Backflow and Floating point exception

harsh.bansal · June 1, 2011, 09:24

Hi,

The geometry for my problem is :
-----------------------------------------------------

=========================================
=========================================

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These are concentric cylinders with the solid(thick) part denoted by '=' sign.
i.e. There are two diameters for inner-cylinder (solid part in between) and one outer diameter.
I have just started using CFX

After writing the solver file, the solver runs and shows a notice(and not an error) which I am attaching in the form of a .txt file.

I also encounterd: +--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Floating point exception: Overflow |
+--------------------------------------------------------------------+

which is a common error, for which i tried increasing the memory upto '1.5x'
but still it shows the same error again and again.
I am attaching a .txt file(the error output file) for this as well specifying what exact conditions that I gave.(I have skipped many iterations because of the limit for posting)

If anyone has a solution for this, please do let me know...
Thanks...

ghorrocks · June 1, 2011, 18:32

This error has nothing to do with memory allocation. It means the linear solver has diverged. You need to improve the numerical stability - suggestions include smaller time steps, better mesh, lower order differencing, better initial conditions.

harsh.bansal · June 2, 2011, 01:12

Hello ghorrocks,
Thank you for your reply.

I have tried changing the mesh, decreasing the timestep and also changing the Advection scheme from High Resolution to Upwind and some of those conditions, but the error still remains.

Also, I am unable to find the solution for the backflow problem which the solver lists as a wall been placed at the outlet.

If you know them, then please do reply...

Thanks...

ghorrocks · June 2, 2011, 02:19

Well then you need to make the timestep smaller again or improve your mesh still further.

There has been plenty of posts on the forum about the wall at an outlet issue. Move the outlet boundary further downstream.

harsh.bansal · June 3, 2011, 01:52

Thank you ghorrocks for your reply

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June 1, 2011, 18:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	This error has nothing to do with memory allocation. It means the linear solver has diverged. You need to improve the numerical stability - suggestions include smaller time steps, better mesh, lower order differencing, better initial conditions.

June 2, 2011, 01:12		#3
harsh.bansal New Member Harsh Bansal Join Date: Jun 2011 Posts: 6 Rep Power: 14	Hello ghorrocks, Thank you for your reply. I have tried changing the mesh, decreasing the timestep and also changing the Advection scheme from High Resolution to Upwind and some of those conditions, but the error still remains. Also, I am unable to find the solution for the backflow problem which the solver lists as a wall been placed at the outlet. If you know them, then please do reply... Thanks...

June 2, 2011, 02:19		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	Well then you need to make the timestep smaller again or improve your mesh still further. There has been plenty of posts on the forum about the wall at an outlet issue. Move the outlet boundary further downstream.

June 3, 2011, 01:52		#5
harsh.bansal New Member Harsh Bansal Join Date: Jun 2011 Posts: 6 Rep Power: 14	Thank you ghorrocks for your reply