Small motions of the mooring line with buoys around its static configuration are simulated by time domain analysis, based on the collocation method. Also, the effect of the position and the number of the submerged buoys on the static and dynamic characteristics of the cable-buoy system IS investigated. Four different cases are considered and the pretensions given at the top of the cable remain the same in all cases. First, two very small artificial buoys are attached to the inclined cable in order to establish the validity of the theory and numerical schemes, second, one buoy is put in the middle of the cable length, third, one buoy is placed in two thirds of the cable length from the bottom, fourth, two buoys are added to the cable m one third and two thirds of the cable, respectively. There was an increase in the holding force of the cable-buoy system due to the submerged intermediate buoys and, therefore, It is possible to decrease the diameter of the cable by adding the buoys to the mooring line. Also, there was an substantial increase in the maximum dynamic tensions and, therefore, attention should be paid when designing a cable-buoy system for a particular purpose.
A time domain simulation of a cable subjected to nonlinear drag forces has been done by Bliek (1984) and Burgess (1985). Bliek used the natural modes of the cable as the set of orthogonal functions, and Burgess used sine functions. Burgess found in his study some advantages of the sine functions over the natural modes of the cable Both used Galerkin" s method, rather than the collocation method used in this paper. Mighore and McReynolds (1981 and 1982) studied the dynamic effects of paying out and reeling to the cable system using the collocation method.
