A Novel Reduced Column Approach for the Mitigation of Earthquake-Induced Vibrations of Wind Turbines

Abstract Wind power is a sustainable and renewable energy source which becomes fundamental in order to meet the worldwide rising demand for energy. New onshore and offshore wind farms will be rapidly constructed in challenging environments, especially in earthquake-prone areas. Although a flexible structure, the wind turbine tower is slender and lightly damped which may exhibit a high susceptibility to earthquake-induced vibration. Whilst past studies have been based on traditional passive control devices, such as tuned mass dampers or tuned liquid column dampers, this study aims to propose a novel approach, the Reduced Column Section (RCS), to design an innovative transition piece to mitigate the vibrations on fixed wind turbines. The novel transition piece of hourglass shape will allow the control of the fundamental period of the wind turbine as well as it will limit the maximum stresses within the device by protecting the tower and the monopile. The proposed approach will be numerically tested on the 15MW benchmark wind turbine proposed by the International Energy Agency. A 3-dimensional finite element model will be generated using the commercial ADINA software and verified through the 1-dimensional baseline model provided for the open-source OPENFAST code. Therefore, the novel transition piece will be implemented and tested under a combination of multi-hazards such as wind and seismic loading. Two proposed devices, with and without auxetic lattice structure, will be investigated. The benefits of the proposed devices will be demonstrated in terms of the mitigation of the stresses on the tower wall and on the soil.