Friday, October 9, 2015

Some Recent FDS Validation Exercises

With the release of FDS 6.3, we'd like to take this opportunity to point out a few notable FDS validation cases that have been added to the FDS Validation Guide.

NRCC Smoke Tower Experiments 

About 10 years ago, researchers at the National Research Council Canada conducted fire experiments in a 10 story tower that was specially designed to study fire and smoke movement in a high rise building. The experiments and subsequent FDS simulations are described in the following papers:

Y. Wang, E. Zalok, and G. Hadjisophocleous. An Experimental Study of Smoke Movement in Multi-Storey Buildings. Fire Technology, 47:1141–1169, 2011.

G. Hadjisophocleous and Q. Jia. Comparison of FDS Prediction of Smoke Movement in a 10-Storey Building with Experimental Data. Fire Technology, 45:163–177, 2009.

However, the FDS simulations were done with FDS 4 and up until now there has been no mention of these experiments in the FDS Validation Guide. So, if you wanted to cite these papers as evidence that FDS is an appropriate model for this kind of fire scenario, you would probably be challenged because FDS 4 was last released in 2005, about the same time the experiments were performed. Thankfully, Paul Tyson, a student at Ulster University (formerly the U. of Ulster), re-analyzed the experimental data and performed simulations with the latest version of FDS. He then worked with us to get these simulations permanently archived in the FDS Validation Guide. This was not an easy job. Paul had to dig up old plans of the building, talk to the various researchers involved, weed through the various experimental data sets, and then figure out how to use the new ventilation features in FDS to model the leakage in the building. In the end, Paul found that leakage was a significant factor in the modeling, but this information was not well-quantified in the existing documentation.

PRISME DOOR Experiments

PRISME is the name of a fire test program conducted under the auspices of the Organization for Economic Cooperation and Development, Nuclear Energy Agency (OECD/NEA). The experiments were conducted at the French Institut de radioprotection et de sûreté nucléaire (IRSN) at Cadarache. A variety of experiments were conducted to study ventilation effects, electrical cable failure, and leakage. The test reports are not publicly available, but an entire edition of Fire Safety Journal documented various experimental and modeling studies. Two notable papers are:

L. Audouin, L. Rigollet, H. Prétrel,W. LeSaux, and M. Röwekamp. OECD PRISME project: Fires in confined and ventilated nuclear-type multi-compartments–Overview and main experimental results. Fire Safety Journal, 62:80–101, 2013.

J.Wahlqvist and P. van Hees. Validation of FDS for large-scale well-confined mechanically ventilated fire scenarios with emphasis on predicting ventilation system behavior. Fire Safety Journal, 62:102– 114, 2013.

As with the NRCC experiments, the FDS simulations were not added to the FDS Validation Guide until recently, for various reasons. We would like to give thanks to Jonathan Wahlqvist of Lund University, who analyzed the HVAC system of the test facility using FDS. He provided us his FDS input files and now these calculations are permanently archived in the FDS Validation Guide. These experiments and simulations demonstrate that the HVAC functionality in FDS that was added by Jason Floyd over the past decade works quite well. Thanks to Jonathan for his perseverance in setting up the fairly complex series of ducts, nodes, and fans.

What you can do to help

Even with the help of students, it is a tremendous amount of work to add a new data set to the FDS Validation Guide. In our experience, fire experiments are typically documented in a variety of test reports, student theses, papers, and conference proceedings. Rarely is there a single comprehensive test report and electronic file containing the data in an easy to understand format. So if you are now performing validation simulations using FDS or considering it, please contact us as soon as possible. Waiting until your thesis is done or your paper published is usually too late -- we need to work with you now so that when you are done the input files, data sets, and documentation will be in a form that is easy for us to incorporate into our Validation Guide. The final paper or thesis is rarely good enough -- there is always information that falls between the cracks.

The value added in contacting us early is that we have developed a fairly elaborate set of scripts to analyze and compare experimental data and FDS simulations. We would want to get your data and results into this system early so that both you and the rest of the community can benefit from the added set of validation.

Tuesday, October 6, 2015

Realizability paper accepted

Issue 2261 posted by Dan Swenson of Thunderhead Engineering led to a revamp of the species transport scheme to guarantee realizable mass fractions.  These changes were incorporated into FDS 6.2.0.  The approach we developed has a few novel aspects and so Jason Floyd and I submitted the work for publication in Fire Safety Journal.  Today we got word that the final version has been posted online and may be viewed here.

Thursday, October 1, 2015

FDS-SMV 6.3.0 Release

Today we posted a new minor release of FDS and Smokeview, version 6.3.0.  Please visit the downloads page on the FDS-SMV website to download the bundle for your platform.

The changes made to FDS are in some ways quite minor and likely will not affect most users.  The two most important changes are (1) the heat release rate limiter has been removed from the combustion model and (2) new default values of radiative fraction have been assigned to select fuels (such as methane, which has a radiative fraction of approximately 0.2; a complete list is given in the FDS User Guide).

We have also implemented a multi-fuel model for the radiative fraction where we weight the local value by the reaction rate for each fuel.  Because of this change, the RADIATIVE_FRACTION input parameter has been moved from the RADI line to the REAC line.  This should be the only input parameter change required for this new version.

We realize there has been a lot of chatter on the discussion forum recently about running MPI on Windows machines.  Unfortunately, we have not been able to simplify this process as of yet.  Our best advice is contained in the wiki Running FDS MPI on Windows. Please let us know as soon as possible if you run into trouble with this latest release.  Issues may be submitted here.

GitHub pull requests are welcome!

This is the first release since our migration from Google Code to GitHub.  We have, I believe, managed to maintain a balance between the stability of our old Subversion workflow and the flexibility and power of a distributed Git workflow.  We have basically adopted what Atlassian refers to as the Forking Workflow [insert bad joke here].  Each project member "forks" the repository and sends pull requests to the project maintainer.  What this means is that YOUR workflow and MY workflow for FDS development are nearly identical---the only difference is that I can accept pull requests.  We hope this will take collaboration to a new level.

If you are new to Git, the following link may be helpful:

FDS-SMV Git User Workflow

What's on the horizon?

The migration from Google Code to GitHub was a fairly heavy lift.  But with this minor release we hope to be in a position in the coming year to focus on development of chemistry, complex geometry, and scalability for multi-mesh calculations.

Please continue to monitor progress on Issues you care about and present enhancement requests for features you feel would be helpful.