Modelling the interaction of VIV and galloping for rectangular cylinders

Abstract

Several bluff bodies, such as rectangular cylinders with moderate side ratio, in particular conditions of mass and damping of the mechanical system can experience the interaction of vortex-induced vibration (VIV) and galloping, giving rise to an instability with peculiar features.Two analytical models are available in literature to simulate this phenomenon and they were tested so far only in the case of a square cylinder.Both models rely on the linear superposition of the unsteady forces producing vortex-induced vibration, obtained through nonlinear wake-oscillator models, and the quasi-steady forces that are responsible for galloping.These models are reviewed here and they are tested in the case of a rectangular 3:2 cylinder, which showed a strong proclivity to VIV-galloping interference and for which the authors carried out a large number of experimental tests.An extensive sensitivity study on the parameters appearing in the equations of the two models was carried out to better understand their actual behavior and their potentialities.Despite the theoretical limits, these models are able to reproduce some interesting features of the complex phenomenon of interaction observed in the wind tunnel tests.In particular, Tamura and Shimada's model seems to be able to reproduce the nearly linear increase of the oscillation amplitude for wind speeds higher than the Krmn-vortex resonance velocity, if a key parameter in the equations is suitably set.Therefore, a future effort to further explore and improve this model is doubtless worth.