Numerical simulation of towed cables

Abstract

A numerical method for the dynamic simulation of towed cables is presented. The cable is loaded by fluid drag, tension, gravity and buoyancy, including the effects of weights and floats. The development of a cable can be simulated as well as the separation of a cable under excessive load and the subsequent behavior of the broken parts. The system is constructed from a set of generic elements representing such items as cable or rope strands, knots (reference points on rope sections), kinks (sliding reference points on cable sections that change length), cable ends and winches. A mathematical graph organizes these elements in a general and flexible fashion: it allows construction of complex systems and permits structural redefinition during the simulation. The nodes of the graph coincide with the various reference points of the problem, at which physical parameters are lumped and to which sets of ordinary differential equations are associated that define the motions of the points. The links of the graph describe the physical connections between the nodes. Application of new methods for solving stiff, sparse systems of coupled ordinary differential equations enables efficient simulation of snap-loads and other severe events. Results are presented that compare quantitatively with laboratory measurements. A further example shows the behavior of a breaking cable that is qualitatively reasonable.