Research On Structural Response And Local Structural Optimization Of A Deep-water Semi-submersible Platform

The reserves of the oil and gas resources in the land become less and less due to the massive extraction.The exploitation of offshore petroleum gas has become the main strategic resource of competition in the world.As lots of offshore oils and gases are stored in deep or ultra-deep seas,the development of marine equipment adapting to deep seas or ultra-deep seas has become popular.Deep-water semi-submersible drilling platform,which has excellent performances,has developed the mainstream equipment for the exploitation of deep-sea oil and gas.In case the accident of platform happens,not only inestimable loss of lives and property but also serious environmental pollution due to the leakage of oil and gas will be caused.To ensure the semi-submersible drilling platform having sufficient structural strength and fatigue reliability is the key technology to its long-term safe and reliable operation.In addition,the semisubmersible platform structure inevitably has several sudden changes in stiffness.To optimize the local structure of transformation region plays an important role in the safety and reliability of the structure,which is the focus and hotspot of current domestic and foreign research.In this paper,the deepwater semi-submersible drilling platform operating in the South China Sea is taken as the research object.The hydrodynamic analysis,structural response analysis,local structural optimization and spectrum fatigue analysis of the hotspot are considered and discussed.The main research works are summarized as follows.(1)Various design wave methods for calculating wave loads of deep-water semi-submersible platform are investigated.The process of evaluating structural strength and fatigue life of platform based on SESAM software is summarized.(2)The hydrodynamic analysis and wave load forecasting of the target platform are completed,and the design wave parameters are obtained by long-term prediction design wave method.The global structural response of the platform is analyzed with other design loads.The global stress distribution of the platform is relatively uniform,but there is also obvious local stress concentration.(3)Three local structural optimization schemes are proposed on the basis of the initial model for the outer connecting area between the column and the superstructure.The local fine mesh finite element analysis of various design schemes is carried out by using the sub-model method,and more accurate stress distribution results are obtained.(4)On the basis of global strength analysis and local strength analysis,55 fatigue hotspots were selected for three local optimization schemes.The fatigue strength of hotspots was analyzed by spectral analysis method,and their respective fatigue life were predicted.At last,the sensitivity of fatigue parameters was analyzed for some hotspots.