Hello everyone!
I have a question, which is not directly about PrePoMax- Could you give me some ideas about how to prepare a shell models for PrePoMax?
I tried to do some models in my CAD, but they doesn’t work correctly.
Do You use any open-source CAD or maybe external mesher, to prepare shell elements? I wonder if there is any opensource mesher, which can make shell mesh, from solid model- as generating middle surface, between of 2 existing surfaces in the model?
Thank You in advance
I use FreeCAD for that. It’s not perfect but it’s really powerful, has a lot of useful tools and can help you with almost all the CAD modeling issues if you give it a chance. Unfortunately, it doesn’t have any tools specifically for midsurface extraction so you would have to do it manually - use Draft Facebinder tool to get surfaces from the model and then apply Draft Scale or (even better) Part Offset to it to get the actual midsurfaces. Not very convenient but can work.
Thanks, I will try it!
hi, in another way i use Salome since it has advanced of smoothing features.
below an example models were it was failed when default Netgen mesher without repairing.
lead to nonpositive jacobian determinant error problems.
Hi, what I do normally is export the solid model to Salome, and there I just extract the outer or inner surfaces of the solid to create the meshes. After that in PrePoMax I adjust the shell offset to take in count that I’m working with the inner or outer surface and not the midplane. In some cases I made the middsurfaces directly in Solidedge from the solid model (it doesn´t has a propper tool to create midsurfaces, so they must be created from scracth, but is far easy than using FreeCAD or Salome).
My advice is to be very precice/tidy at modeling to avoid errors like small gaps or supperpositions to be able to connect all the surfaces and avoid the use of TIE for connecting different components. Also be carefull with small radius in case of sheet metal parts, be carefull to made at least inner radius equal or bigger than the shell thikness for taking in count the element expansion in CCX.
Hi, Salome looks like very interesting way to prepare mesh- I will try this also (as I tried Frecad to prepare model for PrePoMax),
Sergio, are there any specific reason, why You do not generate midplanes? Always I thought, that it could be easier, as there is no risk of making mistake in which direction the tickness should be set (I mean “inside” or “outside” direction)
Laziness, is an extra step and as I have ready the 3D I preffer directly use one of his surfaces. Would be nice that Prepomax would allow to choose one surfaces to create the mesh directly in only that face.
@SergioP1975, if I understand correctly, a tool to use one of the solids’ outer surfaces as a shell surface is needed? Maybe a tool that would enable converting the solid to shell and a tool to delete some shell surfaces?
@Matej Such tool will be great option. For prepairing analysys with shell models, one more option will be also very big help for users- some kind of marking in which direction thickness will be “extruded”- for eg. if surface will be a midsurface colors of both sides of it could be the same, if thickness wil be “extruded” in one direction, will be possible to show one side of the surface in different color shade?
Hello @SergioP1975
Im currently struggling to extract a shell 3D model from a spaceframe made from several individual RHS steel parts. Im trying to use Salome, and havent found a great way yet.
Can you elaborate on the proces you use to prepare for prepomax?
@Tor, these are the generic steps for preparing the CAD for FEA:
Can you share your assembly file in neutral format (STEP)?
Thanks for pointing the steps out Sergio.
I should pooint out that i’m working on finding a good workflow where i can take the delivered design from design engineers, and prepare it for FEA, by mainly using Salome-Meca/PrePoMax. I’ve extracted a portion of an example and uploaded in this post, for you to see. This is typical of what i have to work with. It’s often not possible to ask the designers to simplify the models for me. One of my issues is that it is not obvious to me how i should remove all inner/outer fillets on the hollow section profiles, as the desginers make these on sketch level. It’s not simply suppressing a fillet function for them. I’m exploring the defeaturing powers of Salome-Meca, to see if it fits my needs. As beams are not yet supported i PrePoMax, i would like to analyze the structure with shells, preferably with a hex mesh where possible. My initial thought was to extract the fully square hollow section from the faces with the fillets. But i have not been very succesful. Sometimes the structures are large, so it would be preferable if is was not too cumbersome.
How would you approach this?
This is an example of the type of model: frame.STEP - Google Drive
@Tor, for some reason your step file has only lines, no surfaces or solids. Can you check your export settings in the CAD software?
@SergioP1975 Sorry, it should be fixed now. Could you check the link again?
Your file looks good appart from some detail.
Some beams are slighly offset so you should pay attention to which surface is master and slave. Slave should always have projection on to a master.
Plates overlap the beams.A correction of 1mm offset is enought.
I would search for some software that allows you to edit the mesh and work on it. Basic operations like move, erase and search for bad elements has been enought for me to buil an acceptable mesh.
If you are using surfaces, I would definitely try Gmsh. There are some Mesh. Algorithm combinations for quads really impressive.
ANYS, could you tell, which software You use for such a model corrections? Is this any specyfic program for FEA, or just any 3d Cad?
It is a commercial software, but I would say Gmsh itself has most of this feature like extrude, erase, rotate, move,…With the step quality you have I don’t think you need much more. To remove the holes, you could cut that piece of beam and insert a plain copy from other section or merge the nodes.
I would also recommend you run an analysis without BC or Loads just to check there are not invalid elements.
Thank you for checking my model @ANYS
Though the point of my post was to figure out if there was a way to use something open source to prepare a shell model for a solver. I’m trying to work out a workflow with Salome-Meca/PrePoMax.
Could you do what you did with Salome?
I perfectly understand.
My cooment was more oriented to remind you that the model could also be fixed and defeatured after meshing (and also to give a boost to the idea of incorporating gmsh into prepomax, it must be said.) 
Thank you, i appreciate you taking the time 
@SergioP1975 have you had a chance to take a look at the structure, in relation to meshing in salome meca?
