Some considerations of combined effects of galloping and vortex resonance

Abstract Many towers have sectional shapes that are aerodynamically unstable to transverse disturbances in a wind. This type of instability can cause galloping oscillations, predictable by quasi-steady theory. However, the physical constants for towers cause the initial wind speed for galloping to lie close to, or even lower than, the vortex-resonance wind speed. As a result there are strong mutual effects of the two phenomena, and the quasi-steady theory is not obviously applicable. Nevertheless, preliminary experiments under two-dimensional smooth-flow conditions suggest that simple rules derived from a knowledge of the separate responses of a tower to galloping and vortex resonance may be useful for prediction of oscillatory behaviour under the mutual effects.