Fatigue Life Prediction Of The Offshore Jacket Platform Subjected To Random Wave Force

With the rapid development of economy of China, the requirement for amount of energy sources is becoming more and more and the acceleration of ocean exploitation is becoming much more necessarily. Jacket platform, as the main style of engineering structures in ocean petroleum exploitation today, accumulative fatigue damage of the platform will occur due to the member fatigue failure. So it is necessary to make an estimation of the fatigue security during the process of platform design. Because it is impossible to avoid the structure discontinuity and treatment and welding flaw, high SCFs usually take place beside the tubular joints, and this will lead to fatigue breakage. In the circumstances, tubular joint strength design and reliability astimation are the main study direction of the fundamental characteristics of offshore structure today as well as the important security problem of offshore platform.Based on an engineering case, it is studied and analyzed that the fatigue life of offshore platform subjected to random wave force. First, modeling process and analysis way of part model is detailed, and the tubular stresses of full model and part model of the platform are computed using FEM and compared with each other and the tubular SCFs(stress concentration factors) are figured out using FEM. Second, by means of the transient analysis, it yields hot-spots'stress time-history respone through tubular nominal stress time-history respone multiplying the tubular SCF. And effective stress cycle ranges are counted among the hot-spots'stress time-history response by rain-flow method. Third, fatigue lives of tubular joints are calculated using S-N curve method and Miner accumulative damage theory. In the end, the paper evaluates the components'fatigue lives of the skirt pile sleeve using three different models and two different boundary restrictions that are displacement restriction and force restriction. Also, they are compared with each other and are evaluated. The method of predicting the offshore platform fatigue life using in the paper can be referenced in practice project.