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Old   March 7, 2005, 12:31
Default bodies---domain
  #1
phil
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Hi,Guys

In cfx-pre, how to define a domain with multiple dobies?

I use Workbench to build a geometry with multiple bodies. The reason I use multiple dobies is that two areas within the geometry have small dimension. If I build in one body, the total mesh element number will be huge. I tried to use multiple bodies and the number of mesh element was reduced significantly.

However when I import the mesh(by cfx-mesh) into CFX-pre, each body shows as an assembly. How can I define these bodies as one domain? I tried to do so, but the default region always shows the internal faces of all bodies.I think these internal faces will be treated as walls in the domain.

Could you provide some suggestions to this question? Your inputs will be greatly appreciated.

Best regards!

Phil

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Old   March 7, 2005, 15:48
Default Re: bodies---domain
  #2
Rui
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Hi,

You have to create a Domain Interface, where you chose Side 1 (belongs to body 1) and Side 2 (belongs to body 2).

However, notice that if the faces you chose for Side 1 and Side 2 don't match each other, the part which doesn't match is treated as a free-slip wall (you may find information about this in the documentation)

Hope this helps. Regards,

Rui
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Old   March 7, 2005, 16:12
Default Re: bodies---domain
  #3
phil
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Thanks a lot, Rui. Your answer is always so clear.

Actually I tried to use domain interface, but I was not sure if it's the right way.

Could you please clarify the following additional questions?

1. Can I understand that the domain interface is not only for two domains, it can also used for bodies within one single domain.

2. I chose the default domain interface model for above problem(frame change:NO; pitch change:NO). Is it correct?

3. Is multiple bodies method a good approach for reducing mesh number?

Thanks!

Phil

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Old   March 7, 2005, 17:29
Default Re: bodies---domain
  #4
Glenn Horrocks
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Hi Phil,

First to answer your questions: 1) Correct, a domain interface can join two or more domains, or it can join the different parts of the same domain. 2) No frame change and no pitch change means the interface does not move with time, and no rotation effects are to be included. If your geometry is not moving then this is the correct settings. 3) Multiple bodies is a good method to reduce mesh size, but not the only one. Generally I prefer to use a single domain with a strongly graded mesh, so the elements are small where they need to be and large where they don't. For geometries with large aspect ratioes consider a hex grid rather than a tet/prism grid.

I should point out that if you have multiple assemblies in CFX-Pre, you can select more than one assembly in a domain. If the meshes do not match across the joins then you will need to connect them with GGI's, but if they do you don't need an interface.

Glenn Horrocks
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Old   March 7, 2005, 19:26
Default Re: bodies---domain
  #5
phil
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Thank you very much, Glenn. Your inputs clarfied most of my questions.

You mentioned that you prefer to use a single domain with a strongly graded mesh. However in my case,no matter how I adjust the mesh control options (like 'inflaction', 'periority',etc.), the mesh number just kept being huge.This is why I chose multiple bodies.

I did like hexa grid rather than tet/prism grid when I use cfx-build, but right now I only have CFX-mesh, which is not able to generate hexa mesh.

Finally,I tested a simple case: extrude one face to form a body, and extrude the same face as 'add frozen' to other direction to form another body. The meshes of the bodies then were generated. They should match perfectly at jion surface. However if I do not define interface, the solver give error message showing that multiple bodies are used incorrectly. How to explain this?

Thanks!

Best regards!

Phil

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Old   March 8, 2005, 17:10
Default Re: bodies---domain
  #6
Glenn Horrocks
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Hi Phil,

You can create hex meshes using ICEM (or advanced meshing on the workbench). Mesh a surface with either quad or tri elements (or a combination of both) and extrude to give prism/hex elements. However this method only works when the third dimension is a simple extrusion,rotation or other simple shape.

Glenn Horrocks
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Old   March 9, 2005, 17:44
Default Re: bodies---domain
  #7
phil
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Thanks, Glenn.
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