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FDS_Road_Map
The FDS/Smokeview Research Plan
The Road TraveledFDS and Smokeview were officially released in 2000. However, for two decades prior to 2000, various CFD codes using the basic FDS hydrodynamic framework were developed at NIST by Howard Baum, Ron Rehm and Kevin McGrattan for different applications and for research. In the mid 1990s, many of these different codes were consolidated into what eventually became FDS. Before FDS, the various models were referred to as LES (large-eddy simulation), NIST-LES, LES3D, IFS (Industrial Fire Simulator), and ALOFT (A Large Outdoor Fire Plume Trajectory). The early NIST LES model described the transport of smoke and hot gases in an enclosure using the Boussinesq approximation, where it is assumed that the density and temperature variations in the flow are relatively small. Much of the early work with this form of the model was devoted to the formulation of the low Mach number form of the Navier-Stokes equations and the development of the basic numerical algorithm. Early validation efforts compared the model with salt water experiments. Charley Fleischmann, then a graduate student at Berkeley, and eventually his student, Jason Clement, validated the hydrodynamic model in FDS by measuring salt water flows using Laser Induced dye Fluorescence (LIF). Eventually, the Boussinesq approximation was dropped and simulations began to include more fire-specific phenomena, such as fire plumes, ceiling jets, sprinkler activation, warehouse fires, and large oil fires. The early validation efforts were encouraging, but still pointed out the need to improve the hydrodynamic model. To address this, we introduced the Smagorinsky model to close the LES subgrid stress in 1998. This addition improved the stability of the model because of the relatively simple relation between the local strain rate and the turbulent viscosity. The first official version of FDS, released in 2000, was aimed at large scale simulations of smoke movement from prescribed, well-ventilated fires, ideal for design work where the fire's heat release rate is not predicted by the model, but rather specified by the Authority Having Jurisdiction, or AHJ. Over the next few years, Jason Floyd, then a NIST post-doctoral fellow, and Simo Hostikka of VTT, Finland, as a guest researcher at NIST, developed the mixture fraction combustion model and the finite volume radiation transport solver, respectively, that have been the backbone of FDS ever since. These improvements were implemented in version 2 (2001). Versions 3 (2002) and 4 (2004) saw gradual improvements in these routines, along with the development of multiple-meshes (Kuldeep Prasad) and parallel processing (Chuck Bouldin and Kevin McGrattan). During the NIST Investigations of the World Trade Center collapse and the Station Nightclub fire, it became fairly obvious what needed to be done with FDS to make it an effective tool for reconstructing fires. Up to that point, FDS had been used by the FPE community for design applications, and to some extent forensic work, but the scope of the Investigations pushed the model to its limits. By 2005, it was clear that FDS was going to need a major overhaul, so we set about creating a new version (FDS 5) that would dramatically increase the flexibility and functionality of the model. The work proceeded along two broad fronts - the gas phase and the solid phase. In short, better combustion and better pyrolysis. Jason Floyd and Kevin McGrattan tackled the gas phase and Simo Hostikka at VTT tackled the solid. Meanwhile, the FDS user community continued working with FDS 4, and we struggled to keep up with the ever-increasing demand. By 2006, it became painfully evident to all of us that we could not keep up with the tremendous growth in support requests, and we were also not able to efficiently merge our various new algorithms into FDS 5. We decided to open up a new front - IT support, both to service user needs and to help us developers work better together. Glenn Forney, via Smokeview, had up to then played the dual roles of computer support and software support, but he was becoming over-burdened with other responsibilities. So at the end of 2006, we hired Bryan Klein to take some of the weight off our shoulders. Proposing New ConstructionBefore talking about the Road Ahead, a few words about how we decide on new areas of development. First and foremost, suggestions and requests by the user community are given a high priority, especially if the ideas come from different sectors of fire protection. Also, the individual developers, and the organizations they represent, have a specific research agenda. Wherever they come from, proposals for new features in FDS or for changing existing features must meet a number of criteria before they will be considered, which are explained below: This Road was Improved?There is a substantial cost in terms of time and effort to develop and test new source code. Proposed changes must make that effort worth it. In general this occurs by demonstrating that the proposed changes will demonstrably improve the predicton of FDS for a wide range of fire protection applications. For some computed quantities this is a very high bar. For example in well-ventilated fires FDS has been shown to make predictions of far-field gas temperatures and species concentrations within experimental uncertainty. This is an area where it would be difficult to demonstrate significant improvement, especially in light of the results of a recent US NRC V&V exercise (NUREG 1824) in which it was shown that FDS, for certain predicted quantities, is within the uncertainty of the experiments against which it was compared. Obey the Speed LimitOne of the main advantages of FDS over other CFD models is its fast computational speed and relatively modest requirements in terms of computational hardware. FDS was developed for practicing fire protection engineers who typically cannot afford to have a computation take months to complete. Even if the application is not necessarily practical, like a combustion research application, we still insist that any change to FDS must be evaluated for its impact on computational speed. If the end result of a proposed change is to greatly increase the computational time with little added benefit, such a change will not be considered; however, a proposed change that has little benefit in terms of predictive outcome but does reduce computational time is likely to be considered. Along with this is the development concept that routines related to a particular phenomenon should consume computer time in proportion to the impact of that phenomenon. For example, radiation from a fire plume typically accounts for around a third of the energy released by the fire. Thus, the various routines for radiation heat transfer should only consume about a third of the computer time. The basis for this is that if FDS spends a lot of time computing phenomena that have little impact on the overall uncertainty of the computation, then that time would be better spent improving the computation of a more critical phenomenon. No Roads to NowhereWe strive to maintain a high degree of flexibility within the FDS source code. This allows developers to experiment with adding new features or changing how existing features are done without having to overhaul large portions of the source code. A proposed change that restricts this flexibility is not desired. Along with developmental flexibility is the broad applicability of FDS. Proposed changes that would restrict the use of FDS to specific types of fire protection problems are not desired. No Limited Access HighwaysOne reason for the success of FDS is the ability for a fire protection engineer with modest training to use FDS for traditional applications such as smoke control, detector layout, etc. While there are and always will be applications that require a high level of knowledge of FDS, its numerics, and the physics and chemistry behind fire, the developers do not wish that for traditional applications. Changes to the code that would make it difficult for a typical user to use for traditional applications are not desired. The Road AheadTransport EquationsThe core mass, momentum and energy transport algorithms within FDS are fairly robust and efficient, but they do suffer from over-shoots and under-shoots of scalar quantities in regions of steep gradients, a condition common to second order accurate finite-difference schemes. An alternative transport algorithm for the density and species mass fractions has been implemented. It is an option in FDS 5 under the general heading of "FDS 6". We are testing these new algorithms currently and hope to make them the default in FDS 6, which is probably going to be released sometime in 2010. There are no plans to give up the low Mach number assumption or the large eddy simulation (LES) approach, but there is currently an experimental form of the dynamic Smagorinsky model of turbulence. The term dynamic means that the Smagorinsky constant, which is currently 0.2, is no longer assumed constant, but rather computed on the fly. The end result is to increase the dynamic range of the flow solver. Potential Research Topic: Explore ways to increase the speed and decrease the memory requirements of the new transport schemes. Use the FDS Validation Suite to demonstrate equivalent or improved accuracy of the new algorithms. The Pressure SolverWe still need to improve the coupling of the pressure solver across mesh boundaries in a multi-mesh (often called "multi-block") simulation. Discontinuities in the pressure solution across these boundaries is currently the biggest speed bump to broader, more reliable use of the multi-mesh approach. The hope is to determine a computationally efficient way to perform this coupling that still permits the use of the direct pressure solver (CRAYFISHPAK) which is one of the primary reasons why FDS is fast. The addition of a PRESSURE_CORRECTION in FDS 5.2 has not solved the problem, and there are still scenarios where this new feature produces spurious results. Potential Research Topic: Improve efficiency of parallel version of FDS on very large computing clusters (100+ processors). Document scalability using conventional parallel computing terminology. Priority: High. A key component of the FDS algorithm is the projection scheme which enforces the velocity divergence constraint implied by combining the continuity and energy equations. The projection requires the solution of an elliptic PDE and this constraint poses problems for efficient distributed memory parallel computing. We are working in collaboration with Susanne Kilian of hhpberlin to develop a fast global pressure solver. We are also pursuing research in OpenMP parallelization on shared memory machines. This effort is led by Christian Rogsch of the University of Wuppertal. As we move forward both these approaches will be extremely important in establishing a robust algorithm with optimal performance. Potential Research Topic: Adaptive Mesh Refinement (AMR). Explore strategies for structured grid refinement in a low-Mach LES solver and develop refinement criteria for fire applications. A key aspect of this research will focus on load balancing for parallel calculations. Priority: Medium in the short term; High in the long term. CombustionCurrent Activities: Led by Jason Floyd of Hughes Associates, we have developed a more general combustion formulation than previous versions. It still uses the mixture fraction approach to streamline the solution of the species transport equations, but now the mixture fraction is decomposed into 2, 3 and possibly 4 components representing fuel, products of incomplete combustion, and products of complete combustion. In this way, soot and CO growth/destruction can be modeled whereas in the past combustion was always assumed instantaneous and complete. The new algorithm has been validated against experiments ranging from Kermit Smyth's Wolfhard-Parker burner to Craig Beyler's under-ventilated hood series to Bill Pitts' reduced scale enclosure tests. Work continues along these lines with the reduced and full-scale under-ventilated compartment experiments of Johnsson and Bundy at NIST. Details of the model can be found in the FDS Technical Reference Guide. Future Activities: The new CO production algorithm was implemented in FDS version 5, and over the next few years we will monitor its progress. It takes years for any new algorithm to truly sink in with the users. They are always skeptical at first, and it will take a series of independent reviews by interested FDS enthusiasts to really shake out the new features. In the meantime, we plan to tie soot growth/destruction in with the current CO algorithms. Exactly how hasn’t been determined yet. The only thing that is clear is how the potential algorithm will be incorporated into the mixture fraction framework. Lately, we have been working on a more clearly spelled out model for the chemical reaction rates based on the Eddy Dissipation Concept (EDC) model of Magnussen. We have also developed analytical solutions to the system of ODEs that makes up the model. This gives a clear separation between the physics of the model and the numerical method to solve it -- something that had been lacking before. The current three parameter mixture fraction model could be extended to four to account for soot and CO production and transport and local flame extinction. Additional partitionings of the mixture fraction could be added as well; however, there is a point of diminishing returns. The present advantage of using a mixture fraction approach is to track the movement of a number of gas species using a smaller number of scalar variables at the expense of having to use state relationships to obtain species mass fractions. As more mixture fraction variables are added, the net savings in fewer species transport equations vs the expense of state relationships will diminish. The long term goal of FDS is to track the major carbon-carrying species directly (soot, CO, CO2, and unburned fuel). Minor species could potentially be tied to the production of the major ones, or empirically determined. However it is done, we do not want to compromise speed and accuracy. As with the current CO production algorithm in FDS 5, we will give the user the option of including more detailed combustion chemistry in fire scenarios where it is warranted. Recent large scale experiments conducted at NIST under US NRC sponsorship included measurements of smoke concentration that were substantially lower than predictions of both FDS and CFAST, the NIST zone fire model (US NRC, NUREG-1824). A possible explanation has been suggested by researchers at Hughes Associates, who have noted that significant amounts of smoke can be deposited on walls, an effect that is usually neglected by fire models. The Hughes team have not finished their experiments, but if their findings are true, it might mean that FDS will have to track soot/smoke explicitly. Potential Research Topic: Investigate empirical correlations that might help us predict the deposition of soot onto walls if we decide to incorporate soot as a separate species. Priority: Medium. Modeling gas phase suppression (flame extinction) is also a long term goal. FDS 5 has a simple, empirically based model of flame extinction based on the concept of the lower oxygen limit applied locally, grid cell by grid cell. Also available is the same concept for the fuel stream using the lower flammability limit Validation work is on-going to test the simple model, and it is planned to also look at gaseous suppression agents and water mist. Potential Research Topic: Identify and perform simulations of full-scale or reduced-scale experiments where the fire self-extinguished or was extinguished by a diluent or suppressing agent. The results could be added to a new chapter on Suppression in the FDS Validation Guide. Priority: High. Modeling of ignition or re-ignition (deflagrations and backdrafts) is also a long term goal. The new approach to partitioning the mixture fraction will make possible development into these areas. It is noted that the low-Mach number limitations of FDS means that computations on flows that approach a detonation event will not be possible. Potential Research Topic: Modeling backdraft experiments, noting that FDS currently lacks certain necessary physical mechanisms that would need to be developed in cooperation with us. Priority: Medium. Potential Research Topic: Treatment of turbulence/chemistry/radiation interactions. Some potential approaches include: off-line tabulation of reduced-dimensional models, e.g. LEM (linear eddy model), prescribed PDF (probability density function), and direct quadrature method of moments (DQMOM). How important is this issue in fire calculations (especially for CO and soot formation)? And how can these methods be incorporated in FDS in a tractable way (see Obey the Speed Limit above). Priority: Low to Medium, depending on how well it can be shown that any of these techniques or methods improves the current, default operation of FDS. Pyrolysis and the Solid PhaseCurrent Activity: Led by Simo Hostikka of VTT, Finland, we have rewritten the FDS solid phase algorithms to provide a better a description of heat transfer and pyrolysis. First, we added the functionality of doing 1-D heat transfer through multiple layers of materials. This was an obvious improvement to make, given our experience with insulated steel in the WTC Investigation, and polyurethane foam covered plywood in the RI Nightclub Investigation. Next, we generalized the pyrolysis algorithm to allow for multiple materials undergoing multiple reactions, similar to the approach taken by Kashiwagi et al. in the NASA microgravity program. Work will continue in years to come to verify and validate the new solid phase model, which has been implemented in FDS 5. This effort will be complemented by an external thrust (in cooperation with the SFPE) to develop an engineering guide for obtaining material properties for fire models. It is planned that this external effort will be headed up by new grantees and supported by an SFPE task group. Internally, the project led by Greg Linteris, "Experimental Data for Sub-Grid Modeling," will support this effort. Also, the new project headed by Dan Madrzykowski, "Fire Plume/Wall Interaction," will provide validation data to check the new pyrolysis algorithm. All of this effort is driving towards better predictions of flame spread and fire growth. It has been noted by many FDS users that the overly simplistic description of solid materials in FDS versions 1-4 has limited our ability to predict flame spread. Future Activities: Fire models developed by NIST have typically included a "database" of properties for common building materials and potential fuels. These properties are sometimes based on bench-scale measurements done here at NIST, sometimes they are merely plucked from handbooks. For properties like thermal conductivity, specific heat, and density of non-combustibles, this may be OK in the sense that the results of our validation work with US NRC has shown that the model predictions are less sensitive to wall lining properties than many other inputs. However, for properties associated with pyrolysis, we need to do better. One of the biggest mistakes we've made in developing FDS has been to release a "database" of various gas and solid phase properties. Those objecting to the misuse of FDS need only look to this database. Originally, we intended the database to "get the user started" by providing a "template" for developing his/her own properties. Given the scarcity of data for real materials, however, users have simply taken the path of least resistance and rely on the database, using the closest approximation to their materials. Worse, they cite the use of "NIST Standard Data" This is hardly anything of the kind. So, starting in FDS 5, the database has gone away. Users will be expected to provide ALL of their own data for a given simulation. And they will undoubtedly need to provide references for the AHJs as to the source of the data. We expect that this will not be met with overwhelming enthusiasm, but as V&V documentation becomes more important, it is inevitable that the property data will be subject to the same scrutiny as the model itself. ASTM E 1355 even calls for it, and it is bound to come up again as we continue to validate more complicated fire phenomena. The goal of this effort would be an engineering practice guide. The goal is NOT necessarily the development of a new pyrolysis model or new test methods, but rather a balanced description of a burning object along with the corresponding mathematical framework. Balanced means that the complexity of the mathematical equations is consistent with the experiments needed to obtain the empirical parameters. If, for example, the pyrolysis model assumes that the burning rate of a material is linearly proportional to the incoming heat flux divided by a "heat of gasification," then the document should contain this simple equation and the appropriate method for obtaining the effective heat of gasification. In some sense, the heat of gasification is defined by the simple equation. FDS has actually moved beyond this simple model to include the formation of char, multiple layers of materials, and so on. But more complexity typically requires more input parameters; the key is that these parameters should be rigorously based on a mathematical framework. The proposed document would not necessarily focus on any one model. Instead, there would be a hierarchy of pyrolysis models with a description of the necessary means to experimentally determine the input parameters. There have been numerous pyrolysis models developed over the past 30 years by people like di Blasi, Kashiwagi, Atreya, Fernandez-Pello, Quintiere, and others. FDS has borrowed from many of these. A weakness with the various models is that there is little consideration for providing input values for materials other than PMMA or Douglas Fir. The validity of the models has typically not been validated for most materials. The models almost always seem tailor-made for a particular material, and can almost never be used for real applications. There was no pyrolysis model of polyurethane foam on top of wood for the Station Nightclub Investigation. Nor was there a model of the workstation panel for the WTC. A general-purpose description of pyrolysis and a set of experiments to get the necessary inputs is needed. Unfortunately, the fire and combustion literature is replete with overly detailed models of very specific material configurations and phenomena, with a disregard for practical, general-purpose applications. We should not develop complex, multi-dimensional models of the solid phase without a solid foundation for getting material properties. Unlike most ASTM standards, we're not necessarily talking about developing new standard test methods. Rather, we want to re-assess what available now, especially in light of what is needed for application of CFD fire models to actual fire scenarios. As the FDS "database" goes away, users will need guidance. Potential Research Topics: With an eye to the emerging trend of standardizing the measurement and interpretation of solid phase thermo-physical properties, demonstrate that we can, or cannot, model the decomposition and burning of various solids and liquids. For classes of solids that do not seem amenable to standardized measurement methods, suggest alternatives and demonstrate practicality and effectiveness. Priority: High. Potential Research Topic: Create FDS models of standard or common non-standard test methods for the purposes of pyrolysis model validation and parameter estimation. Priority: High. For example, cone calorimeter experiments are commonly used when doing parameter estimation for pyrolysis models. Ultimatelly, the experiments should be made in an inert atmosphere to avoid the flame heat fluxes. In this case, a very simple 3x3x4 cells model of the experiment is sufficient. This kind of model runs in just a few seconds. However, quite often the experiments are only available in air. What is the simple and fast model of cone calorimeter in this case? Potential Research Topic: Find an efficient optimization algorithm for pyrolysis model parameter estimation, demonstrate its use, and compare the efficiency to the methods used in the recent literature. Priority: Medium. Droplets, Particles, and the Dispersed Second PhaseCode development in the areas of spray dynamics, spray heat transfer, and other areas related to dispersed second phases has been modest in comparison to the gas and solid phase efforts. Future areas of work include improved tracking of droplets and particles, improved radiative heat transfer to and from droplets and particles, and improved interaction between droplets and particles and the gas phase. These area would encompass the ability to have combusting particles (fire brands) and to better account for surface wetting, surface suppression, and surface penetration by droplets. Potential Research Topic: Simulate standard ADD (Actual Delivered Density) and RDD (Required Delivered Density) sprinkler approval tests. Add to FDS Validation Guide chapter on Suppression. Priority: Medium. Complex GeometryFDS has always been tied to structured Cartesian block geometries. Given that the zeroth-order specification of the heat release is often the best that can be expected from a fire model, the block geometries have not typically been viewed as a limiting factor. However, at a minimum, it is often a cumbersome process to input geometric information for something as simple as a cylinder. As we begin to tackle more challenging problems with FDS (fire spread, atmospheric flows) we are gradually being forced to account for second-order physical processes and we therefore require second-order numerical treatments at solid interfaces. For example, to first order the spread of wildfires is dictated by surface winds. In mountainous regions where these fires occur, the terrain is complex and simulations using stair-stepped grids lead to spurious fluctuations in the wind field. To address this issue we are experimenting with a new geometry module which treats objects like spheres or polyhedra independently. In the near term, these geometric constructs will be seen as a means to obtain a more accurate flow field. In the future, however, the inherent flexibility in the method will allow for 3D heat and mass transport in solids and even moving geometries such as opening doors or wind turbines. Potential Research Topic: Add finite-element method (FEM) for 3D heat and mass transport in complex solids. Modify and validate radiation model for complex geometry. Priority: Low (short term), Medium (long term). Active Fire Protection SystemsIn the 2006 workshop of The International Forum of Fire Research Directors (FORUM), the improvement of the ability to predict the impact of active fire protection systems on fire growth and fate of combustion products was identified as the most important research topic of the fire research community. Many of the future developments in FDS will focus on this topic. The issues affecting the modeling of fire suppression systems have already been addressed in the sections concerning combustion (modeling gas phase suppression) and Droplets, Particles and Dispersed Second Phase (description of water sprays). The modeling of water mist systems in particular should be addressed because they are rapidly becoming common. In addition to the basic physical submodels of FDS, improvements are needed in the description of the suppression systems. For example, the simultaneous discharge from several sprinkler or water mist nozzles have effects on the pressure of the pipe system, and therefore on the mass flow of suppressant. Potential Research Topic: In cooperation with VTT, Finland, better characterize the spray of fine mist and validate FDS for mist suppression. Priority: Medium. RadiationFDS version 1 used heat emitting particles to represent a fire. Radiation transport consisted of Monte-Carlo ray tracing from the particles to surfaces, essentially painting the radiative fraction of the fire on surfaces. Hot surfaces and hot gas layers were not emitters. Early in the development of FDS 2 it was recognized that FDS was being used for conditions where the participation of surfaces and gases was important, and thus, a new radiation model was needed. The model that was eventually developed consisted of using RADCAL (added by Jason Floyd while a NIST post-doc) to generate look-up tables of absorptivity and a Finite Volume Method radiation transport model (developed by Simo Hostikka of VTT). This approach consumes around 25 % of the computational time and for the simpler versions of the combustion model generally performs well. Ideally, we would prefer to compute absorptivity during the actual simulation rather than attempting to use look-up tables which do not readily support the needs of the more complex combustion models being developed. However, current validation efforts indicate that errors resulting from the use of the look-up tables are not large (indeed it is not clear if the errors are any larger than those in the experimental data we use for validation) so any new approach to generating absorptivities or radiation source terms should not consume significantly more time than currently used by the radiation transport. For example, RADCAL could be called for each grid cell each time radiation transport is computed, but that would consume a tremendous quantity of resources. Potential Research Topic: Determine the feasibility of predicting the source term in the radiation transport equation directly by using the computed temperature and absorption coefficient. Currently, the source term is simply tied to the local heat release rate per unit volume. Priority: High. High Performance ComputingFDS is written in Fortran 90/95, but has one C routine that is needed to produce certain output files for Smokeview, which is primarily written in C. Potential Task: Convert the source code file isob.c to Fortran 90/95 so that FDS can be 100% Fortran. This is not a high priority item, but if someone were handy in both C and Fortran and could do this easily, it would make it much easier to port FDS to other platforms. Currently, there are two versions of FDS - serial and parallel. The serial version uses one process to compute the solution of the governing equations on one or more meshes, serially. This version cannot exploit multi-processor or multi-core architectures. The parallel version uses MPI (Message Passing Interface) to launch multiple processes on multiple machines. The advantage of MPI is that we can break up very large cases to reduce the run time and distribute the memory (RAM) among the different machines. Recently (starting in FDS 5.4), Christian Rogsch of the University of Wuppertal in Germany implemented OpenMP directives in FDS. OpenMP allows FDS to run on a single machine but use its multiple processors and cores. This version is still being tested, but it is hoped that the OpenMP functionality becomes standard in FDS. At that point, both OpenMP and MPI can be used together to break up big jobs over multiple machines while at the same time exploiting multiple processing capabilities on each machine. Potential Research Topic: Develop a strategy by which both OpenMP and MPI can be used on a cluster of dual processor/quad core machines. The end result would be rules for optimizing run times based on number of meshes, cells per mesh, number of machines, number of processes per machine. Fire ToxicityIn the context of FDS+Evac development we are planning to use the Fractional Effective Dose methods presented in the SFPE Handbook of FIRE Protection Engineering (Purser, 2008a). For these computations, we need a capability to define arbitrary toxic species as products of combustion. The concentrations of these species are usually so small, that they need not to be considered in gas transport computation (with possible exceptions). Since some gases are produced in well-ventilated conditions and some in under-ventilated, it might be reasonble to let the user define if the gas appears in fixed proportion to major carbon carrying species, as discussed in Combustion section above. Assuming the CO model works, this would introduce under-ventilted products. We plan that the new FED/FEC algorithm would recognize the following species: Aphyxiants: CO, HCN, Low O2, CO2 Irritants: HCL, HBr, HF, SO2, NO2, CH2CHO (acrolein), CH2O (formaldehyde), X(user defined) Potential Research Topic: Yields of these species under different conditions, in relation to CO2 or CO production. User SupportCurrent Activities: FDS is developed and maintained using fairly common software development tools. The source code and manuals are stored in an external repository and can be accessed by all members of the team. User support is provided via a Discussion Forum hosted by GoogleGroups and an Issue Tracker hosted by GoogleCode. In short, a typical FDS user merely goes to a website and enters a question or bug report, and we all can answer the question or track the bug until it is fixed. This has dramatically improved our ability to help users, as before it was simply one or two people answering emails. FDS has always exploited the availability of cheap, fast computers. Now is no different, but the challenges are growing. No longer do we merely provide a simple executable for a single Windows-based PC. We now have single CPU and parallel versions of FDS that can be compiled and run under almost any operating system. We compile and distribute 32 and 64 bit versions of the serial and parallel (MPI) software for Windows, Mac OSX and Linux. For other OS, users are expected to compile the code themselves. The FDS users are becoming more sophisticated in their use of parallel computing, CAD software, and so on. There are currently two graphical user interfaces (GUIs) for FDS - one on the market and one in development. We need to stay abreast of these activities or we might start to see a proliferation of old versions of various pieces of software. It is absolutely essential that the user community keep up to date with the latest versions of FDS, because we cannot support multiple versions. Going Our Way?FDS has benefitted from the contributions of many people from various sectors of the fire protection community. We encourage collaboration, even though direct funding from NIST and other sources is very limited. Graduate students interested in working with FDS should contact us before embarking on a project so that we can discuss whether or not it meets some of the criterion for improvement that we set out above. Some of the potholes students have encountered in the past are:
The Discussion Group and Issue Tracker should be the first line of communication between someone working on FDS and the user community. We ourselves spend a significant amount of time everyday participating the discussions, answering questions, fixing bugs, and so on. Any student who is working with FDS should be monitoring this traffic, and participating as well.
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Recent NRC sponsored experiemnts suggest that FDS predictions of soot density in compartments may be inaccurate. Underventilated compartment fire experiments at NIST are revisiting the soot and CO issue. It is not clear that a mixture fraction approach will provide a suitable framework to improve the predictions. What is reccommended for users now, and what approaches are being considered to improve predictions? Have inexpensive reduced chemistry methods been considered?
The term "flame spread" does not appear in the Roadmap. Recognizing flame spread as a legitimate long term goal, it would be useful if the Roadmap described how and when this will be addressed.
Marco -- I addressed both of your concerns in an updated Road Map. As for smoke, we might have to track soot explicitly because smoke sticks to walls, but other exhaust gases don't. As for flame spread, the entire section on pyrolysis modeling addresses the issue. I just hadn't said so explicitly.
Thanks for the update. It is very helpful that you have explicitly marked out the potential projects and their priority in terms of usefulness to the community.
All this stuff is very interesting, its amazing the progress that is being made. I think I know the answer to this question after reading the pyrolysis model information, but is there any chance in seeing a feature that would show fire patterns for prescribed fires after the calculations, so that it could be used more as an educational/forensic tool for the fire investigation community?