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Old   August 26, 2013, 04:58
Question solution termination with roughness error
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moein
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hi experts.
I'm simulating a weir containing a rough region in the middle of it. This rough wall band is surrounded by smooth wall. when I set the roughness to 8 mm after 23 iteration solver is terminated by this error:

Parallel run: Received message from slave
-----------------------------------------
Slave partition : 2
Slave routine : cUCOEF
Master location : RCVBUF,MSGTAG=1032
Message label : 002100029
Message follows below - :

+--------------------------------------------------------------------+
| ERROR #002100029 has occurred in subroutine cUCOEF. |
| Message: |
| The solver has detected a negative Uplus in the turbulent wall |
| functions. The likely reason is a wall roughness which is too |
| large. Please check that the wall roughness is correct. |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created. |
+--------------------------------------------------------------------+

End of solution stage.
But when I set high values of roughness to the entire of weir there is no problem!
how can I fix this problem.
thanks in advance.
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Old   August 26, 2013, 06:19
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Have a look at the boundary of the rough region. There is probably some weird flow going on there. You might need to do something at the edge to make the numerics nicer, maybe blend the roughness from rough to smooth rather than a sudden jump.
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Old   August 26, 2013, 16:15
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thank you for your advice.
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Old   August 26, 2013, 16:46
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Also, what is the height of your first element next to the wall? It should not be bigger then your wall roughness height.
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