Grid refinement

[sfraniatte]

Dear community,
I’ve noticed a strange behavior in the example gridRefinement/sphere3d. The pressure is no longer continuous when localized refinement is applied over the entire section of the pipe. Is this a known issue, and is there a way to fix it?

Thanks in advance !

Sylvain

[Adrian]

Can you provide a sketch of your refinement domain?

In general, BCs crossing the refinement frontier can be an issue. The BCs between the adjacent resolution levels need to be consistent and coupling needs to either take them into account or be disabled on the actual BC cells (common).

We have also been increasing the updates to the public Git repository lately. Amongst other things there is now also an implementation of the cell-centered approach by Rohde that you might want to check out.

[sfraniatte]

Hello,

The sketch of my refinement domain is very simple. It is basically the spher3d example with the lines 221 and 222 which are commented. The lines are the following :
cuboidDecompositionLevel0.splitFractional(1, 1, {0.1,0.8,0.1});
cuboidDecompositionLevel0.splitFractional(3, 2, {0.1,0.8,0.1});

So, the localized refinement part is on the entire cross-section of the pipe and no longer on 80% of the cross-section.

Thanks to your respond, I understood how to solve my problem. The solution is to replace “sGeometry.rename(0,1);” by the following lines in “prepareGeometryFine” :
IndicatorCuboid3D<T> domainI(Vector<T,3>{2.5,0.5,0.5},
Vector<T,3>{0.0,0.0,0.0});
IndicatorLayer3D<T> domainLayerI(domainI, converter.getPhysDeltaX());

sGeometry.rename(0,2, domainLayerI);
sGeometry.rename(2,1, domainI);

Thanks a lot !

I will check the cell-centered approach by Rohde when I will have time.

Best regards,

Sylvain

[sfraniatte]

Hello,

I succeeded to make it in my case but the FSI part of my case does not work anymore. Is it possible to have FSI and grid refinement in the same case ?

Best regards,

Sylvain

[Adrian]

Yes, HLBM based FSI interacts well with refinement. I have e.g. a working setup where I coarsen away from a wall-modeled rotor.

There will however be issues when the FSI element moves through refinement regions (due to this not being implemented yet and refinement in general being a very manual process right now in OpenLB). Can you describe your setup in more detail? I assume you converted the static sphere into some moving FSI element?

[sfraniatte]

Hello,

In fact, I converted the showCase/centrifugalPump3d/ example to make my case and it works really well without grid refinement. Then, I tried to make the refinement around the moving part with the sphere3d example. The mouving part is in the refined grid and can not move through refinement regions.

I have solved my problem this morning and it was a mistake in the parameters of the simulation. The motion was physically impossible.

Thanks a lot again for your time to respond me !

Best regards,

Sylvain

[Author]

Posts