Resonance characteristics of offshore wind turbine structures founded on partially embedded pile groups

Resonance occurs when the first natural frequency of wind turbines coincides with frequencies of the rotor rotation and blade passing, which may cause damage to wind turbines in serious conditions. Most existing researches on the resonance of wind turbines are qualitative analysis, assuming a rigid and fixed structure bottom. However, the quantitative analysis is important, especially considering the effect of foundation embedment depth and soil parameters. The resonance of offshore wind turbines supported by partially embedded pile groups is investigated. Based on the simplified method considering the coupled horizontal-rocking properties of wind turbines, the influences of different embedding ratios of pile groups and the elastic modulus of soils on the resonance of wind turbines are analyzed, providing the relationship equation between embedding ratios and resonance frequencies. To investigate the resonance frequencies of offshore wind turbines with different embedding ratios of pile groups, four model tests are carried out, which verify the rationality of the above theoretical analysis.