Effect of long-term horizontal load on the natural frequency of monopile supported offshore wind turbine structures

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Journal of Vibration and Shock ›› 2023, Vol. 42 ›› Issue (2) : 108-115.

SUN Yilong1，XU Chengshun1，XI Renqiang1,2，DU Xiuli1，DOU Pengfei1,3

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Abstract

Offshore wind turbine structures usually suffer wave, wind and other external lateral cyclic loads. The long-term cyclic loadings cause the variation of foundation stiffness. The offshore wind turbine structural system is sensitive to these dynamic cyclic loads, so it is very important to predict the long-term effect of cyclic loading on the natural frequency. This study developed a method to analyze the natural frequency of offshore wind turbine structural system with considering soil-pile interaction and the effect of long-term cyclic loading. This method is based on the kinematic equation of the damped system, considering the long-term effect of cyclic loading on the foundation stiffness by embedding the foundation stiffness degradation model. This method was then validated against engineering data and numerical calculation. Parameter studies were conduct to present the influence of the cyclic loading amplitude, cyclic number and pile diameter on the natural frequency of offshore wind turbine structure system by using the developed method. The results showed that the natural frequency of the offshore wind turbine structural system would decrease with increasing cyclic loading amplitude and cyclic number, and the natural vibration frequency of the fan structural system would be biased towards 1P with increasing the cyclic number. This method can be used to evaluate the natural frequency of monopile supported offshore wind turbine structure under the long-term cyclic loading, and provide some reference for the design of natural frequency of offshore wind turbine.

Key words

offshore wind turbine / Monopile / Long-term cyclic loading / Natural frequency

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SUN Yilong1，XU Chengshun1，XI Renqiang1,2，DU Xiuli1，DOU Pengfei1,3. Effect of long-term horizontal load on the natural frequency of monopile supported offshore wind turbine structures[J]. Journal of Vibration and Shock, 2023, 42(2): 108-115

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