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• Indian Wind Power Association, Chennai
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Speaker Profiles

Shane Colwell

Presentation Type: Oral



Address: 36 Harolds Bridge Court, Harolds Cross, Dublin 6, Ireland
Phone: 00353860806135
Email-ID: colwells@tcd.ie
Organization: Trinity College Dublin
Designation: PhD
Country: Ireland

Paper Title: Tuned Liquid Column Dampers in Offshore Wind Turbines

Abstract of the paper

Tuned liquid dampers (TLDs), of which Sakai et al. (1989) proposed the first U-shaped Tuned Liquid Column Damper (TLCD) as a means of suppressing vibrations within structures, are dampers whose damping effects depend on the liquid residing in the damper and which are specifically tuned to the natural frequency of a structure. The tuning ratio, which is the ratio of the natural frequency of the TLCD to that of the structure, is optimised in order to ensure an efficient transfer of shear force from the TLCD to the structure. Vibrations are suppressed within a structure with an attached TLCD due to the gravitational restoring force acting on the displaced liquid. Energy is also dissipated through orifice(s) which reside within the cross section of the damper. The utilization of TLCDs over TMDs as a means of suppressing vibration energy within structures is being accelerated due to factors such as: they can dissipate very low amplitude excitations, they are consistent over a wide range of excitation levels and they are self-contained passive damping device, with no auxiliary equipment, personnel or power required to operate and maintain it and are easy to install. Compared to TLDs, TLCDs prove more efficient in respect to volumetric efficiency, TLCDs introduce extra damping effects and variable damping due to the orifice, and the damping effect of TLCDs are easier to quantify. TLCDs have been implemented in Hotel Cosima, Hyatt Hotel and Ichida Building in Osaka (Shimizu and Teramura (1994)) and also in One Wall Centre in Vancouver. Vandiver and Mitone (1978) investigated the effects of liquid storage tanks containing glycol on the dynamic response of offshore structures and concluded that prudent selection of the geometry of the storage tanks would dampen the response of the platform of the offshore structure.

. TLCDs typically comprise of 1-2% of the total mass of the structure, compared with 4-5% of that with a pendulum type damper. Reductions of up to 60% in the acceleration response of the turbine-TLCD system over that of the turbine without TLCD mean that less money is spent on the structural tower and foundations of the wind turbine. TLCDs provide a rich response reduction over the spectrum of frequencies. Changing soil properties over time may alter the natural frequencies of the structure and although the TLCD is usually tuned to the natural frequency of the structure, it will also dampen the shifted frequencies. When the excitation frequencies of the wind and wave loadings coincide with those of the natural frequencies of the wind turbine, the dynamic response of the turbine will be such that the harnessing of the winds energy is not possible. Thus, TLCDs will also increase the efficiency of wind turbines.

Numerical simulations are performed on a 100m tall offshore wind turbine, with and without TLCD, subjected to wind and wave loading to show the effectiveness of the TLCD in reducing the structural response. The reduction in base bending moments and shear stresses are calculated as a result of implementing a TLCD. The JONSWAP wave spectrum is used to simulate the wave loading and the Kaimal spectrum is used to simulate the wind excitation. A new approach to correlate the wind and wave loadings which incorporates the phase difference between the respective loadings is undertaken. In certain cases of phase difference between the wind and wave loadings, the structural response may be greater than that when mutually exclusive wind and wave loadings are taken.

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