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Alibre & Calculix- shell elements?

Discussion in 'General Discussion' started by Adi, Mar 20, 2021.

  1. Adi

    Adi Member

    Hello everyone,
    It's my first post here, so it's time to greet You.
    I am Alibre Design user from Poland.

    I am looking for method of exporting files, that could be used on Calculix (with pre-post procesor PrePoMax) as a shell elments- but I am not sure if this is possible in Alibre Design?

    I Tried a few ways of doingthat, but in both I had as an effect a lot of single faces... For unknown reason I had a problem with meshing it in PrePoMax (I am learning how to use this program)

    Is there any way to export the surface model as one face in Alibre Design? I tried to do it in STL or STEP file, but i have an error mesage that this is imposible, until topology data will be avalible, use other file format (sorry, it's not exact error message- I have Polish version of Alibre, so the error is in Polish too- I just translated meaning of that message). Exporting in IGES works fine

    /Adi
     
  2. bigseb

    bigseb Alibre Super User

    Hallo and welcome :)

    Not quite sure exactly what PPM needs and I doubt you are going find a 'single surface' export option. Step and iges are generally the go-to formats and you will get a single imported part (consisting of one or more individual faces, depending on the geometry) which is usually what you want. Stl should technically also work although you need to be aware of difference in the representation of the geometry.

    What does Calculix/PPM require exactly? If it recommends, say, step formats then that should work.
     
  3. Ralf

    Ralf Alibre Super User

    Hi Adi, welcome from me too. :)

    I have found this, maybe it is helpful for you:
    PrePoMax & CalculiX - CAD geometry import:
     
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  4. Adi

    Adi Member

    Thanks for quick answers,

    PPM can use ste, stl, iges, and some mesh files-but on every example I found (of course, also on that movie posted by You- Ralph) I saw that they only use stl or stp formats. And stl or step works fine while I export solids from Alibre. Unfortunetly I can't export surfaces model to stl or step, due to that error message with unavalible topology data :confused:

    /Edit- I just found some strange solution to handle this problem- files in IGES from Alibre converted by free online converter to STL opened just fine in the PPM, as one surface element
     
    Last edited: Mar 20, 2021
  5. NateLiqGrav

    NateLiqGrav Alibre Super User

    Surfaces aren't well supported in Alibre Design (which is generally a solid modeler).
     
  6. TimoCAD

    TimoCAD Senior Member

    You can use Salome as an appropriate Preprocessor for PPM. Just export as step from Alibre and import to Salome.
     
    Ralf likes this.
  7. Adi

    Adi Member

    Timo, you mean that in Salome I will be able to make shell part from solid step file?
    Thanks!, I will try it later, as now I have problem with my Internet connection, and can't download Salome.
     
  8. TimoCAD

    TimoCAD Senior Member

    Hi Adi, Yes should be when you have sheetmetal or deep drawed parts with constant thickness. Explode faces, offset, build partition to have faces for BCs.
     
  9. SergioP.

    SergioP. Member

    Can you share your geometry? Normally for Prepomax shell modeling I preffer to use Salome for meshing, as it allow me more control of the mesh.
     
  10. Adi

    Adi Member

    Hi, I made some model- just for test/learning purposes- "testSolid", and then I changed solid tu surface. Of course, there is a 2,5 mm shift of the part with hole (in surface model) in reference to the solid model (as it was made, from one of "wall/side of this part with hole)- If I have to check some similar, probably I would try to solid model, with changed dimesnions/ positon of part with hole, and then convert from solid tu surface, and delete unnessesary faces... :)

    This file "testSurface" i can't export to stl or stp- works only for IGES, but exporting to IGS causes that PrePoMax see a few different parts, and again (it's other file than I tested a few days ago, when I started this topics), after converting IGS to STL, by some online free converter part in stl loads in PrePoMax as one shell element

    Now I am dowloading Salome, and after that I will try to load my file into it, and mesh it- but, after Your posts, and reading of Salome forum I see that it should "do the job", and manage to convert solid to shell by itself.
     

    Attached Files:

  11. bigseb

    bigseb Alibre Super User

    Looked at your testsurface.igs. Stuff like that is tricky to get in CAD software mainly because its a disjointed surface and makes no sense at all in a design context. Of course for FEA its handy to be able to do. #

    Does testsurface.igs not import into Calculix at all? What error does it give? It should be perfectly acceptable to load the surface model instead of a solid for something like this. Curious...

    I opened testsurface.igs in Lisa. That worked so I think maybe I'm not understanding the problem... :confused:

    Capture.JPG
     
    Adi likes this.
  12. SergioP.

    SergioP. Member

    I have Alibre Atom only, that doesn't do surfaces modeling, but if you have the profesional version of Alibre, and this allow you to work with surfces, I encourage you to use it to prepare the shell models before swithching to Salome. Salome is a nigthmare to do CAD, very basic modifications takes a lot of operations. I wolud use even FreeCAD than Salome for the surface modeling.
     
  13. bigseb

    bigseb Alibre Super User

    Even Alibre's surfacing is no use here. With the geometry in testsurface.igs you have 3 basic surfaces. Any two of the three can be joined into one but not all three as this would be a disjointed (non-continuous) surface.
     
  14. SergioP.

    SergioP. Member

    It doesn't matter if the surfaces vertical and horizontal are not joined in Alibre, they can be easily joined in Salome to force the coincident mesh.
     
  15. bigseb

    bigseb Alibre Super User

    I am aware of this. This is why I posted the Lisa screenshot above. It allows you to import the surfaces as is creates one mesh out of them. Can Calculix not do that?
     
  16. SergioP.

    SergioP. Member

    CalculiX by itself is only the solver, for meshing you could use CGX (the official prepostprocesor included in CalculiX suite), that I'm not sure of it can mesh the surfaces "unglued". You could use other preprocessors to generate the mesh, as Mecway, Lisa, Prepomax, Salome or others. With Salome I'm sure that you can import the surfaces and mesh it with coincident nodes (called conformal mesh), I'm not sure if Prepomax can do, as far as I remember it has a tool to glue surfaces or solids and create conformal meshes, but I had problems in some cases.
     
    Last edited: Mar 24, 2021
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  17. TimoCAD

    TimoCAD Senior Member

    I think prepomax uses the netgen mesher and should also mesh it as one mesh if you do a "build compound" in prepomax as first.
     
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  18. TimoCAD

    TimoCAD Senior Member

    Ok, got it to work. But only with help of Salome: Explode to Faces / Scale to mm / Build Partition of Faces and build Compound in PPM:
    PPM_import.PNG PPM_results.PNG Analysis-1.gif
     
    Last edited: Mar 24, 2021
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  19. Adi

    Adi Member

    In PrePomax this file loads as 3 different parts (while it is in IGES), but after loading this in STL (converted on some website converter) it loads as one part- it's very strange for me, and I have absolutly no idea (maybe someone could help me with this)- while there is no possibility of exporting surface (shell) model directly to the STL (or STP file), from Alibre.

    yesterday I used FreeCad to import IGES file from Alibre, and save as STL- to import in PrePoMax- it also worked fine, the same as using online converter

    Already checked it, as there was video on offical YT channel of PrePoMax author, about calculating shell parts- but for unknown reason I have a problem during meshing compound (compound at all doesn't work on mine computer the same as on that video)- I think that it could be connected with Calculix version I have- I will check some other version, maybe it will be a solution for problem with meshing compunds.


    Thanks a lot!, so next step, for me, will be learning of Salome also :)

    Could you tell, which of my files did you used as file imported in Salome? Shell (IGES), or solid model?
     
    Last edited: Mar 24, 2021
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  20. Adi

    Adi Member

    analiza1.jpg
    model made in "my" strange way, with converting file formats also works, but after I will lern how to use Salome, I will compare the both ways of solving this my problem- I wonder if the results of both calculations will be the comparable- as there could be some problems with "my way" , I think.
     

    Attached Files:

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