The characterization of the presence of bubbles in industrial fluid circuits may be extremely important for many safety issuses. It is well known that the acoustic properties of liquids can be drastically modified by a small amount of gaz content in the liquid. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. The variation of the gas fraction may then induce some variations in the vibroacoustic behavior of the pipe transporting the liquid. Analysis of the pipe vibrations can then help in the monitoring of the bubble presence. In such a context, the aim of this study is to show how the the presence of bubbles in the liquid could affect the resonance frequencies of the pipe. A numerical vibroacoustical model has been developed to predict the vibroacoustical behavior of a stiffened cylindrical shell filled with a bubbly liquid exhibiting low frequency resonances. The model, experimentally verified with a well-characterized bubbly liquid, is then used to analyse the frequency shifts of the shell resonances in function of the bubble.
Keywords : pipe, heavy fluid, numerical modelling, circumferential admittance approach, cylindrical shell, resonance frequency, void fraction