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A Delicate State of Instability

oliver oreilly's picture

Dear Colleague,

It is well known that the straight configuration of a flexible vertical riser conveying fluid destabilizes in a divergence-type buckling instability once the velocity of the transporting fluid exceeds a critical speed. To compute the critical velocity, the dynamics of small amplitude perturbations to the straight configuration are computed. If the perturbations are sufficiently small and the transport speed is above a critical value, then the instability of the vertical riser can be detected.

 As discussed in our recent paper that was published in the Journal of Fluids and Structures: 

https://doi.org/10.1016/j.jfluidstructs.2019.102811

 if the perturbations are of sufficiently large amplitude, then the straight configuration evolves into a catenary shape and the riser stabilizes. This stability persists regardless of the transport speed of the fluid. The explanation of this phenomenon relies on a numerical examination of the in-plane and out-of-plane bending modes of the riser.

 

Comments

Frederick Gosselin's picture

Very interesting finding! I guess the message is that we should look beyond the straight pipe configuration. I looked at the more exotic problem of a hose suspended to an aerostat. I guess that your finding about the horizontal offset would apply here too.

https://www.sciencedirect.com/science/article/pii/S0889974613002478

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