# Particles¶

The analysis type **Particles** allows the simulation of the
dynamics of a large number of particles and the contact interaction
of those particles both among themselves and the environment.
It is based on the Discrete Element Method (DEM). If you
want to simulate particles in a fluid flow you can use
*Discrete phase models*
in a fluid dynamic analysis.

The results enable you to understand the dynamic behaviour of particles for a variety of application as for example bulk material transport. You can check how you should adapt your geometry in order to ensure that no particles are thrown out of the material handling system. For mixing mills you can also optimize the amount of particles and particle size as well as the rotation velocity or acceleration in the start up process in order to get the material mixed as fast and resource-efficient as possible.

## Domain¶

In order to perform a **Particles** analysis you have to define the geometrical domain
for your calculation. Unlike for e.g. solid mechanics finite element analyses you
do not need to create a mesh for the geometrical domain. Thus you can just assign
your geometry to the simulation.

For a complete setup the geometry should contain all geometrical parts that define
the boundaries for the particle movement as well as geometrical domains where you
want insert the particles initially (*Filling zones*).
Please note that although the parts of the geometrical domain are replaced by their
bounding faces in the calculation, all entities in the assigned geometry (both bounding
geometries and Filling zones) have to be solid bodies. You can also add simple
walls represented by planes to the geometrical domain.

You can also define sets for the geometrical entities and define geometry primitives:

## Model¶

In the *model* section everything that
defines the physics of the simulation is specified e.g. material properties,
solid body motions etc. On the top level you can adapt some generic settings.
For this analysis type you can add a gravitational load for the whole domain,
which will be needed for the correct particle movement in almost all applications.

### Materials¶

In order to define the material properties of the whole domain,
you have to assign exactly one material to every part. In a **Particles** analysis
this holds for the geometrical domain (Geometry boundaries, walls) as well as
for the particles (represented by the *Filling zones*).
The material properties define the density as well as the contact interaction parameters
in order to solve the impact equations.

### Solid Body Motions¶

In a Particles analysis **Solid body motions** can be used to define a
movement of bounding geometry parts. It does not apply for the
*Filling zones* containing
the particles itself.

## Numerics¶

Under numerics you can choose an artificial numerical damping. The default value is 0.2.

## Simulation Control¶

The Simulation Control settings define the overall process of the calculation as for example the timestepping interval and the maximum time you want your simulation to run before it is automatically cancelled.

You may also adapt the write interval of the simulation which defines the time steps to be included in the result data. If you choose the interval very low you will produce lots of data that does not differ visibly from one time step to another as the time step is often chosen very small in order to get correct results. Thus it makes sense to separate the calculation time step from the result printing.

## Solver¶

The described **Particles** analysis is solved on the SimScale platform using
the Discrete element method code Yade.
See our *Third-party software section*
for further information.