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Description:
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A numerical scheme , known as CABLE3D , originally developed for the simulation of dynamics of steel chain -wire mooring lines is extended to allow for the large elongation in a mooring line , the dependence of the modulus on tension , and energy dissipation of a polyester rope under mean and cyclic loads . The modified CABLE3D is then integrated into a numerical package , known as COUPLE6D , for computing the interaction between a floating structure and its hybrid polyester mooring system . The Deepstar Spar is chosen in this study to represent the floating structure .
By considering large elongation in polyester ropes in numerical simulation , the static offset curve of a polyester mooring system is softer than that calculated under the assumption of small elongation . That is , about 10 % reduction in restoring force at the mean offset position of the Spar under the impact of 100 -year hurricane storm . The effects of the mean loads on the modulus of polyester ropes are much greater than those of the dynamic loads . Hence , the former is more important in the simulation of the response of floating structures . The energy dissipation in polyester ropes under cyclic loading does not play significant roles in the responses of the Spar and tensions in a polyester mooring system . The above findings , although observed based on the numerical simulation of a particular floating structure , namely Spar , may have implications to other floating offshore structures moored by a polyester mooring system .
Two systems are simulated in two different met -ocean conditions : hurricane and loop current condition . To study the properties of polyester , numerical simulation were conducted in three ways . Those are related to the modulus based on mean load , mean and dynamic loads , and structural damping respectively . Through the simulation , statistics of motions of the hull and tension in the mooring lines are compared with those of a conventional steel mooring system . |