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-   -   Error: Divergence detected in AMG solver: x-momentum (http://www.cfd-online.com/Forums/fluent/108641-error-divergence-detected-amg-solver-x-momentum.html)

Smaras October 29, 2012 10:33

Error: Divergence detected in AMG solver: x-momentum
 
I am doing air injection on water using VOF model with axisymmetric condition. But when i start the calculation it gives me this error
:(

Error: Divergence detected in AMG solver: x-momentum

Please can anyone help

Thanks in advance

Regards,
Smaras

cfd seeker October 29, 2012 13:14

Reduce the under relaxation factors

Smaras October 29, 2012 15:26

Quote:

Originally Posted by cfd seeker (Post 389146)
Reduce the under relaxation factors

Thanks for the prompt answer

Already done that....but still the same problem.
Is it something related to axial or radial direction as i am doing axisymmetric VOF?

Thanks in advance.

Marion October 30, 2012 04:16

Hi Smaras,
Does it run for a few iterations before getting this error?
If you are running 2D-axi, are the mesh checks ok? have you set your domain in the X-Y plane, only positive Y and defined the axis (if you have nodes on Y=0)?
Marion.

ghost82 October 30, 2012 15:40

Quote:

Originally Posted by Smaras (Post 389101)
I am doing air injection on water using VOF model with axisymmetric condition. But when i start the calculation it gives me this error
:(

Error: Divergence detected in AMG solver: x-momentum

Please can anyone help

Thanks in advance

Regards,
Smaras

Make x your axisymmetric axis if it isn't.

Daniele

Smaras October 31, 2012 05:25

Quote:

Originally Posted by ghost82 (Post 389341)
Make x your axisymmetric axis if it isn't.

Daniele

Thanks Daniele and Marion i was doing a mistake by not taking x-axis as axisymmetric which was giving me problem. Now everything is fine...
Thanks everyone

niloogh May 23, 2013 19:10

Quote:

Originally Posted by ghost82 (Post 389341)
Make x your axisymmetric axis if it isn't.

Daniele

hi Daniele
is taking x axis as axisymmetric needed in 3D too???

jziha May 24, 2013 08:04

Try to change the size mesh and if you are employing a tetrahedral mesh change to hexahedral

niloogh May 24, 2013 08:11

Quote:

Originally Posted by jziha (Post 429771)
Try to change the size mesh and if you are employing a tetrahedral mesh change to hexahedral

tnx for your help
but it,s not possible for my geometry to use hexahedral:(

zcarral May 24, 2013 08:17

Change the mesh, time step or relaxation factors

niloogh May 24, 2013 08:25

Quote:

Originally Posted by zcarral (Post 429776)
Change the mesh, time step or relaxation factors

tnx dear
but i tried a lot but i coudnt make my mesh better(using gambit) and i,m using steady solver.
i reduced the relaxation factors too but it didn,t work.
i,m sure that problem is related to my periodic boundaries.but i don't know what is the problem and what to change about them:confused:

oj.bulmer May 24, 2013 09:40

Quote:

Originally Posted by niloogh
hi Daniele
is taking x axis as axisymmetric needed in 3D too???

No you don't, but you won't run the axisymmetric case in 3D though, because running it as axisymmetric is cheaper.

Can you post your domain/BCs and describe your problem more?

OJ

niloogh May 24, 2013 18:06

Quote:

Originally Posted by oj.bulmer (Post 429806)
No you don't, but you won't run the axisymmetric case in 3D though, because running it as axisymmetric is cheaper.

Can you post your domain/BCs and describe your problem more?

OJ

tnx dear oj
i found that the problem was in one of my walls.i set its coroct boundary
and it is working now:D

Honey July 19, 2013 09:20

Error: Divergence detected in AMG solver: x-momentum
 
Hello,

I have the same problem though!

For my problem, I am defining most of the boundary conditions (like inlet velocity, turbulence boundary conditions) with UDF file which is successfully interpreted into the Fluent. However, the solution is not converging and the error of "Divergence detected in AMG solver: x-momentum" is showing up.

I have reduced the under relaxation factors to almost -2 order of magnitude for pressure & momentum+ changed the numerical scheme as well as the descretization order+ lowered the initial guess value for the velocity+ converted the tetrahedral cells to hexahedral one BUT still the divergence error appears without any iterations!! nevertheless, after lowering the initial velocity value, the case run for few iterations (less than 15) then again the error came on the screen :(

So, I have gone through many ways to solve this problem and now have no more idea.

I will really appreciate to hear some suggestion/help from you forum people as I am stuck on my project.

Thank you in advance

flotus1 July 19, 2013 09:25

Does your simulation run if you use (reasonable) constant values at the boundary conditions instead of the UDFs?

Honey July 19, 2013 12:06

Thank you dear Alex.

After what you have asked I have tried to (one by one) replace the UDF with the a constant value wherever necessary in order to find out the problem. Finally, I've noticed that there is something wrong with the UDF that defines a resistance profile in the porous zones. However, I was not able to figure it out what causes the problem!

Any idea now??

flotus1 July 19, 2013 17:15

You could try to figure it out by yourself, or you could post the UDF here along with all relevant information and see if someone can help.

niloogh July 29, 2013 11:21

Quote:

Originally Posted by Honey (Post 440832)
Hello,

I have the same problem though!

For my problem, I am defining most of the boundary conditions (like inlet velocity, turbulence boundary conditions) with UDF file which is successfully interpreted into the Fluent. However, the solution is not converging and the error of "Divergence detected in AMG solver: x-momentum" is showing up.

I have reduced the under relaxation factors to almost -2 order of magnitude for pressure & momentum+ changed the numerical scheme as well as the descretization order+ lowered the initial guess value for the velocity+ converted the tetrahedral cells to hexahedral one BUT still the divergence error appears without any iterations!! nevertheless, after lowering the initial velocity value, the case run for few iterations (less than 15) then again the error came on the screen :(

So, I have gone through many ways to solve this problem and now have no more idea.

I will really appreciate to hear some suggestion/help from you forum people as I am stuck on my project.

Thank you in advance

hi dear
my problem was related to the periodic boundaries.after changing some things in gambit ;i had solved my problem.if your problem has periodic boundaries i,ll explan it in details for you.

dinesh September 26, 2013 03:11

AMG solver divergence
 
Quote:

Originally Posted by Marion (Post 389239)
Hi Smaras,
Does it run for a few iterations before getting this error?
If you are running 2D-axi, are the mesh checks ok? have you set your domain in the X-Y plane, only positive Y and defined the axis (if you have nodes on Y=0)?
Marion.

Hi
My geometry is sym about Y axis, i am giving it sym. But i am getting AMG solver divergence X momentum. I tried changing URF. Also it dont run for even 1 iteration. Can you suggest me the way.
https://www.dropbox.com/sh/udmvmhbiaxsjrl1/Dd9RRnu7OI

thanks

ghost82 September 26, 2013 03:56

Quote:

Originally Posted by dinesh (Post 453643)
Hi
My geometry is sym about Y axis, i am giving it sym.

thanks

You must assign X as the axisymmetric axis.

Daniele


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