A new approach to the definition of self-damping for stranded cables

Aim of the paper is to propose a new approach for the determination of the so termed self-damping, or internal damping, of metallic cables. The formulation is developed starting from a recent mechanical model of a strand, from which the hysteretic bending behavior of stranded cables is derived. Each wire of the cable is individually modeled as an elastic curved thin rod. A kinematic model is defined to relate the axial strain and bending curvature of the strand to the generalized strains of the wire. The interaction among the wires belonging to adjacent layers is then studied by neglecting deformations of the contact surfaces and assuming a classic Amontons–Coulomb friction law. In the adopted strand mechanical model a function is derived, which defines the domain of admissible values of the wire axial force to prevent sliding. A simplified model of the cable hysteretic bending behavior is then derived from the cyclic response predicted with the adopted mechanical formulation of the strand, leading to a closed-form upper-bound estimate of the energy dissipated when the cable cross section is subjected to alternate bending. This expression is used as the starting block for the definition of an analytical equation giving an upper-bound estimate of the cable self-damping. The predictions of the proposed model are compared to available data resulting from experiments and empirical literature equations: the comparison is extended to a wide range of strands and parameters that characterize practically most of the configuration commonly used in overhead electrical lines

Self-similarity in Slightly Heated Annular Jet with Large Diameter Ratios

International audienc

Self-similarity in Slightly Heated Annular Jet with Large Diameter Ratios

International audienceThe study aims at furthering our understanding and quantifying the influence of coherent structures on small-scale turbulence and passive scalar mixing, in an annular jet configuration with large diameter ratios. This ’bluff-body’ geometry is close to that widely used in combustion for flame stabilization [1]. A passive contaminant is introduced in the flow, through a slight heating. We report the evolution along the jet axis of the following quantities: mean values of the longitudinal velocity and passive scalar ( U¯ and Θ¯ ), as well as the energy and scalar dissipation rates ( ε¯ and χ¯ ). It is shown that these statistics: decay as x−1 and x−4 , where x is the streamwise direction, similarly to the decay in the far-field of classical jets (CJ);unlike the CJ, they reach self-similarity faster, a behaviour that may be attributed to the presence of coherent structures