The Research Of Ultimate Strength To Key Structure Of Deepwater Semi-submersible Platforms

Semi-submersible platforms will not only endure complicated environment load, also faceaccidental disasters, accidental load and so on many problems in the service process. the event ofplatform structure’s damage or failure is unimaginable, therefore, the main measures to avoid theaccident of platform structure is no failure or damage, and ultimate strength assessment is to ensureenough strength reserve, it is the most effective method to guarantee the integrity of platform structureUltimate strength is an important indicator of the adaptability to changing environment ofsemi-submersible platforms. As corrosion damage and initial deformaton has significant effects on theultimate strength, Reasonable assessment for ultimate carrying capacity of the damaged platform underthe external load is helpful to carry out hull structure design and reduce accident losses.After studying the limit State of Semi-submersible platform, the critical structures of the offshoreplatform are determined under typical conditions; using Nonlinear Finite Element software Abaqus, theultimate strength analysis to variously key structures of the platform without defects is studied; theultimate strength for the key structures of offshore platform under corrosion damage is also studied; theinfluence of ultimate strength to the key structures on the offshore platform under initial deformaton isresearched. Main content and conclusions are as follows:(1)Analyze the key structures of the offshore platform under typical conditions, and determine thekey structure of the location, the principal stress state and its main failure mode.(2)The failure modes for the key structures of the platform were studied respectively, and theultimate bearing capacity under different failure modes is calculated in perfect condition, ultimatestrength value, stress distribution principle and deformation condition of key structures are obtainedunder different failure modes.(3)The residual ultimate bearing capacity of calculation process of the platform in view of materialcorrosion and influence is provided; based on the corrosion damage, the ultimate bearing capacity of thekey structures (Brace，Column, Pontoon) on the platform are calculated respectively, the evolution rulesfor the residual ultimate strength of the key structures on the platform in the whole life period areobtained, and the forecast formula of the residual ultimate strength for the key structures on the platformin the whole life period is provided..(4)The ultimate bearing capacity calculation method for the key structures containing initialdeformaton on the semi-submersible platform is studied. The linear eigenvalue buckling analysis for thebrace, column, pontoon body structures are carried out. And based on linear buckling analysis, bringing in the initial deformaton, further nonlinear post-buckling analysis is conducted. The ultimate strengths forthe brace, column and pontoon structure under the initial defect are also obtained..