yade-users team mailing list archive

[Václav Šmilauer <eudoxos@xxxxxxxx>]

> >
> > (16) is supposed to update shear force F_s (vector):
> >
> > 	F_s=F_s+K_s*ΔX_s
> >
> > but this is not correct, since you add ΔX_s (which is in the _current_
> > contact plane) to F_s (which is shear force from the previous step, i.e.
> > in the _previous_ contact plane)!!
> I don't understand the problem. F_s and ΔX_s  are in the global 
> coordinate system, not in any contact plane.

Yes, they are in global coordinates, but, at the same time, current F_s
must be always perpendicular to current n (in global coords); otherwise,
we wouldn't call is F_s, right?

Now, F_s from previous step is perpendicular to _previous_ n, while ΔX_s
is perpendicular to _current_ n. Summing these 2 together doesn't make
sense, since the sum not perpendicular to anything (neither current, nor
previous n).

v