I don not understand how to simulate triaxial-test in Yade.

Hello, everybody!

Although Yade provides a tutorial of Periodic triaxial test, I still not understand the role of PeriTriaxController() in every step of DEM simulation.

By documentation, I understand the role of ForceResetter() is to reset force, InsertionSortCollider([Bo1_Sphere_Aabb()]) to create potential interactions, InteractionLoop([Ig2_Sphere_Sphere_ScGeom()], [Ip2_FrictMat_FrictMat_FrictPhys()][Law2_ScGeom_FrictPhys_CundallStrack()]) to make exact collision detection, compute interaction properties and determine force, which coresponds to the sequence of simulation loop respectively.

So could you give me the role of played by PeriTriaxController() in the simulation loop. And what operation PeriTriaxController() in mumerical triaxial test does corespond to in a actual triaxial test?

Here is the codes:
from __future__ import print_function
sigmaIso=-1e5

#import matplotlib
#matplotlib.use('Agg')

# generate loose packing
from yade import pack, qt, plot

O.periodic=True
sp=pack.SpherePack()
if 0:
 ## uniform distribution
 sp.makeCloud((0,0,0),(2,2,2),rMean=.1,rRelFuzz=.3,periodic=True)
else:
 ## create packing from clumps
 # configuration of one clump
 c1=pack.SpherePack([((0,0,0),.03333),((.03,0,0),.017),((0,.03,0),.017)])
 # make cloud using the configuration c1 (there could c2, c3, ...; selection between them would be random)
 sp.makeClumpCloud((0,0,0),(2,2,2),[c1],periodic=True,num=500)

# setup periodic boundary, insert the packing
sp.toSimulation()

O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb()]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_FrictPhys()],
  [Law2_ScGeom_FrictPhys_CundallStrack()]
 ),
 PeriTriaxController(label='triax',
  # specify target values and whether they are strains or stresses
  goal=(sigmaIso,sigmaIso,sigmaIso),stressMask=7,
  # type of servo-control
  dynCell=True,maxStrainRate=(10,10,10),
  # wait until the unbalanced force goes below this value
  maxUnbalanced=.1,relStressTol=1e-3,
  # call this function when goal is reached and the packing is stable
  doneHook='compactionFinished()'
 ),
 NewtonIntegrator(damping=.2),
 PyRunner(command='addPlotData()',iterPeriod=100),
]
O.dt=.5*PWaveTimeStep()

def addPlotData():
 plot.addData(unbalanced=unbalancedForce(),i=O.iter,
  sxx=triax.stress[0],syy=triax.stress[1],szz=triax.stress[2],
  exx=triax.strain[0],eyy=triax.strain[1],ezz=triax.strain[2],
  # save all available energy data
  Etot=O.energy.total(),**O.energy
 )

# enable energy tracking in the code
O.trackEnergy=True

# define what to plot
plot.plots={'i':('unbalanced',),'i ':('sxx','syy','szz'),' i':('exx','eyy','ezz'),
 # energy plot
 ' i ':(O.energy.keys,None,'Etot'),
}
# show the plot
plot.plot()

def compactionFinished():
 # set the current cell configuration to be the reference one
 O.cell.trsf=Matrix3.Identity
 # change control type: keep constant confinement in x,y, 20% compression in z
 triax.goal=(sigmaIso,sigmaIso,-.2)
 triax.stressMask=3
 # allow faster deformation along x,y to better maintain stresses
 triax.maxStrainRate=(1.,1.,.1)
 # next time, call triaxFinished instead of compactionFinished
 triax.doneHook='triaxFinished()'
 # do not wait for stabilization before calling triaxFinished
 triax.maxUnbalanced=10

def triaxFinished():
 print('Finished')
 O.pause()

Thanks!