Comparison of alternative dynamic vibration mitigation approaches for wind turbine towers

Abstract

The application of vibration absorbers to Wind Turbine (WT) towers has the potential to significantly improve the damping of the tower and the nacelle dynamic response, increasing thus the reliability of WTs. The Tuned Mass Damper (TMD) is considered as a benchmark design option for vibration absorption in Wind Turbine towers. However, its effectiveness is limited by the requirement of large masses, in association with its installation location (top of the WT tower). For this reason, two alternative concepts are considered. First, the nacelle is released from the Wind Turbine tower (nacelle isolation concept), using a low stiffness connection. This option is based on the seismic isolation concept of structures with the use of seismic isolation bearings. Alternatively, a novel passive vibration absorption concept is implemented, based on the KDamper concept. The KDamper is essentially based on the TMD, including however an additional negative stiffness element. Instead of increasing the additional mass, the vibration absorption capability of the KDamper can be increased by increasing the value of the negative stiffness element. Thus, the KDamper always indicates better isolation properties than a TMD damper with the same additional mass. In this paper, the performance of these three vibration absorption concepts is examined for increasing the damping of Wind Turbine towers and for the improvement of their dynamic response. Although all methods present a good behavior, the proposed vibration absorption systems present a significant increase of the damping ratio with a minimal value of added mass at the top of the tower.