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Comparing flow thresholds and dynamics for oscillating and inclined granular layers.
S Aumaitre1, C Puls, J N McElwaine
1Physics Department, Haverford College, Haverford, Pennsylvania 19041, USA.
Summary
This study investigates granular flow in oscillating layers, revealing that flow thresholds differ and depend on measurement timing. Granular material exhibits complex, time-varying rheology and mobility patterns unlike static or avalanche models.
Area of Science:
- Physics
- Materials Science
- Fluid Dynamics
Background:
- Granular materials exhibit complex behaviors, including flow dynamics influenced by external forces.
- Understanding the onset and cessation of flow is crucial for predicting granular material behavior.
Purpose of the Study:
- To investigate the onset and dynamics of flow in shallow, horizontally oscillating granular layers.
- To analyze the influence of layer depth and imposed acceleration on granular flow.
- To compare the behavior of oscillating granular layers with inclined avalanches.
Main Methods:
- Measurements of flow velocity from top and side views within the container's frame of reference.
- Systematic variation of layer depth and imposed acceleration (Gamma).
- Analysis of flow profiles in relation to transverse and vertical coordinates.
Main Results:
- Flow start and stop thresholds are distinct and influenced by measurement protocols, with apparent thresholds increasing due to material reorganization.
- Root-mean-square (rms) velocity shows a sharper rise when initial excitation is excluded.
- Granular rheology varies dynamically within each cycle, with jamming occurring before zero inertial force.
- The mobile fraction of the cycle is significantly higher than predicted by static or avalanche models.
- Flow profiles are time-dependent and differ from those observed in avalanche flows.
Conclusions:
- The dynamics of oscillating granular layers are complex and deviate from static predictions and inclined avalanche behaviors.
- Measurement protocols significantly impact observed flow thresholds.
- Time-dependent rheology and flow profiles highlight the unique nature of oscillating granular systems.
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