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Linear stability approach to predict lock-in and time sharing in vortex-induced vibrations

Abstract : In evaluating the service life of marine structures such as risers, one must assess their dynamic response to vortices excitation (vortex-induced vibrations or VIV). At lock-in, i.e. when the frequency of the shedding of vortices synchronizes with the natural frequency of the structure, the amplitude of vibration of the structure is of the order of its diameter. Sustained vibration of this amplitude causes material fatigue which leads with time to failures. Predicting the flow velocity range for which lock-in occurs is thus of importance. It is also important in cases of flexible structures to predict which mode of vibration will lock-in with the wake. The interest here is in predicting lock-in for rigid and flexible structures like tensioned beams using a linear wake oscillator model: here, lock-in is interpreted as a linear instability caused by the merging of the two natural frequencies of a dynamic system that includes two coupled oscillators, namely the wake and the structure. This instability is also referred as couple mode flutter. It is found that the linear wake oscillator model predicts lock-in range for both elastically supported rigid cylinder and for flexible structures subjected to uniform flows. In particular, the linear approach is able to predict transition from one lock-in mode to another for flexible structures (mode-switching). it is also capable of predicting when more than one mode can lock-in with the wake for a fixed velocity (time sharing).
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Contributor : Denis Roura <>
Submitted on : Monday, July 21, 2014 - 4:39:51 PM
Last modification on : Thursday, March 5, 2020 - 6:29:34 PM


  • HAL Id : hal-01026006, version 1



Remi Violette, Emmanuel de Langre, J. Szydlowski. Linear stability approach to predict lock-in and time sharing in vortex-induced vibrations. 9th International Conference on Flow-Induced Vibrations, Jun 2008, Prague, Czech Republic. pp.469-474. ⟨hal-01026006⟩



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