yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/3/25 Václav Šmilauer <eudoxos@xxxxxxxx>

>
> >   Just to say to be carefull with formula in Hentz's thesis: the idea
> > was  to use as inputs for contact properties the Young modulus and
> > Poisson ratio that we want to obtain macroscopically for the granular
> > assembly. The "funny term" are use to compute kn and ks with respect to
> > these macroscopic Young modulus and Poisson ratio
> Yes, I know. I disregarded that funny term, it is close to 1.0 and
> doesn't play any role.
>
> What struct me, though, was that we deviate from any obvious definition
> of contact stiffness. Its dimensionality is correct, but it is scaled by
> some dimensionless constant (π/2 in our case) away from the "intuitive"
> definition (which is the base of what Hentz uses): stiffness of cylinder
> with radius min(r₁,r₂) between spheres' centers, with some average
> Young's modulus.
>
> I say nothing if such constant is properly documented and supported by
> some reasoning, but for me now, even though it works, it is just garbage
> code.
>
> > In my opinion, the only important point is to compute kn and ks such as
> > scale effects are avoided, and I think it is well done in the current
> > formula (*) in Yade.
>
> I disagree with the premise that the only important point is to avoid
> scale effects. I like quantities to have physical meaning, as much as it
> is meaningful with discrete models; the argument (Bruno ;-) ) that
> discrete solution doesn't converge (and doesn't approach continuous
> solution) if you refine "mesh" (packing) does not justify, in my eyes,
> gratuitously introducing random constants to the code.
>
> Besides that, imagine Chiara reading that code (in a few days)... guess
> what happens? ;-)
>

Actually if you have a look at one of my old questions (that is your plan,
right? ;-) ) I asked about the way Yade computes stiffnesses since to me it
was not making sense to call a variable young modulus when physically it is
not (in this sense I totally agree with you). But I remember Bruno said that
it was related with an estimate of the stiffness of the packing. Maybe Bruno
can explain better this concept or we could look at the users mailing list
to recall his answer.

cheers, Chiara


>
> v
>
>
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev>
> Post to     : yade-dev@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev>
> More help   : https://help.launchpad.net/ListHelp
>