about damping

Asked by gholamreza esmaeili on 2019-07-23

hello
below is the code i am reading:

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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,False, 0.95,seed=1) #"seed" make the "random" generation always the same
sp.toSimulation(material='spheres')

triax=TriaxialStressController(
 maxMultiplier=1.+2e4/young, # spheres growing factor (fast growth)
 finalMaxMultiplier=1.+2e3/young, # spheres growing factor (slow growth)
 thickness = 0,
 stressMask = 7,
 max_vel = 0.005,
 internalCompaction=True, # If true the confining pressure is generated by growing particles
)

newton=NewtonIntegrator(damping=0.2)

O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_FrictPhys()],
  [Law2_ScGeom_FrictPhys_CundallStrack()],label="iloop"
 ),
 FlowEngine(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
]

triax.goal1=triax.goal2=triax.goal3=-10000

while 1:
  O.run(1000, True)
  unb=unbalancedForce()
  if unb<0.001 and abs(-10000-triax.meanStress)/10000<0.001:
    break

setContactFriction(radians(finalFricDegree))

## ______________ Oedometer section _________________

#A. Check bulk modulus of the dry material from load/unload cycles
triax.stressMask=2
triax.goal1=triax.goal3=0

triax.internalCompaction=False
triax.wall_bottom_activated=False
#load
triax.goal2=-11000; O.run(2000,1)
#unload
triax.goal2=-10000; O.run(2000,1)
#load
triax.goal2=-11000; O.run(2000,1)
e22=triax.strain[1]
#unload
triax.goal2=-10000; O.run(2000,1)

e22=e22-triax.strain[1]
modulus = 1000./abs(e22)

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

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.bndCondIsPressure=[0,0,0,1,0,0]
flow.bndCondValue=[0,0,0,0,0,0]
newton.damping=0

#we want the theoretical value from Terzaghi's solution
#keep in mind that we are not in an homogeneous material and the small strain
#assumption is not verified => we don't expect perfect match
#there can be also an overshoot of pressure in the very beginning due to dynamic effects
Cv=permeability*modulus/1e4
zeroTime=O.time
zeroe22 = - triax.strain[1]
dryFraction=0.05 #the top layer is affected by drainage on a certain depth, we account for it here
drye22 = 1000/modulus*dryFraction
wetHeight=1*(1-dryFraction)

def consolidation(Tv): #see your soil mechanics handbook...
 U=1
 for k in range(50):
  M=pi/2*(2*k+1)
  U=U-2/M**2*exp(-M**2*Tv)
 return U

triax.goal2=-11000

from yade import plot

## a function saving variables
def history():
   plot.addData(e22=-triax.strain[1]-zeroe22,e22_theory=drye22+(1-dryFraction)*consolidation((O.time-zeroTime)*Cv/wetHeight**2)*1000./modulus,t=O.time,p=flow.getPorePressure((0.5,0.1,0.5)),s22=-triax.stress(3)[1]-10000)
   #plot.addData(e22=-triax.strain[1],t=O.time,s22=-triax.stress(2)[1],p=flow.MeasurePorePressure((0.5,0.5,0.5)))

O.engines=O.engines+[PyRunner(iterPeriod=200,command='history()',label='recorder')]
##make nice animations:
#O.engines=O.engines+[PyRunner(iterPeriod=200,command='flow.saveVtk()')]

from yade import plot
plot.plots={'t':('e22','e22_theory',None,'s22','p')}
plot.plot()
O.saveTmp()
O.timingEnabled=1
from yade import timing
print "starting oedometer simulation"
O.run(200,1)
timing.stats()
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in packing stage damping is equal to 0.2, but after flow engine activation it set to 0, what's the reason? is there any relation between newton.damping and degree of saturation in unsaturated condition?

Question information

Language:
English Edit question
Status:
Solved
For:
Yade Edit question
Assignee:
No assignee Edit question
Solved by:
Bruno Chareyre
Solved:
2019-07-25
Last query:
2019-07-25
Last reply:
2019-07-25

Hi,

> in packing stage damping is equal to 0.2

Yes, it is to accelerated the dynamic convergence to static equilibrium.

> but after flow engine activation it set to 0

Because at equilibrium, and later, there is no reason to introduce artificial damping.

> relation between newton.damping and degree of saturation

No, definitely.

Bruno

gholamreza esmaeili (peymann) said : #2

Thanks Bruno Chareyre, that solved my question.