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What do biomass pellets and biscuits have in common, or pharmaceutical tablets and spaghetti for that matter….?

Well I’ll give you a clue, they are not spherical, nor are they made of many spheres stuck together. They are in fact, and I think you’ll agree, more or less cylindrical. This is lucky because should you be needing to simulate large number of such items, we can now do it accurately with the upcoming release of STAR-CCM+ v11.02.

 Simulation of an Auger Feeding Biomass Pellets into a Boiler

 Enter the cylindrical DEM particle….

Perhaps before we start, let’s have a recap of the status quo in the world of DEM. There are a number of different existing particle types in STAR-CCM+;

Firstly there is the sphere, the most basic primitive particle and building block, and until now the only primitive DEM particle type;

Then there is the coarse grain particle, where one sphere can represent many particles, similar to the Lagrangian parcel;

 

Next there is the composite particle which can be used to represent more complex particle shapes by gluing many spheres together to form a lumpy approximation of the required particle shape;

 

And finally there is the clumped particle which is similar to the composite particle, but can bend and break.

 

We can now add the cylindrical particle in STAR-CCM+ v11.02 to this list.

 

 

Composite DEM particles used for cylindrical objects

Until the release of STAR-CCM+ v11.02, composite particles were needed when modelling anything cylindrical and, to get a realistic representation, this required a large number of spheres. For example, in the images above, the low aspect ratio cylinder is represented by 100 spheres, and the high aspect ratio cylinder 20 spheres. Even with this high number of spheres, the representations are still somewhat lacking, looking more like a rice cake and caterpillar. Such composite particles lead to computationally expensive simulations, and so typically even more approximate representations were used, and the accuracy compromised further. With composite particles, the aspect ratio of the cylinder that can be modelled is also highly limited, with coins and spaghetti definitely being off the table.

Do more, faster, with less

Before we go on, it is interesting to compare the relative performance of cylindrical and composite particles, so how about a race…..

The application for our test is that of tablet coating. Here we have a revolving drum with mixing vanes and a spray coating the tablets. To test how the new cylindrical particles stacked up, I started two serial runs simultaneously on two cores of the same machine. Both runs had 20,000 tablets, one with cylindrical particles and one with composite particles using 20 spheres per particle.

And we’re off…. The image below shows a snapshot of both simulations at a snapshot in time. On the top, composite particles are used and on the bottom cylindrical particles are used.


 

Comparison of simulations with composite particles (top) and cylindrical particles (bottom)

The cylindrical particle simulation is immediately into the lead and during the settling phase it is running at about 3.5x the speed of the composite particle simulation. As the particles settle, the drum begins to rotate and there is more and more contact, the speedup slows down a bit to around 1.7-2.0x faster.

Simulation speed: composite particles vs cylindrical particles

More realism brings more accuracy

The contact modelling of cylindrical particles is very much more sophisticated than that of spheres, where spheres have a single mode of contact, cylinders have multiple modes.

Cylindrical particles can come into contact with walls and other particles in many new ways, for example face to face. In this situation, friction dominates as particles slide across each other and the physics cannot be accurately captured with composite particles because the area in contact is made up of that of the individual spheres.

Contact between a composite particle and a wall

Cylindrical DEM particles also have edges where contact is modelled, again something not true of composite particles comprised of spheres. Below you can see various modes of particle-particle contact involving faces and edges, difficult to accurately and efficiently simulate with composite particles.

Various modes of particle-particle contact

Of course the matrix is much bigger than this when you consider particle contact with walls and other types of particle.

The introduction of cylindrical particles therefore not only reduces the computational time, but increases the accuracy of the representation of the particle, a rare win-win situation in simulation. In fact to approach the accuracy of cylindrical particles, a composite particle would need to tend towards an infinite number of spheres.

The cylindrical DEM particle is a powerful addition to Discrete Element Method  in STAR-CCM+, and can also be used together with other types of particles, and be injected with a distribution of aspect ratios and sizes to be representative of natural materials.

Cylindrical DEM particles are one of the many exciting new features winging their way to you with the upcoming release of STAR-CCM+ v11.02 at the end of February.

Stay tuned to the CD-adapco Blog for all the latest updates.

 

 

 

 

 

 

 

 

 

 

 

 

Matthew Godo's picture
Matthew Godo
STAR-CCM+ Product Manager
Stephen Ferguson's picture
Stephen Ferguson
Marketing Director
James Clement's picture
James Clement
STAR-CCM+ Product Manager
Dr Mesh's picture
Dr Mesh
Meshing Guru
Joel Davison's picture
Joel Davison
Lead Product Manager, STAR-CCM+
Ravindra Aglave's picture
Ravindra Aglave
Director - Chemical Processing
Karin Frojd's picture
Karin Frojd
Sabine Goodwin's picture
Sabine Goodwin
Director, Product Marketing