Molecular dynamics simulations reveal how varying gravity affects flow rates in soft particle systems, suggesting new insights into material behavior.
We present the results of LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) Molecular Dynamics simulations of quasi-2D gravity-driven flows of ∼30 000 soft uniform spheres through a vertical silo. We vary the gravitational field (G), elastic modulus of the particles (E), and silo outlet diameter (D) and measure the effects on mass flow rate and microscale metrics such as granular temperature through the different systems. We introduce a dimensionless parameter Γ, which corresponds to the ratio of E and G, corresponding to the “squishiness” of the system. We find that the flow rate is underpredicted by the Beverloo equation for small outlet sizes and vice versa for large outlets. We find that this divergence is best correlated with granular temperature. There is also a clear dependence on Γ: the transition from under to overprediction happens at lower granular temperatures for squishier systems.
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Tadlock et al. (2026) studied this question.
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