# How to use PSD

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

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2019-11-26
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2019-11-26
2019-11-25
 Robert Caulk (rcaulk) said on 2019-11-24: #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

 Leonard (z2521899293) said on 2019-11-24: #2

Hi Robert,
>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.
###########
num_spheres=1000,
compFricDegree = 30,
key='_triax_base_',
unknownOk=True
)

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=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)

Gl1_Sphere.quality=3

### DEFINING ENGINES ###
triax=TriaxialStressController(
maxMultiplier=1.+2e4/young,
finalMaxMultiplier=1.+2e3/young,
thickness = 0,
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

### 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
print "\r Friction: ",compFricDegree," porosity:",triax.porosity,
sys.stdout.flush()
O.run(500,1)
print "### Compacted state saved ###"
########################
Cheers,
Leonard

 Robert Caulk (rcaulk) said on 2019-11-25: #3

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

 Leonard (z2521899293) said on 2019-11-26: #4

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