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Diffusion acoustique par des coques cylindriques limitées immergées. On des hélicoïdales: analyse des réponses temporelles et identification complète des résonances

Abstract : Acoustic pressure scattered by finite fluid loaded cylindrical shells, is experimentally and theoretically analyzed in Fourier spaces. Spectral and time domain signatures of such objects are interpreted in terms of resonance and propagation of surface waves. The scatterers are made of stainless steel, with inner over outer radii ratio equal to 0.83 and 0.97. They are excited under the far field conditions by broadband ultrasonic signals, for incidence angles comprised between 0° (normal incidence to the shell main axis) and 50°. Resonances present in backscattered spectral responses, associated to S0 an T0 helical waves, are identified. The associated vibration modes are experimentally determined by using two bistatic experimental arrangements. The first setup, in which the receiver transducer rotates in a plane normal to the shell axis, leads to the identification of circumferential mode (n); the second, rather original setup, in which the receiver moves parallel to the shell axis, yields the identification of axial modes (m). The results are in agreement with those obtained with a hybrid modal theoretical approach combining elasticity theory and Kirchhoff diffraction integral. This information (resonance frequency, n, m) makes possible the evaluation of the phase velocity and the propagation angle of the corresponding wave. The complete identification of target resonances is thus achieved (nature of the wave, n, m). Each resonance, expression of a finite length objet eigenmode selected by excitation conditions, is observed at a single frequency for a number of closely spaced incidence angles. A geometrical model depicting wave helical travel paths on the shell renders possible the analysis of time domain responses. Times at which echoes are observed, are related to the travel paths of the T0. The influence on backscattering of the shells' characteristic dimensions (length and diameter) is studied in this way. The geometrical approach also enables the consideration of effects linked to the presence of an internal plate bulkhead: the role of the A wave (interface wave) becomes prominent.
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https://tel.archives-ouvertes.fr/tel-00010047
Contributor : Lionel Haumesser <>
Submitted on : Tuesday, September 6, 2005 - 11:16:17 AM
Last modification on : Tuesday, February 5, 2019 - 11:41:16 AM
Long-term archiving on: : Friday, April 2, 2010 - 10:03:01 PM

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  • HAL Id : tel-00010047, version 1

Citation

Lionel Haumesser. Diffusion acoustique par des coques cylindriques limitées immergées. On des hélicoïdales: analyse des réponses temporelles et identification complète des résonances. Acoustique [physics.class-ph]. Université du Havre, 2001. Français. ⟨tel-00010047⟩

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