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Rocky DEM’s Intra-Particle Collision Statistics feature is amazing

Discrete Element Method (DEM) is routinely used to characterize the bulk behavior of a particulate system. Using Rocky DEM, you can quickly and accurately capture the spatial and temporal evolution of particle bed. Routinely, variables like instantaneous local velocity and stress fields are obtained with the Rocky DEM UI easily.

But what if you want to see more, not just the bulk stress distribution but the stress distribution on a single particle as well? With Rocky DEM’s unique Intra-Particle Collision Statistics feature, now you can!

Rocky DEM collects the collision data for a region of influence (Figure 1) about every vertex on the surface of every particle. The collision data in this region is averaged over the number of particles for all the collisions that happened between two consecutive time outputs. For robust statistical evaluation, it is recommended that the averaging duration should be reasonably large and the number of particles nearly constant between outputs.

Figure 1. Region of influence of a vertex in which the Intra-Particle Collision statistics is collected.

One can then graphically visualize the variation of normal and tangential stresses, contact duration and frequency etc. on the surface of a particle (Figure 2) at the click of a button!

Figure 2. Particles Details window showing Normal Stress distribution on the surface of a particle.

Let’s see how this can be used to differentiate performance for different particle types subject to the same process. A good example is evaluating the variation in performance of different shapes (Figure 3) in a tablet coater, particularly helpful in analyzing chipping tendency. Using Rocky DEM’s state-of-the-art capabilities in modeling custom shapes, you can import a custom geometry as a particle, and then run the simulation.

Figure 3. Different tablet shapes considered for coating.

Figure 4 shows that the dynamics of the particle bed look approximately similar for different shapes.

Figure 4. Bulk behavior for 2 different particle shapes in the drum coater. Only 2 shapes are shown.

But let’s dive a bit deeper and see if there’s any difference in the behavior of the individual tablets in each case using Intra-Particle Collision statistics.

Figure 5. Intra-Particle variation in average shear stress for different tablet shapes.

From Figure 5, it is clear that the particle interaction behavior, as quantified by the shear stresses for the different shapes, is quite different. Shape 2 shows much higher shear stresses near the edges, making it more prone to edge chipping. In contrast, Shape 4 experiences the least shear stresses and with everything else equal, this shape should be the most resistant to chipping. In this case, a data driven decision with regards to choosing the best tablet shape can be taken easily using Intra-Particle Collision statistics.

Can you think of an application where Intra-Particle Collision statistics would be useful? If so, contact us to find out more!

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Saurabh Sarkar

Applications Engineer, Rocky DEM

Dr. Saurabh Sarkar is an Applications Engineer for the Rocky DEM Business Unit. Prior to joining ESSS, Dr. Sarkar worked as an Adjunct Faculty at Rutgers University and an on-site Consultant at Sunovion Pharmaceuticals where he supported drug formulation and process development activities. He obtained his Ph.D. in Pharmaceutics from the University of Connecticut where his focus was understanding and optimization of different pharmaceutical unit operations using DEM and CFD tools in projects with multiple industrial and government collaborators. He is a Senior Member of the AIChE and serves as an expert reviewer for several journals.

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