I am still investigating the cohesionlessMomentRotation.
It is written in the sources files that this code has been "verified
with the paper of Plassiard in GM".
However, Plassiard considers in his paper "and in his thesis" only the
rolling part of the relative rotation of particles (and thus only
bending moment), whereas in the code rolling and twist part of the
relative rotation are considered (and thus bending and twist moment).
There would be no contradiction here, if only it was possible to set
twist stiffness = 0 (so the law with bending and twist would "contain"
the law with bending alone).
For now, Ktwist=Kbending=Kr, so it is indeed not possible...
My question: is there a particular reason for that? What is the
motivation of the person who wrote this code? I don't say that is bad
or good, but I would like to have an idea about advantages and
disavantages, and physical meaning for considering a twist moment.
As soon as there is a finite area of contact between the solids (i.e.
always), it makes sense to include twist resistance I think. The testing
has been done by Boon IIRC.
By the way, I think rolling resistance, Ktwist!=Kbending, and other
features would be ideally implemented in
Law2_ScGeom_CohFrictPhys_CohesionMoment, which is now the cleanest, and
shortest code for moments.
Funky factors η, α, β, would be contained in a collection of Ip
functors, since they are not needed by the law itself, which just needs
4 stiffnesses, and the definition of maximum values for each force/moment.
Any help on this task of unifying duplicates would be welcome.
Cheers.
Bruno
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