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Time frequency analysis of energy distribution for circumferential waves on cylindrical elastic shells

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In order to set up an automatic target recognition system for low frequency sonar, it is required to understand the mechanisms involved in acoustic scattering by simple elastic shapes. Within this scope, this paper investigates the energy distribution of cylindrical shell echoes in the time-frequency plane, when both the geometry (shell thickness) and thc mechanical characteristics (shear wave velocity, density) of the elastic material are varying. A large number of impulse responses are calculated using the classical modal decomposition formalism, and a systematic time-frequency analysis of shell echoes is performed via the Smoothed Pseudo Wigner-Ville Distribution. Symmetric (S0) and antisymmetric (A0) Lamb waves are first identified on some time-frequency images by comparing the group velocity dispersions estimated from both the time-frequency distribution and the Resonance Scattering Theory. It is then shown that, in the case of thin shells, the main energy contribution in the time-frequency plane is concentrated in a broad frequency range around the coincidence frequency that corresponds to the bifurcation of a0+ and a0 waves. The midfrequency enhancement of the energy is then confirmed by a simple wave propagation model for circumferential waves.
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Document Type: Research Article

Publication date: 1996-09-01

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  • Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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