Structure And Fatigue Analysis Of Semi-submersible Communication Platform

As the natural gas resources, oil and mineral resources in the deep water are continuously mining, meanwhile, the island dispute and south sea issue is increasingly serious, developing the marine environment monitoring technology in the deep water has strategic significance. The new semi-submersible offshore communication platform is required in order to investigate the marine environment. As the semi-submersible offshore platform works in worse sea states, fatigue fracture is easy to occur when suffering the cyclic loading for a long time. Therefore, conducting structure strength and fatigue analysis for the semi-submersible offshore communications platform is very important.The structure design and hydrodynamic analysis. The preliminary design and detailed design of three different kinds of structure form were finished based on CCS rules<Offshore platform classification specifications>. Meanwhile, the wet surface and structural models were built by the ’Geni E Module’ in SESAM, the hydrodynamic performance analysis of the three different kinds of structure form were carried out by the ’Hydro D Module’ in SESAM based on the three dimensional potential flow theory. Finally, comparing the added mass, damping factor, motion response, the first order wave exciting force and sectional load, the advantages and disadvantages of the three kinds of offshore platform were discussed.The strength analysis of the offshore platform. Firstly, based on design wave approach and CCS<Offshore platform classification specifications>, the wave load of the semi-submersible communications platform was forecasted. Secondly, the amplitude of design wave was worked out based on response function peak value of the offshore platform sectional load and long term response of wave load, meanwhile, the static analysis of the platform structure was done by the ’Sestra Module’ in SESAM, gaining the equivalent stress contour-plot and deformation contour-plot of the solar deck, column, equipment cabin up deck, equipment cabin coaming, ballast tank coaming and the baseplate. Finally, the allowable stress of combined load cases was determined and the strength of each platform structure has been done based on linear elastic intensity theory.The fatigue analysis of the semi-submersible offshore communication platform. Firstly, identifying the critical areas for fatigue analysis, and finding the coordinates of the nodes and the element number within these areas according to the strength results of the offshore platform, and the substructure model for fatigue analysis is then set up. Secondly, the boundary conditions of the substructure model is determined by the ’Submod Module’ in SESAM software. Then, the fatigue analysis for the semi-submersible offshore communications platform is carried out by the ’Stofat Module’ in SESAM software based on the method of the spectrum analysis. Finally, the sensitive analysis is carried out for the key factors such as S-N curve, wave spectrum and wave scatter diagram.