title: Avalanche dynamics of granular materials under the slumping regime in a rotating drum as revealed by speckle visibility spectroscopy.
abstract: We used speckle visibility spectroscopy to measure the time-resolved dynamcis of avalanching down the inclined surface of a granular material in a half-full rotating drum operating in the slumping regime. The distribution of the avalanche period, t(d), rest time between them, t(r), and peak particle velocity fluctuation, δv(p)(2), are all normally distributed. While the distributions of the two times at the top and bottom of the free surface are very similar, the particle velocity fluctuation is greater at the bottom of the free surface than at the top. The rest time is observed to be inversely related to the drum speed. Combining this with the relation of t(r) and the difference of the upper and lower angle of repose for the granular material, Δθ, we find that the latter decreases linearly with increasing rotational speed. We also observe that t(d) increases in a linear fashion with the drum speed. Using the relation of t(r) and the distance that particles have to move during an avalanche, we further find that a new scaling relation of the mean number of avalanches required to traverse the free surface with drum speed. We find that the slumping frequency increases with the rotating speed before becoming constant in the slumping-to-rolling transition region. Finally, we find that the average peak of the fluctuation speed of the avalanche, δv(p)(2), increases linearly with the drum speed.
authors.affiliation: School of Optical-Electrical and Computer Engineering, Shanghai Key Lab of Modern Optical System, and Engineering Research Center of Optical Instrument and System, Ministry of Education, University of Shanghai for Science and Technology, Shanghai 200093, China.|School of Chemical Engineering, The University of Adelaide, SA, 5005, Australia.
authors.forename: H
authors.initials: H
authors.lastname: Yang
authors.affiliation: School of Optical-Electrical and Computer Engineering, Shanghai Key Lab of Modern Optical System, and Engineering Research Center of Optical Instrument and System, Ministry of Education, University of Shanghai for Science and Technology, Shanghai 200093, China.
authors.forename: R
authors.initials: R
authors.lastname: Li
authors.affiliation: Foundation department, Shanghai Medical Instrumentation College, Shanghai 200093, China.
authors.forename: P
authors.initials: P
authors.lastname: Kong
authors.affiliation: State Key Laboratory for Hydroscience and Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Q C
authors.initials: QC
authors.lastname: Sun
authors.affiliation: School of Chemical Engineering, The University of Adelaide, SA, 5005, Australia.|School of Science, Loughborough University, LE11 3TU, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Biggs
authors.affiliation: School of Chemical Engineering and Advanced Materials, Newcastle University, NE1 7RU, United Kingdom.
authors.forename: V
authors.initials: V
authors.lastname: Zivkovic
mesh_terms: D055875:Avalanches; D004867:Equipment Design; D005898:Glass / Q000737:chemistry; D007834:Lasers; D008962:Models, Theoretical; D016011:Normal Distribution; D052638:Particulate Matter / Q000737:chemistry; D012399:Rotation; D013057:Spectrum Analysis / Q000295:instrumentation; D013995:Time
chemical_list: D052638:Particulate Matter