Nonlinear Dynamic Behavior And Dynamic Response Of Taut-wire Mooring System For Deep Waters With Damaged Synthetic Fiber Mooring Ropes

The design and analysis of mooring system are vital important issues in the deep water oil and gas exploitation of platforms. There are ma ny factors which lead to the different level of damage of synthetic fiber ropes in the engineering application of the new type mooring system such as the material properties, installation, mooring service, etc. Therefore, it is necessary to delve into the dynamic nonlinear properties of damaged synthetic fiber rope mooring lines in complicated ocean environment, especially the evolution of the dynamic stiffness. In this paper, the irretrievably damaged condition and dynamic nonlinear properties of synthetic fiber rope mooring lines in complicated ocean environment are presented. The literature view at home and abroad on these properties are summarized then, together with the prospect to the further research in order to supply significant reference for the experiment study on this special subject in our country.A specially designed experimental system which can exert cycling loading on mooring lines was used to perform experiment on the specimen of polyester and HMPE whose diameters ranged from 6mm to 8mm. After introducing scalar damage index parameter to account for damage, artificial, quantifiable damage was inflicted on rope specimen by cutting yarns to reduce the effective bearing area of rope. Then the influence of the damage index parameter, the mean load, strain amplitude and loading cycles on dynamic stiffness were studied in detail. Moreover, through analyzing these experimental data, a dynamic stiffness empirical expression that took account of these factors was proposed, which was based on the similarity criterion for the dynamic stiffness of damaged fiber ropes, derived from the dimensional analysis. Through analyzing the results from the empirical expression and experiment, we found it was proper. These cognitions can be served as a foundation for further experimental research into the behavior of the full- scale ropes with damage including more sophisticated condition.A full dynamic analysis of new taut-wire mooring system is conducted based on all of the undamaged, windward damaged mooring ropes and leeward damaged mooring ropes to illustrate the effect of the different pattern of damaged synthetic mooring ropes on the calculation of dynamic response. Finally the full dynamic results of the conditions are compared to supply reference for the domes tic engineering application of the damaged taut-wire mooring system.