[snappyHexMesh] failed to snap to a symmetry boundary condition patch

Marpole · January 22, 2021, 20:06

I have a model with a geometry like a 3D wedge. The two sides of the wedge use symmetry boundary condition. I use snappyHexMesh to mesh the wedge with background mesh of a block mesh. All cellls are cubic. The wedge circular end was snapped well but not the two sides. For the two sides, it basically did nothing. I changed the boundary conditions of the two sides to type wall. It snapped perfectly. Anyone has this experience? Any help?

marco.müller · February 26, 2024, 02:31

Hi Charles,

did you find a solution? I'm facing the same issue where shm fails to snap to a symmetry plan not parallel to the main planes. In my case there is a 120 degree section, see attachment. Changing it to wall type shows no problem for the snapping

Marco

AtoHM · February 26, 2024, 03:27

Pragmatic solution: mesh it with "wall" and just change the type back to symmetric in the boundary file once meshing is complete. Obviously you need to work in ASCII.

Marpole · February 26, 2024, 12:35

Yes, I should have updated the solution. snappyHexMesh does not snap "symmetry" patch. It snaps "wall" patch. The solution is as AtoHM said.
1. define the "symmetry" patch type "wall"
2. After generating mesh, edit file boundary in folder constant/polyMesh and change the patch type "wall" back to "symmetry"

marco.müller · February 26, 2024, 13:52

Thanks guys! Though a little hard to understand why shm doesnt snap to it...

January 22, 2021, 20:06	failed to snap to a symmetry boundary condition patch	#1
Marpole Senior Member Charles Join Date: Aug 2016 Location: Vancouver, Canada Posts: 148 Rep Power: 9	I have a model with a geometry like a 3D wedge. The two sides of the wedge use symmetry boundary condition. I use snappyHexMesh to mesh the wedge with background mesh of a block mesh. All cellls are cubic. The wedge circular end was snapped well but not the two sides. For the two sides, it basically did nothing. I changed the boundary conditions of the two sides to type wall. It snapped perfectly. Anyone has this experience? Any help? __________________ Charles L.

February 26, 2024, 12:35		#4
Marpole Senior Member Charles Join Date: Aug 2016 Location: Vancouver, Canada Posts: 148 Rep Power: 9	Yes, I should have updated the solution. snappyHexMesh does not snap "symmetry" patch. It snaps "wall" patch. The solution is as AtoHM said. 1. define the "symmetry" patch type "wall" 2. After generating mesh, edit file boundary in folder constant/polyMesh and change the patch type "wall" back to "symmetry" __________________ Charles L.

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February 26, 2024, 03:27		#3
AtoHM Senior Member M Join Date: Dec 2017 Posts: 643 Rep Power: 12	Pragmatic solution: mesh it with "wall" and just change the type back to symmetric in the boundary file once meshing is complete. Obviously you need to work in ASCII.

February 26, 2024, 13:52		#5
marco.müller New Member Marco Müller Join Date: Feb 2013 Location: Germany Posts: 23 Rep Power: 13	Thanks guys! Though a little hard to understand why shm doesnt snap to it...