This paper presents two simple and efficient frequency domain methods for the calculation of the dynamic tension of Single and multiple segment mooring lines The first method described (MODEL 1) IS an analytical approach based on the catenary equations and an estimate of the line drag resistance To Include inertia loads, drag loads and a dynamic description of the mooring line motion, a dynamic system based on a Single degree of freedom (SDOF) IS developed (MODEL 2) Both methods are extensively tested versus the non-linear finite element computer program RIFLEX, and the correspondance With respect to dynamic tension amplitudes IS very good for a wide range of line configurations, water depths and excitation levels MODEL 2 IS Implemented In the MARINTEK positioning computation program MIMOSA 2
Catenary mooring systems are extensively used for stationing of floating structures at sea Up to now, the basic design method IS still the quasi-static approach, I e the cable force IS determined by the terminal point position only High frequency forces and Imposed first order motions may, however, cause large dynamic tensions In the mooring lines, ref [2], [4] and [7] When moving Into deeper water, the relative Importance of the dynamic mooring line tension Increases The magnitude of the dynamic hne tension IS dependent upon several parameters Elastic, axial stiffness, line pretension and line weight are key parameters In assessing the dynamic load effect Advanced non-linear finite element computation programs are time consuming, which restricts the number of design cases to be considered One 15 an analytical method (MODEL 1) based on the catenary equations and an estimate of the drag resistance of the line The other describes a dynamic system based on a Single degree of freedom (MODEL 2).
