Dynamic stability of an immersed fluid-conveying tube

摘要

This paper considers the dynamic stability of a flexible tube subjected to both an internal fluid flow and an external ambient fluid. Different formulations for the derivation of the fluid-dynamic forces are considered. For the internal fluid flow, plug flow and potential flow models are considered. For the external fluid, a constant local added mass model and a potential flow model are considered. Timoshenko beam theory is used for the description of the dynamics of the tube. Comparisons of quantitative results obtained with the different flow models are made. Special attention is paid to the influence of material damping and external (viscous) damping on the stability boundary, and some analytical results are presented. When the tube is immersed in a fluid, the internal fluid flow is subjected to a velocity gradient at the downstream end of the tube, due to the formation of a turbulent jet. The influence of this effect on the stability boundary is discussed. The energetics of the fluid-structure coupling are discussed in detail. For the internal flow, energy expressions are derived for both the plug flow and the potential flow model, and for the external fluid, derived for both the constant local added mass model and the potential flow model. It is shown that the energy terms derived by these different methods converge as the slenderness of the tube is increased. Finally, in the last part of the paper, results from an experimental study of the problem are presented. (au) 23 refs.