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Vortex-induced vibrations of a long flexible cylinder in shear flow

Bourguet, Rémi and Karniadakis, George E. and Triantafyllou, Michael S. Vortex-induced vibrations of a long flexible cylinder in shear flow. (2011) Journal of Fluid Mechanics, 677. 342-382. ISSN 0022-1120

(Document in English)

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Official URL: http://dx.doi.org/10.1017/jfm.2011.90


We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D =200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

Item Type:Article
Additional Information:Thanks to Cambridge University Press editor. The original PDF of the article can be found at Journal of Fluid Mechanics website : http://journals.cambridge.org/action/displayJournal?jid=FLM
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > Brown University (USA)
Other partners > Massachusetts Institute of Technology - MIT (USA)
Deposited On:14 Nov 2013 10:57

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