Large amount parameters make optimizing multiple tuned mass dampers’ (MTMD) performance difficult. A simplified method of MTMD optimization is proposed. In this method, tuned mass dampers (TMDs) are used to suppress the peak responses in the frequency domain by being tuned to the frequencies of the peaks. In the optimization process, only the mass ratios of the TMDs need to be considered. Finally, additional viscous dampers are arranged to further optimize MTMD's performance. The results show the optimized MTMD is excellent for OWTs seismic response control. The research also shows the importance of considering seismic wave's characteristics for MTMD optimization.
In the context of traditional energy's decreasing supply and demand ratio, the mature offshore wind power industry will play a more critical role in the future energy structure. Except for the design loads (wind, waves, and currents), offshore wind turbines near zones with frequent seismic occurrence and high seismic intensity need additional consideration of seismic dynamic safety. Low-frequency and high-intensity earthquakes will cause severe resonance damage to the wind turbines (see Fig. 1), which will result in a large-scale structural catastrophe of the entire wind farm.
The dynamic safety characteristics of offshore wind turbines under earthquakes have always been a hot research topic. The substructure approach divides the structure response into the lower pile-soil interaction part and the upper wind turbine dynamic response part (Richart et al., 1970; Clough and Penzien, 2003; Kausel, 2010), which can conveniently and effectively solve the complex problems in earthquake engineering. Recent studies have shown that the structural response to vertical seismic excitation cannot be ignored (Kjørlaug and Kaynia (2015); De Risi et al., 2018; Kaynia, 2019; Ali et al., 2020), especially in the pile-soil interaction part. He et al. (2020 2021) studied the dynamic response of monopile and seabed to vertical and oblique seismic waves through a rigorous semi-analytical method and found for the first time that seawater has the damping effect on vertical vibration and the amplification effect on horizontal vibration, which provides a new idea for seismic vibration damping of submarine foundation. However, for the superstructure, the tall and flexible tower is extremely sensitive to the horizontal seismic input, and the resonance effect will cause up to tenfold acceleration amplification. Seismic control devices need to be introduced for offshore wind turbines.
