Dynamic characteristic identification of jacket-type offshore wind turbine using the Hilbert Huang transform under operational condition

Abstract

The dynamic behaviour of jacket-type offshore wind turbine structures becomes more complex due to the combined effect of environmental and rotor machines under operational conditions. Therefore, it is challenging to decompose and identify the dynamic characteristics in the structural health monitoring (SHM) system into natural frequencies of structure, rotor, and wave frequency. This study used the Hilbert Huang transform (HHT) method based on the Ensemble Empirical Mode Decomposition (EEMD) technique to evaluate the dynamic behaviour of the offshore wind turbine with the jacket-type structure. The EEMD algorithm was combined with the Hilbert transform to restrain a mode mixing in the identification process of the offshore structure during the operational condition. The vibration test of an offshore wind turbine model was conducted in the wave tank. The identified frequencies measured from the test using the EEMD-based HHT method were analysed and compared to those of the numerical method using eigenvalue analysis. The results demonstrated that the time-dependent frequency of the structure, wave and rotor excitation was successfully decomposed and identified using the Hilbert Huang transform based on the EEMD technique.