Dear Georg,
I am not quite sure what causes your problem. Could you send the
implementation of your boundary conditions, i.e. your boudaryTypes() and
your dirichlet() function from your problem?
You could also try the following:
1. Just set the pressure as a Dirichlet condition and make the other two
equations outflow BC.
2. Try it with a 2p2c transport only system (set the third component to
zero everywhere), do you still get unphysical values?
Best regards
Alex
On 08/13/2015 01:56 PM, [email protected] wrote:
Hi Alex,
I tried to do the same thing as in the 1p2coutflowproblem only with a
2p3c Fluidsystem and the mpnc model. Initially, only the gas phase is
present in the whole domain (Sg=1) and I set Dirichlet boundary
conditions for all primary variables on the inlet (pg = 1.6 bar, Sg=1
and the mole fractions/fugacities). Then I set Dirichlet conditions
for pressure and saturation on the outlet (Sg=1, pg=1.5 bar). The
Dirichlet conditions are consistent with the initial conditions. For
the component conservation equations I set outflow conditions on the
outlet.
With these boundary conditions, everything should flow from the inlet
to the outlet due to the pressure gradient of the gas phase. The gas
phase composition may change on the way to the outlet due to
reactions: 1 species is consumed, another produced. With the outflow
bc everything that reaches the outlet should be allowed to leave the
domain. Sadly, this is not working.
I get unphysical mole fractions at the outlet (x > 1). Any clues why
this does not work? Is the outflow condition used anywhere in a 2p-system?
Best regards
Georg
*Von:*Dumux [mailto:[email protected]] *Im
Auftrag von *Alexander Kissinger
*Gesendet:* Freitag, 31. Juli 2015 16:21
*An:* DuMuX User Forum
*Betreff:* Re: [DuMuX] Boundary conditions
Dear Georg,
If I understand correctly this means that whatever is on an outflow
boundary is allowed to flow out or into the system. So if we assume
pure fickian diffusion and the concentration in the domain is higher
than on the boundary stuff will flow out while it is vice versa if the
concentration is lower. If that is the case, what exactly is the
difference to a Dirichlet boundary condition? As far as I see, with
this type of boundary condition I would keep e.g. a concentration on
the boundary constant. Am I correct?
In the case of pure fickian diffusion (no advection i.e. constant
pressure) the concentration at your outflow boundary would increase
until the concentration gradient is zero i.e. no more flow. The
difference between a Dirchlet boundary is that your concentration at
the boundary dof is allowed to change with an outflow BC.
Consider this example where the outflow boundary is more useful:
1d flow and transport in a tube (model: 1p2c). Left boundary has
Neumann BC with fluid entering at a certain conentration. The right
boundary has a Dirichlet BC for pressure (constant velocity in the
tube) and an outflow boundary for the transported component. If the BC
for the transported component were Dirichlet the concentration would
stay at zero. With the outflow BC the concentration may increase at
the boundary dof and the component may leave the domain through the
advective flux. See also the test/implicit/1p2coutflowproblem.
Best regards
Alex
On 07/31/2015 02:47 PM, [email protected]
<mailto:[email protected]> wrote:
Dear Alex,
Thanks for your reply!
/“I am not sure if I got you right, you want to have a fixed
Saturation (Dirichlet) for one phase and inject another phase?
In Dumux you can choose the equation that should be replaced by
the Dirichlet condition with the call:
setDirichlet(int pvIdx, int eqIdx)
The equation you choose cannot be assigned to a Neumann BC anymore.
The rest of the equations can be assigned as Neumann BCs.
Maybe you could list the type of BC you would like to have for
each equation?”
/
I found a workaround to calculate the fluxes at the outlet of my
system, so now I set Dirichlet conditions at the inlet and
solDependentNeumann conditions at the outlet. This should work.
“For the box method the outflow condition uses the gradients
evaluated at the integration point of the boundary face to
calculate the flux out of the domain for the equation you choose.”
If I understand correctly this means that whatever is on an
outflow boundary is allowed to flow out or into the system. So if
we assume pure fickian diffusion and the concentration in the
domain is higher than on the boundary stuff will flow out while it
is vice versa if the concentration is lower. If that is the case,
what exactly is the difference to a Dirichlet boundary condition?
As far as I see, with this type of boundary condition I would keep
e.g. a concentration on the boundary constant. Am I correct?
Best regards
Georg
*Von:*Dumux [mailto:[email protected]] *Im
Auftrag von *Alexander Kissinger
*Gesendet:* Donnerstag, 30. Juli 2015 08:53
*An:* DuMuX User Forum
*Betreff:* Re: [DuMuX] Boundary conditions
Dear Georg,
I am not sure if I got you right, you want to have a fixed
Saturation (Dirichlet) for one phase and inject another phase?
In Dumux you can choose the equation that should be replaced by
the Dirichlet condition with the call:
setDirichlet(int pvIdx, int eqIdx)
The equation you choose cannot be assigned to a Neumann BC anymore.
The rest of the equations can be assigned as Neumann BCs.
Maybe you could list the type of BC you would like to have for
each equation?
Secondly, I stumbled across the outflow boundary condition
recently what is the physical idea behind this type of boundary
condition?
For the box method the outflow condition uses the gradients
evaluated at the integration point of the boundary face to
calculate the flux out of the domain for the equation you choose.
Best regards
Alex
On 29.07.2015 16:14, [email protected]
<mailto:[email protected]> wrote:
Hello Dumux,
I am working with the (implicit, box) mpnc-model with a 2p5c
fluidsystem and I would like to specify the following inlet
boundary conditions to my system: gas pressure, saturation and
phase composition. This can be done with a Dirichlet condition
and it works fine. But additionally, I would like to set the
gas flux into the model domain (basically the pressure
gradient) which would mean setting a Neumann boundary
condition. Is there a way to do this in Dumux?
Secondly, I stumbled across the outflow boundary condition
recently what is the physical idea behind this type of
boundary condition?
Thanks for your help!
Georg Futter
——————————————————————————
*German Aerospace Center *(DLR)
Institute of Engineering Thermodynamics | Computational
Electrochemistry | Pfaffenwaldring 38-40 | 70569 Stuttgart
Dipl.-Ing. *Georg Futter* | Ph.D. student
Telefon 0711/6862-8135 | [email protected]
<mailto:[email protected]>
www.DLR.de <http://www.dlr.de/>
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--
Alexander Kissinger
Institut für Wasser- und Umweltsystemmodellierung
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung
Pfaffenwaldring 61
D-70569 Stuttgart
Telefon: +49 (0) 711 685-64729
E-Mail:[email protected]
<mailto:[email protected]>
_______________________________________________
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--
Alexander Kissinger
Institut für Wasser- und Umweltsystemmodellierung
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung
Pfaffenwaldring 61
D-70569 Stuttgart
Telefon: +49 (0) 711 685-64729
E-Mail: [email protected]
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