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[Jan Stránský <question691584@xxxxxxxxxxxxxxxxxxxxx>]

Question #691584 on Yade changed:
https://answers.launchpad.net/yade/+question/691584

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

first of all, I am not sure if periodic simulations are a good very first starting point to learn Yade..
The previous scripts are OK?


> 1.What is the meaning of "O.cell.hSize=Matrix3(2,0,0, 0,2,0, 0,0,2)"?

it assign Matrix3(2,0,0, 0,2,0, 0,0,2) object to O.cell [1] as its hSize
[2] attribute


> What is the meaning of the numbers in the Matrix?

"Base cell vectors (columns of the matrix)" [2].
In this case, diagonal terms are "normal size" (i.e. 2x2x2), zero non-diagonal terms means no skew and no rotation
(non-diagonal terms control skew and/or rotation)


> 2."pack.regularHexa(pack.inAlignedBox((0,0,0),(2,2,2)),radius=.1,gap=0,color=(0,0,1))". What is the meaning of the "color=(0,0,1)"? In some other scripts I also see "color=(1,1,1)"

color of resulting particles

(in ideal case, the documentation should tell that **kw are keywords
passed to utils.sphere function. You are welcome to improve the
documentation! :-)


> 3.What is the meaning of "O.cell.velGrad=Matrix3(-.1,0,0, 0,-.1,0, 0,0,-.1)"?

you assign Matrix3(-.1,0,0, 0,-.1,0, 0,0,-.1) object to O.cell [1] as its hSize [3] attribute.
The components are components of velocity gradient (in matrix form).
In this case, only diagonal negative terms it is isotropic compaction.


> What is the meaning of the numbers in the Matrix?

components of velocity gradient [4]
The indexing of the components is very similar to those of deformation gradient (O.cell.trsf), see below.


> In the "Checkstress()" part, it changes to "O.cell.velGrad=Matrix3(0,0,.1, 0,0,0, 0,0,0)"

now it is changed to shear:
diagonal terms are zero = no change of size
non-diagonal terms are non-zero = some shear or rotation (in this case only one, xz, non-diagonal term is non-zero = shear in xz plane).


> 4.What is the meaning of "O.cell.trsf[0,2]" in the "checkDistorsion" part? What do the numbers in the "trsf" mean?

trsf is deformation gradient [5] of the cell
trsf[0,2] means its xz shear part (see below)


> stress=sum(normalShearStressTensors(),Matrix3.Zero)
> 5.In "plot.addData(exz=O.cell.trsf[0,2],szz=stress[2,2],sxz=stress[0,2],tanPhi=(stress[0,2]/stress[2,2]) if stress[2,2]!=0 else 0,i=O.iter)" part,What is the meaning of the number in the "streess[]"? For example, "stress[2,2]" or "stess[0,2]"

stress here is matrix form of Cauchy stress tensor [6]. Indices are 0=x, 1=y, 2=z
stress[2,2]  means stress_zz, i.e. normal z component
stress[0,2] means stress_xz, i.e. shear xz component

The indices corresponds to those of hSize, velGrad and trsf (where it is
related to strain/strain-rate counterpart)


cheers
Jan

[1] https://yade-dem.org/doc/yade.wrapper.html#cell
[2] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Cell.hSize
[3] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Cell.velGrad
[4] https://www.continuummechanics.org/velocitygradient.html
[5] https://en.wikipedia.org/wiki/Finite_strain_theory#Deformation_gradient_tensor
[6] https://en.wikipedia.org/wiki/Cauchy_stress_tensor

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