Vibration damping of an offshore wind turbine by optimally calibrated pendulum absorber with shunted electromagnetic transducer

Abstract

This paper investigates the use of an augmented pendulum absorber for damping of tower vibrations in monopile-supported wind turbines. A shunted electromagnetic transducer is proposed to replace the classic viscous dashpot for pendulum absorbers, in order to improve performance and durability of the absorber. A series RCL (resistive-capacitative-inductive) network is designed as the supplemental shunt for the electromagnetic transducer, which together with the intrinsic resistive-inductive properties of the transducer coil results in an additional resonance. The system equations of motion are established, from which closed-form expressions for optimal calibration are derived using pole-placement. A fully-coupled 14-degree-of-freedom aero-hydro-servo-elastic wind turbine model is established to evaluate the pendulum absorber performance under realistic conditions by non-linear time-domain simulations. Both frequency- and time-domain results show that the calibration procedure results in an optimal absorber that outperforms the classic dashpot-based pendulum absorber with respect to vibration mitigation.