Study on a three-dimensional variable-stiffness TMD for mitigating bi-directional vibration of monopile offshore wind turbines

Abstract

Bi-directional vibrations of offshore wind turbine (OWT) exist due to the misalignment of wind and wave loadings, which induces the structural fatigue failure. At present, monopile offshore wind turbine (MOWT) is widest utilized in worldwide, which is adopted as the research objective in this study. A novel semi-active three-dimensional magnetorheological elastomer (MRE) based tuned mass damper is proposed to suppress a MOWT bi-directional vibration under misaligned wind, wave, seismic loadings. The proposed MRE-based TMD is installed in the nacelle, which presents dual-directional controllable stiffness properties. Its nonlinear behavior is depicted by bi-lateral Bouc-Wen model. A semi-active control framework is developed, in which current-dependent stiffness of MRE-based TMD is tuned for tracing real-time dominant frequency of the MOWT. The numerical results reveal that MRE-based TMD can effectively attenuate the bi-directional dynamic responses of MOWT under various operation conditions. Additionally, the semi-active MRE-based TMD outperforms passive TMD in reducing the peak and RMS displacement of the tower top in both fore-aft (FA) and side-side (SS) directions, especially in operational state. MRE-based TMD also presents strong robustness under the condition of structural stiffness degradation.