Hi Ana,
I am not sure whether you are right that 1e-14 to 1e-16 should not be
considered as zero. It is the expected precision of a double. In
general, you cannot expect it to be better, just because in the regular
case it by luck is actually better.
Maybe you can run your simulation with quad precision. That might help
to get more knowledge regarding the limits of double precision.
Bye
Christoph
Am 17.11.21 um 11:31 schrieb Ana Carolina Loyola:
Hello,
I have been working on the upscaling of the 2D permeability tensor of
fractured media with the Box Method using the multidomain module of
Dumux 3.2. The code attached has worked well when compared to the
analytical solutions of perpendicular and equally spaced fractures.
I apply linear pressure boundary conditions and integrate flow at the
boundaries using the following equation*
image.png
And for that, I created a "boundary flux" function (at main.cc), which
calls the computeFlux function for all the faces that are located at the
boundary of the domain.
The reason I send this message is that I have noticed some precision
errors that concern me when running another simple test case (one
horizontal and non-persistent fracture, meshes are attached). It is
expected that I have kxy and kyx equal to 0, which seems to work fine
when I use a symmetric mesh (signalized with -sym in the .msh files),
since I get kxy and kyx in the order of < 1e-30 and net flux balances in
the order of <1e-28.
But when I use non-symmetric meshes I get kxy in the order of 1e-17,
which can not be considered to be 0, considering the matrix
permeability, and boundary fluxes summation as high as 1e-14 when I
apply the x gradient. The "error" does not seem to improve when
refining the mesh.
So what I would like to ask here is if I am using the appropriate
functions to integrate flow and if you would have any
implementation-related suggestions to get past this issue.
I am sorry for the long text; this may be more of a theoretical issue
than a code-related one, but I thought it was worth the shot just to see
if I am missing something.
*Equation used by Pouya and Fouché (2009)
Pouya, Amade & Fouché, Olivier. (2009). Permeability of 3D discontinuity
networks: New tensors from boundary-conditioned homogenization. Advances
in Water Resources. 32. 303-314. 10.1016/j.advwatres.2008.08.004.
Thanks
Ana Loyola
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