Dear Ali,
you are right the outflow-condition is implemented in Dumux. It
calculates the fluxes on the boundary in the same manner as the fluxes
are calculated inside the domain. Hence, everything flowing towards the
boundary will leave the domain. Diffusive fluxes are not zero at the
boundary, but contribute to the outflow-flux.
There are a few things, you should keep in mind when using an outflow
condition:
- the main flux should be towards the outflow-condition, not parallel to it
- it is an outflow condition, if the flux is flowing into the domain, it
might cause numerical problems
- the gradients of pressure and mass fraction have to be evaluated at
the boundary, meaning at an element boundary. There, the gradient of the
Ansatz-functions is not necessarily well defined. We found out, that
this does not cause problems, when the flux actually is directed outwards.
- if you use setAllOutflow(), the outflow condition is applied to all
equations. You can specify it for one equation using setOutflow(equationIdx)
The CouplingOutflow-condition is something completely different. It
deals with coupling free (Stokes) and porous-medium (Darcy) flow. You do
not need it in your setting.
Take care,
Katherina
On 07/29/13 06:58, [email protected] wrote:
Dear DuMux users,
I am working on co2 model and I would like to have some information
about the outflow boundary conditions in DuMux box models.
In my conceptual model, I have an unconfined aquifer. The top of the
aquifer is the ground surface at Patm = 1e5 Pa.
In my knowledge, for an unconfined aquifer, we can usually impose the
Outflow boundary condition where the masse fraction gradient of
components is zero (diffusive flux = 0).
I simply used setAllOutflow on the aquifer surface.
On DuMux website, I found that this boundary condition is already
implemented inside DuMux implicit models, however when I used it, I
obtained the same results as Neumann boundary condition.
I would like to check with you if my understanding about the this
boundary condition is correct and if my results make any sense?
Also, I didn't find any documentation on setAllCouplingOutflow
<http://www.dumux.org/doxygen-stable/html-2.1/class_dumux_1_1_boundary_types.php#af1a96abab92c3eb33a37d3d2f371f933>.
Can you explain the difference between setAllOutflow and this one?
Thanks a lot for your help
Best regards
Ali NOWAMOOZ
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Dipl.-Ing. Katherina Baber
Universität Stuttgart
Institut für Wasser- und Umweltsystemmodellierung
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung
Pfaffenwaldring 61
D-70569 Stuttgart
Tel: (+49) 0711/ 685-64676
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