# Packed bed of capsules: export porosity values for each cell in the generated VTK file

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For a packed bed of capsules I want to export porosity values for each cell in the generated VTK file: is this possible with the current version of WooDEM?
commented Nov 26, 2017 by (48,950 points)

Please clarify what is "cell" and how you define porosity on it.

commented Nov 29, 2017 by (160 points)

It is a Voronoi cell around the capsule. I define porosity as the fraction of the cell occupied by the fluid.
I have more or less the same problem reported in this discussion of two years ago:
I want to evaluate the radial porosity profile of a cylindrical packed bed of capsules.

answered Nov 30, 2017 by (48,950 points)

You can try with woo.triangulated.porosity which works on box-shaped domain. The inernal code is here: https://github.com/woodem/woo/blob/master/pkg/dem/Funcs.cpp#L702 . It ignores orientation of Capsules (or Ellipsoids). Another approach would be to use some other tool to analyze the VTK (or STL) file, since the triangulation defines solid/void areas.

commented Dec 24, 2017 by (160 points)

Thanks for your answer. From the structure of the generated packing I noticed it is too loose for my needs. Could you suggest a strategy to obtain a denser packing?

commented Dec 27, 2017 by (48,950 points)
1. Change the size distribution (PSD). Monomodal (same-size) distirbution is the least compact. The wider the better, small particles will fill gaps between big ones. For inspiration, you might find articles about the asymptotically optimal PSD which leads to Apollonian arrangement (I assume it will be similar for capsules).
2. Go for regular arrangement, but I guess that is not what you want.
commented Dec 27, 2017 by (160 points)

Unfortunately I can't change the size distribution (PSD), because I have to use monodisperse capsules.
What about vibrating the column along the axial direction after particle deposition?
Is it easy to obtain with WooDEM?

commented Dec 27, 2017 by (48,950 points)

Yes, see here: https://ask.woodem.org/index.php/909/vibrate-periodically-move-column-with-particles . Vibration in real life mostly reduces friction effects. I assume you already set friction angle to zero to get denser packing - that's why I did not mention it above. If you have not done so yet, do it, porosity will be lower.

commented Dec 30, 2017 by (48,950 points)

You could also perhaps use woo.pack.randomDensePack2 which will generate dense packing with small overlaps (it is based on isotropic compression and unloading to low pressure). See examples/densepack.py for some examples, maybe also examples/tunnel-pack.py and also older document (from yade times) https://yade-dem.org/doc/user.html#sphere-packings which might be useful. You will have to use woo.pack.inCylinder predicate for the volume; now I see the documentation is not as it should be (i.e. the ctor), so quick peek into the source:

py::class<inCylinder,sharedptr,py::bases>("inCylinder","Cylinder
so you can call woo.pack.inCylinder(centerBottom=...,centerTop=...,radius=...) to create your cylinder.