Cable Stay Cantilever Beam Help Please

[FEAnalyst]

@ssashton

I do have a question about implementation. I’m not sure how best to get the required 1D geometry out of Fusion 360 and into PrePoMax alongside the 3D geometry. As far as I can tell, STEP export from Fusion doesn’t include sketch entities. One idea would be to extrude the sketch line into a very thin surface and then select only the edge for meshing, but I’m not sure if that’s good practice. Importing a 3D STEP file and a separate 2D DXF also feels like it could easily lead to alignment issues. Is there a tutorial video that might help me with first time usage?

Actually, if you want to use 1D elements such as trusses or beams in PrePoMax, you can’t just import them as lines because they aren’t supported in GUI yet. You would have to define their elements manually with a built-in CalculiX keyword editor. You can find multiple examples on the forum, especially since beams are often used to represent bolts: Beam Element connections between Two plates (2D)

@ssashton

I also have a question about partitioning geometry. Is this something that’s ideally done at the CAD stage (by splitting bodies or surfaces before export), or is there a straightforward way to do it inside PrePoMax if I didn’t plan far enough ahead in CAD?

Yes, definitely in CAD software. There’s a guide about this for FreeCAD if you want to use it. PrePoMax has only very basic splitting.

@ssashton

Finally, to clarify one point: I’m not actually trying to model the cable sliding over the top of the post. In retrospect, tying the cable at the top of the vertical post would clearly give minimal beam deflection. That was a mistake on my part — I was only thinking about compression in the post and didn’t think about how it might lean under un-equal forces.

Then you should definitely work on the mesh, as I described in the first reply. And keep in mind there are certain rules about contact (mainly make sure master is the coarser one and use linear contact with lower stiffness if you encounter issues).

However, in such a case, it might be best to use solids (at least for part of the cable in contact with the post).

@ssashton

Those research papers are a bit too advanced for me I think. However I’ll have a good read of the forum link about tension_only cables.

I can look for some about contact between cable and drum. There’s a so-called capstan equation that can be used to determine the load from the tensioned cable.

@ssashton

Edit: One more question — possibly a very obvious one. Is there a way to hide or show geometry while a constraint (or similar) dialog is open? At the moment, if the surface I want to select is obscured by another part, I have to select a random surface, exit the dialog, hide the obstructing object, reopen the dialog, make the correct selection, then exit again and restore visibility. That feels very inefficient, so I suspect I’m missing a simpler workflow.

The easiest way is to use View → Exploded View. Or you could create the surfaces in their container under Mesh first and then select them for analysis features.