ACOUSTIC SCANNING OF TUBULAR CHANNELS WITH NARROW CRACKS
The dynamics of perturbations of pressure propagating in a pipe with a crack- shaped damaged zone is studied. The pipe is considered as a waveguide in which one-dimensional pressure waves propagate; dissipation due to viscous friction and thermal conductivity is taken into account in a thin layer of liquid or gas near the wall. A damaged section of a pipe is considered as a reflecting surface. The coefficients of reflection and transmission of a periodic pressure perturbation in a cracked section are obtained. The dynamics of the reflected and transmitted pressure perturbations in the crack are analyzed by dispersion relations depending on the geometric characteristics of the crack and pipe and on the properties of the fluid in the pipe. By the analysis of reflection coefficients and the propagation of harmonic waves propagating along the fluid in the tubular channel, the following parameters are defined: the critical value of the crack thickness ε* at which the acoustic resistance of the surrounding atmosphere is comparable with the hydraulic resistance and the critical value of the relative damage site S* at which the “echo” of the signal is the most informative.