Stability of Vertical Fluid-Conveying Pipes Having the Lower End Immersed in Fluid

This paper concerns a beam-type flutter of vertical pipes containing a flowing fluid and having the lower end immersed in fluid. The effect of surrounding fluid on motions of the pipe is assumed as a mass added to the immersed part of the pipe. The equivalent added mass is estimated using Morison's formula. The effects of the immersed length of the pipe on the critical flutter velocity are investigated. It is predicted theoretically that the lower end immersed in fluid may exert a considerable destabilizing effect, except in the case where the lower end is only slightly immersed in fluid and the mass ratio is as high as 0.75. Experiments with silicone-rubber tubes conveying water were conducted to check the theoretical predictions. It was confirmed that for sufficiently high flow velocities the tube was subject to violent flutter, and that the critical flutter velocity decreased with increasing immersed length of the lower end.