Using Nearest Nodes rather than constant for MultiAppGeneralFieldShapeEvaluationTransfer

[vtnick]

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Question

Is there a way within the current MOOSE framework to have the points that the MultiApp Transfer is unable to process use a nearest neighbor approach to fill the gaps? Something like:

1. Use MultiAppGeneralFieldShapeEvaluationTransfer with an extrapolation constant of -1e6 or a flag rather than a specific value
2. All points with the constant are "fixed" with a nearest node based on the nodes it was able to process rather than from the target mesh.

From what I have seen, I don't think that is possible with the current transfers. But I didn't know if there was a combination of UO or AuxKernels that could do that.

Right now, there seems to be an all or nothing approach. From what I can tell the transfers that support block restrictions don't do extrapolation. So, to use block restriction unless the meshes line up exactly I would have to use a nearest node or accept a constant. Or not use block restriction and have nearby blocks used as the source for the extrapolation. The MultiAppGeometricInterpolationTransfer also doesn't support distributed meshes which makes it harder to use for large meshes.

[GiudGiud]

Hello

You will have to use two transfers, block restricted to different regions (you might have to create additional blocks in your target mesh)

• MultiAppGeneralFieldShapeEvaluationTransfer where the target domain overlaps with the source domain
• MultiAppGeneralNearestLocationTransfer for the trarget regions that do not overlap with the source domain

But I didn't know if there was a combination of UO or AuxKernels that could do that.

This is a good idea too. You could transfer several fields and combine them using auxkernels into the field you want.

From what I can tell the transfers that support block restrictions don't do extrapolation.
So, to use block restriction unless the meshes line up exactly I would have to use a nearest node

The MultiAppGeneralNearestLocationTransfer supports both block restriction and extrapolation, so yes with 1 transfer that is the case

[vtnick]

But does MultiAppGeneralNearestLocationTransfer do interpolation or just grab the nearest node?

[GiudGiud]

it just grabs the nearest node. there is a parameter to interpolate but I am thinking you are actually trying to extrapolate?

[vtnick]

i have a mostly overlapping domain that i want to interpolate the results from. But there are points that are slightly outside which would need extrapolation of some kind.

[GiudGiud]

The only extrapolation we can do is nearest-node / nearest element centroid at this time. We can blend multiple nodes / centroids using the num_nearest_points/locations parameter