Discrete Element Method contact force parameter impact for particle-level interactions in agitated mills

This work analyses the sensitivity of Discrete Element Method (DEM) simulations to contact model parameter values, considering both particle–particle and particle-geometry interactions, and the impact on system response for stirred mills. Determining the correct pairwise parameters in a DEM model remains a non-trivial undertaking. This difficulty is in part due to complex relationships between the parameters and system response; often the parameters themselves are correlated. Differing process regimes may also draw different levels of influence from the contact parameters, e.g. the coefficient of restitution may be deemed insignificant in friction-driven flows, but significant for other regimes. In this study, process settings (mill speed and mass fill) as well as contact model parameters are varied to infer the change in system response. A sensitivity analysis at three levels (empirical, component analysis on simplified derivatives, and considering full derivatives) is presented. It is found that the response of a fully packed system showed little variance with contact parameter values, especially when translational motion is the focus. Furthermore, particle-geometry terms have a greater impact than the particle–particle equivalents. Translational motion is dominated by the coefficient of restitution and rotational motion by the rolling friction coefficient. The corollary is that any parameter estimation should account for the anticipated process conditions, and thus a DEM study should consider sensitivity analysis as a key step of the parameter estimation process. This ensures that variance in contact models is better recognised by estimation methods, and thus provides better parameter estimation.