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Monopile offshore wind turbines (MOWTs) are widely utilized as a desirable choice of clean energy production. MOWT is prone to external vibration under combined loadings such as wind, wave, current, ice and earthquake. With long-term utilization, the turbine tower even present stiffness decay due to the scour effect, which induces the variation of the OWT’s natural frequency and undesired resonance may be occurred. For mitigating dynamic responses of MOWT, this study proposes a semi-active variable stiffness tuned mass damper (TMD) with magnetorheological elastomer (MRE) materials. Firstly, a MOWT dynamic model is established by finite element method. MRE-TMD is installed at the top of MOWT tower. Secondly, the external loadings are simulated by random spectrum analysis. Thirdly, a semi-active fuzzy controller is proposed through which the current-dependent stiffness of MRE-TMD is controlled for balancing the trade-off between the OWT tower responses (e.g. displacement and acceleration) and TMD stroke. The numerical results demonstrate that the semi-active MRE-TMD can effectively suppress the dynamic responses of OWT under combined external loadings, and it outperforms the passive TMD in simultaneously decreasing the tower structure dynamic responses and TMD stroke. Robustness analysis of semi-active MRE-TMD is also conducted by considering OWT sudden loss of structural stiffness under multiple-loadings

Magnetorheological elastomer (MRE), tuned mass damper, offshore wind turbine, fuzzy control, vibration suppression.