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-   -   [ICEM] Can I subtract volumes like I could do on Gambit? (http://www.cfd-online.com/Forums/ansys-meshing/94797-can-i-subtract-volumes-like-i-could-do-gambit.html)

Aoki November 25, 2011 16:10

Can I subtract volumes like I could do on Gambit?
 
Hello. Recently my University stopped buying the gambit licence and now we're on ICEM. Now I'm trying to build a geometry for meshing in ICEM, and I'm trying to create a wind-tunnel-like environment, with a wing in it.

If I were on gambit, I would create a volume for the wing, and a volume for the wind-tunnel, then subtract the small one from the big one. But I couldn't figure out how to do that on ICEM. I could still create two bodies on ICEM, but it doesn't seem to have a subtract function. Can I actually do the subtraction of volumes in ICEM like I did in gambit? If not, could anyone please suggest a way to build such geometry? Thanks in advance.

PSYMN November 26, 2011 12:34

It not like Gambit
 
ICEM CFD doesn't need you to subtract any volumes...

If you have created the two material points, that is enough. It can figure out the rest without needing to subtract solids, etc. This can save you a lot of trouble, particularly with poor geometry.

You will find that you need to shift your way of thinking when you shift tools from Gambit to ICEM CFD. They are very different tools that work with very different processes.

Definitely try some tutorials to get going and don't ever try to do anything "like in Gambit".

Regards,

skrzatchlewny November 26, 2011 12:47

i do not like gambit too
 
I would manage with your geometry like that:
1. draw tunnel (surface)
2. draw airfoil (lines)
3. trim tunnel surface using airfoil contours
4. delete cut geometry

or you can follow this tutorial:
http://www.youtube.com/watch?v=tYrbScUH9RE

cheers

Aoki November 26, 2011 12:59

Thanks guys. Your help is very much appreciated.

waqas77 October 24, 2012 06:04

volume subtraction
 
hi. i am doing an underwater vessel drag analysis. i am using the symmetry approach to save computational time. i have studied that there is no need to subtract volumes as in Gambit but my question is that the symmetry face of body is attached to the face of the domain and i have to subtract that. so how can i cut that part to keep the body hollow in order to satisfy the symmetry condition. can anyone help??

diamondx October 24, 2012 08:39

share a picture, i can help you with that ...

PSYMN October 24, 2012 08:46

We usually create the box in the right location. It would initially pass thru the vessel. The surface that passes thru the vessel can be renamed "SYMMETRY" or something like that.

You need a nice sharp curve along the symmetry plane, so use the geometry tab to create curves of intersection between the symmetry plane and what ever parts the vessel is made of.

Put a material point in the box between the hull and the far boundary... When you mesh with octree tetra, it will only fill this boundary. When you mesh with hexa blocking, you can decide which boundary to fill.

So strictly speaking, you don't need to delete the part of the ship outside the boundary. However, the way octree works, it will be much faster to generate the mesh if it doesn't need to consider the area outside the box. It is better to delete those surfaces.

In many cases, the geometry will already be a collection of surfs that is well divided. You can just use the geometry tab to delete surfaces/curves and points that are outside your box. You can box select or use other selection tools to make this easy on yourself. If you accidentally delete the wrong surface, you can undo it. Others prefer to create a new part and just add those other surfaces to the new part so they can be careful not to delete the wrong thing. When you are sure you have put all the junk in the JUNK part, you can delete the whole part.

If there are surfaces that past thru the box, you can run "Repair Geometry => Build Diagnostic topology". Among other things, this option will use the symmetry plane intersection curves to automatically cut all the surfaces that it passes thru. Then you can delete the bits outside the box.

In some situations, build topo doesn't split the surface. In that case, you can use the geometry tab => Create/Modify surfaces to segment the surfaces one by one based on a curve or plane... Then delete...


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