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slawek.mikula March 29, 2009 12:56

different boundary condition on one volume face

I'm struggling with the Gambit software. I was looking for the correct answer in the forum, but i think i am looking for the wrong keywords. I would be greatly appreciated for a help.

I am modeling a vlsi chip for a thermal simulation. The chip surface is divided in many functional modules. I would like to define different boundary condition for an each area of one volume face (top) in order to define independent heat flux condition for each "module" on the chip. I cannot model it as above.

What i am doing:
- create bottom volume
- create functional module's volumes and place them on top of the bottom volume with no space between vertical faces of the modules
- create a "unite" method on all above volumes
- ... error (this creates one volume without many faces on the top of the chip)

I am doing "unite" on the volumes in order to spread temperature during simulation.

What steps should I take in order to model it correctly? Should I create inner boundary condition for each bottom-module pair and for all module-module pair ? Or there is another way ? Thanks in advance.

-mAx- March 29, 2009 14:39

post a sketch of your issue, for a good understanding.
Your problem right now is just the modelling, not the BC, right?

slawek.mikula March 29, 2009 17:20

1 Attachment(s)
I've attached example file. I've got volume - 'surface' and three "modules" r_a, r_b, r_c. I would like to create in fluent heat flux for the three "modules" independently eg. face.13 will be 'wall' boundary condition and in fluent i'll attach heat flux (transient thermal analysis).

In order to transfer heat to the other volumes earlier i had "unite real volumes" but in previous models i haven't got "modules" that close to each other. When I apply "unite" right now all modules r_a, r_b, r_c are combined together and there is only one "top" face.

Maybe i should model it other way. But what kind of inner boundary condition apply to the faces between modules in order to allow bidirectional heat transfer. Thanks for help.

Sorry for non technical desciption, but i'm only rookie in CFD software.

-mAx- March 30, 2009 02:47

I am not at the office today, so I can't check you model, but if you want to apply 2 BC for the same face, you have to have to split your volume along this face, and disconnect this face.
It should create 2 faces at the same location (take care knowing which face belong to which volume for defining your BC).
I will take a look at your dbs file tomorrow

-mAx- March 31, 2009 03:37

ok I checked your model.
The 3 volumes you have are the solid part or are they already the fluid domain?
Where should be the flowfield?

slawek.mikula April 6, 2009 09:49

I'm really sorry for a late answer, but i haven't received email notification about Your answer (and waited for it).

About the volumes - all of them are solid. The "heat flux" boundary condition will be on the three faces on the top of each volume r_a, r_b, r_c. Everything else should be thermally connected with each other (the heat should spread across all volumes).

-mAx- April 6, 2009 11:45

Is this a pure solid conduction?
no convection through flow?
If yes, then I have no experience
But regarding Gambit side, as I said, if you want to apply 2 BC on both sides from a surface, you have to disconnect your volume at this face. Gambit will create a superposed face (on face belong to one volume).

slawek.mikula April 6, 2009 12:15

Thanks a lot anyway, i'll try to look for an answer with the superposed face.

slawek.mikula May 2, 2009 11:23

I've successfully created model I wanted. For future this is how:

- Task: I would like to create on one face ("main face") of an integrated circuit model different areas for the thermal purposes.

- Attempt 1 (fail): I've created many volumes that build that chip and after using "combine" tool on these volumes the faces are combined to one face - FAIL
- Attempt 2 (success): do as above, use "combine" tool to create one volkume. Next create helper face for the "split" tool. Move the face to the position on the main face and use "split" tool on the "main face". Do it as many times to create needed areas on the "main face". Next apply BC definition, meshing etc.

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