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Soren April 16, 2002 08:37

B.C. on surface or solid

Is it possibel to change a part of the geometry in CFX-build 5.5 without deleting the solid/domain ?

Like say moving a surface without one have to apply all the boundary conditions again !

Furthermore, is it possible to clearup the geometry, like when a lot of change to the model has happende (deleted lines and surfaces) ?

Thanks in advance.



Astrid April 16, 2002 16:34

Re: B.C. on surface or solid
1) in principle not, as far as I know. The only thing you can do is create a new solid and use that as a cutout-solid from the first solid. But I think this is not what you want.

2) You can delete a solid without re-applying all the boundary conditions again. If you have deleted e.g. Surface 32 and created a new Surface 32 on the new position, you don't have to re-apply the BC.

You might be in trouble if you have created a solid from a bunch of surfaces and deleted all these original surfaces right away. Then you end up with surfaces named like Solid 1.2. Then, if you delete Solid 1, I guess you will have to redefine all the BCs as the numbers get mixed up. But I am not sure.

I advice you 1) not to delete the original surface upon creating a solid, 2) If you define a BC, define it on an original surface and not on the solid 1.### surfaces.

3) What do you mean by clean-up? You can renumber the points, curves and surfaces, but then you definitely have to re-apply all the BC's.


Mike April 16, 2002 19:50

Re: B.C. on surface or solid
A nice trick is to create you geometry and mesh in Mesh Only Mode. Create named 2D regions for all the boundary conditions that you need then write out a Definition file. Create a second database using Import Mesh mode, import the Def file, and then define all the domains and boundary conditions. Now, if you want to change your geometry you can just modify the Mesh Only Mode database and write out another definition file. You must make sure that you do not change the names or delete any of the 2D or 3D regions. If you overwrite the definition file containing the first geometry with the one containing the new geometry, then when you re-open you Import Mesh database it will import the new geometry.

Robin April 18, 2002 12:12

Re: B.C. on surface or solid
Hi Soren,

You cannot modify the solid without deleting it, but you can modify it without messing up your boundaries.

One method is to keep define boundary conditions on the original surfaces that make up your B-Rep (as Astrid has suggested).

The other is to dissassemble your solid (deleting the original) and make the modifications. If you do not create more surfaces (by breaking existing ones for instance), but only modify the existing ones, you can get the same surface numbering on the solid by renumbering the modified surfaces to have the same number as the original. By doing this, Build will assemble the surfaces into a new B-Rep. Also make sure to use the same number to identify the B-Rep when you create it.

Since the boundary conditions are refernced to the solid faces by number, this will give you the desired effect.

Regards, Robin

PS: Mike - you will have the same problem with the 2-D regions moving in the mesh-only mode.

mike April 18, 2002 12:28

Re: B.C. on surface or solid
The idea of using Mesh Only Mode was to remove the issues of surface numbering. You could change your geometry and not worry about keeping the same surface numbering, as long as you re-create your 2D Regions using the same names. Yes, you'll still have to re-create the 2D regions, but this can be a lot quicker than re-creating all your boundary conditoins for complex cases - is this what you meant Robin or did i miss something?

Robin April 18, 2002 20:36

Re: B.C. on surface or solid
In the full mode, you never have to delete and re-create your boundary conditions, just modify them selecting the new surfaces. Same with mesh-only mode, so the amount of work is the same (more if you consider the need to re-import the mesh).


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