Help with a 2-D mesh

Famous_MortimerFamous_Mortimer
I am having trouble meshing this dxf file that I have drawn. It is some plates that are welded together to form an accordion. The outside is subjected to high pressure while the inside is open to the atmosphere. Any help would be greatly appreciated. - Mortimer

Comments

  • roberto_proberto_p
    Hi Mortimer,

    normally I fill the dxf perimeter with a surface. After that I can save the surface in step format and import step in MW for meshing.

    Bye
    Roberto
  • prop_designprop_design
    edited March 2020
    hi,

    i did the same thing as the previous poster. I brought your dxf file into Rhino 5 and made a surface. Then exported the surface as a step file. Netgen doesn't seem to allow the import of dxf files. I hid some of your lines, to make the surface. I don't have spring steel properties, so I used Titanium. Not sure, but you might want to add fillets. I'm assuming you left sharp points to aid meshing. You would probably get more accurate FEA results if you added the fillets that the real part has, or will have.

    i attached the step file and the mecway v13 beta file.

    anthony
  • prop_designprop_design
    edited March 2020
    here are some models with spring steel. it has a 1GPa yield strength. the first model has no fillets. the second model adds 1mm fillets. i also broke the surfaces on the second model, to make places to apply BCs. i may have a model size conversion problem. my models seem like they are too small. the first and second models have different BCs as well. i was just playing around for fun, basically. i converted the mecway video file to a gif at https://ezgif.com/video-to-gif

    note; for some reason the second model gave an error when i tried to mesh with quads. the first model would mesh with quads. so that was kind of weird.
  • prop_designprop_design
    here is a picture of a dimension in millimeters. not sure what the size of the model is. i may have an import problem.
  • VictorVictor
    If you were to use the same DXF file, Automesh 2D on lines needs a single closed loop (optionally with internal loops, but you don't have those). So remove the internal lines and merge the open ends (View -> Open cracks shows some gaps). Then you can get a 2D mesh like this picture.


  • Famous_MortimerFamous_Mortimer
    Thanks for all the help. I appreciate the support that this forum provides. Hope I can help you guys out sometime. - Mortimer
  • JohnMJohnM
    edited March 2020
    I didn't think there were enough versions of how to mesh a DXF file, so here goes mine. Two minutes to click the nodes in one half-section to create quads, mirror, copy, copy,refine.
    See attached.
  • prop_designprop_design
    @famous_mortimer,

    I noticed the curves are broken up in a lot of weird ways. I tried to rebuild them but it didn't help much. I also tried recreating them, but that was problematic. It seems like, when I import the dxf file into Rhino 5, it's not the best. I don't know what CAD program you are using, but it might be better to export a surface directly out of it. Maybe the curvature will be better that way. Netgen works the best with step files. So exporting a surface as a step file would be the best way to go. Mecway uses bug fixed versions of Netgen by default. As people have shown, you can work with a dxf file. Just seems like unnecessary headache and possible geometry degradation as well.

    anthony
  • prop_designprop_design
    @victor,

    If you get a chance, the test2 model won't solve when using quad dominate option. it says there is an element with zero width somewhere. the option to try and highlight which element that is doesn't seem to work for me. you can mesh it with tets. the test1 model will run with quads and tets. the only difference is i added some fillets and broke the surfaces in places, to make adding BCs easier. Not sure what the problem is there.
  • VictorVictor
    @prop_design, when the solver fails, you can press the Select elements button in the Details window to find it. It's a poorly shaped one. I guess you'd have to tweak the meshing parameters to get rid of it, or add a local refinement. There's two like that right next to each other.
  • prop_designprop_design
    i tried the button you mentioned but it wasn't showing anything for me. i was using the beta version. i need to download your new beta version. i'll try again. thanks for looking into it.
  • prop_designprop_design
    i tried the new beta version, changed some mesh settings, and used Netgen toggle instead of the Netgen 6 toggle and didn't get a problem this time. I'd like to get the error back to see if it will show the bad elements.
  • VictorVictor
    It's a very small element that can be hidden by the mesh lines. Check the status bar to see if more than 0 elements get selected.
  • barrtibarrti
    Here's my play around. I imported the dxf, automeshed 2D, revolved 360 degrees around x-axis, cut out central section (for fun), pressurised to 1MPa on outside

    Can't figure out why the deformation is not symmetrical around x?
  • barrtibarrti
    Oops, it behaves as expected now that I've added a constraint at the ID! With E=200 GPa and 1MPa external pressure, get 1.13mm deflection along x which is now symmetrical about x as expected.
    Oh, done on V13Beta 2 BTW
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