Dear Sir,
I wonder why the features describe in the below presentation time tag 0:54 minutes, Edit mesh , quad mesh is not available to the one I installed Prepomax Version 2.0.0. My case is shown in my below screen shot.
PrePoMax (CalculiX FEA) - Tutorial 30 - Nonlinear buckling of a cylindrical shell (youtube.com)
Thank you in advance for your kind help.
Best Regards
jess
It is available but you have to switch Mesh settings to Advanced to see this option. There’s also a new tool for quad meshes - Shell Gmsh.
Dear Sir,
Thank you so much for your quick reply. Wow amazing Sir I really appreciate for your very fast reply. To be honest I did not expect that. I am more and more curious and interested in this community. It helps a lot.
Again thank you very much Sir.
Sincerely yours
jess
I am glad that I can help and that you watch my video tutorials 
Let me know if you encounter any other issues.
Greetings,
Jakub
Dear Sir,
I’m having a problem in this [PrePoMax (CalculiX FEA) - Tutorial 30 - Nonlinear buckling of a cylindrical shell. When I run the buckling step, my shell failure is shown in the picture. My shell is tearing off.
I try so many times creating different model but still same output. It seems the tearing is comes from the red line of the shell model.
However I notice when I use the model I downloaded from your link, its fine and its work perfectly. For this problem I have in modeling any advise or rule in modeling a shell.
Thank you and really appreciate for your kind help.
How do you create this shell model then - in which CAD software and in what way ? Can you share this geometry file ?
Dear Sir, please find the attached native file for the shell.
I made the shell model using ACAD and export it using .iges file.
Sorry I’m just new here sir, I want to attached my .iges file model but it seems only this format is allowed?
AutoCAD ? Exactly how did you model it ? By drawing a circle and extruding it in the normal direction or in some other way ?
You can add it to zip archive and then share or use some hosting website and paste the link here.
Yes sir I use AutoCAD2020. I made a circle and extrude it using surface command, extrude. And then I rotate it to make the orientation Y-axis in vertical direction.
Dear Sir,
I try make new model using circle then extrude it in the normal direction by surface command. This time I did not use rotate command, leave as it is. Then I export it using .iges file format. Then I run another buckling analysis and it the same output, my shell is tearing. Please see attached snap shot for the output result of buckling analysis.
I don’t know how 3D modeling works in AutoCAD but this geometry is weirdly complicated for such a simple shape. There are multiple edges forming both ends and apparently the seam edge (that’s how it’s called in CAD software) is partially separated leading to discontinuity in the mesh. It’s also visible in frequency analysis. PrePoMax even shows a warning regarding the geometry. FreeCAD can model this without such issues but there’s probably also a way to achieve it in AutoCAD. You could also try exporting to STEP but it’s unlikely to help.
Dear Sir, thank you very much for your time to check the model. I even try now to make a new model, this time using 3D Autocad command instead of surface command tool and I get the surface of it by explode command. However I got the same result, seam edge occurs again, just different profile of deformation.
Dear Sir, this is only for your additional information. I make another model using 3Dmodel. This time it is not a mesh but it is a solid shell with thickness of 1mm. This means I don’t need to assign thickness in the material since it is a solid model. There is no seam edge occur in the buckling analysis, however the capacity increase a lot. In shell mesh model Buckling capacity = 129148.6N. In shell solid model with thickness 1mm Buckling capacity = 7837180N almost 61x higher.
Thanks and best regards,
jess
Dear Sir, I found some items for your consideration maybe this item is to include in your list as item need to fix.
Case-1: Mesh Parameter >ADVANCED setting, node offset occurs. Buckling result seam edge occur.
Node offset occur after meshing applied.
Case-2: Mesh Parameter >BASIC setting, node offset None. Buckling result seam edge None.
Node offset None after meshing applied.
Buckling Analysis:
Seam edge None
Thanks and best regards
jess
even it’s standard format, still a Step or Iges file have compatibility problem between different CAD programs and Pre-Processor. I seen warning sign at geometry import steps in PrePoMax and the results shown vertical straight edges being separated or not connected, probably it has double edges at the location.
PrePoMax not have advanced feature in geometric healing or repairing since it’s a CAD problem and jobs. In this case, external program need to be used before importing, there’s an opensource one called AnalysisSitus for working in this task.
Dear Synt, thank you very much Sir. Yes you are right. Whatever I tried, the problem always the same problem, vertical edges being separated. I will try to use the AnalysisSitus as per your suggestion.
Again thank you Sir.
Best regards,
jess
The same problem occurs when a cylindrical surface is created in salome and imported as iges file in prepomax. If possible, create a step file.
Thank you Gunnar, appreciate your advise. I will try to find a way how to create a step file. As I need a converter from dxf format to Step file. I tried install the FREECad and it seems it need more time how to use FREECad.
I would recommend FreeCAD for geometry preparation for FEA in PrePoMax. That’s what I always do when preparing my tutorials. FreeCAD has large capabilities and can easily handle such cases. Creating extruded shell is really easy there - just sketch a circle and use the Extrude tool (with solid option disabled) in Part workbench. Then export to STEP.
Dear Sir FEAnalyst, thank you very much. Now I make another model using FREECad. Everything now is ok without seam edge occur in the buckling analysis after I run using PrePomax. Drawback only is in my part. I need to start familiarization of FREECad software. Its totally different compare to using AUTOCAD Software. But anyhow the seam edge issue is gone. Thank you so much for all your advise.
