Stochastic Model for Energy Propagation in Disordered Granular Chains

Abstract

Energy transfer is one of the essentials of mechanical wave propagation (along with momentum transport). Here, it is studied in disordered one-dimensional model systems mimicking force-chains in real systems. The pre-stressed random masses (other types of disorder lead to qualitatively similar behavior) interact through (linearized) Hertzian repulsive forces, which allows solving the deterministic problem analytically. The main goal, a simpler, faster stochastic model for energy propagation, is presented in the second part, after the basic equations are re-visited and the phenomenology of pulse propagation in disordered granular chains is reviewed. First, the propagation of energy in space is studied. With increasing disorder (quantified by the standard deviation of the random mass distribution), the attenuation of pulsed signals increases, transiting from ballistic propagation (in ordered systems) towards diffusive-like characteristics, due to energy localization at the source. Second, the evolution of energy in time by transfer across wavenumbers is examined, using the standing wave initial conditions of all wavenumbers. Again, the decay of energy (both the rate and amount) increases with disorder, as well as with the wavenumber. The dispersive ballistic transport in ordered systems transits to low-pass filtering, due to disorder, where localization of energy occurs at the lowest masses in the chain. Instead of dealing with the too many degrees of freedom or only with the lowest of all the many eigenmodes of the system, we propose a stochastic master equation approach with reduced complexity, where all frequencies/energies are grouped into bands. The mean field stochastic model, the matrix of energy-transfer probabilities between bands, is calibrated from the deterministic analytical solutions by ensemble averaging various band-to-band transfer situations for short times, as well as considering the basis energy levels (decaying with the wavenumber increasing) that are not transferred. Finally, the propagation of energy in the wavenumber space at transient times validates the stochastic model, suggesting applications in wave analysis for non-destructive testing, underground resource exploration, etc.

Multi‐scale characterization of granular media by in situ laboratory X‐ray computed tomography

“…P-waves are compressional or longitudinal waves that oscillate the ground back and forth along the direction of wave travel, in much the same way that sound waves (which are also compressional) move air back and forth as the waves travel from the sound source to a sound receiver. In a longitudinal wave, the particle displacement is parallel to the direction of wave propagation [30,32,33,47,53].…”

“…Granular matter has a heterogeneous nature, this is expressed as force chains through the medium. These force chains spread the forces through the contact with another particle [53,54]. This causes that neighboring particles could have forces of different magnitudes and nonisotropic distributions of stress throughout the medium [2].…”

Sound characteristics of disordered granular disks: effects of contact damping

“…For a better understanding of the sound in granular media, theoretical models incorporating the rotational degrees of freedom in the microstructure are crucial [7], e.g., the model of one-dimensional granular chains [8,9]. In two or three dimensions, theoretical models of granular crystals have been extensively developed [7,[10][11][12][13].…”

A study of wave propagation and stiffness anisotropy in anisotropically loaded granular material-synthetic fiber binary systems

“…Binary granular materials including sand-fiber composites, display significant complexity in their behavior with competitive mechanisms to be encountered with respect to energy transport and dissipation as recent theoretical and experimental studies have shown [40][41][42]. This adds further difficulties in the constitutive modeling of these systems compared, for example, to the analysis of soil-planar block interactions.…”