Moving average in OpenFOAM

openfoam_aero · March 2, 2023, 15:43

Hi,
Objective: Get a volume weighted moving average. What do I mean? I have an unstructured grid with data residing in the cells. I would like to construct a structured "mesh" wherein, I find out the points from my unstructured grid that lie inside each of the cells in this structured "mesh" and take a volume weighted average of those cells and assign it to the structured mesh cell.

What I have tried?

I noticed that topoSet has this feature boxToCell wherein I can define a box with minimum and maximum coordinates. I can then create a cellSet from which a cellZone can be created that has the cell indices stored in it. By using the function object volFieldValue, I can find out the volume averaged value of the quantity in that cellZone. This is all good for one box.

But I would like to create a list of such boxes that encompass my entire unstructured domain and perform the same function till the whole structured domain is populated.

Question: How can this be done?

Remember, I need to insert this into a source code.

Secondly,

Can I get the mesh information for this new "structured" mesh (such as points, faces, cells etc). If so, how can this be done?

joshwilliams · March 14, 2023, 06:26

We have a post-processing tool to do something similar (not sure if you meant at run-time or post-processing). We have used it to apply a top-hat filter convolution to a DNS flow-field to extract a priori LES information. It has only been used on periodic domains (box geometry with periodic BCs).

See the github link: https://github.com/aliozel/coarseningFoam

For the approach you mention, I would probably specify a coarse structured mesh within our coarseningFoam library (just define an array with min and max x,y,z coordinates for each cell).

March 2, 2023, 15:43	Moving average in OpenFOAM	#1
openfoam_aero Member Uttam Join Date: May 2020 Location: Southampton, United Kingdom Posts: 35 Rep Power: 6	Hi, Objective: Get a volume weighted moving average. What do I mean? I have an unstructured grid with data residing in the cells. I would like to construct a structured "mesh" wherein, I find out the points from my unstructured grid that lie inside each of the cells in this structured "mesh" and take a volume weighted average of those cells and assign it to the structured mesh cell. What I have tried? I noticed that topoSet has this feature boxToCell wherein I can define a box with minimum and maximum coordinates. I can then create a cellSet from which a cellZone can be created that has the cell indices stored in it. By using the function object volFieldValue, I can find out the volume averaged value of the quantity in that cellZone. This is all good for one box. But I would like to create a list of such boxes that encompass my entire unstructured domain and perform the same function till the whole structured domain is populated. Question: How can this be done? Remember, I need to insert this into a source code. Secondly, Can I get the mesh information for this new "structured" mesh (such as points, faces, cells etc). If so, how can this be done? __________________ Best Regards Uttam ----------------------------------------------------------------- “When everything seem to be going against you, remember that the airplane takes off against the wind, not with it.” – Henry Ford.

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March 14, 2023, 06:26		#2
joshwilliams Senior Member Josh Williams Join Date: Feb 2021 Location: Scotland Posts: 113 Rep Power: 5	We have a post-processing tool to do something similar (not sure if you meant at run-time or post-processing). We have used it to apply a top-hat filter convolution to a DNS flow-field to extract a priori LES information. It has only been used on periodic domains (box geometry with periodic BCs). See the github link: https://github.com/aliozel/coarseningFoam For the approach you mention, I would probably specify a coarse structured mesh within our coarseningFoam library (just define an array with min and max x,y,z coordinates for each cell).