Partially fluidized shear granular flows: continuum theory and molecular dynamics simulations.

Area of Science:

• Physics
• Materials Science
• Computational Science

Background:

• Granular materials exhibit complex behaviors transitioning between solid and fluid states.
• Continuum theories aim to describe these transitions using macroscopic parameters.
• Order parameters are crucial for characterizing phase transitions in materials.

Purpose of the Study:

• To test and calibrate a continuum theory for partially fluidized shear granular flows.
• To define and validate an order parameter representing the static-to-flowing transition.
• To propose and verify a constitutive relation for granular shear stress.

Main Methods:

• Two-dimensional soft particle molecular dynamics simulations.
• Definition of an order parameter based on the fraction of static contacts.
• Development and verification of a constitutive relation splitting shear stress into fluid and solid parts.

Main Results:

• The continuum theory is successfully tested and calibrated against simulation data.
• The proposed order parameter accurately describes the transition between static and flowing granular regimes.
• The constitutive relation shows good agreement with kinetic theory for granular fluids, even in dense conditions.

Conclusions:

• The validated continuum theory provides a robust framework for understanding granular flow dynamics.
• The developed order parameter and constitutive relation offer predictive capabilities for granular material behavior.
• This work advances the modeling of granular flows under gravity and other external forces.