Clumps made of overlapping spheres

Hi,

I think you can check the codes written in C++ to see. You can also modify the codes to what you need. It is not challenging.

Regards,

Viet

Thank you tranviet for your reply. I'm newbie using Yade with no experience at all. I would appreciate a more specific answer.

Hi,

You can follow the YADE documnetation:

https://yade-dem.org/doc/formulation.html#clumps-rigid-aggregates

Viet

Thank you tranviet. I'll try to follow the documentation.

If the mass that is computed by default is not good, you can always compute it on your side and assign it to the clump. This doesn't need to modify the c++ code, simply some python scripting.
The same remark holds for inertia tensor.

Thank you Bruno for your reply. Your approach sounds easier than modifying the c++ code. I'll try to solve my problem this way.

hi,

You can also try recently included methods (available soon) utils.clumpTemplate() and O.bodies.replaceByClumps(), which is very useful, if you want to model ballast! After an update you will find an example script here: examples/clumps/replaceByClumps-example.py.
There the mass is corrected via clump volume (which is not sum of sphere volumes in case of overlaps).
Also you can test the new code. ;)

Cheers,

Christian.

Hi Christian, thank you for your reply. I'd like to apologize, I haven't been able to continue with this project for a few months, so I couldn't try to solve it.

Right now I'm trying to check the new methods implemented in Yade about clumps to create a ballast particle by means of overlapping spheres. Since I have to consider more than 2 overlaps I can only use the adaptClumpMasses method. I'm trying to check it through simple tests that I expected to have equal mass and inertia:
- Test1 (simple particle):
     sphere1=utils.sphere([0,0,0],2)
- Test2 (clump1):
     sphere2=utils.sphere([0,0,0],2)
     sphere3=utils.sphere([0,0,0],1)
     clump1=O.bodies.appendClumped(sphere2,sphere3)
     O.bodies.adaptClumpMasses([],10000000)
- Test3 (clump2):
     sphere4=utils.sphere([0,0,0],2)
     sphere5=utils.sphere([0,0.5,0],1)
     clump2=O.bodies.appendClumped(sphere4,sphere5)
     O.bodies.adaptClumpMasses([],10000000)
Resulting:
     mass_sphere1 = mass_clump1 = mass_clump2
     inertia_sphere1 ≠ inertia_clump1 ≠ inertia_clump2
Is that wrong? Does the adaptClumpMasses method take into account the overlapping correctly to calculate the inertia?

>Resulting:
> mass_sphere1 = mass_clump1 = mass_clump2
> inertia_sphere1 ≠ inertia_clump1 ≠ inertia_clump2
>Is that wrong? Does the adaptClumpMasses method take into account the overlapping
>correctly to calculate the inertia?

I do not see any problem.

sphere2 = sphere4
sphere3 is completely inside sphere2 and sphere 5 is completely inside sphere4, so they have to have same clump masses.
if densities for all spheres are equal, the sphere1 should also have the same mass as both of the clumps.
that leads to:
mass_sphere1 = mass_clump1 = mass_clump2

inertia is not calculated correctly in this case, because for clumps it is calculated as sum of all inertias of clump members, so inertia_sphere1 should be different from inertia_clump1 and inertia_clump2.
in your case inertia for clumps is calculated too high. maybe some day this will be fixed/improved ...
the inertia of both clumps should be also different, because their geometry is different (different balance point of masses)

regards,

christian

All right! Thank you Christian. As the Yade documentation says about the adaptClumpMasses method that "Adapt clump masses and inertia via deterministic Monte-Carlo algorithm" I thought the inertia was calculated correctly. But that's what I found out, that the inertia of the clump is calculated as the sum of spheres.

Yes, inertia is "adapted", not "correctly calculated". for small overlapping spheres inertia with adaptClumpMasses() is "better", than without adaptClumpMasses().
masses should be correct btw.

Thanks Christian. Now I see how it works. I'll try to introduce the inertia manually.