWTs) are affected by the complex marine environment of wind and waves. Therefore, it is of great significance to clarify the motion response and wake evolution of FOWTs under the combined action of wind and waves. For this purpose, taking the column-type wind turbine as the research object, the pitch motion response and wake evolution of FOWTs under the combined action of wind and waves were studied. The results show that the nonlinear characteristics of waves have a significant impact on the motion phase of the unit. Under the fifth-order Stokes wave, the unit shows a 4.75% phase lag compared to the first-order Airy wave. Moreover, through spectral analysis, it is found that the wave frequency is the main influencing frequency of the aerodynamic force of FOWTs, followed by the rotation frequency of the wind turbine itself, and finally the tower interference frequency. In terms of the wake, the existence of waves accelerates the recovery of the aerodynamic wake, causing the lower tip vortex to rise and thus leading to an upward shift of the wake centerline, resulting in an asymmetric spatial distribution of the wake. Compared with the still water condition, the hub center velocity at 7D under the first-order wave increases by 5.86%, and at 9D it increases by 30.29%. Moreover, the wake recovery under the fifth-order Stokes wave is faster than that under the first-order Airy wave.

Key words: floating offshore wind turbines, wake, combined wind and wave, motion response