| China's economic growth depends upon the petroleum increasingly, the exploitation of the petroleum in deep-water is imminent. It is necessary to do the research of the safety assessment of floating platform under different conditions because of the high risk. Several offshore platform accidents show that the overall collapse, capsizal and excursion of the platform are mostly caused by the local component damage firstly. The safety of local component of the floating platform is the foundation of the general safety.This paper is supported by sub-program of the National High Technology Research and Development Program("863"Program) named "safety evaluation technology of floating structures".This paper studied the limit state functions of the local component of the floating platform with deterministic method firstly, then assessed its safety by the reliability index under different conditions, finally reliability-based design optimization(RBDO) was researched. The main conclusions are summarized as fallows:(1)The limit state functions of stiffened panel and stiffened cylindrical shell of the floating platform under different conditions were summarized.(2)Multi-interpolation method was presented, which enable sub-modeling method be suitable for analyzing the local component of floating platform.(3)The force conditions of connection joints of floating platform were analyzed by finite element software ANSYS 10.0, and the limit state functions of connection joints were established.(4)The reliability for local component of floating platforms (TLP, Spar and SEMI) was analyzed. And also the reliability index of each local components under different load condition were calculated by the program which was edited by C++6.0.(5) The expression of sensitivity analysis for reliability index was derived according to its geometric significance in standard normal space, and using the expression as derivative information, an iteration formula for RBDO was given.
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