Two NIST models, CFAST (Consolidated Fire And Smoke Transport) and FDS (Fire Dynamics Simulator), are the most widely used models worldwide for evaluation of the performance of fire protection systems in buildings and are the principal component in performance-based design practice. This project provides the fire protection community with robust, well-validated numerical models of fire with three components: verification and validation of the NIST models, targeted and novel algorithm development, and continued user support. Verification and validation will focus on including numerous new quantitative comparisons with available experimental data and identify areas of model prediction where data do not currently exist. For FDS, implementation of novel algorithms such as the Immersed Boundary Method (IBM) will improve and expand the predictive capability using sub-models that better describe critical physical and chemical processes in fires and can be validated using advanced fire measurement techniques. For CFAST, a primary focus will be on improving the internal structure of the model to modern programming standards to improve robustness of model calculations and facilitate future enhancements to support performance-based design. User support ensures continued impact and provides feedback and guidance for future improvements.
Objective: To develop, by 2014, verification and validation for major existing and new algorithms in FDS, CFAST, and the visualization tool, Smokeview, so that the models can be used to accurately and efficiently predict fire conditions for performance-based design in buildings.
What is the new technical idea? For the past thirty years, NIST has provided the fire protection community with robust, well-validated numerical models of fire. With increasing use of performance-based design techniques and evolving standards requirements for validated fire models, accurate and efficient fire modeling is critical to realization of performance-based design as a viable alternative to prescriptive code solutions.
With guidance from existing standards, we have now reached the stage in understanding the needs for validation so that we can address model verification and validation (V&V) for both CFAST and FDS in a consistent manner for both models. Continued use of predictive fire models depends on demonstrated accuracy and robustness of the models combined with targeted development based on user needs. Therefore, the present effort consists of three components: V&V, novel algorithm development, and user support. We will focus on including numerous new quantitative comparisons with available experimental data and identify areas of model prediction where data do not currently exist. Implementation of novel algorithms such as the Immersed Boundary Method (IBM) will improve and expand the predictive capability of current fire models using sub-models that better describe critical physical and chemical processes in fires and can be validated using advanced fire measurement techniques. New data generated through solid-phase and gas-phase experiments will guide the development of a framework for sub-models on material burning and soot emission. User support ensures continued impact and provides feedback and guidance for future improvements.
What is the research plan?
Model Validation: Much of our validation work to date has focused on the gas phase, with validation for a range of gas-phase quantities for pre-flashover fires. For buildings, additional validation efforts are needed to ensure we have quantified the accuracy of all major algorithms in the models. This would include both natural and forced ventilation, soot deposition, and post-flashover fires as well as extending the range of validation for other variables. For WUI predictions, we will implement all WUI validation cases in the most recent version of FDS. In out-years, additional validation test data will be collected and evaluated to ensure as broad a base of validation for the models as practical. It is also time to develop a framework for flexible implementation and validation for flame spread as additional research increases our understanding of flame spread on real objects. In addition, the validation suite for CFAST requires additional cases in order to be consistent with the level of validation performed on FDS.
FDS Algorithm Development: The development of FDS will proceed along two major fronts – the gas phase and the solid phase. For the gas phase, we plan to make FDS run in parallel on hundreds of individual processors,. In addition to finer grids, an Immersed Boundary Method (IBM) is to be implemented to enable non-rectangular geometries to be used within the model. This will allow for direct use of computer aided design (CAD) in the processing of FDS fire scenarios. We are also developing a methodology to couple complex geometry with structural finite element (FEM) solvers such as Abaqus. The increased resolution in the gas phase will also lead to more accurate prediction of the heat flux to solid surfaces for real materials in buildings.
Smokeview Algorithm Development: Smokeview presently visualizes smoke by drawing a series of partially transparent planes. A better approach integrates the radiative transport equation over the entire domain rather than from one grid cell plane to the next. This eliminates problems computing smoke opacities over short distances which occur in high resolution computations. We will also implement methods for running Smokeview in parallel and in the background to enable the visualization of massive cases. The end result would be an animation suitable for a presentation. Improvements to Smokeview to aid in FDS algorithm and physics development and debugging, such as adding the ability to visualize raw data for scalar and velocity fields, are also planned.
CFAST Maintenance: CFAST is still a vital design tool for the engineering community because its calculations can be run in minutes as opposed to hours or days for FDS, filling a necessary gap in the numerical fire simulation spectrum. However, CFAST requires a substantial overhaul to bring its source code up to current Fortran standards. While FDS is fully Fortran 2003 compliant, CFAST still uses Fortran 77 features that will eventually be phased out. The initial foundational effort through FY 2013 will result in continued relevance for CFAST and provide the basis for future development. Out-year enhancements will include improved estimation of gas temperature near fire sources (which would improve calculation of heating and ignition of nearby targets), combustion chemistry more consistent with FDS, and the ability to run multiple simulations for sensitivity and scoping analyses.
 Currently, FDS/CFAST have more than 10,000 combined registered users.
 PBD has the potential to deliver over $5B in cost efficiencies (ABCB, 2000). Virtually every major thrust of the Innovative Fire Protection Road Map (Hamins et al., 2010) includes a modeling component.
 For example, NFPA 805, “Performance-Based Standard For Fire Protection For Light Water Reactor Electric Generating Plants,” requires the use of validated fire models and NFPA 101, “Life Safety Code,” includes requirements to document model validation applicable to the design under consideration.
 Includes new and ongoing research in EL by Pitts and Linteris along with cooperative research at VTT in Finland.
 Mell et al. have published numerous validation studies using FDS 4 and 5, and now we must ensure that these cases still work properly, and continue to work properly in future versions. The modeling of vegetation shall be generalized so that “clutter” within a building can be modeled using similar techniques.
 The solid phase work will be led by Kevin McGrattan in partnership with Simo Hostikka at VTT.
 To resolve, for example, fire spread in buildings whose volumes are comparable to 10 floors of the World Trade Center (WTC), but with much finer resolution than that used previously for such a large-scale calculation or fire spread in the wildland-urban interface over areas that are roughly 100 km2.
 The improved resolution of FDS for large volume calculations will be 10 cm instead of the 50 cm used in the WTC calculations. This is roughly 125 times better resolution than was recently possible.
 The gas phase FDS development will be led by Randy McDermott working full time on the problem.
 This work is in collaboration with Global Engineering and Materials, Inc., Princeton, NJ.
 Work will be done in conjunction with a three year grant to WPI/Southwest Research/SFPE whose objective is to develop standard methods of obtaining material properties for fire models.
 The transparencies are related to soot density by using Beers law in the form of exp(-k*s*dx) where s is soot density computed by FDS, k is the extinction coefficient and dx is the distance between computed grid planes.
 As modeling grid sizes increase and the physics used to visualize data becomes more complex, the time required to visualize data increases to the point where non-interactive methods need to be investigated. Two such methods are to take advantage of multiple cores commonly present on computers today and to run Smokeview in an automatic mode with the aim of rendering images automatically in the background rather interactively at the console.
Standards and Codes:
The project delivers impact through changes to codes, regulations, standards, and practices. Validated and computationally efficient predictive fire models enable both routine and highly complex fire safety engineering calculations supporting codes and standards worldwide.
Smokeview rendering of a fire in a cable spreading room of a nuclear power plant. Image: NIST
Start Date:October 1, 2011
Lead Organizational Unit:el
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