yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

> I wrote Shop::totalForceInVolume, which computes stiffness and force
> just for that purpose. I am not sure it is physically correct, but
> should be: if you sum forces on all interactions (abs values of the
> components, that is), you get some summary force in the whole
> simulation. Dividing that force e.g. z-component by xy area of the
> periodic cell, you have average stress in the z sense, right?
>
>   
After 1min of thinking :
mmmh.... probably not. Suppose you have the same stress in a sample that 
is twice higher (y-length) with the same x/z length, the sum of forces 
will be multiplied by 2, you divide by the same area. YOUR stress is 
twice bigger when it should be the same.
You need to divide by a volume like in Love-Weber : Sum(fi*lj)/V  
//component (ij) of the stress tensor
Not a big deal to compute that (its somewhere in a recorder already, it 
needs adaptation for periodic volume though).
> I would be glad if you could check that Shop::totalForceInVolume.
>
> Some control code is in PeriIsoCompressor, you can take that as
> inspiration, I think it is quite readable:
>
> Vector3r cellSize=rb->cellMax-rb->cellMin;
> Vector3r cellArea=Vector3r(cellSize[1]*cellSize[2],cellSize[0]*cellSize[2],cellSize[0]*cellSize[1]);
> Vector3r sumForces=Shop::totalForceInVolume(avgStiffness,rb);
> Vector3r sigma=Vector3r(sumForces[0]/cellArea[0],sumForces[1]/cellArea[1],sumForces[2]/cellArea[2]);
> // etc.
>
>   
If I change the value of, say, rb->cellMax, will it instantly translate 
all particles in proportion? (you remember this old discussion?)


> The cell is defined in MetaBody::cellMin and MetaBody::cellMax (corners
> of the cell) and MetaBody::isPeriodic==true. You can change cell corners
> as you want.
>
> Oh, important note: constitutive laws that as bodies for their
> coordinates (such as ElasticContactLaw) will not work with periodic
> boundaries; the periodicity information is injected into the interaction
> and interaction geometry functor receives adjusted se3's of the bodies.
>
> Law2_Dem3Dof_Elastic_Elastic will work just fine however (Dem3Dof saves
> se3 of bodies inside itself, which is faster and has this (unplanned)
> feature of using fake body coordinates instead of the real ones).
>
>   
I wish I have more time soon....


Bruno


> Cheers, Vaclav
>
>
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>   


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Chareyre Bruno
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