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Fire Dynamics Simulator (Version 5) User's Guide

1. SPRAY _PATTERN_TABLE TABLE1 amp TABL ID TABLE1 TABLE_DATA 40 50 85 95 10 0 5 amp TABL ID TABLE1 TABLE _DATA 40 50 185 195 10 0 5 Note that each set of TABL lines must have a unique ID Specific requirements on ordering the lines will depend upon the type of TABL and those requirements are provided in the appropriate section in this guide Also note that the TABL lines can be specified in any order 11 3 2 Nozzles Nozzles are very much like sprinklers only they do not activate based on the standard RTI model To simulate a nozzle that activates at a given time for example specify a QUANTITY and SETPOINT directly on the DEVC line An example of a nozzle can be found in the verification case water_fuel_sprays fds The following lines amp DEVC XYZ 23 91 21 28 0 50 PROP_ID nozzle ORIENTATION 0 0 1 QUANTITY TIME SETPOINT 0 ID noz_1 amp DEVC XYZ 26 91 21 28 0 50 PROP_ID nozzle ORIENTATION 0 0 1 QUANTITY TIME SETPOINT 5 ID noz_2 amp PROP ID nozzle PART_ID heptane drops FLOW_RATE 2 132 FLOW_TAU 50 DROPLET_VELOCITY 5 SPRAY_ANGLE 0 45 i designate two nozzles of the same type one which activates at zero seconds the other at 5 s Note that nozzles must have an associated PROP line The parameter PART_ID tells FDS to spray liquid droplets 11 3 3 Heat Detectors
2. amp HOLE XB 0 25 0 45 0 20 0 30 0 20 0 30 COLOR RED DEVC_ID timer 1 amp HOLE XB 0 25 0 45 0 70 0 80 0 70 0 80 COLOR GREEN DEVC_ID timer 2 amp OBST XB 0 70 0 80 0 20 0 30 0 20 0 30 COLOR BLUE DEVC_ID timer 3 amp OBST XB 0 70 0 80 0 60 0 70 0 60 0 70 COLOR PINK DEVC_ID timer 4 amp DEVC XYZ ID timer 1 SETPOINT 1 QUANTITY TIME INITIAL _STATE FALSE amp DEVC XYZ ID timer 2 SETPOINT 2 QUANTITY TIME INITIAL _STATE TRUE amp DEVC XYZ ID timer 3 SETPOINT 3 QUANTITY TIME INITIAL _STATE FALSE amp DEVC XYZ ID timer 4 SETPOINT 4 QUANTITY TIME INITIAL _STATE TRUE The blue obstruction appears at 3 s because its initial state is false meaning that it does not exist initially The pink obstruction disappears at 4 s because it does exist initially The red hole is created at 1 s because it does not exist initially it is filled in with a red obstruction The green hole is filled in at 2 s because it does exist as a hole initially You should always try a simple example first before embarking on a complicated creation removal scheme for obstructions and holes To remove an obstruction then re create a different one in its place use 2 lines amp OBST XB SURF_ID whatever DEVC_ID device 1 amp OBST XB SURF_ID whatever DEVC_ID device 2 since the code simply sees this as two different obstruction
3. EC namelist group see Section 9 2 and then designate the appropriate SPEC_ID on the 76 Fuel Droplets FUEL TRUE indicates that the liquid droplets evaporate into fuel gas and burn In this case add the HEAT_OF_COMBUSTION kJ kg of the fuel Fuel droplets are colored yellow by default in Smokeview This feature only works for a mixture fraction based combustion calculation in which case the droplets evap orate into an equivalent amount of fuel vapor such that the resulting heat release rate assuming complete combustion is equal to the evaporation rate multiplied by the HEAT_OF_COMBUSTION Particles that do not Evaporate Unless you declare MASSLESS TRUE on the PART line it is assumed that the particle or droplet has mass and thermal properties that dictate its heat up and evaporation To prevent evaporation set EVAPORATE FALSE The particles will still heat up due to convection but they will not shrink and no additional gaseous species need to be declared Note that the absorption of thermal radiation by water WATER TRUE or fuel droplets FUEL TRUE is handled in FDS with fairly well established physical sub models the details of which are contained in the FDS Technical Reference Guide 1 However for arbitrary particles or droplets there is no assumed radiative absorption 10 5 Coloring Particles and Droplets The pa
4. 0 20 40 60 80 100 120 Time s 136 16 1 3 Leaks and Fans in a Sealed Enclosure leak_test and leak_test_2 A new feature of FDS 5 is the idea of a pressure zone Unlike traditional compartment or zone fire models FDS was not designed under the assumption that there exist rooms connected by doors or ducts Rather the geometry in FDS is completely specified by the user However there are features of simpler models that we want to retain For example a leak through a small crack or the transport of air through a ventilation duct In the following example a simple compartment 3 6 m by 2 4 m by 2 4 m has a small fan at one end and one leak under the door at the other end It is assumed for this example that the compartment is contained within a larger compartment that is perfectly sealed The fan draws air into the compartment from the plenum space increasing the pressure inside and decreasing it outside A steady state is achieved when the volume flow into and out of the compartment falls into balance The volume flow rate of the fan is given by the fan curve Ap A Vian AductUmax Sign Apmax Ap Ap A Prmax Pmax where Ap is the difference in pressure and Aguct 0 16 m Umax 0 1 m s and APmax 1000 Pa The volume flow due to the leak is given by 16 1 2Ap Poo Vieak leak 16 2 where Aleak 0 0001 m and po 1 2 kg m After 5 min the pressure difference is 938 2 Pa
5. establishes that all bounding surfaces are to be made of CONCRETE unless otherwise specified and that the ambient temperature is 25 C The MISC parameters vary in scope and degree of importance Here is a partial list of MISCellaneous parameters Others are described where necessary throughout this guide DNS A logical parameter that if TRUE directs FDS to perform a Direct Numerical Simulation as opposed to the default Large Eddy Simulation LES GVEC The 3 components of gravity in m s The default is GVEC 0 0 9 81 HUMIDITY Relative humidity in units of This need only be specified if there is a source of water in the simulation other than the fire itself Otherwise water vapor is not explicitly tracked Default 40 ISOTHERMAL A logical parameter that indicates that the calculation does not involve any changes in tem perature or radiation heat transfer thus reducing the number of equations that must be solved and simplifying those that are Automatically sets RADIATION to FALSE NOISE FDS initializes the flow field with a very small amount of noise to prevent the development of a perfectly symmetric flow when the boundary and initial conditions are perfectly symmetric To turn this off set NOISE FALSE P_INF Background pressure at the ground in Pa The default is 101325 Pa RADIATION A logical parameter indicating whether radiation transport ought to be c
6. 12 2 1 Point Measurement Devices 65 65 67 69 71 71 73 73 74 75 76 T 77 78 79 79 80 80 82 82 83 83 84 85 85 86 88 88 89 89 90 90 91 91 12 2 2 Integrated non pointwise Measurement Devices oo o 94 12 23 Output Statistics eos or ek ee a eet a e en ae 95 12 2 4 Quantities within Solids The PROF Namelist Group 95 12 2 5 Animated Planar Slices The SLCF Namelist Group 95 12 2 6 Animated Boundary Quantities The BNDF Namelist Group 96 12 2 7 Animated Isosurfaces The ISOF Namelist Group 96 12 2 8 Plot3D Static Data DUMPS e ce bea ereo Sa ea a eR ee A Rae 96 12 3 Special Output Quantities s s s sd aioa a bow oe eo ee ee es a ee ee 98 1231 Heat Release Rate oes ia eo ke ee Be oh ow Gee 98 12 3 2 Visibility and Obscuration ea co cademi ba eaer eaa a 98 12 3 3 Layer Height and the Average Upper and Lower Layer Temperatures 99 12 3 4 The True Gas Temperature vs the Measured Gas Temperature 100 12 33 Heat FIURES pe o a ee A eer a a A 100 12 3 6 Droplet Output Quantities o r cs s ea e e sese E e EO ae 101 12 3 7 Interfacing with Structural Models o o e a 101 12 3 8 Integrated Mass and Energy Fluxes through Openings 101 12 3 9 Wind and the Pressure Coefficient o lt s croes poma ddagr e e 102 12 4 Extracting Numbers from the O
7. IOR 2 ID probe_2 El E to ID In FDS 5 any input record is identified via its ID 127 128 Part II Sample Cases and Verification 129 Chapter 15 Forms of Verification ASTM E 1355 13 outlines methods to evaluate the mathematical and numerical robustness of deterministic fire models This process often referred to as model verification ensures the accuracy of the numerical solu tion of the governing equations The methods include comparison with analytical solutions code checking and numerical tests 15 1 Comparison with Analytical Solutions Most complex combustion processes including fire are turbulent and time dependent There are no closed form mathematical solutions for the fully turbulent time dependent Navier Stokes equations CFD provides an approximate solution for the non linear partial differential equations by replacing them with discretized algebraic equations that can be solved using a powerful computer While there is no general analytical solution for fully turbulent flows certain sub models address phenomenon that do have analytical solutions for example one dimensional heat conduction through a solid These analytical solutions can be used to test sub models within a complex code such as FDS The developers of FDS routinely use such practices to verify the correctness of the coding of the model 14 15 Such verification efforts are relatively simple and routine and the re
8. SURF ID BLOWER VEL 1 2 TMP_FRONT 50 RAMP_V BLOWER RAMP RAMP_T HEATER RAMP amp RAMP ID BLOWER RAMP T 0 0 F 0 0 amp RAMP ID BLOWER RAMP T 10 0 F 1 0 amp RAMP ID BLOWER RAMP T 80 0 F 1 0 amp RAMP ID BLOWER RAMP T 90 0 F 0 0 RAMP ID HEATER RAMP T 0 0 F 0 0 RAMP ID HEATER RAMP T 20 0 F 1 0 amp RAMP ID HEATER RAMP T 30 0 F 1 0 RAMP ID HEATER RAMP T 40 0 F 0 0 Now the temperature and velocity of the incoming air stream would follow the same ramp functions Note that the temperature and velocity can be independently controlled by assigning different RAMPs to RAMP_T and RAMP_V respectively Use TAU_MF N or RAMP_MF N to control the ramp ups for either the mass fraction or mass flux of species N The mass fraction of species N at the surface is given by Yn t Yn 0 f t Yn Yn 0 where Yy 0 is the ambient mass fraction of species N MASS_FRACTION_O in the Nth SPEC namelist line is used to prescribe Yy 0 Yy is the desired mass fraction to which the function f t is ramping MASS_FRACTION N specified in the SURF line is used to prescribe Yy The function f r is either a tanh 1 or user defined function For a user defined function indicate the name of the ramp function with RAMP_MF N a character string 8 5 2 Temperature Dependent Functions Thermal properties like conductivity and specific heat can vary significan
9. QUANTITY LINK TEMPERATURE as in this example defines a heat detector which uses essentially the same activation algorithm as a sprinkler without the water spray amp DEVC ID HD_66 PROP_ID Acme Heat XYZ 2 3 4 6 3 4 amp PROP ID Acme Heat QUANTITY LINK TEMPERATURE RTI 132 ACTIVATION_TEMPERATURE 74 82 Like a sprinkler RTI is the Response Time Index in units of ym s ACTIVATION_TEMPERATURE is the link activation temperature in degrees C Default 74 C INITIAL_TEMPERATURE is the initial temperature of the link in units of C Default TMPA 11 3 4 Smoke Detectors A smoke detector is defined in the input file with an entry similar to amp DEVC ID SD_29 PROP_ID Acme Smoke Detector XYZ 2 3 4 6 3 4 amp PROP ID Acme Smoke Detector QUANTITY spot obscuration LENGTH 1 8 ACTIVATION_OBSCURATION 3 28 for the single parameter Heskestad model Note that a PROP line is mandatory for a smoke detector in which case the DEVC QUANTITY can be specified on the PROP line For the four parameter Cleary model use a PROP line like amp PROP ID Acme Smoke Detector QUANTITY spot obscuration ALPHA_C 1 8 BETA_C 1 1 ALPHA_E 0 98 BETA_E 0 77 ACTIVATION_OBSCURATION 3 28 where the two characteristic filling or lag times are of the form te au Ste au 11 1 The default detect
10. The tangential velocity boundary condition controls how the gas sticks to a solid surface In theory the tangential component of velocity is zero at the surface but increases rapidly through a narrow region called the boundary layer For most practical problems the mesh is not fine enough to resolve the boundary layer which is typically a few millimeters thick For this reason in an LES calculation the velocity at the wall is set to be a fraction of its value in the mesh cell adjacent to the wall Only ina DNS calculation is the velocity at the wall set to zero To alter these defaults set a parameter called SLIP_FACTOR This parameter ranges from 1 to 1 If a no slip wall is desired SLIP_FACTOR 1 If a free slip wall is desired SLIP_FACTOR 1 Numbers in between 1 and 1 can represent partial slip conditions which may be appropriate for simulations involving large mesh cells Default SLIP_FACTOR is 0 5 for LES 1 0 for DNS In the case of a blowing vent or even a solid surface it is possible to prescribe both the normal and tangential components of the flow or just the tangential The normal component is specified with VEL as described above The tangential is prescribed via a pair of real numbers VEL_T representing the desired tangential velocity components For example the line amp SURF ID LOUVER VEL 1 2 VEL_T 0 5 0 3 is a boundary condition for a louver vent that pushes air into the space with a normal ve
11. Two types of transformation functions are allowed The first and simplest is a piecewise linear func tion Figure 6 2 gives an example of a piecewise linear transformation The graph indicates how 15 uni formly spaced mesh cells along the horizontal axis are transformed into 15 non uniformly spaced cells along the vertical axis In this case the function is made up of straight line segments connecting points CC PC in increasing order as specified by the following lines in the input file amp TRNX CC 0 30 PC 0 50 MESH _NUMBER 2 amp TRNX CC 1 20 PC 1 00 MESH _NUMBER 2 The parameter CC refers to the Computational Coordinate located on the horizontal axis PC is the Physical Coordinate x located on the vertical axis The slopes of the line segments in the plot indicate whether the mesh is being stretched slopes greater than 1 or shrunk slopes less than 1 The tricky part about this process is that you usually have a desired shrinking stretching strategy for the Physical Coordinate on the vertical axis and must work backwards to determine what the corresponding points should be for the Computational Coordinate on the horizontal axis Note that the above transformation is applied to the second mesh in a multiple mesh job The second type of transformation is a polynomial function whose constraints are of the form a f cc PC d Figure 6 3 gives an example of a polynomial transformation for whic
12. _H 6 1 es ee and x is the nominal size of a mesh cell The quantity D 6x can be thought of as the number of compu tational cells spanning the characteristic not necessarily the physical diameter of the fire The more cells lThe characteristic fire diameter is related to the characteristic fire size via the relation Q D D gt where D is the physical pny diameter of the fire 29 spanning the fire the better the resolution of the calculation It is better to assess the quality of the mesh in terms of this non dimensional parameter rather than an absolute mesh cell size For example a cell size of 10 cm may be adequate in some sense for evaluating the spread of smoke and heat through a building from a sizable fire but may not be appropriate to study a very small smoldering source As an example in the mesh sensitivity study for NUREG 1824 4 the D 8x values ranged from 4 to 16 These values were used to adequately resolve plume dynamics along with other geometrical characteristics of the models as well This range does not indicate what values to use for all models only what values worked well for that particular set of models 30 6 4 Miscellaneous Parameters The MISC Namelist Group Table 13 12 MISC is the namelist group of global miscellaneous input parameters Only one MISC line should be entered in the data file For example the input line amp MISC SURF_DEFAULT CONCRETE TMPA 25
13. amp MATL ID STEEL EMISSIVITY 10 DENSITY 7850 CONDUCTIVITY 45 8 SPECIFIC_HEAT 0 46 amp MATL ID CONCRETE DENSITY 2200 CONDUCTIVITY 1 2 SPECIFIC_HEAT 0 88 amp SURF ID ETHANOL POOL FYI 4 kg of ethanol in a 0 7 m x 0 8 m pan COLOR YELLOW MATL_ID ETHANOL LIQUID STEEL CONCRETE THICKNESS 0 0091 0 001 0 05 TMP_INNER 18 The inclusion of BOILING_TEMPERATURE on the MATL line tells FDS to use its liquid pyrolysis model It also automatically sets N_REACTIONS 1 that is the only reaction is the phase change from liquid to gaseous fuel Thus HEAT_OF_REACTION in this case is the latent heat of vaporization The gaseous fuel yield NU_FUEL is 0 97 instead of 1 to account for impurities in the liquid that do not take part in the combustion process The thermal conductivity density and specific heat are used to compute the loss of heat into the liquid via conduction using the same one dimensional heat transfer equation that is used for solids Obviously the convection of the liquid is important but is not considered in the model Note also the ABSORPTION_COEFFICIENT for the liquid This denotes the absorption in depth of thermal radiation Liquids do not just absorb radiation at the surface but rather over a thin layer near the surface Its effect on the burning rate is significant An example is given in Secti
14. Properties associated with sprinklers included in the PROP group are RTI Response Time Index in units of ym s Default 165 C_FACTOR in units of v m s Default 0 ACTIVATION_TEMPERATURE in units of C Default 74 C INITIAL TEMPERATURE of the link in units of C Default TMPA FLOW_RATE in units of L min An alternative is to provide the K_FACTOR in units of L min bar and the OPERATING_PRESSURE in units of atm The flow rate is then given by m K p Note that 1 bar is equivalent to 14 5 psi 1 gpm is equivalent to 3 785 L min 1 gpm psi2 is equivalent to 14 41 L min bar OFFSET Radius of a sphere m surrounding the sprinkler where the water droplets are initially placed in the simulation It is assumed that at and beyond the OFFSET the droplets have completely broken up and are transported independently of each other Default 0 05 m DROPLET_VELOCITY Initial droplet velocity Default 5 m s SPRAY_ANGLE A pair of angles in degrees through which the droplets are sprayed The angles outline a conical spray pattern relative to the south pole of the sphere centered at the sprinkler with radius OFFSET For example SPRAY_ANGLE 30 80 directs the water droplets to leave the sprinkler through a band between 60 and 10 south latitude assuming the orientation of the sprinkler is 0 0 1 the default The droplets are uniformly distributed within
15. The equation for pressure in FDS is known as the Poisson equation The Poisson solver consists of large system of linear equations that must be initialized at the start of the calculation Most often an error in the initialization step is due to a mesh IJK dimension being less than 4 except in the case of a two dimensional calculation It is also possible that something is fundamentally wrong with the coordinates of the computational domain Diagnose the problem by checking the MESH lines in the input file 4 3 Support Requests and Bug Tracking Because FDS development is on going problems will inevitably occur with various routines and features The developers need to know if a certain feature is not working and reporting problems is encouraged However the problem must be clearly identified The best way to do this is to simplify the input file as much as possible so that the bug can be diagnosed Also limit the bug reports to those features that clearly do not work Physical problems such as fires that do not ignite flames that do not spread etc may be related to the mesh resolution or scenario formulation and need to be investigated first by the user before being reported If an error message originates from the operating system as opposed to FDS first investigate some of the more obvious possibilities such as memory size disk space etc If that does not solve the problem report the problem with as much information about the error
16. group 1 ASCII American Standard Code for Information Interchange 2A namelist is a Fortran input record 19 The parameters in the input file can be integers T_END 5400 real numbers CO_YIELD 0 008 groups of real numbers or integers XYZ 6 04 0 28 3 65 or IJK 90 36 38 character strings CHID WIC_05_v5 groups of character strings SURF_IDS burner INERT INERT or logical parameters POROUS_FLOOR FALSE A logical parameter is either TRUE or FALSE the periods are a Fortran convention Character strings that are listed in this User s Manual must be copied exactly as written the code is case sensitive and underscores do matter Most of the input parameters are simply real or integer scalars like DT 0 02 but sometimes the in puts are multidimensional arrays For example when describing a particular solid surface you need to express the mass fractions of multiple materials that are to be found in multiple layers The input array MATL_MASS_ FRACTION IL IC is intended to convey to FDS the mass fraction of component Ic of layer IL For example if the mass fraction of the second material of the third layer is 0 5 then write MATL_MASS_FRACTION 3 2 0 5 To enter more than one mass fraction use this notation MATL_MASS_FRACTION 1 1 3 0 5 0 4 0 1 which means that the first three materials of layer 1 have mass fractions of 0 5 0 4 and 0 1 respectively The notation 1 3 mean
17. 1 It is strongly recommended that finite rate reactions be invoked only when FDS is running in DNS mode Set DNS TRUE on the MISC line Note you may use the finite rate reaction scheme in an LES calculation but because the temperature in a large scale calculation is smeared out over a mesh cell some of the reaction parameters may need to be modified to account for the lower temperatures 2 The BACKGROUND_SPECIES on the MISC line is normally set to be NITROGEN E 3 The namelist group SPEC is used to specify each additional species Do not enter a SPEC line for the background species 4 Read Section 9 2 for a description of the boundary conditions for the gas species 5 The REAC namelist group is used to designate the fuel and the reaction rate parameters For a finite rate reaction you can specify multiple REAClines Note that FDS will evalute the reactions in the order they are listed in the input file FUEL Character string indicating which of the listed optional gas species is the fuel OXIDIZER Character string indicating which of the listed optional gas species is the oxidizerl BOF Pre exponential factor in one step chemical reaction in units of cm mole s E Activation energy for one step chemical reaction in units of kJ kmol NU Array containing the stoichiometry of the chemical reaction for each SPEC where negative values indicate reactants and positive values indicate product
18. 229 amp SURF ID BRICK WALL MATL_ID BRICK INSULATOR COLOR RED BACKING EXPOSED THICKNESS 0 20 0 10 Without arguments the parameter MATL_ID is assumed to be a list of the materials in multiple layers with each layer consisting of only a single material component Note also in this example that the BRICK WALL is not symmetric Be careful when applying this SURF line to an entire obstruction because the attribute EXPOSED implies that the back surface of the obstruction is different than the front surface The maximum number of material layers is 20 The maximum number of material components is 20 Mixtures of solid materials within the same layer can be defined using the MATL_MASS_FRACTION keyword This parameter has the same two indices as the MATL_ID keyword For example if the brick layer contains some additional water the input could look like this amp MATL ID WATER CONDUCTIVITY 0 60 SPECIFIC_HEAT 4 19 DENSITY 1000 amp SURF ID BRICK WALL MATL_ID 1 1 2 BRICK WATER MATL_MASS_FRACTION 1 1 2 0 95 0 05 MATL_ID 2 1 INSULATOR COLOR RED BACKING EXPOSED THICKNESS 0 20 0 10 lt for layers 1 and 2 It is important to notice that the components of the solid mixtures are treated as pure substances with no voids The density of the mixture is 1 Y p y at 8 3 7 Pi where Y are the material mass fra
19. By default FDS assumes that the density and pressure decrease with height regardless of the application or domain size For most simulations this effect is negligible but it can be turned off completely by setting STRATIFICATION FALSE on the MISC line 8 2 6 Special Topic A Radially Spreading Fire Sometimes it is desired that a fire spread radially at some specified rate Rather than trying to design material properties to achieve this you can alternatively use a VENT in a special way If the SURF_ID associated with a VENT defines a specified heat release rate HRRPUA and time history RAMP_Q or TAU_Q you can also specify XYZ and SPREAD_RATE on the VENT line Then the fire is directed to start at the point xyz and spread radially at a rate of SPREAD_RATE m s The ramp up begins at the time when the fire arrives at a given point For example the lines amp SURF ID FIRE HRRPUA 500 0 RAMP_Q fireramp amp RAMP ID fireramp T 0 0 F 0 0 amp RAMP ID fireramp T 1 0 F 1 0 amp RAMP ID fireramp T 30 0 F 1 0 amp RAMP ID fireramp T 31 0 F 0 0 amp VENT XB 0 0 5 0 1 5 9 5 0 0 0 0 SURF_ID FIRE XYZ 1 5 4 0 0 0 SPREAD _RATE 0 03 create a rectangular patch at z 0 on which the fire starts at the point 1 5 4 0 0 0 and spreads outwards at a rate of 0 03 m s Each surface cell burns for 30 s as the fire spreads outward creating a widen
20. HEAT_OF_VAPORIZATION 316 SPECIFIC_HEAT 2 25 DENSITY 688 QUANTITIES 1 2 DIAMETER DROPLET_TEMPERATURE DROPLETS_PER_SECOND 2000 DIAMETER 1000 HEAT _OF_COMBUSTION 44500 DT_INSERT 0 02 SAMPLING FACTOR 1 amp PROP ID nozzle CLASS NOZZLE PART_ID heptane droplets FLOW_RATE 1 96 FLOW_RAMP fuel DROPLET_VELOCITY 10 SPRAY_ANGLE 0 30 amp RAMP ID fuel T 0 0 F 0 0 amp RAMP ID fuel T 20 0 F 1 0 amp RAMP ID fuel T 40 0 F 1 0 amp RAMP ID fuel T 60 0 F 0 0 Many of these parameters are self explanatory and the units are given in the User s Guide 37 Note that a 2 MW fire is achieved via 2 nozzles flowing heptane at 1 96 L min each L 1 min kg 1 m 2x 1 96 688 a OO x 44500 2000 kw 16 12 g The parameter HEAT_OF_COMBUSTION over rides that for the overall reaction scheme Thus if other droplets or solid objects have different heats of combustion the effective burning rates are adjusted so that the total heat release rate is that which the user expects However exercises like this ought to be conducted just to ensure that this is the case The HRR curve for this example is given here 2500 spray_burner lt 2000 o tw 1500 cc o Yn oO 1000 0 cc E 500 0 75 90 Time s 158 16 6 3 Measuring Water Flux bu
21. ID Character Identifier FYI Character Comment String has no effect QUANTITY Character Name of output quantity XYZ Real Triplet Coordinates of wall surface 116 13 16 PROP Device Properties Table 13 16 For more information see Section 11 3 PROP Device Properties ACTIVATION_TEMPERATURE Real Threshold link temperature C 74 ACTIVATION_OBSCURATION Real Threshold value of obscuration m 3 28 ALPHA C Real Smoke detector parameter 1 8 ALPHA _E Real Smoke detector parameter 0 0 BETA_C Real Smoke detector parameter 1 0 BETA_E Real Smoke detector parameter 1 0 BEAD_DIAMETER Real Diameter of TC bead m 0 001 BEAD_EMISSIVITY Real Emissivity of TC bead 0 85 C_FACTOR Real Sprinkler activation parameter 0 CHARACTERISTIC_VELOCITY Real See Section 12 3 9 m s 1 0 DROPLET_VELOCITY Real Initial droplet velocity m s 5 0 FLOW_RATE Real Sprinkler or nozzle flow rate L min FLOW_RAMP Character Time RAMP for flow FLOW_TAU Real Time constant for flow 0 0 GAUGE_TEMPERATURE Real See Section 12 3 5 C TMPA ID Character IDentifier INITIAL TEMPERATURE Real Initial link temperature C TMPA K_FACTOR Real Flow parameter L min atm 1 LENGTH Real Smoke detector para
22. OUTLINE Logical Draw as Outline FALSE PERMIT HOLE Logical Allow a Hole TRUE REMOVABLE Logical Allow obstruction to be removed TRUE RGB 3 Integer Triplet Color indices 0 255 SAWTOOTH Logical See Section 7 1 1 TRUE SURF_ID Character Associated Surface SURF_IDS 3 Character Triplet Associated Surfaces top side bot SURF_ID6 6 Character Sextuplet Associated Surfaces like XB HICKEN Logical Force at least one cell thick FALSE EXTURE_ORIGIN 3 Real Triplet See Section 8 6 1 0 0 0 TRANSPARENCY Real Transparency indicator 1 XB 6 Real Sextuplet Min Max Physical coordinates 114 13 14 PART Lagrangian Particles Droplets Table 13 14 For more information see Section 10 PART Lagrangian Particles Droplets AGE Real Droplet lifetime s 100000 COLOR Character Default color of droplets BLACK DENSITY Real Droplet density kg m 1000 DIAMETER Real Median Volumetric Diameter um 500 DROPLETS_PER_SECOND Integer Drops per second per head 1000 DT_INSERT Real Time between particle insertions s 0 05 EVAPORATE Logical Assume liquid evaporation TRUE FYI Character Comment String has
23. There is a short Fortran 90 program provided called fds2ascii f that can convert slice files into text files that can be read into a variety of graphics packages The program combines multiple slice files correspond ing to the same slice of the computational domain time averages the data and writes the values into one file consisting of a line of numbers for each node Each line contains the physical coordinates of the node and the time averaged quantities corresponding to that node In particular the graphics package Tecplot reads this file and produces contour streamline and or vector plots See Section 12 4 for more details about the program fds2ascii 19 8 Boundary Files The boundary files defined under the namelist group BNDF are named CHID_n bf n 01 02 and are written out unformatted These files are written out from dump f with the following lines WRITE LUBF QUANTITY WRITE LUBF SHORT_NAME WRITE LUBF UNITS WRITE LUBF NPATCH WRITE LUBF 11 12 J1 J32 K1 K2 IOR WRITE LUBF 11 12 J1 J32 K1 K2 IOR WRITE LUBF TIME WRITE LUBF 00 1 J K 1I 11 12 J J1 J2 K K1 K2 WRITE LUBF 00 1 J K 1 11 12 J J1 J2 K K1 K2 176 WRITE LUBF TIME WRITE LUBF 00 1 J K 1 11 12 J J1 J32 K K1 K2 WRITE LUBF 00 1 J K 1I 11 12 J J1 J2 K K1 K2 QUANTITY SHORT_NAME and UNITS are character strings of length 30 NPATCH is the
24. amp CTRL ID delay FUNCTION_TYPE TIME_DELAY INPUT_ID check links DELAY 30 amp CTRL ID nozzle 1 trigger FUNCTION_TYPE ALL INPUT_ID delay LINK 1 amp CTRL ID nozzle 2 trigger FUNCTION_TYPE ALL INPUT_ID delay LINK 2 91 92 Chapter 12 Output Data Before a calculation is started carefully consider what information should be saved All output quantities must be specified at the start of the calculation In most cases there is no way to retrieve information after the calculation ends if it was not specified from the start There are several different ways of visualizing the results of a calculation Most familiar to experimentalists is to save a given quantity at a single point in space so that this quantity can be plotted as a function of time like a thermocouple temperature measurement The namelist group DEVC described previously is used to specify point measurements To visualize the flow patterns better save planar slices of data either in the gas or solid phases by using the SLCF SLiCe File or BNDF BouNDary File namelist group Both of these output formats permit you to animate these quantities in time For static pictures of the flow field use the PLot3D files that are automatically generated 5 times a run Plot3D format is used by many CFD programs as a simple way to store specified quantities over the entire mesh at one instant in time Finally tracer part
25. 82 8144 84 3719 84 0506 84 0264 1 0 116 2891 115 4051 114 9656 117 801 117 353 116 7751 10 148 9698 148 9616 148 3947 148 9677 148 4005 148 9695 143 16 4 Solid Phase Phenomena This section contains examples that test the one dimensional heat conduction solver in FDS along with those that include pyrolysis 16 4 1 Simple Heat Conduction Through a Solid Slab heat_conduction Analytical solutions of transient one dimensional heat conduction through a slab can be found in Refs 33 and 34 Four cases are examined here In each a slab of thickness L 0 1 m is exposed on one face to an air temperature of T 120 C The other face is insulated adiabatic The convective heat transfer from the gas to the slab is g A T Ts where h is constant and T is the slab face temperature No thermal radiation is included 140 120 100 O o 80 y g 60 E 2 40 20 140 o o 5 w o o E oO E 50000 Case k p c h Bi W m K kg m kJ kg K W m K hL k A 0 1 100 1 100 100 B 0 1 100 1 10 10 C 1 0 1000 1 10 1 D 10 0 10000 1 10 0 1 140 heat_conduction_a heat_conduction_b 120 100 O e 80 4 w g 60 E 2 40 20 500 1000 1500 2000 0 2000 4000 6000 8000 10000 12000 14000 Time s Time s 70 heat_conducti
26. POROUS 51 PROFILE 47 RAMP_MF 60 RAMP_Q 47 55 59 RAMP_T 59 RAMP_V 59 RGB 62 SHRINK 58 SLIP_FACTOR 46 STRETCH_FACTOR 58 TAU_MF 60 TEXTURE_HEIGHT 62 TEXTURE_MAP 62 TEXTURE_WIDTH 62 THICKNESS 52 THICNKNESS 44 TMP_BACK 58 TMP_FRONT 45 TMP_INNER 58 VEL 45 VOLUME_FLUX 45 ZO 47 Surface Texture Maps 62 System Requirements Hardware 7 MPI 8 Operating System 8 TABL 59 TAIL 20 tangential velocity 46 thermostat 89 TIME 23 DT 24 SYNCHRONIZE 24 27 T_BEGIN 23 T_END 23 WALL_INCREMENT 58 64 TRNX TRNY TRNZ 25 28 CC 29 PC 29 185 Troubleshooting VENT Orientation 41 VENT 40 CTRL_ID 125 Volume Flux 45 ZONE 49 186
27. SLCF Slice File Output 12 2 3 13 20 SPEC Species Parameters 9 2 13 21 SURE Surface Properties 8 2 13 22 IME Simulation Time 6 2 13 24 RNX Mesh Stretching 6 3 3 13 25 VENT Vent Parameters T3 13 26 ZONE Pressure Zone Parameters 8 3 13 27 22 Chapter 6 Setting the Bounds of Time and Space 6 1 Naming the Job The HEAD Namelist Group Table 13 6 The first thing to do when setting up an input file is to give the job a name The name of the job is important because often a project involves numerous simulations in which case the names of the individual simulations can help organize the effort The namelist group HEAD contains two parameters as in this example amp HEAD CHID WIC_05_v5 TITLE WTC Phase 1 Test 5 FDS version 5 CHID is a string of 30 characters or less used to tag the output files If for example CHID WIC_05_v5 it is convenient to name the input data file WTC_05_v5 fds so that the input file can be associated with the output files No periods or spaces are allowed in CHID because the output files are tagged with suffixes that are meaningful to certain computer operating systems TITLE is a string of 60 characters or less that describes the simulation It is simply descriptive text that is passed to various output files 6 2 Simulation Time The TIME Namelist Group Table 13 24 TIME is the name of a group of parameters time define the time duration of the simulation and the
28. SOOT_YIELD Real Fraction of soot from the fuel kg kg 0 01 SOOT_H_FRACTION Real Atom fraction of hydrogen in soot 0 1 VISIBILITY_FACTOR Real Visibility parameter 3 X02 Tila Real Lower Oxygen Limit mol mol 0 15 Y_F_INLE Real Mass Frac of Fuel in Burner kg kg 1 0 Y FO LFL Real Lower Fuel limit mass fraction kg kg 0 0 Y_O2_INFTY Real Ambient Oxygen Mass Frac kg kg 0 23 119 13 20 SLCF Slice File Parameters Table 13 20 For more information see Section 12 2 5 SLCF Slice File Parameters FYI Character Comment String has no effect MESH_NUMBER Integer Save only slices in this mesh PBX Real x plane to save slice file PBY Real y plane to save slice file PBZ Real z plane to save slice file QUANTITY Character Name of Quantity to display VECTOR Logical Include flow vectors FALSE XB 6 Real Sextuplet Min Max coordinates of region to save m 13 21 SPEC Species Parameters Table 13 21 For more information see Section 9 2 SPEC Species Parameters ABSORBING Logical Gas species abosrbs radiation FALSE CONDUCTIVITY Real Conductivity k W m K DIFFUSIVITY Real Diffusivity D m s EPSILONKLJ Real Leonard Jones Parameter 0 FYI Character Comment String has no effect ID Character Name of species MASS_FRACTION_O Real Initial mass fraction 0 MW Real Molecular Weight g mol 29 SIGMALJ Real Leonard Jones Pa
29. The first column contains the time in seconds The second through fifth columns contain integrated energy gains and losses all in units of kW The second column contains the total heat release rate the third contains the radiative heat loss to all the boundaries solid and open the fourth contains the convective and radiative heat loss to the boundaries i e the energy flowing out of or into the domain and the fifth contains the energy conducted into the solid surfaces The sixth column contains the total burning rate of fuel in units of kg s It is included merely as a check of the total heat release rate Let Q denote the unblocked computational domain i e the volume within the bounding rectangle occupied by gas Let JQ by the boundary of Q The boundary can be divided into two parts OQ dQ OQ The first part QQ consists of all the solid walls The second part OQ consists of openings from outside the domain through which gases may flow This could be an open window to the exterior or a forced vent The total heat release rate is given by o f4 dV 12 1 The radiative loss to the boundaries can be computed with either a volume or boundary integral v qav f q d8 f qi dA 12 2 Q oQ dQ It represents the energy radiating away from the fire and hot gases into the solid boundaries or out of the computational domain The convective radiative loss to open boundaries is ees cpp TT w a8 ql dA 12 3 oQ dQ where the
30. amp DEVC XYZ 3 0 5 6 2 3 PROP_ID ID ORIENTATION 1 0 0 the sprinkler would point in the positive x direction For other devices the ORIENTATION would only change the way the device is drawn by Smokeview 11 2 Device Output Each device has a QUANTITY associated with it The output file for all DEVC quantities is a comma delimited ASCII file called CHID_deve csv See Section 19 3 for output file format This file can be imported into most spread sheet software packages If the number of DEvc lines exceeds 256 the limit of some spreadsheet applications the output file will be split into appropriately sized smaller files To prevent the file splitting specify COLUMN_DUMP_LIMIT FALSE on the DUMP line All devices must have a specified QUANTITY Some special devices Section refinfo PROP have their QUANTITY specifed on a PROP line A QUANTITY specified on a PROP line associated with a DEVC line will override an QUANTITY specified on the DEVC line 11 3 Special Devices and their Properties The PROP Namelist Group Table 13 16 Many devices are fairly easy to describe like a point measurement with only a few parameters which can be included on the DEvc line However for more complicated devices it is inconvenient to list all of the properties on each and every DEVC line For example a simulation might include hundreds of sprinklers but it is tedious to list the properties of the s
31. materials making the old SURF line too cumbersome to specify Instead there is a new namelist group called MATL that just contains the properties of a given material What used to be 125 amp SURF ID RGB KS E DENSITY BACKING T HICKNESS BRICK WALL 0 6 0 2 0 2 0 69 0 84 1600 EXPOSE 0 20 is now given by two input lines amp MATL ID BRICK CONDUCTIVITY 0 69 SPECIFIC_HEAT 0 84 DENSITY 1600 amp SURF ID BRICK WALL MATL_ID BRICK RGB 166 41 41 BACKING EXPOSED THICKNESS 0 20 The surface is still specified the same way as before for example amp OBST XB 0 1 5 0 10 1 2 0 0 1 0 SURF_ID BRICK WALL Notice the change in the names of the thermal properties KS and C_P to CONDUCTIVITY and SPECIFIC_HEAT respectively Notice that the color RGB is now specified via integers between O and 255 instead of real num bers between 0 0 and 1 0 Better yet just use the COLOR Table 8 1 144 Reaction Parameters REAC For most applications the specification of the combustion reaction has become easier In past versions you needed to specify the fuel its molecular weight soot and or CO yields and the ideal stoichiometry of the reaction ER EAC ID FYI MW SOOT_YIELD NU_02 NU_CO2 NU_H20 PROPANE C3 HS 44 0 01 Ja 3 4 Now you just need to describe the composition of the
32. planes x XMAX x XMIN y YMAX y YMIN z ZMAX or z ZMIN respectively Like an obstruction the boundary condition index of a vent is specified with SURF_ID indicating which of the listed SURF lines to apply If the default boundary condition is desired then SURF_ID need not be set Be careful when using the MB shortcut when doing a multiple mesh simulation that is when more than one rectangular mesh is used The plane designated by the keyword MB is applied to all of the meshes possibly leading to confusion about whether a plane is a solid wall or an open boundary Check the geometry in Smokeview to assure that the VENTs are properly prescribed Use color as much as possible to double check the set up More detail on color in Section 8 6 and Table 8 1 Also the parameter OUTLINE TRUE causes the VENT to be drawn as an outline in Smokeview 40 7 3 1 Special VENTs There are two reserved SURF_ID s that may be applied to a VENT OPEN and MIRROR The term reserved means that these two SURF_IDs should not be explicitly defined by you Their properties are predefined An OPEN VENT The first special VENT is invoked by the parameter SURF_ID OPEN This is used only if the VENT is applied to the exterior boundary of the computational domain where it denotes a passive opening to the outside By default FDS assumes that the exterior boundary of the computational domain the XBs on th
33. plus various degrees of aggressive optimization Be cautious in using the highest levels of optimization e For the single processor version of FDS compile with main f90 171 e The parallel version of FDS uses main_mpi f90 instead of main f90 plus additional MPI libraries need to be installed More details on MPI can be found at the web site along with links to the necessary organizations who have developed free MPI libraries Table 18 1 Source Code Files File Name Description isob c C Routine for computing isosurfaces and 3D smoke prec f90 Specification of numerical precision smvv f90 Interfaces for C routines used for Smokeview output devc f90 Derived type definitions and constants for devices type f90 Derived type definitions mesh f90 Arrays and constants associated with each mesh cons f90 Global arrays and constants func f90 Global functions and subroutines irad f90 Functions needed for radiation solver including RadCal ieva f90 Support routines for evac f90 evac f90 Egress computations future capability pois f90 Poisson pressure solver radi f90 Radiation solver part f90 Lagrangian particle transport and sprinkler activation ctrl f90 Definitions and routines for control functions dump f90 Output data dumps into files read f90 Read input parameters mass f90 Mass equation s and thermal boundary conditions wall f90 Wall
34. will also speed up the computations significantly If the gas phase computations are needed you may turn off combustion by creating a REAC line with only Y_02_INFTY 0 01 This sets the background oxygen mass fraction to 0 01 too low to support any burning Generate MATL lines plus a single SURF line as you normally would except add EXTERNAL_FLUX to the SURF line This is simply a virtual source that heats the solid Think of this as a perfect radiant panel or cone calorimeter Assign the SURF_ID to a VENT that spans the bottom of the computational domain Create OPEN vents on all other faces Finally add solid phase output devices to the solid surface like WALL_TEMPERATURE HEAT_FLUX BURNING_RATE GAUGE_HEAT_FLUX and WALL_THICKNESS assuming the solid is to burn away Use these to track the condition of the solid as a function of time In particular make sure that the BURNING_RATE is appropriate for the particular external heat flux applied Make sure that the WALL_TEMPERATURE is appropriate Compare your results to measurements made in a bench scale de vice like the cone calorimeter Keep in mind however that the calculation and the experiment are not necessarily perfectly matched The calculation is designed to eliminate uncertainties related to convec tion combustion and apparatus specific phenomena 64 Chapter 9 Combustion and Radiatio
35. 001 a 3 H 8 HEAT_OF_COMBUSTION 46124 IDEAL FALSE amp REAC ID ACRYLONITRILE E 3 H 3 N Side HEAT_OF_COMBUSTION 24500 IDEAL TRUE amp REAC ID CARBON DISULFIDE G 1 Other 2 MW_OTHER 7325 HEAT_OF_COMBUSTION 13600 IDEAL TRUE 9 1 1 Important Issues Related to the Mixture Fraction Models This section explains the various approximations that affect both the gas phase parameters REAC line and the solid or liquid phase parameters SURF line These approximations are needed either to compensate for less than desirable mesh resolution or limitations of the mixture fraction combustion model Heat the RI of Combustion By default the EPUMO2 value is combined wi EAC line to compute the heat of combustion Specifying the H1 th the stoichiometric parameters listed on EAT_OF_COMBUSTION will override that computation However if heats of reaction have been specified on the MATL line and the heat of combustion of the material differs from that specified by the governing reaction then add a HEAT_OF_COMBUSTION kJ kg to the MATL line With the mixture fraction combustion model it is assumed that there is only one fuel However in a realistic fire scenario there may be many fuels originating from the various burning 67 objects in the building Specify the stoichiometry of the predominant reaction via the REAC namelist group If the stoichiometry of the burn
36. 128 114 FIREBRICK E 178 34 34 SANDY BROWN E 244 164 96 FLESH E 255 125 64 SEA GREEN E 84 255 159 FOREST GREEN 34 139 34 SEPIA mW 94 38 18 GOLD E 255 215 0 SIENNA M 160 82 45 GOLDENROD E 218 165 32 SILVER 192 192 192 GRAY E 128 128 128 SKY BLUE 135 206 235 GREEN E 0 255 0 SLATEBLUE E 106 90 205 GREEN YELLOW 173 255 47 SLATE GRAY E 112 128 144 HONEYDEW 240 255 240 SPRING GREEN A O 255 127 HOT PINK E 255 105 180 STEEL BLUE mM 70 130 180 INDIAN RED E 205 92 92 TAN 210 180 140 INDIGO BB 75 0 130 TEAL A 0 128 128 IVORY 255 255 240 HISTLE 216 191 216 IVORY BLACK E 41 36 33 TOMATO M 255 99 71 KELLY GREEN BH 0 128 0 TURQUOISE E 64 224 208 KHAKI 240 230 140 VIOLET E 238 130 238 LAVENDER 230 230 250 VIOLET RED E 208 32 144 LIME GREEN E 50 205 50 WHITE 255 255 255 MAGENTA E 255 0 255 YELLOW E 255 255 0 63 8 7 Verifying the Solid Phase Properties As this chapter has demonstrated real materials can be very complicated Undoubtedly the SURF and MATL lines in the input file will consist of a combination of empirical and fundamental properties often originating from different sources How do you know that the various property values and the associated thermo physical model in FDS constitute an appropriate description of the solid For a full scale s
37. 2 00 2 00 0 1 amp OBST XB 1 95 1 90 0 1 amp OBST XB 1 60 1 55 0 1 amp OBST XB 1 90 1 95 0 1 H H REFERENCE_TEMPERATURE N OO OO PLASTIC 0 2 Ld 1500 1 3000 25000 400 1 0 14 15 I5 wld 15 15 Q O O O LOOS IVORY BLACK PLASTIC COPPI Cabl 4 0 6 EXPOSED 02 o1 0 55 50 0 60 50 0 60 50 0 50 50 0 50 50 0 50 n mun un U U U REZ RFL RFL RF RFL RE ER I I I I I D Loose Cable D SHEET METAL Tray Side SHEET METAL Tray Side D SHEET METAL Rung SHEET METAL Rung SHEET METAL Rung The pile of cables is assumed to be a solid slab 28 cm wide and 2 cm deep The tray is slightly wider and deeper and because it is listed second in the input file its surface properties take precedence wherever the cable slab and tray coincide The mesh cells in this example are 5 cm on a side but the heat transfer within the cable slab are governed by the 2 cm THICKNI ESS The slab is 60 copper by mass Note that we are not assuming multiple layers in this example the slab is a single layer composite of plastic and copper The plastic burns at about 400 but the copper remains Thus the cable does not burn away The point of this test case is merely to propose a simple model of
38. 50 s for example The default for DT_RESTART is 1000000 meaning no restart files are created unless you gracefully stop a job by creating a dummy file called CHID stop It is also possible to use the new control function feature see Section 11 5 to stop a calculation or dump a restart file when the computation reaches some measurable condition such as a first sprinkler activation Between job stops and restarts major changes cannot be made in the calculation like adding or removing vents and obstructions The changes are limited to those parameters that do not instantly alter the existing flow field Since the restart capability has been used infrequently by the developers 1t should be considered a fragile construct Examine the output to ensure that no sudden or unexpected events occur during the stop and restart 6 4 2 Special Topic Defying Gravity Most users of FDS assume that the acceleration of gravity points toward the negative end of the z axis or more simply downward However to change the direction of gravity to model a sloping roof or tunnel for example specify the gravity vector on the MISC line with a triplet of numbers of the form GVEC 0 0 0 0 9 81 units are m s This is the default but it can be changed to be any direction Note if sprinklers are specified the gravity vector must not be changed Much of the logic governing the trajectories of water droplets over solid objects assumes tha
39. 9 Wind and the Pressure Coefficient In the field of wind engineering a commonly used quantity is known as the PRESSURE_COEFFICIENT _ P Px 5 Pool Cp 12 13 Poo is the ambient or free stream pressure and p is the ambient density The parameter U is the free stream wind speed given as CHARACTERISTIC_VELOCITY on the PROP line amp BNDF QUANTITY PRESSURE_COEFFICIENT PROP_ID whatever amp DEVC ID pressure tap XYZ IOR 2 QUANTITY PRESSURE_COEFFICIENT PROP_ID whatever amp PROP ID whatever CHARACTERISTIC_VELOCITY 3 4 Thus you can either paint values of C at all surface points or create a single time history of C using a single device at a single point 12 4 Extracting Numbers from the Output Data Files Often it is desired to present results of calculations in some form other than those offered by Smokeview In this case there is a short Fortran 90 program called fds2ascii 90 with a PC compiled version called fds2ascii exe To run the program just type fds2ascil at the command prompt You will be asked a series of questions about which type of output file to pro cess what time interval to time average the data and so forth A single file is produced with the name CHID_fds2ascii csv 102 12 5 Summary of Output Quantities Table 12 1 spread over the following pages summarizes the various Output Quan
40. DEVC XB x1 x2 yl y2 z1 z2 QUANTITY path obscuration ID beam1 SETPOINT 0 33 11 3 6 Aspiration Detection Systems An aspiration detection system groups together a series of soot measurement devices An aspiration system consists of a sampling pipe network that draws air from a series of locations to a central point where an obscuration measurement is made To define such a system in FDS you must provide the sampling locations sampling flow rates the transport time from each sampling location and if an alarm output is desired the overall obscuration setpoint One or more DEVC inputs are used to specify details of the sampling locations and one additional input is used to specify the central detector amp DEVC XYZ QUANTITY soot density ID soot1 DEVC_ID aspl1 FLOWRATE 0 1 DELAY 20 amp DEVC XYZ QUANTITY soot density ID soot2 DEVC_ID asp1 FLOWRATE 0 2 DELAY 10 amp DEVC XYZ QUANTITY soot density ID sootN DEVC_ID aspl1 FLOWRATE 0 3 DELAY 30 amp DEVC XYZ QUANTITY aspiration ID aspl BYPASS _FLOWRATE 0 4 SETPOINT 0 02 where the DEVC_ID is used at each sampling point to reference the central detector FLOWRATE is the gas flow rate in kg s DELAY is the transport time in seconds from the sampling location to the central detector BYPASS_FLOWRATE is the flow rate in kg s of any air drawn into the system f
41. ID c_ramp T 425 F 1 423 Notice that with temperature dependent quantities the RAMP parameter T means Temperature and F is the value of either the specific heat or conductivity In this case neither CONDUCTIVITY nor SPECIFIC_HEAT is given on the MATL line but rather the RAMP names Prior to FDS5 the thermal radiation from the gas space was always absorbed at the surface of the solid material and the emission to the gas space took place on the surface Starting in FDSS5 the solid material can be given an ABSORPTION_COEFFIENT 1 m that allows the radiation penetrate and absorb into the solid Correspondingly the emission of the material is based on the internal temperatures not just the surface T 8 4 2 Pyrolysis Models FDS has several approaches for describing the pyrolysis of solids and liquids The approach to take depends largely on the availability of material properties and the appropriateness of the underlying pyrolysis model This section provides a description of the input parameters starting with a general solid Solid Fuels A solid object might contain multiple layers with multiple material components per layer The solid object is described by a SURF line which contains the names of the various MATLs it is composed of Each MATL can undergo several reactions that may occur at different temperatures and consume different amounts of heat Each individual reaction can produce a single solid RESIDU
42. Plumes In Twenty Sixth Symposium International on Combustion pages 1523 1530 Combustion Institute Pittsburgh Pennsylvania 1996 131 K B McGrattan H R Baum and R G Rehm Large Eddy Simulations of Smoke Movement Fire Safety Journal 30 161 178 1998 131 H R Baum R G Rehm P D Barnett and D M Corley Finite Difference Calculations of Buoyant Convection in an Enclosure Part I The Basic Algorithm SIAM Journal of Scientific and Statistical Computing 4 1 117 135 March 1983 131 H R Baum and R G Rehm Finite Difference Solutions for Internal Waves in Enclosures SIAM Journal of Scientific and Statistical Computing 5 4 958 977 December 1984 131 H R Baum and R G Rehm Calculations of Three Dimensional Buoyant Plumes in Enclosures Com bustion Science and Technology 40 55 77 1984 131 R G Rehm P D Barnett H R Baum and D M Corley Finite Difference Calculations of Buoyant Convection in an Enclosure Verification of the Nonlinear Algorithm Applied Numerical Mathematics 1 515 529 1985 131 J C Adams W S Brainerd J T Martin B T Smith and J L Wagener Fortran 95 Handbook Com plete ISO ANSI Reference MIT Press Cambridge Massachusetts 1997 132 K B McGrattan T Kashiwagi H R Baum and S L Olson Effects of Ignition and Wind on the Transition to Flame Spread in a Microgravity Environment Combustion and Flame 106 377 391 1996 134 T Kashiwagi K B McGrattan S L Olson O Fujita M Kik
43. The theo retical value obtained by equating the fan and leak volume flow rates and solving for Ap is 938 9 Pa The slight difference is due to the fact that the solid boundaries within the interior of the computational domain admit a slight volume flux related to details of the numerical solver Just for fun we add another leak to the compartment only this time the leak is to the exterior of the entire computational domain an infinite void at ambient pressure Now the fan flow rate ought to balance the sum of the flow rates from the two leaks After 5 min the pressure difference is 935 2 Pa The two cases are summarized in the following plots 137 1000 1000 Compartment Pressure Rise leak_test Compartment Pressure Rise leak_test_2 500 500 T T o oO S 0 S 0 wn n 8 A 8 a as ene ye ea fa a Outside C a a N neide doma 500 500 Mii e Outside Compartment Inside Compartment fof DSe 1000 r r r r 1000 r r r r i 0 50 100 150 200 250 300 50 100 150 200 250 300 Time s Time s 16 1 4 Two Fans in a Wall fan_test Consider two simple compartments divided by a wall with two fans installed blowing in opposite directions 138 16 1 5 Stack Effect stack_effect If the interior temperature of a building is at a different temperature than the surrounding atmosphere up ward or downward air flows within shafts or stairwells connected to the
44. Unlike early versions of FDS particles are no longer colored by gas phase quantities but rather by properties of the particle itself For example DROPLET_TEMPERATURE for a non massless particle refers to the temperature of the particle itself rather than the local gas temperature Also note that if MASSLESS TRUE the SAMPLING_FACTOR is set to 1 unless you say otherwise which would be silly since MASSLESS particles are for visualization only Static Particles or Droplets STATIC is a logical parameter indicating whether particles move or just serve as obstructions or clutter Set ting STATIC TRUE only makes sense in conjunction with a non zero value of NUMBER_INITIAL_DROPLETS The default value of STATIC is FALSE Water Droplets WATER TRUE declares that the liquid droplets evaporate into WATER VAPOR a separate gas phase species that is automatically added to the calculation by this command By default WATER FALSE even though the default properties of droplets are that of water Setting WATER TRUE instructs FDS to add WATER VAPOR as an explicitly defined species and it also invokes appropriate constants related to the absorption of thermal radiation by the water droplets It also causes the droplets to be colored blue in Smokeview If the liquid droplets are to evaporate into some other gaseous species you must explicitly define the species via the SP PART line
45. a door or window can lead to dramatic changes in the course of the fire Sometimes these actions are taken intentionally sometimes as a result of the fire Within the framework of an FDS calculation these actions are represented by the creation or removal of solid obstacles or the opening or closing of exterior vents Remove or create a solid obstruction by assigning the character string DEVC_ID the name of a DEVC 1D on the OBST line that is to be created or removed This will direct FDS to remove or create the obstruction when the device changes state to FALSE or TRUE respectively For example the lines T amp OBST XB SURF_ID DEVC_ID det2 amp DEVC XYZ PROP_ID ID det1 amp DEVC XYZ PROP_ID ID det2 INITIAL_STATE TRUE 85 will cause the given obstruction to be removed when the specified DEVC changes state Gl Note that while single DEVC can be used to control multiple items a DEVC that is being used for a HOLI should not be used for anything else other than additional HOLEs Creation or removal at a predetermined time can be performed using a DEVC that has TIME as its measured quantity For example the following instructions will cause the specified HOLEs and OBSTstructions to appear disappear at the various designated times
46. a positive value and false when the RAMP F value is negative In this case the control would start false and would switch to true when the timer reaches 60 seconds It would then stay in a true state until the timer reaches 120 seconds and would then change back to false Note that when using control functions the IDs assigned to both the CTRL and the DEVC inputs must be unique across both sets of inputs i e you cannot use the same ID for both a control function and a device In the HVAC example above we could set the system to function on a fixed cycle by using a CUSTOM control function based on time amp SURF ID FAN TMP_FRONT 40 VOLUME_FLUX 1 amp VENT XB 0 3 0 3 0 3 0 3 0 0 0 0 SURF_ID FAN CTRL_ID cycling timer amp DEVC ID TIMER XYZ 2 4 5 7 3 6 QUANTITY TIME amp CTRL ID cycling timer FUNCTION_TYPE CUSTOM INPUT_ID TIMER RAMP_ID cycle vi amp RAMP ID cycle T 59 F 1 amp RAMP ID cycle T 61 F 1 amp RAMP ID cycle T 119 F 1 amp RAMP ID cycle T 121 F 1 In the above example the fan will be off initially turn on at 60 s and then turn off at 120 s You can make an obstruction appear and disappear multiple times by using lines like 90 amp OBST XB SURF_ID whatever CTRL_ID cycling timer amp DEVC ID TIMER XYZ QUANTITY TIME amp CTRL ID cycling timer FU
47. a three parameter mixture fraction decomposition can also be used with the first step being oxidation of fuel to carbon monoxide and the second step the oxidation of carbon monoxide to carbon dioxide The three mixture fraction components for the two step reaction are unburned fuel mass of fuel that has completed the first reaction step and the mass of fuel that has completed the second reaction step The mass fractions of all of the major reactants and products can be derived from the mixture fraction parameters by means of state relations Lastly a multiple step finite rate model is also available 3 Radiation Transport Radiative heat transfer is included in the model via the solution of the radiation trans port equation for a gray gas and in some limited cases using a wide band model The equation is solved using a technique similar to finite volume methods for convective transport thus the name given to it is the Finite Volume Method FVM Using approximately 100 discrete angles the finite volume solver requires about 20 of the total CPU time of a calculation a modest cost given the complexity of radi ation heat transfer The absorption coefficients of the gas soot mixtures are computed using RADCAL narrow band model Liquid droplets can absorb and scatter thermal radiation This is important in cases involving mist sprinklers but also plays a role in all sprinkler cases The absorption and scattering coefficients are based on Mie
48. all surfaces associated with a given SURF line be colored the same way prescribe a triplet of integers called RGB on the SURF line The following SURF line amp SURF ID UPHOLSTERY RGB 0 255 0 will cause the furnishings with a SURF of UPHOLSTERY to be colored green in Smokeview It is best to avoid using the primary colors because these same colors are used by Smokeview to draw color contours Obstructions and vents may be colored individually over riding the SURF line s RGB by specifying COLOR value to any of the listed names in Table 8 1 or INVISIBLE on the respective OBST or VENT line Using INVISIBLE causes the vent or obstruction to not be drawn Colors may also be specified using the integer triplet RGB on an OBST or VENT line to gain a wider color palette The use of RGB is preferable especially to create colors that do not clash with the pastel colors used to show temperatures concentrations etc See Table 8 1 for a list of color names and RGB values 8 6 1 Texture Mapping There are various ways of prescribing the color of various objects within the computational domain but there is also a way of pasting images onto the obstructions for the purpose of making the Smokeview images more realistic This technique is known as texture mapping For example to apply a wood paneling image to a wall add to the SURF line defining the physical properties of the paneling the text
49. ambient via leakage paths will occur This phenomena is known as the stack effect The stack_effect test case is a 2D simulation of a 304 m tall building initialized to a temperature of 20 with the surround ambient temperature initialized to 10 Two small openings in the building are defined 2 5 m above the ground floor of the building and 2 5 m below the roof of the building The initial density stratification is defined by assuming a lapse rate of 0 C m polz pa e 16 3 Applying this to the external and internal locations at the lower and upper vents results in densities of 1 2392 1 1969 1 1954 and 1 1546 kg m respectively FDS computes the same values to within machine precision Since the openings in the building are equally spaced over its height the neutral plane of the building will be close to its midpoint The pressure gradient across the building s wall can be computed as sp VEE l 16 4 Ro Tambien Thuilding where h is the distance from the neutral plane Using this pressure gradient in Bernoulli s equation and assuming it remains constant results in a velocity of 10 09 m s through the vent FDS computes a peak velocity of 10 13 m s or an error of 0 5 139 16 1 6 Sawtooth sawtooth Sometimes it is desired to have stair stepped obstructions representing curved or sloped geometry A concern is that this may change the flow pattern near the wall To lessen the impact of stair stepped bound
50. boundary conditions fire f90 Combustion routines pres f90 Spatial discretization of pressure Poisson equation divg f90 Compute the flow divergence init f90 Initialize variables and Poisson solver velo f90 Momentum equations main f90 or main_mpi f90 Main programs serial and parallel versions 172 Chapter 19 Output File Formats The output from the code consists of the file CHID out plus various data files that are described below Most of these output files are written out by the routine dump f and can easily be modified to accommodate various plotting packages 19 1 Diagnostic Output The file CHID out consists of a list of the input parameters and an accounting of various important quanti ties including CPU usage Typically diagnostic information is printed out every 100 time steps Iteration 8300 May 16 2003 08 37 53 esh 1 Cycle 3427 CPU step 2 272 s Total CPU 215 hr Time step 0 03373 s Total time 128 86 s ax CFL number 0 86E 00 at 21 9 80 ax divergence 0 24E 01 at 25 30 22 oy E LA in divergence 39E 01 at 26 18 31 umber of Sprinkler Droplets 615 Total Heat Release Rate 7560 777 kW Radiation Loss to Boundaries 6776 244 kW esh 2 Cycle 2914 CPU step 1 887 s Total CPU T53 hr Time step 0 03045 s Total time 128 87 s ax CFL number 0 96E 00 at 21 29 42 ax divergence 0 20E 01 at 22 20 22 in divergence 60E 01 at 7 26 48 umber of Sp
51. calculation Smokeview can be run and the progress can be checked visually To stop a calculation before 1ts scheduled time either kill the process or preferably create a file in the same directory as the output files called CHID stop The existence of this file stops the program gracefully causing it to dump out the latest flow variables for viewing in Smokeview Since calculations can be hours or days long there is a restart feature in FDS Details of how to use this feature are given in Section 6 4 1 Briefly specify at the beginning of calculation how often a restart file should be saved Should something happen to disrupt the calculation like a power outage the calculation can be restarted from the time the last restart file was saved It is also possible to control the stop time and the dumping of restart files by using control functions as described in Section 11 5 12 Chapter 4 User Support It is not unusual over the course of a project to run into various problems some related to FDS some related to your computer FDS is not a typical PC application It is a serious calculation that pushes your computer s processor and memory to its limits In fact there are no hardwired bounds within FDS that prevent you from starting a calculation that is too much for your hardware Even if your machine has adequate memory RAM you can still easily set up calculations that can require weeks or months to complete It is difficult to p
52. computed using a two flux model In this case the accuracy of the two flux model is tested in the computation of emissive flux from a 0 10 m thick homogenous layer of material at temperature of 1273 15 K and at ambient temperature of 10 K The absorption coefficient is varied to cover a range 0 01 10 of optical depths The exact solutions for radiative flux are the analytical solutions of plane layer emission 32 S t Sp 1 2E3 z 16 10 where S OT is the black body heat flux from the radiating plane and Ez 7 is the exponential integral function order 3 of optical depth t The exact solutions and FDS results are shown below t S t kW m7 FDS kW m 0 01 2 897 2 950 0 1 24 94 26 98 0 5 82 95 93 90 1 0 116 3 128 4 10 149 0 149 0 147 16 4 5 A Liquid Pool Fire ethanol_pan In this example a steel pan 0 7 m by 0 8 m is filled with a thin layer about 5 L 9 mm of ethanol which burns out within about 10 min This case tests a number of features burning liquids multiple layers of solids liquids and most importantly the absorption coefficient of the liquid The pyrolysis models in FDS prior to version 5 assumed that radiative feedback from the fire and hot gases within a compartment were absorbed at the surface In reality this energy is absorbed in depth the extent of which is characterized by the absorption coefficient K This is a property of the liquid as well as the gaseous va
53. existence FYI Character Comment String has no effect RGB 3 Integer Triplet Color indices 0 255 for resulting obstruction s TRANSPARENCY Real Transparency of obstruction XB 6 Real Sextuplet Physical coordinates m 13 8 INIT Initial Conditions Table 13 8 For more information see Section 6 5 INIT Initial Conditions DENSITY Real Initial value of density kg m Ambient MASS_FRACTION II Real Array Initial value of species II kg kg Ambient TEMPERATURE Real Initial value of temperature C TMPA XB 6 Real Sextuplet Coordinates m 13 9 ISOF Isosurface Parameters Table 13 9 For more information see Section 12 2 7 ISOF Isosurface Parameters FYI Character Comment String has no effect QUANTITY Character Quantity to visualize VALUE 1 Real Array Contour value s 110 13 10 MATL Material Properties Table 13 10 For more information see Section 8 4 MATL Material Properties A Real Pre exponential factor 1 s 1E13 ABSORPTION_COEFFICIENT Real Absorption Coefficient 1 m 50000 BOILING_TEMPERATURE Real Boiling temperature C 5000 CONDUCTIVITY Real Thermal conductivity W m K 0 1 CO
54. flame spread along a tray of assorted cable Detailed thermo physical property data for industrial grade cable is usually not available and even if it were it would probably not improve upon the given model The properties given in this example are almost completely fabricated What is important here are the HI obtained in most cases by a bench scale measurement device like the cone calorimeter 154 EAT _OF_ REACTION and R KE ER ENCE F I EMP ERATURE 16 5 Detectors 16 5 1 Aspiration Detector beam_detector A 10 mx 10 m x 4 m compartment is filled with 0 006 kg kg of MIXTURE_FRACTION_2 with the de fault soot yield 0 01 kg kg This results in an initial soot density of 71 9 mg m which using the default extinction coefficient of 8700 m kg results in an optical depth of 0 626 m The compartment has a series of obstructions placed at varying depths that are multiples of 1 m Using the correlation for the output quantity visibility one obtains a visibility distance of 4 8 m When viewing the smoke lev els with Smokeview one can just barely see the fifth obstacle which is at a distance of 5 m Smoke view therefore is properly displaying the obscuration of the initial soot density Three beam detectors are also placed in the compartment These all have a path length of 10 m but are at different orienta tions within the compartment Using the optical depth of 0 626 m and t
55. fuel molecule and any non ideal product yield FDS 5 computes what it needs based on this information ER EAC ID SOOT_YIELD C H PROPANE 0 01 3x 8 7 126 14 5 Device Parameters SPRK SMOD HEAT THCP Past versions of FDS had a variety of ways to specify devices For example a sprinkler was specified via a line of the form amp SPRK XYZ 4 5 6 7 3 6 MAKE Acme_K 17 LABEL spk_34 which located the sprinkler at xyz and indicated that the sprinkler s properties were listed in a file called Acme_K 17 spk Smoke and heat detectors were specified via lines of the form amp SMOD XYZ 4 5 6 7 3 6 LENGTH 2 6 ACTIVATION_OBSCURATION 1 4 LABEL sd_34 amp HEAT XYZ 4 5 6 7 3 6 RTI 45 ACTIVATION_TEMPERATURE 74 LABEL hd_39 In FDS 5 these devices are all specified in the same way amp PROP ID Acme_K 17 QUANTITY SPRINKLER LINK TEMPERATURE RTI 148 C_FACTOR 0 7 ACTIVATION_TEMPERATURE 74 PART_ID water drops FLOW_RATE 189 3 DROPLET_VELOCITY 10 SPRAY_ANGLE 30 80 amp DEVC ID spk_34 XYZ 4 5 6 7 3 6 PROP_ID Acme_K 17 Point output via thermocouples THCPs are now given by devices DEVCs amp DEVC XYZ 0 7 0 9 2 1 The syntax of the old THCP namelist group is almost the same Just swap DEVC for THCP and change LAB QUANTITY WALL_TE MPERATURE
56. installation package or compressed archive which is available for MS Windows Mac OS X and Linux For other operating systems consult the web site If you ever want to keep an older version of FDS and Smokeview copy the installation directory to some other place so that it is not overwritten during the updated installation 2 2 Computer Hardware Requirements FDS requires a fast CPU and a substantial amount of random access memory RAM to run efficiently For minimum specifications the system should have a 1 GHz CPU and at least 512 MB RAM The CPU speed will determine how long the computation will take to finish while the amount of RAM will determine how many mesh cells can be held in memory A large hard drive is required to store the output of the calculations It is not unusual for the output of a single calculation to consume more than 1 GB of storage space Most computers purchased within the past few years are adequate for running Smokeview with the caveat that additional memory RAM should be purchased to bring the memory size up to at least 512 MB This is so the computer can display results without swapping to disk For Smokeview it is also important to obtain a fast graphics card for the PC used to display the results of the FDS computations For Multi Mesh calculations the MPI version of FDS will operate over standard 100 Mbps networks A Gigabit or 1000 Mbps network will further reduce latency and improve data transfe
57. integral is positive if the flow and radiative flux are going out of the domain The conductive loss to solid surfaces is given by Oven L g dA 12 4 1 where the integral is positive if heat is being lost into a wall colder than the gas For scenarios in which the fire is the primary source of energy after the gas temperatures within the computational domain reach a nearly steady state x Onis Qcond 12 5 This is merely a check of the global energy balance that is the energy generated within the space heats up the gases and solid surfaces and then a balance between heat input and output is achieved 12 3 2 Visibility and Obscuration If you are performing a fire calculation using the mixture fraction approach the smoke is tracked along with all other major products of combustion The most useful quantity for assessing visibility in a space is the light extinction coefficient K 8 The intensity of monochromatic light passing a distance L through smoke is attenuated according to Ilp e E 12 6 98 The light extinction coefficient K is a product of the density of smoke particulate pY and a mass specific extinction coefficient that is fuel dependent K Kn pY 12 7 Devices that output a obscuration such as a DEVC witha QUANTITY of aspiration spot obscuration smoke detector or path obscuration beam detector are discussed respectively in Section 11 3 6 Section 11 3 4 and Section 11 3 5 Estimates of visi
58. is set to FALSE The domain is divided into three meshes each 1 m long with identicle gridding We expect the pressure temperature and density to rise during the 60 s injection period Afterwards the temperature density and pressure should remain constant A hand computation is performed at 10 second intervals using the First Law of Thermodynamics and the equation of state The figures below show the results of this verification case As is seen denisty matches exactly showing that FDS is injecting the appropriate quantity of mass and is properly initializing the domain Pressure rise and temperature rise however are overpredicted by 3 and 12 respectively Also a slight drop in pressure is seen from 60 s to 120 s indicating that the current implementation adiabatic boundary condition has a slight error in it FDS Mesh 1 FDS Mesh 2 FDS Mesh 3 Hand Calc FDS Mesh 1 FDS Mesh 2 FDS Mesh 3 Hand Calc co amp 50000 45000 8 40000 v a 35000 w Ss S S S v 8 25000 a v S S S S Temperature Rise K Pressure Rise Pa 15000 gt 10000 a 5000 o o o 20 40 60 80 100 120 0 20 40 60 80 100 120 Time s Time s FDS Mesh 1 FDS Mesh 2 FDS Mesh 3 Hand Calc 1 60 O DNV NS Density kg m3 oy 3 ENS Id 1 A 1 20
59. is 20000 kJ kg The ignitor is a 10 kW burner placed beside the block The integrated heat release rate for a 120 s calculation ought to be 0 4 m x 20 kg m x 20000 kJ kg 10 kW x 120 s 26 8 MJ 16 11 152 16 4 9 A Couch Fire couch In residential fires upholstered furniture makes up a significant fraction of the combustible load A single couch can generate several megawatts of energy and sometimes lead to compartment flashover Modeling a couch fire requires a simplification of its structure and materials to be described as fabric covering foam At the very least we want the upholstery amp MATL ID FABRIC FYI Properties completely fabricated SPECIFIC_HEAT 1 0 CONDUCTIVITY 0 1 DENSITY 100 0 N_REACTIONS ll NU_FUEL 1 REFERENCE_TEMPERATURE 350 HEAT_OF_REACTION 3000 HEAT_OF_COMBUSTION 15000 amp MATL ID FOAM FYI Properties completely fabricated SPECIFIC_HEAT 1 0 CONDUCTIVITY 0 05 DENSITY 40 0 N_REACTIONS iy NU_FUEL 1 REFERENCE_TEMPERATURE 350 HEAT_OF_REACTION 1500 HEAT_OF_COMBUSTION 30000 amp SURF ID UPHOLSTERY FYI Properties completely fabricated COLOR PURPLE BURN_AWAY TRUE MATL_ID 1 2 1 FABRIC FOAM THICKNESS 1 2 0 002 0 1 PART_ID smoke Both the fabric and the foam decompose into fuel ga
60. is exactly reversed From a numerical point of view a MIRROR is a no flux free slip boundary As with OPEN a MIRROR can only be prescribed at an exterior boundary of the computational domain Often OPEN or MIRROR VENTs are prescribed along an entire side of the computational domain in which case the MB notation is handy Note that the mirror image of a scene is not shown in Smokeview 7 3 2 Controlling VENTS VENT functionality can be controlled in some cases using devices and controls specified via a DEVC_ID or a CTRL_ID See Section 11 4 2 for details 7 3 3 Trouble Shooting VENTs If an error message appears requesting that the orientation of a vent be specified first check to make sure that the vent is a plane If the vent is a plane then the orientation can be forced by specifying the parameter IOR If the normal direction of the VENT is in the positive x direction set TIOR 1 If the normal direction is in the negative x direction set IOR 1 For the y and z direction use the number 2 and 3 respectively 41 Setting IOR may sometimes solve the problem but it is more likely that if there is an error message about orientation then the VENT is buried within a solid obstruction in which case the program cannot determine the direction in which the VENT is facing 42 Chapter 8 Boundary Conditions This chapter describes how to specify the properties of the objects tha
61. kg m s BS PART_ID _FLUX_Y See Section 12 3 6 kg m s PS PART_ID _FLUX_Z See Section 12 3 6 kg m s PS PART_ID _MPUA See Section 12 3 6 kg m B D PART_ID _MPUV See Section 12 3 6 kg m D LP S path obscuration See Section 11 3 5 D PRESSURE P Pa D LBS PRESSURE_COEFFICIENT Cp Section 12 3 9 B D RADIANT_INTENSITY JI x s dQ kW m2 D LBS RADIATIVE_FLUX See Section 12 3 5 kW m B D RADIOMETER See Section 12 3 5 kW m B D soot volume fraction PY Z Ps mol mol D LP S soot density pY Z mg m D LP S SPEC_ID Y kg kg D I P S SPEC_ID _VF X mol mol D I P S SPEC_1D _FLUX_X puYy kg m s D LPS SPEC_ID _FLUX_Y pvYa kg m s D LPS SPEC_1D _FLUX_Z pwYa kg m s D LPS spot obscuration See Section 11 3 4 m D SPRINKLER LINK TEMPERATURE See Section 11 3 1 E D EMPERATURE T Section 12 3 4 D I P S HERMOCOUPLE Trc Section 12 3 4 C D I P S IME t Section 11 1 s D U VELOCITY u m s D I P S V VELOCITY v m s D I P S W VELOCITY w m s D I P S UPPER TEMPERATURE See Section 12 3 3 C D VELOCITY Vu v2 w2 m s D LPS VISCOSITY u kg m s D 1 P S visibility S C K Section 12 3 2 m D LP S VOLUME FLOW See Section 12 3 8 m s D WALL TEMPERATURE Ty C B D water vapor Xmo Z mol mol D LPS WATER VAPOR XH 0 mol mol D LBS 104 Chapter 13 Alphabetical List of Input Parameters This Appendix lists all of the input parameters for FDS in seperate tables grouped by Namelist these tables are in alphabetical order along with t
62. kg m MAXIMUM_MASS_ FRACTION Real Array Maximum Gas Mass Fraction kg kg AXIMUM_TEMPERATURE Real Maximum Gas Temperature E INIMUM_DENSITY Real Minimum Gas Density kg m INIMUM_MASS_FRACTION Real Array Minimum Gas Mass Fraction kg kg INIMUM_TEMPERATURE Real Maximum Gas Temperature C 106 13 3 CTRL Control Function Parameters Table 13 3 For more information see Section 11 5 CTRL Control Function Parameters DELAY Real Time delay 0 FUNCTION_TYPE Character Type of control function ID Character IDentifier INITIAL STATE Logical Initial state of control function FALSE INPUT_ID Char Array DEVC and or CTRL input IDs LATCH Logical Control function changes state only once TRUE N Integer Number of TRUE INPUTS 1 ON_BOUND Character Active edge of a DEADBAND LOWER RAMP _ID Character ID for a CUSTOM ramp controller SETPOINT 2 Real Lower and upper bound of a DEADBAND 107 13 4 DEVC Device Parameters Table 13 4 For more information see Section 11 1 DEVC Device Parameters BYPASS_FLOWRATE Real Aspiration smoke detector parameter kg s 0 CTRL_ID Character Associated CTRL line DELAY Real Transport time for an aspiration detector s 0 DEVC_ID C
63. layer Thus Ps i Pso is a quantity that increases as the ith material is produced as a residue of some other reaction and decreases as the ith material decomposes If the layer is composed of only one material and if the reactions produce no solid residues then Psi Pso is always 1 ns j is the reaction order and prescribed under the name N_S j and is 1 by default If the value of n is not known it is a good starting point to assume n 1 The pre exponential factor A is prescribed under the name A j with units of 1 s E the activation energy is prescribed via E j in units of kJ kmol Remember that 1 kcal is 4 184 kJ and be careful with factors of 1000 A and E are not readily accessible for most real materials However if they are known specify both Avoid specifying just one because they act as a pair If A and E are not known which is usually the case specify REFERENCE_RATE 1 s and REFERENCE_TEMPERATURE C This directs FDS to choose A and E so that the reaction rate REFERENCE_RATE is achieved at the REFERENCE_TEMPERATURE The default value of REFERENCE_RATE is 0 1 s It is suggested that unless you have information to the contrary leave REFERENCE_RATE at its default value and just specify the REFERENCE_TEMPERATURE Note that the REFERENCE_TEMPERATURE is not the same as an ignition temperature Rather it is simply the temperature at which the mass fraction of t
64. message and circumstances related to the problem The input file should be simplified as much as possible so that the bug occurs early in the calculation Attach the simplified input file if necessary following the instructions provided at the web site In this way the developers can quickly run the problem input file and hopefully diagnose the problem NOTE Reports of specific problems feature requests and enhancements should be posted to the Issue Tracker and not the Discussion Group 15 16 Part II Writing an FDS Input File Chapter 5 The Basic Structure of an Input File 5 1 Naming the Job The operation of FDS is based on a single input text file containing parameters organized into namelist groups The input file provides FDS with all of the necessary information to describe the scenario The input file is saved with a name such as job_name fds where job_name is any character string that helps to identify the simulation If this same string is repeated under the HEAD namelist group within the input file then all of the output files associated with the calculation will then have this common name There should be no blank spaces in the job name Instead use the underscore character to represent a space Using an underscore characters instead of a space also applies to the general practice of naming directories on your system Be aware that FDS will simply over write the output files of a given case 1f its assigne
65. number of planes or patches that make up the solid boundaries plus the external walls The sextuplet 11 12 J1 J2 K1 K2 defines the cell nodes of each patch IOR is an integer indicating the orientation of the patch 1 2 3 You do not prescribe these Note that the data is planar thus one pair of cell nodes is the same Presently Smokeview is the only program available to view the boundary files 19 9 Particle Data The tracer particles and sprinkler droplets coordinates and related quantities are stored in a FORTRAN unformatted binary file called CHID prt5 Note that the format of this file has changed from previous versions 4 and below The file consists of some header material followed by particle data output every DT_PART seconds The time increment DT_PART is specified on the DUMP line It is T_END NFRAMES by default The header materials is written by the following FORTRAN code in the file called dump f90 WRITE LUPF ONE_INTEGER The number ONE as a 4 byte real WRITE LUPF NI VERSION 100 FDS version number WRITE LUPF N_PART Number of PARTicle classes DO N 1 N_PART PC gt PARTICLE_CLASS N WRITE LUPF PC N_QUANTITIES ZERO_INTEGER ZERO_INTEGER is a place holder DO NN 1 PC N_QUANTITIES ILS WRITE LUPF CDATA PCSQUANTITIES_INDEX NN 30 ch
66. of file to parse PL3D file Enter 1 SLCF file Enter 2 BNDF file Enter 3 Enter Sampling Factor for Data 1 for all data 2 for every other point etc Limit the domain size y or n y Enter min max x y and z 35 Fp SS 520 1 1 MESH 1 water_drops_AMPUA Enter starting and ending time for averaging s 9 10 Enter orientation plus or minus 1 2 or 3 3 Enter number of variables Enter boundary file index for variable 1 Enter output file name bucket_test_fds2ascii csv Writing to file bucket_test_fds2ascii csv 16 6 4 Complex Spray Patterns bucket_test_2 The test case from the prior section is modified to create two jets of water 159 PROP ID K 11 QUANTITY SPRINKLER LINK TEMPERATURE OFFSET 0 10 PART_ID water_drops FLOW_RATE 60 S PRAY PATTERN_TABLE TABLE1 SMOKEVI amp TABL ID TAB E1 TABL _DA A 30 31 0 1 5 0 2 amp TABL ID TAB El TABL _DA A 30 31 179 180 5 0 8 EW_ID sprinkler_upright The jets are separated by 180 degrees The jet in the x direction is given one quarter the flow rate of the jet in the x direction Viewing the particles in Smokeview shows two distinct jets of droplets in opposite directions Following the post processing instructions above you can observe that the x jet does have four times the flow of the x jet 160 1
67. of operation With this setting all meshes are active each iteration For a single processor multiple mesh calculation this strategy reduces and may even eliminate any benefit seen by using multiple meshes However in a parallel calculation if a particular mesh is inactive during an iteration because it is not ready to be updated then the processor assigned to that mesh is also inactive Forcing the mesh to be updated with a smaller than ideal time step does not cost anything since that processor would have been idle anyway The benefit is that there is a tighter connection between meshes It is also possible to synchronize the time step in only a select set of meshes To do this add SYNCHRONIZE TRUE to the appropriate MESH lines and then add SYNCHRONIZE FALSE to the TIME line e Ifa planar obstruction is close to where two meshes abut make sure that each mesh sees the obstruc tion If the obstruction is even a millimeter outside of one of the meshes that mesh does not account for it in which case information is not transferred properly between meshes e When running a case with multiple meshes in parallel the efficiency of the calculation can be checked as follows 1 Set SYNCHRONIZE TRUE on the TIME line 2 Let the program run several hundred time steps 3 Calculate the difference in wall clock time between two 100 iteration print outs in the file CHID out see Section 19 1 Divide the t
68. on the MISc line Even though the algorithm predicts CO formation and its eventual oxidation at elevated temperature it cannot predict the post flame yield of CO For example within a flashed over compartment the algorithm predicts the elevated CO levels but it cannot predict the CO concentration of the exhaust gases that exit the flaming region Thus even if using this model you must specify the CO_YIELD that is expected of a well ventilated fire Note that when active this algorithm requires the use of three parameters for the mixture fraction vs the two parameters used when it is disabled and will therefore increase run times and memory usage accordingly If the simulation you are performing will not result in an under ventilated fire then there will be of little if any benefit to enabling the CO production algorithm 68 9 2 Extra Gas Species The SPEC Namelist Group Normally when you specify a fire via either HRRPUA on the SURF line or reaction parameters on the MATL line the mixture fraction combustion model is applied A a set of two or three scalar variables Z represent the state of the combustion process from pure fuel YZ 1 to pure air Z 0 The major reactants and products of combustion fuel O2 CO H20 N2 CO and soot are all pre tabulated functions of the mixture fraction Z In other words the values of Z in any given mesh cell determines the mass fraction of all the gases listed Th
69. results can be transferred via either DEVC or BNDF output to other models that predict the mechanical response of the walls or structure For many applications the 1 D solution of the heat conduction equation is adequate but in situations where it is not another approach can be followed FDS includes a calculation of the Adiabatic Surface Temperature AST a quantity that is representative of the heat flux to a solid surface Following the idea proposed by Ulf Wickstrom 12 the following equation can be solved via a simple iterative technique to determine an effective gas temperature Tast Gh 0 Thr Ty h Tasr Tw 12 12 The sum 47 is the net heat flux onto the solid surface whose temperature is Ty The heat fluxes and surface temperature are computed in FDS and they are inter dependent The computed wall temperature affects the net heat flux and vice versa However because FDS only computes the solution to the 1 D heat conduction equation in the solid it may be prone to error if lateral heat conduction within the solid is significant Thus in some scenarios neither the FDS predicted heat fluxes or the surface temperature can be used as an accurate indicator of the thermal insult from the hot smokey gases onto solid objects Of course both the heat fluxes and q and the surface temperature T can be passed from FDS to the other model and suitable corrections can be made based on a presumably mo
70. search to only those surfaces Use the STATISTICS feature with caution because it demands that FDS evaluate the given QUANTITY in all gas or solid phase cells 12 2 4 Quantities within Solids The PROF Namelist Group FDS uses a fine non uniform one dimensional mesh at each boundary cell to compute heat transfer within a solid The parameters Table 13 15 to specify a given PROFile are similar to those used to specify a surface quantity in the DEVC group XYZ designates the triplet of coordinates QUANTITY is the physical quantity to monitor IOR the orientation and ID an identifying character string Here is an example of how you would use this feature to get a time history of temperature profiles within a given solid obstruction amp PROF XYZ QUANTITY TEMPERATURE ID TU1SA_FDS IOR 3 Other possible quantities are the total density of the wall QUANTITY DENSITyY or densities of solid material components QUANTITY MATL_ID where MATL_ID is the name of the material Each PROF line creates a separate file This may be more than is needed Sometimes all you want to know is the temperature at a certain depth To get an inner wall temperature you can also just use a device as follows amp DEVC XYZ QUANTITY INSIDE_WALL_TEMPERATURE DEPTH 0 005 ID Temp_1 IOR 3 The parameter DEPTH m indicates the distance inside the solid surface Note that this QUANT
71. set at the planes y YMIN XB 3 or y YMAX XB 4 nor at r XMIN XB 1 in an axially symmetric calculation in which r XB 1 0 For better visualizations the difference between XB 4 and XB 3 should be small so that the Smokeview rendering appears to be in 2 D An example of an axially symmetric helium plume helium_2d is given in the V amp V Guide 25 Figure 6 1 An example of a multiple mesh geometry 6 3 2 Multiple Meshes and Parallel Processing The term multiple meshes means that the computational domain consists of more than one computational mesh usually connected although this is not required In each mesh the governing equations can be solved with a time step based on the flow speed within that particular mesh Because each mesh can have different time steps this technique can save CPU time by requiring relatively coarse meshes to be updated only when necessary Coarse meshes are best used in regions where temporal and spatial gradients of key quantities are small or unimportant To run FDS in parallel you need to break up the computational domain into multiple meshes so that each processor receives one mesh to work on Whether the calculation is to be run on a single processor or on multiple processors the rules of prescribing multiple meshes are similar with some issues to keep in mind Here is a list of guidelines and warnings about the use of multiple meshes e If more than on
72. specifies the Mass Loss Rate of fuel gas Per Unit Area in kg m s Do not specify both HRRPUA and MLRPUA on the same SURF line With either the stoichiometry of the gas phase reaction is set by the parameters on the REAC line All of the species associated with the combustion process are accounted for by way of the mixture fraction variable and should not be explicitly prescribed The exception to this rule is where a non reacting gas is introduced into the domain that merely serves as a diluent like CO from an extinguisher or H20 from evaporated sprinkler droplets see Section 9 2 for details If a finite rate combustion model is desired instead of the default mixture fraction model see Section 9 3 Specifying HRRPUA or MLRPUA automatically invokes the mixture fraction combustion model 44 8 2 2 Simple Thermal Boundary Conditions Usually the thermal properties of a solid boundary are specified via the MATL namelist group which is in turn invoked by the SURF entry via the character string MATL_ 1D However sometimes it is convenient to simply specify a fixed temperature boundary condition in which case set TMP_FRONT to be the surface temperature in units of C For a solid surface of fixed convective heat flux set CONVECTIVE_HEAT_FLUX to be the convective heat flux in units of kW m2 If CONVECTIVE_HEAT_FLUX is positive the wall heats up the surrounding gases If CONVECTIVE_HEAT_FLUX is negative the wall cools th
73. the comma delimited file CHID_state_ILesv The file consists of nominally 10 columns the first column containing the mixture fraction the last column the average molecular weight and the rest the mass fractions of the various gases Where II represents the chemical reaction for which the state relationships represent For the two parameter model these are 01 for the complete reaction formation 175 of combustion products and 02 for the null reaction extinction For the three parameter model these are 01 02 and 03 for the incomplete CO production reaction complete CO production reaction and the null reaction respectively 19 7 Slice Files The slice files defined under the namelist group SLCF are named CHID_n sf n 01 02 and are written out unformatted unless otherwise directed These files are written out from dump f with the following lines WRITE LUSF QUANTITY WRITE LUSF SHORT_NAME WRITE LUSF UNITS WRITE LUSF 11 12 J1 32 K1 K2 WRITE LUSF TIME WRITE LUSF QQ I J K I 11 12 J J1 J32 K K1 K2 WRITE LUSF TIME WRITE LUSF QQ I J K I 11 12 J J1 J32 K K1 K2 QUANTITY SHORT_NAME and UNITS are character strings of length 30 The sextuplet 11 12 J1 J2 K1 K2 denotes the bounding mesh cell nodes The sextuplet indices correspond to mesh cell nodes or corners thus the entire mesh would be represented by the sextuplet 0 IBAR 0 JBAR 0 KBAR
74. thermal properties of the fabric covering but the steady burning rate is sensitive to the properties of the underlying foam 166 e Moisture content of wooden fuels is very important and difficult to measure e Flame spread over complicated objects like cables laid out in trays can be modeled if the surface area of the simplified object is comparable to that of the real object This suggests sensitivity not only to physical properties but also geometry It is difficult to quantify the extent of the geometrical sensitivity There is little quantification of the observed sensitivities in the study Fire growth curves can be linear to exponential in form and small changes in fuel properties can lead to order of magnitude changes in heat release rate for unconfined fires The subject is discussed in the FDS Validation Guide where it is noted in many of the studies that predicting fire growth is difficult Recently Lautenberger Rein and Fernandez Pello 53 developed a method to automate the process of estimating material properties to input into FDS The methodology involves simulating a bench scale test with the model and iterating via a genetic algorithm to obtain an optimal set of material properties for that particular item Such techniques are necessary because most bench scale apparatus do not provide a complete set of thermal properties 17 5 Summary The basis of large eddy simulation is that accuracy increases as the numerical me
75. this belt SPRAY_PATTERN_TABLE Name of a set of TABL lines containing the description of the spray pattern PART_ID The name of the PART line containing properties of the droplets See Section 10 for additional details Be aware that sprinklers produce many droplets that need to be tracked in the calculation To limit the bur den sprinkler droplets disappear when they hit the lower boundary of the computational domain regardless of whether it is solid or not To stop FDS from removing sprinkler droplets from the lower boundary of the computational domain add the phrase POROUS_FLOOR FALSE to the MISC Section 6 4 line Be aware however that droplets that land on the floor continue to move horizontally in randomly selected directions bouncing off obstructions and consuming CPU time For more information about sprinklers their activation and spray dynamics is included in the FDS Technical Reference Guide 1 Special Topic Specifying Complex Spray Patterns If a more complex spray pattern is desired than can be achieved by using SPRAY_ANGLE VELOCITY and FLOW_RATE then a SPRAY_PATTERN_TABLE can be specified using the TABL Section 8 5 namelist group For a spray pattern specify the total flow using FLOW_RATE of the PROP line the name of the spray pattern using SPRAY_PARTTERN_TABLE and then one or more TABL lines of the format Past versions of FDS used a separate file to
76. to change this Details are in the next section VAPORIZATION_TEMPERATURE Boiling temperature of liquid droplet Default 100 C MELTING_TEMPERATU YU E Melting solidification temperature of liquid droplet Default 0 C INITIAL TEMPERATURE Ds Initial temperature of liquid droplet Default TMPA HEAT_OF_VAPORIZATION Latent heat of vaporization of liquid droplet Default 2259 kJ kg 10 4 Special Types of Particles and Droplets There are several useful attributes that you can assign to particles or droplets usually via a simple logical parameter Be aware with each of these parameters that specifying it as TRUE may cause other parameters to be functionally useless or may cause conflicts that FDS may or may not detect A good rule of thumb is always to ask yourself what is the basic information that must be conveyed to the program and stick to that For example if the particles are to be MASSLESS there is no point in declaring anything else except maybe a COLOR for Smokeview Massless Particles The simplest use of Lagrangian particles is for visualization in which case the particles are considered massless tracers In this case the particles are defined via the line amp PART ID trace rs MASSLESS TRUE Note that if the particles are MASSLESS it is not appropriate to color them according to any particular property
77. 0 1 0 1 112 13 12 MISC Miscellaneous Parameters Table 13 12 For more information see Section 6 4 MISC Miscellaneous Parameters ASSUMED_GAS_TEMPERATURE Real See Section 8 7 BACKGROUND_SPECIES Character See Section 9 2 AIR BAROCLINIC Logical Baroclinic torque correction FALSE BNDF_DEFAULT Logical See Section 12 2 6 TRUE CFL MAX Real See Section 6 4 6 1 0 CFL_MIN Real See Section 6 4 6 0 8 CSMAG Real Smagorinsky constant 0 20 CONDUCTIVITY Real See Section 9 2 W m K CO_PRODUCTION Logical See Section 9 1 1 FALSE DNS Logical Direct Numerical Simulation FALSE FYI Character Comment String has no effect GVEC Real triplet Gravity vector m s 0 0 9 81 H_FIXED Real See Section 8 7 HUMIDITY Real Relative Humidity 40 ISOTHERMAL Logical Isothermal calculation FALSE AAPSE_RATE Real See Section 8 2 5 C m 0 ES Logical Large Eddy Simulation TRUE MW Real Molecular Weight Section 9 2 g mol NOISE Logical Toggle initial noise on and off TRUE PR Real Prandtl number LES only 0 5 P_INF Real Ambient pressure Pa 101325 POROUS_FLOOR Logical See Section 11 3 1 TRUE RADIATION Logical Radia
78. 1000 kW m after a linear ramp up of 10 s following its ignition when its surface temperature reaches 500 C Burning shall continue for 5 min and then ramp down in 10 s Note that the time T in the RAMP means time from ignition Note also that now the ignition temperature is a surface property not material property After the surface has ignited the heat transfer into the solid is still being solved but there is no coupling between the burning rate and the surface temperature As a result the surface temperature may increase too much To account for the energy loss due to the vaporization of the solid fuel HEAT_OF_VAPORIZATION can be specified for the surface For example when using the lines below the net heat flux at the material surface is reduced by a factor 1000 kJ kg times the instantaneous burning rate amp SURF ID my surface COLOR GREEN MATL_ ID stuff HRRPUA 1000 IGNITION_TEMPERATURE 500 HEAT_OF_VAPORIZATION 1000 RAMP_Q fire_ramp THICKNESS 0 01 The parameters HRRPUA IGNITION_TEMPERATURE and HEAT_OF_VAPORIZATION are all telling FDS that you want to control the burning rate yourself but you still want to simulate the heating up and ignition of the fuel When these parameters appear on the SURF line they are acting in concert If HRRPUA appears alone the surface will begin burning at the start of the simulation like a piloted burner The additi
79. 6 7 General Functionality This section contains a variety of simple tests to check the functionality of the code These examples are good demonstrations of how to make things happen in FDS 16 7 1 Creating and Removing HOL ES and opstructions create_remove It is often convenient to create or remove solid obstructions or conversely remove or create empty holes They are essentially the same thing as far as the logic in FDS is concerned but the input can be tricky To avoid confusion here is an example of holes and obstructions being created and removed amp HOLE amp HOLE amp OBST amp OBST amp DEVC amp DEVC amp DEVC amp DEVC 80 0 80 0 HEHH oooo 20 0 30 0 20 0 0 70 0 80 0 70 0 r r r Rh r 20 0 30 0 20 0 60 0 70 0 60 0 ID timer ID timer ID timer ID timer COLOR RED COLOR BLUE COLOR PINK r 0 0 0 0 r QUANTITY TIME QUANTITY TIME QUANTITY TIME QUANTITY TIME DEVC_ID timer 1 COLOR GREEN DEVC_ID timer 2 DEVC_ID timer 3 DEVC_ID timer 4 INITIAL_STATE FALSE INITIAL_STATE TRUE INITIAL_STATE FALSE INITIAL_STATE TRUE 162 Chapter 17 Sensitivity Analysis A sensitivity analysis considers the extent to which uncertainty in model inputs influences model output Model parameters can be the physical properties of solids and gases boundary conditions initial conditions etc The parameters ca
80. 69 SPECIFIC_HEAT 0 84 DENSITY 1600 amp SURF ID BRICK WALL MATL_ID BRICK COLOR RED BACKING EXPOSED THICKNESS 0 20 amp OBST XB 0 1 5 0 1 0 1 2 0 0 1 0 SURF_ID BRICK WALL define a brick wall that is 4 9 m long 1 m high and 20 cm thick 43 The thickness of the wall indicated by the OBST line need not match that indicated by the SURF line The thickness of the material on the surface of the wall is dictated by the parameter THICKNESS These two parameters are independent for each other the OBST line describes the overall geometric structure the SURF line describes the characteristics of the surfaces of the geometry which includes the thickness of the layers of materials applied to that surface 8 2 Describing the Bounding Surfaces The SURF Namelist Group Table 13 22 SURF is the namelist group Table 13 22 that defines the structure of all solid surfaces or openings within or bounding the flow domain Boundary conditions for obstructions and vents are prescribed by referencing the appropriate SURF line s whose parameters are described in this section The default boundary condition for all solid surfaces is that of a cold inert wall If only this boundary condition is needed there is no need to add any SURF lines to the input file If additional boundary con ditions are desired they are to be listed one boundary condition at a time Each SURF line consists of an identification s
81. 73 19 2 PotD Dale etarra ea ea oe Seda Bo ee earned baree bea eae ee da Paes 174 19 3 Device Output Dita o e s eae ie a od A Rd Pe ee ee io de da ae A ed Be 174 194 Control Output Data so fae ak ds PE ER eee ee eR EOE BR 175 19 Ga s Mass Data 4 tue kee ee hw eee be ae ee ee ee Be 175 19 6 Mixture Fraction State Relations 404 us e oe eee a a A Re 175 19 7 Slice Files s cocaina a ee ee Pe eae es 176 19 8 Boundary Files os c ei a ean be SO wa ks Mee do Ee ee ee A 176 19 9 Particle Dita ui ias bea ama a See ee ed ha we ee ea eh ea BU ea bs 177 TO TOPrONIE Piles vied naw Go a a A baa a i a Se A 177 Bibliography 179 Index 183 XVi Part I Running FDS Chapter 1 Introduction The software described in this document Fire Dynamics Simulator FDS is a computational fluid dynamics CFD model of fire driven fluid flow FDS solves numerically a form of the Navier Stokes equations appropriate for low speed thermally driven flow with an emphasis on smoke and heat transport from fires The formulation of the equations and the numerical algorithm are contained the FDS Technical Reference Guide 1 Smokeview is a separate visualization program that is used to display the results of an FDS simulation A detailed description of Smokeview is found in the User s Guide for Smokeview Version 5 2 1 1 Features of FDS The first version of FDS was publicly released in February 2000 To date about half of the applications of the model have
82. 80 XYZ 79 Device Aspiration Detector 84 Beam Detector 83 Heat Detector 82 Smoke Detector 83 Spray Nozzle 82 Sprinkler 80 Download 7 dry pipe sprinkler system 91 DUMP 93 COLUMN_DUMP_LIMIT 80 fan 89 fds2ascii 102 Features 3 Recent Changes 4 Fire from Heat Release Rate 44 fixed surface temperature 45 Flame Extinction 68 gravity 32 HEAD 23 CHID 23 TITLE 23 HOLE 39 COLOR 39 CTRL_ID 39 125 DEVC_ID 39 RGB 39 183 TRANSPARENCY 39 XB 39 HRRPUA 44 HVAC 33 88 90 INIT 35 initial solid temperature 58 Input File Overview 19 ISOF 96 Large Eddy Simulation 33 Liquid Fuels 56 louver 46 Mass Flux 45 Material layers 52 MATL 52 A 53 ABSORPTION_COEFFICIENT 53 BOILING_TEMPERATURE 57 CONDUCTIVITY 53 DENSITY 53 E 33 EMISSIVITY 53 HEAT_OF_COMBUSTION 55 HEAT_OF_REACTION 55 N_S 53 N_T 54 NU_FUEL 53 NU_RESIDUE 53 NU_WATER 53 REFERENCE_RATE 54 REFERENCE_TEMPERATURE 54 RESIDUE 53 SPECIFIC_HEAT 53 THRESHOLD_TEMPERATURE 54 MB Mesh Boundary 40 MESH 25 IJK 25 SYNCHRONIZE 27 XB 25 mesh dimensions 29 MISC 31 RADIATION 72 MLRPUA 44 multi mesh efficiency 27 Multiple Meshes 26 Namelist Group 19 Namlist Groups Table 22 Navier Stokes 3 non planar geometries 48 OBST 37 CTRL_ID 125 PERMIT_HOLE 40 outdoor fires 47 Output 93 Adiabatic Surface Temperature 101 Boundary File 96 fds2ascii 102 Integrated Measurements 94 I
83. AT_OF_COMBUSTION 44500 DT_INSERT 0 02 SAMPLING_FACTOR 1 amp PROP ID nozzle PART_ID heptane droplets FLOW_RATE 1 96 FLOW_RAMP fuel DROPLET_VELOCITY 10 SPRAY_ANGLE 0 30 amp RAMP ID fuel T 0 0 F 0 0 amp RAMP ID fuel T 20 0 F 1 0 amp RAMP ID fuel T 40 0 F 1 0 amp RAMP ID fuel T 60 0 F 0 0 TT The vaporization boiling temperature of the liquid fuel is in degrees Celsius the heat of gt is in units of kJ kg the specific heat is in units of kJ kg K and the density is in units of kg m FUEL TRUE automatically invokes a mixture fraction calculation in which fuel from the evaporating 5 droplets is burned according to the overall reaction scheme Note that this construct is fragile and subject to mesh dependence If the mesh cells are too coarse the evaporating fuel is diluted to such a degree that it never burns Proper resolution depends on the type of fuel and the amount of fuel being ejected from the nozzle Simulations with both fuel and water droplets are possible unlike versions of FDS prior to 5 10 7 Special Topic Suppression by Water Mixture Fraction Model Only Modeling suppression of a fire by a water spray is challenging because the relevant physical mechanisms occur at length scales smaller than a single mesh cell
84. Common Error Statements An FDS calculation may end before the user prescribed time limit Following is a list of common error statements and how to diagnose the problems Input File Errors The most common errors in FDS are due to mis typed input statements These errors result in the immediate halting of the program and a statement like ERROR Problem with the HEAD line For these errors check the line in the input file named in the error statement Make sure the parameter names are spelled correctly Make sure that a forward slash is put at the end of each namelist entry Make sure that the right type of information is being provided for each parameter like whether one real number is expected or several integers or whatever Make sure there are no non ASCII characters being used as can sometimes happen when text is cut and pasted from other applications or word processing software Make sure zeros are zeros and O s are O s Make sure 1 s are not s Make sure apostrophes are used to designate character strings Make sure the text file on a Unix Linux machine was not created on a DOS machine and vice versa Make sure that all the parameters listed are still being used new versions of FDS often drop or change parameters to force you to re examine old input files Numerical Instability Errors It is possible that during an FDS calculation the flow velocity at some loca tion in the domain can increase due to numerical error c
85. E water vapor and or fuel gas For example the evaporation of water from a solid material is described by the reaction that converts liquid water to water vapor This reaction occurs close to 100 C and produces only water vapor It does not produce a solid RESIDUE nor fuel gas However a pyrolyzing solid might undergo a reaction that produces a solid RESIDUE water vapor and fuel gas For each MATL entry in the input file decide how many reactions it can undergo It may not undergo any it may only just heat up However if it is to change form via one or more reactions designate the number 53 of reactions with the integer N_REACTIONS It is very important that you designate N_REACTIONS or else FDS will ignore all parameters associated with reactions Note that quite often the empirical observation of multiple reactions does not imply N_REACTIONS gt 1 but is caused by the fact that the examined sample is a mixture of multiple materials reacting at different temperatures Currently the maximum number of reactions for each material is 10 and the chain of consecutive reactions may contain up to 20 steps Next decide what each reaction produces a single solid RESIDUE water vapor and or fuel gas This information is conveyed to FDS via the yields NU_RESIDUE j NU_WATER j and NU_FUEL j respectively Here 3 indicates which reaction the parameters pertain to If like the evapora
86. E_HEAT_FLUX is that the former is the rate at which energy is absorbed by the solid surface the latter is the amount of energy that would be absorbed if the surface were cold or some specified temperature Gr E 4 h Ty Tx 0 Ty To E If the heat flux gauge used in an experiment has a temperature other than ambient set GAUGE_TEMPERATURE on the PROP line associated with the device When comparing against a radiometer measurement use RADIOMETER Gr 0 Ty To For diagnostic purposes it is sometimes convenient to output the INCIDENT_HEAT_FLUX Gi e oT 40 There is a gas phase output quantity called RADIANT_INTENSITY This is used mainly for diagnosing problems with the radiation solver Even though its units are kW m it should not be interpreted as the heat flux to an object that would occupy that particular point in space Rather it is the integral over all directions of the radiation intensity x s a function of both space and direction It is denoted by U as in Eq 12 11 Note that in FDS 5 and beyond these quantities are no longer available as slice files 100 12 3 6 Droplet Output Quantities It is possible to record various properties of evaporating droplets Some of the output quantities are asso ciated with solid boundaries For example PART_ID _MPUA is the Mass Per Unit Area of the droplets named PART
87. FDS are appropriate for most large scale fire scenarios but may need to be refined for more detailed simulations such as a low sooting methane burner 17 4 Sensitivity of Thermophysical Properties of Solid Fuels An extensive amount of verification and validation work with FDS version 4 has been performed by Hi etaniemi Hostikka and Vaari at VTT Finland 52 The case studies are comprised of fire experiments ranging in scale from the cone calorimeter ISO 5660 1 to full scale fire tests such as the room corner test ISO 9705 Comparisons are also made between FDS results and data obtained in the SBI Single Burning Item Euro classification test apparatus EN 13823 as well as data obtained in two ad hoc experimental configurations one is similar to the room corner test but has only partial linings and the other is a space to study fires in building cavities All of the case studies involve real materials whose properties must be prescribed so as to conform to the assumption in FDS that solids are of uniform composition backed by a material that is either cold or totally insulating Sensitivity of the various physical properties and the boundary conditions were tested Some of the findings were e The measured burning rates of various materials often fell between two FDS predictions in which cold or insulated backings were assumed for the solid surfaces FDS lacks a multi layer solid model e The ignition time of upholstery is sensitive to the
88. INERT puts a fire on top of the obstruction This is a simple way of prescribing a burner Some additional features of obstructions are as follows e In addition to SURF_ID and SURF_IDS you can also use the sextuplet SURF_ID6 as follows S OBST XB 2 3 4 5 1 3 4 8 0 0 9 2 SURF_ID6 FIRE INERT HOT COLD BLOW INERT where the six surface descriptors refer to the planes x 2 3 x 4 5 y 1 3 y 4 8 z 0 0 and z 9 2 respectively Note that SURF_ID6 should not be used on the same OBST line as SURF_ID or SURF_IDS 37 e Obstructions can have zero thickness Often thin sheets like a window form a barrier but if the numerical mesh is coarse relative to the thickness of the barrier the obstruction might be unnecessarily large if it is assumed to be one layer of mesh cells thick All faces of an obstruction are shifted to the closest mesh cell If the obstruction is very thin the two faces may be approximated on the same cell face FDS and Smokeview render this obstruction as a thin sheet but it is allowed to have thermally thick boundary conditions This feature is fragile especially in terms of burning and blowing gas A thin sheet obstruction can only have one velocity vector on its face thus a gas cannot be injected reliably from a thin obstruction because whatever is pushed from one side is necessarily pulled from the other For full functionality the obstruction should b
89. ITY is allowed only as a DEVC not a BNDF output Also note that if the wall thickness is decreasing over time due to the solid phase reactions the distance is measured from the current surface and the measurement point is moving towards the back side of the solid Eventually the measurement point may get out of the solid in which case it starts to show ambient temperature 12 2 5 Animated Planar Slices The SLCF Namelist Group The SLcF slice file namelist group parameters Table 13 20 allows you to record various gas phase quantities at more than a single point A slice refers to a subset of the whole domain It can be a line plane or volume depending on the values of xB The sextuplet xB indicates the boundaries of the slice plane XB is prescribed as in the OBST or VENT groups with the possibility that 0 2 or 4 out of the 6 values be the same to indicate a volume plane or line respectively A handy trick is to specify for example 95 PBY 5 3 instead of XB if it is desired that the entire plane y 5 3 slicing through the domain be saved PBX and PBZ control planes perpendicular to the x and z axes respectively Animated vectors can be created in Smokeview if a given SLCF line has the attribute VECTOR TRUE If two SLCF entries are in the same plane then only one of the lines needs to have VECTOR TRUE Otherwise a redundant set of velocity component slices will be created Slice file information is
90. In the gas phase flames are extinguished due to lowered temperatures and dilution of the oxygen supply See Section 9 1 1 for more information about gas phase suppression For the solid phase water reduces the fuel pyrolysis rate by cooling the fuel surface and also changing the chemical reactions that liberate fuel gases from the solid If the solid or liquid fuel has been given reaction parameters via the MATL line there is no need to set any additional suppression parameters It is assumed that water impinging on the fuel surface takes energy away from the pyrolysis process and thereby reduces the burning rate of the fuel If the surface has been assigned a HRRPUA Heat Release Rate Per Unit Area a parameter needs to be specified that governs the suppression of the fire by water An empirical way to account for fire suppression by water is to characterize the reduction of the pyrolysis rate in terms of an exponential function The local mass loss rate of the fuel is expressed in the form mt hh olt e 10 di 10 2 Here my o t is the user specified burning rate per unit area when no water is applied and k is a function of the local water mass per unit area m expressed in units of kg m k t E_COEFFICIENTM t s7 10 3 The parameter E_COEFFICIENT must be obtained experimentally and it is expressed in units of m kg s Usually this type of suppression algorithm is invoked when the fuel is complicated like a carto
91. LUX Real Normal velocity x vent area m s 0 ZO Real Atmospheric profile origin m 10 13 23 TABL Table Parameters Table 13 23 For more information see Section 8 5 TABL Table Parameters ID Character IDentifier FYI Character Comment String has no effect TABLE_DATA Real Array Data for one row of the table 13 24 TIME Time Parameters Table 13 24 For more information see Section 6 2 TIME Time Parameters DT Real Initial time step FYI Character Comment String has no effect SYNCHRONIZE Logical Sync time step of multiple meshes TRUE _BEGIN Real Starting time for calculation 0 _ ENDOrTWF IN Real Ending time for calculation 1 WALL_INCREMENT Integer Time steps between 1D wall solution updates 2 122 13 25 TRNX TRNY TRNZ MESH Transformations Table 13 25 For more information see Section 6 3 3 TRNX TRNY TRNZ MESH Transformations ee Real Computational coordinate m FYI Character Comment String has no effect IDERIV Integer Order of polynomial transformation MESH NUMBER Integer Number of mesh to transform PC Real Physical coordinate or derivative 13 26 VENT Vent Parameters Table 13 26 For more informat
92. MP T 0 F 0 10 amp RAMP ID K_RAMP T 100 F 0 15 amp RAMP ID K_RAMP T 200 F 0 20 amp RAMP ID C_RAMP T 0 F 1 00 amp RAMP ID C_RAMP T 100 F 1 20 amp RAMP ID C_RAMP T 200 F 1 00 amp SURF ID SLAB STRETCH_FACTOR 1 0 GEOMETRY CYLINDRICAL MATL_ID MAT_1 THICKNESS 0 01 220 2001 o Cartesian o Cylindrical 180 v Spherical 1607 140 z 120 j EXPOSED SURFACE E lt 100 80 60 40 UNEXPOSED SURFACE CENTER 20 9 E ee T 0 100 id 200 300 400 500 600 700 800 900 1000 Time s 145 16 4 3 A Simple Two Step Pyrolysis Example two_step_solid_reaction Consider the set of ordinary differential equations describing the mass fraction of three components of a solid material undergoing thermal degradation dY a E abYa dY ae KabYa KbcY 16 7 dY 7 KbcYa where the mass fraction of component a is 1 initially The analytical solution is Y t exp Kzpt Ka Y t Ko za exp K t exp Kpct 16 8 Y t Kap 1 exp Kpct Kpe exp Kapt 1 Kab Koc 16 9 The analytical and numerical solution for the parameters Kap 0 389 and Kpc 0 262 are shown here Analytical Solution e Y e Y e Y Y Numerical Solution Y Mass Fraction 146 16 4 4 Wall Internal Radiation wall_internal_radiation The radiative flux inside the walls is
93. MPERATURE 330 amp SURF ID PMMA SLAB COLOR BLACK MATL_ID PMMA THICKNESS 0 025 TERNAL_FLUX 50 External Flux is ONLY for this simple demo exercise virtual heat flux The solid in this example is a slab of plastic similar The material undergoes only one reaction the conversion of solid to gaseous fuel vapor In this case the HEAT_OF_REACTION is essentially the latent heat of vaporization The REFERENCE T EMPERATURE indicates that the reaction is to occur at a default rate of 0 1 s at 330 C The HEAT_OF_COMBUS1 refers to the combustion of the gaseous fuel vapor which does not occur in this example TION 500 F 0 025 thermoplastic thermoplastic 400 2 0 020 o E lt Es o 300 5 2 0 015 k e 2 200 a 0 010 E ov o at r o 100 lt 0 005 0 7 7 7 0 000 r T T 0 200 400 600 800 0 200 400 600 Time s Time s 800 The figures above show that both the temperature and burning rate of the thermoplastic are more or less constant over the burning phase The slab burns away after about 10 min 149 16 4 7 A Charring Solid charring_solid This example just exercises the solid phase algorithm in FDS Essentially the gas phase is shut off except for the imposition of a 50 kW m virtual heat flux The reaction mechanism is fairly complicated as it includes various solids like cellulose char and
94. N MASS_FRACTION_0 0 1 MW 40 As an example the lines amp SPEC ID ARGON MASS _FRACTION_0 0 1 MW 40 amp SPEC ID HELIUM amp SURF ID INLET MASS_FRACTION 2 0 2 VEL 0 3 TAU_MF 2 0 5 TAU_V 0 5 specify that ARGON and HELIUM are to be included in the calculation in addition to the unlisted default BACKGROUND_SPECIES AIR At the INLET a mixture of helium 0 2 by mass argon 0 1 by mass because nothing different is specified and air 0 7 by mass making up the rest flows out at a velocity of 0 3 m s into the flow domain The mass fraction of helium and the velocity are both ramped up according to the function tanh 0 5 If the simulation does not involve the mixture fraction model either because no combustion is desired or if a finite rate reaction s is being specified see Section 9 3 you can specify that the background gas species be something other than air For a gas mixture comprised of n species FDS only solves transport equations for n 1 because it also solves an equation for total mass conservation To set the properties of the implicitly defined BACKGROUND_SPECIES use the MISC line If this species is not listed in Table 9 1 specify its molecular weight Mw and optionally its VISCOSITY and CONDUCTIVITY In the absence of any of these parameters the appropriate values of AIR are assumed 1 Often an extra gas introduced into a calculation i
95. NCTION_TYPE CUSTOM INPUT_ID TIMER RAMP_ID cycle amp RAMP ID cycle T 0 F 1 amp RAMP ID cycle T 59 F 1 amp RAMP ID cycle T 61 F 1 amp RAMP ID cycle T 119 F 1 amp RAMP ID cycle T 121 F 1 The above will have the obstacle initially removed then added at 60 s and removed again at 120 s Experiment with these combinations using a simple case before trying a case to make sure that FDS indeed is doing what is intended 11 5 6 Combining Control Functions A Pre Action Sprinkler System For a pre action sprinkler system the normally dry sprinkler pipes are flooded when a detection event occurs For this example the detection event is when two of four smoke detectors alarm It takes 30 s to flood the piping network The nozzle is a DEVC named NOZZLE 1 controlled by the CTRL named nozzle trigger The nozzle activates when both detection and the time delay have occurred Note that the DEVC is specified with QUANTITY CONTROL amp DEVC XYZ 1 1 3 PROP_ID Acme Smoker ID SD_1 amp DEVC XYZ 1 4 3 PROP_ID Acme Smoker ID SD_2 amp DEVC XYZ 4 1 3 PROP_ID Acme Smoker ID SD_3 amp DEVC XYZ 4 4 3 PROP_ID Acme Smoker ID SD_4 amp DEVC XYZ 2 2 3 PROP_ID Acme Nozzle QUANTITY CONTROL ID NOZZLE 1 CTRL_ID nozzle trigger amp CTRL ID nozzle trigger FUNCTION_TYPE ALL INPUT_ID
96. NDUCTIVITY_RAMP Character Ramp ID for conductivity DENSITY Real Solid mass per unit volume kg m 500 E Real Activation energy kJ kmol EMISSIVITY Real Emissivity 0 9 FYI Character Comment String has no effect HEAT _OF_ COMBUSTION Real Heat of combustion kJ kg HEAT OF REACTION Real Heat of reaction kJ kg 0 ID Character IDentifier THRESHOLD_TEMPERATURE Real Threshold temperature C 273 15 N_REACTIONS Character Number of Reactions 0 N_S Real Exponent of mass fraction 1 N_T Real Exponent of temperature 0 NU_FUEL Real Fuel Yield kg kg 0 NU_RESIDUE Real Residue Yield kg kg 0 NU_WATER Real Steam Yield kg kg 0 REFERENCE _RATE Real Reaction rate at ref temp sI 0 10 REFERENCE_TEMPERATURE Real Reference temperature C RESIDUE Character ID of residue MATL SPECIFIC_HEA Real Specific heat kJ kg K 1 0 SPECIFIC_HEAT RAMP Character Ramp ID for specific heat 111 13 11 MESH Mesh Parameters Table 13 11 For more information see Section 6 3 MESH Mesh Parameters COLOR Character Mesh Line Color BLACK CYLINDRICAL Logical 2 D Axi symmetric calculation FALSE ID Character MESH IDentifier IJK Integer Triplet No cells in x y and z directions 10 FYI Character Comment String has no effect RGB Integer Triplet Color indices 0 255 0 0 0 SYNCHRONIZE Logical Sync time steps of multiple meshes TRUE XB Real Sextuplet Min Max Coordinates of the MESH 0 1
97. NIST Special Publication 1019 5 Fire Dynamics Simulator Version 5 User s Guide Kevin McGrattan Bryan Klein Simo Hostikka Jason Floyd In cooperation with VTT Technical Research Centre of Finland NIST National Institute of Standards and Technology U S Department of Commerce NIST Special Publication 1019 5 Fire Dynamics Simulator Version 5 User s Guide Kevin McGrattan Bryan Klein NIST Building and Fire Research Laboratory Gaithersburg Maryland USA Simo Hostikka VIT Technical Research Centre of Finland Espoo Finland Jason Floyd Hughes Associates Inc Baltimore Maryland USA October 1 2007 SVN Repository Revision 726 n De y 2 e o Alo A 4 30 Sa TEs Of U S Department of Commerce Carlos M Gutierrez Secretary National Institute of Standards and Technology James M Turner Acting Director Certain commercial entities equipment or materials may be identified in this document in order to describe an experimental procedure or concept adequately Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology nor is it intended to imply that the entities materials or equipment are necessarily the best available for the purpose National Institute of Standards and Technology Special Publication 1019 5 Natl Inst Stand Technol Spec Publ 1019 5 186 pages October 2007 CODEN NSPUE2 U S GOVER
98. NMENT PRINTING OFFICE WASHINGTON 2007 For sale by the Superintendent of Documents U S Government Printing Office Internet bookstore gpo gov Phone 202 512 1800 Fax 202 512 2250 Mail Stop SSOP Washington DC 20402 0001 Preface This guide describes how to use the Fire Dynamics Simulator FDS Version 5 It does not provide the background theory A companion document called the FDS Technical Reference Guide 1 contains details about the governing equations and numerical methods The FDS User s Guide contains limited information on how to operate Smokeview the companion visualization program for FDS Its full capability is described in the User s Guide for Smokeview Version 5 2 11 Disclaimer The US Department of Commerce makes no warranty expressed or implied to users of the Fire Dynamics Simulator FDS and accepts no responsibility for its use Users of FDS assume sole responsibility under Federal law for determining the appropriateness of its use in any particular application for any conclusions drawn from the results of its use and for any actions taken or not taken as a result of analyses performed using these tools Users are warned that FDS is intended for use only by those competent in the fields of fluid dynamics thermodynamics combustion and heat transfer and is intended only to supplement the informed judgment of the qualified user The software package is a computer model that may or may not ha
99. NTITY LAYER HEIGHT ID whatever produces a time history of the smoke layer height at x 2 and y 3 between z 0 and z 3 If multiple meshes are being used the vertical path cannot cross mesh boundaries 12 3 4 The True Gas Temperature vs the Measured Gas Temperature The output quantity THERMOCOUPLE is the temperature of the thermocouple itself usually close to the gas temperature but not always It is determined by solving the following equation for Trc iteratively 11 Erc OTrc U 4 h Trc Tz 0 12 11 where Erc is the emissivity of the thermocouple U is the integrated radiative intensity T is the true gas temperature and h is the heat transfer coefficient to a small sphere h k Nu Pr drc The bead BEAD_DIAMETER and BEAD_EMISSIVITY are given on the associated PROP line See the discussion on heat transfer to a water droplet in the Technical Reference Guide for details of the convective heat transfer to a small sphere 12 3 5 Heat Fluxes There are various ways of recording the heat flux at a solid boundary If you want to record the net heat flux to the surface q use the QUANTITY called HEAT_FLUX The individual components the net convective and radiative fluxes are CONVECTIVE_FLUX and RADIATIVE_FLUX respectively If you want to compare predicted heat flux with a measurement you often need to use GAUGE_HEAT_FLUX The difference between HEAT_FLUX and GAUG
100. Protection Association Quincy Massachusetts 2004 164 J A lerardi and J R Barnett A Quantititive Method for Calibrating CFD Model Calculations In Pro ceedings of the CIB CTBUH International Conference on Tall Buildings pages 507 514 International Council for Research and Innovation in Building and Construction CIB 2003 164 181 44 45 46 47 48 49 50 51 52 53 G Heskestad SFPE Handbook of Fire Protection Engineering chapter Fire Plumes Flame Height and Air Entrainment National Fire Protection Association Quincy Massachusetts 3rd edition 2002 164 N M Petterson Assessing the feasibility of reducing the grid resolution in fds field modeling Fire Engineering Research Report 2002 6 University of Canterbury Christchurch New Zealand March 2002 164 A Musser K B McGrattan and J Palmer Evaluation of a Fast Simplified Computational Fluid Dynamics Model for Solving Room Airflow Problems NISTIR 6760 National Institute of Standards and Technology Gaithersburg Maryland June 2001 165 W Zhang A Hamer M Klassen D Carpenter and R Roby Turbulence Statistics in a Fire Room Model by Large Eddy Simulation Fire Safety Journal 3717 121 752 2002 165 J Smagorinsky General Circulation Experiments with the Primitive Equations I The Basic Experi ment Monthly Weather Review 91 3 99 164 March 1963 165 J W Deardorff Numerical Investigation of Neutral and Unst
101. RE CTRL ID thermostat FUNCTION_TYPE DEADBAND INPUT_ID TC ON_BOUND LOWER SETPOINT 23 27 LATCH FALSE 41 Here we want to control the VENT that simulates the FAN which blows hot air into the room A DEVC called TC is positioned in the room to measure the TEMPERATURE The thermostat uses a SETPOINT to turn on the FAN when the temperature falls below 23 C ON_BOUND LOWER and it turns off when the temperature rises above 27 C Note that a deadband controller needs to have LATCH set to FALSE Fl 89 11 5 4 Control Function RESTART and KILL There are times when one only wishes to run a simulation until some goal is reached Previously this could generally only be done by constantly monitoring the simulation s output and manually stopping the calculation when one observed the goal being met By using the KILL control function this can be done automatically Additionally there are analyses where one wishes to create some baseline condition and the run multiple permutations of that baseline For example one may wish to run a series of simulations where different mitigation strategies are tried once a detector alarms By using the RESTART control function one can cause a restart file to be created once a desired condition is met The simulation can continue and the restart files can be copied to have the CHID of the vari
102. RF line The other is to specify a HEAT_OF_REACTION along with other thermal parameters on a MATL line in which case the burning rate of the fuel depends on the net heat feedback to the surface In both cases the mixture fraction combustion model is used In fact the mere presence of these parameters automatically invokes the mixture fraction model Do not specify explicitly gas species like oxygen if you have also specified heat release rates or solid phase reaction rates A single REAC line is used with the mixture fraction model If the REAC line is not found in the input file propane will be used as the surrogate fuel and all burning rates will be adjusted accordingly If you only specify the fire s heat release rate with HRRPUA then the reaction parameters may not require adjusting and no REAC line need be added to the input file However if you know something about the predominant fuel gas you might want to consider specifying at the very least the basic stoichiometry via the REAC line Using the mixture fraction model each reaction is assumed to be of the form C HyO NyOthery Vo O2 Vco CO2 Vno H20 vco CO Vsoot Soot VN N2 Vother Other 9 1 You need only specify the chemical formula of the fuel along with the yields of CO soot and H2 and the amount of hydrogen in the soot H frac For completeness you can specify the N2 content of the fuel and the presence of other species FDS will use that i
103. SI and ISO standards with a few exceptions that are discussed below The source files should be compiled in the order in which they are listed in Table 18 1 because some routines are dependent on others For Unix Linux users Makefiles for various platforms are available that assist in the compilation Compiler options differ from platform to platform Note the following e The source code consists mainly of Fortran 90 statements organized into about 25 files plus an extra file containing some additional C routines needed for output to Smokeview All of the C code is contained within the file called isob c Be aware that different compilers handle the names of C subroutines differently Some compilers append an underscore to the names of the C routines called by the Fortran code If the compiler produces an error involving the names of routines that are not recognized invoke the C compiler pre processing directive pp_noappend to stop the compiler from appending the underscore to the names of the C routines There is only one non standard call in the Fortran code The non standard call is GETARG in func f90 This routine reads the name of the input file off of the command line This call cannot be simply commented out a suitable alternative must be found The only compiler option necessary in addition to any needed to address the above issues is for full optimization usually O or some variant Some compilers have a standard optimization level
104. T but be aware that in the latter case the resulting velocity on the face or faces of the obstruction will be given by the specified VOLUME_FLUX divided by the area of that particular face For example SURF ID LOUVER VOLUME_FLUX 5 0 VEL_T 2 0 1 0 COLOR GREEN amp OBST XB SURF_ID6 BRICK LOUVER BRICK BRICK BRICK BRICK 45 dictates that the forward x facing surface of the obstruction is to have a velocity equal to 5 m s divided by the area of the face as approximated within FDS flowing into the computational domain Finally note that if HRRPUA or solid phase reaction parameters are specified no velocity should be prescribed The combustible gases are ejected at a velocity computed by the code As an example a simple blowing vent would be described by the line amp SURF ID BLOWER VEL 1 2 TMP_FRONT 50 The vent with SURF_ID BLOWER would blow 50 C air at 1 2 m s into the flow domain Making VEL positive would suck air out in which case TMP_FRONT would not be necessary At other times the user may wish that a specific flux of mass be added or removed at a vent This can be accomplished by specifying the quantity MASS_FLUX_TOTAL MASS_ FLUX_TOTAL uses the same sign convention as VEL In fact the value entered for MASS_FLUX_TOTAL is converted internally into a velocity boundary condition whose value for an outflow is adjusted based on the local density
105. T _HRR Real Heat release dump interval s At NFRAMES DT_ISOF Real Iso surface dump interval s At NFRAMES DT_MASS Real Mass diagnostic dump interval s At NFRAMES DT PART Real Particle dump interval s At NFRAMES DT_PL3D Real PLOT3D dump interval s At 5 DT_PROF Real Profile dump interval s At NFRAMES DT RESTART Real Restart core dump interval s 1000000 DT_SLCF Real Slice dump interval s At NFRAMES FLUSH_FILE_BUFFERS Logical Periodically empty file buffers TRUE ASS_FILE Logical Flag for species MASS file FALSE AXIMUM_DROPLETS Integer Max particles per mesh 500000 NFRAMES Integer Number of Frames of output data 1000 PLOT3D_QUANTITY 5 Char Quint Names of PLOT3D Quantities See Section 12 2 8 SMOKE 3D Logical Flag for 3D Smoke Visualization TRUE WRITE_XYZ Logical Flag for writing PLOT3D xyz file FALSE At T_END T_BEGIN 13 6 HEAD Header Parameters Table 13 6 For more information see Section 6 1 HEAD Header Parameters CHID Character Job Identification String output FYI Character Comment String has no effect TITLE Character Title for job 109 13 7 HOLE Obstruction Cutout Parameters Table 13 7 For more information see Section 7 2 HOLE Obstruction Cutout Parameters COLOR Character Color name of obstruction color CTRL_ID Character ID of ConTRoL to control hole s existence DEVC_ID Character ID of DEViCe to control hole s
106. VE_FRACTION on the RADI line a mesh cell cut by the flame radiates that fraction of the chemical energy being released into it Some of that energy may be reabsorbed elsewhere yielding a net radiative loss that is less than RADIATIVE_FRACTION T 71 depending mainly on the size of the fire and the soot loading If it is desired to use the radiation transport equation as is then RADIATIVE_FRACTION ought to be set to zero and the source term in the radiative transport equation is then based solely on the gas temperature and the chemical composition By default the RADIATIVE_FRACTION is 0 35 for an LES calculation and zero for DNS There are several ways to improve the performance of the Finite Volume Method in solving the radia tion transport equation RTE most of which increase the computation time The solver has two modes of operation a gray gas model default and a wide band model 1 Modifications to these models can be made via a namelist group called RADI If running in gray gas mode default increase the number of an gles from the default 100 with the integer parameter NUMBER_RADIATION_ANGLES The frequency of calls to the radiation solver can be reduced from every 3 time steps with integer TIME_STEP_INCREMENT The increment over which the angles are updated can be reduced from 5 with the integer ANGLE_INCREMENT Briefly if TIME_STEP_INCREMENT and ANGLE_INCREMENT are both set to 1 the radiation field is com pletely updat
107. Z mol mol D LP S CONTROL See Section 11 5 D CONVECTIVE_FLUX Section 12 3 5 kW m B D DENSITY p kg m D LPS DIVERGENCE V u s D ILP S DROPLET_DIAMETER 2ra um PA DROPLET_VELOCITY juz m s PA DROPLET_TEMPERATURE Ta C PA DROPLET_MASS Ma kg PA DROPLET_AGE ta s PA extinction coefficient K Section 12 3 2 1 m D I P S fuel Xr Z mol mol D I P S GAUGE_HEAT_FLUX See Section 12 3 5 kW m B D H H ul 2 p po m s D LPS HEAT FLOW See Section 12 3 8 kW D HEAT_FLUX See Section 12 3 5 kW m B D HRR fd dv kW D HRRPUV an kW m D LP S INCIDENT_HEAT_FLUX See Section 12 3 5 kW m B D INSIDE_WALL_TEMPERATURE See Section 12 2 4 C D AYER HEIGHT See Section 12 3 3 m D LINK TEMPERATURE See Section 11 3 3 C D OWER TEMPERATURE See Section 12 3 3 C D 103 Output QUANTITY Symbol Units File Type MASS FLOW See Section 12 3 8 kg s D MIXTURE_FRACTION Z kg kg D LBS nitrogen Xn Z mol mol D LBS oxygen Xo Z mol mol D I P S oxygen mass fraction Yo Z kg kg D LPS PART _ID _AMPUA See Section 12 3 6 kg m B D PART_ID _CPUA See Section 12 3 6 kW m B D PART_ID _FLUX_X See Section 12 3 6
108. _ID Likewise PART_ID _AMPUA is the Accumulated Mass Per Unit Area Both of these are given in units of kg m Think of these outputs as measures of the instantaneous mass density per unit area and the accumulated total respectively The accumulated total is analogous to a bucket test where the droplets are collected in buckets and the total mass determined at the end of a given time period The cooling of a solid surface by droplets of a given type is given by PART_ID _CPUA the Cooling Per Unit Area in units of kW m Be aware of the fact that the default behavior for droplets hitting the floor that is the plane z ZMIN is to disappear POROUS_FLOOR TRUE on the MISC line In this case PART_ID _MPUA will be zero but PART_ID _AMPUA will not FDS stores the droplet mass just before removing the droplet from the simulation for the purpose of saving CPU time Away from solid surfaces PART_ID _MPUV is the Mass Per Unit Volume of the droplets as they fly through the air in units of kg m PART_ID _FLUX_X PART_ID _FLUX_Y and PART_ID _FLUX_Z produce only slice and Plot3D files of the mass flux of droplets in the x y and z directions respectively in units of kg m s 12 3 7 Interfacing with Structural Models FDS solves a one dimensional heat conduction equation for each boundary cell marking the interface be tween gas and solid assuming that material properties for the material layer s are provided The
109. a leakage and duct paths There are several restrictions to assigning pressure zones First the pressure zones must be completely surrounded by obstructions an external boundary also suffices Second the obstructions cannot be re moved during the calculation In other words the door or window cannot suddenly fly open equivalently there must be no OPEN vents if one of the zone boundaries is an external boundary of the computational domain Third the pressure zones can span multiple meshes but check the pressure in each mesh to ensure consistency 8 3 1 Leaks The volume flow V through a leak of area Az is given by y lee 00 Vieak Az sign Ap 8 1 where Ap is the pressure difference between the adjacent compartments in units of Pa and p is the ambient density in units of kg m The discharge coefficient normally seen in this type of formula is assumed to be 1 Leakage is inherently a submesh scale phenomenon because the leakage area is usually very small In other words it is not possible to define a leak directly on the numerical mesh It is sometimes possible to lump the leaks into a single mesh resolvable hole but this is problematic for two reasons First the leakage area rarely corresponds neatly to the area of a single mesh cell sized hole Second the flow speeds through the hole can be large and cause numerical instabilities A better way to handle leakage is by exploiting pressure zones A pressure zone is a
110. a solid wall The DUCT_PATH defines the pressure ZONE downstream and upstream of the fan respectively The fan with ID BLOW LEFT for example blows air into ZONE 1 from ZONE 2 In more complicated scenarios it is possible to tie the fan behavior to disconnected compartments where it is assumed that a virtual duct connects the two spaces The HOLEs in the Partition Wall serve only to carve out space for the obstructions that represent the fans Note the obstructions have zero thickness as required by the POROUS surface The attribute PERMIT_HOLE FALSE tells FDS not to reject the obstructions because they are embedded within the Partition Wall 51 8 4 Describing Real Materials The MATL Namelist Group A solid boundary can consist of multiple layers of different materials and each layer can consist of multiple material components These combinations of layers and material components are specified on the SURF line via the array called MATL_ID IL IC The argument IL is an integer indicating the layer index starting at 1 the layer at the exterior boundary The argument IC is an integer indicating the component index For example MATL_ID 2 3 BRICK indicates that the third material component of the second layer is BRICK In practice the materials are often listed as in the following example amp MATL ID INSULATOR CONDUCTIVITY 0 041 SPECIFIC_HEAT 2 09 DENSITY
111. able Planetary Boundary Layers Journal of Atmospheric Sciences 29 91 115 1972 165 M Germano U Piomelli P Moin and W H Cabot A Dynamic Subgrid Scale Eddy Viscosity Model Physics of Fluids A 3 7 1760 1765 1991 165 D K Lilly A Proposed Modification of the Germano Subgrid Scale Closure Method Physics of Fluids A 4 3 633 635 1992 165 J Hietaniemi S Hostikka and J Vaari FDS Simulation of Fire Spread Comparison of Model Results with Experimental Data VTT Working Paper 4 VTT Building and Transport Espoo Finland 2004 166 C Lautenberger G Rein and C Fernandez Pello The application of a genetic algorithm to estimate the material properties for fire modeling from bench scale fire test data Fire Safety Journal 41 204 214 2006 167 182 Index 2D Calculations 25 atmospheric stratification 47 Axially Symmetric Calculations 25 baroclinic torque 32 BNDF 96 QUANTITY 96 boundary conditions 43 44 boundary layer 46 CLIP 35 CO Production 68 Colors 62 Controls 88 Create and Remove Obstructions 85 Function List 88 Using DEVC 85 CTRL 88 DELAY 89 FUNCTION_TYPE 88 ALL 89 ANY 89 AT_LEAST 89 CUSTOM 90 DEADBAND 89 KILL 90 ONLY 89 RESTART 90 TIME_DELAY 89 ID 88 INITIAL_STATE 89 INPUT_ID 88 LATCH 88 N 89 ON_BOUND 89 RAMP_ID 90 SETPOINT 89 DEVC 79 BYPASS_FLOWRATE 84 DELAY 84 FLOWRATE 84 ID 79 IOR 79 ORIENTATION 79 PROP_ID 79 QUANTITY
112. aland Vili Csaba Szilagyi Szolnok Fire Department Hungary Charlie Thornton Thunderhead Engineering USA Sebastian Ukleja University of Ulster Northern Ireland Giacomo Villi Dipartimento Fisica Tecnica DfT UNIPd Italy Andreas Vischer RWTH Aachen University Germany Karl Wallasch Hoare Lea Fire Engineering UK Kaoru Wakatsuki National Research Institute of Fire and Disaster Japan Yang Shan You State Key Laboratory of Fire Science China Robin Zevotek C amp S Engineers Life Safety Services Syracuse New York USA GIDAI University of Cantabria Spain 1x Contents Preface Disclaimer About the Authors Acknowledgments II Running FDS Introduction Li Features of FDS a co wad a Ge oct e be at lee wd es che a ei Rn doe he oe 12 Whats Newin PDS r anrea Pd Hale es be he ba a Se ae BS ad Hae eS Getting Started 2 1 How to Acquire FDS and Smokeview 0 000 ee eee ee eee 2 2 Computer Hardware Requirements 2 2 2 2 2 0 eee eee ee eee 2 3 Computer Operating System OS and Software Requirements Running FDS 3 1 Starting an FDS Calculation s cos e e mens ee ee er ed leas 3 1 1 Starting an FDS Calculation Single Processor Version 3 1 2 Starting an FDS Calculation Multiple Processor Version 3 2 Monitoring Progress e vse ed swm ansi a BE a a O E User Support 41 The Versio
113. alculated The default is TRUE SUPPRESSION A logical parameter indicating whether FDS should include gas phase flame extinction The default is TRUE SURF_DEFAULT The SURF line that is to be applied to all boundaries unless otherwise specified The default is INERT TMPA Ambient temperature the temperature of everything at the start of the simulation The default is 20 C U0 VO WO Initial values of the gas velocity in each of the coordinate directions Normally these are all 0 m s but there are a few applications where it is convenient to start the flow immediately like in an outdoor simulation involving wind 6 4 1 Stopping and Restarting Calculations An important MISC parameter is called RESTART Normally a simulation consists of a sequence of events starting from ambient conditions However there are occasions when you might want to stop a calculation make a few limited adjustments and then restart the calculation from that point in time To do this first bring the calculation to a halt gracefully by creating a file called CHID stop in the directory where the 31 output files are located Remember that FDS is case sensitive The file name must be exactly the same as the CHID and stop should be lower case FDS checks for the existence of this file at each time step and if it finds it gracefully shuts down the calculation after first creating a final Plot3D file and a file or fi
114. ally upon activation of a heat detector is a feature of FDS commonly used in the fire protection engineering community but less so at NIST As a result numerous reports have been made over the years in which a complicated sequence of events prescribed by the user is not carried out by the program The errors are easy to fix but the number of possible permutations of events make it difficult to check them all Another problem reported by users are scenarios that extend the parameter range beyond which the model was originally conceived Walls made of foam fires in refrigerators gas leaks fuel spills etc are just some of the phenomena that users have attempted to model but have run into difficulty because the model parameters either have never been exercised e g very low thermal conductivities or are not allowed e g temperatures below ambient These reports by the users help to improve and extend the use of the model 15 3 Numerical Tests Numerical techniques used to solve the governing equations within a model can be a source of error in the predicted results The hydrodynamic model within FDS is second order accurate in space and time This means that the error terms associated with the approximation of the spatial partial derivatives by finite differences is of the order of the square of the grid cell size and likewise the error in the approximation of the temporal derivatives is of the order of the square of the time step As the numerica
115. alues meaning that they are computed on a numerical grid The other diffusive parameters the thermal conductivity and material diffusivity are related to the turbulent viscosity by _ Mes C Kies oe gt PD ies Sc 6 5 The turbulent Prandtl number Pr and the turbulent Schmidt number Sc are assumed to be constant for a given scenario Although it is not recommended for most calculations you can modify C 0 2 Pr 0 5 and Sc 0 5 via the parameters CSMAG PR and SC on the MISC line A more detailed discussion of these parameters is given in the FDS Technical Reference Guide 1 6 4 6 Special Topic Numerical Stability Parameters The time step of an FDS simulation is constrained by the convective and diffusive transport speeds via two conditions The first is known as the Courant Friedrichs Lewy CFL condition The CFL condition asserts that the solution of the equations cannot be updated with a time step larger than that which would allow a 33 parcel of fluid to travel further than a single mesh cell In each mesh cell of dimension 6x by dy by 6z with velocity components u v and w the CFL number is defined u v wl CFL t max 6 6 5 dy z a Every time step the CFL number is computed in each mesh cell and the time step t is adjusted if the maximum value of the CFL number is not between CFL_MIN and CFL_MAX whose default values are 0 8 and 1 0 respectively These values are included in t
116. amics e e a a eg ae Bee ee eS ee a aoa ee weak a Gok ase 135 16 1 1 Axially Symmetric Helium Plume helium_2d 135 16 1 2 Pressure Rise in a Sealed Enclosure pressure_rise 136 16 1 3 Leaks and Fans in a Sealed Enclosure leak_test and leak_test_2 137 16 1 4 Two Fans in a Wall fan_test 138 16 1 5 Stack Effect stack effect cos ba iia da be ae be eae hb 139 16 1 6 Sawtooth sawtooth aaa aaa 140 16 2 Combustion Be dca 141 16 2 1 A Simple Under Ventilated Compartment Fire door_crack 141 163 Radiation A soeone wa ae ea fed ow eed ee ha Ba aS Phe RG ak Pw Le Dares 142 16 3 1 Radiation inside a box radiation_in_a_box 0 4 142 16 3 2 Radiation from a plane layer radiation_plane_layer 143 16 4 Solid Phase Phenomena a soe s a ma cca ta ka eg e aoea ka ee 144 16 4 1 Simple Heat Conduction Through a Solid Slab heat_conduction 144 16 4 2 Temperature Dependent Thermal Properties heat_conduction_kc 145 16 4 3 A Simple Two Step Pyrolysis Example two_step_solid_reaction 146 16 4 4 Wall Internal Radiation wall_internal_radiation 147 16 4 5 A Liquid Pool Fire ethanol_pan o e 148 16 4 6 A Thermoplastic thermoplastic o o o eee 149 16 4 7 A Charring Solid charring solid o o 150 16 4 8 Testi
117. amp SURF ID wood paneling TEXTURE_MAP paneling jpg TEXTURE_WIDTH 1 TEXTURE_HEIGHT 2 Assuming that a JPEG file called paneling jpg exists in the working directory Smokeview should read it and display the image wherever the paneling is used SGI Users use rgb files instead of jpg Note that the image does not appear when Smokeview is first invoked It is an option controlled by the Show Hide menu The parameters TEXTURE_WIDTH and TEXTURE_HEIGHT are the physical dimensions of the image In this case the JPEG image is of a 1 m wide by 2 m high piece of paneling Smokeview replicates the image as often as necessary to make it appear that the paneling is applied where desired Consider carefully how the image repeats itself when applied in a scene If the image has no obvious pattern there is no problem with the image being repeated If the image has an obvious direction the real triplet TEXTURE_ORIGIN should be added to the VENT or OBST line to which a texture map should be applied For example amp OBST XB 1 0 2 0 3 0 URF_ID wood paneling TEXTURE_ORIGIN 7420750274078 1 0 3 0 5 0 applies paneling to an obstruction whose dimensions are 1 m by 1 m by 2 m such that the image of the paneling is positioned at the point 1 0 3 0 5 0 The default value of TEXTURE_ORIGIN is 0 0 0 and the global default can be changed by added a TEXTURE_ORIGIN stat
118. ample below the parameter N is used to specify the number of activated or TRUE inputs required for the conditions of the Control Function to be satisfied The control function amp CTRL ID SD FUNCTION_TYPE ONLY N 3 INPUT_ID SD_1 SD_2 SD_3 SD_4 changes the state from FALSE to TRUE when 3 and only 3 detectors activate 11 5 2 Control Function TIME_DELAY There is often a time delay between when a device activates and when some other action occurs like in a dry pipe sprinkler system amp DEVC XYZ 2 2 3 PROP_ID Acme Sprinkler_link QUANTITY LINK TEMPERATURE ID Spk_29_link CTRL_ID dry pipe amp DEVC XYZ 2 2 3 PROP_ID Acme Sprinkler QUANTITY CONTROL ID Spk_29 CTRL_ID dry pipe CTRL ID dry pipe FUNCTION_TYPE TIME_DELAY INPUT_ID Spk_29_link DELAY 30 This relationship between a sprinkler and its pipes means that the sprinkler spray is controlled in this case delayed by the dry pipe which adds 30 s to the activation time of Spk_29 measured by Spk_29_link before water can flow out of the head 11 5 3 Control Function DEADBAND For an HVAC example the following lines of input would set up a simple thermostat SURF ID FAN TMP_FRONT 40 VOLUME_FLUX 1 amp VENT XB 0 3 0 3 0 3 0 3 0 0 0 0 SURF_ID FAN CTRL_ID thermostat amp DEVC ID TC XYZ 2 4 5 7 3 6 QUANTITY TEMPERATU
119. an be redirected to a file via the alternative command fds5 job_name fds gt job_name err Mac OS X Unix Linux Depending on the type of installation you may need to set various path or environment variables in order to invoke FDS without a full path reference to the executable The easiest way to do this is via an alias in your shell start up script For the example below it is assumed that fds5 is aliased to its full path name You may also need to chmod x to make the file executable Once this is done run FDS from the command line by typing fds5 job_name fds The input parameters are read from the file job_name fds and error statements and other diagnostics are written out to the screen To run the job in the background fds5 job_name fds gt amp job_name err amp Note that in the latter case the screen output is stored in the file job_name err and the detailed di agnostics are saved automatically in a file CHID out where CHID is a character string usually the same as job_name designated in the input file It is preferable to run jobs in the background so as to free the console for other uses 3 1 2 Starting an FDS Calculation Multiple Processor Version Running FDS across a network using multiple processors and multiple banks of memory RAM is more difficult than running the single processor version More is required of the user to make the connections between the machines as seamless as possible This i
120. aracter output quantity WRITE LUPF UDATA PCSQUANTITIES_INDEX NN 30 character output units ENDDO ENDDO Every DT_PART seconds the coordinates of the particles and droplets are output as 4 byte reals WRITE LUPF REAL T FB Write out the time T as a 4 byte real WRITE LUPF NPLIM Number of particles to write out for this time step WRITE LUPF XP I I 1 NPLIM YP 1 1 1 NPLIM ZP 1 1 1 NPLIM WRITE LUPF TA I I 1 NPLIM Integer tag for each particle IF PCSN_QUANTITIES gt 0 WRITE LUPF QP 1I NN I 1 NPLIM NN 1 PCSN_QUANTITIES The particle tag is used by Smokeview to keep track of individual particles and droplets for the purpose of drawing streamlines It is also useful when parsing the file The quantity data OP I NN is used by Smokeview to color the particles and droplets Note that it is now possible with the new format to color the particles and droplets with several different quantities 19 10 Profile Files The profile files defined under the namelist group PROF are named CHID_prof_mn csv nn 01 02 and are written out formatted These files are written out from dump f with the following line WRITE LU_PROF T NWP 1 X_S I I 0 NWP Q I I 0 NWP 177 After the time T the number of node points is given and then the node coordinates These are written out at every time step because the wall thickness and the local solid phase me
121. are cross section with a separate heat transfer calculation performed at each face and no communication among the four faces Obviously this is not an ideal way to do solid phase heat transfer but it does provide a reasonable bounding surface temperature for the gas phase calculation More detailed assessment of a cable would require a two or three dimensional heat conduction calculation which is not included in FDS Use GEOMETRY SPHERICAL to describe a spherical object 48 8 3 Pressure Related Effects The ZONE Namelist Group Table 13 26 The basic FDS equation set assumes pressure to be composed of a background component p z t plus a perturbation p x f Most often p is just the hydrostatic pressure and is the flow induced pressure field that FDS calculates at each time step Originally FDS v 1 4 it was possible to create a single sealed compartment whose walls conformed to the exterior of the computational domain A fire or fan could increase or decrease the background pressure in this single compartment and a leakage area could be defined between the compartment and the ambient exterior Flow through the cracks was simply a function of the background pressure via the usual empirical rules This idea has been generalized starting in FDS 5 Now you can specify any number of sealed portions of the computational domain to have their own background pressures and these zones can be connected vi
122. aries near the edges of the obstructions one may specify the option SAWTOOTH FALSE If SAWTOOTH is set to FALSE then the velocity boundary conditions will be applied in such a way as to minimize the impact of the boundaries due to vortices at sharp corners as shown in the following example amp OBST XB 0 00 0 05 0 01 0 01 0 00 0 05 SAWTOOTH FALSE COLOR EMERALD GREEN amp OBST XB 0 05 0 10 0 01 0 01 0 00 0 10 SAWTOOTH FALSE COLOR EMERALD GREEN amp OBST XB 0 10 0 15 0 01 0 01 0 05 0 15 SAWTOOTH FALSE COLOR EMERALD GREEN amp OBST XB 0 15 0 20 0 01 0 01 0 10 0 20 SAWTOOTH FALSE COLOR EMERALD GREEN In the figure below the top set of obstructions are using the default SAWTOOTH TRUE and the bottom set of obstructions are using SAWTOOTH FALSE The adjacent obstructions that have SAWTOOTH FALSE are displayed in Smokeview as one smooth obstruction shown in green Notice that as the air moves across the different sets of obstructions the air velocity on the bottom set of obstructions is not affected as much by the vortices 140 16 2 Combustion 16 2 1 A Simple Under Ventilated Compartment Fire door_crack This example uses the same simple compartment that was used to test leakage and fan curves in the previous section Now we add a small 160 kW fire with the same fan and leak under the door The compartment now opens to the atmosphere not a sealed plenum We expect a rapid press
123. ash Each are input via MATL lines as follows amp SURF ID SPRUCE STRETCH_FACTOR 1 CELL_SIZE_FACTOR 0 5 MATL_ID 1 1 3 CELLULOSE WATER LIGNIN MATL_MASS_FRACTION 1 1 3 0 70 0 1 0 20 MATL_ID 2 1 CASI THICKNESS 1 2 0 01 0 01 EXTERNAL_FLUX 50 amp MATL ID CELLULOSE CONDUCTIVITY_RAMP k_cell SPECIFIC_HEAT 23 DENSITY 400 N_REACTIONS 1 A 2 8E19 E 2 424E5 HEAT_OF_REACTION 0 NU_RESIDUE 1 0 RESIDUE ACTIVE amp MATL ID ACTIVE EMISSIVITY 1 0 CONDUCTIVITY_RAMP k_cell SPECIFIC_HEAT 2 3 DENSITY 400 N_REACTIONS 2 A 1 2 1 3E10 3 23514 E 1 2 1 505E5 1 965E5 HEAT_OF_REACTION 1 2 418 418 NU_RESIDUE 1 2 0 35 0 0 NU_FUEL 1 2 0 65 1 50 RESIDUE 1 CHAR amp MATL ID WATER EMISSIVITY 1 0 DENSITY 1000 CONDUCTIVITY 0 6 SPECIFIC_HEAT 4 19 N_REACTIONS 1 A 1E20 E 1 62E 05 NU_WATER 1 0 HEAT_OF_REACTION 2260 amp MATL ID CASI CONDUCTIVITY_RAMP k_CASI DENSITY 200 SPECIFIC_HEAT 1 0 amp MATL ID LIGNIN EMISSIVITY 1 0 DENSITY 550 CONDUCTIVITY 0 1 SPECIFIC_HEAT 1 1 amp MATL ID CHAR EMISSIVITY 1 0 DENSITY 140 CONDUCTIVITY_RAMP k_char SPECIFIC_HEAT 1 1 150 amp RAMP ID k_cell amp RAMP ID k_cell amp RAMP ID k_char G amp RAMP ID k_char amp RAMP ID k_CASI amp RAMP ID k_CASI Note the edition of the paramet
124. ass flux of species To obtain a guaranteed mass flux of a species you should use MASS_FLUX N 8 2 5 Special Topic Fires and Flows in the Outdoors Simulating a fire in the outdoors is not much different than a fire indoors but there are a few issues that need to be addressed First the velocity of the wind profile at any exterior boundary will be a top hat constant by default but the parameter PROFILE on the SURF line can yield other profiles For exam ple PROFILE PARABOLIC produces a parabolic profile with VEL being the maximum velocity and ATMOSPHERIC produces a typical atmospheric wind profile of the form u uy z z0 If an atmospheric profile is prescribed also prescribe Z0 for zo and PLE for p VEL specifies the reference velocity ug Gl Another useful parameter for outdoor simulations is the temperature lapse rate of the atmosphere Typ ically in the first few hundred meters of the atmosphere the temperature decreases several degrees Celsius per kilometer These few degrees are important when considering the rise of smoke since the temperature of the smoke decreases rapidly as it rises The LAPSE_RATE of the atmosphere can be specified on the MISC line in units of C m A negative sign indicates that the temperature decreases with height This need only be set for outdoor calculations where the height of the domain is tens or hundreds of meters The default value of the LAPSE_RATE is 0 C m
125. assumption will affect the plume behavior if the boundary of the computational domain is too close to the plume lerardi and Barnett 43 used FDS version 3 to model a 0 3 m square methane diffusion burner with heat release rate values in the range of 14 4 kW to 57 5 kW The physical domain used was 0 6 m by 0 6 m with uniform grid spacings of 15 10 7 5 5 3 1 5 cm for all three coordinate directions For both fire sizes a grid spacing of 1 5 cm was found to provide the best agreement when compared to McCaffrey s centerline plume temperature and velocity correlations 44 Two similar scenarios that form the basis for Alpert s ceiling jet correlation were also modeled with FDS The first scenario was a 1 m by 1 m 670 kW ethanol fire under a 7 m high unconfined ceiling The planar dimensions of the computational domain were 14 m by 14 m Four uniform grid spacings of 50 33 3 25 and 20 cm were used in the modeling The best agreement for maximum ceiling jet temperature was with the 33 3 cm grid spacing The best agreement for maximum ceiling jet velocity was for the 50 cm grid spacing The second scenario was a 0 6 m by 0 6 m 1000 kW ethanol fire under a 7 2 m high unconfined ceiling The planar dimensions of the computational domain were 14 4 m by 14 4 m Three uniform grid spacings of 60 30 and 20 cm were used in the modeling The results show that the 60 cm grid spacing exhibits the best agreement with the correlations for both maximum ceiling je
126. ation try running the case with a modest sized mesh and gradually make refinements until the computer can no longer handle it Then back off somewhat on the size of the calculation so that the computer can comfortably run the case Trying to run with 90 to 100 of computer resources is risky In fact for a typical Windows PC with 4 GB RAM only 2 GB will be available to FDS based on user feedback 14 Run Time Errors An error occurs either within the computer operating system or the FDS program An error message is printed out by the operating system of the computer onto the screen or into the diag nostic output file This message is most often unintelligible to most people including the programmers although occasionally one might get a small clue if there is mention of a specific problem like stack overflow divide by zero or file write error unit These errors may be caused by a bug in FDS for example if a number is divided by zero or an array is used before it is allocated or any number of other problems Before reporting the error to the SourceForge Support Tracker try to systematically simplify the input file until the error goes away This process usually brings to light some feature of the calculation responsible for the problem and helps in the debugging Poisson Initialization Sometimes at the very start of a calculation an error appears stating that there is a problem with the Poisson initialization
127. ausing the time step size to decrease to a point where logic in the code decides that the results are unphysical and stops the calculation with an error message in the file CHID out In these cases FDS ends by dumping out one final Plot3D file giving the user some means by which to see where the error is occurring within the computational domain Usually a numerical instability can be identified by fictitiously large velocity vectors emanating from a small region within the domain Common causes of such instabilities are mesh cells that have an aspect ratio larger than 2 to 1 high speed flow through a small opening a sudden change in the heat release rate or any number of sudden changes to the flow field There are various ways to solve the problem depending on the situation Try to diagnose and fix the problem before reporting it It is difficult for anyone but the originator of the input file to diagnose the problem Inadequate Computer Resources The calculation might be using more RAM than the machine has or the output files could have used up all the available disk space In these situations the computer may or may not produce an intelligible error message Sometimes the computer is just unresponsive It is the user s responsibility to ensure that the computer has adequate resources to do the calculation Remember there is no limit to how big or how long FDS calculations can be it depends on the resources of the computer For any new simul
128. been for design of smoke handling systems and sprinkler detector activation studies The other half consist of residential and industrial fire reconstructions Throughout its development FDS has been aimed at solving practical fire problems in fire protection engineering while at the same time providing a tool to study fundamental fire dynamics and combustion Hydrodynamic Model EDS solves numerically a form of the Navier Stokes equations appropriate for low speed thermally driven flow with an emphasis on smoke and heat transport from fires The core algo rithm is an explicit predictor corrector scheme second order accurate in space and time Turbulence is treated by means of the Smagorinsky form of Large Eddy Simulation LES It is possible to perform a Direct Numerical Simulation DNS if the underlying numerical mesh is fine enough LES is the default mode of operation Combustion Model For most applications FDS uses a single step chemical reaction whose products are tracked via a two parameter mixture fraction model The mixture fraction is a conserved scalar quantity that represents the mass fraction of one or more components of the gas at a given point in the flow field By default two components of the mixture fraction are explicitly computed The first is the mass fraction of unburned fuel and the second is the mass fraction of burned fuel i e the mass of the combustion products that originated as fuel A two step chemical reaction with
129. bility through smoke can be made by using the equation S C K 12 8 where C is a nondimensional constant characteristic of the type of object being viewed through the smoke i e C 8 fora light emitting sign and C 3 for a light reflecting sign 8 Since K varies from point to point in the domain the visibility S does as well Keep in mind that FDS can only track smoke whose production rate and composition are specified Predicting either is beyond the capability of the present version of the model Three parameter control smoke production and visibility each parameter is input on the REAC line The first parameter is SOOT_YIELD which is the fraction of fuel mass that is converted to soot The second parameter is called the MASS_EXTINCTION_COEFFICIENT and it is the Km in Eq 12 7 The default value is 8700 m kg a value suggested for flaming combustion of wood and plastics The third parameter is called the VISIBILITY_FACTOR the constant C in Eq 12 8 It is 3 by default The gas phase output quantity extinction coefficient is K The visibility S is output via the keyword visibility Note that each is tied to the mixture fraction formulation of combustion 12 3 3 Layer Height and the Average Upper and Lower Layer Temperatures Fire protection engineers often need to estimate the location of the interface between the hot smoke laden upper layer and the cooler lower layer in a burning compartment Relatively simple fire m
130. bles Currently only sprinklers and nozzles use this group of parameters to define a complex spray pattern Note that each set of TABL lines must have a unique ID Specific requirements on ordering the lines will depend upon the type of TABL and those requirements are provided in the appropriate section in this guide 61 8 6 Coloring Obstructions Vents Surfaces and Meshes Colors for many items within FDS can be prescribed in two ways a triplet of integers after keyword RGB or one of many COLOR name character strings The three RGB integer numbers range from 0 to 255 indicating the amount of Red Green and Blue that make up the color If you define the COLOR by name it is important that you type the name EXACTLY as it is listed in the color tables here in this document and on the FDS website Table 8 1 provides a small sampling of RGB values and COLOR names for a variety of colors A complete listing of all 500 colors that can be specified by name after the COLOR keyword is available on the FDS website If the COLOR name is not listed in the table on the website then that name does not exist to FDS It is highly recommended that colors be assigned to surfaces via the SURF line because as the geometries of FDS simulations become more complex it is very useful to use color as a spot check to determine if the desired surface properties have been assigned throughout the room or building under study For example if you desire that
131. can be found in Section 9 1 1 T 72 Chapter 10 Particles and Droplets The PART Namelist Group Lagrangian particles are used in FDS as water or liquid fuel droplets flow tracers and various other objects that are not defined or confined by the numerical mesh Sometimes the particles have mass sometimes they do not Some evaporate absorb radiation etc PART is the namelist group that is used to prescribe parameters associated with Lagrangian particles All Lagrangian particles must be explicitly defined via the PART namelist group In versions of FDS prior to 5 water droplets and smoke particles were implicitly defined Shortcuts for defining water droplets and smoke particles are possible via parameters like WATER TRUE and MASSLESS TRUE 10 1 Basics Properties of different types of Lagrangian particles are designated via the PART namelist group Much like SURF lines contain the properties of a solid surface or vent PART lines contain information about particles and droplets Once a particular type of particle or droplet has been described using a PART line then the name of that particle or droplet type is invoked elsewhere in the input file via the parameter PART_ID There are no reserved PART_IDs all must be defined For example an input file may have several PART lines that include
132. cket_test A common way of measuring the spray distribution for any fire sprinkler is called a bucket test Usually one or several sprinklers is mounted a specified distance above an array of catch bins the water flows for a given period of time and the water flux distribution is calculated from the accumulated water mass in each bin In the test case bucket_test a single sprinkler is mounted 10 cm below a 5 m ceiling Water flows for 5 s at a constant rate of 60 L min The simulation continues for another 5 s to allow water drops time to reach the floor The total mass of water discharged is L kg 1 min MA L x 2 z x5s 5kg 16 13 In the simulation the boundary quantity water_drops_AMPUA Accumulated Mass Per Unit Area records the total water mass per unit area kg m analogous to actual buckets the size of a grid cell Summing the values Of water_drops_AMPUA over the entire floor yields 4 96 kg Where is the missing water Some droplets evaporate and some droplets fly beyond the computational domain Also there remain a small number of suspended drops at the end of the simulation Note that there are no actual buckets in the simulation The accumulated water mass at the floor is extracted from the boundary BNDF file via the command line program fds2ascii Here is a transcript of the session used to convert the binary FDS output file into ASCII format gt gt fds2ascii Enter Job ID string CHID bucket_test What type
133. collection of Verification and Validation cases This improves the quality of each FDS update and release as a standard test suite will now be used to insure that changes made to the source code do not degrade FDS output This also provides users with a standard data set to verify their own installation of FDS and to compare the results that FDS is returning on their system to published data Chapter 2 Getting Started FDS is a computer program that solves equations that describe the evolution of fire It is a Fortran program that reads input parameters from a text file computes a numerical solution to the governing equations and writes user specified output data to files Smokeview is a companion program that reads FDS output files and produces animations on the computer screen Smokeview has a simple menu driven interface FDS does not However there are various third party programs that have been developed to generate the text file containing the input parameters needed by FDS This guide describes how to obtain FDS and Smokeview and how to use FDS A separate document 2 describes how to use Smokeview Other tools related to FDS and Smokeview can be found at the web site 2 1 How to Acquire FDS and Smokeview Detailed instructions on how to download executables manuals source code and related utilities can be found on the FDS SMV Website http fire nist gov fds for more information The typical FDS Smokeview distribution consists of an
134. ctangular cells the number of which depends on the desired resolution of the flow dynamics MESH is the namelist group that defines the computational domain A mesh is a single right parallelepiped i e a box The coordinate system within a mesh conforms to the right hand rule The origin point of a mesh is defined by the first third and fifth values of the real number sextuplet xB and the opposite corner is defined by the second fourth and sixth values For example amp MESH IJK 10 20 30 XB 0 0 1 0 0 0 2 0 0 0 3 0 defines a mesh that spans the volume starting at the origin and extending 1 m in the positive x direction 2 m in the positive y direction and 3 m in the positive z direction The mesh is subdivided into uniform cells via the parameter IJK In this example the mesh is divided into 10 cm cubes If it is desired that the mesh cells in a particular direction not be uniform in size then the namelist groups TRNX TRNY and or TRNZ may be used to alter the uniformity of the mesh See Section 6 3 3 Any obstructions or vents that extend beyond the boundary of the mesh are cut off at the boundary There is no penalty for defining objects outside of the mesh and these objects will not appear in Smokeview either Note that it is best if the mesh cells resemble cubes that is the length width and height of the cells ought to be roughly the same Because an important part of the calculation uses a Poisson solver based
135. ction Parameters 2 2 ee 118 13 JOREAG Reaction Parameters io a ware a ee ee a ee 119 13 20SLCF Slice File Parameters a s 2402 4 624 2 ad A we dd 120 IZ 21SPEC Species Parameters oa s 0d dn a we ee ee ee ee e de 120 13 22 SURF Surface Properties s o 2 sii a abissi ers eae eee ee Ee a aes 121 13 23 TABL Table Parameters as oaa 4 aa olka aeons Radom a eA Moa AG eA aA 122 18 24 TIME Time Parameters 04 244 da sac a Ra bd a BO al we aS 122 13 25TRNX TRNY TRNZ MESH Transformations 0000008 123 IS 26VENT Vent Parameters ula era dd OA eae SW we A ee 123 13 27 ZONE Pressure Zone Parameters cubas ka Ba bad ba ee be ee Ye a 124 XIV 14 Conversion of Old Input Files to FDS 5 125 14 1 Numerical Domain Parameters GRID and PDIM 125 14 2 Obstructions Vents and Holes OBST VENT and HOLE 125 14 3 Surface Parameters SURE asc 4 Goo aise a a ace bare AR ad he A wR BR ere 125 14 4 Reaction Parameters REAG wc s a m in eie eR ee ee ee A A A E 126 14 5 Device Parameters SPRK SMOD HEAT THCP 127 TI Sample Cases and Verification 129 15 Forms of Verification 131 15 1 Comparison with Analytical Solutions o ee eee 131 15 2 Cade Checking 2 0 22 5446 sms ad a ed Ae a hea A 132 15 35 Numerical Tests cc dee og kee Ree on Se ss bo we a ena e 134 16 Verification Test Suite 135 16 1 Hydrodyn
136. ctions and p are the material bulk densities defined on the MATL lines In the example above the resulting density of the wall would be about 1553 kg m The fact that the wall 52 density is smaller than the density of pure brick may be confusing but can be explained easily If the wall can contain water the whole volume of the wall can not be pure brick Instead there are voids pores that are filled with water If the water is taken away there is only about 1476 kg m of brick left To have a density of 1600 kg m for a partially void wall a higher density should be used for the pure brick 8 4 1 Thermal Properties T For any solid material specify its thermal CONDUCTIVITY W m K DENSITY kg m SPECIFIC_HEAT kJ kg K and EMISSIVITY 0 9 by default Both CONDUCTIVITY and SPECIFIC_HEAT can be functions of temperature DENSITY and EMISSIVITY cannot Temperature dependence is specified using the RAMP convention As an example consider marinite a wall material suitable for high temperature applications amp MATL ID MARINITE EMISSIVITY 0 8 DENSITY 737 SPECIFIC_HEAT_RAMP c_ramp CONDUCTIVITY_RAMP k_ramp amp RAMP ID k_ramp T 24 F 0 13 amp RAMP ID k_ramp T 149 F 0 12 amp RAMP ID k_ramp T 538 F 0 12 amp RAMP ID c_ramp T 93 F 1 172 amp RAMP ID c_ramp T 205 F 1 255 amp RAMP ID c_ramp T 316 F 1 339 amp RAMP
137. cular boundary condition to a rectangular patch on a solid surface A fire for example is usually created by first generating a solid obstruction via an OBST line and then specifying a VENT somewhere on one of the faces of the solid with a SURF_ID with the characteristics of the thermal and combustion properties of the fuel For example the lines amp OBST XB 0 0 5 0 2 0 3 0 0 0 4 0 SURF_ID big block amp VENT XB 1 0 2 0 2 0 2 0 1 0 3 0 SURF_ID hot patch specify a large obstruction with the properties given elsewhere in the file under the name big block with a patch applied to one of its faces with alternative properties under the name hot patch This latter surface property need not actually be a vent like a supply or return duct but rather just a patch with different boundary conditions than those assumed for the obstruction Note that the surface properties of a VENT over ride those of the underlying obstruction Unlike previous versions of FDS you can no longer specify a free standing fan using the VENT construct A VENT must always be attached to a solid obstruction See Section 8 3 for instructions on specifying different types of fans An easy way to specify an entire external wall is to replace XB with MB Mesh Boundary a character string whose value is one of the following XMAX XMIN YMAX YMIN ZMAX or ZMIN denoting the
138. d name is the same This is convenient when developing an input file because you save on disk space Just be careful not to overwrite a calculation that you want to keep 5 2 Namelist Formatting Parameters are specified within the input file by using namelist formatted records Each namelist record begins with the ampersand character followed immediately by the name of the namelist group then a comma delimited list of the input parameters and finally a forward slash For example the line amp DUMP NFRAMES 1800 DT_HRR 10 DT_DEVC 10 DT_PROF 30 sets various values of parameters contained in the DUMP namelist group The meanings of these various parameters will be explained in subsequent chapters The namelist records can span multiple lines in the input file but just be sure to end the record with a or else the data will not be understood Do not add anything to a namelist line other than the parameters and values appropriate for that group Otherwise FDS will stop immediately upon execution Parameters within a namelist record can be separated by either commas spaces or line breaks It is a good idea to use commas or line breaks Some machines do not recognize the spaces Comments and notes can be written into the file so long as nothing comes before the amp except a space and nothing comes between the ampersand amp and the slash except appropriate parameters corresponding to that particular namelist
139. d valuable feedback on how to improve the functionality of the model in the area of forensic science Paul Hart of Swiss Re GAP Services and Pravinray Gandhi of Underwriters Laboratories provided useful suggestions about water droplet transport on solid objects Finally on the following pages is a list of individuals and organizations who have volunteered their time and effort to beta test FDS and Smokeview prior to its official release Their contribution is invaluable because there is simply no other way to test all of the various features of the model vii FDS 5 Beta Testers Nick Agnew Maunsell Australia Camille Azzi Universities of Glasgow and Strathclyde Scotland Matthew Bilson Maunsell Australia George Braga Federal District Fire Department Brazil Keith Calder Senez Reed Calder Engineering Canada Steven Chi Heng Lam Hoare Lea Fire Engineering UK Doo Chan Choi Rolf Jensen amp Associates Inc USA Marco Cigolini Italferr spa Italy John Cutonilli Hughes Associates Inc USA Sylvain Desanghere CTICM Centre Technique Industriel de la Construction M tallique France Montu L Das Gage Babcock amp Associates USA and Canada Franck Didieux Laboratoire National de M trologie et d Essais LNE France Johannes Dimyadi AstraVision Solutions New Zealand Bill Ferrante Roosevelt Fire District USA Paul Fuss NIST USA Andrea
140. ded financial support for the maintenance and de velopment of FDS along with valuable insights into how fire models are used as part of probabilistic risk assessments of nuclear facilities Special thanks to Mark Salley and Jason Dreisbach of NRC and Francisco Joglar of SAIC The Society of Fire Protection Engineers SFPE sponsors a training course on the use of FDS and Smokeview Chris Wood of ArupFire Dave Sheppard of the US Bureau of Alcohol Tobacco and Firearms ATF and Doug Carpenter of Combustion Science and Engineering developed the materials for the course along with Morgan Hurley of the SFPE Prof David McGill of Seneca College Ontario Canada has conducted a remote learning course on the use of FDS and he has also maintained a web site that has provided valuable suggestions from users Thanks to Chris Lautenburger and Carlos Fernandez Pello for their assistance with the two reaction test case Thanks to Ian Thomas Khalid Moinuddin and Ian Bennetts for their description of and data for the ethanol pan fire example Prof lan Thomas of Victoria University has also presented short courses on the use Of EDS in Australia His students have also performed some validation work on compartment fires Prof Charles Fleischmann and his students at the University of Canterbury New Zealand have provided valuable assistance in improving the documentation and usability of the model James White Jr of the Western Fire Center has provide
141. e MESH line is a solid wall To change this use an OPEN vent as if it were an open door or window To create a totally or partially open domain use OPEN vents on the exterior mesh boundaries MBs By default it is assumed that ambient conditions exist beyond the OPEN vent However in some cases you may want to alter this assumption for example the temperature If you assume a temperature other than ambient specify TMP_EXTERIOR along with SURF_ID OPEN Use this option cautiously in many situations if you want to describe the exterior of a building it is better to include the exterior explicitly in your calculation because the flow in and out of the doors and windows will be more naturally captured See Section 6 4 4 for more details As with exterior temperature to change the exterior mass fraction of a particular gas species set MASS_FRACTION N on the VENT line where N denotes the species index See Section 9 2 for more infor mation about gas species Vents to the outside of the computational domain OPEN vents may not be opened or closed during a simulation See Section 11 4 2 for details A MIRROR VENT A VENT with SURF_ID MIRROR denotes a symmetry plane Usually a MIRROR spans an entire face of the computational domain essentially doubling the size of the domain with the MIRROR acting as a plane of symmetry The flow on the opposite side of the MIRROR
142. e transformations that alter the aspect ratio of cells beyond 2 or 3 should be avoided Keep in mind that the large eddy simulation technique is based on the assumption that the numerical mesh should be fine enough to allow the formation of eddies that are responsible for the mixing In general eddy formation is limited by the largest dimension of a mesh cell thus shrinking the mesh resolution in one or two directions may not necessarily lead to a better simulation if the third dimension is large Transformations in general reduce the efficiency of the computation with two coordinate transformations impairing efficiency more than a transformation in one coordinate direction Experiment with different meshing strategies to see how much of a penalty you will pay Here is an example of how to do a mesh transformation Suppose your mesh is defined amp MESH IJK 15 10 20 XB 0 0 1 5 1 2 2 2 3 2 5 2 and you want to alter the uniform spacing in the x direction First refer to the figures above You need to define a function x f amp that maps the uniformly spaced Computational Coordinate cc 0 lt amp lt 1 5 to the Physical Coordinate PC 0 lt x lt 1 5 The function has three mandatory constraints it must be monotonic always increasing it must map 0 to x 0 and it must map 1 5 to x 1 5 The default transformation function is f for a uniform mesh but you need not do anything in this case 28
143. e fuel chemistry listed under the REAC namelist group is used to generate the table associating the mass fractions with Z You need not and should not explicitly list the reactants and products of combustion Suppose however that gases are introduced into the domain that are neither reactants nor products of combustion This gas can be tracked separately from the mixture fraction via an additional scalar transport equation In fact there does not need to be any fire at all FDS can be used to transport a mixture of non reacting ideal gases The namelist group SPEC is used to specify each additional species Each SPEC line should include at the very least the name of the species via a character string called 1D Next if the ambient initial mass fraction of the gas is something other than 0 then the parameter MASS_FRACTION_0 is used to specify it Several gases that can be included in a calculation are listed in Table 9 1 The physical properties of these gases are known and do not need to be specified However if a desired gas is not included in Table 9 1 its molecular weight Mw must be specified in units of g mol In addition if a DNS calculation is being performed either the Lennard Jones potential parameters O SIGMALJ and k EPSILONKLJ should be specified or the VISCOSITY kg m s CONDUCTIVITY W m K and DIFFUSIVITY m s between the given species and the background species should be specified amp SPEC ID ARGO
144. e mesh is used there should be a MESH line for each The order in which these lines are entered in the input file matters In general the meshes should be entered from finest to coarsest FDS assumes that a mesh listed first in the input file has precedence over a mesh listed second if the two meshes overlap Meshes can overlap abut or not touch at all In the last case essentially two separate calculations are performed with no communication at all between them Obstructions and vents are entered in terms of the overall coordinate system and need not apply to any one particular mesh Each mesh checks the coordinates of all the geometric entities and decides whether or not they are to be included e Avoid putting mesh boundaries where critical action is expected especially fire Sometimes fire spread from mesh to mesh cannot be avoided but if at all possible try to keep mesh interfaces relatively free of complicated phenomena since the exchange of information across mesh boundaries is not yet as accurate 26 as cell to cell exchanges within one mesh e Information from other meshes is received only at the exterior boundary of a given mesh This means that a mesh that is completely embedded within another receives information at its exterior boundary but the larger mesh receives no information from the mesh embedded within Essentially the larger usually coarser mesh is doing its own simulation of the scenario and is not affected by the sma
145. e specified to be at least one mesh cell thick Thin sheet obstructions work fine as flow barriers but other features are fragile and should be used with caution To prevent FDS from allowing thin sheet obstructions set THICKEN_OBSTRUCTIONS TRUE on the MISC line or THICKEN TRUE on each OBST line for which the thin sheet assumption is not allowed T e Unlike earlier versions of FDS obstructions that are too small relative to the underlying numerical mesh are rejected Be careful when testing cases on coarse meshes e Obstructions may be created or removed during a simulation See Section 11 4 1 for details e Iftwo obstructions overlap at one or more faces the one listed last in the input file takes precedence over the one listed first in the sense that the latter s surface properties will be applied to the overlapping face Smokeview renders both obstructions independently of each other often leading to an unsightly cross hatching of the two surface colors where there is an overlap A simple remedy for this is to shrink the first obstruction slightly by adjusting its coordinates XB accordingly Then in Smokeview toggle the 6699 q key to show the obstructions as you specified them rather than as FDS rendered them e Obstructions can be protected from the HOLE punching feature Sometimes it is convenient to create a door or window using a HOLE For example suppose a HOLE is punched in a wall to repres
146. e surrounding gases The radiative heat flux can be specified only by setting both TMP_FRONT and EMISSIVITY Fixed temperature or fixed heat flux boundary conditions are easy to apply but only of limited usefulness in real fire scenarios In most cases walls ceilings and floors are made up of several layers of lining materials It is assumed that the innermost layer backs up to an air gap at ambient temperature like a sheet of gypsum board attached to wood studs or it backs up to an insulated material in which case no heat is lost to the backing material or it backs up to the room on the other side of the wall By default it is assumed that the wall liner backs up to an air gap BACKING VOID If the wall liner is assumed to back up against an insulating material like a sheet of steel attached to a fiber insulating board the expression BACKING INSULATED on the SURF line prevents any heat loss from the back side of the material Finally if it is desired that the heat transfer through the wall into the space behind the wall the attribute BACKING EXPOSED should be listed This feature only works if the wall is less than or equal to one mesh cell thick and if there is a non zero volume of computational domain on the other side of the wall Obviously if the wall is an external boundary of the domain the heat is lost to the void For some special applications it is often desired that a s
147. ectangular mesh such as a sloped ceiling or roof In 38 these cases construct the curved geometry using rectangular obstructions a process sometimes called stair stepping A concern is that the stair stepping changes the flow pattern near the wall To lessen the impact of stair stepping on the flow field near the wall prescribe the parameter SAWTOOTH FALSE on each OBST line that makes up the stair stepped obstruction The effect of this parameter is to prevent vorticity from being generated at sharp corners in effect smoothing out the jagged steps that make up the obstruction This is not a complete solution of the problem but it does provide a simple way of ensuring that the flow field around a non rectangular obstruction is not inhibited by extra drag created at sharp corners Do not apply SAWTOOTH FALSE to obstructions that have any SURF_IDs with the attribute BURN_AWAY TRUE 7 2 Creating Voids The HOLE Namelist Group Table 13 7 The HOLE namelist group is used to define parameters Table 13 7 to carve a hole out of an existing ob struction or set of obstructions To do this add lines of the form amp HOLE XB 2 0 4 5 1 9 4 8 0 0 9 2 Any solid mesh cells within the volume 2 0 lt x lt 4 5 1 9 lt y lt 4 8 0 0 lt z lt 9 2 are removed Obstruc tions intersecting the volume are broken up into smaller blocks If the hole represents a door or window a good rule of thumb is t
148. ed in a single time step but the cost of the calculation increases significantly A few parameters affecting the absorption of radiation by water droplets are as follows RADTMP is the assumed radiative source temperature It is used in the computation of the mean scattering and absorption cross sections of water droplets The default is 900 C NMIEANG is the number of angles in the numerical integration of the Mie phase function Increasing NMIEANG improves the accuracy of the radiative properties of water droplets The cost of the better accuracy is seen in the initialization phase not during the actual simulation The default value for NMIEANG is 15 If the optional six band model is desired set WIDE_BAND_MODEL TRUE It is recommended that this option only be used when the fuel is relatively non sooting because it adds significantly to the cost of the calculation To add three additional fuel bands set CH4_BANDS TRUE See FDS Technical Reference Guide for more details Note also that it is possible to turn off the radiation transport solver saving roughly 20 in CPU time by adding the statement RADIATION FALSE to the MISC line For isothermal calculations the radiation is turned off automatically If burning is taking place and radiation is turned off then the total heat release rate is reduced by the RADIATIVE_FRACTION which is input on the RADI line This radiated energy completely disappears from the calculation More on this feature
149. effect ID Character Identifier T Real Time or Temperature s or C 118 13 19 REAC Reaction Parameters Table 13 19 For more information see Section 9 1 REAC Reaction Parameters BOF Real Pre exponential Factor Finite Rate cm mol s C Real Carbon atoms in fuel 3 CO_YIELD Real Fraction of CO from the fuel kg kg 0 CRITICAL_FLAME_TEMPERATURE Real Suppression criterion C 1427 E Real Activation Energy Finite Rate kJ kmol EPUMO2 Real Energy per Unit Mass Oxygen kJ kg 13100 FUEL Character Name of Fuel Finite Rate FYI Character Comment String has no effect H Real Hydrogen atoms in fuel 8 H2_YIELD Real Fraction of Hz from the fuel kg kg 0 HEAT_OF_COMBUSTION Real Energy per Unit Mass Fuel kJ kg HRRPUA_SHEET Real Upper limit on flame HRR kW m 200 ID Character Identifier IDEAL Logical Adjust for minor product yields FALSE MASS_EXTINCTION_COEFFICIENT Real Visibility parameter m kg 8700 MAXIMUM_VISIBILITY Real Visibility parameter m 30 MW_OTHER Real Molecular Weight of OTHER g mol 28 N Real Nitrogen atoms in the fuel 0 N_S N Real Arrhenius Exponents Finite Rate NU N Real Reaction stoichiometry Finite Rate O Real Oxygen atoms in the fuel 0 OTHER Real Other atoms in the fuel 0 OXIDIZER Character Name of Oxidizer Finite Rate
150. el MPI Message Passing Interface must be in stalled on each of the computers within the network that will be used for FDS computations Information about installing MPI on different computer platforms is given on the FDS website See the Development section of the website for more information Chapter 3 Running FDS This chapter describes the procedure to run an FDS calculation The primary requirement for any calculation is an FDS input file The creation of an input file is covered in detail in Part II If you are new to FDS and Smokeview it is strongly suggested that you start with an existing data file run it as is and then make the appropriate changes to the input file for the desired scenario Sample input files are included as part of the standard installation By running a sample case you become familiar with the procedure learn how to use Smokeview and ensure that your computer is up to the task before embarking on learning how to create new input files 3 1 Starting an FDS Calculation FDS can be run from the command prompt or with a third party Graphical User Interface GUI In the discussion to follow it is assumed that FDS is being run from the command prompt FDS can be run on a single computer using only one CPU or it can be run on multiple computers and use multiple CPUs For any operating system there are two FDS executable files The single CPU Windows executable is called fds exe The parallel executable is called
151. em can be lessened by the inclusion of more solid angles but at a price of longer computing times In most cases the radiative flux to far field targets is not as important as those in the near field where coverage by the default number of angles is much better Hostikka et al examined the sensitivity of the radiation solver to changes in the assumed soot pro duction number of spectral bands number of control angles and flame temperature Some of the more interesting findings were e Changing the soot yield from 1 to 2 increased the radiative flux from a simulated methane burner about 15 e Lowering the soot yield to zero decreased the radiative flux about 20 e Increasing the number of control angles by a factor of 3 was necessary to ensure the accuracy of the model at the discrete measurement locations e Changing the number of spectral bands from 6 to 10 did not have a strong effect on the results e Errors of 100 in heat flux were caused by errors of 20 in absolute temperature The sensitivity to flame temperature and soot composition are consistent with combustion theory which states that the source term of the radiative transport equation is a function of the absorption coefficient mul tiplied by the absolute temperature raised to the fourth power The number of control angles and spectral bands are user controlled numerical parameters whose sensitivities ought to be checked for each new sce nario The default values in
152. ement to the MISC line 62 Table 8 1 Sample of Color Definitions A complete list is included on the website Name R G B Name R G B AQUAMARINE E 127 255 212 MAROON E 128 0 0 ANTIQUE WHITE 250 235 215 MELON E 227 168 105 BEIGE 245 245 220 MIDNIGHT BLUE W 25 25 112 BLACK li 0 0 0 INT 189 252 201 BLUE EH 0 0 255 NAVY E 0 0 128 BLUE VIOLET E 138 43 226 OLIVE m 128 128 0 BRICK E 156 102 31 OLIVE DRAB E 107 142 35 BROWN E 165 42 42 ORANGE E 255 128 0 BURNT SIENNA W 138 54 15 ORANGE RED E 255 69 0 BURNT UMBER BM 138 51 36 ORCHID E 218 112 214 CADET BLUE mM 95 158 160 PINK 255 192 203 CHOCOLATE E 210 105 30 POWDER BLUE 176 224 230 COBALT BH ol 89 171 PURPLE A 128 0 128 CORAL E 255 127 80 RASPBERRY M 135 38 87 CYAN E 0 255 255 RED E 255 0 0 DIMGRAY E 105 105 105 ROYAL BLUE mM 65 105 225 EMERALD GREEN Ml 0 201 87 SALMON E 250
153. ensional Cartesian coordinate sys tem However a two dimensional Cartesian or two dimensional cylindrical axially symmetric calculation can be performed by setting the number of cells in the y direction to 1 An example of an axially symmetric helium plume is shown here along with the input file amp HEAD CHID helium_2d TITLE Axisymmetric Helium Plume amp MESH IJK 72 1 144 XB 0 00 0 08 0 001 0 001 0 00 0 16 CYLINDRICAL TRUE amp TIME TWFIN 5 0 amp MISC DNS TRUE ISOTHERMAL TRUE amp SPEC ID HELIUM amp SURF ID HELIUM VEL 0 673 MASS_FRACTION 1 1 0 TAU_MF 1 0 3 amp VENT MB XMAX SURF_ID OPEN amp VENT MB ZMAX SURF_ID OPEN amp OBST XB 0 0 0 036 0 001 0 001 0 00 0 02 SURF_IDS HELIUM INERT INERT amp DUMP PLOT3D_QUANTITY 1 PRESSURE PLOT3D_QUANTITY 5 HELTUM amp SLCF PBY 0 000 QUANTITY DENSITY VECTOR TRUE amp SLCF PBY 0 000 QUANTITY HELIUM amp TAIL 135 16 1 2 Pressure Rise in a Sealed Enclosure pressure_rise This example tests several basic features of FDS A narrow channel 3 m long 0 002 m wide and 1 m tall has air injected at a rate of 0 1 kg m s over an area of 0 2 m by 0 002 m for 60 s with a linear ramp up and ramp down over 1 s The total mass of air in the channel at the start is 0 00718 kg The total mass of air injected is 0 00244 kg The domain is assumed two dimensional the walls are adiabatic and STRATIFICATION
154. ent a door or window An obstruction can be defined to fill this hole presumably to be removed or col ored differently or whatever so long as the phrase PERMIT_HOLE FALSE is included on the OBST line In general any OBSTruction can be made impenetrable to a HOLE using this phrase By default PERMIT_HOLE TRUE meaning that an OBSTruction is assumed to be penetrable unless otherwise directed e If the obstruction is not to be removed or rejected for any reason set REMOVABLE FALSE This is sometimes needed to stop FDS from removing the obstruction if it is embedded within another like a door within a wall e In rare cases you might not want to allow a VENT to be attached to a particular obstruction in which case set ALLOW_VENT FALSE e Obstructions can be made semi transparent by assigning a TRANSPARENCY on the OBST line This real parameter ranges from 0 to 1 with O being fully transparent The parameter should always be set along with either COLOR or an RGB triplet It can also be specified on the appropriate SURF line along with a color indicator e Obstructions are drawn solid in Smokeview To draw an outline representation set OUTLINE TRUE 7 1 1 Non rectangular Geometry and Sloped Ceilings The efficiency of FDS is due to the simplicity of its numerical mesh However there are situations in which certain geometric features do not conform to the r
155. er EXT T 20 T 500 T 20 T 900 T 20 T 400 AH oll fant O Il i 15 29 08 225 06 25 ERNAL_FLUX on the SURF line This produces a 50 kW m flux on the sample without any additional input lines in the file It is just to test the solid phase model and should not be copied into an actual fire simulation The figures below show the surface temperature and burning rate of the wood under the 50 kW m external heat flux The burning rate peaks at the start of the simulation decreases throughout the burning phase and then peaks again at the end due to presence of an external backing material The initial peak is typical of char forming solids 800 600 400 200 Surface Temperature C charring_solid 100 200 300 Time s 400 500 600 151 Burning Rate kg m s 0 020 0 015 0 010 0 005 0 000 charring_solid 100 200 300 400 500 600 Time s 16 4 8 Testing the Burn Away Feature box_burn_away This is a silly example of a solid block of foam that is ignited and burns until it is completely consumed The properties of the block of foam were chosen simply to assure a quick calculation The objective of the test is to check that the integrated heat release rate is consistent with the material properties of the block The block is 0 4 m on a side with a density of 20 kg m Its heat of combustion
156. es have been performed comparing DNS simulations of a simple burner flame to laboratory experiments 28 Another study compared FDS simulations of a counterflow diffusion flames to experimental measurements and the results of a one dimensional multi step kinetics model 29 Early work with the hydrodynamic solver compared two dimensional simulations of gravity currents with salt water experiments 30 In these tests the numerical grid was systematically refined until almost perfect agreement with experiment was obtained Such convergence would not be possible if there were a fundamental flaw in the hydrodynamic solver 134 Chapter 16 Verification Test Suite This Chapter contains a set of relatively simple calculations that are used to verify the major physical algo rithms within FDS That is these samples confirm that the equations have been properly coded They do not imply that the equations actually represent some physical phenomena That is part of the Validation process Note that the names in parentheses in each section header correspond to the names of the input files for the cases 16 1 Hydrodynamics There are no analytical solutions of the fully turbulent Navier Stokes equations but 1t is possible to simulate well known fluid flows to determine if the basic fluid flow solver in FDS is working properly 16 1 1 Axially Symmetric Helium Plume helium_2d The governing equations solved in FDS are written in terms of a three dim
157. esults at the expense of computational time Accurate contaminant dispersal modeling re quired a significantly finer grid The results of her study indicate that non fire simulations can be completed more quickly than fire simulations because the time step is not limited by the large flow speeds in a fire plume 17 2 Sensitivity of Large Eddy Simulation Parameters FDS uses the Smagorinsky form of the Large Eddy Simulation LES technique This means that instead of using the actual fluid viscosity the model uses a viscosity of the form Mies p CA S 17 1 where C is an empirical constant A is a length on the order of the size of a grid cell and the deformation term S is related to the Dissipation Function given by Eq Related to the turbulent viscosity are comparable expressions for the thermal conductivity and material diffusivity _ Utes Cp LES Pr Utes PD tes Sc 17 2 The Prandtl number Pr and the Schmidt number Sc are likewise considered to be turbulent values Thus Cs Pr and Sc are a set of empirical constants Most FDS users simply use the default values of 0 2 0 5 0 5 but some have explored their effect on the solution of the equations In an effort to validate FDS with some simple room temperature data Zhang et al 47 tried different combinations of the Smagorinsky parameters and suggested the current default values Of the three pa rameters the Smagorinsky constant C is the most sen
158. eter G Buning PLOT3D User s Manual version 3 5 NASA Technical Memorandum 101067 NASA 1989 97 G W Mulholland SFPE Handbook of Fire Protection Engineering chapter Smoke Production and Properties National Fire Protection Association Quincy Massachusetts 3rd edition 2002 98 99 M L Janssens and H C Tran Data Reduction of Room Tests for Zone Model Validation Journal of Fire Science 10 528 555 1992 99 Y P He A Fernando and M C Luo Determination of interface height from measured parameter profile in enclosure fire experiment Fire Safety Journal 31 19 38 1998 100 S Welsh and P Rubini Three dimensional Simulation of a Fire Resistance Furnace In Fire Safety Science Proceedings of the Fifth International Symposium International Association for Fire Safety Science 1997 100 U Wickstrom D Duthinh and K B McGrattan Adiabatic Surface Temperature for Calculating Heat Transfer to Fire Exposed Structures In Proceedings of the Eleventh International Interflam Confer ence Interscience Communications London 2007 101 American Society for Testing and Materials West Conshohocken Pennsylvania ASTM E 1355 04 Standard Guide for Evaluating the Predictive Capabilities of Deterministic Fire Models 2004 131 132 179 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 W Mell K B McGrattan and H Baum Numerical Simulation of Combustion in Fire
159. etization error in the governing equations by a factor of 4 Because of the non linearity of the equations the decrease in discretization error does not necessarily translate into a comparable decrease in the error of a given FDS output quantity To find out what effect a finer grid has on the solution model users usually perform some form of grid sensitivity study in which the numerical grid is systematically refined until the output quantities do not change appreciably with each refinement Of course with each halving of the grid cell size the time required for the simulation increases by a factor of 2 16 a factor of two for each spatial coordinate plus time In the end a compromise is struck between model accuracy and computer capacity Some grid sensitivity studies have been documented and published Since FDS was first publicly re leased in 2000 significant changes in the combustion and radiation routines have been incorporated into the model However the basic transport algorithm is the same as is the critical importance of grid sensitivity In compiling sensitivity studies only those that examined the sensitivity of routines no longer used have been excluded As part of a project to evaluate the use of FDS version 1 for large scale mechanically ventilated enclo sures Friday 38 performed a sensitivity analysis to find the approximate calculation time based on varying grid sizes A propylene fire with a nominal heat release rate was m
160. ew sections provide a list of error statements and suggestions on how to solve problems 4 1 The Version Number If you encounter problems with FDS it is crucial that you submit along with a description of the problem the FDS version number Each release of FDS comes with a version number like 5 2 6 where the first number is the major release the second is the minor release and the third is the maintenance release Major releases occur every few years and as the name implies dramatically change the functionality of the model Minor releases occur every few months and may cause minor changes in functionality Release notes can help you decide whether the changes should effect the type of applications that you typically do Maintenance releases are just bug fixes and should not affect code functionality To get the version number just type the executable at the command prompt fds5 13 and the relevant information will appear along with a date of compilation useful to you and a so called SVN number useful to us The SVN number refers to the Subversion repository number of the source code It allows us to go back in time and recover the exact source code files that were used to build that executable Simply get in the habit of checking the version number of your executable periodically checking for new releases which might already have addressed your problem and telling us what version you are using if you report a problem 4 2
161. extinguish itself as the oxygen volume fraction decreased below about 15 But its re ignition at the door crack and fan opening would depend on the presence of a spark or hot spot of some sort FDS continues to flow fuel into the compartment past the point of local extinction but the compartment cools The default combustion algorithm in FDS assumes that in every grid cell there is a virtual spark plug that initiates combustion if the local ratio of fuel and oxygen are appropriate 141 16 3 Radiation 16 3 1 Radiation inside a box radiation_in_a_box This verification case tests the computation of three dimensional configuration factor inside a cube box with one hot wall and five cold 0 K walls An overview of the test geometry is shown here The configuration factors are calculated at the diagonal of the cold wall opposite to the hot wall The exact values of the configuration factor from plane element dA to parallel rectangle H are calculated using the analytical solution 31 yz Praa yz Puan 0 025 0 1457 0 275 0 2135 0 075 0 1603 0 325 0 2233 0 125 0 1748 0 375 0 2311 0 175 0 1888 0 425 0 2364 0 225 0 2018 0 475 0 2391 Different variations of the case include the mesh resolution 20 and 100 cells and the number of radiation angles 50 100 300 1000 2000 The exact and FDS results are shown here Spatial resolution 20x20x20 Spatial resolution 100
162. f orientation 1 for the positive x direction 1 for negative and so on 12 2 7 Animated Isosurfaces The 1 SOF Namelist Group The 1SoF ISOsurface File namelist group is used to specify the output of gas phase scalar quantities as three dimensional animated contours For example a 300 C temperature isosurface shows where the gas temperature is 300 C Three different values of the temperature can be saved via the line amp ISOF QUANTITY TEMPERATURE VALUE 1 50 VALUE 2 200 VALUE 3 500 where the values are in degrees C Note that the isosurface output files CHID_n iso can become very large so experiment with different sampling rates Any gas phase quantity can animated via iso surfaces but use caution To render an iso surface the desired quantity must be computed in every mesh cell at every output time step For quantities like TEMPERATURE this is not a problem as FDS computes it and saves it anyway However soot density or oxygen demand substantial amounts of time to compute at each mesh cell 12 2 8 Plot3D Static Data Dumps By default flow field data in Plot3D format is output 5 times a run Five quantities are written out to a file at one instant in time The default specification is amp DUMP PLOT3D_QUANTITY 1 5 TEMPERATURE U VELOCITY V VELOCITY W VELOCITY HRRPUV 96 It s best to leave
163. face is going to shrink when the surface reacts The shrinking behavior can be prevented in the numerical model by setting SHRINK FALSE on the SURF line However setting SHRINK FALSE may introduce numerical problems in the wall solver When all the material of a shrink ing surface is consumed but BURN_AWAY is not prescribed the surface temperature is set to TMP_BACK convective heat flux to zero and burning rate to zero 8 4 4 Special Topic Initial and Backside Boundary Conditions By default the initial temperature of the solid material is set to ambient temperature Use TMP_INNER on the SURF line to specify a different initial temperature Also the backside temperature boundary condition of a solid can be set using the parameter TMP_BACK on the SURF line TMP_BACK is not the actual backside surface temperature but the gas temperature that the surface transfer heat with This parameter has no meaning for surfaces with BACKING EXPOSED or BACKING INSULATED Note that the parameters TMP_INNER and TMP_BACK are only meaningful for solids with specified THICKNESS and material properties via the MATL_ID keyword 8 4 5 Special Topic Numerical Accuracy and Stability To compute the temperature and reactions inside the solids FDS solves the one dimensional heat transfer equation numerically The size of the mesh cells on the surface of the solid is automatically chosen using a rule that makes the ce
164. fds _mpi exe The letters mpi in the filename denote Message Passing Interface MPI which will be discussed below Note that the input file for both single and parallel versions of FDS are the same In fact it is recommended that before embarking on parallel processing you should run your input file in serial mode to ensure that it is properly set up 3 1 1 Starting an FDS Calculation Single Processor Version Sample input files are provided with the program for new users who are encouraged to first run a sample calculation before attempting to write an input file Assuming that an input file called job_name fds exists in some directory run the program either in a DOS or Unix command prompt as follows MS Windows Open up a Command Prompt window and change directories cd to where the input file for the case is located then run the code by typing at the command prompt fds5 job_name fds The character string job_name is usually designated within the input file as the CHID It is recommended that the name of the input file and the CHID be the same so that all of the files associated with a given calculation have a consistent name The progress of a simulation is indicated by diagnostic output that is written out onto the screen Detailed diagnostic information is automatically written to a file CHID out where CHID is a character string usually the same as job_name designated in the input file Screen output c
165. fuel vapors from different materials combust to produce the proper amount of energy it is very important to specify a HEAT_OF_COMBUSTION for each material That way the mass loss rate of fuel gases is automatically adjusted so that the effective mass loss rate multiplied by the single global gas phase heat of combustion produces the expected heat release rate Several other examples of solid phase reactions can be found in various Verification examples See Sections 16 4 6 and 16 4 7 Solid Fuels that Burn at a Specified Rate Real objects like furnishings office equipment and so on are often difficult to describe via the SURF and MATL parameters Sometimes the only information about a given object is its bulk thermal properties its ignition temperature and what its subsequent burning rate is as a function of time from ignition For this situation add lines similar to the following amp MATL ID stuff CONDUCTIVITY 0 1 SPECIFIC_HEAT 1 0 DENSITY 900 0 amp SURF ID my surface 55 COLOR GREEN MATL_ID stuff HRRPUA 1000 IGNITION_TEMPERATURE 500 RAMP_Q fire_ramp THICKNESS 0 01 amp RAMP ID fire_ramp T 0 0 F 0 0 amp RAMP ID fire_ramp T 10 0 F 1 0 amp RAMP ID fire_ramp T 310 0 F 1 0 amp RAMP ID fire_ramp T 320 0 F 0 0 An object with surface properties defined by my surface shall burn at a rate of
166. function types the logical value output of the devices and control functions and the time they last changed state are used as the inputs Table 11 2 Control function types for CTRL Function Type Description ANY Changes state if any INPUTs are TRUE ALL Changes state if all INPUTs are TRUE ONLY Changes state if and only if N INPUTs are TRUE AT_LEAST Changes state if at least N INPUTs are TRUE TIME_DELAY Changes state DELAY s after INPUT becomes TRUE CUSTOM Changes state based on evaluating a RAMP of the function s input DEADBAND Behaves like a thermostat KILL Terminates code execution 1f its sole INPUT is TRUE RESTART Dumps restart files if its sole INPUT is TRUE A control is identified by the ID parameter The inputs to the control are identified by the INPUT_ID parameter INPUT_ID would be passed one or more ID strings from either devices or other controls If you want to design a system of controls and devices that involves multiple changes of state include the attribute LATCH FALSE on the relevant DEVC or CTRL input lines By default devices and controls may only change state once like a sprinkler activating or smoke detector alarming LATCH TRUE by default for both devices and controls 11 5 1 Control Functions ANY ALL ONLY and AT_LEAST Suppose you want an obstruction to be remo
167. h the parameters are specified assum ing that this is the third mesh amp TRNX IDERIV 0 CC 0 75 PC 0 75 MESH_NUMBER 3 amp TRNX IDERIV 1 CC 0 75 PC 0 50 MESH_NUMBER 3 which correspond to the constraints f 0 75 0 75 and a 0 75 0 5 or in words the function maps 0 75 into 0 75 and the slope of the function at 0 75 is 0 5 The transform function must also pass through the points 0 0 and 1 5 1 5 meaning that FDS must compute the coefficients for the cubic polynomial f E cote1 E 2 3 3 More constraints on the function lead to higher order polynomial functions so be careful about too many constraints which could lead to non monotonic functions The monotonicity of the function is checked by the program and an error message is produced if it is not monotonic 6 3 4 Choosing the Right Mesh Dimensions A common question asked by new FDS users is What size mesh should I use The answer is not easy because it depends considerably on what you are trying to accomplish In general you should build an FDS input file using a relatively coarse mesh and then gradually refine the mesh until you do not see appreciable differences in your results Formally this is referred to as a mesh sensitivity study For simulations involving buoyant plumes a measure of how well the flow field is resolved is given by the non dimensional expression D 5x where D is a characteristic fire diameter 5 Di
168. haracter Associated DEVC line for aspiration detector DEPTH Real Depth into surface for internal wall temp m 0 FLOWRATE Real Suction flowrate for an aspiration detector kg s 0 FYI Character Comment String has no effect IOR Integer Index of Orientation 1 2 3 ID Character Identifying label for output INITIAL_STATE Logical Initial state of device FALSE LATCH Logical Device cannot change state multiple times TRUE ORIENTATION Real Triplet Direction vector 0 0 1 PROP_ID Character Associated PROPerty line QUANTITY Character Name of Quantity to output ROTATION Real Triplet Rotation Angle deg 0 SETPOINT Real Value at which device changes state STATISTICS Character See Section 12 2 3 SURF_ID Character See Section 12 2 3 TRIP_DIRECTION Integer Sign of derivative at first state change 1 XB 6 Real Sextuplet Coordinates of non point measurement m XYZ Real Triplet Physical coordinates m 108 13 5 DUMP Output Parameters Table 13 5 For more information see Section 12 1 DUMP Output Parameters COLUMN_DUMP_LIMIT Logical Limit text output to 255 columns TRUE DT_BNDF Real Boundary dump interval s 2At NFRAMES DT CTRL Real Control status dump interval s At NFRAMES DT_DEVC Real Device output dump interval s At NFRAMES D
169. he MISC namelist group A similar condition but one constraining the time step when diffusive transport dominates is sometimes called the Von Neumann condition The Von Neumann number is defined k 1 1 1 VN 2 max v0 2 t 52 Ea 52 6 7 Like the CFL number VN is computed in each mesh cell and the time step is adjusted if VN is outside the range between VN_MIN and VN_MAX which are 0 8 and 1 0 by default Note that this constraint is applied to the momentum mass and energy equations via the relevant diffusion parameter viscosity material diffusivity or thermal conductivity This constraint on the time step is typical of any explicit second order numerical scheme for solving a parabolic partial differential equation To save CPU time the Von Neumann criterion is only invoked for DNS calculations or for LES calculations with mesh cells smaller than 5 mm Resetting the stability parameters is not recommended except in very special circumstances as they can lead to simulations failing due to numerical instabilities 34 6 5 Special Topic Unusual Initial Conditions The INIT Namelist Group Table 13 8 Usually an FDS simulation begins at time t 0 with ambient conditions The air temperature is assumed constant with height and the density and pressure decrease with height the z direction This decrease is not noticed in most building scale calculations but it is important in large outdoor simulations There a
170. he fidelity of the numerical solution of the entire system of equations is tied to the pressure velocity coupling because often simulations can involve hundreds of thousands of time steps with each time step consisting of two solutions of the Pois son equation to preserve second order accuracy Without the use of the direct Poisson solver build up of numerical error over the course of a simulation could produce spurious results Indeed an attempt to use single precision 4 byte arithmetic to conserve machine memory led to spurious results simply because the error per time step built up to an intolerable level 15 2 Code Checking An examination of the structure of the computer program can be used to detect potential errors in the nu merical solution of the governing equations The coding can be verified by a third party either manually or automatically with profiling programs to detect irregularities and inconsistencies 13 At NIST and elsewhere FDS has been compiled and run on computers manufactured by IBM Hewlett Packard Sun Microsystems Digital Equipment Corporation Apple Silicon Graphics Dell Compaq and various other personal computer vendors The operating systems on these platforms include Unix Linux Microsoft Windows and Mac OSX Compilers used include Lahey Fortran Digital Visual Fortran Intel Fortran IBM XL Fortran HPUX Fortran Forte Fortran for SunOS the Portland Group Fortran and several others Each combination of ha
171. he functionality with a simple example Until further notice a MIRROR or OPEN VENT should not be activated or deactivated The reason for this restriction is that abrupt changes in pressure can cause numerical instabilities 87 11 5 Advanced Control Functions The CTRL Namelist Group There are many systems whose functionality cannot be described by a simple device with a single setpoint Consider for example a typical HVAC system It is controlled by a thermostat that is given a temperature setpoint The system turns on when the temperature goes below the setpoint by some amount and then turns off when the temperature rises above that same setpoint by some amount This behavior can not be defined by merely specifying a single setpoint You must also define the range or deadband around the setpoint and whether an increasing or decreasing temperature activates the system For the HVAC example crossing the lower edge of the deadband activates heating crossing the upper edge activates cooling While HVAC is not the primary purpose of FDS there are numerous situations where a system responds to the fire in non trivial way The CTRL input is used to define these more complicated behaviors A control function will take as input the outputs of one or more devices and or control functions In this manner complicated behaviors can be simulated by making functions of other functions For most of the control
172. he ith material decreases at a rate of 0 1 s You should check the sensitivity of these parameters following the procedure explained in Section 8 7 Tihr ij 18 an optional threshold temperature that allows the definition of non Arrhenius pyrolysis func tions and ignition criteria and is prescribed by THRESHOLD_TEMPERATURE j By default Tjn is 273 15 degrees Celsius n is zero thus the last term of Equation 8 4 does not affect the pyrolysis rate The term can be used to describe a threshold temperature for the pyrolysis reaction by setting T nr ij and ns j 0 Then the term is equal to 0 at temperatures below T nr j and 1 at temperatures above n j is prescribed under the name N_T j 54 Remember that all temperatures are specified in degrees Celsius but are then converted to degrees Kelvin within the program Thus the formulae in this section ought to be interpreted in terms of the absolute temperature One last issue before a few examples the most important one of all Eq 8 4 describes the rate of the re action as a function of temperature Most solid phase reactions require energy that is they are endothermic The amount of energy consumed per unit mass of reactant that is converted into something else is specified by the HEAT_OF_REACTION
173. he namelist group RAMP and TABL as it names imply allow you to control the behavior of selected parameters RAMP allows you to specify a function with one independent variable such as time is mapped to one dependent variable such as velocity TALB allows for the specification of a mapping from multiple independent variables such as a solid angle to multiple dependent variables such as a sprinkler flow rate and droplet speed 8 5 1 Time Dependent Functions At the start of any calculation the temperature is ambient everywhere the flow velocity is zero everywhere nothing is burning and the mass fractions of all species are uniform When the calculation starts temper atures velocities burning rates efc are ramped up from their starting values because nothing can happen instantaneously By default everything is ramped up to their prescribed values in roughly 1 s However control the rate at which things turn on or turn off by specifying time histories for the boundary condi tions that are listed on a given SURF line The above boundary conditions can be made time dependent using either prescribed functions or user defined functions The parameters TAU_Q TAU_T and TAU_V in dicate that the heat release rate HRRPUA surface temperature TMP_FRONT and or normal velocity VEL VOLUME_FLUX or MASS_FLUX_TOTAL are to ramp up to their prescribed values in TAU seconds and re main there If TAU_Q is positive then the heat release rate ra
174. he next section For example water has a DENSITY of 1000 kg m whereas a liter of water broken up into droplets and spread over a cubic meter has a MASS_PER_VOLUME of 1 kg m Also to limit the particles droplets to a certain region of the domain add the real sextuplet xB to designate the coordinates of a rectangular volume The format for XB is the same as that used on the OBST line Droplets that Strike Solid Surfaces When a droplet strikes a solid surface it sticks and is reassigned a new speed and direction If the sur face is horizontal the direction is randomly chosen If vertical the direction is downwards The rate at which the droplets move over the horizontal and vertical surfaces is difficult to quantify The parameters HORIZONTAL_VELOCITY and VERTICAL_VELOCITY on the PART line allow you to control the rate at which droplets move horizontally or vertically downward The defaults are 0 2 m s and 0 5 m s respec tively Be aware that when droplets hit obstructions the vertical direction is assumed to coincide with the z axis regardless of any change to the gravity vector GVEC 10 3 Particle and Droplet Properties For Lagrangian particles that are not MASSLESS the following parameters should be included on the PART line DENSITY The density of the liquid or solid droplet particle Default 1000 kg m SPECIFIC_HEAT Specific heat of liquid or solid dr
175. he parameters within them This is intended to be used as a quick reference and does not replace reading the detailed description of the parameters in the main body of this guide See Table 5 1 for a cross reference of relevant sections and the tables in this Appendix The reason for this statement is that many of the listed parameters are mutually exclusive specifying more than one can cause the program to either fail or run in an unpredictable manner Also some of the parameters trigger the code to work in a certain mode when specified For example specifying the thermal conductivity of a solid surface triggers the code to assume the material to be thermally thick mandating that other properties be specified as well Simply prescribing as many properties as possible from a handbook is bad practice Only prescribe those parameters which are necessary to describe the desired scenario 105 13 1 BNDF Boundary File Parameters Table 13 1 For more information see Section 12 2 6 BNDF Boundary File Parameters FYI Character Comment String has no effect PROP_ID Character Source of specific property info QUANTITY Character Quantity to visualize 13 2 CLIP MIN MAX Clipping Parameters Table 13 2 For more information see Section 6 6 CLIP Specified Upper and Lower Limits FYI Character Comment String has no effect MAX IMUM_DENSITY Real Maximum Gas Density
176. he path length of 10 m the expected total obscuration is 99 81 which is the result computed by FDS for each of the three detectors 155 16 5 2 Aspiration Detector aspiration_detector A cubical compartment 2 m on a side with a fire has a three sampling location aspiration system The three locations have flow rates of 0 1 0 5 and 0 8 kg s respectively and transport times of 0 2 0 1 and 0 3 s respectively No bypass flow rate is specified for the aspiration detector The input file fixes the initial time step to 0 01 s so that the initial output times in the aspiration_detector_devc csv file will line up exactly with the transport times At 0 75 s when FDS begins reducing the time step below 0 01 s the time delayed soot densities at the three sampling locations are 7 4x10 kg m 9 5x107 kg m and 1 6x107 8 kg m respectively Using these values along with the respective flow rates results in a detector obscuration of 0 000823 m which is the same obscuration as predicted by FDS 156 16 6 Droplets and Sprays This section considers cases involving evaporating droplets both water and fuel 16 6 1 Water Droplet Evaporation water_evaporation The case called water_evaporation is nothing more than stationary water droplets in an adiabatic box with dimensions of 1 m on a side The air within the box is stirred to maintain uniform conditions and there are no leaks or heat losses The initial air temperature is 40 C Ini
177. hese comments do not fall within the namelist records The general structure of an input file is shown below with many lines of the original validation input file WTC_05_v5 fds removed for clarity amp HEAD CHID WTC_05_v5 TITLE WIC Phase 1 Test 5 FDS version 5 amp MESH IJK 90 36 38 XB 1 0 8 0 1 8 1 8 0 0 3 82 amp TIME T _END 5400 20 amp MISC SURF_DEFAULT MARINITE BOARD TMPA 20 POROUS_FLOOR FALSE amp DUMP NFRAMES 1800 DT_HRR 10 DI_DEVC 10 DT_PROF 30 amp REAC ID HEPTANE TO CO2 FYI Heptane C_7 H_16 C 7 H 16 CO_YIELD 0 008 SOOT_YIELD 0 015 amp OBST XB 3 5 4 5 1 0 1 0 0 0 0 0 SURF_ID STEEL FLANGE Fire Pan amp SURF ID STEEL FLANGE COLOR BLACK MATL_ID STEEL BACKING EXPOSED THICKNESS 0 0063 amp VENT MB XMIN SURF_ID OPEN amp SLCF PBY 0 0 QUANTITY TEMPERATURE VECTOR TRUE amp BNDF QUANTITY GAUGE_HEAT_FLUX amp DEVC XYZ 6 04 0 28 3 65 QUANTITY oxygen ID EO2_FDS amp TAIL End of file It is strongly recommended that when looking at a new scenario first select a pre written input file that resembles the case make the necessary changes then run the case at fairly low resolution to determine if the geometry is set up correctly It is best to sta
178. ial Topic Setting Limits The CLIP Namelist Group Table 13 2 7 Building the Model 7 1 Creating Obstructions The OBST Namelist Group Table 13 13 7 1 1 Non rectangular Geometry and Sloped Ceilings o o 7 2 Creating Voids The HOLE Namelist Group Table 13 7 7 3 Applying Surface Properties The VENT Namelist Group Table 13 26 TA Special VENTS s 4624 Baht EGG Mek oe ee bE eae ee ee a Ba eS Taz Controls VENTS orion de Pag bare oe WA ade i Se ares fa lrouble Shooune VENTS e sis 4 dee eee ee A Bae 8 Boundary Conditions 8 1 Basics 8 2 Describing the Bounding Surfaces The SURF Namelist Group Table 13 22 8 2 1 8 2 2 8 2 3 8 2 4 8 2 5 8 2 6 8 2 7 Specifying a Fire with a Known Heat Release Rate Simple Thermal Boundary Conditions ooa Velocity and Total Mass Flux Boundary Conditions aaa Species and Species Mass Flux Boundary Conditions Special Topic Fires and Flows in the Outdoors ooa Special Topic A Radially Spreading Fire oaoa Special Topic Non Planar Walls and Targets oaoa 8 3 Pressure Related Effects The ZONE Namelist Group Table 13 26 8 3 1 8 3 2 Fans 8 4 Describing Real Materials The MATL Namelist Group o 8 4 1 8 4 2 8 4 3 8 4 4 8 4 5 Thermal Properties po c cc
179. icles can be injected into the flow field from vents or obstacles and then viewed in Smokeview Use the PART namelist group to control the injection rate sampling rate and other parameters associated with particles Note unlike in FDS version 1 particles are no longer used to introduce heat into the flow thus particles no longer are ejected automatically from burning surfaces 12 1 Output Control Parameters The DUMP Namelist Group The namelist group DUMP contains parameters Table 13 5 that control the rate at which output files are written and various other global parameters associated with output files This namelist group is new starting in FDS 5 although its parameters have been specified via other namelist groups in past versions NFRAMES Number of output dumps per calculation The default is 1000 Device data slice data parti cle data isosurface data 3D smoke data boundary data solid phase profile data and control function data are saved every T_END T_BEGIN NFRAMES seconds unless otherwise specified using DT_DEVC DT_SLCF DT_PART DI_ISOF DT_BNDF DT_PROF or DT_CTRL Note that DT_SLCF controls Smoke3D output DT_HRR controls the output of heat release rate and associated quantities MASS_FILE If TRUE produce an output file listing the total masses of all gas species as a function of time It is FALSE by default because the calculation of all gas species in all mesh ce
180. ime difference by 100 This is the average elapsed wall clock time per time step 4 Look at the CPU step for each mesh The largest value should be less than but close to the average elapsed wall clock time The efficiency of the parallel calculation is the maximum CPU step divided by the average wall clock time per step If this number is between 90 and 100 the parallel code is working well 27 E TRUE 6 3 3 Mesh Stretching The TRNX TRNY and or TRNZ Namelist Groups Table 13 25 By default the mesh cells that fill the computational domain are uniform in size However it is possible to specify that the cells be non uniform in one or two of the three coordinate directions For a given co 1 5 1 5 1 2 7 1 2 4 0 9 0 9 x x 0 6 y 0 6 y 0 3 y 0 3 y 0 0 t 0 0 T 0 0 0 3 0 6 0 9 1 2 1 5 0 0 0 3 0 6 0 9 1 2 1 5 amp amp Figure 6 2 Piecewise Linear Transformation Figure 6 3 Polynomial Transformation ordinate direction x y or z a function can be prescribed that transforms the uniformly spaced mesh to a non uniformly spaced mesh Be careful with mesh transformations If you shrink cells in one region you must stretch cells somewhere else When one or two coordinate directions are transformed the aspect ratio of the mesh cells in the 3D mesh will vary To be on the safe sid
181. imulation 1t is hard to untangle the uncertainties associated with the gas and solid phase routines However it is easy to perform a simple check of any set of surface properties by essentially turning off the gas phase no combustion and no convective heat transfer There are several parameters that allow you do this spread out over the various namelist groups l Create a trivially small mesh just to let FDS run Since the gas phase calculation is essentially being shut off you just need 4 cells in each direction I JK 4 4 4 for the pressure solver to function properly On the TIME line set WALL_INCREMENT 1 to force FDS to update the solid phase every time step normally it does this every other time step and set DT to whatever value appropriate for the solid phase calculation Since there is no gas phase calculation that will limit the time step it is best to control this yourself Put H_FIXED 0 on the MISC line This turns off the convective heat flux from gas to surface and vis verse The heat flux to the solid is specified via EXTERNAL_FLUX kW m on the SURF line that is assigned to the solid surface If you want to specify a particular convective heat flux to the solid surface you can set ASSUMED_GAS_ TEMPERATURE on the MISC line along with a non zero value of H_FIXED Turn off all the gas phase computations by setting SOLID_PHASE_ONLY TRUE onthe MISC line This
182. ing material differs from the global reaction the HEAT_OF_COMBUSTION is used to ensure that an equivalent amount of fuel is injected into the flow domain from the burning object Gas Phase Fire Suppression Modeling suppression of a fire due to the introduction of a suppression agent like CO or water mist or due to the exhaustion of oxygen within a compartment is challenging because the relevant physical mechanisms occur at length scales smaller than a single mesh cell Flames are extinguished due to lowered temperatures and dilution of the oxygen supply A simple suppression algorithm has been implemented in FDS that attempts to gauge whether or not a flame is viable at the fuel oxygen interface The Technical Reference Guide 1 contains more details about how the mech anism works The only parameters you can control are the Limiting Oxygen Index X_02_LL and the CRITICAL FLAME TEMPERATURE Both are set on the REAC line The default values are 0 15 volume fraction and 1427 C respectively To eliminate any gas phase suppression set X_O2_LL to 0 To turn off suppression completely set SUPPRESSION FALSE on the MISC line CO Production An algorithm has been implemented that computes the combustion as a two step reaction that predicts the formation and destruction of CO The Technical Reference Guide 1 contains more details about how the mechanism works This algorithm is used when CO_PRODUCTION is set to TRUE
183. ing ring of fire Note that the RAMP_0 is used in this construct to turn the burning on and off to simulate the consumption of fuel as the fire spreads radially It should not be used to mimic the t squared curve the whole point of the exercise is to mimic this curve in a more natural way Eventually the fire goes out as the ring grows past the boundary of the rectangle Some trial and error is probably required to find the SPREAD_RATE that leads to a desired time history of the heat release rate 47 8 2 7 Special Topic Non Planar Walls and Targets All obstructions in FDS are assumed to conform to the rectilinear mesh and all bounding surfaces are assumed to be flat planes However many objects like cables pipes and ducts are not flat Even though these objects have to be represented in FDS as boxes you can still perform the internal heat transfer calculation as if the object were really cylindrical or spherical For example the input lines amp OBST XB 0 0 5 0 1 1 1 2 3 4 3 5 SURF_ID CABLE amp SURF ID CABLE MATL_ID PVC GEOMETRY CYLINDRICAL THICKNESS 0 01 can be used to model a power cable that is 5 m long cylindrical in cross section 2 cm in diameter The heat transfer calculation is still one dimensional that is it is assumed that there is a uniform heat flux all about the object This can be somewhat confusing because the cable is represented as an obstruction of squ
184. initial time step used to advance the solution of the discretized equations Usually only the duration of the simulation is required on this line via the parameter T_END Time End The default is 1 s Note TWFINTWFIN will still work but it has been deprecated it is recommended that T_END be used now instead For example the following line will instruct FDS to run the simulation for 3400 seconds S TIME T_END 5400 If T_END is set to zero only the set up work is performed allowing you to quickly check the geometry in Smokeview If you want the timeline to start at a number other than zero you can ues the parameter T_BEGIN Time Begin to specify the time written to file for the first timestep This would be useful for matching timelines of experimental data or or video recordings This does not run any of the simulation prior to the T_BEGIN value It is only used to offset the reported starting time from zero 23 Time based RAMPs are evaluated using the actual time if the RAMP activation time is the same as T_BEGIN otherwise the are evaluated using the time from when the RAMP activates Therefore if you are setting _BEGIN in order to test a time based CTRL or DEVC that is ultimately linked to a RAMP then you should set T_BEGIN to be slightly less than the time the RAMP will activate For example if you were testing a VENT that is to open at 10 s whose SURF_ID uses a RAMP T_BEGIN shou
185. ion see Section 7 3 VENT Vent Parameters COLOR Character See Section 8 6 CTRL_ID Character ID of Control Function DEVC_ID Character ID of Controlling Device FYI Character Comment String has no effect IOR Integer Orientation Index MASS_FRACTION N Real Array Mass Fraction of species N at OPEN vent kg kg MB Character Mesh Boundary OUTLINE Logical Draw vent as outline FALSE PBX PBY PBZ Real Coordinate Plane RGB 3 Integer Triplet See Section 8 6 SPREAD RATE Real See Section 8 2 6 m s 0 0 SURF_ID Character Associated Surface INERT EXTURE_ORIGIN 3 Real Triplet See Section 8 6 1 m 0 0 0 P_EXTERIOR Real Temperature at OPEN vent C TRANSPARENCY Real Transparency indicator 1 0 XB 6 Real Sextuplet Min Max physical coordinates m XYZ 3 Real Triplet See Section 8 2 6 m 123 13 27 ZONE Pressure Zone Parameters Table 13 27 For more information see Section 8 3 ZONE Pressure Zone Parameters ID Character IDentifier LEAK_AREA N Real Leakage area to pressure zone N m XB 6 Real Sextuplet Coordinates of Zone m 124 Chapter 14 Conversion of Old Input Files to FDS 5 Many changes and improvements have been made in the latest release FDS 5 To make an FDS 4 input data file compatible with the new FDS 5 application a few changes must be made to the file This appendix will point out all the changes that need to be made to convert an FDS 4
186. ir influence on the heat release rate Validation studies have shown that FDS predicts well the transport of heat and smoke when the HRR is prescribed In such cases minor changes in the properties of bounding surfaces do not have a significant impact on the results However when the HRR is not prescribed but rather predicted by the model using the thermophysical properties of the fuels the model output is sensitive to even minor changes in these properties The sensitivity analyses described in this chapter are all performed in basically the same way For a given scenario best estimates of all the relevant physical and numerical parameters are made and a baseline simulation is performed Then one by one parameters are varied by a given percentage and the changes in predicted results are recorded This is the simplest form of sensitivity analysis More sophisticated techniques that involve the simultaneous variation of several parameters are impractical with a CFD model because the computation time is too long and the number of parameters too large to perform the necessary number of calculations to generate decent statistics 17 1 Grid Sensitivity The most important decision made by a model user is the size of the numerical grid In general the finer the numerical grid the better the numerical solution of the equations FDS is second order accurate in space and 163 time meaning that halving the grid cell size will decrease the discr
187. j Technically this is the enthalpy difference between the products and the reactant A positive value indicates that the reaction is endothermic that is the reaction takes energy out of the system Usually the HEAT_OF_REACTION is accurately known only for simple phase change reactions like the vaporization of water For other reactions it must be determined empirically Here is an example of a material that burns in the neighborhood of 350 C converting all its mass to fuel gases NU_FUEL 1 amp MATL ID My Fuel FYI Properties completely fabricated SPECIFIC_HEAT 1 0 CONDUCTIVITY 0 1 DENSITY 100 0 HEAT_OF_COMBUSTION 15000 N_REACTIONS 1 NU_FUEL 1 1 REFERENCE_TEMPERATURE 1 350 HEAT_OF_REACTION 1 3000 Note that the 1 has been added to the reaction parameters to emphasize the fact that these parameters are stored in arrays of length equal to N REACTIONS If there is only one reaction you need not include the 1 but it is a good habit to get into Note also that the HEAT_OF_COMBUSTION is the energy released per unit mass of fuel gas that mixes with oxygen and combusts This has nothing to do with the pyrolysis process so why is it specified here The answer is that there can be only one gas phase reaction of fuel and oxygen in FDS but there can be dozens of different materials and dozens of solid phase reactions To ensure that the
188. l Area Network LAN 100 Mbps or on a cluster of Linux PCs linked together with a dedicated fast 1000 Mbps network The Windows computers use MPICH2 a free implementation of MPI from Argonne National Laboratory USA 10 MPICH2 With MPICH2 a parallel FDS calculation can be invoked either from the command line or by using a Graphical User Interface GUI After the MPICH2 libraries are installed on each computer and the neces sary directories are shared FDS is run using the command issued from one of the computers mpiexec file config txt where config txt is a text file containing the name and location of the FDS executable name of the FDS input file the working directory and the names of the various computers that are to run the job For example the config txt file might look like this for a job run at NIST with computers named fire_1 fire_2 and fire_3 exe fire_l nist gov NIST FDS fds5_mpi exe job_name fds dir fire_1l nist gov Projects hosts fire_l nist gov 2 fire_2 nist gov 1 fire_3 nist gov 2 The numbers following the host machines represent the number of threads to run on that particular ma chine In this example 5 threads are run for an FDS calculation that has 5 meshes The exe and dir directories need to be shared with the latter having read and write permissions All the computers must be able to access the executable and the working directory on fire_1 This is achieved u
189. l grid is refined the discretization error decreases and a more faithful rendering of the flow field emerges The issue of grid sensitivity is extremely important to the proper use of the model and will be taken up in the next chapter A common technique of testing flow solvers is to systematically refine the numerical grid until the computed solution does not change at which point the calculation is referred to as a Direct Numerical Solution DNS of the governing equations For most practical fire scenarios DNS is not possible on conventional computers However FDS does have the option of running in DNS mode where the Navier Stokes equations are solved without the use of sub grid scale turbulence models of any kind Because the basic numerical method is the same for LES and DNS DNS calculations are a very effective way to test the basic solver especially in cases where the solution is steady state Throughout its development FDS has been used in DNS mode for special applications For example FDS or its core algorithms have been used at a grid resolution of roughly 1 mm to look at flames spreading over paper in a microgravity environment 21 22 23 24 25 26 as well as g jitter effects aboard spacecraft 27 Simulations have been compared to experiments performed aboard the US Space Shuttle The flames are laminar and relatively simple in structure and the comparisons are a qualitative assessment of the model solution Similar studi
190. lame extinction Material Layers Past versions of FDS have assumed that solid boundaries consist of a single homogenous layer Now solid boundaries can be modeled with multiple layers of materials with each material specified via a new namelist group called MATL This change makes past input files obsolete Command Line Format FDS is still run from the command line but the syntax is slightly different than in previous versions See Section 3 for details Database Previous versions of FDS used a separate database file to store material and reaction parame ters This file is no longer available and now all parameters must be specified within the input file Device Descriptions The method used to describe a device and or sensor Sprinkler Heat Detector Ther mocouple etc has changed See Section 11 1 for more information on defining devices and their properties Any device can be used to control sprinkler activation and the creation and removal of vents or obstacles Sprinklers The external sprinkler files used in previous versions are no longer used All information about sprinklers and other fire specific devices are conveyed in the input file Sprinklers are now defined with the new method of describing devices mentioned above See Section 11 1 for more information Control Functions A new group of input parameters is available to describe functions that control sprinkler activation the creation and removal of vents or obstacles a
191. ld be set slightly less than 10 s 1 The initial time step size can be specified with DT This parameter is normally set automatically by dividing the size of a mesh cell by the characteristic velocity of the flow During the calculation the time step is adjusted so that the CFL Courant Friedrichs Lewy condition is satisfied The default value of DT is 5 dxdy 5z 3 gH s where x Sy and z are the dimensions of the smallest mesh cell H is the height of the computational domain and g is the acceleration of gravity If something sudden is to happen right at the start of a simulation like a sprinkler activation it is a good idea to set the initial time step to avoid a numerical instability caused by too large a time step Experiment with different values of DT by monitoring the initial time step sizes recorded in the output file job_name out One additional parameter in the TIME group is SYNCHRONIZE a logical flag TRUE or FALSE indi cating that in a multi mesh computation the time step for each mesh should be the same thus ensuring that each mesh is processed each iteration More details can be found in Section 6 3 2 The default value of SYNCHRONIZE is TRUE 24 6 3 Computational Meshes The MESH Namelist Group Table 13 11 All FDS calculations must be performed within a domain that is made up of rectilinear volumes called meshes Each mesh is divided into re
192. les in the case of a multiple mesh job called CHID restart or CHID_nn restart To restart a job the file s CHID restart should exist in the working directory and the phrase RESTART TRUE needs to be added to the MISC line of the input data file For example suppose that the job whose CHID is plume is halted by creating a dummy file called plume stop in the directory where all the output files are being created To restart this job from where it left off add RESTART TRUE to the MISC line of the input file plume fds or whatever you have chosen to name the input file The existence of a restart file with the same CHID as the original job tells FDS to continue saving the new data in the same files as the old If RESTART_CHID is also specified on the MISC line then FDS will look for old output files tagged with this string instead of using the specified CHID on the HEAD line In this case the new output files will be tagged with CHID and the old output files will not be altered When running the restarted job the diagnostic output of the restarted job is appended to the file CHID out that was created by the original job All of the other output files from the original run are appended as well There may be times when you want to save restart files periodically during a run as insurance against power outages or system crashes If this is the case at the start of the original run set DT_RESTART 50 on the DUMP line to save restart files every
193. lgorithm within FDS He is currently funded by NIST under grant 6ONANB53D1205 from the Fire Research Grants Program 15 USC 278f He is the principal developer of the multi parameter mixture fraction combustion model and control logic within FDS Bryan Klein is an Information Technology Specialist in the Building and Fire Research Laboratory of NIST Before coming to NIST Bryan worked for five years with Western Fire Center Inc performing a wide range of activities including fire modeling data acquisition programming and quantitative fire measurements His current focus is on FDS development and user support along with experimental model validation work vi Acknowledgments The Fire Dynamics Simulator in various forms has been under development for almost 25 years However the publicly released software has only existed since 2000 Since its first release continued improvements have been made to the software based largely on feedback from its users Included here are some who made important contributions At NIST thanks to Dan Madrzykowski Doug Walton Bob Vettori Dave Stroup Steve Kerber and Nelson Bryner who have used FDS and Smokeview as part of several investigations of fire fighter line of duty deaths As part of these studies they have provided valuable information on the model s usability and accuracy when compared to large scale measurements made during fire reconstructions The US Nuclear Regulatory Commission has provi
194. ll size smaller than the square root of the material diffusivity k pc By default the solid mesh cells increase towards the middle of the material layer and are smallest on the layer boundaries The default parameters are usually appropriate for simple heat transfer calculations but sometimes the use of pyrolysis reactions makes the temperatures and burning rate fluctuate The numerical stability of the solid phase solution may then be improved by making the mesh density more uniform inside the material and by making the mesh cells smaller Adjustments may also be needed in case of extremely transient heat transfer situations Use STRETCH_FACTOR 1 on the SURF line to have a perfectly uniform mesh Values between 1 and 2 give different levels of stretching The size of all the mesh cells can be scaled by setting CELL_SIZE_FACTOR less than 1 0 For example CELL_STZE_FACTOR 0 5 makes the mesh cells half the size Setting WALL INCREMENT 1 on the TIME line forces the solid phase temperatures to be solved on every time step See Section 8 7 for ways to check and improve the accuracy of the solid phase calculation 58 8 5 User Specified Functions The RAMP and TABL Namelist Groups Many of the parameters specified in the input file are fixed constants However there are several parameters that may vary in time temperature or space These functions can be complex thus you have to have some way to convey them T
195. ller usually finer mesh embedded within it Details within the fine mesh especially related to fire growth and spread may not be picked up by the coarse mesh In such cases it is preferable to isolate the detailed fire behavior within one mesh and position coarser meshes at the exterior boundary of the fine mesh Then the fine and coarse meshes mutually exchange information e Experiment with different mesh configurations using relatively coarse mesh cells to ensure that infor mation is being transferred properly from mesh to mesh There are two issues of concern First does it appear that the flow is being badly affected by the mesh boundary If so try to move the mesh bound aries away from areas of activity Second is there too much of a jump in cell size from one mesh to another If so consider whether the loss of information moving from a fine to a coarse mesh is tolerable e Be careful when using the shortcut convention of declaring an entire face of the domain to be an OPEN vent Every mesh takes on this attribute See Section 7 3 for more details e It is possible starting with FDS 5 to have a background pressure rise in multiple pressure zones even if the pressure zones cross mesh boundaries See Section 8 3 for more information e Ina parallel calculation you can force the time steps in all meshes to be the same by setting SYNCHRONIZ on the TIME line Starting in FDS 5 this is the default for all modes
196. lls is time consuming The parameter DT_MASS controls the frequency of output 93 MAXIMUM_DROPLETS Maximum number of Lagrangian particles that can be included on any mesh at any given time Default 500000 SMOKE3D If FALSE do not produce an animation of the smoke and fire Itis TRUE by default FLUSH_FILE_BUFFERS By default every 10 time steps FDS purges the output file buffers and forces the data to be written out into the respective output files To stop this from happening set this parameter to FALSE 12 2 Output Options 12 2 1 Point Measurement Devices For many commonly used measurement devices there is no need to associate a specific PROP line to the DEVC entry In such cases use the character string QUANTITY to indicate that a particular gas or solid phase quantity at the point should be recorded in the output file with the suffix _devc csv The quantities are listed in Table 12 1 Many of the gas phase quantities are self explanatory For example if you just want to record the time history of the temperature at a given point add amp DEVC XYZ 6 7 2 9 2 1 QUANTITY TEMPERATURE ID T 1 and a column will be added to the output file CHID_deve csv under the label T 1 In this case the ID has no other role than as a column label in the output file Note that versions of FDS prior to version 5 used an 8 cell linear interpolation for a given gas phase point measure
197. locity of 1 2 m s and with a tangential velocity of 0 5 m s in either the x or y direction and 0 3 m s in either the y or z direction depending on what the normal direction is 8 2 4 Species and Species Mass Flux Boundary Conditions There are two species boundary conditions that can be specified see Section 9 2 for details on inputting and using species These boundary conditions are MASS_FLUX N and MASS_FRACTION N where N refers to a given species is via its place in the input file For example the second listed species is N 2 If a simple no flux condition is desired at a solid wall do not set anything If the mass fraction of the Nth species is to be some value at a forced flow boundary VEL or MASS_FLUX_TOTAL set MASS_FRACTION N equal to the desired mass fraction on the appropriate SURF line If the mass flux of the Nth species is desired set MASS_FLUX N instead of MASS FRACTION N If MASS _FLUX N is set no VEL should be set It is automatically calculated based on the mass flux The inputs MASS_FLUX N and typically MASS_FRACTION N should only be used for inflow boundary conditions MASS_FLUX N should be positive with units of kg m s 46 Note that specifying MASS_ FRACTION N sets the ghost cell values for the species mass fractions Since the mass conservation equation is an advection diffusion equation if the specified velocity is small then the diffusion term can dominate resulting in an unintended m
198. ly transparent See Section 16 7 1 for an example 39 If an obstruction is not to be punctured by a HOLE add PERMIT_HOLE FALSE to the OBST line It is a good idea to inspect the geometry by running either a setup job T_END 0 on the TIME line or a short time job to test the operation of devices and control functions Note that a HOLE has no effect on a VENT or a mesh boundary It only applies to OBSTstructions 7 3 Applying Surface Properties The VENT Namelist Group Table 13 26 Whereas the OBST group is used to specify obstructions within the computational domain the VENT group Table 13 26 is used to prescribe planes adjacent to obstructions or external walls The vents are chosen in a similar manner to the obstructions with the sextuplet xB denoting a plane abutting a solid surface Two of the six coordinates must be the same denoting a plane as opposed to a solid The term VENT is somewhat misleading Taken literally a VENT can be used to model components of the ventilation system in a building like a diffuser or a return In these cases the VENT coordinates form a plane on a solid surface forming the boundary of the duct No holes need to be created through the solid it is assumed that air is pushed out of or sucked into duct work within the wall Less literally a VENT is used simply as a means of applying a parti
199. mbustion and Flame 133 499 502 2003 134 180 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 A Hamins M Bundy I K Puri K B McGrattan and W C Park Suppression of Low Strain Rate Non Premixed Flames by an Agent In Proceedings of the 6th International Microgravity Combustion Workshop NASA CP 2001 210826 pages 101 104 National Aeronautics and Space Administration Lewis Research Center Cleveland Ohio May 2001 134 K B McGrattan R G Rehm and H R Baum Fire Driven Flows in Enclosures Journal of Computa tional Physics 110 2 285 291 1994 134 R Siegel and J R Howell Thermal Radiation Heat Transfer Taylor amp Francis New York 4th edition 2002 142 Y B Zel dovich and Y P Raizer Physics of shock waves and high temperature hydrodynamic phenom ena Dover Publications New York 2002 Translated from the Russian and then edited by W D Hayes and R F Probstein 143 147 D Drysdale An Introduction to Fire Dynamics John Wiley and Sons New York 2nd edition 2002 144 H S Carslaw and J C Jaegar Conduction of Heat in Solids Oxford University Press 2nd edition 1959 144 K W Childs HEATING 7 Multidimensional Finite Difference Heat Conduction Analysis Code System Technical Report PSR 199 Oak Ridge National Laboratory Oak Ridge TN 1998 145 LR Thomas K A M Moinuddin and I D Bennetts The Effect of Fuel Quantity and Locati
200. ment In other words if you specified a point via the triplet of real numbers xyz FDS would calculate the value of the quantity by linearly interpolating the values defined at the centers of the 8 nearest cells Starting in FDS 5 this is no longer done Instead FDS reports the value of the QUANTITY in the cell where the point xyz is located When prescribing a solid phase quantity be sure to position the probe at a solid surface It is not always obvious where the solid surface is since the mesh does not always align with the input obstruction locations To help locate the appropriate surface the parameter IOR must be included when designating a solid phase quantity If the orientation of the solid surface is in the positive x direction IOR 1 negative x direction IOR 1 positive y IOR 2 negative IOR 2 positive z IOR 3 and negative z IOR 3 There are still instances where FDS cannot determine which solid surface is being designated in which case an error message appears in the diagnostic output file Re position the probe and try again For example the line amp DEVC XYZ 0 7 0 9 2 1 QUANTITY WALL_TEMPERATURE IOR 2 ID designates the surface temperature of a wall facing the negative y direction 12 2 2 Integrated non pointwise Measurement Devices In addition to point measurements the DEVC group can be used to report integrated quantities See Ta ble 12 1 For example you may want to know the mass fl
201. meter 1 8 OFFSET Real Droplet offset distance m 0 05 OPERATING_PRESSURE Real Sprinkler pipe pressure atm 1 PART_ID Character Name of associated PART line QUANTITY Character Name of associated output RTI Real Response Time Index yms 100 SMOKEVIEW_ID Character Name of drawn object SPRAY_ANGLE 2 Real Cone angles for water spray deg 60 75 SPRAY_PATTERN_TABLE Character TABL for spray pattern 117 13 17 RADI Radiation Parameters Table 13 17 For more information see Section 9 4 RADI Radiation Parameters ANGLE_INCREMENT Integer Number of angles skipped per update 5 CH4_BANDS Logical Include extra fuel bands FALSE KAPPAO Real Constant absorption coefficient 1 m 0 NMIEANG Integer Number of polar angles 15 NUMBER_RADIATION_ANGLES Integer Number of solid angles 104 PATH_LENGTH Real Path length for radiation calc m RADIATIVE_FRACTION Real Radiative Loss Fraction 0 35 RADTMP Real Assumed radiative source temp C 900 TIME_STEP_INCREMENT Integer Number time steps skipped 3 WIDE_BAND_MODEL Logical Non gray gas assumption FALSE 13 18 RAMP Ramp Function Parameters Table 13 18 For more information see Section 8 5 RAMP Ramp Function Parameters FYI Character Comment String has no effect F Real Function value FYI Character Comment String has no
202. mps up like tanh t t If negative then the HRR ramps up like 1 7 If the fire ramps up following a 1 curve it remains constant after TAU_Q sec onds These rules apply to TAU_T and TAU_V as well The default value for all TAUs is 1 s If something other than a tanh or t ramp up is desired then a user defined burning history must be input To do this set RAMP_Q RAMP_T or RAMP_V equal to a character string designating the ramp function to use for that particular surface type then somewhere in the input file generate lines of the form amp RAMP ID rampnamel T 0 0 F 0 0 amp RAMP ID rampnamel T 5 0 F 0 5 amp RAMP ID rampnamel T 10 0 F 0 7 amp RAMP ID rampname2 T 0 0 F 0 0 amp RAMP ID rampname2 T 10 0 F 0 3 amp RAMP ID rampname2 T 20 0 F 0 8 Here T is the time and F indicates the fraction of the heat release rate wall temperature velocity mass fraction etc to apply Linear interpolation is used to fill in intermediate time points Be sure that the prescribed function starts at T 0 0 Note that each set of RAMP lines must have a unique ID and that the lines must be listed with monotonically increasing T Note that the TAUs and the RAMPs are mutually exclusive For a given surface quantity both cannot be prescribed 59 As an example the simple blowing vent from above can be controlled via the lines
203. n A common source of confusion in FDS is the distinction between gas phase combustion and solid phase pyrolysis The former refers to the reaction of fuel vapor and oxygen the latter the generation of fuel vapor at a solid or liquid surface Whereas there can be many types of combustibles in an FDS fire simulation there can only be one gaseous fuel The reason is cost It is expensive to solve transport equations for multiple gaseous fuels Consequently the burning rates of solids and liquids are automatically adjusted by FDS to account for the difference in the heats of combustion of the various combustibles In effect you specify a single gas phase reaction as a surrogate for all the potential fuel sources The gas phase reaction can be described in two ways By default a so called mixture fraction model is used to account for the evolution of the fuel gas from its surface of origin through the combustion pro cess The alternative is what is referred to as the finite rate approach where all of the individual gas species involved in the combustion process are defined and tracked individually This is a costlier and more compli cated approach than the mixture fraction model This chapter describes both methods with an emphasis on the more commonly used mixture fraction model 9 1 Mixture Fraction Combustion The REAC Namelist Group There are two ways of designating a fire the first is to specify a Heat Release Rate Per Unit Area HRRPUA on a SU
204. n Number Writing an FDS Input File The Basic Structure of an Input File Del Naming he A a ee a hae Cer aaa as Be ig ade eek ne 5 2 Namelst Formats on caso he de eG ed a aS ba wa BR ae Aa 2 3 Input Pile Structure 2 1 2 deme oh RAO HAE Eb Oe ea hee bed bo xi 6 Setting the Bounds of Time and Space 6 1 Naming the Job The HEAD Namelist Group Table 13 6 6 2 Simulation Time The TIME Namelist Group Table 13 24 6 3 Computational Meshes The MESH Namelist Group Table 13 11 6 3 1 Two Dimensional and Axially Symmetric Calculations 6 3 2 Multiple Meshes and Parallel Processing o oo 6 3 3 Mesh Stretching The TRNX TRNY and or TRNZ Namelist Groups Table 13 25 6 3 4 Choosing the Right Mesh Dimensions o 6 4 Miscellaneous Parameters The MISC Namelist Group Table 13 12 6 4 1 6 4 2 6 4 3 6 4 4 6 4 5 6 4 6 Stopping and Restarting Calculations oo o e Special Topic Defying Gravity ss e eos oe es aa S Special Topic Restoring the Baroclinic Vorticity Special Topic Stack Bech 4 4 0 cosa ba ee bare wo a Bad Pa do Special Topic Large Eddy Simulation Parameters Special Topic Numerical Stability Parameters 6 5 Special Topic Unusual Initial Conditions The INIT Namelist Group Table 13 8 6 6 Spec
205. n also be purely numerical like the size of the numerical grid FDS typically requires the user to provide several dozen different types of input parameters that describe the geometry materials combustion phenomena efc By design the user is not expected to provide numerical parameters besides the grid size although the optional numerical parameters are described in both the Technical Reference Guide and the User s Guide FDS does not limit the range of most of the input parameters because applications often push beyond the range for which the model has been validated FDS is still used for research at NIST and elsewhere and the developers do not presume to know in all cases what the acceptable range of any parameter is Plus FDS solves the fundamental conservation equations and is much less susceptible to errors resulting from input parameters that stray beyond the limits of simpler empirical models However the user is warned that he she is responsible for the prescription of all parameters The FDS manuals can only provide guidance The grid size is the most important numerical parameter in the model as it dictates the spatial and tem poral accuracy of the discretized partial differential equations The heat release rate is the most important physical parameter as it is the source term in the energy equation Property data like the thermal conduc tivity density heat of vaporization heat capacity etc ought to be assessed in terms of the
206. n is modeled simply as a solid boundary that blows or sucks air regardless of the surrounding pressure field In reality fans operate based on the pressure drop across the duct or manifold in which they are installed A very simple fan curve is given by Ap APmax APmax 8 2 Vfan ductUmax sign Apmax Ap where A quer is the area of the duct m Umax is the air velocity m s and Apmax is the maximum pressure difference the fan can operate upon Figure 8 1 displays a typical fan curve 1000 500 Static Pressure Pa cS 500 1000 15 10 5 0 5 10 15 Volume Flow Rate m s Figure 8 1 Fan curve corresponding to VOLUME_FLUX 10 and MAX_PRESSURE 500 The ideal velocity of the fan Umax is specified via the parameter VEL on the appropriate SURF line Alternatively the volume flow rate AguctUmax can be specified using VOLUME_FLUX Do not use both These parameters were already introduced in Section 8 2 To simulate the behavior of a real fan a few extra parameters need to be specified To set Apmax the maximum operating over pressure add MAX_PRESSURE to the SURF line Note that MAX_ PRESSURE should always be positive and in units of Pa If in the simulation the computed pressure exceeds the specified MAX_PRESSURE then there will be a backflow in the duct Here is an example how fans can be specified The actual case fan_test is included in the V am
207. nd code execution termination or dumping of restart files See Section 11 5 for details Numerical Mesh Previous versions of FDS used separate input groups to define the numerical grid and the computational domain Now the two groups have been merged into a single simplified MESH namelist group Namelist groups PDIM and GRID shall no longer be used in the input file See Section 6 3 for more detail Pressure Zones It is possible in FDS 5 to declare individual regions in the computational domain to have background pressures different from ambient allowing for calculations of leakage fan curves and so forth See Section 8 3 for more details Stack Effect and Atmospheric Stratification Improvements have been made to better characterize a strat ified atmosphere and the movement of air in a tall building due to temperature differences between inside and outside Adiabatic Surface Temperature A new output quantity has been added to facilitate using FDS output in thermal and mechanical finite element models See Section 8 2 2 for more information Development Distribution and Formal User Support Starting with FDS 5 the open source development environment SourceForge net is being used for configuration management code archiving revision tracking bug fixes user suggestions and so on See Section 2 1 for more information FDS Verification and Validation Guide Starting with FDS 5 more emphasis has been placed on main taining a permanent
208. nder Windows by sharing Under Unix Linux and OS X the process involves cross mounting the file systems of the various machines LAM MPI On the Linux cluster in the Building and Fire Research Lab at NIST LAM MPI a free implemenation from Indiana University is installed With LAM MPI the computers to be used are linked prior to the actual execution of FDS with a separate command called a lamboot FDS is then run using the command mpirun np 5 fds5_mpi job_name fds where the 5 indicates that 5 processors are to be used In this case the executable fds5_mpi is located in the working directory To make the process run in the background mpirun np 5 fds5_mpi job_name fds gt amp job_name err The file job_name err contains what is normally printed out to the screen Note that there are several other implementations of MPI some free some not Support for the software varies thus FDS has been designed to run under any of the more popular versions without too much user intervention However keep in mind that parallel processing is a relatively new area of computer science and there are bound to be painful growth spurts in the years ahead nttp www lam mpi org 11 3 2 Monitoring Progress Diagnostics for a given calculation are written into a file called CHID out The CPU usage and simulation time are written here so you can see how far along the program has progressed At any time during a
209. ne TRIP_DIRECTION A positive integer means the device will change state when its value increases past the setpoint and a negative integer means the device will change state when its value decreases past the setpoint The default value is 1 LATCH If this logical value is set to TRUE the device will only change state once The default value is TRUE INITIAL_STATE This logical value is the initial state of the device The default value is FALSE For example if an obstruction associated with the device is to disappear set INITIAL STATE TRUE If you desire to control FDS using more complex logic than can be provided by the use of a single device and its setpoint control functions can be specified using the CTRL input See Section 11 5 for more on CTRL functions The simplest example of a device is just a timer amp DEVC XYZ 1 2 3 4 5 6 ID my clock QUANTITY TIME SETPOINT 30 v Anything associated with the device via the parameter DEVC_ID my clock will change its state at 30 seconds For example if the text were added to an OBST line that obstruction would change from its INITIAL STATE Of FALSE to TRUE after 30 s In other words it would be created at 30 s instead of at the start of the simulation This is a simple way to open a door or window 11 4 1 Creating and Removing Obstructions In many fire scenarios the opening or closing of
210. ned com modity 78 Chapter 11 Devices and Control Logic Sprinklers smoke detectors heat flux gauges and thermocouples may seem to be completely unrelated but from the point of view of FDS they are simply devices that operate in specific ways depending on the properties assigned to them They can be used to record some quantity of the simulated environment like a thermocouple or they can represent a mathematical model of a complex sensor like a smoke detector and in some cases they can trigger events to happen like a timer Past versions of FDS used device specific namelist groups like SPRK HEAT SMOD and THCP but the number and variety of fire specific sensing and measurement devices continues to expand and the data structures in FDS could not easily accommodate all possibilities In addition the logic associated with sensor activation and subsequent actions like a vent opening had become too complicated and prone to bugs Devices are now specified with a new format that streamlines and expands the possibilities of sensor profiles Starting in FDS 5 all devices in the broadest sense of the word are designated via the namelist group DEVC In addition advanced functionality and properties are accommodated via additional namelists groups called CTRL Control and PROP Properties 11 1 Device Location and Orientation The DEVC Namelist Group Table 13 4 Regardless of the specific properties each de
211. nformation internally to determine the amount of combustion 65 products that are formed Vco VHmo Z Vo Veo t 5 a Veco X Vco 1 z H frac Vsoot H frac VO gt Vsoot VHy Wr Veo Wo Wr VA Wy YH 2 W Vsoot v Vv VN 2 Vother W W H fracWH ag 1 H frac Wc The following parameters may be prescribed on the REAC line Note that the various YIELDs are for well ventilated post flame conditions There are options to predict various species yields in under ventilated fire scenarios but these special models still require the post flame yields for CO soot and any other species listed below ID A character string naming the reaction C H O N OTHER The fuel chemical formula All numbers are positive Mixture Fraction only de fault values are those of propane MW_OTHER Average molecular weight for OTHER g mol Mixture Fraction only default is the molecular weight of N2 28 g mol Y_O2_INFTY Ambient mass fraction of oxygen Mixture Fraction only default 0 23 Y_F_INLET Mass fraction of fuel in fuel stream Mixture Fraction only default 1 0 SOOT_YIELD The fraction of fuel mass converted into smoke particulate ys Note that this parameter does not apply to the processes of soot growth and oxidation but rather to the net production of the smoke particulate from the fire Mixture Fraction only default 0 01 SOOT_H_FRACTION The fraction of the a
212. ng the Burn Away Feature box_burn_away 152 16 49 A Couch Fire couch 2020 e a A a 153 16 4 10 Flame Spread along a Cable Tray cable_tray 154 16 3 DeCS gt oane e ade a hE ee ee ee Se he e a ha 155 16 5 1 Aspiration Detector beam_detector o o 155 16 5 2 Aspiration Detector aspiration_detector o 156 16 6 Droplets and Sprays haras eR aa baw aa A 157 16 6 1 Water Droplet Evaporation water_evaporation 157 16 6 2 A Liquid Fuel Spray Burner spray_burner 158 16 6 3 Measuring Water Flux bucket_test 0 o 159 16 6 4 Complex Spray Patterns bucket_test_2 o o 159 16 7 General Functionalily s o ec e se 482528 b4 ida esos ad vel ba es 161 XV 16 7 1 Creating and Removing HOLEs and OBSTructions create_remove 161 17 Sensitivity Analysis 163 Vil Grid Sensitivity caridad do ad A ed es 163 17 2 Sensitivity of Large Eddy Simulation Parameters o o 165 17 3 Sensitivity of Radiation Parameters 2 ee 165 17 4 Sensitivity of Thermophysical Properties of Solid Fuels 166 LS SUIS vA ala a a aa aaa eae ed a de 167 IV Working with the FDS Source Code 169 18 Compiling FDS 171 18 1 PDS Source Codes sopas o dde o A a dl eee 171 19 Output File Formats 173 191 Diasnostie Output 2a aa corres aa aa RARA ee awa 1
213. no effect FUEL Logical Liquid Fuel FALSE GAMMA _D Real Parameter for size distribution 2 4 HEAT_OF_ COMBUSTION Real Heat of Combustion kJ kg HEAT_OF_VAPORIZATION Real Latent Heat of Vaporization kJ kg 2259 HORIZONTAL_VELOCITY Real Droplet speed horizontal m s 0 2 ID Character Identifier INITIAL_TEMPERATURE Real Initial Temperature C TMPA IASSLESS Logical Massless tracers FALSE IASS_PER_VOLUME Real Droplet mass per unit volume kg m 1 AXIMUM_DIAMETER Real Above which droplet breaks up um oo INIMUM_DIAMETER Real Below which droplet evaporates um 20 ELTING_TEMPERATURE Real Melting Temperature C 0 ONODISPERSE Logical Uniform droplet size FALSE NUMBER_INITIAL_DROPLETS Integer Number of droplets at start 0 QUANTITIES 10 Character Quantities for coloring RGB 3 Integers Color indices 0 255 SAMPLING_FACTOR Integer Filter for output file 1 SPEC_ID Character Name of gas species SPECIFIC_HEA Real Droplet specific heat kJ kg K 4 184 STATIC Logical Stationary Particles FALSE VAPORIZATION_TEMPERATURE Real Liquid Droplet Boiling Temp C 100 VERTICAL_VELOCITY Real Droplet speed vertical m s 0 5 XB 6 Real Initial particle placement region m WATER Logical Water Droplet FALSE 115 13 15 PROF Wall Profile Parameters Table 13 15 For more information see Section 12 2 4 PROF Wall Profile Parameters TOR Real Orientation of wall surface
214. nvolves creating accounts for a given user on each machine sharing directories increasing the speed of the network making each machine aware of the others etc Some of these details are handled by the parallel processing software others are not Undoubtedly the process will be simplified in years to come but for the moment parallel processing is still relatively new and requires more expertise in terms of understanding both the operating system and the network connections of a given set of computers FDS uses MPI Message Passing Interface 3 to allow multiple computers to run a single FDS job Actually the job must be broken up into multiple meshes and a processor is assigned to work on each mesh Each processor runs an FDS job called a thread for its given mesh and the MPI handles the transfer of information between meshes There are different implementations of MPI much like there are different Fortran and C compilers Each implementation is essentially a library of subroutines called from FDS that transfer data from one thread to another across a fast network The format of the subroutine calls has been widely accepted in the community allowing different vendors and organizations the freedom to develop better software while working within an open framework The way FDS is executed in parallel depends on which implementation of MPI has been installed At NIST the parallel version of FDS is presently run on Windows PCs connected by the Loca
215. o punch more than enough to create the hole This ensures that the hole is created through the entire obstruction For example if the OBST line denotes a wall 0 1 m thick amp OBST XB 1 0 1 1 0 0 5 0 0 0 3 0 and you want to create a door add this amp HOLE XB 0 99 1 11 2 0 3 0 0 0 2 0 The extra centimeter added to the x coordinates of the hole make it clear that the hole is to punch through the entire obstruction When a HOLE is created the affected obstruction s are either rejected or created or removed at pre determined times See Section 11 4 1 for details To allow a hole to be controlled with either the CTRL or DEVC namelist groups you will need to add the CTRL_ID or DEVC_ID parameter respectively to the HOLE line If it is desired that the obstruction s to be cut out should have a different color than the original obstruc tion set the COLOR or integer triplet RGB on the HOLE line see Section 8 6 When a HOLE is in a FALSE state an obstruction is placed in the hole To make this obstruc tion transparent the TRANSPARENCY parameter should be specified by a real number from 0 1 Note that if TRANSPARENCY is specified then either a COLOR or RGB triplet ought to be specified as well A TRANSPARENCY value near but not equal to zero can be used to simulate a window when the HOLE s INITIAL_STATE FALSE When the DEVC or CTRL is activated and changes the state of the hole to TRUE the HOLE is then open and complete
216. odeled in FDS There was no mechanical ventilation and the fire was assumed to grow as a function of the time from ignition squared The compart ment was a 3 m by 3 m by 6 1 m space Temperatures were sampled 12 cm below the ceiling Four grid sizes were chosen for the analysis 30 cm 15 cm 10 cm 7 5 cm Temperature estimates were not found to change dramatically with different grid dimensions Using FDS version 1 Bounagui et al 39 studied the effect of grid size on simulation results to de termine the nominal grid size for future work A propane burner 0 1 m by 0 1 m was modeled with a heat release rate of 1500 kW A similar analysis was performed using Alpert s ceiling jet correlation 40 that also showed better predictions with smaller grid sizes In a related study Bounagui et al 41 used FDS to evaluate the emergency ventilation strategies in the Louis Hippolyte La Fontaine Tunnel in Montreal Canada Xin 42 used FDS to model a methane fueled square burner 1 m by 1 m in the open Engineering correlations for plume centerline temperature and velocity profiles were compared with model predictions to assess the influence of the numerical grid and the size of the computational domain The results showed that FDS is sensitive to grid size effects especially in the region near the fuel surface and domain size effects when the domain width is less than twice the plume width FDS uses a constant pressure assumption at open boundaries This
217. odels often re ferred to as two zone models compute this quantity directly along with the average temperature of the upper and lower layers In a computational fluid dynamics CFD model like FDS there are not two distinct zones but rather a continuous profile of temperature Nevertheless there are methods that have been developed to estimate layer height and average temperatures from a continuous vertical profile of temperature One such method 9 is as follows Consider a continuous function T z defining temperature T as a function of height above the floor z where z 0 is the floor and z H is the ceiling Define T as the upper layer temperature T as the lower layer temperature and Zin as the interface height Compute the quantities H H zint Tu Zint Tr T z dz m ao Da T r ko a3 h H Zint Solve for Zint 7 11 h H h hbT 2T H 12 9 Zint Let 7 be the temperature in the lowest mesh cell and using Simpson s Rule perform the numerical integra tion of J and h T is defined as the average upper layer temperature via H H 2m T J T z dz 12 10 Zint 99 Further discussion of similar procedures can be found in Ref 10 The quantities LAYER HEIGHT UPPER TEMPERATURE and LOWER TEMPERATURE can be designated via device DEVC lines in the input filet For example the entry amp DEVC XB 2 0 2 0 3 0 3 0 0 0 3 0 QUA
218. ole and unformatted Note that there is blanking that is blocked out data points are not plotted If the statement WRITE_XYZ TRUE is included on the DUMP line then the mesh data is written out to a file called CHID xyz WRITE LU13 IBAR 1 JBAR 1 KBAR 1 WRITE LU13 X I 1 0 IBAR J 0 JBAR K 0 KBAR CUY J I 0 IBAR J 0 JBAR K 0 KBAR Z K I 0 IBAR J 0 JBAR K 0 KBAR IBLK I J K I 0 IBAR J 0 JBAR K 0 KBAR where X Y and Z are the coordinates of the cell corners and IBLK is an indicator of whether or not the cell is blocked If the point x Y Z is completely embedded within a solid region then IBLK is 0 Otherwise IBLK is 1 Normally the mesh file is not dumped The flow variables are written to a file called CHID_ _ q where the stars indicate a time at which the data is output The file is written with the lines WRITE LU14 IBAR 1 JBAR 1 KBAR 1 WRITE LU14 ZERO ZERO ZERO ZERO WRITE LU14 00 1 J K N I 0 IBAR J 0 JBAR K 0 KBAR N 1 5 The five channels N 1 5 are by default the temperature C the u v and w components of the velocity m s and the heat release rate per unit volume KkW m Alternate variables can be specified with the input parameter PLOT3D_QUANTITY 1 5 on the DUMP line Note that the data is interpolated at cell corners thus the dimensions of the Plot3D data sets are one larger than the dimension
219. olid surface be adiabatic that is there is no net heat transfer radiative and convective from the gas to the solid For this case all that must be prescribed on the SURF line is ADIABATIC TRUE nothing else FDS will compute a wall temperature so that the sum of the convective and radiative fluxes is zero 8 2 3 Velocity and Total Mass Flux Boundary Conditions Velocity boundary conditions affect both the normal and tangential components of the velocity vector at boundaries The normal component of velocity is controlled by the parameter VEL If VEL is negative the flow is entering the computational domain If VEL is positive the flow is exiting the domain Sometimes it is desired that a given volume flux through a vent be prescribed rather than a velocity If this is the case then VOLUME_FLUX can be prescribed instead of VEL The units are m s If the flow is entering the computational domain VOLUME_FLUX should be a negative number Note that either VEL or VOLUME_FLUX should be prescribed not both The choice depends on whether an exact velocity is desired at a given vent or whether the given volume flux is desired The dimensions of the vent that are prescribed usually change because the prescribed vent dimensions are sometimes altered so that the vent edges line up with mesh cells Also note that a SURF group with a VOLUME_FLUX prescribed can be invoked by either a VENT or an OBS
220. on 16 4 5 T 8 4 3 Special topic Making Fuels Disappear BURN_AWAY If a burning object is to disappear from the calculation once it is exhausted of fuel set BURN_AWAY TRUE Use this parameter cautiously If an object has the potential of burning away a significant amount of extra memory has to be set aside to store additional surface information as the rectangular block is eaten away If BURN_AWAY is prescribed as a SURF parameter then a solid object with this SURF_ID disappears from a calculation as the mass of each of its mesh cells are consumed The mass of each mesh cell is the volume of the mesh cell multiplied by the DENSITY of the materials making up the the obstruction Note also that if BURN_AWAY is prescribed the SURF should be applied to the entire object not just a face of the object because it is unclear how to handle edges of solid obstructions that have different SURF_IDs on different faces Also note that the amount of combustible fuel equals the DENSITY of the designated materials multiplied by the volume of the mesh cell If the volume of the obstruction changes because it has to conform to the 57 uniform mesh FDS does not adjust the burning rate to account for this as 1t does with various quantities associated with areas like HRRPUA If all the material components of the surface are reacting and the pyrolysis reactions have no solid residue the thickness of the sur
221. on Fast Fourier Transforms FFTs in the y and z directions the second and third dimensions of the mesh should each be of the form 2 3 57 where m and n are integers For example 64 2 72 233 and 108 273 are good mesh cell divisions but 37 99 and 109 are not The first number of mesh cell divisions the I in IJK does not use FFTs and need not be given as a product of small numbers However you should experiment with different values of divisions to ensure that those that are ultimately used do not unduly slow down the calculation Here is a list of numbers between 1 and 1024 that can be factored down to 2 s 3 s and 5 s 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 27 30 32 36 40 45 48 50 54 60 64 72 75 80 81 90 96 100 108 120 T25 128 135 144 150 160 162 180 192 200 216 225 240 243 250 256 270 288 300 320 324 360 CES 384 400 405 432 450 480 486 500 512 540 576 600 625 640 648 675 720 729 750 768 800 810 864 900 960 972 1000 1024 6 3 1 Two Dimensional and Axially Symmetric Calculations The governing equations solved in FDS are written in terms of a three dimensional Cartesian coordinate system However a two dimensional Cartesian or two dimensional cylindrical axially symmetric calcu lation can be performed by setting the J in the IJK triplet to 1 on the MESH line For axial symmetry add CYLINDRICAL TRUE to the MESH line and the coordinate x is then interpreted as the radial coordi nate r No boundary conditions should be
222. on of an IGNITION_TEMPERATURE delays burning until your specified temperature is reached The addition of HEAT_OF_VAPORIZATION tells FDS to account for the energy used to vaporize the fuel For any of these options if a MATL line is invoked by a SURF line containing a specified HRRPUA then that MATL ought to have only thermal properties It should have no reaction parameters product yields and so on like those described in the previous sections By specifying HRRPUA you are controlling the burning rate rather than letting the material pyrolyze based on the conditions of the surrounding environment Liquid Fuels For a liquid fuel the thermal properties are similar to those of a solid material with a few exceptions The evaporation rate of the fuel is governed by the Clausius Clapeyron equation see FDS Technical Reference Guide for details The only drawback of this approach is that the fuel gases burn regardless of any ignition source Thus if a liquid fuel is specified the fuel begins burning at once Here is an example of a steel pan filled with a thin layer of ethanol Note that the material properties have not all been verified amp MATL ID ETHANOL LIQUID EMISSIVITY 1 0 U_FUEL 0 97 56 HEAT_OF_REACTION 880 CONDUCTIVITY 0 17 SPECIFIC_HEAT 2 45 DENSITY 787 ABSORPTION_COEFFICIE 40 BOILING_TEMPERATURE 76
223. on on Small Enclosure Fires Journal of Fire Protection Engineering 17 2 85 102 May 2007 148 K B McGrattan B W Klein S Hostikka and J E Floyd Fire Dynamics Simulator Version 5 User s Guide NIST Special Publication 1019 5 National Institute of Standards and Technology Gaithersburg Maryland October 2007 158 P Friday and F W Mowrer Comparison of FDS Model Predictions with FM SNL Fire Test Data NIST GCR 01 810 National Institute of Standards and Technology Gaithersburg Maryland April 2001 164 A Bounagui N Benichou C McCartney and A Kashef Optimizing the Grid Size Used in CFD Simulations to Evaluate Fire Safety in Houses In 3rd NRC Symposium on Computational Fluid Dynamics High Performance Computing and Virtual Reality pages 1 8 Ottawa Ontario Canada December 2003 National Research Council Canada 164 R L Alpert SFPE Handbook of Fire Protection Engineering chapter Ceiling Jet Flows National Fire Protection Association Quincy Massachusetts 3rd edition 2003 164 A Bounagui A Kashef and N Benichou Simulation of the Dynamics of the Fire for a Section of the L H La Fontaine Tunnel IRC RR 140 National Research Council Canada Ottawa Canada KI1AOR September 2003 164 Y Xin Assessment of Fire Dynamics Simulation for Engineering Applications Grid and Domain Size Effects In Proceedings of the Fire Suppression and Detection Research Application Symposium Orlando Florida National Fire
224. on_c heat_conduction_d 60 50 2 40 A 5 30 20 r r 7 10 T 7 r 7 10000 20000 30000 40000 50000 0 10000 20000 30000 40000 Time s Time s 144 16 4 2 Temperature Dependent Thermal Properties heat_conduction_kc This example demonstrates the 1 D heat conduction in cartesian cylindrical and spherical geometries with temperature dependent thermal properties The reference results were computed using HEATING ver sion 7 3 a multi dimensional finite difference general purpose heat transfer model 35 In cartesian and cylindrical cases the results have also been verified using a commercial finite element solver ABAQUS The sample of homogenous material is initially at 0 C and at t gt 0 exposed to a gas at 700 C A fixed heat transfer coefficient of 10 W Km is assumed The density of the material is 10000 kg m The conductivity and specific heat are functions of temperature with the following values k 0 0 10 W m K k 200 0 20 W m K c 0 1 0 kJ kg K c 100 1 2 kJ kg K c 200 1 0 kJ kg K The thickness radius of the sample is 0 01 m In the cartesian case the back surface of the material is exposed to a gas at 0 C In the Figure below the solid lines are FDS results and the open symbols are the HEATING results An example input with cylindrical geometry looks like amp MATL ID MAT_1 EMISSIVITY 0 0 CONDUCTIVITY_RAMP K_RAMP SPECIFIC_HEAT_RAMP C_RAMP DENSITY 10000 amp RAMP ID K_RA
225. oplet particle Default 4 184 kJ kg K DIAMETER Median volumetric diameter of droplets particles with the distribution assumed to be a combi nation of Rosin Rammler and log normal Default 500 um The width of the distribution is controlled by the parameter GAMMA_D default 2 4 The Rosin Rammler log normal distribution is given by i dpe Mae ad Sd F d 4 Eh 84 pans 10 1 1 07 9 693 fe dn lt a Note that the parameter o is given the value o 2 v2x In 2 y 1 15 y which ensures that the two functions are smoothly joined at d dm The larger the value of y the narrower the droplet size is distributed about the median value Note that you can prevent droplets or particles from ex ceeding MAXIMUM_DIAMETER which is infinitely large by default Also note that droplets less than MINIMUM_DIAMETER are assumed to evaporate in a single time step eliminating numerical instabilities that can occur when droplets get very very small The default MINIMUM_DIAMETER is 20 um To pre vent FDS from generating a distribution of droplets particles altogether set MONODISPERSE TRUE on the PART line in which case every droplet or particle will be assigned the same DIAMETER 75 The following parameters pertain to the evaporation of liquid droplets It is assumed by default that non massless particles are liquid droplets but you can specify EVAPORATE FALSE
226. or parameters are for the Heskestad model with a characteristic LENGTH of 1 8 m For the Cleary model the ALPHAs and BETAs must all be listed explicitly Suggested constants for unidentified ionization and photoelectric detectors presented in Table 11 1 ACTIVATION_OBSCURATION is the thresh old value in units of m The threshold can be set according to the setting commonly provided by the manufacturer The default setting is 3 28 m 1 ft Table 11 1 Suggested Values for Smoke Detector Model See Ref 6 for others Detector Qe Be amp c L Be Cleary Ionization I1 2 5 0 7 0 8 0 9 Cleary Ionization I2 1 8 1 1 1 0 0 8 Cleary Photoelectric P1 1 8 1 0 1 0 0 8 Cleary Photoelectric P2 1 8 0 8 0 8 0 8 Heskestad Ionization 1 8 11 3 5 Beam Detection Systems A beam detector can be defined by specifying the endpoints x1 y1 z1 x2 y2 z2 of the beam using XB and the total total obscuration at which the detector activates The two endpoints must lie in the same mesh FDS determines which mesh cells lie along the path specified by the two endpoints The beam detector response is evaluated as N Obscuration exp x Y Psoot as x 100 11 2 i l where i is a mesh cell along the path of the beam Psoo is the soot density of the mesh cell and Ax is the distance within the mesh cell that is traversed by the beam 83 amp
227. order of 10 000 lines of Fortran statements various researchers outside of NIST have been able to work with it add enhancements needed for very specific applications or for research purposes and report back to the developers bugs that have been detected The source code is organized into 14 separate files each containing subroutines related to a particular feature of the model like the mass momentum and energy conservation equations sprinkler activation and sprays the pressure solver etc The lengthiest routines are devoted to input output and initialization Most of those working with the source code do not concern themselves with these lengthy routines but rather focus on the finite difference algorithm contained in a few of the more 133 important files Most serious errors are found in these files for they contain the core of the algorithm The external researchers provide feedback on the organization of the code and its internal documentation that is comments within the source code itself Plus they must compile the code on their own computers adding to its portability Some of the work performed by researchers who have modified the source code is discussed in Volume 2 However most of the routine error reports are via electronic mail and are undocumented Most of the current error reports involve routines that are not frequently used by the FDS developers For example the opening of compartment doors or the breaking of windows especi
228. ource code DTDX TMP I 1 J K TMP 1 J K RDXN I KDTDX I J K 5 KP 1 1 J K KP 1 J K DTDX DIDY TMP 1 J 1 K TMP 1 J K RDYN J KDTDY I J K 5 KP I J 1 K KP I J K DTDY DTDZ TMP 1 J3 K 1 TMP 1I J K RDZN K KDTDZ I J K 5 KP I J K 1 KP I J K DTDZ DELKDELT KDTDX 1 J K KDTDX I RDX I NS KDTDY 1 3 K KDTDY I J 1 K RDY J KDTDZ I J K KDTDZ 1 J K 1 This is one of the simpler constructs because the pattern that emerges within the lines of code make it fairly easy to check However a mis typing of an I or a J a plus or a minus sign or any of a hundred different mistakes can cause the code to fail or worse produce the wrong answer A simple way to eliminate many of these mistakes is to run simple scenarios that have perfectly symmetric initial and boundary conditions For example put a hot cube in the exact center of a larger cold compartment turn off gravity and watch the heat diffuse from the hot cube into the cold gas Any simple error in the coding of the energy equation will show up almost immediately Then turn on gravity and in the absence of any coding error a perfectly symmetric plume will rise from the hot cube This checks both the coding of the energy and the momentum equations Similar checks can be made for all of the three dimensional finite difference routines So extensive are these types of checks that the release version of FDS has a routine tha
229. ous permutations providing of course that the usual restrictions on the use of restart files are followed For example the lines amp DEVC ID temp QUANTITY TEMPERATURE SETPOINT 1000 XYZ 4 5 6 7 3 6 amp DEVC ID velo QUANTITY VELOCITY SETPOINT 10 XYZ 4 5 6 7 3 6 amp CTRL ID kill FUNCTION_TYPE KILL INPUT_ID temp CTRL ID restart FUNCTION_TYPE RESTART INPUT_ID velo will lead to the job being stopped gracefully with restart files output when the temperature at a given point rises above 1000 C or to just restart files being output when the velocity at a given point exceeds 10 m s 11 5 5 Control Function CUSTOM For most of the control function types the logical true false output of the devices and control functions and the time they last changed state are taken as inputs A CUSTOM function uses the numberical output of a DEVC along with a RAMP to determine the output of the function When the RAMP output for the DEVC value is negative the CTRL will have the value of its INITIAL STATE When the RAMP output for the DEVC value is positive the CTRL will have the opposite value of its INITIAL_STATE In the case below the CUSTOM control function uses the numerical output of a timer device as its input The function returns true the default vaule for INITIAL_STATE is FALSE when the F parameter in the ramp specified with RAMP_ID is
230. ow out of a door or window To report this add the line amp DEVC XB 0 3 0 5 2 1 2 5 3 0 3 0 QUANTITY MASS FLOW ID whatever Note that in this case a plane is specified rather than a point The sextuplet xB is used for this purpose Notice when a flow is desired two of the six coordinates need to be the same Another QUANTITY HRR can be used to compute the total heat release rate within a subset of the domain In this case the sextuplet xB 94 ought to define a volume rather than a plane Specification of the plane or volume over which the integration 1s to take place can only be done using XB avoid planes or volumes that cross multiple mesh boundaries FDS has to decide which mesh to use in the integration and it chooses the finest mesh overlapping the centroid of the designated plane or volume 12 2 3 Output Statistics A useful feature of a device DEVC is to specify an output quantity along with a desired statistic For example amp DEVC XYZ 2 3 4 5 6 7 QUANTITY TEMPERATURE ID whatever STATISTICS MAX causes FDS to write out the maximum gas phase temperature over the entire mesh containing the point xYZ Note that it does not compute the maximum over the entire computational domain just that particular mesh Other STATISTICS include MIN and MEAN They can be used for both gas and solid phase output quantities In the case of solids the specification of a SURF_ID limits the
231. p V Guide In it two simple compartments share a common wall Both compartments are considered as separate pressure zones Two fans are mounted in the Partition Wall blowing in opposite directions amp SURF ID BLOW LEFT POROUS TRUE VEL 0 2 DUCT_PATH 1 2 MAX _PRESSURE 1000 amp SURF ID BLOW RIGHT POROUS TRUE VEL 0 4 DUCT_PATH 2 1 MAX _PRESSURE 1000 amp ZONE XB 3 0 0 0 1 0 1 0 0 0 2 0 Pressure Zone 1 amp ZONE XB 0 0 3 0 1 0 1 0 0 0 2 0 Pressure Zone 2 amp OBST XB 0 0 0 0 1 0 1 0 0 0 2 0 Partition Wall SURF_ID BLOW RIGHT PERMIT_HOLE FALSE amp HOLE XB 0 amp OBST XB 0 bh o Ly 05 Lp O21 Ost 0 0 1 0 1 0 4 oo 6 6 o o 50 amp HOLE XB 0 1 amp OBST XB 0 0 OL O S 00d dias 0 0 0 1 0 1 1 4 SURE_ID BLOW LEFT PERMIT_HOLE FALSE 7 Consider a few of the extra parameters The attribute POROUS TRUE allows hot smokey gases to pass through the obstructions that represent the fans These obstructions are merely flat plates by necessity The velocity VEL associated with a POROUS surface is meant to represent the velocity in the positive or negative coordinate direction as indicated by its sign This is different than the convention used when the SURF is attached to
232. phenomena closer in to the fire However grid resolution is more critical for near field phenomena because numerical diffusion near the fire on coarse grids does not have the same fortuitous effect as it does on far field results In general coarse resolution will decrease temperatures and velocities by smearing the values over the large grid cells This can affect the radiative flux convection to surrounding solids and ultimately flame spread and fire growth 167 168 Part IV Working with the FDS Source Code 169 Chapter 18 Compiling FDS This section describes what you need to know if you want to compile the FDS source code yourself It is not a step by step guide more detailed instructions can be found on the web site http fds sv sourceforge net If a compiled version of FDS exists for the machine on which the calculation is to be run and no changes have been made to the original source code there is no need to re compile the code For example the file fds5 exe is the compiled single processor program for a Windows based PC thus PC users do not need a Fortran compiler and do not need to compile the source code For machines for which an executable has not been compiled you must compile the code Fortran 90 95 and C compilers are needed for compilation 18 1 FDS Source Code Table 18 1 lists the files that make up the source code The files with suffix f90 contain free form Fortran 90 instructions conforming to the AN
233. pors FDS now uses an absorption coefficient for both the gas and solid liquid phases Here are the input lines that describe the properties of ethanol and the pan in which it lies amp MATL ID ETHANOL LIQUID EMISSIVITY 1 0 NU_FUEL 0 97 HEAT_OF_REACTION 880 CONDUCTIVITY 0 17 SPECIFIC_HEAT 2 45 DENSITY 787 ABSORPTION_COEFFICIENT 40 BOILING_TEMPERATURE 76 amp SURF ID ETHANOL POOL FYI 4 kg of ethanol in a 0 7 m x 0 8 m pan COLOR YELLOW MATL_ID ETHANOL LIQUID STEEL CONCRETE THICKNESS 0 0091 0 001 0 05 TMP_INNER 18 The results of three calculations are shown below each identical except for the value of the ABSORPTION_COEFFICIENT The results of a single experiment are also shown courtesy of Ian Thomas Victoria University Australia 36 1000 ethanol_pan 800 Ed hs Experiment e FDS 40 m i A FDS x 150 m 600 7 7 p AA FDS x 1000 m 7 D D 400 14 F I 200 0 T 0 100 200 300 400 500 Time s 148 16 4 6 A Thermoplastic thermoplastic This example just exercises the solid phase algorithm in FDS Essentially the gas phase is shut off except for the imposition of a 50 kW m in composition to PMMA amp MATL ID PMMA CONDUCTIVITY 0 25 SPECIFIC_HEAT 1 0 DENSITY 500 N_REACTIONS 1 NU_FUEL 1 HEAT_OF_REACTION 1578 HEAT_OF_COMBUSTION 25200 REFERENCE_TE
234. pressure for fan Pa 1E12 LRPUA Real Mass loss rate per unit area kg m s 0 NPPC Integer Number of particles per cell 1 PARTICLE _MASS_ FLUX Real See Section 10 2 kg m s 0 PART_ID Character Lagrangian Particle ID POROUS Logical Non solid boundary FALSE PLE Real Atmospheric profile exponent 0 3 PROFILE Character Name of velocity profile RAMP _MF I Character Ramp ID for species I RAMP _Q Character Ramp ID for HRR RAMP_T Character Ramp ID for temp RAMP_V Character Ramp ID for velocity RGB 3 Integer Triplet Color indices 0 255 255 204 102 SHRINK Logical Shrinking material TRUE SLIP_FACTOR Real Velocity Slip Condition 0 5 STRETCH_FACTOR Real See Section 8 4 5 2 0 TAU_MF 1 Real Array Ramp time for species I s 1 TAU_O Real Ramp time for HRR s 1 TAU_T Real Ramp time for temp s 1 121 TAU_V Real Ramp time for velocity s 1 EXTURE_HEIGHT Real Height of texture image m 1 EXTURE_MAP Character Name of texture map file EXTURE_WIDTH Real Width of texture image m 1 HICKNESS IL Real Array Thickness of Layer IL m 0 TMP_BACK Real Back surface temperature BC C 20 TMP_FRONT Real Front surface temperature C 20 TMP_INNER Real Initial solid temperature C 20 TRANSPARENCY Real Transparency of obstruction 1 VEL Real Normal velocity m s 0 VEL_T Real Pair Tangential velocity comps m s 0 VOLUME_F
235. prinkler each time the sprinkler is sited For these devices use a separate namelist group called PROP to store the relevant parameters Each PROP line is identified by a unique ID and invoked by a DEVC line by the string PROP_ID The ID might be the manufacturer s name like ACME Sprinkler 123 for example The best way to describe the PROP group is to list the various special devices and their properties 11 3 1 Sprinklers Here is a very simple example of sprinkler amp PROP ID K 11 QUANTITY SPRINKLER LINK TEMPERATURE RTI 148 C_FACTOR 0 7 ACTIVATION_TEMPERATURE 74 OFFSET 0 10 PART_ID water drops FLOW_RATE 189 3 DROPLET_VELOCITY 10 SPRAY _ANGLE 30 80 amp DEVC ID Spr_60 XYZ 22 88 19 76 7 46 PROP_ID K 11 amp DEVC ID Spr_61 XYZ 22 88 21 76 7 46 PROP_ID K 11 A sprinkler known as Spr_60 is located at a point in space given by xYZ It is a K 11 type sprinkler whose properties are given on the PROP line Note that the various names IDs mean nothing to FDS 80 except as a means of associating one thing with another so try to use IDs that are as meaningful to you as possible The parameter QUANTITY SPRINKLER LINK TEMPERATURE does have a specific meaning to FDS directing it to compute the activation of the device using the standard RTI algorithm The various sprinkler properties will be discussed below
236. r rates between nodes 7 2 3 Computer Operating System OS and Software Requirements The goal of making FDS and Smokeview publicly available has been to enable practicing fire protection engineers to perform fairly sophisticated fire simulations at a reasonable cost Thus FDS and Smokeview have been designed for computers running Microsoft Windows Mac OS X and various implementations of Unix Linux MS Windows An installation package is available for Windows operating system It is not recommended to run FDS Smokeview under any version of MS Windows released prior to Windows 2000 Mac OS X A Mac OS X Tiger FDS zip archive is available for both the PowerPC and Intel architectures OS X 10 4 x or better is recommended versions of OS X prior to 10 4 x are not officially supported Users can always download the latest version of FDS source and compile FDS for other versions of OS X See Appendix 18 for details Unix Linux Unix Linux users can run FDS and Smokeview by downloading the appropriate pre compiled executables and installing them wherever they see fit If the pre compiled FDS executable does not work usually because of library incompatibilities the FDS source code can be downloaded and compiled using a Fortran 90 and C compiler See Appendix 18 for details If Smokeview does not work on the Linux or Unix workstation you should use a Windows or Mac PC to view FDS output FDS in Parallel For those wishing to run FDS in parall
237. rameter 0 VISCOSITY Real Dynamic Viscosity mu kg m s 120 13 22 SURF Surface Properties Table 13 22 For more information see Section 8 2 SURF Surface Properties ADIABATIC Logical Adiabatic thermal BC FALSE BACKING Character Back boundary condition VOID BURN_AWAY Logical Object can vanish FALSE CELL SIZE FACTOR Real See Section 8 4 5 1 0 COLOR Character Surface Color CONVECTIVE_HEAT_FLUX Real Heat flux at surface kW m 0 DUCT_PATH Integer Pair Pressure Zones for fans 0 0 _ COEFFICIENT Real Extinguishing coefficient 1 s 0 EMISSIVITY Real Emissivity 0 9 EXTERNAL FLUX Real Heat flux to surface kW m 0 FYI Character Comment String GEOMETRY Character Geometry type CARTESIAN HEAT_OF_VAPORIZATION Real For specified HRR only kJ kg 0 HRRPUA Real HRR Per Unit Area kW m 0 ID Character IDentifier IGNITION_TEMPERATURE Real Ignition temperature C 5000 LEAK_PATH Integer Pair Pressure Zones for leakage ASS_FLUX I Real Array For species I 0 ASS_FLUX_TOTAL Real Total Mass Flux MASS FRACTION I Real Array For species I fATL_ID Char 2D Array Layer Component fATL_MASS_FRACTION Real 2D Array Layer Component AX_ PRESSURE Real Max over
238. rameter QUANTITIES is an array of character strings indicating which scalar quantities should be used to color the particles or droplets when viewed as an animation The choices are DROPLET_TEMPERATURE C DROPLET_DIAMETER Um DROPLET_VELOCITY m s DROPLET_MASS kg DROPLET_AGE s As a default if no QUANTITIES are specified and none are selected in Smokeview then Smokeview will display particles with a single color To select this color specify either RGB or COLOR By default water droplets are colored blue and fuel droplets yellow All others are colored black 10 6 Special Topic Droplet Fuel Sprays The evaporation of water droplets from sprinklers has been generalized so that a liquid fuel spray nozzle can be modeled Fuel evaporation is triggered by the inclusion of the phrase FUEL TRUE on the appropriate PART line The spray nozzle characteristics are specified in the same way as those for a sprinkler Here is an example of a liquid fuel spray nozzle also see Section 16 6 2 amp DEVC ID nozzle_1 XYZ 4 0 3 0 5 PROP_ID nozzle QUANTITY TIME un ETPOINT 0 amp PART ID heptane droplets FUEL TRUE VAPORIZATION_TEMPERATURE 98 HEAT_OF_VAPORIZATION 316 SPECIFIC_HEAT 2 25 DENSITY 688 QUANTITIES 1 2 DROPLET_DIAMETER DROPLET_TEMPERATURE DROPLETS_PER_SECOND 2000 DIAMETER 1000 HE
239. rays 10 7 Special Topic Suppression by Water Mixture Fraction Model Only 11 Devices and Control Logic 11 1 Device Location and Orientation The DEVC Namelist Group Table 13 4 11 2 Device Output 11 3 Special Devices and their Properties The PROP Namelist Group Table 13 16 11 3 1 Sprinklers 11 352 Nozzles vovere wee ws 11 3 3 Heat Detectors 11 3 4 Smoke Detectors 11 3 5 Beam Detection Systems 11 3 6 Aspiration Detection Systems cor es cecce cedran aaro a a 11 4 Basic Control Logic 11 4 1 Creating and Removing Obstructions o e e e 11 4 2 Activating and Deactivating VEMS lt 2 4 dick ado ie dO es da 11 5 Advanced Control Functions The CTRL Namelist Group 4 11 5 1 Control Functions ANY ALL ONLY and AT_LEAST 11 5 2 Control Function TIME_D BEA Sia sae a Smid pina thm ee ge ae ae OO Ce aay cients CBs Re rede eng 11 5 3 Control Function DEADBAND lt 0 e eae a e a a 11 5 4 Control Function RESTART and KILL 0 0 000 11 5 5 Control Function CUSTOM 11 5 6 Combining Control Functions A Pre Action Sprinkler System 11 5 7 Combining Control Functions A Dry Pipe Sprinkler System 12 Output Data 12 1 Output Control Parameters The DUMP Namelist Group 12 2 Output Options
240. rdware operating system and compiler involves a slightly different set of compiler and run time options and a rigorous evaluation of the source code to test its compliance with the Fortran 90 ISO ANSI standard 20 Through this process out dated and potentially harmful code is updated or eliminated and often the code is streamlined to improve its optimization on the various machines However simply because the FDS source code can be compiled and run on a wide variety of platforms does not guarantee that the numerics are correct It is only the starting point in the process because it at least rules out the possibility that erratic or spurious results are due to the platform on which the code is running Beyond hardware issues there are several useful techniques for checking the FDS source code that have been developed over the years One of the most best ways is to exploit symmetry FDS is filled with thousands of lines of code in which the partial derivatives in the conservation equations are approximated as finite differences It is very easy in this process to make a mistake Consider for example the finite difference approximation of the thermal diffusion term in the i jkth cell of the three dimensional grid Ae a Ti jk Tijk WN Tijk Ti 1 jk dx 2 x i z jk x 132 EN Ponce Titik o Ty jx Ti j 1k dy i j z k dy i j 3k dy ES k e Tik i Pea bz kta z a z which is written as follows in the Fortran s
241. re some scenarios for which it is convenient to change the ambient conditions within some rectangular region of the domain If so add lines of the form amp INIT XB 0 5 0 8 2 1 3 4 2 5 3 6 TEMPERATURE 30 Here within the region whose bounds are given by the sextuplet xB the initial temperature shall be 30 C instead of the ambient This construct can also be used for DENSITY or MASS_ FRACTION N where N indicates the Nth species listed in the input file The INIT construct may be useful in examining the influence of stack effect in a building where the temperature is different inside and out Note that a solid obstruction can be given an initial temperature via the parameter TMP_INNER on the SURF line An initial velocity can be prescribed via U0 VO and WO on the MISC line 6 6 Special Topic Setting Limits The CLIP Namelist Group Table 13 2 On rare occasions you might need to set upper or lower bounds on the density temperature or species mass fractions The parameters listed in Table 13 2 are for diagnostic purposes only 35 36 Chapter 7 Building the Model A considerable amount of work in setting up a calculation lies in specifying the geometry of the space to be modeled and applying boundary conditions to these objects The geometry is described in terms of rectangular obstructions that can heat up burn conduct heat efc and vents from which air or fuel can be either injected into or drawn f
242. re accurate prediction of the solid temperature Alternatively the single quantity 7 57 can be transferred as this is the temperature that the solid surface effectively sees It represents the gas phase thermal environment however complicated but it does not carry along the uncertainty associated with the simple solid phase heat conduction model within FDS Obviously the objective in passing information to a more detailed model is to get a better prediction of the solid temperature and ultimately its mechanical response than FDS can provide 12 3 8 Integrated Mass and Energy Fluxes through Openings The net flow of mass and energy into or out of compartments can be useful for many applications There are several outputs that address these All are prescribed via the device DEVC namelist group only For 101 example amp DEVC XB 0 3 0 5 2 1 2 5 3 0 3 0 QUANTITY MASS FLOW ID whatever outputs the net integrated mass flux through the given planar area oriented in the positive z direction in this case The three flows VOLUME FLOW MASS FLOW and HEAT FLOW are defined V Juas m pu as AE fowt T Ju dS The addition of a or to the QUANTITY names yields the integral of the flow in the positive or negative direction only In other words if you want to know the mass flow out of a compartment use MASS FLOW Or MASS FLOW depending on the orientation of the door 12 3
243. recorded in files See Section 19 7 labeled CHID_n sf where n is the index of the slice file A short fortran program fds2ascii f produces a text file from a line plane or volume of data See Section 12 4 for more details 12 2 6 Animated Boundary Quantities The BNDF Namelist Group The BNDF boundary file namelist group parameters allows you to record surface quantities at all solid obstructions As with the SLCF group each quantity is prescribed with a separate BNDF line and the output files are of the form CHID_n bf No physical coordinates need be specified however just QUANTITY See Table 12 1 For certain output quantities additional parameters need to be specified via the PROP namelist group In such cases add the character string PROP_ID to the BNDF line to tell FDS where to find the necessary extra information Note that BNDF files Section 19 8 can become very large so be careful in prescribing the time interval One way to reduce the size of the output file is to turn off the drawing of boundary information on desired obstructions On any given OBST line if the string BNDF_OBST FALSE is included the obstruction is not colored To turn off all boundary drawing set BNDF_DEFAULT FALSE onthe MISC line Then individual obstructions can be turned back on with BNDF_OBST TRUE on the appropriate OBST line Individual faces of a given obstruction can be controlled via BNDF_FACE IOR where IOR is the index o
244. redict at the start of a simulation just how long and how much memory will be required Learn how to monitor the resource usage of your computer Start with small calculations and build your way up Although many features in FDS are fairly mature there are many that are not FDS is used for practical engineering applications but also for research in fire and combustion As you become more familiar with the software you will inevitably run into areas that are of current research interest Indeed burning a roomful of ordinary furniture is one of the most challenging applications of the model So be patient and learn to dissect a given scenario into its constitutive parts For example do not attempt to simulate a fire spreading through an entire floor of a building unless you have simulated the burning of the various combustibles with relatively small calculations The examples described in Part III should help you to develop larger more complicated simulations from smaller building blocks Along with the FDS User s Guide there are resources available on the Internet These include an Issue Tracker that allows you to report bugs feature requests and ask specific clarifying questions and Group Discussions which support more general topics than just specific problems Before using these on line resources it is important to first try to solve your own problems by performing simple test calculations or debugging your input file The next f
245. rinkler Droplets 301 50 Mc dae Ta The Iteration number indicates how many time steps the code has run whereas the Cycle number for a given mesh indicates how many time steps have been taken on that mesh The date and time wall clock time are on the line starting with the word Iteration The quantity CPU step is the amount of CPU time required to complete a time step for that mesh Total CPU is the amount of CPU time elapsed since the start of the run Time step is the time step size for the given mesh Total time is the time of the simulation 173 Max Min divergence is the max min value of the function V u and is used as a diagnostic when the flow is incompressible i e no heating and Max CFL number is the maximum value of the CFL number The Radiation Loss to Boundaries is the amount of energy that is being radiated to the boundaries As compartments heat up the energy lost to the boundaries can grow to be an appreciable fraction of the Total Heat Release Rate Finally Number of Tracer Particles indicates how many passive particles are being tracked at that time Following the completion of a successful run a summary of the CPU usage per subroutine is listed This is useful in determining where most of the computational effort is being placed 19 2 Plot3D Data Quantities over the entire mesh can be output in a format used by the graphics package Plot3D The Plot3D data sets are single precision 32 bit reals wh
246. rom the flow domain A boundary condition needs to be assigned to each obstruction and vent describing its thermal properties A fire is just one type of boundary condition This chapter describes how to build the model The next chapter describes how to assign properties to the boundaries 7 1 Creating Obstructions The OBST Namelist Group Table 13 13 The namelist group OBST contains parameters used to define obstructions Each OBST line contains the coordinates of a rectangular solid within the flow domain This solid is defined by two points x1 y1 21 and x2 y2 22 that are entered on the OBST line in terms of the sextuplet XB X1 X2 Y1 Y2 Z1 22 In addition to the coordinates the boundary conditions for the obstruction can be specified with the parameter SURF_ID which designates which SURF group Section 8 2 to apply at the surface of the obstruction If the obstruction has different properties for its top sides and bottom do not specify only one SURF_ID Instead use SURF_IDS an array of three character strings specifying the boundary condition IDs for the top sides and bottom of the obstruction respectively If the default boundary condition is desired then SURF_ID S need not be set However if at least one of the surface conditions for an obstruction is the inert default it can be referred to as INERT For example amp SURF ID FIRE HRRPUA 1000 0 amp OBST XB 2 3 4 5 1 3 4 8 0 0 9 2 SURF_IDS FIRE INERT
247. rom outside the computational domain accounts for portions of the sampling network lying outside the domain defined by the MESH inputs and SETPOINT is the alarm threshold obscuration in units of m The output of the aspiration system is computed as N A 1 Psoot i t tai Mi Obscuration 1 exp Kin Liar Pes di x 100 m 11 3 i 1 Mi where m is the mass FLOWRATE of the ith sampling location Psoor i t tdi is the soot density at the ith sam pling location ty s prior DELAY to the current time t and Km is the MASS_EXTINCTION_COEFFICIENT associated with visible light 84 11 4 Basic Control Logic Devices can be used to control various actions like creating and removing obstructions or activating and deactivating fans and vents Every device has an associated QUANTITY whether it is included directly on the DEVC line or indirectly on the optional PROP line Using the DEVC parameter SETPOINT you can trigger an action to occur when the QUANTITY value passes above or below the given SETPOINT The choice is dictated by the given TRIP_DIRECTION which is just a positive or negative integer The following parameters dictate how a device will control something SETPOINT The value of the device at which its state changes For a detection type of device e g heat or smoke this value is taken from the device s PROP inputs and need not be specified on the DEVC li
248. rt off with a relatively simple file that captures the main features of the problem without getting tied down with too much detail that might mask a fundamental flaw in the calculation Initial calculations ought to be meshed coarsely so that the run times are less than an hour and corrections can easily be made without wasting too much time As you learn how to write input files you will continually run and re run your case as you add in complexity Table 5 1 provides a quick reference to all the namelist parameters and where you can find the reference to where it is introduced in the document and the table containing all of the keywords for each group 21 Table 5 1 Namelist Group Reference Table Group Name Namelist Group Description Reference Section Parameter Table BNDF Boundary File Output 12 2 6 13 4 CTRL Control Function Parameters IS 133 DEVC Device Parameters 11 1 13 4 DUMP Output Parameters 12 1 13 5 HEAD Input File Header 6 1 13 6 HOLE Obstruction Cutout El 13 7 INIT Initial Condition 6 5 13 8 ISOF Isosurface File Output 12 2 7 13 9 ATL Material Property 8 4 13 10 ESH Mesh Parameters 6 3 13 11 ISC Miscellaneous 6 4 13 12 OBST Obstruction al 13 13 PART Lagrangian Particle 10 13 14 PROF Profile Output 12 2 4 13 15 PROP Device Property 11 3 13 16 RADI Radiation 9 4 13 17 RAMP Ramp Profile 8 5 13 18 REAC Reactions 9 1 13 19
249. s Until further notice an obstruction that makes up the boundary of a pressure zone see Section 8 3 should not be created or removed The reason for this restriction is that abrupt changes in pressure can cause numerical instabilities 11 4 2 Activating and Deactivating Vents When a device or control function is applied to a VENT the purpose is to either activate or deactivate any time ramp associated with the VENT via its SURF_ID For example to control a fan with the device det2 do the following SURF ID FAN VOLUME _FLUX 5 amp VENT XB SURF_ID FAN DEVC_ID det2 amp DEVC ID det2 XYZ QUANTITY TIME SETPOINT 30 INITIAL _STATE FALSE Note that at 30 seconds the state of the FAN changes from FALSE to TRUE or more simply the FAN turns on Since there is no explicit time function associated with the FAN the default 1 second ramp up will begin at 30 seconds instead of at 0 seconds If in this example INITIAL_STATE TRUE then the fan should deactivate or turn off at 30 sec onds Essentially activation of a VENT causes all associated time functions to be delayed until the device SETPOINT is reached Deactivation of a VENT turns off all time functions Usually this means that the 86 parameters on the SURF line are all nullified so it is a good idea to check t
250. s Note that the background species cannot participate in the reaction N_S Array containing the exponents for the finite rate equation for each SPEC Note that a SPEC can be given an N_S but not a NU i e the rate equation can be dependent on a species that does not participate directly in the reaction Note that the background species cannot participate in the reaction HEAT_OF_COMBUSTION The effective heat of combustion the chemical reaction in units of kJ kg De fault 40 000 kJ kg 9 4 Radiation Transport The RADI Namelist Group For most FDS simulations thermal radiation transport is computed by default and you need not set any parameters to make this happen However there are situations where it is important to be aware of issues related to the radiative transport solver The most important issue involves the fraction of energy released from the fire as thermal radiation commonly referred to as the radiative fraction It is a function of both the flame temperature and chemical composition neither of which are reliably calculated in a large scale fire calculation because the flame sheet is not well resolved on the mesh In calculations in which the mesh cells are on the order of a centimeter and larger the temperature near the flame surface cannot be relied upon when computing the source term in the radiation transport equation especially because of the T4 dependence To compensate if you prescribe a non zero value of RADIATI
251. s Gerndt University of Louisiana USA Emanuele Gissi Corpo Nazionale dei Vigili del Fuoco Comando Prov di Genova Italy Paul Hart Swiss Re GAP Services USA Hsiao Li Kai Gary Fire Bureau Taipei Taiwan Hu Zhi Xin University of Maryland USA Ilya N Karkin SITIS Ltd Russia Susanne Kilian hhpberlin Fire Safety Engineers Germany Sung Chan Kim School of Mechanical Engineering Chung Ang University Korea Pierre Louis Lamballais Flashover Backdraft France A Leonardi StIL Studio di Ingegneria Leonardi Italy Davy Leroy Arup Fire UK Jason Liu Warrington Fire Research Australia Timothy Liu Locke Carey Fire Consultants UK Dave McGill Seneca College Ontario Canada Ken Miller Las Vegas Fire amp Rescue USA Pete Muir Safe Consulting UK Stephen Olenick Combustion Science amp Engineering Inc USA Kristopher Overholt University of Houston Downtown USA PENG Wei State Key Labortory of Fire Science China Andrew Purchase Maunsell Australia Christian Rogsch University of Wuppertal Germany Michael Roth RWDI Canada Ahmed Salem Alexandria University Egypt Robert Schmidt Combustion Science amp Engineering Inc USA Joe Skaggs CASE Forensics USA Piotr Smardz Ahearne Fire Engineering Consultants Ireland Jamie Stern Gottfried Arup Fire UK Boris Stock BFT Cognos Gmb Germany Blair Stratton Beca New Ze
252. s array element 1 through 3 inclusive Gl Note that character strings can be enclosed either by apostrophes or quotation marks Be careful not to create the input file by pasting text from something other than a simple text editor in which case the punctuation marks may not transfer properly into the text file 5 3 Input File Structure In general the namelist records can be entered in any order in the input file but it is a good idea to organize them in some systematic way Typically general information is listed near the top of the input file and detailed information like obstructions devices and so on are listed below FDS scans the entire input file each time it processes a particular namelist group With some text editors it has been noticed that the last line of the file is often not read by FDS because of the presence of an end of file character To ensure that FDS reads the entire input file add amp TAIL as the last line at the end of the input file This completes the file from HEAD to amp TAIL FDS does not even look for this last line It just forces the end of file character past relevant input Another general rule of thumb when writing input files is to only add to the file parameters that are to change from their default value That way you can more easily distinguish between what you want and what FDS wants Add comments liberally to the file so long as t
253. s ee a ee a ee a eee ee a ee Pyrolysis Models isos a4 dt dow oe aa A a ea Se aed Special topic Making Fuels Disappear BURN_AWAY Special Topic Initial and Backside Boundary Conditions Special Topic Numerical Accuracy and Stability 8 5 User Specified Functions The RAMP and TABL Namelist Groups 8 5 1 Time Dependent PUMCHORS s a sse ss a wo ee ee a Se xii 23 23 23 25 25 26 28 29 31 31 32 32 33 33 33 35 35 8 5 2 Temperature Dependent Functions 8 5 3 Tabular Functions 8 6 Coloring Obstructions Vents Surfaces and Meshes o o 8 6 1 Texture Mapping 8 7 Verifying the Solid Phase Properties lt e e o o e ee 9 Combustion and Radiation 9 1 Mixture Fraction Combustion The REAC Namelist Group 9 1 1 Important Issues Related to the Mixture Fraction Models 9 2 Extra Gas Species The SPEC Namelist Group o o 9 3 Finite Rate Combustion 9 4 Radiation Transport The RADI Namelist Group o o 10 Particles and Droplets The PART Namelist Group TOM Basics micci n a da 10 2 Controlling Particles and Droplets 10 3 Particle and Droplet Properties 10 4 Special Types of Particles and Droplets oo cccisecescdss ondaa 10 5 Coloring Particles and Droplets 10 6 Special Topic Droplet Fuel Sp
254. s of the computational mesh Smokeview can display the Plot3D data In addition the Plot3D data sets can be read into some other graphics programs that accept the data format This particular format is very convenient and recognized by a number of graphics packages including AVS IRIS Explorer and Tecplot 19 3 Device Output Data Data associated with particular devices link temperatures smoke obscuration thermocouples etc spec ified in the input file under the namelist group DEVC is output in comma delimited format in a file called CHID_devc csv The format of the file is as follows With the exception of Smokeview the graphics packages referred to in this document are not included with the source code but are commercially available 174 N_DEVC FDS Time ID 1 ID 2 r ID N_DEVC IME QUANTITY 1 QUANTITY 2 QUANTITY N_DEVC s UNITS 1 UNITS 2 UNITS N_DEVC T 1 VAL 1 1 VAL 2 1 r VAL N_DEVC 1 T 2 VAL 1 2 VAL 2 2 es VAL N_DEVC 2 where N_DEVC is the number of devices ID 1 is the user defined ID of the Ith device QUANTITY I is the physical quantity represented UNITS I the units T J the time of the Jth dump and VAL I J the value at the Ith device at the Jth time The files can be imported into Microsoft Excel or almost any other spread sheet program If the number of columns exceeds 256 the file will automatically be
255. s the same as a product of combustion like water vapor from a sprinkler or carbon dioxide from an extinguisher These gases are tracked separately thus water vapor generated by the combustion is tracked via the mixture fraction variable and water vapor generated by evaporating sprinkler droplets is tracked via its own transport equation In the case of sprinklers do not specify WATER VAPOR as an extra species it is done automatically 69 Table 9 1 Optional Gas Species 5 Species Mol Wet lo k e g mol A K AIR 29 3 711 78 6 CARBON DIOXIDE 44 3 941 195 2 CARBON MONOXIDE 28 3 690 91 7 HELIU 4 2 551 10 22 HYDROGEN 2 2 827 59 7 METHANE 16 3 758 148 6 NITROGEN 28 3 798 71 4 OXYGEN 32 3 467 106 7 PROPANE 44 5 118 237 1 WATER VAPOR 18 2 641 809 1 Recognized species that are emissive will been defined as ABSORBING and radiative absorption for those species will be computed The keyword ABSORBING can be specified on the SPEC line as well If TRUE and the species is not in the recognized list then it will be assumed to be a fuel when invoking RADCAL to compute its absorptivity 70 9 3 Finite Rate Combustion Usually FDS uses mixture fraction concepts to describe combustion However FDS can also explicitly track gas species and reactions that can occur between them This section describes how to do this
256. ses via single step reactions The fuel gases from each have different composition and heats of combustion FDS automatically adjusts the mass loss rate of each so that the effective fuel gas is that specified by the user on the RI EAC line The attribute BURN_AWAY forces FDS to break up the couch into individual cell sized blocks that will disappear from the calculation as soon as the fuel is exhausted The surface is specified as consisting of two layers with a thickness of 2 mm for the FABRIC and 10 cm for the Foam The 10 cm is chosen to be the same as the mesh cell size 153 16 4 10 Flame Spread along a Cable Tray cable_tray A common combustible in industrial settings are power control and instrument cables The cables may be bundled in a variety of conduits the most common of which is a ladder like tray From the point of view of FDS the pile of cables in a tray is a composite of a variety of plastics insulators and metal usually copper Here is one way to describe a tray of cables amp MATL ID CONDUCTIVITY SPECIFIC_HEAT DENSITY N_REACTIONS EAT_OF_REACTION EAT_OF_COMBUSTION U_FUEL amp MATL ID COPP SPECIFIC_HEAT 0 38 CONDUCTIVITY 387 DENSITY 8940 amp SURF ID COLOR MATL_ID 1 1 2 MATL _MASS_ FRACTION 1 1 2 BACKING THICKNESS amp OBST XB 2 00 2 00 0 1 amp OBST XB 2 00 2 00 0 1 amp OBST XB
257. sh is refined For fire applications the grid sensitivity studies have shown that the accuracy of the model is a function of the characteristic fire diameter D divided by the grid cell size It is not enough to describe the resolution of the calculation solely in terms of the grid cell size but rather the grid cell size relative to the heat release rate For non fire applications there are no simple means to evaluate good resolution As a rule of thumb in simulations of limited resolution FDS predictions are more reliable in the far field because the substantial numerical diffusion mimics the unresolved sub grid scale mixing This is hard to quantify other than through comparisons with experiment In some of the sensitivity studies discussed above the authors conclude that the model works best with a cell size of a given value and often this cell is not the smallest one tested In these cases the authors have found a flow scenario where the unresolved convective mixing is almost exactly offset by numerical diffusion This is fortuitous but the conclusion does not necessarily extend to other scenarios The disadvantage of any turbulence model large eddy simulation included is that good results are not guaranteed on grids of limited resolution The advantage of LES over other turbulence models is that the solution of the actual governing equations not a temporal or spatial average is obtained as the mesh is refined The same can be said for
258. sh may change over time due to the solid phase reactions Array Q contains the values of the output quantity which may be wall temperature density or component density 178 Bibliography 1 2 LL 3 LL 4 Ly 5 6 7 _ 8 9 10 11 12 13 K B McGrattan S Hostikka J E Floyd H R Baum and R G Rehm Fire Dynamics Simulator Ver sion 5 Technical Reference Guide NIST Special Publication 1018 5 National Institute of Standards and Technology Gaithersburg Maryland October 2007 i 3 33 68 72 77 81 G P Forney User s Guide for Smokeview Version 5 A Tool for Visualizing Fire Dynamics Simulation Data NIST Special Publication 1017 1 National Institute of Standards and Technology Gaithersburg Maryland August 2007 i 3 7 W Gropp E Lusk and A Skjellum Using MPI Portable Parallel Programming with the Message Passing Interface MIT Press Cambridge Massachusetts 2 edition 1999 10 Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications NUREG 1824 United States Nuclear Regulatory Commission Washington DC 2007 30 R C Reid J M Prausnitz and B E Poling Properties of Gases and Liquids McGraw Hill New York 4th edition 1987 70 P J DiNenno editor SFPE Handbook of Fire Protection Engineering National Fire Protection Asso ciation Quincy Massachusetts 3rd edition 2002 83 Pamela P Walatka and Pi
259. sitive Smagorinsky 48 originally proposed a value of 0 23 but researchers over the past three decades have used values ranging from 0 1 to 0 23 There are also refinements of the original Smagorinsky model 49 50 51 that do not require the user to prescribe the constants but rather generate them automatically as part of the numerical scheme 17 3 Sensitivity of Radiation Parameters Radiative heat transfer is included in FDS via the solution of the radiation transport equation for a non scattering gray gas and in some limited cases using a wide band model The equation is solved using a technique similar to finite volume methods for convective transport thus the name given to it is the Finite Volume Method FVM There are several limitations of the model First the absorption coefficient for 165 the smoke laden gas is a complex function of its composition and temperature Because of the simplified combustion model the chemical composition of the smokey gases especially the soot content can effect both the absorption and emission of thermal radiation Second the radiation transport is discretized via approximately 100 solid angles For targets far away from a localized source of radiation like a growing fire the discretization can lead to a non uniform distribution of the radiant energy This can be seen in the visualization of surface temperatures where hot spots show the effect of the finite number of solid angles The probl
260. smokey delay amp CTRL ID delay FUNCTION_TYPE TIME_DELAY INPUT_ID smokey DELAY 30 amp CTRL ID smokey FUNCTION_TYPE AT_LEAST N 2 INPUT_ID SD_1 SD_2 SD_3 SD_4 11 5 7 Combining Control Functions A Dry Pipe Sprinkler System For a dry pipe sprinkler system the normally dry sprinkler pipes are pressurized with gas When a link activates in a sprinkler head the pressure drop allows water to flow into the pipe network For this example it takes 30 s to flood the piping network once a sprinkler link has activated The sequence of events required for operation is first ANY of the links must activate which starts the 30 s TIME_DELAY Once the 30 s delay has occurred each nozzle with an active link the ALL control functions will then flow water amp DEVC XYZ 2 2 3 PROP_ID Acme Sprinkler Link ID LINK 1 amp DEVC XYZ 2 3 3 PROP_ID Acme Sprinkler Link ID LINK 2 amp PROP ID Acme Sprinkler Link QUANTITY LINK TEMP ACTIVATION_TEMPERATURE 74 RTI 30 T RATURE amp DEVC XYZ 2 2 3 PROP_ID Acme Nozzle QUANTITY CONTROL ID NOZZLE 1 CTRL_ID nozzle 1 trigger amp DEVC XYZ 2 3 3 PROP_ID Acme Nozzle QUANTITY CONTROL ID NOZZLE 2 CTRL_ID nozzle 2 trigger CTRL ID check links FUNCTION_TYPE ANY INPUT_ID LINK 1 LINK 2
261. sosurface File 96 Plot3D 96 Point Measurements 94 Slice File 96 Statistics 95 Summary of Quantities 103 Output Files out 12 stop 12 _devc csv 80 _hrr csv 98 PART 73 Poisson initialization 15 POROUS_FLOOR output issues 101 pre action sprinkler system 91 pressure leakage 49 PROF 95 IOR 95 QUANTITY 95 XYZ 95 PROP 80 Pyrolysis models 53 RADL 71 ANGLE_INCRMENT 72 CH4_BANDS 72 NMIEANG 72 NUMBER_RADIATION_ANGLES 72 RADIATIVE_FRACTION 71 RADTMP 72 TIME_STEP_INCREMENT 72 WIDE_BAND_MODEL 72 radial fire spread 47 184 RAMP 59 REAC 65 Restart 31 Running FDS 9 Parallel 10 LAM MPI 11 MPICH2 11 Serial 9 Sawtooth 38 SLCE 95 Sloped Ceilings 38 Solid fuels 53 SPEC 69 spinkler Spray Pattern 81 Spray Pattern 81 sprinkler 80 89 Sprinkler Suppression 78 stack effect 33 35 Support 13 Error Statements 14 Inadequate Resources 14 Input File 14 Numerical Instability 14 Poisson 15 Run Time 15 Issue Reporting 15 Version Number 13 SURE 44 ADIABATIC 44 45 BACKING 45 BURN_AWAY 57 CELL_SIZE_FACTOR 58 COLOR 62 CONVECTIVE_HEAT_FLUX 45 DUCT_PATH 51 E_COEFFICIENT 78 EMISSIVITY 45 EXTERNAL_FLUX 64 GEOMETRY 48 HEAT_OF_VAPORIZATION 55 HRRPUA 47 55 IGNITION_TEMPERATURE 55 LEAK_PATH 49 MASS_FLUX 46 MASS_FLUX_TOTAL 46 MASS_FRACTION 46 60 MATL_ID 52 MATL_MASS_FRACTION 52 MAX_PRESSURE 50 NPPC 74 PART_ID 74 PARTICLE_MASS_FLUX 74 PLE 47
262. split into smaller files 19 4 Control Output Data Data associated with particular control functions specified in the input file under the namelist group CTRL is output in comma delimited format in a file called CHID_ctrl csv The format of the file is as follows N_CTRL FDS Time ID 1 ID 2 P ID N_CTRL IME 7 Lo oy S status status rr y Status N_CTRL T 1 VAL 1 1 ova 271 p oes op VAL N_CTRL 1 T 2 VAL 1 2 VAL 2 2 7 we oe op WAL N_CTRIG 2 where N_CTRL is the number of control functions ID I is the user defined ID of the Ith control function and VAL I J the state 1 FALSE and 1 TRUE of the Ith control function at the Jth time The files can be imported into Microsoft Excel or almost any other spread sheet program If the number of columns exceeds 256 the file will automatically be split into smaller files 19 5 Gas Mass Data The total mass of the various gas species at any instant in time is reported in the comma delimited file CHID_mass csv The file consists of several columns the first column containing the time in seconds the second contains the total mass of all the gas species in the computational domain in units of kg the next lines contain the total mass of the individual species 19 6 Mixture Fraction State Relations The functional dependence of the mass fraction of the reactants and products of combustion on the mixture fraction is reported in
263. store properties of a given sprinkler This file is no longer used 81 amp TABL ID table_id TABLE_DATA LAT1 LAT2 LON1 LON2 VELO FRAC where each TABL line for a given table_id provides information about the spherical distribution of the spray pattern for a specified solid angle LAT1 and LAT2 are the bounds of the solid angle measured in degrees from the south pole 0 is the south pole and 90 is the equator 180 is the north pole Note that this is not the conventional way of specifying a latitude but rather a convenient system based on the fact that a typical sprinkler sprays water downwards which is why 0 degrees is assigned to the south pole or the z direction The parameters LON1 and LON2 are the bounds of the solid angle also in degrees where 0 or 360 is aligned with the x axis and 90 is aligned with the y axis VELO is the velocity m s of the droplets at their point of insertion FRAC the fraction of the total flow rate of liquid that should emerge from that particular solid angle In the example below the spray pattern is defined as two jets each with a velocity of 10 m s and a flow rate of 20 L min the total FLOW_RATE is 40 L min and the fraction for each jet is 0 5 The jets are centered at points 45 below the equator and are separated by 180 amp PROP ID y pipe QUANTITY SPRINKLER LINK TEMPERATURE FLOW_RATE 40 PART_ID water_drops
264. sults may not always be published nor included in the documentation Examples of routine analytical testing include e The radiation solver has been verified with scenarios where simple objects like cubes or flat plates are positioned in simple sealed compartments All convective motion is turned off the object is given a fixed surface temperature and emissivity of one making it a black body radiator The heat flux to the cold surrounding walls is recorded and compared to analytical solutions These studies help determine the appropriate number of solid angles to be set as the default Solid objects are heated with a fixed heat flux and the interior and surface temperatures as a function of time are compared to analytical solutions of the one dimensional heat transfer equation These studies help determine the number of nodes to use in the solid phase heat transfer model Similar studies are performed to check the pyrolysis models for thermoplastic and charring solids Early in its development the hydrodynamic solver that evolved to form the core of FDS was checked against analytical solutions of simplified fluid flow phenomena These studies were conducted at the National Bureau of Standards NBS by Rehm Baum and co workers 16 17 18 19 The emphasis of this early work was to test the stability and consistency of the basic hydrodynamic solver especially The National Institute of Standards and Technology NIST was formerly known as
265. t generates a tiny amount of random noise in the initial flow field so as to eliminate any false symmetries that might arise in the numerical solution The process of adding new routines to FDS is as follows typically the routine is written by one person not necessarily a NIST staffer who takes the latest version of the source code adds the new routine and writes a theoretical and numerical description for the FDS Technical Reference Guide plus a description of the input parameters for the FDS User s Guide The new version of FDS is then tested at NIST with a number of benchmark scenarios that exercise the range of the new parameters Provisional acceptance of the new routine is based on several factors 1 it produces more accurate results when compared to experimental measurement 2 the theoretical description is sound and 3 any empirical parameters are obtainable from the open literature or standard bench scale apparatus If the new routine is accepted it is added to a test version of the software and evaluated by external users and or NIST grantees whose research is related to the subject Assuming that there are no intractable issues that arise during the testing period the new routine eventually becomes part of the release version of FDS Even with all the code checking performed at NIST it is still possible for errors to go unnoticed One remedy is the fact that the source code for FDS is publicly released Although it consists of on the
266. t gravity points in the negative z direction There are a few special applications where you might want to vary the gravity vector in time for in stance for spacecraft applications The gravity vector GVEC can be made a function of time using ramps for the individual components RAMP_GX RAMP_GY and RAMP_GZ all specified on the MISC line More about RAMPs can be found in Section 8 5 6 4 3 Special Topic Restoring the Baroclinic Vorticity There is an approximation made when solving for the pressure where it is assumed that Tos liga V a e P 6 2 The consequence of this approximation is that the vorticity generated due to the non alignment of the density and pressure gradients or the baroclinic torque is neglected For most large scale applications the assump tion is justified by the fact that the vorticity generated by buoyancy is the dominant source of vorticity By 32 neglecting the baroclinic torque the solution of the elliptic partial differential equation obtained by taking the divergence of the momentum equation is greatly simplified However an option exists in the code to restore the baroclinic torque by decomposing the relevant term in the pressure equation 1 1 1 1 VV av aver y Vp 6 3 and evaluating the second term on the right hand side with values of pressure from the previous time step The expression p is an average density equal to 2PminPmax Pmin Pmax To make this correction simply incl
267. t make up the bounding surfaces of the flow domain This is the most challenging part of setting up the simulation Why First for both real and simulated fires the growth of the fire is very sensitive to the thermal properties of the surrounding materials Second even if all the material properties are known to some degree the physical phenomena of interest may not be simulated properly due to limitations in the model algorithms or resolution of the numerical mesh It is your responsibility to supply the thermal properties of the materials and then assess the performance of the model to ensure that the phenomena of interest are being captured 8 1 Basics By default the outer boundary of the computational domain is assumed to be a solid boundary that is maintained at ambient temperature The same is true for any obstructions that are added to the scene To specify the properties of solids use the namelist group SURF Section 8 2 Starting in FDS 5 solids are assumed to consist of layers which can be made of different materials The properties of each material required are designated via the MATL namelist group Section 8 4 These properties indicate how rapidly the materials heat up and how they burn Each MATL entry in the input file must have an ID or name so that they may be associated with a particular SURF via the parameter MATL_ID For example the input file entries amp MATL ID BRICK CONDUCTIVITY 0
268. t temperature and velocity on a qualitative basis Petterson 45 also completed work assessing the optimal grid size for FDS version 2 The FDS model 164 predictions of varying grid sizes were compared to two separate fire experiments The University of Canter bury McLeans Island Tests and the US Navy Hangar Tests in Hawaii The first set of tests utilized a room with approximate dimensions of 2 4 m by 3 6 m by 2 4 m and fire sizes of 55 kW and 110 kW The Navy Hangar tests were performed in a hangar measuring 98 m by 74 m by 15 m in height and had fires in the range of 5 5 MW to 6 6 MW The results of this study indicate that FDS simulations with grids of 0 15 m had temperature predictions as accurate as models with grids as small as 0 10 m Each of these grid sizes produced results within 15 of the University of Canterbury temperature measurements The 0 30 m grid produced less accurate results For the comparison of the Navy Hangar tests grid sizes ranging from 0 60 m to 1 80 m yielded results of comparable accuracy Musser et al 46 investigated the use of FDS for course grid modeling of non fire and fire scenarios Determining the appropriate grid size was found to be especially important with respect to heat transfer at heated surfaces The convective heat transfer from the heated surfaces was most accurate when the near surface grid cells were smaller than the depth of the thermal boundary layer However a finer grid size produced better r
269. the National Bureau of Standards 131 the velocity pressure coupling that is vitally important in low Mach number applications Many numer ical algorithms developed up to that point in time were intended for use in high speed flow applications like aerospace Many of the techniques adopted by FDS were originally developed for meteorologi cal models and as such needed to be tested to assess whether they would be appropriate to describe relatively low speed flow within enclosures A fundamental decision made by Rehm and Baum early in the FDS development was to use a direct rather than iterative solver for the pressure In the low Mach number formulation of the Navier Stokes equations an elliptic partial differential equation for the pressure emerges often referred to as the Pois son equation Most CFD methods use iterative techniques to solve the governing conservation equations to avoid the necessity of directly solving the Poisson equation The reason for this is that the equation is time consuming to solve numerically on anything but a rectilinear grid Because FDS is designed specifically for rectilinear grids it can exploit fast direct solvers of the Poisson equation obtaining the pressure field with one pass through the solver to machine accuracy FDS employs double precision 8 byte arithmetic meaning that the relative difference between the computed and the exact solution of the discretized Poisson equation is on the order of 10 T
270. the properties of different types of Lagrangian particles amp PART ID my smoke amp PART ID my water These Lagrangian particles can be introduced at a solid surface via the SURF line that defines the properties of the material for example amp SURF PART_ID my smoke or the PART type can be invoked from a PROP line to change the properties of the droplets ejected by a sprinkler or nozzle for example amp PROP ID Acme Spk 123 QUANTITY SPRINKLER LINK TEMPERATURE PART_ID my water Throughout this section the terms droplets and particles are used interchangeably From the point of view of FDS they are all Lagrangian particles that is point elements that are not bound by the structure of the underlying grid 73 Note that a surface on which particles are specified must have a non zero normal velocity directed into the computational domain This happens automatically if the surface is burning but must be specified if it is not 10 2 Controlling Particles and Droplets Depending on how the particles or droplets are introduced into the computational domain the following are important parameters for controlling them DT_INSERT Time increment in seconds between the introduction of a batch of particles or droplets The number per batch depends on how they are introduced If more particles are desired lower the input value of this parameter The default
271. the velocity components as is because Smokeview uses them to draw velocity vectors The first and fifth quantities can be changed with the parameters PLOT3D_QUANTITY 1 and PLOT3D_QUANTITY 5 on the DUMP line Note that there can only be one DUMP line Data stored in Plot3D 7 files See Section 19 2 use a format developed by NASA and used by many CFD programs for representing simulation results Plot3D data is visualized in three ways as 2D contours vector plots and iso surfaces Vector plots may be viewed if one or more of the u v and w velocity compo nents are stored in the Plot3D file The vector length and direction show the direction and relative speed of the fluid flow The vector colors show a scalar fluid quantity such as temperature Plot3D data are stored in files with extension q There is an optional file that can be output with coordinate information if another visualization package is being used to render the files If you write WRITE_XYZ TRUE on the DUMP line a file with suffix xyz is written out Smokeview does not require this file because the coordinate information can be obtained elsewhere 97 12 3 Special Output Quantities 12 3 1 Heat Release Rate Quantities associated with the overall energy budget are reported in the comma delimited file CHID_hrr csv This file is automatically generated the only input parameter associated with it is DT_HRR on the DUMP line The file consists of six columns
272. theory Geometry FDS approximates the governing equations on a rectilinear mesh Rectangular obstructions are forced to conform with the underlying mesh Multiple Meshes This is a term used to describe the use of more than one rectangular mesh in a calculation It is possible to prescribe more than one rectangular mesh to handle cases where the computational domain is not easily embedded within a single mesh Parallel Processing It is possible to run an FDS calculation on more than one computer using the Message Passing Interface MPI Details can be found in Section 3 1 2 Boundary Conditions All solid surfaces are assigned thermal boundary conditions plus information about the burning behavior of the material Heat and mass transfer to and from solid surfaces is usually handled with empirical correlations although it is possible to compute directly the heat and mass transfer when performing a Direct Numerical Simulation DNS 1 2 What s New in FDS 5 FDS 5 differs from previous versions in its treatment of solid boundaries and gas phase combustion Among the more important changes are Multi Step Combustion Previous versions of FDS have assumed only one gas phase reaction Now multiple step reaction schemes are available to describe local extinction CO production among var ious other phenomena The most important improvements to the combustion model are a more accurate heat release rate calculation and a better treatment of local f
273. tially the droplets have a median volumetric diameter of 100 um a temperature of 90 C and a total mass of 0 02 kg It is expected that a steady state will be achieved after several minutes The initial energy content sum of the air and water enthalpies of the box is 360 000 kJ After a short period of time 0 0141 kg of water evaporate and the box reaches an equilibrium temperature of 16 2 C see the figure below At this point the energy content of the box is 372 000 kJ or a 3 error At 16 2 C the expected evaporation is 0 0142 kg Slice Part 17 0 17 0 16 9 16 9 16 8 16 8 16 7 16 7 16 6 16 6 16 5 16 5 16 4 16 4 16 3 16 3 16 2 16 2 16 1 16 1 16 0 16 0 157 16 6 2 A Liquid Fuel Spray Burner spray_burner Controlled fire experiments are often conducted using a spray burner where a liquid fuel is sprayed out of a nozzle and ignited In this example spray_burner data heptane from two nozzles is sprayed downwards into a steel pan The flow rate is increased linearly so that the fire grows to 2 MW in 20 s burns steadily for another 20 s and then ramps down linearly in 20 s The key input parameters are given here amp DEVC ID nozzle_1 XYZ 4 0 3 0 5 PROP_ID nozzle QUANTITY TIME SETPOINT 0 amp DEVC ID nozzle_2 XYZ 4 0 0 3 0 5 PROP_ID nozzle QUANTITY TIME SETPOINT 0 amp PART ID heptane droplets FUEL TRUE VAPORIZATION_TEMPERATURE 98
274. tion calculation flag TRUE RAMP_GX Character Time function x comp of gravity RAMP_GY Character Time function y comp of gravity RAMP_GZ Character Time function z comp of gravity RESTART Logical Restart previous calculation FALSE RESTART_CHID Character Restart file CHID CHID SC Real Schmidt number LES only 0 5 SOLID_PHASE_ONLY Logical See Section 8 7 FALSE STRATIFICATION Logical See Section 8 2 5 TRUE SUPPRESSION Logical See Section 9 1 1 TRUE SURF_DEFAUL Character Default SURFace type INERT EXTURE_ORIGIN 3 Char Triplet See Section 8 6 1 m 0 0 0 HICKEN_OBSTRUCTIONS Logical See Section 7 1 FALSE TMPA Real Ambient Temperature C 20 U0 VO WO Reals Prevailing velocity field m s 0 VISCOSITY Real See Section 9 2 kg m s VN_MAX Real See Section 6 4 6 1 0 VN_MIN Real See Section 6 4 6 0 8 113 13 13 OBST Obstruction Parameters Table 13 13 For more information see Section 7 1 OBST Obstruction Parameters ALLOW_VENT Logical Allow vents on obstruction TRUE BNDF_FACE 3 3 Logical Array See Section 12 2 6 TRUE BNDF_OBST Logical See Section 12 2 6 TRUE COLOR Character Color name of obstruction color CTRL_ID Character ID of Controlling ConTRoL DEVC_ID Character ID of Controlling DEViCe FYI Character Comment String has no effect
275. tion of water only water vapor is produced set NU_WATER 3 1 0 and the other two to zero The yields are all zero by default If NU_RESIDUE 3 is non zero then you must indicate what the solid residue is via RESIDUE 3 the ID of another MATL that is also listed in the input file Ideally the sum of the yields should add to 1 meaning that the mass of the reactant is conserved However there are times when it is convenient to have the yields sum to something less than one For example the spalling or ablation of concrete can be described as a reaction that consumes energy but does not produce any product because the concrete is assumed to have either fallen off the surface in chunks or pulverized powder The concrete s mass is not conserved in the model because it has essentially disappeared from that particular surface Now you must specify at what temperature the reaction occurs and how fast the reaction occurs at that temperature The reaction rate at the temperature Ts of the ith material i e the MATL that you are currently describing undergoing its jth reaction is given by d Psi Psi ei Eij T v 35 S Ay ep 7 max 0 75 Tiari 4 a s pe 2 j exo RT ax 0 ihr 8 4 Ps is the density of the ith material within that particular layer in the sense of the mass of the ith material divided by the volume of the layer Pso is the initial density of the
276. tities Note that lower case quantities are appropriate only for calculations involving the mixture fraction Z If individual species are listed via SPEC namelist lines the quantity for mass and volume fractions are SPEC_ID and SPEC_ID _VF respectively For example the quantities water vapor and WATER VAPOR denote the volume fraction of water vapor generated by combustion and the mass fraction of water vapor from evaporated sprinkler droplets respectively The column File Type lists the allowed output files for the quantities B is for Boundary BNDF D is for Device DEVC TI is for Iso surface ISOF P is for Plot3D PA for PArticle PART S is for Slice SLCF Be careful when specifying complicated quantities for Iso surface or Plot3D files as it requires computation in every gas phase cell Table 12 1 Summary of all Output Quantities Output QUANTITY Symbol Units File Type ABSORPTION_COEFFICIENT K 1 m D LP S ADIABATIC_SURFACE_TEMPERATURE See Section 12 3 7 C B D aspiration See Section 11 3 6 D BURNING_RATE mi kg m s B D carbon dioxide Xco Z mol mol D LP S carbon monoxide Xco
277. tly with temperature In such cases use the RAMP function like this amp MATL ID STEEL FYI A242 Steel SPECIFIC_HEAT_RAMP c_steel CONDUCTIVITY_RAMP k_steel DENSITY 7850 amp RAMP ID c_steel T 20 F 0 45 amp RAMP ID c_steel T 377 F 0 60 amp RAMP ID c_steel T 677 F 0 85 amp RAMP ID k_steel T 20 F 48 amp RAMP ID k_steel T 677 F 30 Note that here as opposed to time ramps the parameter F is the actual physical quantity not just a fraction of some other quantity Thus if CONDUCTIVITY_RAMP is used there should be no value of CONDUCTIVITY given Note also that for values of temperature T below and above the given range FDS will assume a constant value equal to the first or last F specified Note that each set of RAMP lines must have a unique ID and that the lines must be listed with monotonically increasing T 60 8 5 3 Tabular Functions Some input quantities such as a sprinkler spray pattern vary multi dimensionally In such cases use the TABL namelist group The format of the TABL lines is application specific but in general look like this amp TABL ID TABLE1 TABLE_DATA 40 50 85 95 10 0 5 amp TABL ID TABLE1 TABLE_DATA 40 50 185 195 10 0 5 A detailed description of the various table entries is given in the sections that describe quantities that use such ta
278. toms in the soot that are hydrogen Mixture Fraction only default 0 1 CO_YIELD The fraction of fuel mass converted into carbon monoxide yco Mixture Fraction only default 0 0 H2_YIELD The fraction of fuel mass converted into hydrogen yy Mixture Fraction only default 0 0 HEAT_OF_COMBUSTION AH kJ kg The amount of energy released per unit mass of fuel consumed Note that if the heat of combustion is not specified it is assumed to be Vo W Hx O YYOo EPUMO2 KJ k vi Wr gt 66 EPU ry IDEA 02 The amount of energy released per unit mass of oxygen co L Logical value indicating whether or not the EPUMO2 or H values for complete combustion TRUE or for incomplete account for the specified yco ym and ys If IDEAL then FDS products of incomplete combustion nsumed kJ kg Default is 13 100 kJ kg Note that if both EPUMO2 and HEAT_OF_COMBUSTION are specified that FDS will ignore the value for EPUMO2 EAT_OF_COMBUSTION values represent combustion FALSE i e the values will internally adjust AH to account for A few sample REAC lines are given here The values are for demonstration only amp REAC ID METHANE E 1 H 4 amp REAC ID PROPANE SOOT_YIELD 0 00 E 3 H 8 HEAT_OF_COMBUSTION 46460 IDEAL TRUE amp REAC ID PROPANE SOOT_YIELD
279. tring ID to allow references to it by an obstruction or vent Thus on each OBST and VENT line the character string SURF_ID indicates the ID of the SURF line containing the desired boundary condition parameters If a particular SURF line is to be applied as the default boundary condition CONCRETE for example set SURF_DEFAULT CONCRETE on the MISC line The default boundary condition INERT does allow for heat loss and is not the same as an adiabatic surface If you wish to define a surface as adiabatic then you should set ADIABATIC TRUE on the SURF line 8 2 1 Specifying a Fire with a Known Heat Release Rate Solids and liquid fuels can be modeled by specifying their relevant properties via the MATL namelist group However if you simply want to specify a fire of a given heat release rate HRR you need not specify any material properties A specified fire is basically modeled as the ejection of gaseous fuel from a solid surface or vent This is essentially a burner with a specified Heat Release Rate Per Unit Area HRRPUA in units of kW m For example amp SURF ID FIRE HRRPUA 500 applies 500 kW m to any surface with the attribute SURF_ID FIRE See the discussion of Time Depen dent Conditions in Section 8 5 to learn how to ramp the heat release rate up and down An alternative to HRRPUA with the exact same functionality is MLRPUA except this parameter
280. truction that ejects non evaporating red particles with a mean volumetric diameter of 750 um out of its sides at a rate of 0 1 kg m s FDS will adjust the mass flux if the obstruction or vent dimensions are changed to conform to the numerical grid Note that the IDs have no meaning other than as identifiers The particles are colored red in Smokeview but can also be colored according to their diameter temperature or age Droplets Introduced at a Sprinkler or Nozzle DROPLETS_PER_SECOND is the number of droplets inserted every second per active sprinkler or nozzle Its default value is 1000 Note that this parameter only affects sprinklers and nozzles Changing this parameter does not change the flow rate but rather the number of droplets used to represent the flow Also note that the number of droplets introduced per batch is DROPLETS_PER_SECOND times DT_INSERT 74 Particles or Droplets Introduced Initially Sometimes it is convenient to introduce droplets or particles at the start of the simulation For this purpose NUMBER_INITIAL_DROPLETS is the number of particles droplets within the computational domain at the start of the simulation Its default value is 0 meaning that initially there are no particles or droplets present If non zero also specify MASS_PER_VOLUME kg m which specifies the particle droplet mass per unit volume Default 1 kg m Do not confuse this parameter with DENSITY explained in t
281. uchi and K Ito Effects of Slow Wind on Localized Radiative Ignition and Transition to Flame Spread in Microgravity In Twenty Sixth Symposium International on Combustion pages 1345 1352 Combustion Institute Pittsburgh Penn sylvania 1996 134 W Mell and T Kashiwagi Dimensional Effects on the Transition from Ignition to Flame Spread in Microgravity In Twenty Seventh Symposium International on Combustion pages 2633 2641 Combustion Institute Pittsburgh Pennsylvania 1998 134 W Mell S L Olson and T Kashiwagi Flame Spread Along Free Edges of Thermally Thin Sam ples in Microgravity In Twenty Eighth Symposium International on Combustion pages 2843 2849 Combustion Institute Pittsburgh Pennsylvania 2000 134 K Prasad Y Nakamura S L Olson O Fujita K Nishizawa K Ito and T Kashiwagi Effect of Wind Velocity on Flame Spread in Microgravity In Twenty Ninth Symposium International on Combus tion pages 2553 2560 Combustion Institute Pittsburgh Pennsylvania 2002 134 Y Nakamura T Kashiwagi K B McGrattan and H R Baum Enclosure Effects on Flame Spread over Solid Fuels in Microgravity Combustion and Flame 130 307 321 2002 134 W E Mell K B McGrattan and H R Baum g Jitter Effects on Spherical Diffusion Flames Micro gravity Science and Technology 15 4 12 30 2004 134 A Mukhopadhyay and I K Puri An Assessment of Stretch Effects on Flame Tip Using the Thin Flame and Thick Formulations Co
282. ude the statement BAROCLINIC TRUE on the MISC line In a DNS calculation DNS TRUE the correction is made by default However for an LES calculation the default mode in FDS the correction must be explicitly invoked The cost of the correction is not prohibitive try calculations with and without the correction to determine if its inclusion is warranted 6 4 4 Special Topic Stack Effect Tall buildings often experience buoyancy induced air movement due to temperature differences between inside and outside known as stack effect To simulate this phenomenon in FDS you must include the entire building or a substantial fraction of it both inside and out in the computational domain It is important to capture the pressure and density decrease in the atmosphere based on the specified temperature LAPSE_RATE C m that is entered on the MISC line Experiment with different meshing strategies before including any fire or HVAC functionality Slowly build in complexity See Section 16 1 5 for an example 6 4 5 Special Topic Large Eddy Simulation Parameters In default mode FDS uses the Smagorinsky form of Large Eddy Simulation LES to model subgrid scale turbulence The viscosity is modeled 1 2 His P C Ay 2 Sij Sij 0 0 6 4 where C is an empirical constant and A is a length on the order of the size of a grid cell The bar above the various quantities denotes that these are the resolved or filtered v
283. ure rise in the compartment due to the effect of the fire and the fan Initially the pressure rise is approximately dp V 7 y 1 E YP y 3200 Pals 0 03 atm s 16 5 where y 1 4 O 160 000 W V 20 7 m and V 0 016 m s In roughly 150 s the pressure rises about 0 6 atm at which point the fire dies due to lack of oxygen Then the pressure decreases and the fan starts up again it had stalled due to high pressure in the compartment The fan and the leak under the door increase the oxygen concentration at least near these openings and the fuel rich gases in the compartment continue to burn 1 0 200 Pressure Rise door_crack Heat Release Rate door_crack 0 8 x 150 E 0 w 0 6 w amp T 2 100 2 0 4 2 D A cc 50 0 2 2 0 0 r r r r r 0 r 1 1 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Time s Time s While this case has a number of interesting physical effects and it verifiies several features of FDS it is very important to note the following e Although there is smoke seen flowing backwards out the fan duct in reality there would have been much more Most conventionally built structures will not withstand over pressures of 0 6 atm without some sort of relief The fan and the crack under the door obey simple formulae based on pressure differences but these assumptions have limits It is likely that the fire in this scenario would indeed
284. user specified volume within the computational domain that is entirely surrounded by solid obstructions For example the interior of a closed room can be and should be declared a pressure zone Leakage from one compartment to another is then designated on the input lines defining the individual pressure ZONEs amp ZONI amp ZONI XB 0 2 0 4 2 9 0 3 XB 2 8 1 4 2 9 6 8 5 LEAK_AREA 0 0 0001 4 2 9 7 FEAK_AREA 1 0 0002 Ls 4 Dis Je Gl Fl 3 3 The first line designates a region of the computational domain to be Pressure Zone 1 Zone 0 is by default the ambient pressure exterior In this example a leak exists between Zone 1 and the exterior Zone 0 and the area of the leak is 0 0001 m 1 cm by 1 cm hole for example Zone 2 leaks to Zone 1 and vis verse with a leak area of 0 0002 m At least one of the obstructions that form the walls of Zone 1 must have the attribute LEAK_PATH 1 0 meaning that the leak between Zones 1 and 0 is uniformly distributed over solids defined with amp SURF ID whatever LEAK_PATH 1 0 Likewise the boundaries of Zone 1 and Zone 2 must include solids whose SURF properties include LEAK_PATH 1 2 This tells FDS to lump all of the leakage over these surfaces The order of the pressure zones designated by LEAK_PATH is unimportant 49 8 3 2 Fans In Section 8 2 there is a discussion of velocity boundary conditions in which a fa
285. utput Data Files o 102 12 5 Summary of Output Quantities s lt soe e eacee e a i ee o od a E e a 103 13 Alphabetical List of Input Parameters 105 13 1 BNDF Boundary File Patametets i o cc ores 82 26 2s ea Daa a a OG oo Sawa 106 13 2 CLIP MIN MAX Clipping Parameters coes aw et ecra r g i e i eee a 106 13 3 CTRL Control Function Parameters e 6 a ae a bad ale e keera nar cr a 107 13 4 DEVE Device Parameters cuz da eA debo al sl a e dd eh 108 13 5 DUMP Output Parameters lt lt os 246 ba bebe cies ces ee ee eed bs 109 13 6 HEAD Header Parameters oao 2 4 40 26 ba ed ba Ra ba aw Ra aw a 109 13 7 HOLE Obstruction Cutout Parameters e 110 13 8 INIT Initial Conditions ico ee a tee ee ee ee 110 13 9 TSOF Usosurtace Parameters oa oa be as ok ew ee Pa a a 110 IZ 10MATI Material Properties o e s a seal oe Ww ae Ad we ee ee ee 111 13 MESH Mesh Parameters lt s e ance a Boh ee ee oe He ae ae fa ia eS 112 13 12MI SC Miscellaneous Parameters 24 2 3 2 4024084 na a kA RM bw aoa doa A 113 13 130BST Obstruction Parameters 2 4 ee amp doe Boy Ak he RR AA Ee 114 13 14PART Lagrangian Particles Droplets o o e a 115 13 15PROF Wall Profile Parameters a aa a0 oa Aw Aw da ee we de we ee 116 13 J6P ROP Device Properties i ie ve See babe ba ede ORE ee be ede 4d ad 117 13 17 RADI Radiation Parameters oo e c ou sa ba dha BEE a Oe eae Bb ak Sd 118 13 18RAMP Ramp Fun
286. value is 0 05 s SAMPLING_FACTOR Sampling factor for the output file CHID prt5 This parameter can be used to reduce the size of the particle output file used to animate the simulation The default value is 1 for MASSLESS particles meaning that every particle or droplet will be shown in Smokeview The default is 10 for all other types of particles MASSLESS particles are discussed in Section 10 4 AGE Number of seconds the particle or droplet exists after which time it is removed from the calcula tion This is a useful parameter to use when trying to reduce the number of droplets or particles in a simulation Particles Introduced at a Solid Surface If the particles have mass and are introduced from a solid surface specify PARTICLE_MASS_FLUX on the SURF line The number of particles inserted at each solid cell every DT_INSERT seconds is specified by NPPC on the SURF line defining the solid surface The default value of NPPC is 1 As an example the following set of input lines amp PART ID drops QUANTITIES 1 3 DROPLET_DIAMETER DROPLET_TEMPERATURE DROPLET_AGE DIAMETER 750 SAMPLING FACTOR 1 COLOR RED EVAPORATE FALSE amp SURF ID HOLE PART_ID drops VEL 5 PARTICLE_MASS_FLUX 0 1 COLOR RED OBST XB 0 2 0 2 0 2 0 2 4 0 4 4 SURF_IDS INERT HOLE INERT creates an obs
287. ve predictive capability when applied to a specific set of factual circumstances Lack of accurate predictions by the model could lead to erroneous conclusions with regard to fire safety All results should be evaluated by an informed user Throughout this document the mention of computer hardware or commercial software does not con stitute endorsement by NIST nor does it indicate that the products are necessarily those best suited for the intended purpose 111 iv About the Authors Kevin McGrattan is a mathematician in the Building and Fire Research Laboratory of NIST He received a bachelors of science degree from the School of Engineering and Applied Science of Columbia Uni versity in 1987 and a doctorate at the Courant Institute of New York University in 1991 He joined the NIST staff in 1992 and has since worked on the development of fire models most notably the Fire Dynamics Simulator Simo Hostikka is a Senior Research Scientist at VIT Technical Research Centre of Finland He is the principal developer of the radiation and solid phase sub models within FDS Jason Floyd is a Senior Engineer at Hughes Associates Inc in Baltimore Maryland He received a bache lors of science degree and a doctorate from the Nuclear Engineering Program of the University of Mary land After graduating he won a National Research Council Post Doctoral Fellowship at the Building and Fire Research Laboratory of NIST where he developed the combustion a
288. ved a door is opened for example after any of four smoke detectors in a room has activated Use input lines of the form amp OBST XB SURF_ID CTRL_ID SD amp DEVC XYZ 1 1 3 PROP_ID Acme Smoker ID SD_1 amp DEVC XYZ 1 4 3 PROP_ID Acme Smoker ID SD_2 amp DEVC XYZ 4 1 3 PROP_ID Acme Smoker ID SD_3 amp DEVC XYZ 4 4 3 PROP_ID Acme Smoker ID SD_4 amp CTRL ee D FUNCTION_TYPE ANY INPUT_ID SD_1 SD_2 SD_3 SD_4 88 INITIAL _STATE TRUE The INITIAL_STATE of the control function SD is TRUE meaning that the obstruction exists initially The change of state means that the obstruction is removed when any smoke detector alarms By default the INITIAL STATE of the control function SD is FALSE meaning that the obstruction does not exist initially Suppose that now you want the obstruction to be created a door is closed for example after all four smoke detectors in a room have activated Use a control line of the form T amp CTRL ID SD FUNCTION_TYPE ALL INPUT_ID SD_1 SD_2 SD_3 SD_4 The control functions AT_LEAST and ONLY are generalizations of ANY and ALL For example amp CTRL ID SD FUNCTION_TYPE AT_LEAST N 3 INPUT_ID SD_1 SD_2 SD_3 SD_4 changes the state from FALSE to TRUE when at least 3 detectors activate Note that in this example and the ex
289. vice needs to be sited either at a point within the computational domain or over a span of the domain like a beam smoke detector For example a sprinkler is sited within the domain with a line like amp DEVC XYZ 3 0 5 6 2 3 PROP_ID Acme Sprinkler 123 ID Spk_39 The physical coordinates of the device are given by a triplet of real numbers xyz The properties of the device are contained on the PROP line PROP_ID which will be explained below for each of the special devices included in FDS The character string ID is merely a descriptor to identify the device in the output files and if any action is tied to its activation Some devices have a particular orientation which can be specified with various parameters IOR ORIENTATION ROTATION IOR or the Index of Orientation is necessary for any device that is placed on the surface of a solid The values 1 or 2 or 3 indicate the direction that the device points where 1 is parallel to the X axis 2 is parallel to the Y axis and 3 is parallel to the Z axis ORIENTATION is used for devices that are not on a surface and require a directional specification like a sprinkler ORIENTATION is specified with a triplet of real number values that indicate the components of the direction vector The default value of ORIENTATION is 0 0 1 79 For example a default downward directed sprinkler spray can be redirected in other direction If you were to prescribe
290. x input file to the new FDS 5 x format 14 1 Numerical Domain Parameters GRID and PDIM In previous versions the computational domain and numerical mesh were specified via lines of the form amp GRID IBAR 30 JBAR 20 KBAR 10 amp PDIM XBARO 0 0 XBAR 3 0 YBARO 0 0 YBAR 2 0 ZBARO 0 0 ZBAR 1 0 In FDS 5 these two lines are now written via the single line amp MESH IJK 30 20 10 XB 0 0 3 0 0 0 2 0 0 0 1 0 Rules for multiple meshes and mesh transformations still apply 14 2 Obstructions Vents and Holes OBST VENT and HOLE The syntax for these lines is fairly similar to past versions with the following exceptions e For a VENT that spans an entire mesh boundary CB XBARO is now MB XMIN The character string XBAR is now XMAX The same applies for the y and z coordinate parameters e Control parameters like T_ACTIVATE HEAT_REMOVE etc are now consolidated into DEVC_ID and CTRL_ID In brief any change to an obstruction vent or hole is tied to a specific device or control function See Sections 11 1 and 11 5 for details 14 3 Surface Parameters SURF The most significant change to the input file format has been splitting of the SURF line In past versions the SURF namelist group contained all the information about a particular boundary type its material properties color thickness and so on However in FDS 5 solid boundaries can now consist of multiple layers of
291. x100x100 142 16 3 2 Radiation from a plane layer radiation_plane_layer This case tests the computation of three dimensional radiation from a homogenous infinitely wide layer of radiating material The temperature of the layer is 1273 15 K and absorption coefficients are varied The thickness of the layer is fixed at 1 0 m and the optical depth is 1 0k Wall temperatures are set to 0 K The results are compared against the exact solution S T presented in 32 S t Sp 1 2E3 7 16 6 where Sp OT is the black body heat flux from the radiating plane and Ex 7 is the exponential integral function order 3 of optical depth 7 The FDS results are computed at two mesh resolutions in the x direction I 20 and I 150 For I 20 both one band and six band versions are included to test the correct integration of heat fluxes over multiple bands For I 20 2D versions are also computed J 1 A special case with KAPPAO 0 and an opposite wall temperature of 1273 15 K is computed to test the wall heat flux computation The exact values and FDS predictions of the wall heat fluxes are given here T S t FDS 1220 J 20 FDS 1220 J 1 FDS 1 150 1 band 6 bands 1 band 6 bands 1 band 0 148 9709 148 9709 148 4037 147 9426 147 3793 148 9709 0 01 2 8970 2 9180 2 9069 2 8364 2 8256 2 9258 0 1 24 9403 25 5501 25 4529 25 1078 25 0122 25 7045 0 5 82 9457 83 1309

Fire Dynamics Simulator (Version 5) User's Guide

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