And in fact the rate of loading is what you'll find in Thornton
and Cundall when defining the relative velocity across periods, it
is my best bet before reading the papers.
Yes, supposing a strain-controlled test you will find the usage of the
strain rate of loading to update relative velocities. Maybe is that
what we need once adopting ScGeom?
Yes, this is what we need. Note that updating velocity should be done on
bodies themselves to be really correct (i.e. there is really no "edge"
of the packing, what is supposed to be obtained with
homotheticCellResize>0).
Updating relative velocity for interactions across period is another
independant problem.
I'll keep posting changes in periodicity in this thread, as I fix stuff.
For today, I just commited (r2249) those changes, which seems to give
stable packings (before, it was exploding). I think it makes things
correct regarding homothetic resize. See point (4) for the interractions
part :
1 - stress definition in PeriIsoCompressor was wrong for ScGeom (sign
mistake due to double-reverse);
2 - applyForceAtContactPoint cannot be used in periodic + ScGeom, since
this function needs the wrapped position of each body (in Dem3Dof,
wrapped position is an attribute, in ScGeom there is no such attribute
and we don't want to define it as it costs cpu). The function call is
replaced by separate applyForce/applyTorque using a "branch" computed
using radius, normal, and penetration depth.
3 - Implement homothetic=2 properly. The acceleration of the period
(i.e. change in velGrad) is applied on particles as an equivalent
impulse. If velGrad is constant, there is no effect on particles. If
velGrad changes, each particle is accelerated with
(delta_velGrad*position). This is like giving initial velocities to
particles so that they move homothetically.
TODO :
4 - Define relative velocity across period correctly. It should be done
adding a velGrad*shift2 term, but shift2 is unknown in Law2... I'll
maybe exploit the "shear" attribute of ScGeom to precompute a shifted
shear disp increment in Ig2, and use it later in Law2.
(btw : isn't that an interesting option to merge ScGeom and Dem3?
Letting shear be the total OR incremental displacement?)
Cheers.
Bruno
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