Hi Gilian,
you have switched on gravity, right? I have encountered a quite similar
problem in my Stokes model when I use a fixed pressure
BC in combination with a hydrostatic pressure gradient and gravity. If
you fail to get the pressure distribution at the boundary
"very exact" you will have spurious in- and outflows there. Have you
tried using a fixed density?
Have you tried only injecting pure water without any component that
might change your density?
Best wishes
Kilian
On 08/15/2018 11:31 AM, Schout, G. (Gilian) wrote:
Hey Timo,
Thanks for helping out.
I have tried your suggestions but unfortunately it doesn’t seem to
change the strange velocity fields I get. In the examples below I have
Dirichlet conditions on the lateral boundaries only between 10 < y <
50 (domain is 60 m high in total) to avoid the corner vertices. Also,
I removed the outflow boundary and changed all the other boundaries to
a solDependentNeumann (zero flux). That gives the following result:
Which is still relatively ok, but if I for example increase the
overall pressure in the domain, conceptually moving the model to a
depth of 240 m while keeping hydrostatic pressure, I get the following:
The fact that increasing pressures makes the problem worse makes me
believe that the problem is related to the implementation of the
density/pressure on the boundaries, but looking at the results in
Paraview the pressure and density distribution don’t appear to me as
they should be producing these velocities. I also get weird kind of
convection cells when I completely remove the lateral head gradient,
but keep the dirichlet conditions.
In earlier communications with Dennis about the same problem is sent
him the results of 2 simulations through wetransfer
(_https://we.tl/OxogWezIhV_), maybe they can give you some clue as to
the solution.
With regards to your question, I would like to have the groundwater
table / atmosphere at the top of my domain in most scenarios. So,
ideally, I would have an unsaturated zone at the top of the model as
well. I noticed one test problem (3p3c/infiltrationproblem.hh) which
has the same, but haven’t been able to implement that so far. That’s
another subject for another day though ;)
Kind regards,
Gilian
*From:*Timo Koch [mailto:[email protected]]
*Sent:* 14 August 2018 20:46
*To:* DuMuX User Forum <[email protected]>
*Cc:* Schout, G. (Gilian) <[email protected]>
*Subject:* Re: [DuMuX] problem inducing strictly lateral groundwater
flow in 2p2c model
Hi Gilian,
I’m just guessing what the problem could be.. Have you tried not to
set Dirichlet boundary conditions for the corner vertices? This can be
tricky with the box method and its dual grid as you can’t control the
flow over the sub control volume face adjacent to the corner vertex on
the bottom and the top boundary if the corner is set to Dirichlet.
This may cause the water to escape this weirdly through that single scvf.
Also, the outflow boundary condition only works, if you’re flow
direction is always strictly outwards. So in the beginning it might
not work out that well. You can use solDependentNeumann to weakly
enforce any boundary condition, like a Robin/Cauchy-type. What’s on
top of your domain conceptually?
Best wishes
Timo
On 13. Aug 2018, at 17:27, Schout, G. (Gilian) <[email protected]
<mailto:[email protected]>> wrote:
Dear dumux-team,
I hope you can help me solve a problem in my models that I’ve been
trying to figure out for some time now without success.
Conceptually, I have been modelling leakage of natural gas into a
fully saturated unconsolidated sedimentary aquifer. In the most
basic version I use a 2D, 2p2c model where methane enters the from
the base of a fully saturated aquifer. The domain is 120 by 60 m,
and the injection occurs by way of a Neumann boundary between x=30
and x=31 m. Besides this I have no flow boundaries at the top and
bottom, with an outflow boundary at the top for methane so that it
can leave the domain once it reaches the top (due to buoyancy).
Then, to induce lateral flow, I use a hydrostatic pressure
distribution with a minor increase in pressure towards the left of
the domain, such that water flows to the right. This distribution
I have assigned as both the initial pressure and at sides as
dirichlet boundaries. The code can be seen on my GitLab of this
version of the modelhere
<https://git.iws.uni-stuttgart.de/gilianschout/CH4Leak/blob/master/2p2c/leak2p2c.hh>.
Now the problem is that however I try to implement the lateral
boundaries, I always get unexpected velocity vectors around the
corners of the domain as you can see in this figure:
<image002.jpg>
Now this is not even that bad - in the middle of the domain the
velocity profile is as I would like it to be. However, when I
increase the absolute pressure in the domain, it becomes much
worse. For example, here is the same image for a depth of 240 m.
<image005.jpg>
This obviously influences the results of the simulation
significantly. I have been trying different solutions the last
couple of days but haven’t been able to put my finger on it.
Presumably, there is some discrepancy between the model calculated
pressures and the pressures/densities set at the boundaries. My
hope is that someone in the team has perhaps run into similar
issues and has a solution. The goal is obviously to have strictly
lateral groundwater flow, without a vertical component (unless
induced by the gas injection at the bottom).
Thanks in advance, kind regards,
*Gilian Schout**|*PhD Candidate|Faculty of Geosciences|Utrecht
University|+31 6 16523607|[email protected] <mailto:[email protected]>
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Kilian Weishaupt M.Sc.
Institut für Wasser- und Umweltsystemmodellierung (IWS)
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung
Universität Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart
Email: [email protected]
Telefon: 0049 711 685-60461 ** fax: 0049-711-685-60430
http://www.hydrosys.uni-stuttgart.de
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