Dynamic response analysis of offshore cable structures under wave forces

本文提出了一种海洋结构缆索在潮流和波浪力作用下的动力响应分析方法。本文采用作者以前建立的三节点曲线有限元，导出了索杆在流体力作用下的运动方程。对与海洋电缆连接的桁架构件、刚架构件和浮体也进行了有限元分析，并编制了相应的计算程序。完成的程序提供三个主要功能，即，(i)三维大变形静力学，（ii）特征值分析和（iii）动力响应时程分析。此外，时程分析的数值结果可以在自动过程中以图形方式显示，这使得容易读取计算结果。通过大量算例验证了程序的实用性，并对数值解的精度和非线性迭代的收敛性进行了充分的检验。为了使程序更好地使用，对程序进行了进一步的改进，并通过建立实际海洋结构物的拉索模型进行了数值计算。本文对静潮流作用下斜拉索的大变形和时变波浪力作用下斜拉索的动力响应进行了数值模拟，得到了海洋结构物斜拉索和系泊拉索的基本特性。

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.