Effects of Coupled Extensional-Torsional Oscillations in Wire Rope During Ocean Salvage and Construction Operations

It is well established, and intuitively clear from the geometry of a wire rope, that a tensile load produces not only an extension but also a rotation of the rope (or a torque if both ends of the rope are prevented from rotating). This property of a wire rope leads, in a dynamic situation, to coupling of the extensional and rotational waves propagating through the rope. Classically, this coupling has been neglected, and only extensional waves treated, when analyzing the dynamic behavior of wire ropes used as lifting lines. Here, the effects of including the coupled oscillations in the dynamic analysis of lifting lines are considered, and the results are compared to those generated by the classical technique. Significant differences in the predicted dynamic response of the lifting line are found. A comparison of the predictions with experimental data also shows the importance of considering coupled extensional-torsional oscillations for obtaining an accurate description of lifting line dynamics.