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[Fedor <question699605@xxxxxxxxxxxxxxxxxxxxx>]

Question #699605 on Yade changed:
https://answers.launchpad.net/yade/+question/699605

    Status: Answered => Open

Fedor is still having a problem:
Thank you very much , but I thought  that orthogonal packing ( max porosity) would have turned into hexagonal packing ( min porosity) during compression and the porosity would decrease. But now I realized that change of porosity occurs thank to intersection (overlapping) particles. Does my suggestion make sense?
But in the real soil porosity changes due to particles compaction not intersection. 
But again when I started working with initial script I obtained good relation pressure/porosity but when I added E , I was confused. 


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> On 24 Nov 2021, at 01:41, Jan Stránský <question699605@xxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> Your question #699605 on Yade changed:
> https://answers.launchpad.net/yade/+question/699605
> 
>    Status: Open => Answered
> 
> Jan Stránský proposed the following answer:
>>  porrr=utils.voxelPorosity(200,(0.75,0.75,0.75),(1.25,1.25,1.25))
> 
> The problem here is voxelPorosity and its parameters.
> resolution=200 might be too little, you can try higher values.
> 
> More importantly, you are using some random region for evaluation, porosity computed there has (or at least may have) no relation to the true total porosity. Randomly omitting / adding some border parts of spheres influence significantly the result.
> You can play with shifting the region.
> 
> If I use an analytical formula
> ###
> def porosity():
>    volTot = O.cell.volume
>    r = 0.09
>    volSphs = len(O.bodies) * 4/3. * pi * r**3
>    ds = [2*r - i.geom.penetrationDepth for i in O.interactions]
>    # https://mathworld.wolfram.com/Sphere-SphereIntersection.html
>    volContactss = [1/12.*pi*(4*r+d)*(2*r-d)**2 for d in ds]
>    volContacts = sum(volContactss)
>    volSolid = volSphs - volContacts
>    volVoid = volTot - volSolid
>    return volVoid / volTot
> ###
> I get consistent results:
> 0.47577 (isotropic pressure -1e5)
> 0.47326 (isotropic pressure -5e5)
> 0.47202 (isotropic pressure -7e5)
> 
> Cheers
> Jan
> 
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