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-   -   Limit error (http://www.cfd-online.com/Forums/cfx/93234-limit-error.html)

Chander October 9, 2011 09:13

Limit error
 
COEFFICIENT LOOP ITERATION = 5 CPU SECONDS = 1.601E+05
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| U-Mom | 3.09 | 1.3E-04 | 1.9E-02 | 4.5E-01 ok|
| V-Mom | 2.37 | 6.0E-05 | 2.1E-02 | 5.5E-01 ok|
| W-Mom | 2.47 | 3.0E-04 | 7.2E-02 | 1.1E-01 ok|
| P-Mass | 1.20 | 6.5E-06 | 1.2E-03 | 43.2 7.5E-01 ok|
+----------------------+------+---------+---------+------------------+
| H-Energy | 2.46 | 1.3E-04 | 5.8E-02 | 1.3E-05 OK|
| T-Energy-Manifold so | 1.95 | 6.3E-04 | 1.2E-04 | 1.3E-05 OK|
| T-Energy-Bottom plat | 2.50 | 6.5E-04 | 7.2E-05 | 6.1 1.3E-05 OK|
+----------------------+------+---------+---------+------------------+

+--------------------------------------------------------------------+
| ****** Notice ****** |
| While evaluating Temperature, |
| Absolute Pressure |
| went outside of its lower limit. Its minimum value was |
| -1.7657E+05. The bounds error was handled by clipping. |
| If this situation persists, consider increasing the table range. |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| ****** Notice ****** |
| While evaluating Static Entropy, |
| Absolute Pressure |
| went outside of its lower limit. Its minimum value was |
| -1.7657E+05. The bounds error was handled by clipping. |
| If this situation persists, consider increasing the table range. |
+--------------------------------------------------------------------+


Hi ,

I am getting error as shown above in my transient simulation. I am using adaptive timestepping with timestep adapted on the basis of number of coefficient iterations required to meet convergence criteria in any timestep.
The solver keeps reducing the timestep size and sometimes it is able to come out of this limit error and sometimes it seems to be trapped in such error forever. Actually mine is a steady state problem but since the convergence was stalling in steady state runs, I am pursuing transient runs to evolve the steady state as per my discussion with Glen (ghorrocks) on this forum.
A previous thread by another user had also discussed this problem to which Glen had suggested divergence as the cause.
However, as you see above, the coefficient loop iteration just before this error occur seems to be fine as shown by ' OK` or `ok`.
I am using a uniform and fine mesh and the mesh quality is 1 throughout which I have checked thoroughly. Why is the adaptive time stepping facing such error and why it is not able to come out of this in some cases? what should I check in my simulations? I have checked my problem setup again and again but could not spot any obvious error in that. I am using CFX 12.1.

ghorrocks October 9, 2011 17:39

Read "Obtaining Convergence" in the CFX documentation, and this link has some tips: http://www.cfd-online.com/Wiki/Ansys...gence_criteria


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