Interference of vortex-induced vibration and galloping: experiments and mathematical modelling

This paper deals with the phenomenon of interference between vortex-induced vibration and transverse galloping, which occurs in the case of low-damped rectangular cylinders with a side ratio comprised between about 0.75 and 3. The results of a wide experimental campaign carried out in the wind tunnel are discussed, focusing on the key role played by the mass-damping parameter (Scruton number) of the oscillating body. It was found that a high value of the Scruton number is required to decouple completely the ranges of excitation due to vortex-induced vibration and galloping, and for the quasi-steady theory to predict correctly the galloping critical wind speed. Moreover, the problem is analytically addressed through a nonlinear wake-oscillator model, which is able to reproduce several features of the complicated phenomenon, provided that a crucial parameter is correctly calibrated.