Experimental and numerical investigations on seismic responses of wind turbine structures with amplifying damping transfer system

Wind turbine (WT) with a long period is a dynamic sensitive but lightly damped structure, which may be prone to earthquakes, especially for the near-fault pulse-like records containing large amplitude of velocity pulse with a period close to WT's period. An efficient and convenient solution to enhance the damping effect of WT, amplifying damping transfer system (ADTS), is applied by transferring the upper rotation of the wind turbine to its bottom with an amplified damping mechanism. The feasibility of the ADTS is experimentally validated through free vibration tests, sinusoidal excitation tests, and shaking table tests for both non-pulse-like earthquakes and pulse-like earthquakes. Test results of free vibration validate that more than 6.2% extra damping ratio is provided by the ADTS to the tested WT model; while the supplemental stiffness of ADTS shifts the frequency of the tested WT model from 2.16 Hz to 2.61 Hz. Sinusoidal tests show ADTS reduces the displacement (acceleration) response of the tested WT by about 73.88% (58.16%) when subjected to resonant frequency. It is also observed that the ADTS is effective in controlling the seismic responses of non-pulse-like earthquakes and pulse-like earthquakes, providing at least 30% of the reduction in displacement and acceleration. Simulations with high accuracy indicate that the pulse signal usually concentrates the majority of the input energy of near-fault pulse-like earthquakes; while the ADTS can absorb most of the input energy (over 90%), protecting the WT away from undergoing excessive vibration.