I make a final work as a bicycle mechanics student.
I build a long recumbent bicycle. The shop in which I make my apprenticeship make such bicycles since the 80's.
The aim is to integrate a new gearbox to the frame. In order to do this, I already used the wonderful FREECAD to design the "Bridge" (Link between GearBox and Frame).
I would like to:
- First, run a Fem analysis on the original frame (at the bottom);
- second, I would like to compare the results with the other frame, with the Bridge;
- Finally, I would like to make several tests for several designs of this Bridge.
I've made 3d meshes on the Frame with hollow tubes (that was without the crank), i obtained negative Jakobians. is it that bad (what is it anyway)? can we see for which region of the mesh the Jakobian is negativ? would I profit from this parameter (or was it implemented at all ?)
I've read that the use of 3d elements is not good in this case, as the lengths are far bigger as the widths.
We can then use shell elements and overlook the shearing forces.
As Bernd suggested I've read the study from HarryvL about Tubular connection and got a few questions:
- I've read somewhere that the information of the width of the material is embedded in the shell element. Is it the case with this study, and where?
- what kind of mesh is applied to the model, 3D? because the model consists already of shell elements (through the downgrade of the 3d model)
- Should I use a similar method to do my work?
There are 2 objects : the frame and the crank.
I thought I would make the crank rigid (with a very hight young's modulus), because I want to test only the frame. The frame consists of 0.9mm dick 25CrMo4 tubes. at some place dicker.
So I guess I have to use this method to combine the 2 objects
What I tried
I tried the "Boolean fragment + Compsolid option + Compoundfilter" on the 2 objects. here's what I got :
I tried to run a "from shape" and 3d mesh with Gmsh and it didn't work ( Unexpected error when creating mesh: <class 'RuntimeError'> )
Here's the result with the 2d mesh from gmsh (part of the tubes are hollow, other not)
Do you have any idea, Is the shape too complicated? Is it possible? Any books to read? I want to learn.
Unfortunately I can't share the original file.
OS: Ubuntu 18.04.3 LTS (GNOME/gnome)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.19107 (Git) AppImage
Build type: Release
Python version: 3.7.6
Qt version: 5.12.5
Coin version: 4.0.0a
OCC version: 7.3.0