Dynamic Resonance Response and Mitigation of Wind Turbine Towers in Warm Permafrost

摘要

Wind turbine towers built in warm permafrost usually adopt steel pile group foundations due to construction cost and structural safety. This foundation may be softer than expected. In addition, the fundamental frequency of the tower-foundation-soil system fluctuates as the ambient temperature and ground condition changes significantly from season to season in cold regions. Therefore, it is possible, particularly for tall towers, that the fundamental frequency may match the operational frequency in the starting or braking cases or during normal operation; hence, resonance between the tower-foundation system and the rotor may occur. This paper simulates the resonance situation by numerical methods and compares it with field monitoring data. An aerodynamic model was built for the rotor system to simulate its interaction with the wind and provide dynamic loads for the wind turbine tower-foundation-soil system. P-y, t-z, and Q-z curves were used to model the interaction between the pile foundation and the permafrost. Modal analysis shows that the tower fundamental frequency is very close to what is observed in the field data. Time history analysis with the wind load as input on the tower top shows resonance is possible when the rotor operates at a speed around 50 rpm; the peak acceleration on the tower top can reach 0.5 g and peak displacement can reach 20 cm, both of which agree with field observation. A tuned mass damper (TMD) is proposed to reduce the peak acceleration and displacement. Computer models show that a properly designed TMD can be effective in reducing the resonance response and has potential to lengthen the service life of the wind turbine.