How to use PSD

Asked by Leonard on 2019-11-23

Hi,
I'm trying to generate an assembly with PSD like Fig. 9 in [1] or Fig. 1 in [2]. Firstly, I set distributeMass = True, then, I pick up several point (xi,yi) from Fig. 9 in [1] or Fig. 1 in [2] and make psdSizes=[x1,x2,x3,x4],psdCumm=[0,y2,y3,1]. I am not sure if above mentioned way is correct, especially in terms of the following issues.

1. Should I set distributeMass = True or False.

2. In TriaxialStressController engine during triaxial test simulation[3], internalCompaction is set as True to reach confining pressure by growing particles. I wonder if all the particles are scaled up with the same scalar? Like the scale up in Fig. 1 in [2]?

3. By the way, I'm very curious about how it is achieved in Fig. 9 in [1], the numerical PSD is almostly agreed with experimental PSD, is there no particle growing during the isotropic compaction phase?

Thanks a lot.
Leonard

[1]https://link.springer.com/article/10.1007%2Fs10035-016-0687-0
[2]https://link.springer.com/article/10.1007/s11440-017-0593-6
[3]https://github.com/yade/trunk/blob/master/examples/triax-tutorial/script-session2.py

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Leonard
Solved:
2019-11-26
Last query:
2019-11-26
Last reply:
2019-11-25
Robert Caulk (rcaulk) said : #1

Hello,

>Should I set distributeMass = True or False.

Depends on what you want to simulate. Do you want the psd distribution applied to particle count or mass fraction? Quote from the doc[1]:

"By default (with distributeMass==False), the distribution is applied to particle radii. The usual sense of “particle size distribution” is the distribution of mass fraction (rather than particle count); this can be achieved with distributeMass=True."

> I wonder if all the particles are scaled up with the same scalar?

If internalCompaction=True, TriaxialStressController uses growParticles [2], which changes the size of the spheres using a common multiplier [3].

> is there no particle growing during the isotropic compaction phase?

Maybe they used internalCompaction=False.

Cheers,

Robert

[1]https://yade-dem.org/doc/yade.pack.html#yade._packSpheres.SpherePack.makeCloud
[2]https://gitlab.com/yade-dev/trunk/blob/master/pkg/dem/TriaxialStressController.cpp#L274
[3]https://gitlab.com/yade-dev/trunk/blob/master/pkg/dem/Shop_02.cpp#L848

Leonard (z2521899293) said : #2

Hi Robert,
Many thanks for your reply.
>Depends on what you want to simulate.
What I want to simulate is the common PSD curve for a soil. For a general particle size distribution curve of soil, the Y-axis is percentage passing by mass, the x-axis is particle size (diameter) based on what I understand.
What I am confused is whether the distributeMass command controls on Y-axis or on X-axis?
For example, if distributeMass command controls on Y-axis, it may mean that percentage passing by mass (distributeMass=True) or by count (distributeMass=False)?
If distributeMass command controls on X-axis, it may mean that X-axis is particle diameter (distributeMass=False) or particle mass (distributeMass=True)?

>spheres using a common multiplier
Thanks, it is clear.

>Maybe they used internalCompaction=False.
I'm still interested in how it is achieved by setting internalCompaction=False.
I have also tried internalCompaction=False, the problem is that when set internalCompaction=False, the size of the sample changed.
For example, the size of initial packing is 0.7*0.7*1.4 (mn,mx=Vector3(0,0,0),Vector3(0.7,0.7,1.4)), when I set internalCompaction=True, after compacted state completed, the size of the packing stays around 0.7*0.7*1.4. However, when I set internalCompaction=False, after compacted state completed, the size of the packing is changed to 0.26*0.26*0.9, and in this case, I can not obtain a reasonable sample in terms of size. The following MWE may show this question by changing internalCompaction= True to False.
###########
from yade import pack, plot
nRead=readParamsFromTable(
 num_spheres=1000,
 compFricDegree = 30,
 key='_triax_base_',
 unknownOk=True
)
from yade.params import table

num_spheres=table.num_spheres
key=table.key
targetPorosity = 0.43
compFricDegree = table.compFricDegree
finalFricDegree = 30
rate=-0.02
damp=0.2
stabilityThreshold=0.01
young=5e6
mn,mx=Vector3(0,0,0),Vector3(0.7,0.7,1.4)

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)
O.bodies.append([sphere(center,rad,material='spheres') for center,rad in sp])

Gl1_Sphere.quality=3

### DEFINING ENGINES ###
triax=TriaxialStressController(
 maxMultiplier=1.+2e4/young,
 finalMaxMultiplier=1.+2e3/young,
 thickness = 0,
 stressMask = 7,
 internalCompaction=True,## please change True to False here to look at what I say
)

newton=NewtonIntegrator(damping=damp)

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()]
 ),
 GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8),
 triax,
 newton
]

Gl1_Sphere.stripes=0
if nRead==0: yade.qt.Controller(), yade.qt.View()

### APPLYING CONFINING PRESSURE ###
triax.goal1=triax.goal2=triax.goal3=-10000
while 1:
 O.run(1000, True)
 unb=unbalancedForce()
 print 'unbalanced force:',unb,' mean stress: ',triax.meanStress
 if unb<stabilityThreshold and abs(-10000-triax.meanStress)/10000<0.001:
  break

print "### Isotropic state saved ###"
### REACHING A SPECIFIED POROSITY PRECISELY ###
import sys
while triax.porosity>targetPorosity:
 # we decrease friction value and apply it to all the bodies and contacts
 compFricDegree = 0.95*compFricDegree
 setContactFriction(radians(compFricDegree))
 print "\r Friction: ",compFricDegree," porosity:",triax.porosity,
 sys.stdout.flush()
 O.run(500,1)
print "### Compacted state saved ###"
########################
Cheers,
Leonard

Robert Caulk (rcaulk) said : #3

distributeMass=True ensures your PSD is mass percent passing instead of particle count percent passing.

Leonard (z2521899293) said : #4

Thanks Robert, this solved my problem, and I will open a new question about my last doubt.
Cheers,
Leonard