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Old   September 15, 2008, 04:01
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  #1
Rishikesh
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I am doing cfd analysis of an air gap in a foil bearing used in turbomachines.While solving the mesh in fluent,when i put 'compute from' in the initialization panel,it reads non-positive volumes exist.

What is the solution for the problem i am encountering?

Reply eagerly awaited.

Rishikesh

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Old   September 15, 2008, 06:14
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  #2
CL
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Hi rishikesh check ur grid first, i think u may have negaive volume in ur domian thats why its showing like that. X,Y grid should be in positive value suppose if its in negative means fluent cant solve that...
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Old   September 15, 2008, 06:20
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  #3
Rishikesh
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Dear CL

when we put up grid check in fluent,if it says done,does that mean that the grid is correct?

i have already used smoothing during meshing in gambit.

please elaborate a bit on 'negative volumes' and how are they created?

my meashing area is really small(350 microns) as compared to the circumference.

could this be a reason why negative volumes are being created?
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Old   September 15, 2008, 06:59
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  #4
CL
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Hi rishi, A negative value for the minimum and maximum volume indicates that one or more cells have improper connectivity. So check ur grid in that see minimum and maximum volume, check whether its showing positive value or negative value.
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Old   September 16, 2008, 01:31
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  #5
Rishikesh
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Dear CL

i checked the min and max volunme values.both are positive.still it is showing 'non-positive values exist'.

what would be the problem now?
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Old   September 16, 2008, 02:30
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  #6
Venkatesh V
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Hi Cl and Rishikesh,

I have got one more query though not related to yours, it is related the problem you are simulating. In the bearings usually the gaps will be in the order of microns. In that case surface tension effects will play a major role and the surface roughness will be in the order of our mesh size.

Do you have any puplished literature on CFD analysis using fluent on bearings? If you have documents can share it with me.

Thanks Venkatesh V
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Old   September 16, 2008, 02:33
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  #7
Rishikesh
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hey venkatesh there is very less literature available on bearing cfd.

i do have come pdf files

gimme your email and i will forward it to u

and yes your point about surface tension seems to be correct.
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Old   September 16, 2008, 06:02
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  #8
Rishikesh
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venkatesh i am about to complete the 1st trial for my foil bearing. ucan ask me if u hv any difficulties.....

Rishikesh
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Old   September 16, 2008, 06:04
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  #9
Rishikesh
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Hey CL

the problem is solved

thnx a ton for your help.
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Old   September 16, 2008, 06:07
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  #10
CL
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Hi rishi, can u tell me what was the reason of the problem pls.

With regards, CL
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Old   September 16, 2008, 06:12
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  #11
Rishikesh
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well the reason was that i was not re-ordering the domain when i read the case file in fluent Rishikesh
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Old   September 17, 2008, 01:15
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  #12
Rishikesh
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hey venkatesh have u done cfd analysis of any bearing? please reply asap

Rishikesh
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Old   September 18, 2008, 01:02
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  #13
Rishikesh
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CL can u tell me how to import an igs file into gambit?
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Old   September 18, 2008, 03:33
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  #14
CL
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Open the gambit- file- import-geometry- iges file.
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Old   September 18, 2008, 04:08
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  #15
Rishikesh
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i tried it.its saying translation failed.

is it possible to import a geometry in a pirated version?
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Old   September 18, 2008, 04:31
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  #16
CL
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Tell me in which modeeling software u modeled ur geometry.
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Old   September 18, 2008, 04:40
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  #17
Rishikesh
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hey CL

i was able to import the geometry. but since i am using a pirated version,i can only use the native mode.

btw,i created the geometry in SOLID EDGE

thanks a lot for your help!

Rishikesh
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