Vibration mitigation in offshore wind turbine under combined wind-wave-earthquake loads using the tuned mass damper inerter

This study proposes the application of a tuned mass damper inerter (TMDI) to mitigate vibrations in offshore wind turbines (OWTs) under combined wind-wave-earthquake loads. Primarily, the governing equation for the TMDI system is derived, which combines the tuned mass damper (TMD) with a linear inerter. Then the TMDI submodule is developed and integrated into the updated FAST v8. Further, an optimization framework that considers the influence of higher modes has been proposed to optimize the TMDI. The coupled analyses of OWTs under typical seismic cases are performed, and the effectiveness of the optimized TMDI is evaluated based on the mitigated structural responses. The results demonstrate that the TMDI outperforms the TMD in suppressing the coupled wind-wave-earthquake responses by considering smaller attached mass. This superiority can be attributed to the multi-frequency and enhanced fundamental frequency suppression capabilities of the TMDI, resulting from the higher-mode damping effect and mass amplification effect of the inerter device. Meanwhile, the inclusion of the inerter device significantly reduces the damper stroke. Moreover, it is found that the preferred position for the TMDI is situated at the upper part of the maximum amplitude of the second structural mode of the OWTs where significant variations in the modal shape occur.