User-Defined Contact Force Model Reference

Define a vector field function that returns a vector for the contact force between two particles or particle and a wall. For example, you can define a linear spring model with added cohesion or dissipation. These additions can be made velocity-dependent, or given other conditions.


Provided By	[physics continuum] > Models > Multiphase Interaction > Phase Interactions > [interaction] > Models > DEM Contact Model
Example Node Path	Continua > Physics 1 > Models > Multiphase Interaction > Phase Interactions > Phase Interaction 1 > Models > User-Defined Contact Force
Requires	Optional Models: Lagrangian Multiphase Optional Models: Discrete Element Method (DEM) Multi-Phase Interactions: Multiphase Interaction selected automatically Under Multiphase Interaction, select Phase Interaction Topology: DEM Phase Interaction if it has not been automatically selected.
Properties	See below

Properties

Dimensions

Read only. The dimensions for the field function that is selected for the model, usually Force.

Function

The field function that is selected for the model. To define a customized field function, write a user field function. You can reference primitive field functions in your own field function, including any of the following:

Contact Centroid
Contact Contact Mass 0 | 1
Contact Contact Radius 0 | 1
Contact Normal
Contact Normal Overlap
Contact Overlap
Contact Physics Radius 0 | 1
Contact Poisson Ratio 0 | 1
Contact Relative Velocity
Contact Surface Velocity 0 | 1
Contact Tangential Overlap
Contact Youngs Modulus 0 | 1

See the Discrete Element Method Field Function Reference and Creating a User Field Function.

When this model is activated, the Contact Torque field function uses the force computed by the model crossed with the torque arm of parcel centroid to point of contact.

Note	Do not use Contact Damping Force or Contact Elastic Force in customized field functions or for post analysis.

Example Field Functions

Example 1

$$ContactNormalOverlap * -100000

The contact force is set equal to -100000 times the overlap vector. The minus sign is necessary to set the correct force direction.

Example 2

$${FCnormal}-$${FCtang}

The contact force is the vector difference between FCnormal and FCtang, which are defined in terms of Contact Normal Overlap and Contact Tangential Overlap:

FCnormal = -1.72E7*$${ContactNormalOverlap}
FCtang = (mag(1.48E7*$${ContactTangentialOverlap}) < mag(1.72*$${ContactNormalOverlap})*0.092) ? 1.48*$${ContactTangentialOverlap}:mag(1.72E7*$${ContactNormalOverlap})*0.092*unit($${ContactTangentialOverlap})