Merge boundaries of two parts

Hello,
I have two solids that are defined by trimmed NURBS surfaces. One
should "sit on top of" the other, ideally. But, as it's happened the
surfaces overlap ever so slightly (the forms are built from anatomical
data, and some overlap occurred at some point in the conversion). I
can subtract one part from the other, or intersect & merge the parts,
but either of those options is undesirable: it creates a lot of
surface boundaries, which interfere later with finite element meshing.
Does anybody know a way to merge the bodies so that the top surface of
one will be coincident with the bottom surface of the other? (without
creating lots of extra boundaries)
Thanks,
Adam
Reply to
Adam Baker
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Adam Baker wrote in news:7207b3e3-a1be-4a60-a94e- snipped-for-privacy@e1g2000hsh.googlegroups.com:
There is no clean easy way to merge them with solid operations. Look up the "curvy stuff" presentations by Ed Eaton at the DiMonte Group web site:
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One of those, I can't remember which, has an explanation of what's going wrong. The example is almost exactly this situation, just not an anatomical application. I think it's one of the early presentations, maybe even 101. Your time won't be wasted even if it's in the last presentation though. Great stuff.
What you need to do is edit the two solid bodies so that you have two open surface bodies meeting each other where you want to join them. Then use a surface knit to combine them into a solid.
Reply to
Dale Dunn
Hi, Thanks for this response. I downloaded those tutorials, and they are very good quality. I am not sure if they address this particular question, though. The issue is that the object intersect in several different places. It's not the case that there's uniform overlap. So, when I intersect (Combine "common") the objects, I get a large number of slivers. (I realize that this wasn't stated in my previous email.) Then of course there are also small gaps between the objects where there aren't slivers. Is there a way to merge the surfaces for a problem like this?
Thanks, Adam
Reply to
Adam Baker
What is not clear to me is whether or not the mating scanned/converted surfaces have curvature (but I'll assume this),... or maybe they are closer to a planar, spherical, cylinderical, faceted or other (combination of) topology? The slivers tells me it maybe a faceted topology or a set of surface patches with different curvatures or there maybe overlay issues with the tessellation of the analysis model? What I would suggest is to copy (offset copy 0.0 or more if needed) one of the better surfaces of the two and use that copy surface to replace (replace face) the other mating surface. So, to help get past the slivers, create a analytical surface to mate the two halfs or create a surface interface which best mimics the topology and replace face both sides? You should now have a equally mated or offset interface (increase if tessellation for the analysis is causing the overlap?) for your two parts.
..
Reply to
zxys
I have to agree with Paul. What you're describing could be a range of different issues. Can you post somewhere before-and-after images of the problem areas? Paul and other (more so than me) can better tell you what needs to be done if they can see precisely what the issue is.
Reply to
Dale Dunn
Thanks Dale and zxys.
Here are my two objects:
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Here is what happens when the bottom object is subtracted from the top:
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(I just noticed that Merge "common" fails.)
The issue is all the extra edges/boundaries it creates.
I attempted the replace face approach. I'm getting various error messages. It's difficult to see, but the edges in the NURBS surfaces are not really in convenient places. Also, one surface is not really "above" another, since the parts are curved. Would you expect the replace face technique to work in spite of that?
Thanks, Adam
Reply to
Adam Baker
Well,... you got a problem here... but, I think you can still do it if it's alright to have some extra surface hanging over the edges? What you could do is create a few cross sections of the two bodies and try to do a average surface of your own, trim away the area which is common to both and thicken (mid) your common surface so that the other bodies are added to the merge?
Another way to creating a surface patch using the fill feature,.. create a 3dsketch which is as close the to common boundary as possible and then use a few cross sections for your control curves used for surface fill. Then thicken to merge both.
..
Reply to
zxys
Are you sure that the overlaps are a conversion problem? Maybe they are real and you need to space your two parts slightly to account for the way in which the high points on the two parts meet.
Jerry Steiger
Reply to
Jerry Steiger

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