Influence of Seismic Direction on Dynamic Responses of Wind Turbine in Operation: An Experimental Study by Combining Wind Tunnel and Shaking Table Tests

This study investigates dynamic responses of wind turbines subjected to combined seismic and wind loads, with a particular focus on the influence of seismic input angles and the effect of aerodynamic damping. A wind tunnel-shaking table (WTST) test platform was developed, capable of applying seismic and wind loads simultaneously. A 1:100 scale model wind turbine was tested using El-Centro and Taft seismic records, sourced from the Pacific Earthquake Engineering Research (PEER) Strong Ground Motion Database, which were adjusted for amplitude and time to simulate realistic loading conditions. The experiments included a fixed wind input direction and seven different seismic input directions across six operational conditions (including the parked condition) to assess the influence of seismic direction on the dynamic responses of wind turbines in operation. The results show that as the seismic input angle increases from 0° to 180°, nacelle displacement initially decreases and then increases, with similar trends in nacelle acceleration and vibration. Increasing wind speed leads to a gradual reduction in nacelle displacement. While the standard deviation of acceleration initially decreases as the turbine transitions from stopped to operational, it becomes wind-speed independent thereafter. The peak tower moment occurs in the side-to-side (S-S) direction at a seismic input angle of 90°, and the acceleration amplification factor can soar to 4 at 0° and 180° seismic input angles, indicating up to a fourfold magnification of input acceleration at the nacelle. This study provides experimental evidence that seismic direction and aerodynamic damping are critical factors when evaluating the safety and reliability of operational wind turbines in earthquake-prone areas.