Research On Non-linear Method Of Structural Strength Evaluation For An In-place Jack-up Platform

As the exploration of marine oil and gas resources progresses toward deeper waters,the marine environment of jack-up platform is becoming worse.Due to the greater flexibility of the overall structure of the jack-up platform,the vibration frequency is reduced and the response to environmental excitation becomes more pronounced as the working water depth increases.In this case,the resonance phenomenon is easy to happen,which causes the overall structure to respond too large and affect the safety of operation.Therefore,it is especially important to analyze the nonlinear dynamic response and performance of the jack-up platform in service.In this paper,we have done the following researches on the nonlinear method of performance evaluation of jack up platform.(1)The wind,wave and ocean current loads subjected by jack up platform under the actual working condition are analyzed and determined.The superiority of the constrained New Wave theory to the stochastic wave theory of the deterministic wave theory(design wave)and random wave theory based on the complete time domain simulation is compared and analyzed,which is to say considering the randomicity,spectrum and nonlinearity of the actual wave,we can save the computer time by presetting the maximum wave height;welch algorithm is used to verify the validity of P-M spectrum as wave power spectrum.(2)The nonlinear dynamic response analysis of jack up platform under real working condition is carried out to determine the inertial load.First,on the basis of the model construction of structure?pile foundation and wave load,the modal analysis of the jack up platform is carried out.Through the analysis results,the rationality and effectiveness of the three pile foundation models of nonlinear spring pile foundation model relative to the fixed,reaming and linear springs are verified.Secondly,based on the constrained New Wave wave theory and nonlinear spring pile soil model,the nonlinear dynamic response of the platform is analyzed.By comparing the dynamic and quasi-static response analysis results,the dynamic magnification coefficient of the maximum deck displacement,the base shear and the overturning moment is calculated,thus the inertial load of the platform is determined.Compared with the random wave method,the effectiveness of the proposed method is verified.(3)Based on the inertial load determined by dynamic analysis,the nonlinear structural strength evaluation of jack up platform under the actual working condition is carried out.Different from the dynamic analysis model,a three-dimensional finite element model of the jack up platform is established when evaluating the static structure strength.In addition towind,wave and current load,the applied load also includes functional load,P-delta effect and inertia load.On this basis,the yield structure strength evaluation and buckling strength evaluation are carried out on the platform structure,and the evaluation results meet the requirements.