Resonances of Scholte‐Stoneley waves propagating on cylindrical shells at oblique incidence

Abstract

This paper deals with the oblique scattering of an incident monochromatic plane wave by a circular cylindrical shell immersed in water. The propagation direction of the incident wave makes an angle α with a normal to the longitudinal axis of the shell. Experiments are carried out over the broad reduced frequency range 0 < ka > 35, involving the method of isolation of resonances, for two targets: (1) an air‐filled aluminum shell with b/a = 0.94 (b = inner radius of the shell: a = outer radius of the shell) whose length is infinite with regard to the incident acoustic beam cross section; and (2) the same shell of the finite length: In this case, the incident beam insonifies the entire target. With α varying from 0° to 35°, the backscattered spectra—obtained from the signals scattered by both targets—exhibit wide minima which are due to the reemission of Scholte‐Stoneley waves. Resonance peaks are located at the same frequencies on the corresponding resonance spectra. The frequency position of these peaks slowly increases with the increasing values of α. Follow‐up of these frequencies is easy, especially beyond the shear critical angle, which confirms that these resonances are related to external waves. These new experimental results are similar to theoretical ones obtained for an infinite pipe by Kaplunov et al.