Abstract
Offshore wind turbines (OWTs) installed in seismically active regions are subjected to severe multihazard dynamic loading consisting of combined seismic ground motions, hydrodynamic wave actions, and aerodynamic forces. To mitigate catastrophic structural vibrations and fatigue damage, this study presents the development and evaluation of a semi-active Tuned Mass Damper equipped with a Magnetorheological fluid damper (MR-TMD) located within the nacelle of a multi-megawatt monopile offshore wind turbine. A high-fidelity, coupled dynamic model integrating aero-hydro-servo-elastic interactions with a modified Bouc-Wen phenomenological model of the MR damper is formulated. The MR-TMD is controlled using a clipped-optimal control algorithm based on continuous state feedback of tower-top velocity and acceleration. Dynamic time-history simulations under multiple historical seismic records demonstrate that the MR-TMD achieves superior vibration suppression compared to conventional passive TMDs. Specifically, peak tower-top fore-aft displacements and base overturning moments are reduced by up to 38.4% and 31.2%, respectively, while root-mean-square responses are attenuated by over 42%. Furthermore, the proposed semi-active system demonstrates robust adaptive capability against structural frequency detuning induced by blade rotation and soil-pile stiffness degradation, highlighting its potential for enhancing the structural resilience and operational lifespan of next-generation offshore wind infrastructure.
