yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Hi Chiara,
> allow me a question about the way we compute the shear part. Following 
> the Cundall's model, no problem of ratcheting would arise since he 
> defines the branch vectors as radius*normal. 

I recently checked PFC manual, and it defines shear with OC vector, 
resulting in ratcheting. Maybe you'll find radius*normal in other 
Cundall's papers, not sure, but at least PFC3D gives ratcheting.

> Now in Yade if we avoid granular ratcheting we follow exactly the same 
> way. So, apart from ratcheting, why should the current length of the 
> interaction be preferred? Why this was introduced in the code?

I think it is often introduced by DEM programmers because it is somehow 
intuitive, once you admit that particles can overlap each other, with a 
"contact point" somewhere in the overlap. Current length is also used in 
torque definition, whatever the definition of shear displacement. 
Personally, I try to never use the words "overlap" or "penetration", and 
refer to relative displacement of centers instead. The "overlap" concept 
is not needed to derive the equations and it misleads people (another 
example is the computation of void ratio : people sometimes tend to 
remove the "overlapping" volume, which not suitable in most cases IMHO).

Bruno

--
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Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : +33 4 56 52 86 21
Fax : +33 4 76 82 70 43
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