Resolve "Set water content as initial condition"

What does this MR do?

Add the option to insert water content values as initial condition for the Richards model. The option is activated via richards.initial.quantity = waterContent.

For computing the actual initial condition in terms of the matric head h_m, some additional parameterization functions and a new grid function adapter has been added. Previouly, saturation and water content \theta_w have been computed from the matric head, but not vice versa. The InitialConditionFactory of the Richards model now additionally requires the FlowParameters information.

Changes:

• Update MualemVanGenuchten and FlowParameters with required methods for computing h_m(\theta_w).
• Add WaterContentInitialCondition and MatricHeadAdapter.
• Pass FlowParameters to RichardsInitialConditionFactory.
• Update the test-initial-condition unit test and make it employ Google Test.
• Added docs on new initial condition quantity and updated default config file parameters.

Is there something that needs to be double checked?

I had some trouble with the unit test. The Dune::GridView seems to be updated/changed when it is passed to a new thread. Apparently, this is what Google Test does when creating a fixture and passing it to a test case. Therefore, I have to re-build the grid view in every test although it is already built in the test fixture, see f2ada9f3. @sospinar, do you have any knowledge of Dune::GridView not being thread safe?

Can this MR be accepted?

• Implemented water content as initial condition
• Added/Updated tests:
  • test-initial-condition
• Added/Updated documentation
• Pipeline passing
• Squash option set
• Delete branch option set
• Added entry to CHANGELOG.md

Assignee: If the Squash option is set, check/update the commit message right before merging!

Related issues

Closes #148 (closed)