SCATTERING OF AN OBLIQUELY INCIDENT PLANE ACOUSTIC-WAVE BY A CIRCULARCYLINDRICAL-SHELL - EXPERIMENTAL RESULTS

To explain the mechanisms of the acoustic scattering of an obliquely i ncident plane wave by a circular cylindrical shell, it is necessary to know the acoustic propagation in a similar shell of infinite length. Theoretical studies have been published which have shown that these me chanisms are related to the propagation of the guided waves with circu mferential modes in the axial direction of the shell. These guided wav es can be characterized by a thickness mode (Lamb waves) and by a circ umferential mode. This last mode is made up by the phase matching of t wo helical waves that entwine the shell in the two directions. In this paper, the results and the analysis of measurements of the acoustic p ressure scattered by an infinitely long circular cylindrical shell are presented. This paper uses and verifies the theoretical results publi shed in Acustica/Acta-Acustica by N. Veksler et al. [1] (''Scattering of an obliquely incident plane acoustic wave by a circular cylindrical shell. Results of computations''). The measurements are carried out f or an aluminium shell with relative thickness h = 1/10 (h = 1 - b/a, b : inner radius, a: outer radius) immersed in water. The range of the n ondimensional frequency is 5 < x = ka < 150 (k: wave number of the aco ustic wave in water). The plane wave is incident from an oblique angle . The various incidence angles are between 0 degrees and 46 degrees. I t is shown that with an increasing of the angle of incidence every hel ical wave undergoes qualitative and quantitative changes, especially s o near the cut-off frequencies.