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Effect Of Hydrodynamic Drag On The Stability Of A Cantilever Pipe Conveying Fluid


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G. L. Kuiper & A. V. Metrikine


When studying the stability of a vertically suspended, fully submerged pipe conveying water upwards, researchers found a contradiction between theoretical predictions and experiments. Experiments did not show any instability, while theory predicted instability at small fluid velocities. Recently, searching for a resolution of this contradiction, Païdoussis et al. postulated a new description of the boundary conditions at the free end of the pipe. With these boundary conditions, the pipe becomes unstable by divergence (stable focus to saddle bifurcation) at a higher fluid velocity, than predicted earlier and than was reached in the experiments so far. Thus, it might seem that the reason for the contradiction has been found. However, in this paper another explanation is given why the experiments should not have shown any instability. This explanation is based on a realistic description of hydrodynamic drag, based on experimental data available in the literature. Using this drag description, it is shown that the pipe becomes unstable by flutter (stable focus to unstable focus bifurcation) at a much higher fluid velocity than predicted by Païdoussis et al. Keywords: cantilever pipe, stability, hydrodynamic drag, fluid-structureinteraction, flexible cylinder. 1 Introduction In recent years different theories have been developed to predict the dynamic behaviour of submerged, cantilever pipes conveying fluid upward. It was first thought, that once all dissipation mechanisms are neglected, the cantilevered pipe loses stability at infinitesimally low fluid velocities (Païdoussis and Luu, [2]). However, this was in contrast with experiments, which did not show


cantilever pipe, stability, hydrodynamic drag, fluid-structureinteraction, flexible cylinder.