On the hysteresis of wire cables in Stockbridge dampers

Abstract

Stockbridge dampers are used e.g. for reducing wind-excited oscillations due to vortex shedding in conductors of overhead lines. In these dampers, mechanical energy is dissipated in wire cables (“damper cables”). The damping mechanism is due to statical hysteresis resulting from Coulomb (dry) friction between the individual wires of the cable undergoing bending deformation. Systems with statical hysteresis can be modelled by means of Jenkin elements arranged in parallel, consisting of linear springs and Coulomb friction elements. The damper cable is a continuous system and damping takes place throughout the whole length of the cable, so that distributed Jenkin elements are used. The local mechanical properties of the wire cable are identified experimentally in the time domain. In particular, the moment–curvature relation is determined experimentally at every location of the wire cable subjected to dynamic flexural deformations. Using such a model for the damper cables, the equations of motion can be formulated for a Stockbridge damper, and discretization of the damper cable leads to a system of non-linear ordinary differential equations. In order to test this dynamical model of a Stockbridge damper we compute impedance curves and compare them to experimental results.