Time and number of simulation threads
To specify the simulation time and the number of threads for running the simulation, do the following:
- Navigate to Simulation | Fire simulation parameters.
- Open the General tab.
- Select the desired scenario.
- Specify the desired simulation time and the number of threads for multi-threaded mode.
Enable or disable multi-threaded calculation mode
The purpose of the multi-threaded simulation mode is to reduce the fire dynamics simulation time.
To use the multi-threaded mode to simulate the dynamics of fire development, do the following:
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Specify the number of processes, which is larger than 1.
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Select the path to the mpiexec.exe file and, if necessary, add it to the exclusions list of the Windows firewall and the installed anti-virus software. For more information, see General settings.
Increasing the number of threads used for fire dynamics simulation does not always lead to a proportional reduction of simulation time. For example, doubling the number of threads will not halve the modeling time. This is because additional resources are needed for coordinating the results between threads.
Initial conditions
To specify the initial conditions of the fire development, do the following:
- Navigate to Simulation | Fire simulation parameters.
- Open the Initial Conditions tab.
- Select the desired scenario.
- Specify the desired parameter values.
Temperature is ambient temperature;
Background pressure is pressure;
Relative humidity is humidity;
Temperature gradient is temperature change with height change;
Room temperature is the initial air temperature inside the premises. The volume of a room is the area of space bounded by the contours of the room and a height equal to the height of the floor on which the room is located. It means that if an area inside the building is not marked as a room, then the initial temperature in this room is equal to the ambient temperature (the value specified in the Room temperature field). By default, the indoor temperature is equal to the ambient temperature.
The Material properties section defines the influence of the thermophysical properties of construction materials on the initial conditions of the fire development. Possible values: Inert - the thermophysical properties of construction materials do not affect the initial conditions of fire development. The Actual material - the thermophysical properties of materials affect the initial conditions of fire development.
By default, Fenix+ 3 application uses the value of the Room temperature parameter for all rooms except those where a different value is specified. This condition is met only if the Use specified value parameter is selected in the properties of such rooms. For more information, see Room.
Doors and windows behavior
By default, all doors (except those marked as Fire resistant and/or With closer) are displayed by FDS as open doorways. Fire-proof doors and doors with closers are treated as obstacles. Windows are also displayed by FDS as obstacles.
Consequently, the dangerous fire factors spread through doors unhindered. They do not spread through fire-proof doors and doors with door closers.
However, this may lead to significant differences between the simulation results and the real dynamics of dangerous fire factors (DFF) spread.
To make fire dynamics simulation more realistic, you can define the behavior of windows and doors depending on the dynamics of DFF spread and people evacuation.
To determine the behavior of doors and windows, do the following:
- Navigate to Simulation | Fire simulation parameters.
- Open the Doors and Windows tab.
- Select the desired scenario.
- Specify desired parameter values.
Doors
The parameters located on this tab affect only doors marked as Fire resistant.
The With closer parameter determines whether doors must open when people pass through them and close after a certain time. The default Closing time is 25 seconds. If necessary, you can specify a different value. For more information, see the specification of the door closer.
With this parameter, you can determine the closing time for all fire-proof doors in the scenario. If you need to specify a different value for a certain door, then select the With closer parameter in the door properties and set the desired closing time. For more information, see Door.
If a fire resistant door is also marked as With closer, then the closing time value specified in its properties is used and the closing time value specified in the fire dynamics simulation parameters is ignored.
Since it is necessary to know the moments in time when people pass through the doors to open/close them, it is essential to conduct the evacuation simulation of people before simulating the fire dynamics.
If you run the fire dynamics simulation before the evacuation simulation, then fire-proof doors and doors with closers are closed all the time.
Windows
The Closed parameter determines how windows are displayed by FDS: as open doorways or obstacles.
The Allow destruction at critical temperature parameter determines whether windows should be destroyed when temperature reaches the critical value in the place where they are located.
By default, the Destruction temperature is 250 °C.
The temperature is measured in the center of the upmost point of the window.
Fire source
When a room with a fire source is equipped with an automatic fire extinguishing system that meets the fire safety requirements specified in regulatory documents, the calculation assumes that the value of the burnout rate is reduced by half.
If you want to use this option, you need to check the box for the parameter Reduce burning rate by half.
Then, if the properties of the building (for civilian projects) or the room specification (for industrial projects) indicate that the automatic fire extinguishing systems (AFES) are installed according to standards, then during the fire dynamics simulation, the burning rate is reduced by half.
If at least one of the conditions is not met (the parameter is not used, or the AFES does not meet the standards or is absent), then the burning rate is not reduced.
The maximum burning area for rooms of functional fire hazard classes F1-F4 must be equal to two areas of the room with the fire source. For rooms of the F5.2 class with a storage height of less than 5.5 meters - equal to four areas of the room with the fire source. For rooms of the F5.2 class with a storage height more than 5.5 meters - equal to the actual surface of combustible materials (but not less than 10 areas of the room).
To ensure compliance with this requirement, it is not sufficient to locate the fire source on the surface of the fire load. The maximum area that can be achieved in this way is equal to the area of the room.
The Flame spread to side surfaces parameter allows to increase the maximum combustion area without increasing the area occupied by the fire load.
The spread of flame to the side surfaces occures in accordance with the the linear flame spread rate for the material and the geometric dimensions of the fire load on which the fire source is located.
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The spread of flame occures on those side surfaces of the fire load that coincide with the boundaries of the fire source and are at least one cell size of the calculation area away from other objects. That is, if the fire load is placed with one side close to other objects (for example, to a wall), then the fire does not spread to the corresponding surface.
In the scenario illustrated below, the flame does not spread to the rear surface.
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In the report section Results of Fire Risk Assessment Calculations, the table describing scenarios specifies two values:
- Possible maximum burning area is the the maximum burning area possible for the given scenario. This area is determined by the area of the fire source and the area of the side surfaces to which flame can spread.
- Actual maximum burning area is the maximum burning area, which is actually created in the scenario
Calculation Areas
All calculation areas in the scenario represent one or several cell groups in the FDS source file. For more information, see Calculation Area. FDS makes a lot of requirements to the cell groups and their mutual arrangement on the scene.
By default, the application processes calculation areas so that they meet all necessary requirements (the Adjust automatically parameter is checked).
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The application processes calculation areas in the following way:
- First, the application attempts to merge all calculation areas into larger ones with regard to their cell size. As a result:
- Intersections of areas are eliminated;
- Calculation areas increase in directions where the number of cells is less than 3.
- If the number of threads that you want to use for fire dynamics simulation is less than the number of resulting cell groups, then calculation areas with the largest number of cells are split in half in the direction wich has the largest number of cells. This operation is interrupted in the following cases:
- The boundary of the resulting cell groups falls on one of the vent groups (i.e., on the fire source or ventilation)
- The number of cells is equal to the number of threads
- There are no more cells that can be divided
As a result, cell groups can be larger than the original calculation areas.
If you select the Do not adjust calculation areas parameter, then calculation areas are not merged into larger ones. If necessary, the application can devide calculation areas.
In this case, the resulting cell groups completely match the location of the original calculation areas. The height of the calculation areas is equal to the height of the floor.
If you are not sure about the correct location of calculation areas, it is not recommended to use the Do not adjust calculation areas parameter. If calculation areas are not arranged correctly, the fire dynamics simulation ends with an error.
Calculation area cell size
Possible values for the calculation area cell size are determined by the parameters displayed in the image above.
The image displays the default parameters. If these parameters are used, the following set of cell sizes is possible: 0.5, 0.25, 0.125, 0.0625 and 0.03125 meters. Each value is obtained by dividing 1 (BaseSize) by the factor of 2. The factor to which two is raised - is any integer in the range of 1 (MinRate) to 5 (MaxRate). That is, the number of valid values is determined by MinRate and MaxRate.
For example, if during the fire dynamics simulation it is necessary to use a cell size that equals to 0.3 meters, then you only need to set the value of the BaseSize parameter to 0.6 meters. This allows you to use the cell sizes that belong to the following range: 0.6, 0.3, 0.15, 0.075 and 0.0375 meters.
You can specify the parameters that define the possible set of calculation area cell sizes only when there aren’t yet any calculation areas in the scenario.
Wind speed and direction
Fenix+ 3 application can consider the presence of wind during the fire dynamics simulation.
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The Speed parameter defines the speed of the wind. If its value is bigger than 0, then the application considers the action of the wind during the fire dynamics simulation.
The Scene direction parameter (m.u.: degree) defines the angle between the north and the Y axis in the scene editor. You can use dropdown lists to specify fixed values in the range from 0 to 315. To specify any angle, select the Custom option and enter a desired value.
The Wind direction parameter (m.u.: degree) defines the angle between the north and the wind direction. You can use dropdown lists to specify fixed values in the range from 0 to 315. To specify any angle, select the Custom option and enter a desired value.
Setting critical values for dangerous fire factors
If necessary, you can specify a different critical value for any dangerous fire factor in the application. The application uses the specified value to determine the blocking time. To restore the default value, use the Default button.
If the fire dynamics simulation is conducted to determine the calculated values of fire risk in accordance with the Methodologies, changing critical values is NOT ALLOWED.
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