Safety Reliability Analysis And Optimization Design Of Deep Water Jacket Platform

The deep water jacket platform has been fast developed and generalized,because of the advantages of greater operating water depth and convenient construction. However, in consideration of the complicated structure, huge size, expensive cost and the adverse working conditions, the safety and economics of deep water jacket platform has been put forward higher demand. In this study, the safety reliability analysis and optimization design of deep water jacket platform were emphatically researched by means of theoretical derivation, numerical simulation, engineering example analysis and corresponding software development, on the basis of applied basic research project of China Petroleum & Chemical Corporation-"The key technology research of deep water jacket platform"The main research contents of this thesis are as follows:(1)Based on the nonlinear foundation beam theory, the nonlinear dynamic analysis model of deep water jacket platform was established, with the nonlinear soil spring model used to simulate the interaction of pile and soil. The vibration mode and the dynamic response rules of displacement, velocity and acceleration of key position, which were computed respectively by equivalent pile method and pile-soil interaction method, were comparatively analyzed; The group effect was considered when the pile-soil interaction method was used, and the influence laws of seabed surface layer property, pile spacing and pile diameter to dynamic response of platform were analyzed.(2)The nonlinear dynamic response of the deep water jacket platform under the earthquake load, was computed by the time history analysis method and the results were compared with response spectrum method. The seismic behavior of the deep water jacket platform was analyzed by IDA method and Pushover method respectively;The accuracy and applicability of different lateral load patterns for Pushover analysis method was studied, and the most suitable lateral load patterns for deep water jacket platform was obtained. Aiming at the randomness of design parameters, material parameters and seismic load, the dynamic probability analysis module for deep water jacket platform was established, and then the influence of soil liquefaction caused by earthquake on dynamic probability of platform was analyzed.(3)Considering the fatigue problems of deep water jacket platform under random wave forces, the spectrum analysis method was introduce, which can describe the distribution of wave energy exactly along the whole frequency domain. Then, the fatigue reliability model was established by the structural reliability theory and the calculation results were compared with those by equivalent Weibull method.(4)Because the fatigue problem was a serious problem for deep water jacket platform, to get a reasonable platform structure design, it is necessary to consider the fatigue property of the platform.The Hooke-Jeeves direct search optimization algorithm was realized by using the MATLAB software; the ANSYS program was used as an equation solver to calculate the dynamic response and fatigue reliability of deep water jacket platform; the ANSYS program was circularly called in patch model by MATLAB, so the optimization analysis process was performed with the fatigue reliability index as an optimization constraint.At the same time, a feasible simplified optimization method was introduced, in which a static optimizing analysis of platform under static extreme load was performed firstly, and then the dynamic optimum analysis was performed on the basis of the static optimization analysis results with natural frequency and fatigue reliability index as constraint conditions.(5)The optimization lectotype of deep water jacket platform is a complicated system question. According to analytic hierarchy process method and comprehensive fuzzy evaluation method, the fuzzy optimization model for optimum lectotype of deep water jacket platform was established, basing on three-level fuzzy evaluation method and expert group credit degree methods. Finally, a jacket platform for 200 m water was taken as an example; a fuzzy optimum selection was performed between the four initial schemes.(6)Basing on risk assessment theory and fuzzy mathematics theory, the potential risks caused by uncertain factors during the process of loading-out, towing and launching for deep water jacket platform were analyzed, in consideration of the design- construction properties of deep water jacket platform .The risk factors for each process were identified by fault tree method, and the corresponding fault tree model was established. The relative weights, the memberships of occurrence probability and accident consequences of risk factors were obtained by expert group credit degree methods. Finally, the risk assessment software was developed for the process of loading-out, towing, and launching.