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Meenu May 7, 2007 01:39

3D geometry in gambit

I want to make a geometry in 3D(have never used gambit for 3D, though have done some work in 2D)

simple geometry

a cube with a hole on the top surface -- i created a cube and then a circle -- tried to subtract this circle from top face

but got an error'operation cannot be performed as

face has upper topology (its a volume) -- if i retain the top surface of cube then there is no

problem, also retained circle as need to define velocity inlet on tht...but not sure how would i msh n define conditions on top face face of cube which i dont need --do i need to connect circle with any face

Please help!! Thanks

Pavs May 7, 2007 13:14

Re: 3D geometry in gambit
I am little confused with what you want to do. But here is a solution I will suggest based on what I understand.

Create the cube, create the circular face on the top (the hole). Now split (not subtract) the top face of the cube with the circular face. This leaves your volume intact. You can now mesh the top face and the circular face and then the volume. But I would think that you would then be able to only use the cooper or the T-Grid scheme for the volume mesh.

About the BC's, it depends on what you're trying to do. If, physically, all you need is like a cubic container with an inlet hole on the top, what you would do is define the circular face as an inlet and the rest of the top surface as a wall.

Hope this helps.

Meenu May 7, 2007 13:46

Thanks, have another doubt
Thanks Pavs,

This definitely will help. have one more ques, was trying to read about using split but couldn't understand which one should i choose out of retain, bidirectional and connected. I basically need a top plate with a hole and a bottom plate on which air from this hole is hitting I'll define sides of cube as outflow or pressure outlet. Hole as velocity inlet and top face of cube with hole as wall(i guess!!)

Hope this explains my ques better.

Thanks again.


Rohan May 8, 2007 02:37

Re: Thanks, have another doubt

Its so simple. Create the cube.

Create the face and do a face split operation.

Should click the option connected.

Thanks Regards Rohan

Pavs May 9, 2007 14:14

Re: Thanks, have another doubt
Yes, Rohan has the steps right. The idea is to have two faces (the top wall and the hole) with a common boundry. When you perform the split operation, you don't have to choose the retain option. Hope this helps.

Meenu May 10, 2007 12:55

Re: have another doubt
Hey Rohan and Pavs,

Thanks, split operation definitely helped me but I'm not able to open the msh file in fluent it gives me an error.

I used quad and pave mesh for all the faces I defined the boundary conditions as pressure outlet at all four sides of cube and top and bottom as walls also the hole as velocity inlet. I defined the continuum types for side faces and hole as fluid and for top and bottom as solid

Then i exported it but it gives me error for continuum types that i have defined

next i deleted the continuum types and tried exporting and it did but it gave me an error while opening it in fluent.

Thanks alot for your help, i'm a total naive for 3D geometry and appreciate your patience for telling me step by step.



Pavs May 10, 2007 14:58

Re: have another doubt
The side/top/bottom etc faces are all boundaries. You cannot specify the continuum conditions for those. The interior region is the continuum which will be a fluid in your case.

If I am not mistaken, you have only meshed the faces and not the entire volume. Once you mesh the face, go to volume mesh, select the volume and mesh it using the appropriate scheme. You don't have to specify a continuum zone in this case since by default it will be assigned a fluid and that works fine for you. Once the 3D mesh is created, Fluent should have no problem reading it.

I think you need to do some of the tutorials from Gambit. You can not jump directly to a physical problem without understanding what is going on in the program. You need to get your basics cleared first. Hope this helps.

Meenu May 10, 2007 15:51

Thanks Pavs.

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