Reliability Analysis And Preventive Maintenance Strategy Research For Floating Offshore Wind Turbine

As a clean and renewable energy,offshore wind energy has attracted worldwide attention.Reasonable development and utilization of offshore wind energy can effectively improve the energy supply structure.Floating offshore wind turbine(FOWT)convert wind energy into electricity through wind power generation and are gradually applied to the development of wind energy resources in deep-water areas.However,due to the harsh marine environment and other impacts,various failure modes will occur in the FOWT system,posing a great threat to the safe operation of the FOWT and causing huge economic losses.Therefore,risk analysis,failure prediction,and maintenance strategy are of great practical reference significance to ensure the FOWT safe operation according to the structural characteristics of the FOWT.Traditional and intelligent optimization methods will be used to analyze the reliability of the FOWT subsystem structure,and the optimization process will be applied to practical projects.The main works are summarized as follows:Firstly,aiming at the failure problem of FOWT system,the risk of FOWT system is studied by using fault tree analysis method.By collecting and analyzing the system failure cases,the main failure modes and failure mechanisms of the FOWT system are identified,and the fault tree model of the FOWT system is established.Based on the fault tree model,it is comprehensively analyzed that the main failure subsystems of the FOWT are the mooring system and the generator system.The failure probability,mean time between failures,and system reliability of the main failure subsystems are calculated,and the critical importance of each bottom event is ranked.For the identified failure causes,risk prevention and control measures are proposed from design,maintenance and other aspects.Secondly,in order to solve the failure problem of FOWT mooring system,a reliability analysis model of FOWT mooring system is established.The NREL 5MW OC4 semisubmersible wind turbine is selected as the basic model,and the SESAM software is used for hydrodynamic analysis to obtain the time domain curve and characteristic value of the mooring chain axial tension.Based on the intelligent optimization algorithm,the structural reliability of the FOWT mooring system is simulated,and the load probability model and the mooring chain resistance probability model are constructed as the population in the algorithm.The improved intelligent optimization algorithm is compared with the basic algorithm,and the results show that the improved algorithm is better.Comparing the reliability index values of the intelligent optimization algorithm with the first-order second-moment method and the Monte Carlo method,the results show that the intelligent optimization algorithm has a stronger convergence speed,which verifies the efficiency and accuracy of the algorithm.Thirdly,aiming at the failure of FOWT generator system,a preventive maintenance model based on fault prediction is established.Markov method is used to quantitatively analyze the results of maintainable state,and calculate the system reliability and mean time between failures.Fault prediction is carried out based on preventive maintenance strategy and the system optimization model is built through the objective function.The intelligent optimization algorithm is used to solve the time interval of fault prediction and minimum remaining life in the optimization model,so that the system maintenance cost,reliability and risk can reach an optimal combination state.The results show that the maintenance strategy optimization model can significantly improve the system reliability and the mean time between failures.