Václav Šmilauer a écrit :
(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).
Well, in the code you rotate F_s before summing dF_s : no problem.
In a paper, you want to split the problems usually, and you comment on
the contact law disregarding the rest. But ok, the equations for
rotation should be explained somewhere.
The incremental approach is very common in the DEM litterature, but
usually not explained in details in papers (perhaps because it is so
common?). I'll send you a detailed paper in a separate mail. It is using
the same "approximate" rotation equations than yade, with
cross-product(oldN,newN), and then it defines the shear increment like
in (16).
Bruno
v
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Bruno Chareyre
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Grenoble INP
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