Page 213 - Fluid-Structure Interactions Slender Structure and Axial Flow (Volume 1)

PIPES CONVEYING FLUID: LINEAR DYNAMICS I 195

It is found that in the case of > stability is lost by divergence - as found by
Benjamin for + = 0 - no matter what the value of +. In the case of B < i, however,
stability can be lost either by divergence of by flutter, depending on +. Typical results
are shown in Figure 3.83, together with experiments. It is not clear from the text in Bohn
& Herrmann (1974b) whether the theoretical results have been computed with the full
theoretical model, i.e. taking into account kl and kz and also the damping at the joints
(ignored here).
In the experiments, the joints were made of ball bearings and light brackets, attached as
a ‘backing’ to the pipe system, while the flow was conducted from the upper to the lower
tube by a latex-tubing connector. Great care had to be exercised in eliminating, to the
extent possible, small eccentricities and the effect of a permanent bow in the latex tubing,
as well as controlling and measuring the stiffening of this tubing with increasing internal
pressure. Nevertheless, agreement between theory and experiment in Figure 3.83 is good,
notably demonstrating the existence of a critical value of ~, separating the domains of
flutter and divergence. One unusual feature of the results in Figure 3.83 is that, apparently,
divergence at a higher flow velocity than flutter materializes; unfortunately, this is not
discussed by Bohn & Herrmann.