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floating point error in multiphase model

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Old   July 7, 2004, 20:15
Default floating point error in multiphase model
  #1
Sebastian
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Hi,

I tried to simulate an Eulerian Granular Multiphase model (gas-solids fluidized bed reactor) with more than 1 solid phase (2 or 3 solid phases with different mean diameters). I cannot start the calculation due to this error message right after pushing the iterate button: 'floating point error: invalid number Error Object: ()'. When I reduce the amount of solid phases to one, it works without any problems. I use Fluent 6.1.22 in the 2ddp mode and I modify the Syamlal-O'Brien drag law with a compiled UDF.

Any help would be great, Sebastian.
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Old   July 7, 2004, 21:12
Default Re: floating point error in multiphase model
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TAMO2(from Japan)
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Perhaps it occurs by velocity divergence.

Solution is here: At first, calculate only gas-phase in single-phase at steady mode.

Next, in Solve/Initialize/Patch, patch the fluidized region.

Next, Calculate unsteady mode.
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Old   July 9, 2004, 15:39
Default Re: floating point error in multiphase model
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Sebastian
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Thanks TAMO2,

but this also didn't work. Any other idea? I also tried it with the mixture multiphase model but then received an overflow after 7 iterations.

Regards, Sebastian.
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Old   July 12, 2004, 02:17
Default Re: floating point error in multiphase model
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TAMO2(from Japan)
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Mmmmmmmm, very difficult.

I think if you set shorter timestep, it may be good. Or changing little Under-Relaxiation-Factors, it may be good.

In my experience, I set 1/3 Under-Relaxiation-Factors as default.
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Old   July 18, 2004, 07:42
Default Re: floating point error in multiphase model
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ap
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I think the problem is in your UDF.

What does it happen if you start the calculation using the Syamlal-O'Brien drag implemented in FLUENT?

If it works, try to check how do you read data of the solid phases in the drag UDF. Pay particular attention to the use of phases threads.

Hi

ap
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Old   July 18, 2004, 07:49
Default Re: floating point error in multiphase model
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ap
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Not a good idea. If you want, you can start solving only for the gas phase, but still in unsteady condition, until you reach a stable solution, then you could start to solve for the solid phases.

But I don't think this is the problem in this case. Usually a velocity divergence gives the message: "Divergence detected in AMG solver: X-Momentum" or similar.

Hi

ap
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