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Divergence detected in AMG solver

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Old   May 28, 2014, 09:52
Default Divergence detected in AMG solver
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Marianna Mercogliano
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Hi everyone!

I am new to simulations of multiphase flow, and I am trying to simulate a fluidized bed using a DEM approach. I am using Fluent to simulate the fluid part. Unfortunately I am encountering an error when I launch the coupled simulation. After a few time-step this error is displayed:

# Divergence detected in AMG solver: mp-x-momentum -> Decreasing coarsening group size!
# Divergence detected in AMG solver: mp-x-momentum -> Increasing relaxation sweeps!

# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
# Divergence detected in AMG solver: pressure correction -> Increasing relaxation sweeps!

Error: Divergence detected in AMG solver: pressure correction

Do you have any suggestion about how to solve this issue?
Any reply will be appreciated!
Thank you
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Old   May 28, 2014, 16:33
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Sean Delfel
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Quote:
Originally Posted by mary91 View Post
Hi everyone!

I am new to simulations of multiphase flow, and I am trying to simulate a fluidized bed using a DEM approach. I am using Fluent to simulate the fluid part. Unfortunately I am encountering an error when I launch the coupled simulation. After a few time-step this error is displayed:

# Divergence detected in AMG solver: mp-x-momentum -> Decreasing coarsening group size!
# Divergence detected in AMG solver: mp-x-momentum -> Increasing relaxation sweeps!

# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
# Divergence detected in AMG solver: pressure correction -> Increasing relaxation sweeps!

Error: Divergence detected in AMG solver: pressure correction

Do you have any suggestion about how to solve this issue?
Any reply will be appreciated!
Thank you
Hi there,

As this isn't occurring on the first time step/iteration, it is likely that your simulation is simply diverging. I would suggest lowering your Courant number and relaxation factors for pressure, momentum and volume fraction. You may need to reduce them significantly until the simulation has advanced far enough to become stable.

Regards,
Sean
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Old   May 29, 2014, 07:52
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Marianna Mercogliano
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Sean, thank you for your reply! I have tried to lower significantly the URF but unfortunately this didn't help...
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