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Understanding the effect of particle angularity on granular flows

Extensive experimental and simulation results show that particle angularity and shape have a significant impact on granular flows. However, it is very challenging to incorporate the particle shape parameters into the rheological models for more accurate predictions of complex and realistic granular flows.

Dem model particle angularity on granular flows using Rocky
Figure 1. DEM model of shear flows of polyhedral particles in a cylindrical cell. The top lid installed with blades rotates to drive the bulk material to shear.

We are using Rocky DEM to simulate the shear flow processes of polyhedral particles in a cylindrical shear cell, as shown in Figure 1. The set-up of the shear cell is similar to that in an FT4 rheometer (Freeman Technology Inc.). The number of faces a regular polyhedral particle has reflects its angularity. The smaller the number of faces, the larger the particle’s angularity. Thus, it is important to model the polyhedral particles with various face numbers (tetrahedra, hexahedra, octahedra, etc.). This way, we can explore the effect of particle angularity on the microstructural and macroscopic properties of material flows. 

In these simulations, the position and orientation of each particle and the contact force for each contact can be obtained. Therefore, we can obtain the particle-scale information. In addition, the macroscopic quantities, such as stress tensor, bulk friction coefficient and granular temperature of the bulk material, can also be calculated. Based on the simulation results, it is possible to establish the connections between the microstructural properties and macroscopic flow behaviors. Furthermore,  DEM simulations of complex granular flows provide opportunities to develop new rheological models for non-spherical particle flows. These models can go beyond the conventional kinetic theories of granules and the inertial number theory (also known as the μ(I)-rheology), in which the effect of particle shape is usually neglected.

Using Rocky DEM to simulate particle angularity

Rocky DEM not only solves particle handling problems in industry. It’s also helpful for the fundamental research of the mechanics and physics of granular materials. Rocky has a large library of particle models—from convex to concave and from rigid to flexible. So that a wide range of granular materials can be investigated. In our research, shear flows of various particles are simulated. As a result, we got a better understanding of how the particle properties (shape, friction, etc.) affect the bulk flow behaviors.

Yu Guo, Ph.D.

Research Professor and a Principal Investigator in the Department of Engineering Mechanics at Zhejiang University in China

His research interests lie in granular and multiphase flows, particle science and technology, and computational particle mechanics. Two of his recent representative projects include firstly, an investigation on the effect of particle shape on the constitutive models of solid-phase stresses for the complex granular flows and secondly, the development of a flexible fiber model based on the Discrete Element Method (DEM), implemented in the commercial software, and the application of the fiber model to the studies of flexible fiber flows. Dr. Guo holds a B.E. from Beihang University (China), a M.E. from Tsinghua University (China), and a Ph.D. from University of Birmingham (UK).

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