New Type Deep-Water Mooring System And Numerical Analytical Techniques

With the offshore exploitation of oil and gas moving gradually to the deep water, the conventional catenary mooring system encounters problems that cannot be solved successfully both in economics and techniques. The taut-wire mooring system is a new type of mooring system which is applicable and effective in the deep or ultra-deep water, hence it faces a wide engineering application. The taut-wire mooring system has several advantages over the catenary mooring system in deep water: higher strength, smaller mooring radius, and lower manufacturing cost. This mooring system is constituted of synthetic fiber cables and anchored with Suction Piles or Vertically Loaded Anchors, and now it becomes the most important mooring type in deep water.The cables will be slack when the cables are not subject to axial tension due to the excessive motions of platform. In addition, synthetic cables have non-linear property: dynamic axial stiffness is dependent upon mean load, load amplitude and load period under cyclic loading. The study of these two characteristics is the key of analyzing the dynamic response of mooring system.In this paper, static equilibrium method is established to calculate tension and coordinates of steel cables toward the conventional catenary mooring system. In the work of the taut-wire mooring numerical calculation is based on MSC.Marc software, subroutine is used to exchange the slack and taut states of cables, and iteration method is used to calculate dynamic axial stiffness of fiber cables. The responses of motion and tension are computed, and the influences of damping and cyclic loading frequency are investigated. So the works of this paper have established a foundation of study the mooring system in deep water for the future.