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Vortex-induced vibrations of flexible structures and energy harvesting

25 mars 2013

Vortex-induced vibrations of flexible structures and energy harvesting

Clément Grouthier, LadhyX, Ecole Polytechnique, 91128 Palaiseau, France

Lundi 15 Avril à 10 h 30 - Amphithéâtre Nougaro

Résumé :

Vortex-induced vibrations (VIV) are self-sustained oscillations of an immersed bluff body originating in a strong coupling between the structure’s dynamics and its induced fluctuating wake.
This coupling may lead to a synchronization of the solid vibrations and vortex shedding frequencies, a phenomenon known as lock-in, resulting in large amplitude oscillations. When a long flexible structure is placed transverse to a flow, large amplitudes may occur over a wide range of flow velocities because of the successive synchronizations of the structure’s vibration modes with the shedding frequency. VIV of flexible structures, like cables, consequently appear to be a good mechanism
for extracting energy out of a transverse flow.
In this presentation, the ideal case of a periodic tensioned cable is first investigated using a reduced-order model. An optimal harvesting configuration is derived and explained. The reached efficiency is significant, justifying further studies on a more realistic system.
Energy harvesting from the VIV of a finite hanging cable using a single energy extractor is then analyzed. The VIV of such a device, where tension varies along the structure, is first characterized both experimentally and theoretically without any energy extraction. The effect of a harvesting
boundary condition on the dynamics of the hanging cable is finally investigated, allowing the definition of a high efficiency region of the phase space of the harvesting properties.

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