Discover how Rocky DEM’s fiber model expands the types of problems that DEM can now solve

In Rocky DEM, Fibers are a relatively new category of particle shapes that are mainly one-dimensional, i.e., the geometry of a fiber can be described by a line (or several lines) in a three-dimensional space.

Fibers can be made rigid or flexible, straight or multi-branched, so they’re ideal for modeling particles with large aspect ratios like hay, hair, nets, logs, and more.

Read this post for a better understanding of this particle type and find some cool application examples.

Rigid vs. Flexible Fibers

Fibers can be rigid, or flexible if they’re composed of multiple segments. In this approach, a flexible fiber is built by connecting sphero-cylinders by means of virtual bonds with elastic and viscous properties [1], as depicted schematically in Figure 1.

Figure 1. Schematic representation of a flexible fiber.


For flexible fibers, when the adjacent elements move, the relative movements between them produce linear and angular deformations on the virtual bonds. In response, forces and moments are induced and exerted on the adjacent elements to resist the normal, tangential, bending, and torsional deformations, as can be seen in Figure 2.

Figure 2. Forces and moments acting over a virtual bond.


Example 1: Pet hair in a vacuum cleaner

This simulation shows a 1-way DEM-CFD coupled simulation of a large number of pet hair strands inside a vacuum cleaner, depicting behaviors such as flexibility and inter-fiber interaction. The hair strands were modeled using flexible fibers with different diameters and the fluid field, obtained in ANSYS Fluent, was taken into account when solving the particle trajectory inside this multi-cyclonic device.

For more information about this simulation, click here.

Example 2: Demonstration of Rocky DEM particle types

This simulation shows the various particle types available in Rocky DEM: flexible fibers for the spaghetti, concave particles for the gummy bears, shell particles for the potato chips, and the flexible shell particle for the towel.

Straight vs. Custom Fibers

The fiber model allows you to model straight fibers (a linear shape, as shown in Figure 1) or create your own custom fiber shape by importing a .txt file. With custom fibers, sphero-cylinder segments can be arranged arbitrarily forming complex multi-branched geometries, as exemplified in Figure 3. The branches can have different diameters and nonuniform flexibility, enlarging the range of applications that can be modeled using DEM.


Figure 3. Examples of multi-branched custom fiber shapes.

The modeling of flexible custom fibers is exactly the same described in the previous section for flexible straight fibers. Between any pair of connected segments, an elastic-viscous virtual bond is considered, that exerts forces and moments on the segments that oppose to translational and angular deformations. The major difference is that, as stated before, custom fibers can be defined with nonuniform flexibility.

Example 3: Compression of hay particles

This example shows a fiber compression test simulated to acquire the force-deformation response curve and the hysteretic behavior of the hay. Both characteristics are then used to calibrate the hay material for future DEM simulations.

Example 4: Log unscrambler

This example shows a log unscrambler simulation using rigid custom fibers. The logs have different diameters along their length.

Example 5: Gummy bears on a net

This example shows gummy bears (modeled using the concave particle model) falling on an elastic net that is modeled using the custom fiber particle shape. And it also shows that we love gummy bears.



[1] Guo, Y., C., W., Curtis, J. S., and Xu, D. (2018). A bonded sphero-cylinder model for the discrete element simulation of elastic-plastic fibers. Chemical Engineering Science, 175:118–129

Lucilla Almeida

Global CAE Specialist, ESSS

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 joined ESSS in 2008 and has spent 5 years focused on applying CFD to solve common engineering problems in the Oil and Gas industry, dealing with turbulent and multiphase flow simulations. Since 2013, she is an Application Engineer for Rocky DEM, supporting users, working on consultancy projects and validating models implemented for the CFD-DEM coupling.

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