Keywords: wind turbine blades, passive tuned liquid dampers, vibration control, tuned liquid damper, structural damping, multiple tuned liquid dampers.

The dynamic behaviour and control of wind turbine blades is becoming an important design consideration with turbines being designed with larger rotor diameter. The aim of this paper is to study the effectiveness of using passive tuned liquid dampers (TLDs) for the dynamic control of wind turbine blades when in a stationary horizontal position. The blade has been assumed to be in its first mode of vibration. Wind turbine blades have relatively long natural periods as do shallow TLDs, making them suitable for use in the vibration mitigation of the blades.

TLDs have been studied for use in the dynamic control of structures for many years. Reed et al. [1] found that the effectiveness of TLDs in mitigating the dynamic response of structures increased with the amplitude of vibration. Much research has also been carried out into wind turbine blades. Chaviaropoutos et al. [2] studied the aeroelastic vibration and fatigue performance of wind turbines and aimed to improve these characteristics by the development of passively damped blades. This was achieved by investigating the use of materials with high damping properties including polyesters and composites. As of yet, little research has been carried out investigating the use of dampers in the blades.

In this paper the blade has been modelled as a simple cantilever beam with uniformly distributed parameters. The dampers have been modelled as mass, spring, dashpot systems attached along the length of the blade.

Displacement transfer functions were plotted for the undamped blade and for the blade with one, two and three dampers attached. These damping configurations corresponded to mass ratios of 0.34%, 0.68% and 1.02% respectively. It was interesting to note that the average tuning ratio for the two and three damper case that achieved the greatest reduction in response was equal to the ideal tuning ratio for the single damper case. As expected the greatest reduction in vibration was observed for the three damper configuration.

A time history analysis was carried out using ten realizations of random turbulent wind loading time histories compatible with a wind spectra. The RMS acceleration values were determined by ensemble averaging ten response time histories to study the reduction in response achieved when dampers were attached to the blade. A significant reduction in vibration was observed when dampers were included in the model. This was particularly true for cases where the undamped blade suffered large accelerations induced by the turbulent wind loading.

1

D. Reed, H. Yeh, J. Yu, and S. Gardarsson, "Tuned Liquid Dampers under large amplitude excitation", Journal of Wind Engineering and Industrial Aerodynamics, 74-76, 923-930, 1998. doi:10.1016/S0167-6105(98)00084-1

2

P.K. Chaviaropoutos, E.S. Politis, D.J. Lekou, N.N. Sorensen, M.H. Hansen, B.H. Bulder, D. Winkelaar, C. Lindenburg, D.A. Saravanos, T.P. Philippidis, C. Galiotis, M.O.L. Hansen and T. Kossivas, "Enhancing the Damping of Wind Turbine Rotor Blades, the DAMPBLADE Project", Wind Energy, 9, 163-177, 2008. doi:10.1002/we.183

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