Laboratory experiment and discrete-element-method simulation of granular-heap flows under vertical vibration

Area of Science:

• Physics of granular materials
• Fluid dynamics
• Nonlinear systems

Background:

• Granular flow dynamics under vibration are complex.
• Previous work established a nonlinear diffusion model for depth-averaged velocity.
• Understanding surface velocity and internal flow profiles is crucial.

Purpose of the Study:

• To investigate granular flow dynamics on a vertically vibrated pile.
• To validate and extend the nonlinear diffusion transport model.
• To characterize the shear band structure and velocity profiles within the pile.

Main Methods:

• Laboratory experiments using high-speed laser profilers.
• Particle-scale numerical simulations employing the discrete element method.
• Analysis of depth-averaged and surface velocities, as well as internal velocity profiles.

Main Results:

• A nonlinear diffusion transport model accurately describes the relation between surface velocity and slope.
• Numerical simulations reproduce experimental findings.
• Flow velocity decreases exponentially with depth, indicating a surface-localized shear band.
• Shear band thickness scales with pile height, not constant.

Conclusions:

• The nonlinear diffusion model is applicable to both depth-averaged and surface granular flow dynamics.
• The observed exponential velocity profile integrates consistently with the depth-averaged velocity predictions.
• Findings enhance the understanding of granular material behavior under vibration.