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[FAQ]

The timestep is inversely proportional to the square root of the critical stiffness. Therefore, stiffer particles (e.g. rigid spheres) require smaller timesteps. In order to increase your timestep and speed up the calculation, you should consider the other way around, with softer particles. This can be done by reducing the particle’s Young Modulus or by applying the so-called numerical softening factor. It is a global reduction parameter that affects all stiffnesses. For guidance, it is recommend to go to Help > Manuals and reading the following sections: Offline User Manual: 1.5.2. Best Practices for Faster Processing 3.3.1.2. About Physics Parameters – numerical softening factor DEM Technical Manual: 5.2 Timestep calculations. Please bear in mind that the stiffness also affects particle overlaps, so setting those values too small may lead to simulation instability, and inaccurate results, since the force calculations during collision are based on the overlap. It is part of the Discrete Element Method to have particle overlap. The particles are rigid and do not suffer deformation. The overlap can be minimized but it still occurs. The higher the stiffness, the lower the overlap. However, this also leads to longer calculations, as mentioned in the previous reply. In short, there is a trade-off between calculation time and overlap. Thus, faster simulations can be obtained by using higher timesteps, which usually result in larger overlaps (but note that the particles are still modeled as rigid). Regarding friction between particles, this can be done in Materials Interaction > Particles – Particles and set the static and dynamic coefficients. They are considered in tangential force calculations and are part of DEM calculations. For faster simulation, the following article is recommended: https://support.esss.co/hc/en-us/articles/4415637577236 Keywords: Rocky, DEM, calculation, faster, time, deformation, non-spherical particles