yade-users team mailing list archive

["Sergei D." <sj2001@xxxxxxxxx>]

16.03.2010 20:41, chiara modenese:

> Second I am looking at the ViscoelasticPM contact law and I see that the
> total shear force is given by:
> shearForce -= (phys.ks*dt+phys.cs)*shearVelocity;
> Why do we account the viscous force with the same sign of the shear one?
> Should not always oppose the motion?
> 

shearForce is opposite to the movement, so it is opposite to the
displacement (elastic term) and the velocity of displacement (viscous
term). So, elastic term and viscous term have the same sign.

For normalForce viscous term is added to the elastic force if loading,
and substracted if unloading, so we have different paths of
loading/unloading => energy dissipation.

The signs in ViscoelasticPM is correct (consistent) but not as it should
be, indeed. It is because we have contact normal from body1 to body2:

normal = body2_pos - body1_pos,

so we should have

relative_vel = body1_vel - body2_vel

in order to rel_vel>0 if loading and rel_vel<0 if unloading.

but in ViscoelasticPM:

rel_vel = body2_vel - body1_vel

so, rel_vel is inversed...

I corrected it in last rev.

-- 
Best regards,
Sergei D.