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[Alireza Sadeghi <question683375@xxxxxxxxxxxxxxxxxxxxx>]

New question #683375 on Yade:
https://answers.launchpad.net/yade/+question/683375

Hello All,

I was encountered to a problem in my dem modeling. I want to simulate the bulk behavior of material. Due to reach this goal, I have to choose a number of particles which could represent the bulk behavior as similar as experiment. I did two type of simulation.
in the first one, I put the particles in the box and the the box faces compress the paricles, after in the x and y direction, stress remain constant and in the z direction, we increase stress and plot the strain-stress in z direction. Due to initial conditions (randomness of initial position of particles) we will reach to different results in each realization. The code is as below:

from yade import utils, plot
from yade import pack, qt
from datetime import datetime
from yade import export

O.periodic=True
O.cell.refSize=(2e-1,2e-1,2e-1)

O.materials.append(CohFrictMat(normalCohesion= 1e20, shearCohesion= 1e20, isCohesive= True, young=6.81e8, density=1377.5, poisson=0.3, frictionAngle= 0.31, fragile=False, label='Coke'))

nums=['t']

mats=['Coke']

coke=(5e-3,3000)

nums=pack.SpherePack()

nums.makeCloud((0,0,0),(2e-1,2e-1,2e-1),rMean=coke[0],rRelFuzz=0,num=coke[1])

O.bodies.append([utils.sphere(c,r,material=mats[0],color=(0,0,1)) for c,r in nums])

sigmaIso=-1e5

O.engines=[
     ForceResetter(),

     InsertionSortCollider([Bo1_Sphere_Aabb()]),
     InteractionLoop(
        [Ig2_Sphere_Sphere_ScGeom()],
        [Ip2_FrictMat_FrictMat_FrictPhys()],
        [Law2_ScGeom_FrictPhys_CundallStrack()]
     ),

     PeriTriaxController(label='triax',
		goal=(sigmaIso,sigmaIso,sigmaIso),stressMask=7,
		dynCell=True,maxStrainRate=(1,1,1),
		maxUnbalanced=.01,relStressTol=1e-3,
		doneHook='compactionFinished()'
     ),
     NewtonIntegrator(damping=0.4),
     PyRunner(command='history()',iterPeriod=1000,label='recorder'),
]

O.dt=1e-6

O.saveTmp()

def compactionFinished():

	O.cell.trsf=Matrix3.Identity
	triax.goal=(sigmaIso,sigmaIso,-0.5)
	triax.stressMask=3
	triax.maxStrainRate=(0.1,0.1,0.1)
	triax.doneHook='triaxFinished()'
	triax.maxUnbalanced=1
        dataOld = plot.data
        plot.saveDataTxt('RVE3000-iso_part-e5-5.txt')
        plot.data = {}
        plot.plot()




def history():
	plot.addData(unbalanced=unbalancedForce(),
		sxx=-triax.stress[0],syy=-triax.stress[1],szz=-triax.stress[2],
		exx=-triax.strain[0],eyy=-triax.strain[1],ezz=-triax.strain[2],
                sxz=-0.5*(triax.stress[2]+triax.stress[0]), ev=(triax.strain[2]+triax.strain[1]+triax.strain[0]),
                q=-(triax.stress[2]-triax.stress[1]), p=-(triax.stress[2]+triax.stress[1]+triax.stress[0])/3 ,
                D=(triax.stress[2]-triax.stress[1])/sigmaIso,
                R=3*(triax.stress[2]-triax.stress[1])/(triax.stress[2]+triax.stress[1]+triax.stress[0]+1e-2),
                por=porosity(),i=O.iter,)

        print 'porosity:', porosity()
        print 'iteration', O.iter

O.run(8000000,True)

plot.saveDataTxt('RVE3000-dev_part-e5-5.txt')
plot.plots={'ezz':('szz')}
plot.plot()

def triaxFinished():
	print 'Compaction finished'
	O.pause()


In the second one, I made the sample first with the code below:

from yade import utils, plot
from yade import pack, qt
from datetime import datetime
from yade import export

O.periodic=True
O.cell.refSize=(2e-1,2e-1,2e-1)

O.materials.append(CohFrictMat(normalCohesion= 1e20, shearCohesion= 1e20, isCohesive= True, young=6.81e8, density=1377.5, poisson=0.3, frictionAngle= 0.31, fragile=False, label='Coke'))

nums=['t']

mats=['Coke']

coke=(5e-3,3000)

nums=pack.SpherePack()

nums.makeCloud((0,0,0),(2e-1,2e-1,2e-1),rMean=coke[0],rRelFuzz=0,num=coke[1])

O.bodies.append([utils.sphere(c,r,material=mats[0],color=(0,0,1)) for c,r in nums])

sigmaIso=-1e5

O.engines=[
     ForceResetter(),

     InsertionSortCollider([Bo1_Sphere_Aabb()]),
     InteractionLoop(
        [Ig2_Sphere_Sphere_ScGeom()],
        [Ip2_FrictMat_FrictMat_FrictPhys()],
        [Law2_ScGeom_FrictPhys_CundallStrack()]
     ),

     PeriTriaxController(label='triax',
		goal=(sigmaIso,sigmaIso,sigmaIso),stressMask=7,
		dynCell=True,maxStrainRate=(1,1,1),
		maxUnbalanced=.01,relStressTol=1e-3,
		doneHook='compactionFinished()'
     ),
     NewtonIntegrator(damping=0.4),
     PyRunner(command='history()',iterPeriod=1000,label='recorder'),
]


O.dt=1e-6

O.saveTmp()


def compactionFinished():
	print 'Finished'
	O.pause()
        plot.saveDataTxt('Uncertainty-Pre-compact3000.txt')
        plot.data = {}
        O.save('Pre-compact3000.yade')

O.run(1500000,True)


and after that, I compress the sample of "Pre-compact3000.yade" in the z direction and plot the stress-strain in the z direction with code below:

from yade import utils, plot
from yade import pack, qt
from datetime import datetime
from yade import export

O.load('Pre-compact300.yade')


sigmaIso=-1e5


def compactionFinished():

	O.cell.trsf=Matrix3.Identity
	triax.goal=(sigmaIso,sigmaIso,-0.5)
	triax.stressMask=3
	triax.maxStrainRate=(0.1,0.1,0.1)
	triax.doneHook='triaxFinished()'
	triax.maxUnbalanced=1
        dataOld = plot.data
#        plot.saveDataTxt('iso_part-e4.txt')
        plot.data = {}
        plot.plot()

def history():
	plot.addData(unbalanced=unbalancedForce(),
		sxx=-triax.stress[0],syy=-triax.stress[1],szz=-triax.stress[2],
		exx=-triax.strain[0],eyy=-triax.strain[1],ezz=-triax.strain[2],
                sxz=-0.5*(triax.stress[2]+triax.stress[0]), ev=(triax.strain[2]+triax.strain[1]+triax.strain[0]),
                q=-(triax.stress[2]-triax.stress[1]), p=-(triax.stress[2]+triax.stress[1]+triax.stress[0])/3 ,
                D=(triax.stress[2]-triax.stress[1])/sigmaIso,
                R=3*(triax.stress[2]-triax.stress[1])/(triax.stress[2]+triax.stress[1]+triax.stress[0]+1e-2),
                por=porosity(),i=O.iter,)

        print 'porosity:', porosity()
        print 'iteration', O.iter

O.run(5000000,True)

plot.saveDataTxt('Uncertainty-compect300-6.txt')
plot.plots={'ezz':('szz')}
plot.plot()

def triaxFinished():
	print 'Compaction finished'
	O.pause()


However, when I run the code again, I reach to a different results. But we know that the initial sample is the same.
Where does this uncertainty come from?Why the stress-strain curves are different for the same initial sample?

Thank you very much for your patient and help in advance.

Best Reagrds

Alireza

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