Hi Leo,
I forgot to respond to your remark regarding the high saturation above
the layer at z=9m:
The point at z=9m should, in my opinion, belong to the clay layer, so
the high saturation should be fine. At the vertex above, the saturation
is low, as expected (the grid in the gnuplot output corresponds to the
model grid). If this point belongs to the sand layer the high capillary
pressure should also be fine, as you said.
It seems to me that I and my code do not agree about whether the point
at z = 9m belongs to the clay layer or to the sand layer. Unfortunately
I don't see where the problem is. The function that decides which layer
a position belongs to is:
bool isClay_(const GlobalPosition& pos) const
{
return (pos[1] > clayBottom_ - eps_) && (pos[1] < clayTop_ + eps_);
}
where clayBottom_ and clayTop_ are read from the params.input and
should be 5 and 9 respectively. eps_ is 1e-4.
Best regards,
Samuel
On Wed, 2019-03-06 at 15:27 +0100, Stadler, Leopold wrote:
> Hi Samuel,
>
> I haven't simulated flow in the unsaturated zone in the last years.
> But so far I can remeber, it is hard to find good boundary
> conditions.
>
> So I have some small comments on the boundary conditions on the top.
> If you have a no-flow condition in the middle for water and gas in
> combination
> with a high infiltation rate on both sides, this can lead to a fully
> saturated wetting
> front where the gas can not escape.
>
> One solution is to check if the infitration rate is higher than the
> infiltraion
> capacity of your soil. If so, it is often better to switch to a
> Dirichlet
> condition with (fully saturated + pressure).
>
> Looking on your inital SW_profile, the saturation above the layer
> (z=9m) is high,
> so a low capillary pressure looks realistic. In general it is easier
> to let the problem
> settle for a while to get realistic initial conditions.
>
> Paraview is not the best tool for looking at your results since it
> interpolates also
> data that is constant inside your scv. You should imangine a scv
> arround every
> node.
>
> If you have a fully saturated clay layer above the coarser sand, the
> air can be traped
> in the corser material. There are some nice movies "Water moevement
> in soil" on
> youtube.
>
> Kind regards,
> Leo
>
> > Samuel Scherrer <[email protected]> hat am 6.
> März 2019 um 14:36 geschrieben:
> >
> >
> > Hi,
> >
> > I'm currently trying to set up a 2D model for water, air, and heat
> flow
> > in the unsaturated zone with a clay layer between two sand layers.
> >
> > The upper boundary is partly no-flow, partly fixed air pressure,
> > temperature, and water infiltration flux.
> > The side boundaries are no-flow boundaries.
> > The groundwater table is inside the domain, 1 m above the bottom
> > boundary, and the bottom boundary has a constant temperature and
> gas
> > content in water (since only the liquid phase is present) and it is
> a
> > no-flow boundary for air.
> >
> > The formulation I'm using is air pressure - water saturation.
> >
> > As a initial condition I'm using hydrostatic air pressure and a
> water
> > saturation calculated from hydrostatic capillary pressure, initial
> > temperature is the same as the boundaries.
> >
> > I'm using the Box discretization.
> >
> > The clay layer extends from 5m to 9m and the spatial parameters are
> > assigned such that vertices at 5m or at 9m still belong to the clay
> > layer (function isClay_ in problem.hh and spatialparams.hh).
> >
> > When I run this setup I get high spikes in capillary pressure at
> the
> > boundaries between clay and sand, even in the initial output file
> (*-
> > 00000.vtu, shown in pc_initial.png). I also use the gnuplot
> interface
> > to plot the initial capillary pressure and saturation vs depth
> along
> > x=0 using the same method as for setting the initial conditions
> (i.e.
> > using the method initialSwitchVariable_(pos) for getting the
> saturation
> > and calculating the capillary pressure using the material law).
> > In this plot no capillary pressure discontinuities are visible.
> >
> > In the first output this is only visible at the upper clay-sand
> > interface, where the capillary pressure is much lower than it
> should
> > be, but over time a very high pc develops at to lower clay-sand
> > interface(up to 1000 bar, see pc_5min.png and pc_final.png).
> >
> > During inspection of the vtk-output with Paraview I also saw that
> the
> > porosity of the clay only reaches to slightly below 9m, while the
> > initial water saturation has the values it should have in clay up
> to
> > slightly above 9m (see porosity.png and
> initial_water_saturation.png).
> > The porosity is set using porosityAtPos in spatialparams.hh, the
> > initial water saturation with initialAtPos.
> >
> > I figured it might be either due to my poor understanding of the
> Box
> > method, or might be related to the discontinuous water saturation
> (see
> > initial_Sw_profile.png).
> >
> > Does anyone know what my problem is or what the solution could be?
> >
> > Kind regards,
> > Samuel
> > _______________________________________________
> > Dumux mailing list
> > [email protected]
> > https://listserv.uni-stuttgart.de/mailman/listinfo/dumux
> Im Auftrag
>
> Dr.-Ing. Leopold Stadler
>
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> Dumux mailing list
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