Research On Fatigue Life Of Jack-up Platform Leg

Work environment of Jack-up platform is extremely badly, which often cause huge economic losses when security issues appear, so it is necessary to research on fatigue life of the jack-up platform leg, and it is also cannot be ignored in the overall design. The Super M2 jack-up platform as the research object, combining the theory of wave and relevant environmental load formula on the static strength analysis; Then, the platform leg tube node position are analyzed under the action of axial force of the stress distribution around the weld and its geometric parameters on the stress sensitivity; Finally, the fatigue life of the key platform legs are analyzed based on the two types of fatigue theory. The specific research content is as follows:(1) The Super M2 jack-up platform is the research object in the paper. And the paper discusses the paper studies related to fatigue theory and theory of environmental load, finite element model of platform was established by reasonable simplification, the spring elements are adopted to simulate the platform and the connection relationship between pile legs, through the definition of quality point on way to simulate the platform the weight distribution of the gravitational field, in addition, considering the complexity of the pile-boots connected with soil, using Abaqus in some linear elastic model for processing, so as to improve the accuracy of the simulation analysis of jack-up platform.(2) Through setting the reasonable environment variable, using the five order stokes wave theory and Morision formula, and considering the dynamic pressure and hydrostatic pressure wave caused by the buoyancy effect, the analysis and calculation the jack-up platform under preloading self-storage and storm conditions of stress distribution on the basis of CCS specification and intensity, the results conform to the strength requirement.(3) With regard to weak place platform leg tube node location, analyzes the place under the action of axial force of the stress distribution around the weld; Then combining the theory of orthogonal test, the paper analyzes the pipe node on the impact of geometric parameters on the stress sensitivity.(4) Using the method of spectrum fatigue life analysis was carried out on the platform residual life of key point, first of all, using stokes fifth- order wave theory to analysis and calculation with different wave direction Angle and wave frequency under typical node hot spot stress transfer function, coupled with the south China sea waves scatter diagram and fatigue theory, the completion of various typical node leg fatigue strength evaluation. The fatigue life of leg is 41.3 years, which is near the water surface, which is the splash zone of pile legs.(5) Through the numerical simulation analysis was carried out on the crack tip, obtained the distribution of stress field and displacement field near the crack. Based on ABS design specifications, using fracture mechanics to analysis fatigue life of the offshore platform pile legs dangerous point, finally obtain the service life of the leg is 33.2 years, to meet the requirements of the platform service life. Compared with the S-N curve of fatigue design calculation method, the calculation method of crack extension takes into account the welding defects existing in the structure itself and the initial crack, and thus makes the calculation of fatigue life is shorter, more conservative.