Analysis of the acoustic scattering at variable incidences from an extra thin cylindrical shell bounded by hemispherical endcaps

Through an experimental approach, in this paper we investigate the acoustic wave scattering processes involved in the acoustic backscattering at varia ble incidences from an air-filled submerged cylindrical shell with hemisphe rical endcaps. Given the 1% shell thickness and the explored low frequency domain, the wave types studied are the circumferential or helical S-0 wave and the helical T-0 wave only. Between the axial (in the direction of the m ain axis of the object) and the normal incidences (normal to the main axis) , two distinct angular zones can be observed depending on hemispherical or cylindrical excitation. In these zones, after a pressure wave excitation, d ifferent series of echoes on the echo wave forms are identified by their ar rival times and related wave types. From results in the time domain and tho se obtained in the frequency domain, each acoustic response from the target corresponding to the two zones of excitation is compared with the acoustic response of canonical objects (spherical shell for axial excitation and tu be for normal excitation). This analysis of the acoustic response from the target at various incidences, highlights the influence of both the endcaps and the finite length for a cylindrical shell on scattering. The study is i ntended to make a contribution to the knowledge of the identification of su ch geometrically complex objects. (C) 2000 Acoustical Society of America.