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[Václav Šmilauer <eudoxos@xxxxxxxx>]

> Now I want to 
> do a simulation that I need to keep a mean stress ((S1+S2+S3)/3) constant, and
> Did anybody handle this before or how is it handled in YADE? can you give
> any suggestion?
> If YADE has already includes this kind of algorithm, can you tell me where is it?

Hi Sayeed,

to me it is not clear what are you trying to achieve. Can you be more
precise?

In particle models, stress tensor is not defined, only forces on
interactions between particles; you can approximate stresses by looking
at interactions around each particle (which I did just recently for
postprocessing purposes in CpmStateUpdater::update, but only for the
concrete model).

If you mean something like triaxial test where mean stress in the whole
specimen is constant, then you should have a look at
TriaxialStressController (that gives you ways to control individual
stress components) and derive your own engine from it.

For periodic compression (simpler, since no walls and other funny
things, but less mature code otherwise), have a look at the
PeriIsoCompressor class; you would have to write something very similar,
just changing the lines that compute displacements to keep mean stress
constant.

For those, you have to touch c++, though -- unless Bruno has some other
idea.

Cheers, Vaclav