# Interactions in a clump

Hi all,

Do the particles of a clump interact between themselves? Is it possible to get an interaction between two particles that are part of the same clump?
For example, particles A, B, C and D form the clump 1. I would like to get the interaction, for example, between particles A and B or see if the body A has any interaction with another sphere of the clump. Is it possible?

Thanks a lot for your help!

Bruna.

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Jérôme Duriez
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 Revision history for this message Jérôme Duriez (jduriez) said on 2016-10-21: #1

Hello,

No, Yade would not define any interaction between e.g. particles A and B in this case. Give a try with the following:

******** Example **********
O.bodies.append(sphere(Vector3(0,0,0),1,fixed='True'))
O.bodies.append(sphere(Vector3(0,0,1.99),1,fixed='True'))
O.bodies.clump([0,1])
O.step()
O.interactions.has(0,1) # returns false here (true without O.bodies.clump() line)
***************************

It is because colliders (which perform the first operations to define interactions) skip such interactions within a clump [*]. Hence interactions within a clump are never defined, which is not bad since they would be useless.

Jerome

PS: Exception to this behavior is when particles are clumped during a simulation. In this case it seems the clump operation does not erase previously existing interactions. In the example above, move the O.step() before O.bodies.clump(..) to observe it

 Revision history for this message bruna (brunamot) said on 2016-10-25: #2

Jerome, thank you for the clarifications.

I still have a question in this subject. Does the same that happens with the interactions happen with forces? Is it possible to get forces between two bodies that form the same clump?

I am trying to simulate a particle breakage and a maximum force or the existence of interactions between the bodies of the clump would be my criteria to release a body from the clump. Like this, when a body inside my clump reach a limit, this body would be released simulating a breakage. Do you know if there is another way to simulate this? I want to create a particle that is formed by a determined number of spheres and separate them because of determined criteria.

Once more, thanks a lot!

Bruna.

 Revision history for this message Jérôme Duriez (jduriez) said on 2016-10-25: #3

In my opinion it makes little sense (no offense ;-) ) to speak of forces outside of interactions in DEM in general / Yade in particular.
So yes "the same happens with interactions as with forces"

I see your goal now, and Yade clumps are just not the right tool for you. I would recommend instead you define your breakable particles from cohesive aggregates of Yade bodies.

You're not the first one to perform such task with Yade, and you might get some ideas in these previous discussions (in case you do not get lost along these threads..):