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[Chareyre <bruno.chareyre@xxxxxxxxxxxxxxx>]

--------- Merging with (closed) bug 585771 --------------------
UNLIKE WHAT PRECEDES, WHAT FOLLOWS CONCERNS PERIODIC PROBLEMS, the bugs might have the same origin however.

I made comparisons between Law2_Dem3DofGeom_FrictPhys_Basic and
Law2_ScGeom_FrictPhys_Basic in periodic triaxial tests. Damping was very
law (2%), 400 spheres with identical positions.

The result is attached. You'll see in gray the curve of unbalanced force for ScGeom, resp. pink for Dem3Dof.
Different stress curves is ok, we can get almost the same difference between identical simulations in multithread (here, everything is run in 1 thread).

The surprising thing is unbalanced force is exploding, even with very low strain rate, after enough deformation, even though the same unbalanced force can go as low as 1e-8 in the initial isotropic compaction. I could repeat that with different number of spheres and different dampings.
With ScGeom, unbalanced force stagnate at very low value (so close to x-axis that you just see a few picks), exactly as what we would have with rigid boundaries.

Carefull examination and comparisons with usual DEM results on spheres
show that the evolution of stress and porosity is impacted by this
growing instability (the inverse would be surprising).

It needs more comparisons to know when this happens exactly. Those results were obtained in r2255, with :
PeriTriaxController(dynCell=True)
NewtonIntegrator(damping=0.02, homotheticCellResize=True)

I didn't test without homothetic resize.


** Attachment added: "gnuplotfile.png"
   http://launchpadlibrarian.net/49507794/gnuplotfile.png

-- 
TriaxialTest gives different results with ScGeom and Dem3DofGeom, cause is not known
https://bugs.launchpad.net/bugs/399963
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Status in Yet Another Dynamic Engine: In Progress

Bug description:
Seems that there is too much friction with the walls, but inspecting the XML file gives nothing suspicious. UnbalancedForce sits constantly at 1.1407 after a small while, without going down.