CFAST - Model Validation

[fazil...@gmail.com]

Hi,

I have been working on a model as shown in the attached .in CFAST input file. The plant of the building is exactly as per the geometry of the attached file. I ran the file with a fire at the Compartment 2 at the ground level. I was getting the smoke distribution in an illogical way. Someone could please check my inputs to the CFAST and tell me whether I have gone wrong on any parameters. I would be so thankful for the help since I a beginner at this software.

My intention of modelling this was to find out the smoke spread in the model. I needed to know wether the doom at the centre can contain the smoke or it would get transported to the lower occupiable levels of the building. If yes I have to provide a mechanical ventilation at the ceiling level to transport the smoke outside the structure and provide safe egress path for the occupants.

Someone who could help me on this subject please show up 

Thanks,

Fazil Yoosuf

[Andy Tam]

I ran your case, but it did not complete successfully and the output files are all empty.

It seems you have over-lapping vents. Since you are not familiar with CFAST, I would suggest you should build up the complexity of your model gradually. For the first run, you should only keep the fire and one vent between compartment 1 and compartment 2 with the current geometry. Please remove the wall connections and 3-D outputs for now. With that, I think you model can run now.

I notice that you have one-zone approximation for compartment 1. I bring this up just to double check if you intend to do so.

Also, I should point out that CFAST does not model the transport equation, so CFAST will not be able to provide you the detailed information about the smoke spread. However, if you have vent openings, CFAST can calculate the smoke concentration for each compartment.

Thanks,

Andy

[Fazil Yoosuf]

Hi Andy,

Thanks for your reply. But, This same input file was working fine with me. Please see the inline attachment.

 Could you please point out the vents that are overlapped?. So that I can correct it and reach to reliable model. So for knowing the smoke concentration, the wall connections are not required. right? That's what I could understand from your mail.  

What you said is right. I have a single zone as compartment -1. But at the base level the comp-1,2 & 3 are connected each other and they formulate another single compartment. I hope my geometry justify that idea.

Awaiting your reply.

Thanks,

Fazil Yoosuf Electrical Engineer +1 (845) 600 7324 | +966 550 699 897 | Jeddah, K.S.A Please consider your environmental responsibility. Before printing this e-mail message, ask yourself whether you really need a hard copy. IMPORTANT: The contents of this email and any attachments are confidential. They are intended for the named recipient(s) only. If you have received this email by mistake, please notify the sender immediately and do not disclose the contents to anyone or make copies thereof.

--
You received this message because you are subscribed to the Google Groups "CFAST" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cfast+un...@googlegroups.com.
To post to this group, send email to cf...@googlegroups.com.
Visit this group at https://groups.google.com/group/cfast.
For more options, visit https://groups.google.com/d/optout.

[Andy Tam]

Dear Fazil,

I made a mistake and my input file was not opened correctly. The vents are setup correctly as well.

Now, I am being able to ran your case successfully. For your concern in smoke spread, CFAST provides output quantities: ULOD and LLOD (with unit of mass) in the _m.csv and ULOD and LLOD (with unit of reciprocal meter) in the _zone.csv.

You mentioned that the smoke concentration distribution is illogical. Can you further clarify what you mean by that?

Wall connection is used when you want to facilitate conductive heat transfer for surfaces between compartments.

Zone approximation: CFAST allows you to have one-zone approximation and two-zone approximation for a compartment in a simulation. One assumption in zone approximation (i.e. one-zone) is that mixture medium (air in the compartment) is well mixed within the compartment. This means that species concentration at any location in the compartment will be the uniform. From experimental studies, it is observed that there are normally two distinct gas layers (hot and cold) in a fire scenario at the fire developing stage. In order to better capture this effect, two zone approximation is used. In general, the upper gas layer is hot and more sooty and the lower gas is cooler and less sooty. For that, you will have to make a decision to choose which approximations best fits your case.

Sorry for the confusion from the previous email.

Thanks,

Andy