Timo,
Thank you! I cherry-picked the commit into my DuMux installation and now
my numerical derivative matches the analytical one.
Best regards,
Dmitry
On 27.05.2020 15:08, Timo Koch wrote:
Hi Dmitry,
to follow up on your bug report, I opened an issue
https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/-/issues/892.
There is a simple fix here:
https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/-/merge_requests/2146
Can you try if this improves your convergences / fixes your problem?
The problem with this solution is that it significantly increases the
runtime for models where it is known that there is no dependence
of the scv volume variables on the other dofs of the same element. It
might be possible to deduce this somehow.
Timo
--
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On 26. May 2020, at 17:13, Dmitry Pavlov <dmitry.pav...@outlook.com
<mailto:dmitry.pav...@outlook.com>> wrote:
Hello,
I am trying to do a 1D porous medium flow simulation where one of the
components is a surfactant that affects krw and krn. The effect of
the surfactant depend on pressure gradient.
Earlier, an attempt [1] was made to apply CC method for this kind of
problem. It turned out that DuMux API does not easily allow to
estimate a gradient in TPFA, and, following Timo Koch's advice, I
gave a try to Box method.
I think I am having some trouble with derivatives now. Looking at
this comment in boxlocalassembler.hh, I am beginning to understand why.
// Calculate derivatives of all dofs in stencil with respect
to the dofs in the element. In the //
// neighboring elements we do so by computing the derivatives
of the fluxes which depend on the //
// actual element. In the actual element we evaluate the
derivative of the entire residual. //
Why the trouble? Well, I am calculating the pressure gradient (by
calling evalGradients) inside this method
MaterialLawParams materialLawParams(const Element& element,
const SubControlVolume& scv,
const ElementSolution&
elemSol) const
Here, I store the needed numbers for krw and krn calculation in
MaterialLawParams, and they are properly downstream at
MaterialLaw::krw and MaterialLaw::krn.
Now, let my have two neighbor boxes, 0 and 1. Pressure in box 1
affects the krw/krn in box 1. evalGradients, when called, duly
calculates pressure gradient in box 0 depending, among others, on the
pressure value in box 1. That is good.
But it turns out that the numerical differentiation algorithm does
not bother to call materialLawParams() for scv-s in box 0 when it
calculates the derivatives of fluxes in box 0 w.r.t. pressure in box
1. I suppose that it has to do with the comment above. I suppose that
it takes into account only the "transmissibility" part of the effect
of pressure in box 1 to flux in box 0, and skips the part that comes
from krw/krn sensitivity to the pressure gradient.
Also this comment in boxlocalassembler.hh may be relevant too.
// TODO additional dof dependencies
I will very much appreciate answers to the following questions:
1. Am I correct about the behavior of the numerical Jacobian
assembler, or it should be all right and there is a bug somewhere in
my code or DuMux's?
2. In case I am correct, is there an easy (or not) way to force DuMux
into recalculating the material law parameters for scv-s that belong
to DOFs w.r.t. which we take the derivative? Or take some other approach?
3. If not, will the hand-made analytic Jacobian help? Or it will fail
due to some other assumption in the DuMux engine that is not true for
my problem?
(I actually have the analytic Jacobian implemented, but not quite
sure it is correct, partially because, well, I never had a chance to
test it against a correct numeric Jacobian).
Thank you for your time.
Best regards,
Dmitry
[1] https://listserv.uni-stuttgart.de/pipermail/dumux/2020q2/002516.html
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