Hi @Anonymous,
I see that you are visiting as a new member to the AutoCAD forum. Welcome to the Autodesk Community!
This is a rather involved process and depending on the original geometry, you may or may not be able to get this to work in AutoCAD.
I started closing the ends of each of the tubes with SURFPATCH
I then used ConvToSurface, MeshSmooth (faceted, not optimized), and then finally SurfSculpt.
One of the tubes converted fairly easily in this manner. The other two were more troublesome.
I suspect that doing this work in Fusion 360 would be much easier. It looks (visually) that many of the normals are reversed. In Fusion 360 these can be corrected and then stitched together
Please select the Accept as Solution button if my post solves your issue or answers your question.
John Vellek
Join the Autodesk Customer Council - Interact with developers, provide feedback on current and future software releases, and beta test the latest software!
Autodesk Knowledge Network | Autodesk Account | Product Feedback