Research on the along-wind aerodynamic damping and its effect on vibration control of offshore wind turbine

The aerodynamic damping of the offshore wind turbine structure (OWT), which can be divided into along-wind aerodynamic damping and across-wind aerodynamic damping, is complex, changeable and closely related to the operation status of the wind turbine, the adopted control strategy and the wind speed. Further, the along-wind aerodynamic damping always plays a significant role in an operational OWT, which can effectively mitigate the dynamic response of the OWT structure. In this research, a new theoretical calculation method of the along-wind aerodynamic damping was firstly derived considering the contributions resulted from the changes in rotor speed with respect to wind speed. Then, this new proposed theoretical calculation process was verified by the simulation method in open-source software FAST and the parameters, which affect the along-wind aerodynamic damping such as wind speed, rotor speed and pitch angle, were also investigated. It is shown that the along-wind aerodynamic damping increases as the value of above influencing factors increases until the rotor speed approaches the rated rotor speed and the pitch angle is greater than the critical angle. Finally, the effect of aerodynamic damping on the performances of tuned mass damper (TMD) for an 5 MW OWT under operational condition was studied. The results demonstrate that the effectiveness of TMD is weakened with the increase of aerodynamic damping. Specifically, when the along-wind aerodynamic damping of the 5 MW OWT increases from 4.97% to 6.87%, the additional damping of the TMD decreases from 7.301% to 6.386%.