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[Václav Šmilauer <question136034@xxxxxxxxxxxxxxxxxxxxx>]

Question #136034 on Yade changed:
https://answers.launchpad.net/yade/+question/136034

Václav Šmilauer proposed the following answer:

> 1.a) PeriTriaxController (with dynCell=True) is not confounding statics and dynamics : it
> is purely dynamic.
Eh, that is exactly what I said... It has no notion of static response, 
counfindg the two together (if you don't agree, it is a matter of words, 
I think)
> 1.b) I recall there is no exact theoretical derivation of stiffness from contact list for
> "granular" materials (i.e. 3-4 interactions per element, no cohesion nor rolling
> friction); and that is the reason why I didn't use for periodic case the static strategy
> used for TT with boxes.
Peri3dController is getting the response from the packing, not from 
formulas...

>> 2. The measure of staticity depends on the formulation used (damping,
>> for instance);
> I don't see why unbF would depend on formulation, since it only employs
> forces.
I meant that choice of a suitable staticity criterion depends on what 
type of damping is employed.
> I see no problem in that. It is not really different than
> breaking a contact at iteration N, so that unbF(N+1)>unbF(N) due to ongoing internal
> reorganisations.
The point was that free energy is always non-increasing (unless there is 
external work), that's why I though it was better.
> Energy measure is consistent, but evaluating staticity and energy conservation are two
> different things. Kinetic vs. elastic energy ratio is a good measure of staticity, but I
> still have to hear what is the disadvantage of unbF, I don't see any.
Above.
> Considering that tracing energy is cpu-time consuming, and that there are so many laws,
> damping methods, and boundary conditions for which energy tracing is not implemented, and
> will not any time soon due to excessive complexity, I don't see energy as a candidate for
> routine staticity evaluation.
Eh, alright.... I think this has become too confused a discussion to be 
meaningful.

v.

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