Cannot join surfaces to polysurface

I have some surfaces on top and bottom of the polysurface and I want to join all of them together with the box. However, join doesn’t work.
What should I do?

Test.3dm (8.5 MB)

Hello - the file you posted appears to be all joined up…?


No those small surfaces on the top and bottom are not joined with the box.

Ah, so you do not want to just Join but to build new connecting surfaces, correct?


I tried joining them, but it cannot select the box, although it is a polysurface. I don’t know why

Hello - the box thing is a closed object - it has no ‘naked’ or free edges, so cannot be joined to anything as is. If your other surfaces are at some distance away, they cannot be joined anyway… So I am not clear on what the end result is that you are looking for.


I had some curvy geometries, I used boolean difference to subtract them from the box. So now, there are those gaps on the surface of the box, and I want to close those gaps, in order to only have the voids inside the box.

This is what you are looking for ?, you must leave a space between the poly surfaces, the solids cannot be touched so that both are closed. that way you get multiple cavities inside

Yes, that’'s what I’m looking for. but if I leave a space between them, then how can I subtract them? cause then boolean difference won’t work because they are not intersecting

Yes, that’s normally the case - Rhino does not automatically create disjoint solids. What do you need this object for?

I have to run a CFD simulation in Ansys Fluent and to keep the number of mesh faces below the limit of the software, I want to use the solid box as a fluid domain (which the geometry is subtracted from). In this case, I can only use the fluid domain to get fewer mesh elements instead of using both the geometry and the domain.

You can to make a group or change them to mesh and join them.

Hello - if you have disjoint objects, you can make them one Brep using NonManifoldMerge. You can do this as well with the original wiggly objects and the box…

testNonManifoldmerge.3dm (1.5 MB)

The inputs are the simple box, and the six wiggly objects with open top and bottom.


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