Hi Essi,

On 08/11/2015 11:04 PM, Serge-Étienne Parent wrote:

Hi,

I'm trying to solve the Richards-Buckingham equation for single-phase water flow in unsaturated porous media. Constitutive relationships and the variational formulation are developed here:

https://www.authorea.com/users/23640/articles/61529

I created a problem description file inspired from the examples in the diffusion section of the web site. However, the solution doesn't converge. Maybe the variational form wrong, maybe the equations part of the PDF is wrong, maybe its the options. I don't know. The PDF is hosted on GitHub.

https://github.com/sergeetiparent/EnvGeotech/blob/master/Richards-Buckingham...

Anyone interested in giving a hand on this case? My ultimate goal is to model solute transport in unsaturated soils.

I have tried to run the file, and noticed three things:

- sfepy: nls: iter: 0, residual: 3.107828e-09 (rel: 1.000000e+00)

- the initial residual is almost zero - this might mean that you need some

scaling of parameters, so that the entries in the rhs (and the matrix) are not too small.

- UmfpackWarning: Singular matrix

- this might be related to one.

- The Gamma_Bottom region seems wrong - it does not contain only the bottom

face, but the whole bottom half of the cube.

Using

```
'Gamma_Bottom' : ('vertices in (z < -0.49999)', 'facet'),
```

fixes that.

Use:

./simple.py Richards-Buckingham_SfePy.py --save-regions-as-groups ./postproc.py cube_big_tetra_regions.vtk

to verify your region definitions.

r.