GS did not converge in 20k iterations

Hello,
I used PeriodicFlowEngine to simulate Fluid-Structure Interaction, but I get ERROR :GS did not converge in 20k iterations (maybe because the reference pressure is 0?).I always faild to use PeriodicFlowEngine.I think I used PeriodicFlowEngine incorrectly.
Thanks for your any suggestion.
#################MWE######################
O.periodic=True
O.cell.setBox(1,1,1)

from yade import pack

num_spheres=1000# number of spheres
young=1e6
compFricDegree = 3 # initial contact friction during the confining phase
finalFricDegree = 30 # contact friction during the deviatoric loading
mn,mx=Vector3(0,0,0),Vector3(1,1,1) # corners of the initial packing

O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=radians(compFricDegree),density=2600,label='spheres'))
#O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=0,density=0,label='walls'))
#walls=aabbWalls([mn,mx],thickness=0,material='walls')
#wallIds=O.bodies.append(walls)

sp=pack.SpherePack()
sp.makeCloud(mn,mx,-1,0.3333,num_spheres,True, 0.95,seed=1) #"seed" make the "random" generation always the same
sp.toSimulation(material='spheres')

triax=PeriTriaxController(
        dynCell=True,
        mass=.2,
        maxUnbalanced=0.001,
        relStressTol=0.02,
        goal=[-1e4,-1e4,-1e4],
        stressMask=7,
        globUpdate=5,
        maxStrainRate=[1.,1.,1.],
        label='triax')

newton=NewtonIntegrator(damping=0.2)

O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()],allowBiggerThanPeriod=True),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_FrictPhys()],
  [Law2_ScGeom_FrictPhys_CundallStrack()],label="iloop"
 ),
 PeriodicFlowEngine(dead=1,label="flow"),#introduced as a dead engine for the moment, see 2nd section
 GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8),
 triax,
 newton
]

while 1:
  O.run(1000, True)
  unb=unbalancedForce()
  if unb<0.001 :
    break

setContactFriction(radians(finalFricDegree))

## ______________ Oedometer section _________________

#B. Activate flow engine and set boundary conditions in order to get permeability
flow.dead=0
flow.defTolerance=0.3
flow.meshUpdateInterval=200
flow.permeabilityFactor=1
flow.viscosity=10
flow.bndCondIsPressure=[0,0,1,1,0,0]
flow.bndCondValue=[0,0,1000,0,0,0]
flow.boundaryUseMaxMin=[0,0,0,0,0,0]
O.dt=0.1e-3
O.dynDt=False

O.engines=O.engines+[PyRunner(command='flow.saveVtk()',iterPeriod=1)]
O.run(1,1)
Qin = flow.getBoundaryFlux(2)
Qout = flow.getBoundaryFlux(3)
permeability = abs(Qin)/1.e-4 #size is one, we compute K=V/∇H
print "Qin=",Qin," Qout=",Qout," permeability=",permeability

#C. now the oedometer test, drained at the top, impermeable at the bottom plate
flow.updateTriangulation=True #force remeshing to reflect new BC immediately
newton.damping=0
####################