Contact Force: van der Waals Force
Select the Compute van der Waals Force checkbox in the physics interface’s Force section to compute the van der Waals force between grains and between grains and walls. The Compute van der Waals force checkbox is only available when Hertz–MD or Hertz–MD with adhesion is selected in the Contact force model list in the physics interface Force section. Generally when the grain sizes are less than 10 microns, contribution of van der Waals force becomes nonnegligible. In such cases, the van der Waals force is added to the normal component of contact force and is given by (Ref. 4)
where
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γ is surface energy per unit area
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Dmax is the cutoff distance for the van der Waals force
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Dmin is a parameter to avoid the singularity
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δn is normal overlapping distance and is defined using Equation 3-6 and Equation 3-11 between grains and between grain and wall, respectively
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Req is the equivalent radius between grains in contact (Equation 3-13) or between grain and wall (Equation 3-17)
The van der Waals force is calculated as an addition to the normal force, Equation 3-7, as follows:
The effect on the tangential force component is not considered in the current formulation of the van der Waals force.