FDS 6.2.0 released

We just posted a release of FDS 6.2.0. This is a minor release, meaning that you can expect to see some changes in model results due to minor changes in various algorithms. We would urge you to finish out existing projects or studies with your current version and then upgrade to 6.2 as soon as you can. The reason why is that when bugs are reported for older versions, there is nothing we can do until the bug is observed in the latest version.

A significant change in this release is that there is now only one FDS executable for each of the three operating systems we support, Windows, Linux, and Mac OS X. Thus if you type "fds" or the old "fds_mpi", you will be issuing the same command. OpenMP and MPI are built in to this single executable and we urge you to take a look at the FDS User's Guide chapter called "Running FDS". There has been considerable confusion about OpenMP and MPI, and hopefully this new chapter will help clear some of it up. FDS still works like it always has from the command line if you just type

fds job_name.fds

but there are now a number of options you have to make the job run faster.

One other thing to note is that in the Windows release, we have switched from an older MPI scheduler to the one that is currently maintained by Intel. That is, when you run an MPI calculation by issuing the mpiexec command, you are using a newer version of the scheduler called "hydra_service". Those of you who are curious what this is, just do an Internet search. You should not notice a change in functionality from what we were doing in the last release, 6.1.2; it's just that a different background process will be running. Let us know as soon as possible if you notice anything different about the MPI on Windows.

FDS 6.1.2 released

A maintenance version of FDS has been released and is available for download at

https://code.google.com/p/fds-smv/

A few things to note:

1. We are only releasing the 64 bit versions of the software from now on. Of course, the source code is available for anyone who wishes to compile the code. 
2. We have switched the Windows implementation of MPI from MPICH to Intel MPI. Instructions are in the updated User's Guide. As we discussed in an earlier blog post, MPICH, the free implementation of MPI from Argonne National Labs, is no longer supported under Windows. The new Windows download of FDS has all of the necessary libraries to run Intel MPI and no extra download is needed, however our appeal for beta testing of the software was disappointing. Only a handful of testers volunteered. This is especially frustrating for us because we've heard no end of complaints about the fact that FDS 6 is slower than 5, even though it is more accurate, robust, and so on. If you want the code to run faster, support our efforts to make this happen.
3. Those of you who have submitted bug reports in the last few months, please go to the Issue Tracker and see if the issue has been "fixed." If so, download the new version and verify that it has been fixed. If it has not been fixed, let us know. For 9 out of 10 issues, we never hear back from the person who originally posted the bug report. Thus, we never really know if the issue has been fixed. Sometimes years later we meet this person at a meeting or wherever and the person tells us that the problem is not fixed. We cannot make progress this way.

Windows Test Bundle for FDS Parallel Processing using Intel MPI

We are looking for volunteers to test a bundle of FDS that uses the Intel MPI libraries for Windows. The installation procedure is the same as that of the current release of FDS. The test bundle can be downloaded from:

https://drive.google.com/folderview?id=0B_wB1pJL2bFQcURod1UyZTJUaEE&usp=sharing#list

A few things. First, we have only tested this version on a Windows domain network; that is, a network where user accounts are centrally managed. It is OK if this network has a firewall; the installation script will set up the necessary exceptions to allow FDS to run in parallel across the network even with the firewall in place. Second, the test installation will install FDS 6.1.1, but the old MPICH executable (fds_mpi.exe) will be overwritten. So anyone who has MPICH working and wants to continue using MPICH until we officially release should avoid the test installation because it will not only overwrite the executable, it will also install the Intel variant of mpiexec. Finally, there is no need to install the MPI package yourself. Everything you need to run should be in the test package. At least, this is what we want to test.

Volunteers should post to the FDS discussion group whether they have succeeded or failed to run a simple test case. Do not spend too much time fussing with this -- if the installation procedure is not simple then we have to rethink it. We have found that the old MPICH procedure was fairly difficult, and we think we have a much simpler process now.

FDS formulation to appear in Journal of Computational Physics

I apologize for the shameless self promotion.  But we code grunts need citations, too.

I am happy to report that the formulation developed and implemented in FDS 6 will appear in the high impact, peer-reviewed Journal of Computational Physics.  Please cite the article in addition to the FDS Tech Guide when referring to the mathematical formulation.  Here is a link to the article:

A velocity divergence constraint for large-eddy simulation of low-Mach flows

Abstract:

The velocity divergence (rate of fluid volumetric expansion) is a flow field quantity of fundamental importance in low-Mach flows. It directly affects the local mass density and therefore the local temperature through the equation of state. In this paper, starting from the conservative form of the sensible enthalpy transport equation, we derive a discrete divergence constraint for use in large-eddy simulation (LES) of low-Mach flows. The result accounts for numerical transport of mass and energy, which is difficult to eliminate in relatively coarse, engineering LES calculations when total variation diminishing (TVD) scalar transport schemes are employed. Without the correction terms derived here, unresolved (numerical) mixing of gas species with different heat capacities or molecular weights may lead to erroneous mixture temperatures and ultimately to an imbalance in the energy budget. The new formulation is implemented in a publicly available LES code called the Fire Dynamics Simulator (FDS). Accuracy of the flow solver for transport is demonstrated using the method of manufactured solutions. The conservation properties of the present scheme are demonstrated on two simple energy budget test cases, one involving a small fire in a compartment with natural ventilation and another involving mixing of two gases with different thermal properties.

Good-bye to 32 bit apps?

We currently compile FDS and Smokeview for MS Windows, Linux, and Apple OS X. We release both a 32 bit and 64 bit version of each program for each OS. Maintaining the 32 bit apps is becoming increasingly troublesome, and we anticipate that in the coming year we will drop support for 32 bit operating systems. I suspect that this will not be an issue for Linux and OS X users, but we do not know about Windows. MS no longer supports Windows XP, the last OS to come with 32 bit as the default, but there might still be a lot of these machines around. So this is an opportunity for any and all 32 bit users to make their case for us to continue supporting 32 bit. If we do not see a significant call for keeping 32 bit, we will drop it to simplify our compilation and release activities.