A CABLE GALLOPING MODEL FOR THIN ICE ACCRETIONS

Cable galloping is a complex phenomenon of fluid-structure interaction . A two-dimensional quasi-static analysis for modelling this phenomeno n is successful in explaining galloping for a minimal aspect ratio of accretion shapes, but it fails to account for galloping occurring in t he presence of thinner ice accretions. This paper explores a new appro ach for the analysis of this phenomenon, by including in the quasi-sta tic analysis the effect of the torsional vibration on the Lift force. It adds to the lift forces generated by the change in angle of attack, those created by the cable rotation itself. Lift forces measured for steady-state rotation of a two-dimensional cylinder are used to relate lift to rotational speeds in the galloping model. The torsional vibra tion instability conditions are satisfied, even for thin ice accretion s, for a wide range of angles. Since a rotational motion once created is sufficient to generate lift forces independently of the eccentricit y of the ice shape, this approach shows that it is possible to simulat e galloping for thin ice accretions with the assumption of the vortex lock-in effect. This could explain the importance of the torsional vib rations in initiating cable galloping for thin ice accretions. (C) 199 8 Elsevier Science B.V.