Research Of Fatigue Limit Capacity Of Jacket Offshore Wind Turbine Using Fully Coupled Analysis Method

The offshore wind energy exploitation confront with various technical challenges,such as the fatigue damage of substructure tubular joints under wind and wave loads,and the accurately estimation of structural fatigue limit capacity shall significantly influence the structural safety and economy at the moment.Presently and in the near furture,the offshore wind energy in the water depth of 40m-60 m is prior exploited,and the jacket structure is extensively applied in the offshore wind farms located in the above mentioned depth from the economic perspective.Hence,in order to improve the estimation accuracy of fatigue capacity and consider the influence of interaction between the environmental loads and offshore wind turbine(OWT),the fully coupled analysis method is applied to analyze the fatigue damage of OWT jacket substructure located in the water depth of 40m-60 m.With the intention of eatablish the fatigue capacity evaluation method based on the fully coupled analysis method,the tubular joint stress concentration factor(SCF)and fatigue stress analysis modules are developed using Phyton,in combination with the fully coupled analysis model in the time domain.Sequentially,the coupled fatigue analysis method is established based on the joint distribution of winds and waves,and the linear fatigue cumulative criteria.Based on the coupled fatigue analysis method,the coupled dynamic responses and fatigue stress of tubular joints of OWT under typical fatigue load cases are analyzed.Then,the influence of coupling effects between environmental loads and OWT on the fatigue damage of tubular joints are proved.Moreover,the dominant influence of SCF on the equivalent fatigue strees and accumulated fatigue damage of tubulat joints is discovered.According to the calculated fatigue damage,the dominant tubular joints for the fatigue capacity of jacket substructure in the water depth of 40m-60 m are recommended.The research achievements are summarized as follows based on the performed study,(1)The jacket substructures for the water depth of 40m-60 m in South China Sea are designed based on the recorded environmental conditions and DTU 10 MW baseline WT.(2)Based on the fully coupled analysis model,the tubular joint SCF and fatigue stress analysis modules are developed using Phyton.Then,in combination with the joint distributin of winds and waves,and liner fatigue accumulation criteria,the long term coupled analysis method is recommended.(3)The coupling effects of jacket OWT in the water depth of 40m-60 m under typical fatigue load cases are proved using the fully coupled analysis method,and the necessity of applying coupled analysis method to the fatigue capacity evaluation is validated.(4)Based on the coupled fatigue analysis method,the influence of stochasatic of environmental loads and coupled model parameters on the fatigue damage of tubular joints is studied,and the appropriate values are recommended.(5)The fatigue limit capacities of jacket substructures in the water depth of 40m-60 m is evaluated using the coupled fatigue analysis method,and the dominant tubular joints for the safety of OWT in differen water levels are summarized.Meanwhile,the influence of SCF on the fatigue damage of tubular joints are also studied.