Nonlinear and Hysteretic Twisting Effects in Ocean Cable Laying

Abstract

Armored ocean cable unlays under the action of installation tensions and restraining moments applied by the ocean bottom and the ship’s bow sheave. The process of elongation and twist is nonlinear and hysteretic. This process has often been assumed linear and reversible. The equations describing the moment which is developed in laying cable on the ocean bottom are worked out, without assuming linearity and reversibility. These equations are applied to some cases likely to arise. For a typical armored coaxial cable laid in 3700-m (2000-fathoms) depth without bottom tension, a steady-state laying-up moment of 134 Nm (99 lbf. ft) is developed. For the reversible case, no moment is developed. If the bottom tension is increased from zero to 33,375N (7500 lbf) and then returned to zero, a peak moment of 198Nm (146 lbf. ft) is developed.