Intruder dynamics in a frictional granular fluid: A molecular dynamics study

Area of Science:

• Physics
• Granular Dynamics
• Fluid Mechanics

Background:

• Understanding granular materials is crucial for industrial processes.
• The dynamics of intruders in granular media are complex and depend on particle interactions.
• Fluidized granular systems offer unique properties for material transport and processing.

Purpose of the Study:

• To investigate the steady-state velocity of an intruder in a 3D fluidized granular medium under an external force.
• To analyze the relationship between force and velocity (F-V_{s}) and its dependence on granular volume fraction.
• To characterize the intruder's motion, including its diffusive behavior.

Main Methods:

• Simulating a 3D granular system with translational and rotational degrees of freedom for intruder and grains.
• Employing solid friction as the primary energy dissipation mechanism.
• Maintaining fluidization via random perturbations of grain velocities.
• Applying a constant external force to the intruder and measuring its steady-state velocity.

Main Results:

• The force-velocity relationship (F-V_{s}) was determined for various volume fractions.
• Mobility, inversely proportional to viscosity, diverges at the jamming volume fraction.
• For small forces, intruder velocity scales linearly with force (V_{s}∼F).
• For large forces, velocity scales with the square root of force (V_{s}∼F^{1/2}).
• The intruder exhibits diffusive motion perpendicular to the applied force.

Conclusions:

• The study provides insights into the rheology of granular materials.
• The observed force-velocity scaling and diffusive motion are key characteristics of intruder dynamics.
• Results have implications for the design and optimization of industrial processes involving granular matter.