yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/3/31 Václav Šmilauer <eudoxos@xxxxxxxx>

> > You can repeat the test, is simple. The fact that the shear force
> > changes sign from one case to the other, is not correct. The shear
> > force is dependent on the relative shear velocity that in turn depends
> > on the ids at contact as we define them. To me this happens because we
> > do not define a local system.
> >
> > Please correct me if you see I am wrong or please explain me why the
> > shear force changes sign (if it was really a global system as was
> > already pointed out, it should not happen).
>
> Hi Chiara, if I understand right, shearForce get negated if you swap
> ids. That is consistent. shearForce is in global coordinates, but to one
> body (id1*), it applies positive (action), while to the other body
> (id2*) negated (reaction).
>

Hi V., if I correctly understood, the shear force (the incremental one)
behaves as you describe, but the TOTAL shear force (the one that we store in
the simulation) is really expressed in the global system (right?). At least
this is what I understood.. Moreover if my external force on the particle is
in one direction, I would always expect an opposite sign for the total shear
force (we oscillates around the same value but the sign should always be
opposite to it).


>
> Does this explain what you describe?
>
> * This is not directly related to which body we assign the positive
> force; we already agreed it should be id1 everwhere
> (https://bugs.launchpad.net/yade/+bug/493102 and our discussion
> http://www.mail-archive.com/yade-users@xxxxxxxxxxxxxxxxxxx/msg01285.html);
> while it is not consistent in the code ATM, one way or another, you will
> always end up with the inverse force on the other particle.
>
> Cheers, Vaclav
>
>
>
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