# difference between ScGeom and PolyhedraGeom

Asked by lip on 2019-05-20

hello
i have used law2_PolyhedraGeom_polyhedraPhys_Volumetric and Law2_ScGeom_frictPhys_cundallstrack to simulated packing of polyhedra, the contain is formed by polyhedra, when i used the first law,everything is all right, but when it comes to the second law, the particle get through the boundary, i want to know is there any difference between these two law? By the way, i have set correct relation between igeom, iphys and law

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2019-05-21
2019-05-21
 Jan Stránský (honzik) said on 2019-05-20: #1

Hello,

use higher stiffness for the case where "the particle get through the boundary"

> i want to know is there any difference between these two law?

yes

================

1)
please read and follow [1], a MWE would really help here..
Also please be consistent in the title and actual problem. Title describes IGeom, question Law2..

> By the way, i have set correct relation between igeom, iphys and law

see above. Someone who wants to help you might want to a) check it and b) know exactly what you have used

2)
difference between ScGeom [2] and PolyhedraGeom [3]
The main difference is the geometry described. ScGeom uses penetrationDepth [m], PolyhedraGeom uses penetrationVolume [m^3]

3)
difference between Law2_PolyhedraGeom_PolyhedraPhys_Volumetric and Law2_ScGeom_FrictPhys_CundallStrack
- normal force is evaluated similarly, stiffness * penetrationSomething. The main difference is penetrationSomething (depth or volume) and therefore also different physical dimension of contact stiffness.
- shear force and friction is also treated similarly, but differs in details.

cheers
Jan

 lip (mr.xie) said on 2019-05-21: #2

thank you for your answer, it do helped me a lot.
but i do not think the problem is about stiffness, for the same possion ratio and young moudles, law2_PolyhedraGeom_polyhedraPhys_Volumetric can handle the simulation quite well, but when it comes to Law2_ScGeom_frictPhys_cundallstrack, the particle just get through the boundary, i was wondering if that law can not be applied in polyhedra contact?

 Jan Stránský (honzik) said on 2019-05-21: #4

Hello,

please read [1] and provide a MWE

> but i do not think the problem is about stiffness, for the same possion ratio and young moudles, law2_PolyhedraGeom_polyhedraPhys_Volumetric can handle the simulation quite well, but when it comes to Law2_ScGeom_frictPhys_cundallstrack, the particle just get through the boundary

I do think the problem is about stiffness, since how the stiffness is treated and what it actually means is the main difference between the two Law2s.
Without a MWE, to think (aka guess) is the best I can do..

> i was wondering if that law can not be applied in polyhedra contact?

Law2_ScGeom_FrictPhys_CundallStrack can be applied in polyhedra contacts if the contact geometry is ScGeom

cheers
Jan

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