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.
Highlights
Floating offshore wind turbines (FOWTs) must safely withstand harsh environmental impacts including stochastic wind and wave loads
This paper investigated two different types of liquid column dampers for controlling tower side-side and blade edgewise vibrations of floating offshore wind turbines (FOWTs), namely the tuned liquid column damper (TLCD) and the circular liquid column damper (CLCD)
This paper investigated the performance of two types of liquid column dampers on vibration control of FOWTs subjected to wind and wave loads
Summary
Floating offshore wind turbines (FOWTs) must safely withstand harsh environmental impacts including stochastic wind and wave loads. Order to evaluate the performance of the liquid column dampers, a 16-DOF aero-hydro-servo-elastic model is established for the FOWT system, taking into consideration the full coupling of bladedrivetrain-tower-spar vibrations. This can be verified by evaluating the off-diagonal terms in the system mass matrix between the 8th DOF and the 14th DOF. As will be shown in the following simulation results, CLCD with the same amount of liquid mass will have better damping effect on the blade edgewise vibration than TLCD
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