yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Hi again,
Vaclav told me this answer was not fully satisfying. If the question was 
"why ratcheting has been implemented in yade in the first place", I'm 
not the good person to answer. My best guess is it was inherited from 
SDEC, which was itself more or less reproducing PFC3D.
I suspect many DEM codes gives the "avoidRatcheting=false" behaviour. In 
most cases, nobody will notice (Mc Namara and co. got to simulate 
cycling loadings with a large number of cycles to exhibit problems).
I don't think it can give big differences in the most usual situations, 
and I suspect explosions in periodic BCs have another explanation.

Cheers.

Bruno

On 30/09/10 16:35, Bruno Chareyre wrote:
> 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
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