Experiments and characterization of low-frequency oscillations in a granular column

TL;DR

This study investigates low-frequency oscillations in a confined vibrated granular bed, revealing their dependence on system parameters and their relation to inherent noise, through experiments and simulations.

Contribution

It provides a detailed characterization of the LFO in a granular Leidenfrost state, linking oscillation frequency to inertial and dissipative time scales.

Findings

LFO frequency is inversely proportional to inertial time scale.

LFO decorrelates with a decay time proportional to dissipative time scale.

LFO driven by inherent noise in the granular system.

Abstract

The behaviour of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters, and more specifically allows for a thorough characterisation of the low-frequency oscillation (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO frequency from the power spectral density of the centre of mass signal of the grains, varying the amplitude and frequency of the driving, the particle diameter and the number of layers in the system. We thus find that (i) the LFO frequency is inversely proportional to the fast inertial time scale and (ii) decorrelates with a typical decay time proportional to the slow dissipative time scale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles.