Dynamic analysis of MTMD vibration reduction for offshore wind turbine under combined wind-wave-seismic loads

The rapid expansion of OWT (offshore wind turbine) capacity has intensified vibration challenges under complex loading conditions, particularly excessive vibrations and fatigue failures induced by environmental excitations This study examines the vibration response of the NREL 5 MW monopile OWT through a refined 3D finite element model under combined wind, wave and seismic excitations. A MTMD (Multi-tuned mass damper) system targeting the 1st-order and 2nd-order natural-frequency of the tower is designed to evaluate its vibration mitigation performance. The tower dynamic response is predominantly governed by its low-order natural-frequency and the spectral characteristics of external excitations. Seismic loads, especially their low-frequency components, exert a pronounced influence on structural accelerations and bending moments. Under combined wind-waveseismic excitation, the vibration response reflects intricate load interaction effects, with seismic excitations significantly amplifying the bending moment response. The MTMD system exhibits superior performance compared to a single TMD, effectively attenuating low-frequency vibrations and reducing overall amplitude. The maximum response attenuation-ratio reaches 58 % under wind-wave excitation and 55 % under combined windwave-seismic excitation. These findings provide essential theoretical and technical support for OWT vibration reduction design.