Slow Acoustics Fluctuation In The Granular Medium.

Results of experimental research of nonlinear properties of the granular medium with fluid in the field of acoustics oscillations are considered. It is found that the acoustical respond of some separate granule of the medium is drastically changes in time under the pure tone excitation. Granular oscillation occurs essentially nonlinear rather under moderate amplitude elastic wave propagation when the granular acceleration is essentially less then gravity acceleration. Sound intensity fluctuations for the harmonic and subharmonic components are revealed in the records of up to 62 hours long. Viscous fluid suppresses fluctuations and makes the granular medium more linear for acoustical excitation. Data of the experiments are compared with the results of a simulation of sound wave propagation in granular medium with nonlinear contacts between the granules. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]