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Setting pressure point constraint in closed fluid mechanics problem

Posted Jan 15, 2010, 6:37 p.m. EST Version 4.2a 6 Replies

Shahriar Khushrushahi
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Hi

My problem involves a closed sphere filled with magnetic fluid put near a rectangular bar magnet. Physically when this is done there is a pressure build up in the fluid because of the magnetic body force generated and there is no steady state flow.

The magnetic fluid magnetization is kept simple and is described by the linear relation M=Xi *H in the different directions. The volume body force density is given as follows
Fx=Mx*d(Hx,x)+My*d(Hx,y)+Mz*d(Hx,z)
Fy=Mx*d(Hy,x)+My*d(Hy,y)+Mz*d(Hy,z)
Fz=Mx*d(Hz,x)+My*d(Hz,y)+Mz*d(Hz,z)

The boundary condition on the fluid is no-slip and continuity for the normal magnetic flux density.
If I specify a non-correct pressure then COMSOL gives me a static result of positive flow when this is not physically correct. The problem I am having is I dont know the pressure point constraint that I need to specify so that the problem converges. I would like for the problem to solve the pressure automatically.

I have attached the problem. Any help on this will greatly help me and people with similar problems in closed fluid mechanics problems
Thanks
Shahriar
6 Replies Last Post Oct 24, 2012, 5:45 p.m. EDT
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Hello Shahriar Khushrushahi

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Giti Karimi
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Posted: 1 decade ago Jan 19, 2012, 3:53 p.m. EST
Hi,
I have the same problem, could you find any answer for pressure point condition?
Thanks,
Giti
Hi, I have the same problem, could you find any answer for pressure point condition? Thanks, Giti
Shahriar Khushrushahi
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Posted: 1 decade ago Jan 19, 2012, 6:35 p.m. EST
It was a long time ago, and I dont remember how I resolved it. I think it shouldnt matter what the pressure is set at any point because the solution will just scale relative to that initial set pressure.
It was a long time ago, and I dont remember how I resolved it. I think it shouldnt matter what the pressure is set at any point because the solution will just scale relative to that initial set pressure.
Giti Karimi
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Posted: 1 decade ago Jan 19, 2012, 7:04 p.m. EST
Thanks
Thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 20, 2012, 2:02 a.m. EST
Hi

as for all physics one need to sett get dependent variables defined fully, in FCD the pressure is often a relative or gauge pressure, and the results are correct for any value + a constant at some time one need to fix this constant and if a p=o output BC is not used, and setting a "p=0" at one point within the fluid domain might be enough to define the constant (=0 in this case)

--
Good luck
Ivar
Hi as for all physics one need to sett get dependent variables defined fully, in FCD the pressure is often a relative or gauge pressure, and the results are correct for any value + a constant at some time one need to fix this constant and if a p=o output BC is not used, and setting a "p=0" at one point within the fluid domain might be enough to define the constant (=0 in this case) -- Good luck Ivar
Akmal
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Posted: 1 decade ago Oct 24, 2012, 7:16 a.m. EDT
Hi Shahriar Khushrushahi,

i know it was a very long time ago.

could you send me the latest modell about ferromagnetic fluid. Or maybe the modell that has been presented on comsol converece on 2011 with title "Planar Geometry Ferrofluid Flows in Spatially Uniform Sinusoidally Time-varying Magnetic
Fields"

i'm trying to going into these theme but it's very complex.

thank you

best regards
hidayat
Hi Shahriar Khushrushahi, i know it was a very long time ago. could you send me the latest modell about ferromagnetic fluid. Or maybe the modell that has been presented on comsol converece on 2011 with title "Planar Geometry Ferrofluid Flows in Spatially Uniform Sinusoidally Time-varying Magnetic Fields" i'm trying to going into these theme but it's very complex. thank you best regards hidayat
Shahriar Khushrushahi
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Posted: 1 decade ago Oct 24, 2012, 5:45 p.m. EDT
The file was already attached in the first thread of mine



Hi Shahriar Khushrushahi,

i know it was a very long time ago.

could you send me the latest modell about ferromagnetic fluid. Or maybe the modell that has been presented on comsol converece on 2011 with title "Planar Geometry Ferrofluid Flows in Spatially Uniform Sinusoidally Time-varying Magnetic
Fields"

i'm trying to going into these theme but it's very complex.

thank you

best regards
hidayat


The file was already attached in the first thread of mine [QUOTE] Hi Shahriar Khushrushahi, i know it was a very long time ago. could you send me the latest modell about ferromagnetic fluid. Or maybe the modell that has been presented on comsol converece on 2011 with title "Planar Geometry Ferrofluid Flows in Spatially Uniform Sinusoidally Time-varying Magnetic Fields" i'm trying to going into these theme but it's very complex. thank you best regards hidayat [/QUOTE]

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