The density relaxation phenomenon is modeled using both Monte Carlo and discrete element simulations to investigate the effects of regular taps applied to a vessel having a planar floor filled with monodisperse spheres. Results suggest the existence of a critical tap intensity which produces a maximum bulk solids fraction. We find that the mechanism responsible for the relaxation phenomenon is an evolving ordered packing structure propagating upwards from the plane floor.
The manner in which signals propagate through dense granular systems in both space and time is not well understood. In order to probe this process, we carry out discrete element simulations of the system response to excitations where we control the driving frequency and wavelength independently. Fourier analysis shows that properties of the signal depend strongly on the space-time scales of the perturbation. The features of the response provide a test bed for models that predict statistical and continuum space-time properties. We illustrate this connection between microscale physics and macroscale behavior by comparing the system response to a simple elastic model with damping.
In order to probe the process of energy propagation through dense granular systems, we carry out discrete element simulations of the system response to excitations where we control the driving frequency and wavelength independently. The soft-disk simulations are carried out in two spatial dimensions, and include the effects of energy loss due to inelasticity of collisions, frictional damping, rotations, and polydispersity. Our ability to control independently spatial and temporal properties of the imposed perturbations allows us to extract significant new information. In particular, Fourier analysis of the system response shows that properties of the propagating signal strongly depend on the spatial scales introduced by the perturbation itself. Then, we consider a sheared granular system and discuss how shearing influences the nature of the propagating signal. The simulations are carried out using realistic system sizes and material properties, allowing for direct experimental verification of the obtained results.
The density relaxation phenomenon is modeled using both Monte Carlo and discrete element simulations to investigate the effects of regular taps applied to a vessel having a planar floor filled with monodisperse spheres. Results suggest the existence of a critical tap intensity which produces a maximum bulk solids fraction. We find that the mechanism responsible for the relaxation phenomenon is an evolving quasi-ordered packing structure propagating upwards from the plane floor.
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