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[Robert Caulk <question688116@xxxxxxxxxxxxxxxxxxxxx>]

Question #688116 on Yade changed:
https://answers.launchpad.net/yade/+question/688116

Robert Caulk proposed the following answer:
Hello,

>>My understanding is that, different from BPM where constraint is added
so that large difference in two bonded particles' motion is prevented

Let me try to clarify the difference between the two models. In [1], the
cement is modeled explicitly and contributes to the total force on
incident bodies. Thus, the bodies can still move, the cement model helps
reduce movements. In [1], they also briefly suggest a "simplified"
version of BPM where no slip is allowed to occur for bonded particles.
That sounds like what you are referring to, but I have not seen many DEM
studies using that.

In JCFpm, the cement is not modeled explicitly, however, the normal
force is allowed to become negative (pulling on both bodies) until the
tensile strength is reached. Thus, the bond is also restricting body
movement in a similar manner as the original BPM.

>> I am wondering whether it is feasible to make the bonded particles in
the cluster have the same ( or not quite different) velocity?

Assign the same velocity to all the spheres. Am I missing something in
the question?

>> However, my idea is that as a rigid rock,

If the particles are simply bonded in JCFpm, the cluster is not (and
should not be) perfectly rigid. If you want a perfectly rigid clump, you
can clump the bodies, but I dont think that is what you are looking for.
If you want your cluster to be "more rigid", then you can increase the
contact stiffnesses.

>>Why torque is ignored and is such practice making sense？

Depends what you are studying. JCFpm, as the name implies, is designed
to study rock joint behavior in DEM. CohFrictPhys on the other hand,
does consider rolling resistance.

Cheers,

Robert

[1]Potyondy, D. O., & Cundall, P. A. (2004). A bonded-particle model for
rock. International Journal of Rock Mechanics and Mining Sciences,
41(8), 1329–1364. https://doi.org/10.1016/j.ijrmms.2004.09.011

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