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Message #02399
Re: DEM equations, written down.
Up on this one. I don't see how formulas for incremental shear
computation you present in the pdf [3] correspond to the code. IIRC
those formulas were supposed to describe CohesiveFrictionalLaw, right?
In particular:
(14), (15) compute ΔV_s and ΔX_s. Fair enough.
(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)!! Not a single word about transforming
F_s to the current plane first, which must be done and really happens in
yade code [2].
Anyone has a good reference to a serious (preferrably reviewed &
published) paper [1] describing the incremental algorithm accurately?
(I'm writing a few lines about different algorithms to compute shear
strain in yade).
Thanks.
Vaclav

[1] I know about F. AlonsoMarroquin &co: Micromechanical investigation
of the granular ratcheting. It has nothing to say about this, since they
never show how they evaluate the integral (2) expressing total shear
displacement.
[2] pkg/dem/Engine/GlobalEngine/CohesiveFrictionalContactLaw.cpp:102:
axis = currentContactPhysics>prevNormal.Cross ( currentContactGeometry>normal );
shearForce = shearForce.Cross ( axis );
angle = dt*0.5*currentContactGeometry>normal.Dot ( Body::byId ( id1 )>state>angVel+Body::byId ( id2 )>state>angVel );
axis = angle*currentContactGeometry>normal;
shearForce = shearForce.Cross ( axis );
// the comes the part described in (14) and (15)
[3] https://lists.launchpad.net/yadeusers/pdfEgGt5bLIql.pdf
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