Sound scattering and attenuation in aqueous suspensions of sand : comparison of theory and experiment

Sheng, Jinyu (1986) Sound scattering and attenuation in aqueous suspensions of sand : comparison of theory and experiment. Masters thesis, Memorial University of Newfoundland.

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Abstract

Theoretical estimates of scattered acoustic intensity and attenuation coefficient are compared with all available data for aqueous suspensions of sand, for both bistatic and monostatic systems. This appears to be the first comparison of theoretical and experimental attenuation coefficients in suspensions of mineral grains at wavelengths comparable to or less than the scatterer circumference, and it is shown that as far as the existing data are concerned, this comparison is crucial. Three theoretical models are used, in which the scatterer is assumed to be either elastic, or completely rigid, or both rigid and immovable. The rigid movable model with a Gaussian size distribution provides the best fit to the data. The failure of the elastic model indicates that resonance excitation does not occur, probably because natural sand grains are irregularly shaped and inhomogeneous in composition. The rigid immovable model fits the data the least well, indicating that the inertia of the particles is important. Approximate expressions for the form factor and attenuation coefficient have been constructed, based on the so-called high-pass model introduced by Johnson [1977]. The high-pass model provides a fit to the data which is as good as the rigid movable case. Multiple scattering is discussed briefly, and approximate estimates of the correction for multiple scattering are made. In addition, the geometry of scattering and attenuation in suspensions for bistatic systems is analyzed for the narrow beam case, and approximate analytical expressions for the detected volume and scattered intensity are obtained.

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