Experimental analysis of acoustic scattering from lengthwise soldered cylindrical shells

Abstract

Through an experimental approach, this paper explores the acoustic wave scattering processes involved in the acoustic backscattering from air-filled submerged cylindrical shells having axial discontinuity. The discontinuity is caused by lengthwise soldering along the tubes in the course of manufacture from flat sheets, and is represented as an internal axial mass layer. The tubes are excited by a plane wave at normal incidence. In the time domain, different echoes on short pulse responses (echo wave forms), are identified by the arrival times and related wave type. This enables the localization of additional wave generating sites and scattering centers due to the solder. A number of detected echo series are thus identified. In the frequency domain analysis, the influence of supplementary echoes and that of inter-echo interferences on both backscattering and resonance spectra is presented. The influence of the angular position of the solder, relative to the direction of the incident sound wave, on the amplitudes of spectra, is analyzed. The key phenomena in this study are wave generation at the solder when it is directly insonified (prevalent over classical wave generations of considered waves) and the wave type conversions observed when propagating waves encounter obstacles in the shell, geometric or material discontinuities (in this case the solder). The wave types studied are the A wave (Scholte–Stoneley) and the S0 compressional wave, in the midfrequency region, ka=25–90, where k=ω/C1 is the wave number in water, C1 is the sound velocity in water and a the external radius of the tube. This analysis of the influence of discontinuities in the propagation medium on the acoustic scattering is carried out with a view to the investigation of scattering of assembled objects such as cylindrical shells with hemispherical endcaps.