Yade

Problems for allowBiggerThanPeriod

Asked by chuanqi liu

hi, everyone.
allowBiggerThanPeriod can be used for large deformation. However, i found that if the shear strain is largger than a specific value (e.g. 2.8 in the following script), the contact stress would decrease to zero. Initially, i thought shear dilation cause this phenomenon. So i checked the volume fraction, which kept constant in the shear process since the spheres were frictionless. So, how to explain this. Here is my script.
/****************************/
O.periodic=True
O.cell.refSize=(2,2,2)

from yade import pack,plot,qt

O.bodies.append(pack.regularHexa(pack.inAlignedBox((0,0,0),(2,2,2)),radius=.1,gap=0,color=(0,0,1)))
O.materials[0].frictionAngle=0

O.engines=[
   ForceResetter(),
   InsertionSortCollider([Bo1_Sphere_Aabb()],allowBiggerThanPeriod=True,verletDist=0.01),
   InteractionLoop(
      [Ig2_Sphere_Sphere_L3Geom()],
      [Ip2_FrictMat_FrictMat_FrictPhys()],
      [Law2_L3Geom_FrictPhys_ElPerfPl()]
   ),
   NewtonIntegrator(damping=.4),
   PyRunner(command='checkStress()',realPeriod=1,label='checker'),
   PyRunner(command='addData()',iterPeriod=100)
]

O.dt=.2*PWaveTimeStep()
O.cell.velGrad=Matrix3(-.1,0,0, 0,-.1,0, 0,0,-.1)
limitMeanStress=-5e5

def checkStress():
   stress=sum(normalShearStressTensors(),Matrix3.Zero)
   print 'mean stress',stress.trace()/3.
   if abs(stress.trace()/3.) > abs(limitMeanStress):
      O.cell.velGrad=Matrix3(0,0,.1, 0,0,0, 0,0,0)
      checker.command='checkDistorsion()'
      O.materials[0].frictionAngle=.5 # radians
      for i in O.interactions: i.phys.tangensOfFrictionAngle=tan(.5)

def checkDistorsion():
   if abs(O.cell.trsf[0,2])> 3.0:
      plot.saveDataTxt(O.tags['id']+'.txt')
      O.pause()

def addData():
   stress=sum(normalShearStressTensors(),Matrix3.Zero)
   plot.addData(exz=O.cell.trsf[0,2],szz=stress[2,2],sxz=stress[0,2],tanPhi=stress[0,2]/stress[2,2],i=O.iter,vf=1-utils.porosity(),z=utils.avgNumInteractions())

plot.plots={'i':('exz'),'exz':('szz','sxz'),'i ':('tanPhi'), 'i':('z')}

Gl1_Sphere.stripes=True
plot.plot()
O.saveTmp()
/****************************/

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Bruno Chareyre (bruno-chareyre) said : 		#1

Hi,

> allowBiggerThanPeriod can be used for large deformation

Absolutely not, as you find. This is for large bodies, not large deformations.
Bruno

Revision history for this message
Jan Stránský (honzik) said : 		#2

Hello,
I could not reproduce your problem. I ran the simulation until exz=3.0 with
more or less constant stresses..
What version of Yade do you use?
cheers
Jan

2016-06-23 12:08 GMT+02:00 Bruno Chareyre <
<email address hidden>>:

> Question #295592 on Yade changed:
> https://answers.launchpad.net/yade/+question/295592
>
> Status: Open => Answered
>
> Bruno Chareyre proposed the following answer:
> Hi,
>
> > allowBiggerThanPeriod can be used for large deformation
>
> Absolutely not, as you find. This is for large bodies, not large
> deformations.
> Bruno
>
> --
> You received this question notification because your team yade-users is
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Revision history for this message
chuanqi liu (liuchuanqi1988) said : 		#3

So, Bruno, is there any possible for applying large deformation? I mean shear a sample without ceasing.

Thanks, Jan , I use Yade 1.12.0, maybe i can update to the newest version, and try again.

Revision history for this message
Jan Stránský (honzik) said : 		#4

I used relatively new version without the problem you reported, so a newer
version could help..
Jan

2016-06-24 10:09 GMT+02:00 chuanqi liu <<email address hidden>
>:

> Question #295592 on Yade changed:
> https://answers.launchpad.net/yade/+question/295592
>
> Status: Answered => Open
>
> chuanqi liu is still having a problem:
> So, Bruno, is there any possible for applying large deformation? I mean
> shear a sample without ceasing.
>
> Thanks, Jan , I use Yade 1.12.0, maybe i can update to the newest
> version, and try again.
>
> --
> You received this question notification because your team yade-users is
> an answer contact for Yade.
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users
> Post to : <email address hidden>
> Unsubscribe : https://launchpad.net/~yade-users
> More help : https://help.launchpad.net/ListHelp
>

Revision history for this message
Bruno Chareyre (bruno-chareyre) said : 		#5

> is there any possible for applying large deformation? I mean shear a sample without ceasing.

I assume you refer to true 3-periodic boundary conditions. Then the answer is:
- In theory yes, it is possible
- In Yade no, it is not possible although we are not very far from it and incomplete steps in this direction have been taken in the past
- In other DEM codes, usually not.

Can you help with this problem?

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