strain deviator

Asked by ytang

Hi All,

I use the following command to get the position of particles and then export it.
###########################################################
 xposition = [] ; yposition = [] ; zposition = [] ; ballid = [] ; radius = []
 for b in O.bodies:
  if isinstance(b.shape,Sphere):
   xposition.append( b.state.pos[0] ) ; yposition.append( b.state.pos[1] )
   zposition.append( b.state.pos[2] ) ; radius.append( b.shape.radius ) ; ballid.append( b.id )
 f = open('./global-position'+'-' +str(m)+'.txt',"w")
 f.write('x\ty\tz\tr\tbid\n')
 f.close
 j = 0
 while j < len(xposition):
  f.write(str(xposition[j])+'\t'+str(yposition[j])+'\t'+str(zposition[j])+'\t'+str(radius[j])+'\t'+str(ballid[j])+'\n')
  f.close
  j = j +1
#################################################################################
after that I use the TW module to get the micro strain filed. I can get the micro strain field.
##########################################################################
    O .bodies.append(ymport.text("./global"+"-"+"position"+"-"+str(i)+".txt"))
    TW = TesselationWrapper()
    TW.triangulate()
    TW.computeVolumes()
    TW.setState(0)
    O.reset()
    O.bodies.append(ymport.text("./global"+"-"+"position"+"-"+str(i+1)+".txt"))
    TW.setState(1)
    TW.defToVtk("./strain"+"-"+"control"+str(i)+".vtk")
##################################################################################
when i import the .vtk files into the PARAVIEW.
we can see two potions to coloring the strain. one is strain_deviator, another one is the strain_matrix.
here I use the strain_deviator.
undering the coloring mode. I choose the: rescale to data range. the colorbar gives me the range from 0 to 4.8e+00. which means the maximum value of the strain deviator is around 4.8. when we see the offcial website for the micro strain. the maximum value of the strain deviator is 0.478597 [1]. I also saw this post[2]. it mentioned that the strain devitor is the second invariant.
In my opinion, this value should be smaller than one. but for my case, it's larger than one. is there anyone who can give me some hints?

I post the .vtk files here [3].
best,
Yong.

references: [1]https://yade-dem.org/doc/user.html?highlight=micro%20strain
[2] https://answers.launchpad.net/yade/+question/266331
[3]https://www.dropbox.com/sh/lal17mtarct8u51/AAApMr6QgxUY53UopAHtinGEa?dl=0

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Jan Stránský (honzik) said :
#1

Hello,

please provide full script [4], otherwise we can just guess..
(also note the section "Please, no external links!")

> In my opinion, this value should be smaller than one.

the value can be arbitrary (net necessarily smaller than one), it really depends on the specific situation (which we know nothing about).

cheers
Jan

[4] https://www.yade-dem.org/wiki/Howtoask

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