Abstract
In many granular material simulation applications, DEM capability is focused on the dynamic solid particulate flow properties and on systems in which millions of particles are involved. The time of relevance is many seconds or even minutes of real time. Simplifying assumptions are made to achieve run completion in practical timescales. There are certain applications, typically involving manufactured particles, where a representative pack is of the order of a thousand particles. More accurate capturing of the influence of complex shape is then often possible. Higher accuracies are necessary to model the topology of the void space, for example, for further CFD simulation and optimisation of fluid flow properties. Alternatively, the accuracy may be critical for structural performance and the force or stress transmission through the contact points is to be controlled to avoid material damage and poor function. This paper briefly summarises methods for simulation of shape effects on packing structures in the granular community and narrows the scope to problems where shape effects are of overriding concern. Two applications of mono-sized, mono-shaped packing problems are highlighted: catalyst support pellets in gas reforming and concrete armour units in breakwater structures. The clear advantages of FDEM for complex-shaped particle interactions in packed systems with relatively few particles are discussed. A class of particulate problems, ‘FDEM-suited’ problems, ones that are ideal to be solved by FDEM rather than by DEM, is proposed for science and engineering use.
Highlights
In industry, the purpose of applying DEM is commonly to gain a better understanding of how to optimise a manufacturing process, one which invariably includes dynamic granular flows
Moghaddem et al [30] applied a ‘contact point treatment’ with volume inflation to overcome this problem and derive a computationally robust mesh for fluid flow modelling. This enabled them to use ANSYS-RBM workbench software to compute fluid flow within the void topology bounded by the solid skeleton surface which was modelled with a rigid body dynamics (RBM) solver
To illustrate how simple it is to explore ideas of science and engineering with FDEM codes such as Solidity, two armour unit types were modelled as catalyst pellet size particles of equal volume and deposited from an identical evenly spaced array into a cylinder to compare random packing behaviour for two armour unit shapes used widely in coastal structures, Core-Loc and X-bloc [47]
Summary
The purpose of applying DEM is commonly to gain a better understanding of how to optimise a manufacturing process, one which invariably includes dynamic granular flows. Many industrial packing structures are physically generated by a relatively fast container-filling deposition process that brings coalescing moving particles rapidly in real time to a rest state If in addition, they do not involve too many particles, they make ideal target problems because the associated smaller time steps required for the smaller elements and accurate contact dynamics can still be achieved within reasonable run times. As an alternative to using DEM for sedimentation process models to create soil and rock fabrics and thereby investigate the effect of grain shape on geomaterial strength and flow properties, direct sampling of the actual grain fabric from rock cores, for example, by X-ray micro-CT is an option that is growing in popularity with digital imaging This approach is discussed by Jia and Garboczi [8] in relation to shape acquisition and representation of realistic angular rock grains. We present a short summary of available numerical methods for modelling packing processes before focussing on two niche applications requiring high accuracy in the representation of complex shape, as made possible by FDEM
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