Description
In this study, long-term monitoring of a 900-kW onshore wind turbine with a tubular steel tower of 54 meters high and foundation with 26 reinforced concrete piles is performed based on vibration data. Modal properties such as frequency, mode shape and damping ratios were obtained by Enhanced Frequency Domain Decomposition method. Then, 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.
Finite element model of the wind turbine was developed in ANSYS including piles. Soil-structure interaction was modeled by p-y, t-z and q-z soil springs. Finite element model of wind turbine was updated based on identified modal parameters.
Finally, nonlinear time histories were performed to obtain seismic fragility curves of the structure with limit states being the local buckling under different levels of wind speed. 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.
