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-   -   Divergence detected in AMG solver: pressure correction (http://www.cfd-online.com/Forums/fluent/72019-divergence-detected-amg-solver-pressure-correction.html)

emlejeen January 22, 2010 11:14

Divergence detected in AMG solver: pressure correction
 
I am having major issues with convergence of my solution. I am running a moving/deforming boundary UDF and cannot seem to get past a certain time step in the flow solution. I have now began a guess and check method to find the relaxation factors that best suit my needs. However, I cannot seem to find the correct parameters to successfully converge the solution. Ironically, the solution errors at the same time for every case I run and I always get the same error: "Error: divergence detected in AMG solver: pressure correction". I have tried to use two different solvers: the default with relaxation factors of 0.2, 0.8, 0.8, 0.1 for pressure, density, body forces, and momentum, respectively...and PISO with second order pressure and momentum (using the same relaxation factors as above). I have also decreased my pressure relaxation factor down to 0.5 and am still getting an error. As a last attempt, I re-ran all of my cases with the varying solvers and relaxation factors with a smaller time step (0.025s was used first then 0.01). I am willing to provide my UDF and case files is desired. Thank you.

DoHander January 22, 2010 11:22

Try to run the same case at t=0 but using the steady solver, wait until convergence or until the residual is flat. Then switch to the unsteady solver - this will give you a good initial solution.

Do

emlejeen January 22, 2010 12:59

Quote:

Originally Posted by DoHander (Post 243467)
Try to run the same case at t=0 but using the steady solver, wait until convergence or until the residual is flat. Then switch to the unsteady solver - this will give you a good initial solution.

Do

I am using a dynamic mesh which cause fluid motion. If i used a steady state solver, the fluid remains static because the mesh does not move. I could, however, apply a steady flow rate to the inlet, but then my model would just continue to move and would never converge. I am using a closed bulb model, similar to a boiling flask. The inlet of my bulb acts like the outlet because there is only one point of entry. Hope this helps to clear up my methods.

mmentzos January 26, 2010 11:17

Check if
When you use PISO neighbor correction, under-relaxation factors of 1.0 or near 1.0 are recommended for all equations. If you use just the PISO skewness correction for highly-distorted meshes (without neighbor correction), set the under-relaxation factors for momentum and pressure so that they sum to 1 (e.g., 0.3 for pressure and 0.7 for momentum). If you use both PISO methods, follow the under-relaxation recommendations for PISO neighbor correction, above.

almostafa67 August 7, 2010 06:45

pressure correction
 
hi dear all...
i'm trying to simulate peristaltic pump,when i was iterating simulated case i this error message showed up:
Error: Divergence detected in AMG solver: pressure correction.
i tried a lot to get rid of it,decreased urf from 0.6 to 0.1,changed meshing,changed skewness correction,....
but this message again and again showed up!
dear all i will be thankful if u help me out:o
thank u in advance for any help provided.


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