Upper‐Bound Prediction of Cable Damping under Cyclic Bending

Abstract

A theoretical formulation has been proposed for obtaining upper bounds to single‐layer helical strand damping under cyclic bending to a constant radius of curvature. The model employs an alternative interwire/interlayer friction formulation to the traditional rigid‐plastic Coulomb model: this, then, enables one to follow the no‐slip‐to‐full‐slip friction transition over the individual contact patches. Results are presented for cables in which the helical outer wires only touch the core and also for spiral strands with no core whose outer wires just touch each other in line contact. Parametric studies show that the traditional Coulomb friction model tends to grossly overestimate cable damping for large radii of curvature such as those found in connection with vortex shedding dynamic instabilities of, for example, overhead transmission lines and underwater cables where the maximum amplitude of vibration is of the order of one cable diameter. For small enough radii of curvature, however, the present model's predictions approach those based on the Coulomb rigid‐plastic model. It is found that cable damping may be increased by increasing the number of wires and/or decreasing the helix angle. However, for sufficiently large levels of radii of curvature and cable axial strain, the present theory suggests that for certain ranges of helix angle, increasing helix angle leads to increases in cable damping that can only be predicted with the newly proposed model, which takes no‐slip‐to‐full‐slip interwire friction interaction into account.