DEM simulations of polydisperse media: efficient contact detection applied to investigate the quasi-static limit
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DEM simulations of polydisperse media: efficient contact detection applied to investigate the quasi-static limit Tom Shire1
· Kevin J. Hanley2 · Kevin Stratford3
Received: 19 December 2019 / Revised: 15 April 2020 / Accepted: 3 September 2020 © The Author(s) 2020
Abstract Discrete element modeling (DEM) of polydisperse granular materials is significantly more computationally expensive than modeling of monodisperse materials as a larger number of particles are required to obtain a representative elementary volume, and standard contact detection algorithms become progressively less efficient with polydispersity. This paper presents modified contact detection and inter-processor communication schemes implemented in LAMMPS which account for particles of different sizes separately, greatly improving efficiency. This new scheme is applied to the inertial number (I), which quantifies the ratio of inertial to confining forces. This has been used to identify the quasi-static limit for shearing of granular materials, which is often taken to be I 10−3 . However, the expression for the inertial number contains a particle diameter term and therefore it is unclear how to apply this for polydisperse media. Results of DEM shearing tests on polydisperse granular media are presented in order to determine whether I provides a unique quasi-static limit regardless of polydispersity and which particle diameter term should be used to calculate I . The results show that the commonly used value of I 10−3 can successfully locate the quasi-static limit for monodisperse media but not for polydisperse media, for which significant variations of macroscopic stress ratio and microscopic force and contact networks are apparent down to at least I 10−6 . The quasi-static limit could not be conclusively determined for the polydisperse samples. Based on these results, the quasi-staticity of polydisperse samples should not be inferred from a low inertial number as currently formulated, irrespective of the particle diameter used in its calculation. Keywords DEM · Inertial number · Granular materials · Polydispersity · Contact detection
1 Introduction Polydisperse granular materials (i.e., those containing a range of particle sizes) occur in many physical and industrial settings, such as geomaterials, avalanches and landslides, crushing of mining ores and food processing. Often the range of particle sizes in such systems covers several orders of magnitude. For example, the granular filter material used to construct the Bennett Dam in Canada contains particles ranging from 0.08 to 75 mm [1]. Such a range of length
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Tom Shire [email protected]
1
James Watt School of Engineering, University of Glasgow, Glasgow, UK
2
School of Engineering, University of Edinburgh, Edinburgh, UK
3
Edinburgh Parallel Computing Centre, University of Edinburgh, Edinburgh, UK
scales presents significant computation challenges to the discrete element method (DEM), typically used to model such systems. These challenges reflect the fact that in polydispe
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