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Pipe flow module / Falied to evluate variable Jacobian

Posted Apr 19, 2013, 7:48 a.m. EDT Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD) Version 4.3 4 Replies

Ishant Jain Certified Consultant
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I am working over a simple pipe flow problem, where I encountered with an Jacobial Error saying ;

Failed to evaluate variable Jacobian.
- Variable: mod1.nipfl.u3
- Geometry: 1
- Boundary: 7 10 13

I request you to kindly help me.

This is a coupled HT and Isothermal pipe flow problem, where three straight pipes are used to cool the structure. I think, I am facing problem with the initial value i.e. Tangential velocity for which I don't know the sifnificance of it niether it is explained with the mold cooling module ( example model )

Please see the Jpeg Image.

PFA



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Ishant Jain
R&DSS, TSL, Jamshedpur
4 Replies Last Post Apr 24, 2013, 3:30 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 19, 2013, 10:02 a.m. EDT
Hi

I do no longer have the pipe flow so I'm not sure about the settings in particular for the pressure, but you would certainly NOT have a constant pressure all the way ALONG the tubes, at best at entry or exit, exclusively.

Then there is the question about relative or absolute pressure, normally you set the gauge pressure to 1[atm] in the physics node and you solve for "differential pressure

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Good luck
Ivar
Hi I do no longer have the pipe flow so I'm not sure about the settings in particular for the pressure, but you would certainly NOT have a constant pressure all the way ALONG the tubes, at best at entry or exit, exclusively. Then there is the question about relative or absolute pressure, normally you set the gauge pressure to 1[atm] in the physics node and you solve for "differential pressure -- Good luck Ivar
Certified Consultant
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Posted: 1 decade ago Apr 23, 2013, 1:15 a.m. EDT
Dear Ivar,

I even couldn't be able to figure it out. There is no issue with the pressure, however it is showing error with the tangential velocity (u3) of pipe.

---------------------------------------------------------------------------------
Failed to evaluate variable Jacobian.
- Variable: mod1.nipfl.u3
- Geometry: 1
- Boundary: 7 10 13

-------------------------------------------------------------------------------------------------------------

I am unaware of this terminology, tangential velocity, therefore request you to out some light on it.




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ishantiitk@gmail.com
Dear Ivar, I even couldn't be able to figure it out. There is no issue with the pressure, however it is showing error with the tangential velocity (u3) of pipe. --------------------------------------------------------------------------------- Failed to evaluate variable Jacobian. - Variable: mod1.nipfl.u3 - Geometry: 1 - Boundary: 7 10 13 ------------------------------------------------------------------------------------------------------------- I am unaware of this terminology, tangential velocity, therefore request you to out some light on it. -- ishantiitk@gmail.com
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 23, 2013, 5:18 a.m. EDT
Hi

the most frequent issue with Jacobian errors, are related to non-continuous BC equations, be sure you give scalars, or CONTINUOUS functions for all entries in the BC settings. At best use the "smooth" step or rectangle functions under Model Definitions Functions

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Good luck
Ivar
Hi the most frequent issue with Jacobian errors, are related to non-continuous BC equations, be sure you give scalars, or CONTINUOUS functions for all entries in the BC settings. At best use the "smooth" step or rectangle functions under Model Definitions Functions -- Good luck Ivar
Ishant Jain Certified Consultant
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Posted: 1 decade ago Apr 24, 2013, 3:30 a.m. EDT

Thanks, But, as asked earlier, please help me to understand the meaning of Tangential Velocity and its significance.

I only have the Flow velocity, Which I have defined in inlet.



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Ishant Jain
Thanks, But, as asked earlier, please help me to understand the meaning of Tangential Velocity and its significance. I only have the Flow velocity, Which I have defined in inlet. -- Ishant Jain

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