ERROR: Output QUANTITY VISIBILITY requires a SPEC_ID

[Henning]

Hello

I`m using Pyrosim version 2011.1.1114.

I have several slices were the "Gas Phase Quantity = Visibility (Mixure Fracion), and the "Smoke Quantity (Simulation Parameters/Output) = Soot Mass Fraction (Default). This combination results in "ERROR: Output QUANTITY VISIBILITY requires a SPEC_ID".

If I change from Soot Mass Fraction (Default) to (example) "[Extra Species: other] Mass Fraction" I get no error message.

I have used "Soot Mass Fraction" in the previous Pyrosim version, without receiving error. The Pyrosim/FDS manual or Release notes don`t mention the need to define a "SPEC_ID" when using the default value.

My bet is that the SURF_ID is not written in the FDS file when using "Soot Mass Fraction (Default)".

[Charlie Thornton]

Thank you for reporting this problem. Right off hand, I don't know much about that particular piece of the code but we'll check it out and let you know what we learn.

[Richard O'Konski]

Your observations are correct.  The quantity, VISIBILITY, is only valid when you either include a SPEC_ID on the same record or invoke the mixture fraction model in FDS, such as by including a fire.  When you use this quantity without a species and without specifying a fire, FDS complains.  

PyroSim used to detect this situation and write out an unused surface (INERT_FIRE) that forced FDS to invoke the mixture fraction model.  Due to a regression in our latest release, however, this was no longer happening.  When you changed the smoke quantity to a species Mass Fraction (which also requires the mixture fraction model), PyroSim still worked in detecting this and included the INERT_FIRE surface.  That's why it started working when you changed the smoke quantity.

Thanks for reporting this regression.  The next release of PyroSim will include a fix for this.

[Charlie Thornton]

The fix is now posted: http://www.thunderheadeng.com/2011/12/pyrosim-2011-1-1219/