Vibrations of a Cantilever Pipe Aspirating Fluid

Abstract

Dynamics of pipes conveying fluid represents quite an old problem. The first references to the empirical observations are dated 1885 [1]. The first published results of study of the dynamics of pipes conveying fluid belong to Bourrières and dated 1939 [1]. Most of the studies related to this topic are devoted to the case of pipe discharging fluid [2] while the case of the pipe aspirating fluid received less attention [1]. The interest to this topic is basically dictated by industrial needs. In particular, pipes aspirating fluid are planned to be used in the offshore industry being an integral part of the cooling system of gas-liquefying floating platforms. Early experiments conducted in the past did not show any instability that has been predicted theoretically until Kuiper et al carried out an experiment that demonstrated that the pipe can be unstable [1,3]. However, no explanation has been found so far as to the particular features of the observed instability, namely for the alternation between a nearly periodic orbital motion and a small noise-like vibration near the equilibrium. Also, it remained unclear why for two similar sets of the experiments carried out with the time delay of about one month, the amplitude of orbital motion was quite different (~0.25 and ~1.5 pipe diameters, respectively). None of the existing theories is capable to predict the alternating motion. Thus, one still needs to answer the following questions: what is the physical origin of the observed dynamics? What could cause such a difference in the amplitude of the orbital motion in two identical experiments? This report presents an attempt to answer these questions.