Why use DEM + FEA?

Imagine you’re tasked with designing a bucket conveyor or a loader at a given throughput. How would you approach such a project?

One way is to start with a known design, run some hand calculations with due assumptions, and perform a field test. Then in the likely event it fails on the first trial, make design changes based on your best assessment and try again. This physical prototyping approach involves a lot of time, cost, and physical effort.

Alternately, you can try what engineers throughout the world are doing – use high-fidelity simulation tools like Discrete Element Method (DEM) and Finite Element Analysis (FEA) to optimize the process and design parameters virtually.

DEM and FEA basics

Today, DEM is an integral tool across many industries that handle bulk material like rocks, soil, powdered chemicals, food chips, and pharmaceutical tablets. By taking into account all the forces acting on each particle in the bulk system, DEM brings insight into how these materials would perform within the given equipment over a range of process conditions. With its ability to handle large particle counts of real shapes and sizes to provide a quick and accurate prediction of process performance, Rocky DEM is used across multiple industrial sectors, including mining, heavy machinery, agricultural, chemical, and pharmaceuticals.

FEA is widely used for structural analysis in the civil, automotive, and aviation sectors. For a given load, FEA software such as ANSYS Mechanical solves for an equilibrium condition in the structure. For transient simulations, the equilibrium conditions account for both deformation and kinematic energies, while for static simulations, only the deformation is considered.

Coupling Principle

During a simulation, Rocky DEM tracks the loads on each node of the geometry mesh. These loads are then exported as a pressure field for further analysis using ANSYS Mechanical, which discretizes the geometry and then solves for the equilibrium condition as discussed above. Figure 1 shows how the loads are exported from the DEM simulation for static structural analysis.

static structural simulation
Figure 1. Exporting loads from Rocky DEM for static structural simulation within Rocky DEM.

Why use Rocky DEM for DEM-FEA coupling?

Choosing Rocky DEM for structural analysis provides great value, as can be seen from the following highlights:

1- Static and transient analysis

Both static and transient structural analysis problems can be solved using Rocky DEM and ANSYS Mechanical. With the latter program, engineers can simulate transient cases while incorporating geometry motion and time-varying loads on boundary elements. This animation shows how the instantaneous bulk material loads on a bucket excavator are captured.

2- Full integration with ANSYS

Rocky DEM is fully integrated into ANSYS Workbench (Figure 2) and does not require any other external software for coupling.

Rocky DEM ANSYS Workbench
Figure 2. Integration of Rocky DEM into ANSYS Workbench.

This also allows engineers to use Design Exploration tools for virtual parametric studies and to perform optimization and robustness analyses with ease. This can be done by generating a response surface with well-defined input and output parameters, as shown in Figure 3.

response surface
Figure 3. Design of experiments within ANSYS Workbench to generate a response surface and assess the impact of geometry and process changes.

3. Complex motion

Rocky DEM can replicate complex motions within its UI, including combined motion and particle-induced free body motion with 6 degrees of freedom. No external coupling software is needed! The animation below shows the instantaneous loads on the blades and the shaft of harrow equipment as it plows the soil. Note that the assembly has free body motion, enabling it to move as it encounters a tough particle – just like it would in reality.

Solving Real-Life Problems

Armed with these state-of-the-art features, Rocky DEM has helped clients across the globe improve their equipment and process design at a fraction of the cost associated with trial and error experimentation.

Let’s see an example.

Vale, one of the largest producers of iron ore in the world, faced poor production efficiency when crushed ore jammed the moving screens at the base of its hoppers. This also increased the maintenance downtime caused by frequent grid cleaning.

Using Rocky DEM and ANSYS FEA coupling, Vale engineers were able to accurately characterize the loads induced on the screens following their regular process, allowing the company to implement effective design changes (Figure 4).

roller screen
Figure 4. Roller screen before (top) and after (bottom) with design changes based on Rocky DEM-ANSYS FEA simulations.

Rocky DEM captured the broad size and shape distribution of the incoming feed. Vale engineers then virtually optimized the tilt angle, rotation speed, distance, and profile of the roller disks–leading to significant improvements.

After the changes were implemented, production increased by 11.4%, saving $100 million in just over 3 months!

If you have a similar challenge, contact us to see how Rocky DEM can help.

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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