Dynamic response analysis of offshore cable structures under wave forces

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A method of dynamic response analysis of marine structural cables, which are used for the purpose of mooring, staying or guying the offshore structures under the action of tidal current and/or wave forces, is presented. Equations of motion of cable members under the action of fluid forces are derived by employing three node curvilinear finite elements which were formulated by the authors in the past. Truss members, rigid frame members and floating bodies, which are to be connected with marine cables, are also analyzed in the form of finite element formulation.Computer program based on the above theory is developed for practical use. The completed program provides three main functions, i.e., (i) three dimensional statics with large deformation, (ii) Eigenvalue analysis and (iii) time history analysis of dynamic response. Further, the numerical results of time history analysis can be displayed graphically in an automatic process, which makes it easy to read the results of computation. The accuracy of numerical solutions and convergence of nonlinear iteration were fully checked and the practicability of the program was cofirmed after many case studies. Further improvement is intended for the better usage of the program.Numerical examples are shown by setting up cable models which are supposed to be ones utilized in practical offshore structures. Numerical results obtained in this research as to large deformation of cables under the action of statical tidal current and dynamic response of cables subject to time-varying wave forces show fundamental behavior of staying or mooring cables of offshore structures.