Study On The Ultimate Strength Of Semi-submersible Platform Structures

To meet the needs of deep-sea oil exploration,semi-submersible platforms have gradually become the major tools for the development of offshore oil and gas due to their obvious advantages.To accurately evaluate the strength reserve of the platform structure,ensure the safety and reliability of the structure and improve the utilization rate of the platform materials,it is necessary to study the ultimate strength of the platform structure.In this paper,starting from the stiffened plate structure,the ultimate strength nonlinear finite element technique was studied.The accuracy of the numerical method was verified by experiments.Based on this,the further research of local parts of the target platform and the ultimate strength assessment of the whole platform were carried out.The main research contents are as follows:(1)The nonlinear finite element analysis technology of the ultimate strength of stiffened plates was studied.The sensitivity analysis of the ultimate strength of the stiffened plate under various influencing factors was carried out by using the nonlinear finite element method,and the ultimate strength analysis method of the stiffened plate was formed.(2)The research on ultimate strength test of stiffened plates was carried out.The test device and the test program were designed,and the ultimate strength test of stiffened plate was completed.The ultimate strength of the stiffened panels under axial pressure with clamped boundary condition at the end of the panel and restrained boundary condition at the transverse frames was obtained.Finally,the nonlinear finite element analysis method was validated through the comparison of the numerical prediction and the test results.(3)Based on the quasi-static method,the ultimate strength of the local structure of the platform was studied.The typical stress state of each structure under different load conditions were obtained.Then the ultimate bearing capacity and failure mode of the local structures were calculated under typical load condition.(4)Based on quasi-static method,the ultimate bearing capacity of the whole platform was analyzed.First,a three-dimensional non-linear finite element model was developed,and then the ultimate strength of the target platform under transverse load condition,longitudinal shear condition,torsion condition and coupling load condition and its behavior after collapse were analyzed.In the end,combined with DNV rules,the ultimate strength evaluation method was derived and established and applied to the target platform.