# Domain "collapses"

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March 10, 2013, 10:33
Domain "collapses"
#1
Senior Member

Lefteris
Join Date: Oct 2011
Location: UK
Posts: 199
Rep Power: 8
Hello everyone!

I have one more question and I'd really appreciate it if someone could help.

When I use 4 connectors to assemble an unstructured domain, the mesh that is created is as if it has collapsed inwards. I attach a picture of the resulting domain.
It would be nice if I understood why this is happening and how to fix it.

Update
-------
I think I found the solution by reading this post:
http://www.cfd-online.com/Forums/poi...-question.html

I selected the database lines and then I selected
Create --> Coons Patch --> Generate Surfaces --> OK

and afterwards I assembled the domain and it seems ok...
Attached Images
 domain.png (13.5 KB, 12 views)
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Lefteris

Last edited by Aeronautics El. K.; March 10, 2013 at 11:46.

March 10, 2013, 12:59
#2
Senior Member

Chris Sideroff
Join Date: Mar 2009
Location: Ottawa, ON, CAN
Posts: 405
Rep Power: 15
Good to see you found that post. I didn't give much of an explanation though.

Creating unstructured domains from curved connectors _without_ underlying geometry will result in the initialized points being created like you saw because the algorithm it uses for unconstrained domains is a very simple interpolation of the boundary points.

This however is not the case for unconstrained structured domains which uses transfinite interpolation (TFI) and will do a much better job at creating the internal point locations such that it better represents the curvature of the bounding connectors. In fact, the structured domain TFI creates domains in a similar manner to how b-spline surface geometry is created.

The moral is for unstructured domains with curved bounding connectors you need to create an underlying database surface by which it can constrain it's internal points otherwise you end up with what you saw.

-Chris

Quote:
 Originally Posted by Aeronautics El. K. Hello everyone! I have one more question and I'd really appreciate it if someone could help. When I use 4 connectors to assemble an unstructured domain, the mesh that is created is as if it has collapsed inwards. I attach a picture of the resulting domain. It would be nice if I understood why this is happening and how to fix it. Update ------- I think I found the solution by reading this post: http://www.cfd-online.com/Forums/poi...-question.html I selected the database lines and then I selected Create --> Coons Patch --> Generate Surfaces --> OK and afterwards I assembled the domain and it seems ok...

March 10, 2013, 14:15
#3
Senior Member

Lefteris
Join Date: Oct 2011
Location: UK
Posts: 199
Rep Power: 8
Chris, thank you so much for the answer and the thorough explanation.
I had, in fact, nocited while experimenting with the software's features that - as you said - this is happening only with the unstructured domains while the structured ones are perfect. Now, I found out how to do it properly and thanks to you, I know the underlying theory as well! I appreciate your help!

Quote:
 Originally Posted by cnsidero Good to see you found that post. I didn't give much of an explanation though. Creating unstructured domains from curved connectors _without_ underlying geometry will result in the initialized points being created like you saw because the algorithm it uses for unconstrained domains is a very simple interpolation of the boundary points. This however is not the case for unconstrained structured domains which uses transfinite interpolation (TFI) and will do a much better job at creating the internal point locations such that it better represents the curvature of the bounding connectors. In fact, the structured domain TFI creates domains in a similar manner to how b-spline surface geometry is created. The moral is for unstructured domains with curved bounding connectors you need to create an underlying database surface by which it can constrain it's internal points otherwise you end up with what you saw. -Chris
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Lefteris

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