The Dynamics of Slack Marine Cables

Abstract

Examples of the uses of slack cables in marine and offshore applications include deepwater moorings and the guy lines of towers and platforms. A brief summary is given of some of the important aspects of the linear theory for the vibration of horizontal and inclined slack cables. Then the important differences between the two cases are pointed out through the use of analytical and computational examples. These examples use typical methods which have been developed in recent years for predicting the dynamics of slack cables with and without arrays of attached discrete masses.

Free vibration of complex cable/mass systems: theory and experiment

“…Consider next the in-plane response problem defined by the co-ordinates u 1 and u 2 and governed by the coupled equations (11) and (12). Use of the separable solutions u 1 (s, t) = v 1 (s) e jvt and u 2 (s, t) = v 2 (s) e jvt in equations (11) and (12) leads to the associated eigenvalue problem…”

“…The linear response of cable/mass systems is the subject of several recent studies [6][7][8][9][10][11], which are distinguished by their use of particular modelling assumptions and solution methods. The simplest model [6,7] is that of a taut string/mass system which is readily analyzed in closed form using transfer matrix methods.…”

“…For arbitrarily supported cables or cables with lower static tension (large curvature), the equations governing linear response require numerical solution. Numerical solutions for free vibration have been evaluated using Stodola's method and by finite elements [10,11], with elements developed by references [12,13]. As reported in references [10,11], both numerical methods become unwieldy as the number of masses and the modal order become large, as may arise in hydrophone array applications.…”

“…Numerical solutions for free vibration have been evaluated using Stodola's method and by finite elements [10,11], with elements developed by references [12,13]. As reported in references [10,11], both numerical methods become unwieldy as the number of masses and the modal order become large, as may arise in hydrophone array applications. For example, suspensions with 380 attached masses and modes of order 100 and higher are considered in reference [6].…”

“…For example, suspensions with 380 attached masses and modes of order 100 and higher are considered in reference [6]. Consequently, attention is focused in references [10,11] on relatively low order vibration modes (order 10 or less) and small numbers of attached masses (six or less). The higher order modes, however, might also contribute significantly to the response of very long suspensions which have high modal densities.…”