Investigation of natural frequency of wide-shallow composite bucket supported offshore wind turbine: Application to real data

Wide-shallow composite bucket structure is a new offshore wind power foundation structure developed in recent years. The field information on long-term natural frequency of composite bucket supported offshore wind turbine under complex marine environment is necessary for structural design, maintenance and serviceability assessment. In this paper, an analysis of 170 days of field data from Jiangsu offshore wind farm, China is presented in detail. The natural excitation technique combined with eigen system realization algorithm is used for the analysis of natural frequency. Subsequently, the long-term features of the natural frequency, and the effect of environmental factors (wind and wave) on natural frequency and their statistical characteristics are comprehensively investigated. The normal distribution is found to be suitable for characterizing the statistical feature of natural frequency. Pearson's correlation revealed that there is a negative correlation between natural frequencies and wind speed/wave height. Furthermore, considering the uncertainty of wind speed and wave height, the probability distribution of first natural frequency of offshore wind turbine is acquired by Monte Carlo simulation, which can lay the foundation for the structure design, modal validation and damage diagnosis of wind turbine.