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CAE with ROCKY DEM for material processes

Wallat, P.; Lohrengel, A. – TU Clausthal
Translated by: Benvenuti, L. – CADFEM GmbH

By using simulation methods, it is possible to generate value-added data for the design process. If this data generated early in the process, a higher-quality final product is more likely.

Background in the product design

In the product development process (PCP), various steps are processed sequentially and iteratively. Solutions and their combinations are searched to solve a given problem. An evaluation of the available solutions is necessary in order to pursue appropriate ones and reject unsuitable ones.

In this way, the resources in the PCP can be used specifically to drive the process forward.

The particle geometry is crucial for the processing of the material flow, both in manufacturing processes and in recycling processes. This must be treated with different methods to obtain the desired result or to extract the required material.

Solution evaluation in the development process

Evaluating the generated solutions is essential to advance the development process. A well-known example of the evaluation is the definition of the solutions in a diagram with the technical and economic values. The technical solution is placed in a business value context.

Figure 1 shows four examples in an evaluation chart. The bisecting line is defined as line of development. Solutions on this line have the same value in technical and economic areas. This is in many cases desirable, deviations from the development line can also represent a better solution in individual cases.

When evaluating modules for an entire system, assessment the individual components and their compatibility with each other is crucial for the function. The performance of the components is considered a technical value.

As the complexity of the components increases, the predictability of system performance decreases. Thus, determining technical value is always a demanding task; especially in the handling of material flows of geometrically unspecified objects, no accurate prediction can be given.

Although a subjective ranking of the solution can be created, but this does not reflect the quality of the solutions.

Economic and technical value of solutions
Figure 1: The numbers are no longer given to the points.

Particle properties in the process

In large-scale automated production, individual parts are designed to be suitable for automatic handling.

For this, engineers need toy be able to influence the product design. This is not given in the treatment of bulk solids. Bulk materials can be ores from a mine or – as in this case more precisely – material from a recycling process. Recyclable materials undergo classifying and sorting processes to be handled in reprocessing.

The material flow is broken down until it is manageable. Afterwards, the materials are separated by material and type and can be brought, as secondary material from a recycling process, back on the market.

Digital sample particle from a recycling process
Figure 2: Digital sample particle from a recycling process

The preparation process and the software ROCKY DEM

The materials in treatment processes are very different from each other. To extract the contained materials in the desired quality, mechanical aid is necessary in many cases.

A variety of solutions are possible for every step of the process, butit is difficult to reliably evaluate such solutions in advance, given the random variables in the process.

As mentioned above, a ranking is possible. The ranking is based essentially on the experience of the development engineer.

The software ROCKY DEM from ESSS

With Rocky DEM, it’s possible to guide defined particles over configurations of CAD geometries. Subsequently, the particle behavior can be evaluated via the DEM method (Discrete Element Method). This defines the particles as geometrically discretized objects.

The parameters can be varied within the particle-geometry.There are templates with spherical but also edged particles. Parameter variation allows adjustments in various ways, such as density.

Several different particles can be defined in the simulation. In addition, identically defined particles will be implemented into the process via sieve classification in various sizes.

It is possible to define the behavior of the particles in relation to the same or other particles, as well as to other objects in the process; or example, to friction coefficients–so the particles behave correspondingly on different surfaces.

It is possible in the simulation process to allow the particles to break. As a result, fragments are generated in addition to the particles.

Rocky DEM enables loading CAD geometries in STL format (Standard Triangulation Language). It is also possible to load assemblies into Rocky while recognizing the individual parts. The number of STL facets on the geometries affects simulation calculation time. Should fast, rough results be required, the number of facets should be low at the same time.

The loaded geometries can be moved and rotated in the program. These movements exert forces on the objects as they meet. Likewise, for simplicity, surfaces may be defined as “moving.”

This saves a lot of effort, for example, in defining conveyor belts, because here only a flat surface must be defined as moving. Combinations of movements, the speed, and the start and end time can be freely defined within the program.

Rocky DEM + ANSYS Mechanical™

For later component designents, the results from ROCKY can be transferred to ANSYS® Mechanical™. ANSYS® Mechanical™ can determine the stresses of the components by FEM (Finite Element Method). The strain on the components are a result from the simulation in Rocky DEM.

For a high level of detail, the number of STL facets must be as high as possible. For evaluation, a variety of variables is available. To compare solution approaches, a uniform evaluation must be defined.

The variety of possible variables must be considered with caution, as it can too quickly lead to an unmanageable overload of data. A well-considered selection of variables leads to good knowledge about the process.

Evaluable parameters for particles include, for example, speed, location, impact energy, and rotation around all axes. Furthermore, an area can be defined for the evaluation. Here, among other factors, the number of incoming and outgoing particles and the total mass of the particles in the area can be calculated. These data can be plotted referring to each other in a diagram.

The data points are also stored in a table within the previously defined time intervals. The data inside the tabular can be evaluated directly with a formula or further analyzed by exporting to other programs.


Simulation in Rocky DEM with many particles.
Figure 3: Simulation in Rocky DEM with many particles. The green particles on the right are in the evaluation area. Other colors depend on the particle size.


Integration in the development process

Through the simulation, the performance of the principle solutions will be estimated non-subjectively also the quality differences from each other.

Through high-quality assessment, a solid statement can be made early in the development process about the quality of each solution, and lower quality solutions won’t be pursued. For the better solutions, real-life tests must be carried out to verify the information.

In automated processes, many stations are often set up, one following the other, and a connection between them is necessary. Rocky DEM can be used to investigate this system behavior.

The stations can be evaluated individually and then combined into overall systems to be checked afterwards. Either interfaces for material transfer can be defined, or the entire system can be simulated. In either case, the increased computing time should be considered.

The extended possibilities for solution investigation brings many valuable possibilities into the product development process. However, it must be noted that this is associated with additional work.

Depending on the complexity of the geometry within the process and variety of possible solutions, combined with the computing time, this can take a lot more time and other resources.


Product development cannot progress without decisions. A decision must be based on evaluations, which are increasingly difficult to determine as complexity increases.

Simulation in different areas can support decision-making. In a plant design for handling bulk materials, Rocky DEM software can contribute valuable information. Simulation is a powerful tool, and with carefully prepared input parameters from engineers, can make a very valuable contribution to the design process.

To understand more about Rocky DEM and ANSYS coupling, check-out the link below:


Luca Benvenuti

Business Developer und Vertriebsingenieur / Pre Sales Engineer at CADFEM GmbH

After a M.Sc. in Engineering, I aimed to improve the world, during my PhD in Mechatronics, reducing the CO2 emission in steel production. Now in my work as Business Developer for ROCKY DEM, the particle simulation software, I run the extra mile, i.e. I commit to increase the use of the software in the DACH area. The software is used to understand and optimize processes, thus saving money. My goals are understanding customer processes and issues, using the software to solve these issues, and then offering the package - solution plus software - to the customer.

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