Abstract
We investigate the avalanches of spherical and non-spherical granular particles inside half-filled rotating drums. The time series of the center of gravity of the particle assemblies are obtained via image analysis and their single-sided amplitude (SSA) spectra are analyzed. The spectra features of this new indicator turn out to be characteristic for the avalanches, in terms of the existence of peaks in the low-frequency range and the decay rate of high frequency components. The SSA spectrum has a peak for the packings of non-spherical particles but not for the spherical particles. The high frequency part is characterized by a power law decay 1/ f a (a > 0) . A 1/ f -decay is found only for the spherical particles. For the packings of cornered particles, the exponents significantly deviate from a = 1. As 1/ f spectra are often associated with self-organized criticality and therefore a scale invariance of the dynamics, we may conclude that there is no scale-invariant structure for granular avalanches. Considering the small number of particles and the regularity of convex particle shapes being used, the spectral features revealed in this study could be utilized for validating particle simulations.
Highlights
IntroductionWe show that the spectral features of this indicator can capture the characteristics of avalanches with di↵erent par-
We show that the spectral features of this indicator can capture the characteristics of avalanches with di↵erent par-There exists a vast literature on granular avalanches due to ticle shapes
We focus on a novel indicator, the time series of the height of the projected center of gravity, instead of conventional slope angles
Summary
We show that the spectral features of this indicator can capture the characteristics of avalanches with di↵erent par-. Two drums were used to ensure the number of particles are large enough for statistical measurement: a large drum with inner radius of r = 96 [mm] and a small one with r = 71.5 [mm] The depth of both drums was fixed to 65 [mm], about 4 polyhedral particles. Depends on the drum dimensions and rotation speed, the granular avalanches can be discrete or continuous [6, 7]. To admit discrete avalanches of polyhedral particles, we kept the rotation speed ⌦ relatively slow, as ⇡/6 ± 0.01, ⇡/4 ± 0.01 and ⇡/3 ± 0.01 [rad/s] (or 5±0.1, 7.5±0.1, 10±0.1 [rpm] respectively). For su ciently large rotation speeds, the dynamics is dominated by the rotation of the drum and the avalanches become continuous even for polyhedral particles. For each case (combination of particle shape, drum size and rotation speed), four experiments have been conducted
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