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jai February 2, 2010 02:01

bounds error
 
i've got the below error notice and problem not converging.
what's the cause for this error and how to rectify it?



****** Notice ****** |
| While evaluating Static Enthalpy, |
| Absolute Pressure |
| went outside of its lower limit. Its minimum value was |
| -8.2688E+08. The bounds error was handled by clipping. |
| If this situation persists, consider increasing the table range.

****** Notice ****** |
| While evaluating Temperature, |
| Static Enthalpy on domain adaptor |
| went outside of its upper limit. Its maximum value was |
| 1.4247E+04. The bounds error was handled by extrapolation. |
| If this situation persists, consider increasing the table range. |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| ****** Notice ****** |
| While evaluating Temperature, |
| Absolute Pressure |
| went outside of its lower limit. Its minimum value was |
| -1.1240E+09. The bounds error was handled by clipping. |
| If this situation persists, consider increasing the table range.
Parallel run: Received message from slave
-----------------------------------------
Slave partition : 2
Slave routine : EX_TABLE
Master location : End of Continuity Loop
Message label : 009100008
Message follows below - :
+--------------------------------------------------------------------+
| ****** Notice ****** |
| While evaluating Static Enthalpy, |
| Absolute Pressure |
| went outside of its lower limit. Its minimum value was |
| -7.5023E+08. The bounds error was handled by clipping. |
| If this situation persists, consider increasing the table range.

ghorrocks February 2, 2010 17:19

Almost always this is caused by your simulation diverging. Improve the simulation stability by smaller timesteps or a better initial guess.

shubham jain July 3, 2014 04:04

I am simulating a Brush seal on shaft with porous medium approach in CFX using BSL model.
I have taken Bristle pack as a porous medium and need to solve it for different pressure differentials and different porosity values.


I have calculated it with air successfully but now I am trying it with steam but it is giving some errors.

While evaluating |
| Pressure |
| on interface "per side porous", |
| the variable |
| Static Enthalpy |
| went outside of its lower limit. Its minimum value was |
| 1.5541E+06. The bounds error was handled by extrapolation. |
| If this situation persists, consider increasing the table range.


similar errors came for Pressure and Temperature earlier, which were fixed by increasing the table range of steam. But I am not able to fix this static enthalpy error.

for Epsilon 0.8, inlet pressure 5 bar.
Out pressure 1 bar. Initially also the enthalpy is out of bounds, but CFX takes care of it by extrapolating and the notice stops after 25-30 iterations, then the case converges.

But if I decrease the epsilon or increase the out pressure to 2 bar, notice keeps coming only for 25-30 iterations.

A wall has been placed at portion(s) of an INLET |
| boundary condition (at 100.0% of the faces, 100.0% of the area) |
| to prevent fluid from flowing out of the domain. |
| The boundary condition name is: inlet. |
| The fluid name is: Fluid 1. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead.

Then this error comes and simulations stops.
I have tried the timescales upto 1e-7 but it is not working.

Please help.

ghorrocks July 3, 2014 06:03

Something is making the pressure go weird. It could be numerical instability, it could be a result of how you set the simulation up or it could be real.

If it is numerical instability then you need to improve mesh quality, double precision numerics, a better initial condition or a smaller time step. If it is your set up then you need to look at what you are doing - what is generating the low pressure? If they are both under control then it might be real, so you better make sure the table bounds are wide enough to cover it.


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