Tube on tube joint meshing problem

I'm doing a FEM analysis of tubular structure and I have one problem with mesh generation in tube on tube joint area.

I've attached some screenshots from Solidworks and Mecway.

I generate a surface model first in Solidworks and then import it as STEP file in Mecway. Meshing in Mecway works fine if I import surface model as one surface - in Solidworks it is called "knit" operation and makes one surface body out of many. If knitting operation is not done then Mecway treats every edge of every surface as its own and I have nodes that are not merged on common surface edges. It is also a lot of work to merge them because they are not on same coordinates.

Problem is that knitting operation in Solidworks can be done only if I cut tubes as it is shown on attached screenshots (manifold/non manifold condition if I understand corectlly). The main tube needs to have a hole on its side which is made with smaller joint tube. In reality I don't have these holes - just smaller tube joining on bigger tube.

The question now is what is the simplest solution to fill these holes? I've tried it with importing just these cut parts of tubes separately in Mecway, but when I mesh these surface parts I get nodes that are not on same coordinates and merging is again hard and time consuming.

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  • Have you tried with Salome? It has some ways to join the parts and make a continuos meshes. I have made with solids and works, maybe with meshes would work also. If you share the files I could give a try.
  • Another way should be to make each tube a separate part without the hole and join them with bonded contact. Make the edge "faces" of the end of one tube the slave and the surface of the other tube the master.

    edited November 2016

    You can export each surface as step files into FreeCAD and "union" them together without first cutting the hole so you dont have to fill the hole up after.  If you can provide the files, I can give it a quick try and let you know.
  • I didn't try Salome and FreeCAD. I don't know and use these softwares. I also would like to have merged nodes and not bonded contacts.
    Here is the geometry. Please try it and I will use the optin that is the simplest. Please upload edited file so I can check the meshing.
    Thank you very much.
  • edited November 2016

    Have tried with Netgen but it makes a non continuos meshes, even I have used the geometry doctor to heal it. In Salome, just meshing the part using simple parameters looks like if all where conected, but after checking in Mecway with Open Cracks, we can see some unconected elements. Luckily they have the nodes very close, so with a simple node merge (0.1 mm) we have all conected.

    Victor, is possible to improve this viewing (open cracks) with some emphasis on the free edges? In this case the unconected elements where not visible easily.

    Maybe if every comonent be a separated part (file), in Salome could be created a Compound (don't remember well if that the correct denomination) to inforce the merged meshes. I have done with solids and it works, it create a continuos mesh but keeping the separation surface
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  • You can highlight free edges with Tools -> Labs -> Find non-manifold shells. If the Labs menu isn't visible, turn it on through Tools -> Options -> General -> Labs. I'd like to make this into a proper feature eventually.

    JRP, can I ask why you don't want to use bonded contact? It's supported by most analysis types in both Mecway and CCX. Even though it can reduce accuracy at the contact surface, corners between shells are inaccurate anyway. If you're interested in stress right on those joints, you should use solids and may need to model the weld bead too.

  • I tried to "union" in FreeCAD but was not successful. The surface model in the step file seems to have alot of overlap or maybe gap that I couldn't "union" them.  I have done several surface models for pipe on pipe connections and was able to "union" and mesh them without any issues.
    edited November 2016
    OK, is it possible to create elements in these holes after the meshing in Mecway?

    I will try bonded contact as the last option, because it is one thing that complicates the analysis and I like them clean with continuos meshes.
  • This is another option as I said before. I knited together surfaces as in my first post here. There is just another surface added that fills the hole. I cannot knit that. Maybe now you can try it.
    In Mecway I get nodes that are very close together and can merge them, but I don't know if that will always be the option. If I specifiy too much merge tolerance I could end up merging nodes of same elements somewhere in the model.
    Is it possible just to select nodes on these edges and then merge them without merging any other nodes on the model?
  • Mecway doesn't have a tool to fill in holes with mesh.

    If you just select the nodes on the edges, then the Merge nearby nodes tool will only affect those nodes.

  • In Mecway, with a 1mm mesh and after mergin nodes at 0.2 distance you get all the elements stitched.
  • Sorry, I forgot to add the attachment to my previous post.

    Is it possible to select edges of imported step and with that all the nodes that are on that edge?
  • I have tried in the past but guess that there is no automatic way. In such situations I preffer to select nodes (by means of a box selection and playing with the orientation of the model) and after swhitch to edges on the nodes/edges/element selector to conver the node selection to an edge selection.

  • JRP,

    I guess it depends on you surface model.  For me the cope of the braces need to be along the surface of the chord without any gap for FreeCAD "union" to work well.  See attachment and below for a simple overlap braces surface model I created in FreeCAD and then export into Mecway.

    edited November 2016
    Thanks for answers. I found another way, that is quite easy to do. I've tried it on STEP model I posted in my last post.
    I generate mesh for whole model and then I delete elements that are on the edge of small surface part that fill the hole I previusly had on my model. Then I simply add new elements manually and I have a continous mesh. 
  • "In Mecway, with a 1mm mesh and after mergin nodes at 0.2 distance you get all the elements stitched."

    No need to make any manual editing, just merging.
  • I've seen that Sergio, but I can't achieve it. I merge some nodes of same elements. Can you please specify meshing parameters and procedure, please? A screenshot maybe. Thanks.
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