Exercise Properties (DuMuX course)

The problem setup is identical to the previous Exercise Basic.

Preparing the exercise

• Navigate to the directory exercise-properties

Exercise 2 deals with a two-phase compositional problem (2p2c). Goal is to learn how to use compile and runtime parameters and the DuMu^x property system.

Task 1: Getting familiar with the code

Locate all the files you will need for this exercise

• The main file: exercise2.cc
• The problem file: injection2p2cproblem.hh
• The spatial parameters file: injection2p2cspatialparams.hh
• The input file: exercise2.input
• Two header files containing:
  • a custom local residual in: mylocalresidual.hh
  • a custom material law in: mymateriallaw.hh

• Change to the build-directory

cd ../build-cmake/exercise_properties

• Compile the executable exercise_properties

make exercise_properties

• Run the problem and inspect the result

./exercise_properties

Note: Because the input file has the same name as the executable, DuMuX will find it automatically.

If gnuplot is installed on your system, you should see a plot of the capillary pressure - saturation relationship.

DuMuX uses the term material law to describe the law used to compute

• pc-Sw relations
• kr-Sw relations
• their inverse relations

The file mymateriallaw.hh contains a custom implementation of such a material law.

• Implement the method Scalar pc(const Params &params, Scalar swe) by implementing your own capillary pressure relationship, e.g. a simple linear relationship p_C(S_w) = 1\cdot 10^5 \cdot (1-S_w) + p_e.

Note: MyMaterialLaw uses the BrooksCoreyParams class as parameter input. You can get the entry pressure that is set in the spatial params as follows

const auto pe = params.pe();

The type (i.e. C++ type) of the material law is set in the file injection2p2cspatialparams.hh by declaring the following alias in the public section of the spatial parameters class:

using MaterialLaw = EffToAbsLaw<RegularizedBrooksCorey<Scalar>>;

• Make DuMuX use your own material law by including the header mymateriallaw.hh and changing the alias MaterialLaw. This will make sure that your material law is used everywhere else in the code.

Note: Also use the wrapper class EffToAbsLaw. It takes care of converting absolute to effective saturations considering residual saturations. MyMaterialLaw as other material laws (like Brooks-Corey, VanGenuchten, ...) in DuMuX only deals with effective saturations.

• Verify your changes by recompiling and running the program. You should see a plot of your new function.

For the next task, disable the plotting feature by changing the settings in the input file exercise2.input

[Problem]
OnlyPlotMaterialLaws = false

Most types in DuMuX are properties that can be changed just like the material law. In the following task we implement our own 2p2c local residual, i.e. the class that computes the element residual in every Newton iteration. The file mylocalresidual.hh contains a copy of the similar to the original local residual class used for all compositional models renamed to template<class TypeTag> class MyCompositionalLocalResidual.

• Make DuMuX use this new local residual by inluding the header mylocalresidual.hh and setting the corresponding property in the Property namespace in the file injection2p2cproblem.hh

// note that every property struct knows about TypeTag
SET_PROP(Injection2p2cTypeTag, LocalResidual)
{
    using type = MyCompositionalLocalResidual<TypeTag>;
};

// or using the convenience macro
SET_TYPE_PROP(Injection2p2cTypeTag, LocalResidual,
              MyCompositionalLocalResidual<TypeTag>);

You want to make the new local residual special by adding a switch enabling / disabling diffusion. We will achieve this with a DuMuX parameter which is read from the input file and defaults to a property value if the input file doesn't contain the parameter.

• Modify the computeFlux method to only call the diffusiveFlux method if diffusion is enabled. You can get the new parameter by adding the lines

// ... in the computeFlux method of MyCompositionalLocalResidual
auto enableDiffusion = getParam<bool>("Problem.EnableDiffusion", true);

You can now enable and disable diffusion through the input file

[Problem]
EnableDiffusion = true / false

• Verify the difference in the parameter x_w^{N2}, i.e. the mole fraction of nitrogen in the water phase, with and without diffusion.

Note that due to diffusion being a slow process you can only see the difference in later times.