Diffusion acoustique vers l'avant d'objets élastiques immergés dans l'eau

Abstract : Forward acoustic scattering for solid spherical and LINE (limited cylinder bounded by hemispherical endcaps) objects immersed in water in bistatic configuration is the topic of this study. First, bistatic configuration analysis is carried out for a spherical object whose analytical theory has already been developped. Experimental and theoretical angular diagrams show, for differents frequencies, a peak of strong amplitude located in the shadow area. After the temporal analysis for a solid sphere in the shadow area, two important echoes revealing at least two different kind of waves are isolated. Then, the waves mainly responsible for these echoes are then identified comparing experimental results and theretical calculations. These are the Franz wave F0 and the whispering gallery wave l=2. Their propagation velocities on the object are calculated experimentally. Considering a solid LINE excited axially, on its spherical part, it is interesting to note that the physical mechanisms responsible for the wave generation are the same than for a solid sphere. It is then possible to find for a axially excited solid LINE the same kind of waves than for a solid sphere. Others waves are then identified (mainly caused by parasite difraction and by the cylinder/hemispherical discontinuity of the LINE). At last, the caracterization of the LINE as an acoustic target by the mean of a numerical simulation is performed, first with the target strenght standard, and then with the Rsn criterion. This last number allow us to assess the resonating contributions of the object and then to establish a map of resonance contributions.
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David Soubsol. Diffusion acoustique vers l'avant d'objets élastiques immergés dans l'eau. Acoustique [physics.class-ph]. Normandie Université, 2018. Français. ⟨NNT : 2018NORMLH17⟩. ⟨tel-01947382⟩

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