Response Analysis For Taut-mooring System Of Semi-Submersible Platform In Extreme Conditions

Semi-submersible platforms are widely used in the exploration of ocean oil and gas because they have a good capacity of working equipment,suit for a large scope of water and defend wind well.The semi-submersible platform in deep water usually takes taut-mooring system.In order to make sure the safety of workers and equipment,the response of that must be considerate.The study includes: First,set up a model of mooring line buried in sea-bed soil using Coupling-Euler-Lagrange method(CEL method)in ABAQUS.Dragging the mooring line to cut soil and calculate the “force-distance” relationship on dragging point.Second,set up a semisubmersible platform which works in 1000 m water depth with taut-mooring system in ANSYSAQWA.And taking the relationship between force and distance on dragging point which has been prepared before to represent the influence between mooring line and soil,calculate the response of platform and the tension of mooring cables when specific mooring line breaks under 100 return period extreme environmental condition.Third,stimulate dragging anchors by controlling the relationship between force and extension of cables,calculate the offset of platform and the tension of mooring cables.The results show that the tension of dragging end of the mooring lines increases smoothly at the beginning of dragging action,but sharply at the later period;And in both uniform or nonuniform soil,the tension of dragging end of the mooring lines increases with the increase of soil strength.The tension forces of the mooring lines and platform offsets change immediately when mooring line breaks,while when plate anchor fails those gradually change until they reach a new balance.When two lines fail,the offset of platform and tension of line may beyond the ultimate bearing capacity of plate anchor or the cable broken capacity,which will cause the whole taut mooring system failure.