First up:
OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.2
Locale: English/United States (en_US)
Next, the task: I am attempting to:
- Receive 3D CAD of a fabricated (welded) structure made of tubes and folded sheets, all steel
- Assess the structural performance of the structure. Just linear to start with, in the crawl, walk, run approach.
I've previously done this sort of thing with commercial tools like HyperMesh/OptiStruct, Patran/NASTRAN, SDRC I-DEAS (I did say I was old). When hobbying, such tools are out of scope. So some of my knowledge may be rusty; there's no shame in that for me - just correct me when I err.
I've successfully made and analysed individual tubes, so that's no problem. (As an aside, I willfully overmeshed some of my examples to see what the laptop could manage, and laughed out loud when it took 90 seconds to solve a 500k DoF linear problem. When I was a boy that was a "heroic" scale problem that was sent to a Cray XMP somewhere else in the world.)
But I'm looking for a workflow that lets me generate a shell mesh, just on the outer faces for now (I know, I should offset them to find a midplane - that's for the walking part of the exercise - I am still crawling now) and join the parts of the mesh effectively.
I'd like not to regenerate all the data, if possible, but instead to use the existing CAD data.
So far I am fumbling around and have what looks like a workflow of sorts:
- Defeature and delete details that don't move the needle inside FreeCAD
- Write out a reduced STEP file
- Read the STEP file into Gmsh
- Create a "Physical Group" (unsure of the terminology here, hence the scare quotes)
- Mesh as desired in Gmsh
- Run the Coherence Mesh command to merge coincident nodes
- Export mesh to an I-DEAS universal file (it only exports the Physical Group entities)
- Import Universal file back into FreeCAD
- Add an Analysis thingy (again, terminology) and move mesh into it
- Make material properties and shell thickness on the relevant surfaces of the CAD data
- Add loads & boundary conditions, then solve
And finally, the question: What I'm missing is the understanding of how to make these manual mesh modifications within either FreeCad or Gmsh. Any tips - or wholesale ridicule on my workflow?
Thanks in advance,
Damian