Along-wind Vibration Control of an Offshore Wind Turbine Using TLCD

摘要

This paper investigates the application of a passive control device, namely, a tuned liquid column damper (TLCD), for the mitigation of vibration induced by joint wind and wave forces. The offshore turbine tower and rotating blades are modeled as multi-degree-of-freedom (MDOF) entities. The free vibration of the tower includes the effect of a rigid mass at the top, representing the nacelle and rotor system, and those of the blade include the effects of centrifugal stiffening due to rotation and self-weight. The wind velocity time-histories of the blades are derived from the PNL method, in which the phenomenon of rotationally sampled wind turbulence is included, and the corresponding wind loads are computed using the blade element momentum (BEM) theory. Wind and wave drag loading on the tower is also considered, with a series of spatially-correlated nodal wind velocities time-histories being derived using discrete Fourier transforms (DFTs) of the Kaimal spectrum, and the wave height time histories being derived from the modified JONSWAP wave spectrum. Blade and tower response time-histories are obtained using a precise time-integration method, the base shear forces due to flapping for the three blades is imparted into the top of the tower. Simulations are carried out for the MDOF structure subjected to both wind and wave excitations. The parameters of the damper are designed through an optimization scheme. The bending moments at the bottom of the tower, displacement and acceleration responses at the top of the tower with a TLCD are investigated. Furthermore, a numerical example is included to qualitatively evaluate the influence of the damper.