'flux registers' for edge-centered EMFs?

[BenWibking]

Hi,

We are planning to implement face-centered MHD in Quokka. Is there a 'flux register' to do the correction at coarse-fine interfaces of edge-centered EMFs in AMReX? In Chombo, this can be accomplished with LevelFluxRegisterEdge, which has a similar API to YAFluxRegister.

Example:

There are a number of corner cases (see panels a-d copied below). (In Athena++, this step is also done at all shared edges between grids on the same resolution level in order to avoid roundoff errors, but it's not currently clear whether this will be necessary.)

[WeiqunZhang]

You can use

    void average_down_edges (const Array<const MultiFab*,AMREX_SPACEDIM>& fine,
                             const Array<MultiFab*,AMREX_SPACEDIM>& crse,
                             const IntVect& ratio,
                             int ngcrse = 0);

to average down fine edge data onto coarse. Additionally, you can use

void MultiFab::OverrideSync (const Periodicity& period = Periodicity::NonPeriodic());

to make the data consistent on internal edges.

However, there is an issue with average_down_edges when there are periodic boundaries. This can be fixed. Will let you know.

[BenWibking]

Not the corner cases where there is an overlapping edge, but no overlapping face.

[WeiqunZhang]

Yes, I got it now. We will need to write a new FluxRegister for this.

[BenWibking]

Ok, great. Maybe the Chombo implementation can be partially re-used?

[WeiqunZhang]

I just created an issue from this.

[BenWibking]

Ok, I've subscribed myself to the issue. If there's any input from me that would be helpful, let me know.