Where this error?

[agfic]

Hi.

I have the attached FDS file that has an error but I am not aware of it. When I run the file in the FDS, there is no fire. I can see this in the generated file ... HRR.csv.

The FDS is running but the fire never starts.

What is the error?

Thank you.

Ana

[dr_jfloyd]

For some reason the VENT isn't getting placed on top of the OBST. Until I can figure out why as a workaround remove the VENT and use SURF_IDS on the OBST.

[Robert Peart]

Your fire is in mesh SS2. dz = 0.22 m.

Your burner obstruction will actually have z co-ordinates -6.6, -6.38 (You have put THICKEN = TRUE).

Your Burner vent however will snap to the nearest z co-ordinate -6.6 (z Burner vent -6.5 is closer to z -6.6 than z -6.38.

So your Burner vent ends up on the bottom of your obstruction.  Try putting the Burner vent on z = -6.38.

Cheers

Robert

[o...@aquacoustics.biz]

The problem is that your burner obstruction definition doesn’t actually align with the computational mesh in Z.  With THICKEN=.TRUE. the actual fire object extends from -6.6 to -6.38.  The fire vent is specified at a height of -6.5 so it is actually inside the object!

 

This is a consequence of your mesh definition.  (-3.3 -  -6.6) / 15 = 0.22.

 

If you specify the vent at a height of Z = -6.38 then your fire will simulate.

 

An alternative solution is to apply surfaces in the fire obstruction definition.  This works because the surfaces are adjusted to the THICKEN object.

 

In general you would do well to stick with obstructions aligned to the computational mesh and at least 1 cell thick.  This is often a source of grief and frustration.  As you appear to be using PyroSim turn on the mesh alignment. 

 

I see that your version of PyroSim is somewhat antiquated.  Do make sure that you are using the latest version of FDS as PyroSim tends to link to the FDS version at time of release.

 

In terms of finding the error, when something like this doesn’t work then simplify your model.  Delete all those devices and all the other meshes so that you can focus on the issue.  You will see in SmokeView that the vent is ‘missing’.  Now re-read the FDS Users Guide on obstructions, vents and thicken.

On Thursday, 24 January 2019 17:59:13 UTC+13, agfic wrote: