Divergence detected in AMG solver

mary91 · May 28, 2014, 10:52

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

delfel · May 28, 2014, 17:33

Quote:

Originally Posted by mary91

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

mary91 · May 29, 2014, 08:52

Sean, thank you for your reply! I have tried to lower significantly the URF but unfortunately this didn't help...

May 28, 2014, 10:52	Divergence detected in AMG solver	#1
mary91 New Member Marianna Mercogliano Join Date: May 2014 Posts: 7 Rep Power: 12	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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May 29, 2014, 08:52		#3
mary91 New Member Marianna Mercogliano Join Date: May 2014 Posts: 7 Rep Power: 12	Sean, thank you for your reply! I have tried to lower significantly the URF but unfortunately this didn't help...