Vibration control of floating offshore wind turbines using liquid column dampers

Abstract

This paper investigates the use of two different liquid column dampers for vibration control of spar-type floating offshore wind turbines (FOWTs). A 16-degree-of-freedom (16-DOF) aero-hydro-servo-elastic model for the FOWT is first established using multi-body based formulation and the Euler-Lagrangian equation, taking into consideration the full coupling of the blade-drivetrain-tower-spar vibrations, a collective pitch controller and a generator controller. It is found from the simulation results that due to the coupling to the spar rigid-body motion, the eigenfrequency of the tower vibration is significantly changed, which needs to be accounted for when tuning the liquid dampers. Tuned liquid column damper (TLCD) is investigated for controlling the lightly damped (due to low aerodynamic damping) tower side-side vibration and blade edgewise vibrations. Further, a newly proposed liquid column damper, the circular liquid column damper (CLCD) is also investigated for blade edgewise vibration control. The large centrifugal acceleration from the rotating blade makes it possible to use liquid column dampers with rather small masses for effectively suppressing edgewise vibrations. By properly tuning the dampers, both types of liquid column dampers are effective in mitigating tower and blade vibrations. Performances of the dampers are compared in terms of the control efficiency and practical considerations.