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-   -   Trimmed Surface (CFX5.5) (http://www.cfd-online.com/Forums/cfx/19172-trimmed-surface-cfx5-5-a.html)

Nelson September 18, 2002 09:29

Trimmed Surface (CFX5.5)
 
Hi all,

I like to create a trimmed surface but there is a warning message as follows,

"Loop closure required for trimming. A gap of 0.127649 exists."

However, there is no indication in the viewport to show the location of the gap. Anybody knows how to fix this problem? Can I change any setting, eg tolerance, to fix it?? Please help! Thanks!

Nelson

cfd guy September 18, 2002 10:02

Re: Trimmed Surface (CFX5.5)
 
Nelson,
What kind of trimmed surface you want to create, the one with a hole inside ? If so, use the surface option (under Create->Surface->Trimmed), choose the surface you want to trim and the internal curve (inner curve). Make sure the curve is chained. That's it. I believe in the tutorials you can find the explanation you need to create trimmed surfaces.

Regards, cfd guy

Bob September 18, 2002 11:29

Re: Trimmed Surface (CFX5.5)
 
Hi Nelson, Is your geometry planar ?? If not then making sure your curve sits on the surface could be your problem. You can play with the tollerence but it is not advisable as this can be more problematic in the long run. Better to generate a good surface to start with.

When you chain your curve it is often a good idea to use the edges of the surrounding surfaces as this often can be a problem when matching the trimmed surface to the surrounding surfaces.

Also when creating a chained curve the Auto chainer is very good, especially if you have the pause at each curve turned ON. This way you can often identify if there are more than on curve existing at the same location by stepping through all of the options using the next button. Having stepped through all of the available curves, you can then make sure that you pick the correct curve for the chain. This can be important when fitting a trimmed surface next to another trimmed surface.

Nelson September 18, 2002 14:17

Re: Trimmed Surface (CFX5.5)
 
Hi,

Thanks for the responses of cfd guy and Bob.

Yes, I want to creat a surface which has 2 holes inside. And the surface I want to trim is not a planar surface. It's a surface of a quasi-ellipsoid and there are 2 tubes linked to this quasi-ellipsoid. So, I like to trim the surface to let the fuild pass through those 2 tubes. In fact, I've tried many methods, e.g. create intersect curves which intersect between tubes and the quasi-ellipsoid surface, then I would use that curve as a "inner loop", but the quality of intersect curve is not so good...

Right now, I have no idea about it. So, I want to seek some helps and ideas from the forum.

Any ideas and suggestions? Thanks!

Nelson

Bob September 19, 2002 05:24

Re: Trimmed Surface (CFX5.5)
 
Nelson, I'm not sure if this will help as you may have already tried it. I would create a curve using surface intersect. it sounds like the 2 tubes are made using a single surface each ? if so then it may be a better idea to split the tubes in half longitudinally so they are made up of 2 sufaces, 4 may be even better. Then chain the curves that are created at the intersect to create one single closed curve to be used in your inner loop of the trimmed surface. The problem I guess is in the curve not lying on the quasi ellipsoid. You could also try projecting the curve from the end of your tube onto the surface and us that ?? I've had similar problems, and I've found that it was a real trial and error process to try and find the right combination to get the trimmed surface to work. Good Luck Dave

Nelson September 20, 2002 00:37

Re: Trimmed Surface (CFX5.5)
 
Hi, Bob, thank you for your suggestion. I haven't tried that method yet. But I would like to ask you how to split the tubes in half longitudinally so they can be made up of 2 or 4 sufaces. Could you give me some hints? Thanks.

Nelson

Bob September 20, 2002 04:52

Re: Trimmed Surface (CFX5.5)
 
Hi Nelson Try using edit/surface/break then use the parametric option. You will need to see which option to set u or v but you will soon see which one to set through trial and error. Dave

Nelson September 24, 2002 08:44

Re: Trimmed Surface (CFX5.5)
 
Hi Bob,

I've found the major problem of the "inner loop". It's because there is a gap along the "curve". The warning message is as follows,

"Curves to be chained are not contiguous due to a gap of 5014E-07. The point of discontinuity has been marked."

So, I zoom in the curve and after many times of zoom in, I've found the gap. So, do you know how to "sew" it? I've checked the Edit/Curve function, but it seems there is no suitable function. What do you think? Any idea? Thanks!

Nelson

Dave September 25, 2002 09:26

Re: Trimmed Surface (CFX5.5)
 
Hi Nelson, how did you create the inner loop curve ? this is probably where the problem lies ? Dave

Nelson September 26, 2002 07:53

Re: Trimmed Surface (CFX5.5)
 
Dave,

It's a little bit complicated to create my inner loop. Basically, it's an intersecting curve by Create/Curve/Intersecting/Plane-Surface. This intersecting curve is my inner loop. Sometimes, CFX told me there is a gap, which may be due to a too low tolerance. When I set a higher tolerance or "sew" the curve (by create a curve between the gap and chain the 2 curves to be one curve then to sew the curve), there is a new error message that "Unable to manifold the trim loops to the surface." So, I'm still stuck on this problem.

Btw, Dave, can I send you a email to have further discussion?

Nelson


Dave September 29, 2002 07:04

Re: Trimmed Surface (CFX5.5)
 
Nelson, my email is funster7@hotmail.com feel free to send me any questions, or even a simplified geometry, I'm not sure how large it would be, I may have to send you my work email address if its very large. I know this can be a real pain sometimes to sort out. If possible I'd try and not alter my tolerence as this can lead to later problems eg you can get the curve to chain, but then it wont result in a manifold join between the surfaces. Dave

Carola October 18, 2002 16:16

Re: Trimmed Surface (CFX5.5)
 
I had the same trouble, I used edit/surface/break.

Carola.


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