Provide lift and drag as global data

[uekerman]

We are currently extending preCICE towards handling of global data, so data not associated to meshes: precice/precice#202 @kanishkbh

A potential application could be to write lift and drag integrated over a boundary patch to preCICE.

Two motivations:

• Simply as a useful testcase for the global data feature
• As a building block for a benchmark, @LeonardWilleke could use to test the new FMI Runner coupling OpenFOAM to an FMU PID controller

As long as global data in preCICE is not ready, we could write the data instead to a dummy (0,0,0) vertex and then later change to the new feature.

How complicated does this sound?

[davidscn]

Probably straight-forward to implement. I would add a new locationsType ('meshless`) and then accumulate the data we have in the data fields. Wouldn't it even be possible to use a python or summation action with out current approach/ by just adding the additional interface? Would make things more complicated to configure, though.

[uekerman]

Thought about this one too, but we don't yet have the necessary functionality in preCICE (using a global data in an action). Probably more complicated.

[davidscn]

Regarding the benchmark case you mentioned: Note that there are no adapter modifications required for the force calculation right now. If the receiving side operates only on a single vertex in space, the 'integration' happens through a conservative mapping constraint.