Behavior of first guided wave on finite cylindrical shells of various lengths: experimental investigation

Acoustic backscattering from elastic cylindrical shells of finite lengths, immersed in water, is investigated. These objects, characterized by the ratio of length over diameter (L/2a = 9.76, 4.88, 2.44, a: outer radius), are excited by an obliquely incident plane acoustic wave. In the three cases studied here, the radii ratio b/a (b: inner radius) is fixed at 0.97. The investigated dimensionless frequency range extends over 10 k1a < or = 50 (k1 : wave number in water). The first guided wave, T0, is of particular interest here. The influence of the shell's length on the backscattered pressure is experimentally observed in the time-angle and frequency-angle representations. In support of this experimental study, a time-domain representation is used by extending a theoretical model that provides a geometrical description of the helical propagation of the surface waves around the shell [Bao, J. Acoust. Soc. Am. 94, 1461-1466 (1993)]. Theoretical results on cylindrical shells considered as infinitely long, with identical characteristics, are compared with both experimental representations.