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] 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/>
_______________________________________________
Dumux mailing list
[email protected] <mailto:[email protected]>
https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
_______________________________________________
Dumux mailing list
[email protected]
https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
--
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]
_______________________________________________
Dumux mailing list
[email protected]
https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
