Random vibration analysis of nonlinear floating offshore wind turbine system via statistical linearization process under coupled nonlinear wave excitation

The work presented in this paper investigates the possibility of using statistical linearization approach to predict the stochastic dynamics of nonlinear floating offshore wind turbines (FOWT) system under coupled nonlinear wave excitation. OC3-Hywind Spar floating platform equipped with a 5 MW reference wind turbine offered by NREL is taken as the discussed FOWT of the study. A coupled nonlinear analytical model subjected to coupled irregular wave excitation is established to describe the dynamic characteristics of the FOWT, and further, the governing equation of the model is transformed into the equivalent linear one through the statistical linearization approach. The error caused in the linearization process is minimized through an iterative process. The accuracy, adaptability and efficiency of the model and the proposed method built in this paper are verified by numerical examples and comparison with other methods, such as Monte Carlo method and FAST etc. The research shows that the proposed method based on statistical linearization process to predict the stochastic dynamic response of nonlinear FOWT system under coupled nonlinear wave excitation has not only high accuracy but also high computational efficiency. It is about 4-5 orders of magnitude faster than the deterministic analysis method, and is of great significance for the design and research of the FOWT. An application example conducted in this paper indicates that this method is effective and can be used extensively, such as structural design optimization, reliability analysis, determination of the optimal parameters of vibration control and fatigue analysis of components, etc.