Inerter-enhanced tuned mass damper for vibration damping of floating offshore wind turbines

Abstract

This paper investigates the use of an inerter-enhanced vibration absorber, the rotational inertia double tuned mass damper (RIDTMD), for damping in-plane vibrations of a floating offshore wind turbine (FOWT). First, a 17-degree-of-freedom (17-DOF) aero-hydro-servo-elastic model for the FOWT is developed and verified, based on which the damper performance can be evaluated in the time domain (TD) with realisitc load conditions. Next, a reduced-order 6-DOF model is established for the RIDTMD-controlled FOWT in-plane vibrations including rotor mass moment of inertia, hydrodynamic added mass, as well as stiffness contributions from mooring lines and buoyancy. This model enables revealing the dynamics of the coupled spar-tower-RIDTMD system, and provides an efficient yet robust procedure for optimal tuning of the FOWT-mounted RIDTMD in the frequency domain (FD). Comparison of the optimal RIDTMD and the optimal TMD is performed in both FD and TD. It is seen that both TMD and RIDTMD effectively suppress tower side-side vibrations when mounted at the tower top. RIDTMD consistently outperforms TMD due to the extra DOF (extra resonance) introduced into the device, at the cost of slightly larger damper stroke. Both dampers positively influence spar roll motion and blade edgewise vibration as well.