Study On Dynamic Stiffness Of Deepwater Mooring Line And Mooring Analysis

With the exploitation of offshore oil and gas moving gradually to the deep water, the new type taut-wire mooring system is being widely used as the alternative of the conventional catenary mooring system. The complicated mechanical properties of the mooring line are the key technical problems which need to be solved above all in the engineering application of the new type mooring system with synthetic fiber ropes. In this paper, the dynamic stiffness properties of synthetic fiber rope mooring lines in complicated ocean environment are presented.The research achievements of the domestic and overseas studies on dynamic stiffness properties of synthetic fiber ropes are summarized then, together with the prospect to the further research in order to supply significant reference for the numerical simulation and experiment study on this special subject in our country.Firstly, a viscoelastic and viscoplastic model is proposed to describe the stress-strain property of synthetic fiber mooring lines. The time dependent property and the evolution of the dynamic stiffness can be fully considered in the proposed model. A new method for parameter identification is proposed and the error analysis is carried out. Besides, the model is validated by comparison with the results of polyester ropes both under creep-recovery and sinusoidal load. Secondly, a mooring analysis model is presented based on catenory theory, in which the stress-strain constitutive model for viscoelastic and viscoplastic model of synthetic fiber ropes is introduced to carry out quasi-dynamic analysis. Finally, focused on a certain floating platform, in mooring anylysis, this paper compares the morphology, stress and dip angle distribution of the mooring lines between taut-wire mooring system and catenory mooring system. In the quasi-dynamic analysis of time-variation of platform horizontal load, the time domain response of stress and dip angle are detailed compared in each condition.