yade-users team mailing list archive

[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".

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

Cheers, v.