Axisymmetric element edge selection

badbunnybadbunny
Hi, is there a way to select a continuous edge on an axisymmetric model without selecting one element edge at a time?

Thanks,
Pete.

Comments

  • VictorVictor
    There's no automatic edge-only selection. But you can drag a rectangle or circle to select a group of edges. Do multiple selection and inversion of selection by holding CTRL while selecting.
  • badbunnybadbunny
    edited July 2019
    Hi Victor,

    I found the paint select the quickest way in the end as the curved shapes make the rectangle tool less quick and more prone to picking up the element faces. I did use the rectangle tool on the straight sides of the vessel though.

    Can I add a request for edge selection in axisymmetric and shell elements please.
    Also a polygon select would be useful.

    It also would be much quicker if there was an additional selection filter because the 'face' setting picks up both element edges and surfaces. If it filtered the edges only then you could be much less precise with the selections and would be much much quicker to do.

    If I do this again, I would probably mesh the model very coarsely initially so I don't have to select so many edges manually, then do multiple refines on the mesh (which includes the newly created edges automatically).

    Pete.
  • VictorVictor
    It occurred to me there's a clumsy workaround for 2D/axi:

    1) Extrude the whole mesh to a solid with 1 subdivision.
    2) Select the edge faces of that using Edge detecting selection. If there are a lot of sharp corners that block it, select the two 2D surfaces with it then Invert selection to end up with the edge faces.
    3) Save it as a named selection.
    4) Collapse it back to 2D by selecting the nodes of the extruded surface and dragging them back to the original one and merging nodes.
  • badbunnybadbunny
    edited July 2019
    Hi Victor, I tried this and it works (mostly).

    Some caveats though... I had a 2nd order mesh so needed to convert to linear elements first before the extrude, then convert back to 2nd order again at the end. This loses the real midside node positions on the curved faces.

    Also I don't know why but the merging nodes seemed to work erratically for me, the first time I did it at 0.01mm tolerance it didn't pick anything up. The next at 0.1mm it picked probably 90% up (seemed to mainly be trias it was missing). I hit undo and for some reason I tried that again and then it seemed to pick everything up?

    Also, what does it mean when an element is shown with a red cross in its middle? Is that warning of a quality issue with that element (eg with coincident edge nodes in this case)?

    Is automatic edge selection of 2D elements easy to add?

    Thanks,
    Pete.
  • disladisla
    edited July 2019
    Hi badbunny,

    ¿Have you try to set the viewpoint parallel to the surface? This way you can select with a rectangle the whole model and only the external edges will be selected as the other ones remains behind. See pdf for the sequence. Be sure to select faces (not nodes or elements).
  • VictorVictor
    disla - that's amazing!

    badbunny -

    You might have had some nodes selected using Merge the first time. Most of the meshing tools act only on selected items if there are any or the whole model if nothing is selected. I did the merge with 0 tolerance and it worked OK.

    The extrusion trick works with 2nd order elements too so they retain midside node positions. But probably easier to collapse them by selecting all nodes and setting Z=0.

    Yes, a red cross means it's too distorted and probably won't solve (negative Jacobian determinant).

    It's not too hard but I have a long list of features to add so it'll be a while.
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