Question #248996 on Yade changed:
https://answers.launchpad.net/yade/+question/248996
Status: Open => Answered
Anton Gladky proposed the following answer:
Hi Andy,
2014-05-20 20:11 GMT+02:00 Andy Torres <[email protected]>:
> I have been working in a toy model, trying to figure out how all the
> viscoelastic forces works, and I think there is a bug here, because there are
> forces acting even when the particles are not touching each other. This
> happens if the particles separate after a collision and then meet again.
If penetration depth < 0, then the interaction should be removed, so
no forces at all: line 70-71, 45 [1]
[1]
https://github.com/yade/trunk/blob/master/pkg/dem/ViscoelasticPM.cpp#L45
> The simulation I made is just two aligned spheres ( one right above the
> other, so only normal force is involved) one fixed and the other free to fall
> under gravity force and bounce on the first fixed sphere.
> In the first bounce, the behavior of the system is the right one, the
> Penetration Depth (PD) starts at 0, the normal Force (Fn) has a large
> initial value because of the velocity of the falling particle at time of
> contact. The interaction doesn't disappear after the bounce, but the code has
> an "if" to set the force to zero and prevent an attractive force due to a
> viscous component:
> (line 104-106 of /pkg/dem/ViscoelasticPM.cpp)
> const Real normForceReal = phys.kn * geom.penetrationDepth + phys.cn *
> normalVelocity;
> if (normForceReal < 0) {
> phys.normalForce = Vector3r::Zero();
Please provide minimal working example, so we can test it. Better with
the proposal, how can it be fixed.
Regards
Anton
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