Dynamic response of operating wind turbines under near-field and far-field earthquakes: experimental study through combined wind tunnel and shaking table tests

This study investigates the seismic responses of wind turbines under combined wind and earthquake excitations, with specific focus on near-field (Chi-Chi) and far-field (Superstition) ground motions. A series of wind tunnel-shaking table joint tests were conducted on a 1:100 scaled wind turbine model to capture both peak and cumulative structural responses. Results show that near-field excitation leads to significantly greater nacelle displacement, acceleration, amplification factors along height, and base moment than far-field excitation, with clear response variation as peak ground acceleration (PGA) increases. Time-frequency analysis reveals that near-field motions are characterized by impulsive energy input over medium-to-high frequencies, while far-field excitations deliver relatively low-frequency, long-duration energy. Wind load contributes to seismic response by amplifying peak displacements and may increase nacelle fatigue risk. Cumulative displacement of wind turbines is strongly influenced by wind load. When the turbine is operating, the combined effect of wind and seismic loading leads to much greater overall displacement over time compared to when the turbine is shut down. These findings highlight the necessity of incorporating both ground motion characteristics and operational wind loading in the seismic design and nacelle fatigue assessment of wind turbines.