engleski

An improved stiffness model for polyester mooring lines

The stiffness model of highly extensible polyester mooring lines is studied. Mooring lines are considered within coupled dynamic model of a moored fl oating object. In more detail, deepwater mooring with taut polyester mooring lines is observed. In this case mooring line is modelled as an extensible cable without bending and torsional stiffness. Movements are assumed to be three-dimensional, so it is necessary to examine large displacement model. In longitudinal strain calculation the material of the mooring line is considered as nonlinear. A large elongation value is examined within the stiffness model. Inertial forces of the mooring line are also considered. Hydrodynamic loads due to surrounding fl uid are taken into account with the Morison equation. Due to nonlinear properties of mooring lines calculations have to be done in time domain. On these assumptions, derivation of a mooring line fi nite element is presented for static and dynamic analysis. A fl oating object is modelled as a rigid body with six degrees of freedom and with small displacements assumption. Hydrodynamic coeffi cients are calculated in a specifi ed frequency domain ; therefore, mapping from the frequency to the time domain is necessary. Comparison between the improved model developed in this paper and current equivalent model is done. A simple mooring line that can be analytically described was the base for comparison. The improved model achieved better agreement with the analytical result.

coupled model ; dynamic response ; fi nite element method ; large elongation value ; mooring ; time domain ; polyester rope

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