ABSTRACT:

To study the dynamics of cable during the installation of undersea communications systems a finite difference method centered in time and space is applied to the three dimensional equations of motion for the cable. The algorithm was originally developed for use in predicting the behavior of towed arrays, and has been extended here to allow addition of cable at the ship, and removal of cable at the sea floor. The results of the simulation are compared to results obtained during a full scale sea trial in which the positions of a set of transponders on the cable was tracked in the water column during deployment.

INTRODUCTION

Analysis of cable behavior prior to the installation of undersea communications cable is an important phase in the planning of a new cable system. At this time the analysis is carried out in a piecewise fashion. The bathymetry of the proposed route is studied, and a proper ship speed and payout rate to prevent suspension over sections of the seafloor is determined using the theory developed by Zajac (1957). This result can be used to determine vital installation parameters, such as cable tension, and correct ship speed and payout rate to avoid the creation of suspensions (Rhoden, 1974). To allow prediction of the cable configuration in the presents of shear currents, and with a tension controlled payout rate, Leonard and Karnoski (1990) have used a shooting method in which the static equilibrium equations are solved by direct integration. The touchdown point of the cable is assumed to move with a velocity and direction equal to the ship, and tension at the top of the cable is assumed to be comprised of a steady value and a term proportional to the square of the payout speed.

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