Dissimilar Mesh Joining

[Spirit]

Hi pals.
I have to connect two solids meshed independently from each other, but that are connected in reality.
The nodes on the joined surface are not coincident, save for some lucky coincidence. Any of you can suggest which type of NASTRAN elements can be used to produce a realistic connection? RBE2? RBE3? MPC relations? I tried in the past with MPCs, but I got some odd behaviour both in statics and dynamics.
Thanks, bye.

Spirit
'Ability is 10% inspiration and 90% perspiration.'

 

[vonlueke]

This can be a difficult problem. RBE3 elements are typically recommended for this. Keep in mind, if, e.g., RBE3s are used, you might need to shell coat the solids on the surface where the RBE3 independent (central) nodes are attached, depending on the problem.

If your software does not have a "Join Dissimilar Mesh" button to generate the RBE3s automatically, then one option is to do it by hand, which can be incredibly tedious and infeasible in most cases. Another option is to project the nodes of one surface to the interfacing surface, then hope the geometry-based mesher on the other surface will use the seeded nodes. If this fails, another option is to sacrifice geometry-based mesh and mesh the projected nodes on the other surface by hand, then either hope the tet mesher will use the seeded surface elements, or else extrude brick elements from them. Another option is to try to merge "coincident" nodes, but this requires well-planned manual or perhaps mapped mesh.

Maybe one of the best ways, though also tedious, is to seed the node locations on one surface by meticulously placing an Anchor node (if your software has this feature) on each node of the geometry-based mesh on your first surface, then test remesh it to see if the geometry-based mesher will remesh on exactly the same nodes. At any rate, once node locations are established, project their location to the other surface, place an Anchor node at each of those locations on the other surface, then auto mesh the other surface. If you cannot project to other model, the above node location coordinates can be communicated to owner of the other model manually. Obviously the smaller the model becomes, the more feasible this "communication" and Anchor node option becomes. Of course, another option is to join the two part models, then mesh the assembly after joining.

If there are other, better methods not mentioned above, hopefully someone will mention them. Good luck.

 

[dharni]

Hi,

I think you should use the same mesh density on both the parts on joining area. This will creates nodes almost at same location, if the dimensions of both interfacing surface same. If one part is smaller/different then other you should divide the suface on bigger part with smaller part surface.
After this you can very well merge the nodes and this will eliminate definition of other elements for connection purpose.

 

[dharni]

HI,

Divide means you need to make partition of the surface. Or project the smaller part edge to the bigger part edge with same geometric profile.

 

[vonlueke]

Spirit: I need to clarify, all the methods mentioned in my above write up except for the first and last method, are for the purpose of merging "coincident" nodes as the last step. Also I forgot to mention, even though RBE3 is typically recommended if using other elements, it's still not a very good method and can be problematic. I agree with dharni; a method for merging nodes, if one is possible, is better than a method using RBE3.