Time step criterions for nonlinear dense packed granular materials in time-driven method simulations

• We improve the previous criterions for time step selected in DEM (Discrete-element methods) simulations.
• This improvement is useful for simulation of densely packed granular materials by using DEM.
• Some simulations are carried out to valid this new criterion.

Discrete-element method (DEM) is a powerful tool for simulations of granular materials. As one branch of DEM,time-driven method (TDM) is suitable for the materials in dense phase. Time step is an important parameter in TDM simulations, which decides the CPU time and the computational accuracy. When a granular system under gravity is deep and nonlinear stress–strain relationship is used to model the particle–particle interaction, some current time step models are not applicable anymore, because the nature frequency of a particle is affected by its boundary conditions. To amend this shortage, a new time step criterion is presented in this paper, which involves the effect from the depth of the system due to gravity. Between this new criterion and that based on Rayleigh time, the smaller one should be the upper limitation of time step in TDM simulations.

Time step is an important parameter in TDM simulations. A new criterion for time step is presented in this paper, which involves the effect from the depth of the system due to gravity. This figure shows the convergence of using different time steps for simulating a disturbance propagating in a 1-D particle column. The blue lines are based on this new criterion and the red one is based on Rayleigh time.Figure optionsDownload as PowerPoint slide