Defining DEM Particle Interactions

The DEM particle interactions define how the particles behave when they collide with one another and with the drum walls.

To define the tablet-to-tablet interaction:
  1. Right-click the Physics 1 > Models > Multiphase Interaction > Phase Interactions manager and select New > tablet > tablet.
  2. Right-click the Phase Interactions > Phase Interaction 1 > Models node and select the Linear Spring contact model.
    The Rolling Resistance model is selected automatically. The DEM Phase Interaction model is already selected.
  3. Deactivate Rolling Resistance (in the Enabled Models group box).
  4. Click Close.
  5. Rename the node Phase Interaction 1 to tablet-tablet.
  6. Click Close.
  7. Right-click the tablet-tablet interaction node and select Copy (or use Ctrl-C).
  8. Right-click the Phase Interactions node and select Paste (or use Ctrl-V). Repeat this this operation one further time.
    This action creates two copies of the tablet-tablet interaction node.
  9. Rename the copies to tablet-side and tablet-front & back.
Specify the models and properties for the interaction between tablets:
  1. Edit the tablet-tablet > Models node and set the following model properties:
    Node Property Setting
    Linear Spring Static Friction Coefficient 0.4
    Normal Restitution Coefficient 0.1
    Tangential Restitution Coefficient 0.1
    Normal Spring Stiffness Method > Constant Value 50000
    Tangential Spring Stiffness Method > Constant Value 50000

In this tutorial, different frictional properties are required on the side walls of the cylinder from the front and back walls. To expose the side wall boundary as an item in the Second Phase drop-down list, you must set the Lagrangian Specification on the side wall boundary itself to Specify for Boundary:

  1. Select the Regions > mixer > Boundaries > side > Physics Conditions > Lagrangian Specification node and set Method to Specify for Boundary.
    A new sub-node Phase Conditions appears under the boundary node.

Return to setting up the phase interactions within the Physics DEM continuum.

Within the tablet-side interaction, specify the models and properties for the interaction between tablets and the cylindrical wall of the drum:

  1. Edit the tablet-side > Models node and set the following model properties:
    Node Property Setting
    DEM Phase Interaction Second Phase mixer: side
    Linear Spring Static Friction Coefficient 0.9
    Normal Restitution Coefficient 0.1
    Tangential Restitution Coefficient 0.1
    Normal Spring Stiffness Method > Constant Value 50000
    Tangential Spring Stiffness Method > Constant Value 50000
Specify the models and properties for the interaction between tablets and the back and front of the drum:
  1. Edit the tablet-front & back > Models node and set the following properties:
    Node Property Setting
    DEM Phase Interaction Second Phase Wall (the global wall boundary condition for the Lagrangian phase)
    Linear Spring Static Friction Coefficient 0.0
    Normal Restitution Coefficient 0.6
    Tangential Restitution Coefficient 0.6
    Normal Spring Stiffness Method > Constant Value 50000
    Tangential Spring Stiffness Method > Constant Value 50000
  2. Save the simulation.