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[Bettina Suhr <question404363@xxxxxxxxxxxxxxxxxxxxx>]

New question #404363 on Yade:
https://answers.launchpad.net/yade/+question/404363

Dear all,

in simulations using clumps of overlapping spheres, I was wondering if the porosity is calculated correctly. 
Using the following example, I obtain the same results with yade-1.20.0 and yade-2016.06a:

import numpy as np

#create a clump of two overlapping spheres:
ra=0.5
clump1=O.bodies.appendClumped([ sphere([0,0,0],ra), sphere([ra,0,0],ra) ])
O.bodies.updateClumpProperties(discretization=100)

#define a total volume for porosity calculation
Vtotal=(3*ra)*ra*2

#thanks to Wolfram alpha, the analytic solution should be
print "analytic solution: ",  (Vtotal - (2*4.0/3.0 - 5.0/12.0)*np.pi*ra**3)/Vtotal

print "porosity calculated by yade: ", utils.porosity(Vtotal)

# a correct porosity could be calculated like this (?)
def myClumpPorosity(VolTot, density):
  mass=sum([ b.state.mass for b in O.bodies if b.isClump])
  return (VolTot -mass/density)/VolTot

print  "my porosity: ", myClumpPorosity(Vtotal, O.materials[0].density)


Is there a bug in the porosity calculation or did I understand something wrong?
Thanks for your help.
Regards,
Bettina


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