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Fire Dynamics Simulator
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Numerical instability when using pointwise INIT line #1482

Closed gforney closed 9 years ago

gforney commented 9 years ago 

Application Version:6.0.0 Parallel
SVN Revision Number:7901
Compile Date:Mon, 21 Mar 2011
Operating System:Linux

Describe details of the issue below:

I use the INIT line to insert monodisperse water droplets pointwise, but the droplets
seem to be accumulatting on the floor even if I set "POROUS_FLOOR=.TRUE.". Besides,
the gas velocity near the floor is abnomal.

Still worse, if I increase the number of pointwise INIT (up to 2000, the flow rate
is nearly 40L/min) and add a fire in the domain, it encountered numerical instability
issue. Moreover, if I increase the mesh partitions, in other words, increase the processors,
this issue will occur earlier.

In order to find out the cause, I set up a same case (monodisperse and pointwise) by
using PROP and DEVC line to insert dorplets, which are widely used in previous version.
By doing this, I do not see the accumulating dorplets, and do not face numerical instability
issue, either.

So would you please tell me if there are some difference between these two approaches
(pointwise INIT and PROP+DEVC)?

Original issue reported on code.google.com by lsy19830908 on 2011-10-24 09:28:16

gforney commented 9 years ago 
I'll take a look at the case.

Original issue reported on code.google.com by mcgratta on 2011-10-24 15:00:40

gforney commented 9 years ago 
The latest version of FDS 6.0.0, which is still being tested, is SVN 9277. Update your
repository and recompile.

Original issue reported on code.google.com by mcgratta on 2011-10-24 15:04:21

gforney commented 9 years ago 
Thank you.

I have found the reason why some dorplets are stopping near the floor level and increase
the number of Lagrangian particles in the computational domain significantly.

Because I set the "UVW" of some pointwise INIT to be (0,0,0), these "static" droplets
invoke these issue. On the other hand, "VELOCITY=0" is not allowed in PROP + DEVC method,
so this stopping dorplets are not seen in this method.

However, whether I will ecounter the numerical issue again after avoiding the zero
"UWV", it should be further investigated.

Maybe, the zero "UVW" need be prohibited by giving the user a error message.

Thank you, again

Original issue reported on code.google.com by lsy19830908 on 2011-10-25 06:18:00

gforney commented 9 years ago 
Thanks. We have not tested this feature thoroughly. It might change.

Original issue reported on code.google.com by mcgratta on 2011-10-25 20:08:23