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An introduction to Discrete Element Modeling (DEM)

In this interview, Dr. Lucilla Almeida, CAE Specialist at Rocky DEM, explains what is Discrete Element Modeling, and why this method is crucial for engineers to understand the behavior of equipment and processes that deal with particles in different industries.

What exactly is Discrete Element Modeling?

Discrete Element Modeling (DEM) is a numerical technique to simulate interactions between particles-particles and particles and boundaries. It can account for many types of forces acting on individual particles, and predict particle flow dynamics and bulk solids behavior. This approach is extremely powerful in solving many industrial problems.

What industries typically use DEM?

We see DEM used in geomechanics, agriculture, pharma, chemical processing, process engineering, oil and gas, and environmental and biological systems. For example, DEM is used in grains transport, powder coating of medication, and water purification. 

What physics are involved with DEM?

DEM measures body forces, such as gravity, fluid, and electrostatic or magnetic fields. It also tracks surface forces, such as contact and adhesion or cohesion, such as liquid bridging between particles. 

Virtual Roundtable Forum: Particle mechanics and solids handling in the process industries

Can you explain how DEM methods work?

The core of every DEM code is to detect particle collisions and compute the contact force. With the soft-sphere method, particles are rigid and any deformation at contact is modeled as an overlap. Normal and tangential contact forces are computed as a function of the overlaps. DEM tracks every particle in the domain, and we can learn each particle’s position at the next time step. When needed, we can also measure adhesion cohesion, and the breakage of particles.

Why does particle shape matter in DEM?

Particle shape can affect the flow of particles. Spheres do allow for simple contact detection and a single point of contact. But sphere shapes are pretty rare in the real world, so we need to be able to model other shapes. Rocky DEM, for example, allows for this modeling.

How do real particle shapes differ from spherical particles?

Real particle shapes — like polyhedrals for example — differ in their packing density, the linear and rotational modes of transport, the dilating during shear and interlocking, and the strength of the materials. Note that real particle shape modeling can increase computational demand (cost) due to contact detection and overlap requirements.

How does GPU processing help DEM simulation?

Remember, DEM tracks every particle at every time step. So GPU processing speeds up processing significantly without sacrificing accuracy. For example, using a 4x A100 GPU will complete a solve 700 times faster than 1 CPU core. 

Why might someone use coarse-grain modeling?

Even if you have GPU processing, it may not be feasible or practical to get accurate results if you have millions of particles. Commonly, people use coarse-grain modeling to reduce the total number of particles by using larger particles to represent a group of smaller particles. 

When is CFD coupled with DEM? 

When we need to find ways to account for fluid forces and flow on particles, CFD can be effectively coupled with DEM. This coupling can be used with mesh-based approaches and with any particle shape. 

When is SPH coupled with DEM?

This coupling is increasingly used in hydrodynamics. It can capture the complex-free surface flows with no diffusion errors. Dynamic body interaction is easily handled. It’s suitable when splashing or surface fragmentation is involved, for example. 

SPH-DEM is often used with a Langrangian meshless approach to capture flow dynamics by discretizing them into a set of fluid elements. Particles are interpolated using a kernel function to compute smooth fields for local variables.  

What are the advantages of the SPH-DEM coupling approach?

This coupling naturally captures complex free-surface flows with no diffusion errors, and dynamic body interaction is easily handled. 

Lucilla Almeida

CAE Specialist at Rocky DEM

Lucilla holds a BE (Chemical) undergraduate degree, an M.Sc. in Chemical Engineering and a Ph.D. in Nuclear engineering from the Federal University of Rio de Janeiro. She focuses on applying Computational Fluid Dynamics and Discrete Element Method to solve engineering problems. She is a CAE Specialist at ESSS, responsible for technical sales development, post sales, and the support of Rocky DEM.

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