Inserting concave particles in a box

In this tutorial we insert a pack of concave particles in a box and let them settle under the influence of gravity.

Name of the case: Project_Concave

Setting up the simulation

As a first step, the particle shape, the used material and the simulation domain are defined in the General Settings tab. Please note that in case of multiple dependent simulations, the dimensions of the simulation domain can only be defined in the first simulation. This means that the box forming the simulation domain has to be chosen big enough from the beginning.

General settings

In this simulation we set particles of particle shape concave:

A single materials command with the name default is used:

The simulation domain with x, y and z dimensions ranging from -0.7 to 0.7 is created:

Meshes and regions

We use a box-shaped mesh as container for the particles, which we insert via the mesh command command:

Physics models

The contact models are now defined. For the particles we use the normal contact model hertz and the tangential model history:

Since we added a mesh in the previous section, a wall contact model is also added automatically to this section. We use the same properties as for the particle contact model:

Please note that for convex and concave simulations the setting store_force_contact has to be set to yes.

Finally, the gravity is enabled:

Per default the gravity has a magnitude of 9.807 and acts into negative z-direction. These defaults can be changed by either setting the magnitude or the direction manually.

Particles

In the general settings tab we only defined a single material type (default), whose settings have to be specified here:

	default
Density	2500
Young’s modulus	5e7
Poisson’s ratio	0.45
Coefficient of restitution	0.5
Coefficient of friction	0.5
Coefficient of rolling friction	0.05

A particle template for concave particles consists of a set of convex bodies. We define three of them:

Please note that you can either specify mass and center of mass, or none of them. The moment_of_inertia keyword is optional. If the quantities are not specified, an analytical formula is used for their computation. Apart from defining the moment of inerta for the single convex bodies, it is possible to define this quantity for the complete concave body when adding the template.

We now add a particle template of style concave and use it for a particle distribution:

A pack of particles with a velocity of 0.2 m/s in negative z-direction is inserted using an insertion command command with mode pack:

Simulation control

In this tab, we first define the time-step settings such as the desired simulation timestep of 1e-4 seconds and the total simulation time of 1 second. Per default also the check_timestep command command is enabled, which throws a warning when the time step exceeds 10 % of the Rayleigh or the Hertz time. These thresholds can be changed by setting an alternative value for hertz_fraction or rayleigh_fraction.

Output settings

In this tab we first define the timestep width for the file and the terminal output:

The output_settings command command the takes care that all particle information and the meshes are written to files accordingly. Furthermore it triggers the output of global quantities such as the kinetic energy of the particles or total normal and shear stresses onto meshes to the terminal. Please note that if the output of per-cell information on meshes such as wear, velocity of stress are desired, one has to add the keyword mesh_properties and select the required output.

Running the simulation

After completing the setup and saving it, the simulation can be launched. Hence, change to the Simulation view. First hit the “Check settings” button, and if the check returns “Check settings successfully completed” the simulation can be run by hitting “Start”. As can be seen in the the kinetic energy graph below, the settling process is completed after 6000 steps, i.e. 0.6 s:

Postprocessing with Paraview

After the simulation is completed, all data written with the output_settings command can be visualized automatically by going to the Visualization view and hitting the “Start Paraview” button.

The images below show the final state of the settled particles, the coloring is chosen according to the ids: