Study On Application Of Lump-Mass Method To Calculating Snap Mooring Tension In The Deep Sea

The motion of the cable will be slag and taut alternatively, the tension in the cable might be large under periodic loads. So the sudden change of the restoring force caused by the un-continuity of the cable restoring stiffness will lead to the nonlinear problem of the whole mooring system. For the mooring system of deep water platform, when the load excess a fixed value, the taut-slag phenomenon of the mooring system will be aggravated. The thesis is focused on analysis of snap tension in cables of the Spar platform and the dynamic response of mooring system by lump-mass method, which is referable in design and fabrication of Spar platform.The three-dimensional lump-mass model is used here for analysing cable tension. In this model, the cable is replaced by a discretised model consisting of many point masses and massless elastic segments. All forces along the cable are assumed to be concentrated at the mass points. The equations of the three dimensional motion of a marine cable are sloved considering the boundary conditions of both ends of the cable. In different excitation amplitude and frequency, consider the effect of the weight of the cable, buoyancy, drag and intertia of the fluid to analysis the dynamic tension of the cable. Analyze the dynamic response of the cable and predict the snap loading of the cables operating in alternating taut-slack conditions by motion of the platform. Analysis the dynamic of Jip Spar operating in 1018m water depth, whose cable subject to excitation.It is found that the particles in the lower part of cable have a low motion amplitude when the whole cable is motivated by its top end motion. When the excitation becomes severe, as the minimum tension approaches zero, that is the cable starts to operate in alternating taut-slack conditions, the maximum tension increases significantly.