User Defined
The User Defined subnode is available from the context menu (right-click the Collisions parent node) or from the Physics toolbar, Attributes menu. The User Defined node allows the post-collision particle velocity to be a user-defined expression.
See Elastic for information about the Collision Statistics and New Value of Auxiliary Dependent Variables sections.
Collision Frequency
These settings are the same as for the Elastic subnode.
Reinitialized Particle Velocity
Enter values or expressions for the Reinitialized particle velocity vr (SI unit: m/s) based on space dimension.
Include Secondary Emission
Select the Include secondary emission check box to release a secondary particle when the collision occurs.
Secondary Emission Condition
This section is available when the Include secondary emission check box is selected.
Select a Secondary emission condition: None (the default), Probability, or Expression. For Probability enter the Probability γ (dimensionless) for secondary emission to occur. For Expression enter an Evaluation expression e (dimensionless) that must be nonzero for secondary emission to occur.
Secondary Particles
This section is available when the Include secondary emission check box is selected.
In the Number of secondary particles field Ns, specify the number of secondary particles to release per primary particle. The default value is 1.
Select an Initial velocity: User defined (the default) or Constant speed, spherical.
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Constant speed, spherical releases the secondary particles with a constant speed and spherical distribution of velocity directions. Enter a Speed v0 (SI unit: m/s) with which all secondary particles are released.
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User Defined allows for an arbitrary velocity vector to be set for the secondary particles. Enter values or expressions for the Initial particle velocity v0 (SI unit: m/s) based on space dimension.
Select the Offset initial position check box to offset the positions of the secondary particles before releasing them. Then select an Offset method: Using initial velocity (the default) or Isotropic sphere.
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For Using initial velocity, enter a Time interval Δt (SI unit: s). The default is 0. Each secondary particle is then displaced by the product of its initial velocity and this time interval before being released.
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For Isotropic sphere, enter a Particle displacement magnitude Δr (SI unit: m). The default is 0. All secondary particles are then moved a distance equal to the displacement magnitude before they are released. If the offset would cause secondary particles to be placed outside of the modeling domain, they are instead released at the location of the primary particle.
Released Particle Properties
This section is available if the Include secondary emission check box is selected. Select an option from the Inherit Properties list. At least one Particle Properties node is always available, because it is a default feature. If other instances of the Particle Properties feature have been added to the model, then they can be selected from the list. Use this setting to determine what set of properties is given to the secondary particles that are released by this feature.
Initial Value of Auxiliary Dependent Variables
For each auxiliary dependent variable that is defined in the model, enter the initial value of the auxiliary dependent variable for the secondary particles that are released as a result of the User Defined collision. The default value is 0.