Bruno,

> As some of you might know, sliding mesh approaches are generally used in CFD 
> simulation of rotating geometries without axial symmetry (for instance, an 
> impeller with baffles).
> This is generally achieved by having two triangulation, one that is rotating 
> and one that is static. At the interface between the meshes, constraints are 
> used to "bridge" the two meshes together. Although this generally induces 
> additional interpolation error, this is generally one of the best way to deal 
> with turbomachinery.
> 
> Since dealii is already equipped to deal with contact problem, has anybody 
> ever investigated if a sliding-mesh type of simulation could be carried out 
> using dealii?

I don't know, but then there are 1,200+ publications at
   https://dealii.org/publications.html
that might contain something you're looking for. There's now even a search 
function :-)

There are going to be two challenges:
* Mesh generation. Earl Fairall already commented on that.
* Generation of the constraints. That's going to be difficult because
   you'll have to find quadrature points on the faces of one mesh on the
   faces of the other mesh, and these sorts of point search algorithms
   are always expensive (though easy to parallelize). You need this kind
   of mapping if you want to project between the two mesh surfaces; for
   interpolation, you'll need to find the location of the support points
   of the faces of one mesh on the faces of the other mesh, which is the
   same kind of operation.

You could consider a mortar approach in which you would have a third mesh at 
the interface. In that case, you could choose at least one of the meshes 
involved to be somewhat structured, but in the end, it's probably going to be 
about as expensive as otherwise.

I don't know anyone who has implemented the exact kind of application you 
have, but you might want to look up some of the work done on fluid-structure 
interaction in deal.II (e.g., by Thomas Wick). I *believe* that they too have 
to interpolate between different kinds of meshes. There is also the 
'nonmatching' namespace that was added by Luca Heltai and coworkers in the 
last release that helps you deal with overlay meshes -- which would also be a 
way to do what you're looking at -- the rotating geometry would simply be an 
overlay to a background mesh. I believe there is also a tutorial program for 
that.

Other than that, I have no real pointers. But it's an interesting topic, and 
if you find ways to implement what you are looking for, please feel free to 
post solutions here (and/or make small test programs available as code gallery 
or tutorial program!

Best
  W.


-- 
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Wolfgang Bangerth          email:                 [email protected]
                            www: http://www.math.colostate.edu/~bangerth/

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