Experimental identification of finite cylindrical shell vibration modes.

Abstract

Acoustic scattering from a finite air-filled elastic cylindrical shell, immersed in water, is investigated. The shell is made of stainless steel and has a thickness to outer radius ratio of 17%. The considered dimensionless frequency range extends over 7 << k1a << 22 (k1: wave number in water, a: outer radius). Bistatic measurements are carried out to identify vibration modes related to the phase matching of the first guided wave, T0, propagating on the shell. Both transducers, the emitter and the receiver, are positioned at the same angular distance with regard to the normal axis of the shell. The emitter transducer is fixed at a given position. In order to identify circumferential modes of vibration, the receiver transducer is made to rotate in the azimuthal plane, normal to the shell axis. Results obtained are plotted in functions of dimensionless frequency and azimuthal angle. Vibration modes along the shell's length are identified by moving the receiver transducer parallel to the shell axis. In this case, results are plotted in functions of dimensionless frequency and axial wave number. The experimental investigation is corroborated by theoretical results obtained from approximate calculations for thick finite cylindrical shells [Scot F. Morse et al., J. Acoust. Soc. Am. 103, 785-794 (1998)]. The evolution of the mode position with respect to the incidence angle is discussed so as to clarify peak patterns in backscattered resonance spectra.