Damping and Particle Mass in DEM Simulations under Gravity

Abstract

This paper presents a study on the input parameters used in the discrete-element simulations with gravity. Input parameters of the discrete-element method (DEM) include particle mass (density), damping, gravity constant, strain rate, and contact relationship. This paper focuses on particle mass and damping. The samples consisted of two kinds of ellipsoidal particles. The unit weight of the particles is constant. Samples are prepared by depositing particles under gravity. The final bulk densities of the samples are different for different damping and particle mass. The effect of the reduction of particle density is similar to that of the reduction of damping in sample preparation. For the samples, static equilibrium can be achieved with a damping ratio greater than 0.24%. When the damping ratio is less than 0.24%, some particles are oscillating. The oscillation cannot be reduced with further relaxation. Undrained simulations are carried out on these samples. Shear strength increases with the increase of damping as expected. Different undrained stress paths are found for simulations of loose samples with different damping. For simulations of loose samples with the same damping ratio, particle density affects the results slightly. However, the effect of damping and particle mass is negligible for dense samples. The ultimate shear strength of the granular material is not affected by either damping or particle mass.