yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Václav Šmilauer a écrit :
> > I'm not sure I understand completely.
> > First reaction :
> > Why not change "goal" with time, in comp=M*goal? It would give a strain 
> > rate.
> >     
> Goal is user-defined and shouldn't change. It describes, well, the goal
> state.
>   
This is a problem perhaps. In many cases, what you want is a continuous 
response to a continuously changing loading.
Typically : triaxial loading is constant strain rate + constant 
stresses, the final ("goal") state doesn't really matters, except for 
stopping the simulation at some point.

> > Second :
> > It could be simpler to prescribe strainrates/stresses.
> >     
> Could be right. Not sure if you woudn't want, in some special cases,
> prescribe strain rather than strain rate, though.
>
>   
In some special cases, yes probably.

> Currently, as soon as you reach all the goal components (strains or
> stresses) and the packing is stable etc, doneHook is called. With
> strainRate, that wouldn't work as well. There must be some 4th condition
> regulate rate? Is it meaningful? I am a little at loss, since I have
> only few cases I can imagine, but I want to make it quite generic.
>
>   
I think if you want it very generic you need to introduce, the rate of 
loading AND the final loading. Currently you have only the the final 
loading.
> It is just the cell size that changes, but it really means that (for
> compression) particles on the right get closer to the particles on the
> left. I was thinking about this linear displacement, but then I wasn't
> sure if one should prescribe velocity (and perhaps get adversary inertia
> effects later) or just change position and ignore inertia...
>
>
>   
I think you just linearly transform all coordinates with a matrix. 
Conceptualy, it is like a displacement if the matrix represents the 
transformation, or a a velocity if the matrix represents the rate of 
transformation... Same duality as before.

This is a question for Gaël and Vincent (could you guys keep this 
discussion in yade-dev?).

Also : Gaël just suggested that instead of the (displacement = 
stress_error/stiffness) approach used with boxes, the periodic stress 
could be imposed directly in the periodic cell, provided the cell has an 
inertia. In that case the strain of the cell would be just a result of 
the imposed stress and this artificial inertia. He said this method 
works well.

Bruno

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