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Research of nonlinear interaction of acoustic shearwaves in bottom sediments induced by the parametric radiating array on the boundary surface

Abstract

Research of nonlinear interaction of acoustic shearwaves in bottom sediments induced by the parametric radiating array on the boundary surface

Dushenin Y. V.

Incoming article date: 25.12.2015

Effective application of parametric radiating arrays for detection of objects, buried in bottomsediments, are caused by their possibility to form directed radiation on low frequencies with small initial dimensions. Unlike water, bottom sediments are the environment in which both longitudinal and shift making speeds of acoustic fluctuationsdistribution are presented. Presences of several speed components in bottom sediments give the opportunity toparametric radiating array to generatethe acoustic waves of various types. In given paperthe results of theoretical and experimental researches of the field, created by the parametric radiating array in the multiphase environment «water – bottom sediments» at inclined falling on boundary surface under angles relative to critical are described. It is shown that the longitudinal pump waves, generated in water, and waves of differentialfrequency (DFW) in bottom sediments (BS) are transformed to corresponding shear waves. Besides, because of imaginary passive arrayon boundary surface, the generation of shearedDFWoccurs in BS. Researches were carried out in laboratory hydroacoustic tank. Clay and sand were used asa sample of BS. On the base of time marker the shear DFW in various typeof sediments were allocated. Using obtained theoretical model the basic characteristics of theparametric array in BSwere calculated and experimentally confirmed whileshear DFW excitation.On the results of theoretical and experimental researches, it is proved that transformation, excitation and generation of the shear waves formed by the passive array take placein BS. The results received during research give good coincidence between the theory and practice that illustrate the correctness of the model choice. Besides, experimental results on use of shearDFW in BSfor echo sounder mode are presented. Thus, given method can be used in parametric sonars for BS stratification TO and detection in them of the various alien objects.

Keywords: parametric array, nonlinear interaction, bottom sediments, shear wave of differential frequencies, critical angle