The dynamics of a turret-moored FPSO with 12 catenary chain-steel wire-chain mooring lines are studied to investigate the influence of the hull/mooring coupled system from both linear and nonlinear stiffness of steel wire. The two simulated results are compared with experimental statistics, it indicated that the results using nonlinear stiffness are slightly larger than using linear stiffness and closer when compared with the experimental statistics. Then it illustrates that the polynomial approximation of nonlinearity for steel wire is applicable. The difference between linear and nonlinear results of steel wire is not apparent due to steel wire doesn’t belong to the viscoelastic material. This paper also researches the motion of FPSO with taut chain-polyester-chain mooring lines because polyester rope has viscoelastic properties. The results are unstable when using lower and upper linear stiffness in the time-domain simulation. But the dynamic response of FPSO is good by nonlinear stiffness. Thus, the nonlinear elastic method should be used in engineering works to decrease the damaged risk of the structure.

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