Shell Element / Surface Model - Failed Continuous Mesh

[mitchEFUMS]

Hi All,

I am having a terrible time with a surface model I created to simulate a fabricated structure that will be subjected to hydrostatic loading. My normal technique in situations like this is to employ continuous meshing. On this particular model, I have completely exhausted my bag of tricks for getting continuous meshing to run. 

I have changed mesh size, gone up and down with numerous settings, tried to increase mesh tolerance, all to no avail. What's really frustrating is I had it working before making a slight change in geometry, then it simply refused to continuously mesh. I then even tried removing that change, and it still would not continuously mesh!

If anyone might have a work flow or suggestion to get this model to mesh continuously, I would be eternally grateful...As a work around I tried applying a global offset bonded contact in combination with a normal mesh, but the results are no good - I end up with areas of zero stress that do not make sense.

I'm running Autodesk Inventor Nastran 2022.

Thank You and Take Care,

Mitch

[autodesk428JLG]

Hello Mitch!

See my attatched part! See if you can build it up like that, with that methodology, it should work i.m.o.

I worked alot with surface models and its hard because weird things happen. Sometimes you can try to turn of visibility in Nastran mode of the parts you try to mesh and try with continous meshing again and see it it helps, dont ask me why this is the case thou. Try to delete current mesh, and re-mesh also in combination with turn on/off visibility of parts... Its weird and something Nastran developers should try to fix asap cause its frustrating.

Best regards,

Daniel

[mitchEFUMS]

Greetings Daniel, @autodesk428JLG 

Thanks so much for your reply! - Unfortunately I have not solved my issue, but reading through your post and looking at your example part file has taught me several things. For starters, I didn't know you could create "Extruded" surfaces like you did - this will simplify my work flow going forward a lot!

An interesting data point is the model will continuously mesh if assigned a constant thickness throughout, as your example part has: 

My problem is that for this structure, there will be a few different thicknesses used, 1/4", 3/8", 1/2", etc. So I can't just assign a single idealization and mesh, I have to select a few different planes and assign thicknesses to each. My shells look like:

As soon as I assign multiple thicknesses, I can get most of them to mesh continuously, but as soon as I have all surfaces idealized, the model will not mesh continuously.  

Another thing to note, (just in case you might not be aware), is for the nodes to intersect on the orthogonal planes, they have to be split at the intersection, i.e., the surfaces both can't be continuous but one of them has to have an edge . This is really hard to see, but if you look close in your example part the nodes do not line up at the grid intersections:

(In my particular structure these will be welded together.)

Thanks Again for your reply. I'll also try turning part visibility on and off in the future too!

-Mitch

[autodesk428JLG]

Hi Mitch!

Im not sure that its correct, if you turn off the visibility of the part and only viewing the mesh i cant see what you see. What it seems that you are trying to show in the picture are triangular elements created at the intersections. If you mesh with 20 mm you will see that more clearly.

[autodesk428JLG]

No my bad, ur right, i guess we both learned something here lol 😃

[autodesk428JLG]

I tried different thicknesses also and got errors... however, i tried different mesh sizes, down to 5 mm and then it worked so, maybe you can try that also and see.