| There is abundant energy in ocean, especially oil and gas. Offshore platform and floating oil production structure have become two main methods to exploit ocean oil and gas. To ensure normal work in the ocean long-time and the safety in serious condition for semi-submersible multi-body floating mooring system under flexible connection, it is essential to study coupled motions with mooring multi-body floating system. The study and relevant conclusions are as followed:Firstly, it detailed on the contents of the model test, the test simulation and programmes. Also, it analyzed the effects of the mooring system and the distribution of fender and cable force with different conditions.Secondly, it applied the finite element method in hydrodynamic analysis of mooring system. This paper used the large finite element calculation software MOSES carrying on imitating mooring system with different wave directions.Thirdly, motion cycle of platform is 5.966s when the ship is full load, it is about 1.7% smaller than the motion cycle which is 6.067s when the ship is empty in the mooring system. It demonstrates that the bigger loaded drafts are, the greater rigidity of the system becomes. The fender force is 182.7t and 199.5t when the ship is empty or full load, increasing 9.2%. At the same time, the maximum displacement (Sway) of platform is 1.28m and 1.59m, increasing 24.2%. It indicates that the influence is small to fender force and the bigger loaded drafts are, the greater displacement becomes. The wave direction of 90°is the most disadvantaged mooring conditions. When the wave less than 2m,6s, the maximum displacement (Sway) of platform will not surpass 1.59m, the average amplitude of fender force will not exceed 67.7t and the maximal cable force is 171.2t less than breaking force 311.04t.The research result has some guidance meaning to design for semi-submersible multi-body floating mooring system. At the same time, it provides useful reference value for the actual engineering.
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