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Preprocessing for FEA

Discussion in 'Using Alibre Design' started by Hunter, Mar 31, 2021.

  1. Hunter

    Hunter Senior Member

    When I bought Alibre, I didn't really do my homework regarding the built-in surfacing tools.

    I'm now often in a situation where I need to do one of the following, but cannot really do it in Alibre. I realise Alibre is not a preprocessor, but I could do this in my other (yes, more expensive) 3D software in the past. What I'm missing is the following:
    1. Split a surface with a sketch (line. circle, polygon, etc): For example, a washer face around a hole so that I can model bolts. Or to apply a force/UDL over a certain region on a face.
    2. Create surfaces by extruding sketches: For example, to model thin plates - when meshing in the FEA software I can use shell elements instead of solid elements (which is a bad choice for thin bodies).
    3. Extract midplane surface from sheet metal body: Related to point 2 above. I have found a way of doing this by deleting surfaces, but it is a bit crude and time consuming.
    Any workarounds or other (inexpensive) software I can look at? [Edit: NOT to replace Alibre, but to supplement]

    TimoCAD likes this.
  2. bigseb

    bigseb Alibre Super User

    You kind of can do these things but in a roundabout way....

    (going by memory here, uninstalled AD to install the beta but get the message my maintenance has expired. Haven't looked into this yet so...)

    1. Create surface from your solid model (you knwo to do this, right?) then create a 3D feature that cuts through your surface as desired. Change this feature to a surface too. Trim/split the first using the second.
    2. Take the 3D model of your parts. Use DE to move a set of faces to the centreling of your plate. Convert to surface. Delete all but these centreline faces.
    3. No easy way to do this but to follow a similar method as in point 2.
    Remember that AD does not stitch disjointed (non-continuous) surfaces into one (there was a thread about that here recently) so there are limitations but maybe the above helps.

    And yes, you are correct, AD is not really a great tool for this sort of thing. Moi is great for modelling surfaces but even Moi can't stitch disjointed surface as one surface.
  3. Hunter

    Hunter Senior Member

    Thanks, @bigseb, I'll try your approach, tedious as it is ;-), but currently no alternative within Alibre.

    I did find a free tool called CAD Builder with which I can do quite a bit to STEP files, specifically splitting surfaces. Just by the way.
  4. bigseb

    bigseb Alibre Super User

    Use what ever works. In the end time is money.
  5. SergioP.

    SergioP. Member

    I´m in the same situation, normally what I do is export the part as STEP and import in FreeCAD for dooing the split surfaces for boundary conditions and create midsurfaces for sheet metal parts. Then I export to Mecway to mesh, apply bc and solve (mostly with CalculiX). In case of structured meshes I use Salome before going to Mecway.

    What are you using for FEA?
  6. Hunter

    Hunter Senior Member

    I'm a long time (15+ years) Strand7 user (version 2.4.6, but also using version 3 which is totally revamped and new, but it has not been released yet). Strand7 has some really good grafting and cutting geometry tools, but it is much quicker to do these types of operations in a CAD package. I've tried both the Alibre FEA add-ons, but they don't fulfill my needs (I mix beam, shell and solid elements, and I make use of 'mathematical' elements like rigid links a lot -- the add-on type FEA software generally lacks this kind of feature).
  7. SergioP.

    SergioP. Member

    Have seen Strand7 in the past, meshing capacities looks interesting.

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