USDA Forest Service
 

Fire and Environmental Research Applications Team

 
 

Fire and Environmental Research Applications Team
Pacific Wildland Fire Sciences Laboratory

400 N 34th Street, Suite 201
Seattle, WA 98103

(206) 732-7800

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United States Department of Agriculture Forest Service.

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Wildland-Urban Interface Fire Dynamics Simulator (WFDS)

Simulation ModelSimulation Modeling

"Extend(ing) the current Fire Dynamics Simulator (FDS), developed for structural fires...to fuels that include vegetation."

CautionCaution!

WFDS is in the early stages of development. It should not be used for any practical application. Results have not been validated. Information provided below is for those with an interest in modeling, and outlines the status and theoretical development of this model.


The Wildland-Urban Interface Fire Dynamics Simulator (WFDS) was developed through a collaborative effort between the U.S. Forest Service and the National Institute of Standards and Technology (NIST). It extends the capabilities of NIST's structure fire code FDS (Fire Dynamics Simulator) to fires in vegetation and fire spread over outdoor domains.

The Wildland-Urban Interface Fire Dynamics Simulator (WFDS) model extends the current Fire Dynamics Simulator (FDS), developed for structural fires by the National Institute of Standards and Technlogy, to fuels that include vegetation.

FDS can be obtained from the FDS site. However, the most recent implementation of WFDS is always on the WFDS download web page. For access to the download page please send a request to wuifires@gmail.com along with your gmail address. Your gmail address will be used to allow access and for code update information.

WFDS uses computational fluid dynamics methods to solve the governing equations for buoyant flow, heat transfer, combustion, and the thermal degradation of vegetative fuels. The solution method makes use of large eddy simulation techniques to solve the gas-phase equations on computational grids that are too coarse to directly resolve the detailed physical phenomena.

Basic Structure of the WFDS Extension to FDS

There are currently two ways of representing raised vegetative fuels in WFDS. WFDS is being developed as a suite of models ranging from physics-based to rule or semi-empirical based. The input files and visualization tool are similar or identical for all models.

  • Physics-Based Component (WFDS-PB)
    • The physics based component of WFDS simulates fire behavior via the complete coupling of the three-dimensional, time dependent, processes of combustion, ambient and fire generated winds, solid fuel burning, and convective and radiative heat transfer.
    • Computational fluid dynamics (CFD) methods are used to solve the governing equations for buoyant flow, heat transfer, combustion, and the thermal degradation of vegetative fuels.
    • The solution method makes use of large eddy simulation (LES) techniques to solve the gas-phase equations on computational grids that are too coarse to directly resolve the detailed physical phenomena. More information is here.
  • Semiempirical Component (WFDS-LS)
    • The rule or semi-empirical based component of WFDS is a fire front propagation model. This is similar to FARSITE or cellular automata type models. No physical processes are explicitly simulated.
    • These type of models move a fire perimeter across the landscape using user provided spread rates of the the local fireline.
    • A level set approach is used to propagate the fire line using head, flank, and back fire spread rates provided by the user for each fuel type on the landscape. These spread rates can be from empirical studies, other models, best guesses, etc. More information is here.


Detailed Structure of the WFDS Extension to FDS

Physics-Based Component (Fuel Element Model)

Vegetation can be described by a rectangular, conical, cylindrical volume, or a frustum. In the input files below you'll find:

  • Surface fuels described by a rectangular volume (e.g., pine needles)
  • Crown fuels as conical volumes
  • Tree stems as cylindrical volumes

The stems are present to serve as wind breaks and do not burn.

If you are including stems, please following the format of the input files

#1 Surface with One Tree | #2 Surface with Many Trees | #3 Stationary Fire Line

#1 Fire Spread Through Surface Fuel with One Tree

Single processor input file:

input_surf_onetree_1proc.txt

Run by typing (in Windows command window)

wfsd32.exe
surf_onetree_1proc.fds

Two processor input file:

input_surf_onetree_2proc.txt

Run by typing (in Windows command window with MPICH2)

mpiexec -n 2 wfds32_mpi.exe surf_onetree_2proc.fds

 


  • Burning pine needle bed (5 cm deep)
  • Temperature plume
  • Tree foliage
  • Tree stem
DOMAIN: Domain is 16 m long (160 grid cells, dx=10 cm), 3 m wide (30 grid cells, dy=10 cm), and 6 m tall (60 grid cells, dz = 5 cm at ground to 20 cm at top).

BOUNDARY CONDITIONS: Mirror or symmetry boundary conditions are used along y = 0 plane.

UNITS: Axes units are meters.

RUNNING TIME: Simulation time is 60 s which requires about 2.2 cpu hours.

PROCESSOR SPECIFICATIONS: About 200 MB of memory is required.  The 2 processor simulations required 1.2 cpu hours on each processor (total elapsed wall clock time was also 1.2 hours, this includes start up and writing out data files).

RESULTING IMAGES: Smokeview image on left shows particles that represent the surface and tree crown vegetation. Particles are colored according to their temperature value. A vertical slice file with colors showing the gas-phase temperature is also displayed.

Smokeview image on the right uses a solid object to display the cone shaped crown. The solid object is shown by default. This object can be removed in via the Smokeview commands:

Show/Hide-->Geometry-->Objects-->Canopy.

Particles are loaded or unloaded in Smokeview by:

Load/Unload-->Particle File--> particles


Particle temperature is displayed by:

Show/Hide-->Particles-->Droplet temperature

#2 Fire Spread Through Surface Fuel with Many Trees, on Flat Terrain with No Significant Crowning

Single processor input file:

input_grass_trees_flat_1proc.txt

Two processor input file:

input_grass_trees_flat_2proc.txt

 

 

 

 

 

 




About 90 identical 6 m tall, 3 m wide, cone-shaped trees are randomly distributed across a 30-m wide and 25-m long area. Axes units are meters. A 0.5 m tall grass is underneath the trees. The grass is ignited on the upwind side. The wind speed is uo = 2 m/s at the x=0 plane.


Grid resolution is 0.5 m in all directions. Note that, unlike the more resolved (~7.5 cm grids) isolated tree simulations, validation of the fuel element model at this resolution has not been completed. The simulation time is 60 s and requires about 25 cpu minutes for a single 3.8 GHz processor run and about  About 200 MB of memory is required. The trees in the above image are colored according to the temperature of the crown vegetation.

#3 Stationary Line Fire with Transport of Smoke Downwind

input_grass_trees_burner_1proc.txt


Fire, trees, and smoke plume.

DOMAIN:Same domain size and tree definition as above.

AXES: Axes units are meters.

Fire is held stationary with bed dimensions of 2 m deep by 30 m long with a heat release rate of 500 k/m^2 (based on Australian grassland fires). 

SIMULATION TIME AND PROCESSOR REQUIREMENTS: Simulation time is 30 s which requires about 9 cpu minutes on a 3.8 GHz processor. About 200 MB of memory is required.

Recent Changes to the Fuel Element Version
  1. How to Ouput the Dry Mass and Moisture Mass of Vegetation

    In the following text, placed in the input file,

    &HEAD CHID='Test' /
    &TREE PART_ID='foliage', XYZ=0,0,0,FUEL_GEOM='CONE',
                  CROWN_WIDTH=1,CROWN_BASE_HEIGHT=0.3,TREE_HEIGHT=3,
                  OUTPUT_TREE=.TRUE.,LABEL='Tree_1_foliage' /

    the user specifications in HEAD and TREE namelists will result in the output of following columns of data in a text (.csv) file:

  • Time (s)
  • Dry mass of vegetation (kg)
  • Moisture mass vegetation (kg)
  • Total net convective heat transfer (kW) summed over all fuel elements in the particular &TREE . This measure is the sum of the volume integral of the divergence of the convective heat flux on the fuel element. In other words it is the sum_i integral( divergence of convective heat flux) dVe; where Ve is the volume of the fuel element, and it is the index of the fuel element running from 1 to the number of fuel elements in the computational cell. This is, of course, computed indirectly, the sum is not actually carried out.
  • Total net radiative heat transfer (kW) summed over all fuel elements in the particular &TREE line (i.e., the same computation as was done for the covective heat flux).

The file name will be 'Test_Tree_1_foliage_vegout.csv'. The 'Test' part of the file name is obtained from CHID in the HEAD namelist and the 'Tree_1_foliage'  part of the file name is from LABEL in the TREE namelist. The parameter OUTPUT_TREE must be set to .TRUE. in the TREE namelist.

In addition, the user can specify the time interval between data dumps to the file by the usual use of the DUMP namelist. For example,

&DUMP DT_VEG=0.1 /

will output the dry and moisture mass every 0.1 seconds.


WFDS for Raised Fuels Using the Boundary Fuel Model and the Current Version of FDS

The boundary fuel model is now (as of May 10, 2010) integrated with the current version of FDS (v. 5.5.0). It is still undergoing some testing so use with care and testing. It is obtained by downloading WFDS from above . A sample input file is given below. NOTE: the boundary fuel model is undergoing validation tests and should be used with this in consideration.

 

Example of fire spread up a simple hill. Fuel properties are based on Australian grassland fuel.

input_grass_simplehill_bf.txt

This input file is to illustrate capabilities. This fuel model is still undergoing validation.

 

Validation Studies

Mell, W.; Jenkins, M.A.; Gould, J.; Cheney, P. 2007 A physics based approach to modeling grassland fires. 2007. International Journal of Wildland fire. 16(1): 1-22.


Simulation of Australian grassland fires--This paper describes the modeling approach used to represent the surface vegetation. The validation studies in this paper are being repeated for the current version of WFDS.

Program Download

The same program is used for the boundary fuel and the fuel element vegetation models. Downloads and source code are in the section above.

Input Files for Simulation Models

Current Source Code, Executables, and User Guides

Older Versons of Source Code, Executable Files, and User Guides

 

Wildland-urban Interface Fire Computer Models and Example input files.

Validation of these models is ongoing but far from complete. Please keep this in mind when using the Wildland-Urban Fire Dynamics Simulator (WFDS) to solve for problems outside the current scope of validation. See below for information on the current state of validation.

In general, please use the FDS discussion group and issue tracker when you have questions, and refer to WFDS. You may also email Ruddy Mell at wmell@comcast.net


 

 

We acknowledge funding from the Joint Fire Science Program under Project 07-1-5-08 and 11-2-1-11

 

Team Lead: Ruddy Mell

U.S. Forest Service - PNW- FERA
Last Modified: Monday, 16 December 2013 at 14:18:38 CST


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