Problems on 3D Anisotropic Diffusion Coefficient

[Zhiwen Liang]

Hi all,
Thank you very much for solving my last problem. I learned a lot from the
discussion.

Now I am trying to solve a diffusion problem in 3D. And the diffusivity is
anisotropic. For example:

D=numerix.array(((Dx,0.,0.),(0.,Dy,0.),(0.,0.,Dz)))

I attached a very simple script that use this. But when I run it, I got the
error of "Warning: invalid value encountered in divide".

This feature works fine in 2D. I wonder if anyone has tried the similar
thing. I would greatly appreciate any advice.

Thanks,
Zhiwen

from fipy import *
from fipy.tools import numerix

mesh=Grid3D(nx=50,ny=50,nz=50,dx=0.2,dy=0.2,dz=0.2)
var=CellVariable(mesh=mesh,value=0.,hasOld=1)
X,Y,Z=mesh.getCellCenters()
var.setValue(1.,where=numerix.where(((Z-5.)**2)<=(2.5**2-(X-5.)**2-(Y-5.)**2),1,0))
Dx=1.
Dy=1.
Dz=1.
D=numerix.array(((Dx,0.,0.),(0.,Dy,0.),(0.,0.,Dz)))
dt=0.9*0.2**2/Dx
steps=100

from fipy.boundaryConditions.fixedValue import FixedValue
BCs=(FixedValue(faces=mesh.getFacesRight(),value=1.),
     FixedValue(faces=mesh.getFacesLeft(),value=0.))

eq=TransientTerm()==DiffusionTerm((D,))

for i in range(steps):
    var.updateOld()
    res = 1.
    while res > 1e-2:
        res = eq.sweep(var, dt=dt)