Numerical Instability

[gforney]

Please complete the following lines...

Application Version:  5.1.6 Serial
SVN Revision Number: 1673
Compile Date:
Operating System: Linux

Describe details of the issue below:

Hello,

I am trying to simulate pool pan benzene fire with crib of wood. I have
encountered NUMERICAL STABILITY problem after 24 second. However, I modeled
the wood as has been already described with char_solid.fds case. The
capacity of the pool is 1 liter. 

Thanks in advance

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-02 12:02:43

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• Attachment: wood.fds

[gforney]

You cannot use parameters like EXTERNAL_FLUX and H_FIXED in a simulation like yours.

Those parameters are used in the special case where we only treat the solid phase.

Tell me if this solves the problem, but make sure you go through all the parameters

to make sure you understand them. Do not just blindly copy input lines.

Original issue reported on code.google.com by mcgratta on 2009-07-02 12:22:20

[gforney]

(No text was entered with this change)

Original issue reported on code.google.com by mcgratta on 2009-07-02 12:22:35

[gforney]

I have already modeled pyrolysis including wood with thermal properties k, rho and c

on MATL line. Then, MLRUA and IGNITION_TEMPERATURE on the SURF line. Unfortunately,

I have encounterd the same problem after about 5 iterations. On the other hand, If
I 
am working with burner as a fire source not a pool pan fire, it is working. I do not

know if the problem with modelling wood or pool pan fire.

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-02 16:32:31

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• Attachment: wood.fds

[gforney]

Does the attached file fail after 5 iterations?

Also, have you tried using FDS 5.3.1?

Original issue reported on code.google.com by mcgratta on 2009-07-02 17:00:31

[gforney]

You cannot include only MLPUA and IGNITION_TEMPERATURE on the SURF line -- there is

no way to know how rapidly the object would heat up. You need a MATL_ID and a 
THICKNESS too. Tell me if that helps.

Original issue reported on code.google.com by mcgratta on 2009-07-02 17:11:21

[gforney]

I am turning the issue over to Simo Hostikka.

Simo -- there are various problems with the file wood.fds, but I noticed in the 
latest version that YPRSUM can be zero and lead to an error where PPSURF=0 in the 
denominator of an expression.

Original issue reported on code.google.com by mcgratta on 2009-07-02 17:25:22

[gforney]

The gasoline material did not have HEAT_OF_REACTION. Zero HoR affects the
Clasius-Clapeyron estimate of vapor pressure. I added a checking for this into read.f90.

Kevin -- I also fixed the potential divide-by-zero by YPRSUM.

The file runs now, at least up to 60 s. The updates will appear in FDS 5.4.0

Original issue reported on code.google.com by shostikk on 2009-07-03 08:46:03

[gforney]

I have added the HEAT_OF_REACTION. However, I have not encountered NUMERICAL 
INSTABILITY problem. I have another problem that the crip of wood did not burn. I 
noticed that the HRR increaed and decreased to zero after 60 second. 

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-03 11:08:45

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• Attachment: wood.fds

[gforney]

You haven't specified any product yields of your WOOD material.

Original issue reported on code.google.com by shostikk on 2009-07-03 11:57:16

[gforney]

I have already specified products yelds as shown in attached new file (wood.fds) 
with the same problem. You can check the HRR in the figure attached with increasing

and decreasing to zero. That means there is no burning to the wood crips. I have 
tested this problem with the followng

1- SPRUSE surface as defined in charring_solid.fds example 
2- CHAIR material with described directly the wood material

Unfortunately, I have encountered the same problem but with changing the value of 
HRR but with the same trend.

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-06 07:51:51

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• Attachment: wood.fds
• Attachment: HRR.png
  

[gforney]

Is the problem (a) the wood does not burn, or (b) there is a numerical instability?

Original issue reported on code.google.com by mcgratta on 2009-07-07 11:53:58

[gforney]

The problem now is the wood does not burn.

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-07 11:59:40

[gforney]

Furthermore, pool fire has been extinguished suddenly after about 30 second. 

Original issue reported on code.google.com by aymanhemdan1 on 2009-07-07 12:05:00

[gforney]

I suggest you use positive value for gasoline heat of reaction. Positive means 
endothermic evaporation reaction.

I also suggest that you should use the method presented in User's guide for 
assessing your pyrolysis models piece by piece. Now you put together very 
complicated fuel packages. Finding errors becomes inevitably very difficult.
First make sure your pool burns as you want it to burn. Then make sure your wood 
surface burns realistically under external_flux = 50.

As the original problem (numerical instability) is not an issue anymore, we will 
close this issue.

Original issue reported on code.google.com by shostikk on 2009-07-07 12:46:52

[gforney]

(No text was entered with this change)

Original issue reported on code.google.com by shostikk on 2009-09-15 11:25:51