yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Jerome Duriez a écrit :
>
> - first of all are Da and Db the radii of the spheres in contact ?
Yes.

> - then it is written that the "2.0" that appears in the calculations 
> of the various rigidities are "arbitrary parameters". Why introducing 
> "arbitrary parameters" ?
Two different answers :

For lines 88/89 : I am the author of the "2.0" factor. I can tell it is 
not arbitrary, it is because I define kn as E*diameter (why not 
E*radius? well... this is arbitrary ;)).

For line 94 : This equation is from Jean-Patrick Plassiard and was 
implemented by Janek. I really don't know if it is arbitrary or not (and 
perhaps the comment refers unadequatly to "arbitrary" factors of lines 
88/89 because Janek asked me "why two?", and I answered "arbitrary" 
without thinking twice).

Anyway, elastic behaviour at contacts is somewhat "arbitrary" isn't it? 
So having arbitrary parameters is not a problem in itself, you just need 
to know how things are defined.
>
> I ask this question because I want to use the results (the values of 
> parameters calibrated) of the paper mentionned in the class 
> ("Plassiard & al") and the comparison would be immediate without this 
> 2.0 coefficient (even if I should recognize that with it, it is not so 
> much more complicated...)
It is strange that the factor is not in the paper too as the equations 
are supposed to be the same. Perhaps you are interpretating some values 
the wrong way. Remember that the stiffness of a contact is half of the 
stiffness of one body?

Bruno


>
> Jerome
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