| The semi-submersible platform is made up of several vertical columns and horizontal pontoons that support topside. The waterline area of columns is small. Semi-submersible platform is widely used because of its special characteristics: the great performance of stability, wider ranger of operational water depth, the strong ability of drilling and multi-functioned.The semi-submersible platform is positioned by mooring system in severe environment for long term, the mooring system is normally made up of eight spreading mooring lines. Sometimes the platform is positioned by dynamic positioning, however high initial equipment cost and higher operating cost due to increased fuel consumption, maintenance and specially trained personnel of DP may encourage the use of mooring system. The mooring system should not only maintain the floating unit within both operating and survival offset ranges, but also avoid collision with the vessels in vicinity, drilling rigs and pipelines. Therefore it is important to choose the type of mooring system and analyze the dynamic response of floating system.In this paper, to investigate the type choice and dynamic response for mooring system of a semi-submersible platform, which is proposed to work in the South China Sea, nonlinear time-domain coupling numerical method is adopted.This paper mainly investigates the following items: 1,Coupled effect of floating system The dynamic response of floating system is analyzed in frequency domain and time domain according to potential flow theory and FEM, consider the stiffness, inertial, damping and current effect of mooring line.2,Parameter investigation of mooring line in dynamic analysis The dynamic response of catenary mooring system correlates with the parameter of mooring line, angle between the mooring lines. Reasonable choice of these parameters will control the response of mooring system.3,Numerical simulation of catenary mooring and taut mooring in deep waterComparative analysis of dynamic response and efficiency between catenary mooring and taut mooring is carried out. The response of different mooring systems with the change of drag force is studied. In deepwater mooring the taut mooring has more advantages.4,The dynamic response of mooring system in different water depths The design of mooring system has more challenges with the exploration of ocean oil extend to deep water. The reasonable water depth range of different mooring system is evaluated in the paper.Studies on mooring system type selection, coupled analysis method and dynamic response of mooring systems in different water depths are carried out in this dissertation. The results are possessed of important value for preliminary design of deepwater mooring. |
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