Suppression of structural galloping by applying a harmonic base excitation at certain frequencies

Galloping is an aeroelastic instability which can incite large-amplitude oscillations in lightly damped structures possessing a bluff frontal geometry. Such oscillations have been shown to occur in towers, power transmission cables, and suspension bridges. Since failure in such structures can be costly and catastrophic, there is a pressing demand to devise techniques to effectively suppress these oscillations. These involve adjusting the flow dynamics around the structure, implementing active control algorithms, and employing passive energy sinks. In this manuscript, we present an alternative approach based on subjecting the galloping structure to a high-frequency base excitation. It is shown that the application of the base excitation shifts the galloping speed to higher values, and that the shift can be further increased by increasing the mean square value of the high-frequency component of the response. This can be realized by either increasing the magnitude of the high-frequency excitation or by bringing the excitation frequency closer to one of the higher modal frequencies of the structure. The second option is more efficacious since it can produce the desired shift in the galloping speed without additional power requirements. The proposed methodology is evaluated through an experimental implementation on a galloping structure which consists of a cantilever beam fixed at one end and augmented with a square-sectioned bluff body at the free end. It is shown that the magnitude of the base acceleration required to achieve a unit shift in the galloping speed can be significantly reduced by bringing the excitation frequency closer to the second modal frequency of the system.