Modal dynamics of twisted cables

Abstract

Understanding the dynamic behavior of twisted cables is of great interest because of the wide increase in their uses in various applications. In this study, an efficient numerical procedure is presented to generate the primary elastic stiffness coefficients using elasticity theory where the three-dimensional cable is reduced to a one-dimensional model. The cables are then subjected to axial loads in three-dimensional space. The model gives stiffness coefficients that are in good agreement with seven known analytical models for angles below the maximum lay angle of the cable. The free vibration behavior of these cables is then analyzed using a finite element model, where the ends of the sagged cable are fixed at the same level. The natural frequencies and modal shapes are also found using extensive experimental tests. The frequency spectrum and the six translations and rotations are analyzed and compared with existing analytical solutions and commercial finite element results. Three practical examples are used to demonstrate the validity and applicability of the finite element and experimental models for both twisted and untwisted cables. The results show that cable elasticity, twist coupling and initial sag play a considerable role in the modal coupling behavior. The results also suggest that some simplified models may not be adequate to fully understand the dynamic behavior of twisted cables.