Long-term vibration-based monitoring and seismic performance assessment of a wind turbine

In this study, long-term vibration-based monitoring of a 900-kW onshore wind turbine is presented. Modal properties such as frequency, shape, and damping ratios were obtained using enhanced frequency domain decomposition method. Change in modal parameters due to environmental and operational conditions was determined. Modal parameters after cleansing such effects were obtained by multiple linear regression analyses. Then, finite element model of the wind turbine was developed including piles and soil springs; and updated using identified modal parameters. After all, seismic fragility curves of the structure with the limit state being local buckling were developed considering different levels of wind speed. Stress level at which local buckling occurs was determined by pushover analysis of the turbine using a nonlinear finite element model. In the context of this study, it was observed that identified modal values had significant scattering and level of wind speed significantly changed the seismic fragility curve of the wind turbine.