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Problems understanding mesh mating

Valued Contributor
Valued Contributor


I've a problem understanding mesh mating conditions. I model a simple part (see attached part.png).

Then I split the idealized part, activating mesh mating conditions. The next step is to produce midsurfaces of both new parts (idealized_part.png).

After having switched to fem I want to mesh only the midsurfaces with two different meshes (for which reason ever). The two meshes don't match although I've checked the mesh mating condition checkbox when performing the split body command (fem.png).

I'm using NX 9 now. I'm sure that the above described procedure lead to matching meshes with NX 8 which I used a year ago.

 Probably the problem is sitting in front of the display :-) Could you please help me, anyway? Where is my error?

Thank you in advance



Re: Problems understanding mesh mating


My understanding is that mesh mating conditions only apply for 3D meshes and work by forcing two solid bodies to share the same common face.


For the two sheet bodies in your example, what's required is to have the two sheets share the same edge. This can be accomplished with the sheet bodies in the part by using the Sew command in the Modeling application or it can be done with the polygon faces in the FEM by using the Stitch Edge command in the Advanced Simulation application.


One thing to keep in mind is that only 2 sheet bodies can share the same edge in CAD geometry. If 3 sheet bodies need to share the same edge (i.e. a midsurfaced T-joint geometry) then it has to be done on the polygon faces in the FEM using the Stitch Edge command.

Re: Problems understanding mesh mating

Valued Contributor
Valued Contributor

Thank you so much. This is the solution.


I'll try to find the time to check the behavior of NX 8 versus NX 9. I will report.


Thank you again.

Re: Problems understanding mesh mating

Valued Contributor
Valued Contributor

Again me, same problem. Stichting edges is working in any case.


Using Mesh Mating Conditions leads sometimes to matching meshes in the midsurfaces, sometimes not. In detail:


  • Using NX the meshes of the midsurfece sometimes match, sometimes they don't. We are sure having done the identical steps each time
  • Using NX the meshes never match
  • Using NX 8 the meshes always match

I've attached two zip-Files:

  • 3_10_Kerbwirkung_matching_meshes, the content is produced using NX, the midsurface meshes are matching
  • 3_10_Kerbwirkung_not_matching_meshes, the content is produced useing NX, the midsurface meshes don't match

May I ask you to have a look on my problem.To be honest I'm totally confused. 


Many greetings


Re: Problems understanding mesh mating

Siemens Phenom Siemens Phenom
Siemens Phenom

The shell meshes and midsurface results have no relation to the mesh mating conditions. The mesh mating conditions only apply to the solid bodies. In general, mesh mating conditions are always defined between face pairs. The related edge pairs are treated in the same manner as the face pair. You are expecting it to operate on an edge pair where no face pair exists. You have 2 faces in the same plane, and they have coincident edges. That is not a mesh mating condition use case or supported geometric condition.


You actually have 2 coincident edges in both the Matching and Not Matching examples. In the Matching example you defined a mesh control of 5 elements per edge on both edges. That by itself will produce coincident nodes and element edges between the 2 meshes. Then you turned ON the Match Edge option in the meshing dialog. That will stitch meshes where coincident edges (within the Match Edge tolerance) exist. Your Not Matching model has no mesh controls and has Match Edge turned OFF. Since the element size is different between both meshes, you get different node distributions on the coincident edges.


The most robust way to assure stitched meshes across faces of different bodies is to use the Stitch Edge polygon geometry command. That will convert the geometry from 2 coincident edges to a single edge shared by both faces. No matter what element size the faces use, the single edge shared by both faces assures continuity of the mesh at the edge.





Mark Lamping

Simulation Product Management

Simulation and Test Solutions


Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

Re: Problems understanding mesh mating

Valued Contributor
Valued Contributor



sometimes it takes a long time until I've understood a matter Smiley Wink. This is now the case. Your explanation was totally clear.


Thank you very much