The Viscoelastic Properties Of Synthetic Fiber Mooring Ropes And Its Impact On The Responses Of The Taut-wire Mooring System For Deep Water

With the exploitation of offshore oil and gas moving gradually to the deep water,the floating offshore platform is more widely used.So it’s more important for the study of positioning technology.The taut-wire mooring system is being widely used for many reasons.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.The dynamic stiffness property is one of the complicated mechanical properties which is a big challenge for the study of taut-wire mooring system.Besides,the study of the viscoelastic and viscoplastic model is also important.In this paper,the dynamic stiffness properties and the viscoelastic and viscoplastic model of synthetic fiber rope mooring lines in complicated ocean environment are presented to provide reperence for researchers.There are no numerical studies about dynamic stiffness which inlude the mean load,strain amplitude,cyclic times and the damage degree.The dynamic stiffness of mooring lines changes as a result of their complicated viscous-elastic and viscous-plastic properties and the possible damage resulting from installation,mooring service,etc.And what’s more the dynamic stiffness evolution of mooring lines further affects the dynamic response of the mooring system.Therefore,it’s necessary to delve into the nonlinear dynamic properties of damaged synthetic fiber ropes used as mooring lines.In this paper,the commercial finite element software ABAQUS was used to create a finite element model for a Spar platform with polyester mooring lines in 1020 m water depth.The tension history of mooring lines and the displacement histories of the platform are calculated.These results are of great value to the safe operation of taut-wire mooring systems.Finally,a viscoelastic and viscoplastic model is intrduced to describe the stress-strain property of synthetic fiber mooring lines.Then programs are wrote respectively in Fortran and ABAQUS which are proved effective.It not only expanded the material of the finite element software,but also laid a solid foundation for the numerical analysis of Taut-wire mooring system.