Difference between mapping methods in precice-config.xml

Hello, is there a specific reason why in the turek Hron example, consistent mapping was used for both the Displacement and the stress, while for example for the perpendicular flap example, conservative mapping was used for the Force. If I understand correctly, using consistent mapping wouldn’t violate conservation of the total stresses ?

And another question I had, is using two mapping instances in the same participant with the first one in write direction and the other one on read Equivalent to using two separate mappings, with read direction, each one on a different participant (Like the difference between precice-config in the perpendicular flap tutorial and the turek Hron example) ?

Thank you in advance !

Consistent vs conservative: correct. If I have five points on MeshA with force values 1N each (5N total), and three points on MeshB, on which MeshA needs to be mapped on, then these cannot just take values of 1N, as the total force would be 3N.

Two mappings in one participant vs one mapping in two participants: They are generally equivalent, but:

  • only specific combinations work in parallel simulations
  • if you have, say, an FSI simulation with a very fine mesh and multiple cores on the Fluid side, and a coarse mesh with few cores on the Solid side, then you want to compute the mapping on the Fluid side. This will not only save time due to parallelism, but it will also avoid exchanging the (much finer) Fluid mesh.

Read more about mapping in preCICE in the documentation: Mapping configuration | preCICE - The Coupling Library

Thanks a lot for the clarification, very clever criterion for the choice of participants for mappings.
For the first part :

If I understood correctly, you described why would one want to use a conservative mapping instead of a consistent one ? In that case, I still didn’t get quite clearly why would someone ever use a consistent mapping (as was used in the Turek Hron Fsi tutorial). It seems that it will always lead to incorrect results.

Thank you !

One needs to distinguish here between force (which depends on the area) and stress (which does not depend on the area). We have to map forces in a conservative way and stresses in a consistent way.