How to clean this surface for boolean operations?

I made a surface using grasshopper and then offset that surface and when I offset the surface I went down or inward if you can see the file. I think the problem lies in that the offset overlapped the surface with itself several times and did not trim itself automatically.

I tried running the intersect command so that I could trim and do it like the boolean FAQs talk about, but when you run intersect you can see what I ran into.
I also tried exploding the object and it gave me the bottom surface but I could not explode it anymore to do more trimming.

What can I do to clean that surface or the whole object up so that I can use it in boolean and other operations?

Thank you for any help.
Question.3dm (5.3 MB)

Yes, that offset made a complete mess of an object.
What you can do is to extract curves from that inner surface by making vertical planes and intersecting these with the surface. Clean up the curves (rebuild) and loft them in a closed surface. On the outer surface, run MergeAllEdges to make the bottom edge to be one closed curve. Use the curves to sweep a new border surface. Join all. Boolean with the box.

See attached.
Question-wd.3dm (6.2 MB)

If you can stand to modify how the umbrella surface is made, it will offset more cleanly- the top/singularity is tangent. (1.3 MB)


How did I get the clean curves?
Thank you for such a great split of all the steps.

Thanks for the suggestion, but the top part of the shape needs to stay the same, the bottom is less important.

I created a bunch of planes and polar arrayed them and then ran intersect and deleted all the extra lines. Now when I go to do a sweep the shape wraps back on itself. If I do a loft it doesnt follow the flow of the wave at the bottom. How did you get it to flow like that?

I only made one vertical plane and worked on the intersections from that one.

I’m attaching an updated file with a few more steps - probably the most important one was to cut the two remaining intersections with a vertical line from the center - else you’ll be creating overlapping geometry again. These two curves were then rebuilt with 5 points each before polar arraying.

I’m not sure why you would want to try a sweep on these curves. Is it important that the wave of the lower edge of the inner surface is the same as the wave on the original offset? Are you using the original edge as part of a sweep? I have just lofted the curves and obtained a wave that is more curved at the tips whereas the original offset produced sharp tips.

I exploded the original shape and hid everything except the bottom surface that was overlapping. I then use dupedge to copy the curve that goes around the bottom and the only reason I was trying to keep that same shape was so I could join it to the other surfaces that I had previously hid once the surface was complete. I could just do a blend surface or something like that I suppose. I think you forgot to attach the updated file.

I didn’t look in detail in those side surfaces but the shading of them made me nervous and I therefore thought it would be good to make a new side surface also - using the new inner surface and the existing outer surface as 2 rails for a sweep of a straight line.

I did forgot to attach the new file, yes. Here it is now.
Question-wd.3dm (4.0 MB)