equal number of elements in equal faces?

Hello,

It might be a strange question,

I am creating a 2D mesh to put in another tool to create a 3D volume mesh. (creating region divided stl that will use it in OpenFOAM (OF) snappyHexMesh tool to create the volume mesh)

my issue is that after creating the volume mesh, I finish with different number of faces (really similar but not equal 31730 vs 31721) and here comes my issue, I am looking to use cyclic boundaries (specifically cyclicAMI "Cyclic Arbitrary Mesh Interface") but OF only accept to do this type of boundaries over two patches with the same number of faces. The snappyHexMesh tool does not have any tool to ensure this property, but as this tool uses the points in the 2D mesh (created in salome), I thought of giving a try to have the same number of elements in the 2D regions of the stl to see if this will help/solve my problem. before the meshing the surfaces (I mean the solid , from the STEP file) are equal, the only difference is the boundary faces (see the figure attached). is it possible to divide (or fuse) some triangles in an easy way in salome ? (to finish with the two same number of triangles in each face? not necessary in the exact same place, as it is not necessary for me but that at least have the same number of faces.) )

Best regards,

F.

Hello!

thanks for the suggestion, but if I do these I will loss the "watertightness" of the mesh, no?

Previously Saint Michael wrote:

Hi

You can try Projection 2D algorithm to transfer mesh from one face to another.

St.Michael

No, "watertightness" of the mesh is assured by "watertightness" of the geometry

St.Michael

thanks, would it be possible to give me the workflow that you will do?
right now 

1.Import the STEP file
2.I create groups in the geometry module for each patch
3.create a mesh from the body in the geometry module and apply a netgen 1D-2D.
but if I do this I can not extract one face mesh to use as projection 2D in the other face.
also I know that if I create a mesh for each group separately I had the problem of not being waterthigt (that the nodes of one patch does not be in the same place as the nodes of the other patch (over the boundary that conects the two of them)).
I am missing something?

Previously Saint Michael wrote:

No, "watertightness" of the mesh is assured by "watertightness" of the geometry

St.Michael

It is possible to define mesh projection from a group of faces to another group of faces. This will work provided that a source and a target groups have the same topology. Vertex-vertex association is also needed in this case. I attach a study (v9.6.0) where the projection is from 2 triangles to another 2 triangles.

https://drive.google.com/file/d/1Qu8TUJDKftilMCDkEA4OIifupw5a4ZhU/view?usp=sharing

St.Michael

Thanks a lot! 

Hello,

I am trying to recreate your workflow but I am not succeding.

what I am doing:

1. Importe step as Part 1 in geometry
2. design groups faces (inlet,outlet,walls,sym_1,sym_2)
3.open mesh module
4.create mesh:
     -name: Mesh_1
     -Geometryart 1
     -2D/algorithm netgen 2D/Netgen parameters/very fine
     -1D/algorith wire discretisation/local lenght
     -apply and close
5. in Mesh_1 create sub mesh:
     -Name:Sub-mesh_1
     -Geometryutlet
     -2D/algorithm projection 1D-2D/source Face/
           -source face: inlet
           -source mesh:Mesh_1
           -rest leave it empty
           -OK
           -apply and close
6. select Mesh_1, compute

i am getting: Unexpected geometry. different number of edges in source and target faces 28 and 27

enventhoug the geometries inlet and outlet are equal.

what I am doing wrong?

thanks in advance

Previously Saint Michael wrote:

It is possible to define mesh projection from a group of faces to another group of faces. This will work provided that a source and a target groups have the same topology. Vertex-vertex association is also needed in this case. I attach a study (v9.6.0) where the projection is from 2 triangles to another 2 triangles.

https://drive.google.com/file/d/1Qu8TUJDKftilMCDkEA4OIifupw5a4ZhU/view?usp=sharing

St.Michael

here is the link to the project if necessary

https://drive.google.com/file/d/1kXF-rnxiwhswGzcGTBaVDab5LWp-BOz_/view?usp=sharing

Previously Franco Otaola wrote:

Hello,

I am trying to recreate your workflow but I am not succeding.

what I am doing:

1. Importe step as Part 1 in geometry
2. design groups faces (inlet,outlet,walls,sym_1,sym_2)
3.open mesh module
4.create mesh:
     -name: Mesh_1
     -Geometryart 1
     -2D/algorithm netgen 2D/Netgen parameters/very fine
     -1D/algorith wire discretisation/local lenght
     -apply and close
5. in Mesh_1 create sub mesh:
     -Name:Sub-mesh_1
     -Geometryutlet
     -2D/algorithm projection 1D-2D/source Face/
           -source face: inlet
           -source mesh:Mesh_1
           -rest leave it empty
           -OK
           -apply and close
6. select Mesh_1, compute

i am getting: Unexpected geometry. different number of edges in source and target faces 28 and 27

enventhoug the geometries inlet and outlet are equal.

what I am doing wrong?

thanks in advance

 

 

Previously Saint Michael wrote:

It is possible to define mesh projection from a group of faces to another group of faces. This will work provided that a source and a target groups have the same topology. Vertex-vertex association is also needed in this case. I attach a study (v9.6.0) where the projection is from 2 triangles to another 2 triangles.

https://drive.google.com/file/d/1Qu8TUJDKftilMCDkEA4OIifupw5a4ZhU/view?usp=sharing

St.Michael

 

Hi

For Projection 2D. source and target faces must be topologically equivalent. In your case they are different. One face is bound by 28 edges while another one, by 27 edges.

St.Michael

As a remedy, add a "missing" vertex.

Oh, sorry for that!

three questions arrays if I may:
A.In the original model (it was created in Onshape) here there is only one feature/curve not two. they are topologycally equivalent, do you think this issue came from the exporting to .STEP (the exportation is in version AP214 dont know anything about this) or it is from the importation in salome? shaper might solve this issue maybe? (I will try this.)
B. so, my workflow was correct and the problem was comming from the geometry, but if there wasnt the geometry problem it would have work, no?
C. is there any utility with which I could solve this issue in the geometry?

thanks a lot for the help
franco

Previously Saint Michael wrote:

Hi

For Projection 2D. source and target faces must be topologically equivalent. In your case they are different. One face is bound by 28 edges while another one, by 27 edges.

St.Michael

Okey, I did not see the post sorry, in any case, I just tryed by repear/add point on edge/selectied second option (proyection of vertex i would call it)

select my edge with the "missing" vertex in the face with 27 vertex, select the 28th vertex from the other face and apply. the new geometry shows the extra vertex but still doing the previous workflow I mentionned It is not working, when i do the 2D proyectionor 2D-1D i get invalid input mesh.different number of nodes on edges...

Previously Saint Michael wrote:

As a remedy, add a "missing" vertex.

I am also trying to get a required mesh. I let you know about my result

St.Michael

If snappyHexMesh does not require a watertight mesh, then steps 3) and 4) can be omitted

To get the watertight mesh, the "missing vertex" must be added before meshing in order to have equal nodes on boundaries of Inlet and Outlet