yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/4/25 Václav Šmilauer <eudoxos@xxxxxxxx>

>
> > both TranslationEngine and JumpChangeSe3 work if bodies are dynamic.
> > Now I tried a simple sphere-sphere interaction test using the basic
> > Law2_ScGeom_FrictPhys_Basic() law. One ball is fixed, the other one is
> > moved by using JumpChangeSe3 (setting setVelocities to true). The only
> > thing I notice is that although no damping is present, the moving ball
> > gets the rest at equilibrium (just run the attached script and press
> > F8 to see what I mean, you will see the contact normal force getting a
> > constant value).
> > If I try the same test but using ForceEngine (now it is commented in
> > the attached file but you can try to use it while commenting out
> > JumpChangeSe3) I get the expected result, the moving ball is bouncing
> > around the equilibrium (again just run the script and press F8).
> >
> > Nothing wrong, I just wuold like to understand (and maybe you can help
> > me) why in displacement control I do not any bouncing around the
> > equilibrium. Is not the same as applying a body force according to the
> > code?
>
> I think the result it right. ForceEngine will apply force, which will
> end up in sum with repulsive/attractive force between particles. The
> equilibrium position will be moved by ForceEngine, but you will still
> observe oscillation as if without ForceEngine.
>
> For JumpChangeSe3, particle is displaced by delta at every step. The
> equilibrium ("constant" position) will come at the moment when
> displacement by JumpChangeSe3 will be exactly compensated by
> displacement by NewtonIntegrator later in the same step. That's how I
> would explain the "equilibrium".
>

Hi Vaclav,
thanks for reply. Yes it makes sense.. I let you know if I have any other
thoughts about that.
cheers, chia

>
> Let me know it it makes sense, I will have a look a little bit more
> otherwise -- no problem.
>
> Cheers, v.
>
>
>
>
>
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