Categories
FDS Tutorials

Remove obstructions during a simulation in FDS

In this tutorial you will learn how to remove obstructions during a simulation in FDS.

Download the FDS input fileDownload

1. Introduction

Devices can be used to control various actions. One of the most frequent controls implemented in a FDS simulation is the removal (or creation) of an obstruction.

In this tutorial we will remove obstructions using basic control actions. We will NOT use any Advanced Control Functions: (CTRL Namelist Group).

You will learn how to remove obstructions with FDS with 2 slightly different methods:

  • In the first simulation the window in a room will be removed after a defined number of seconds (like a timer).
  • In the second simulation the same window will be removed when a thermocouple reaches a specified setpoint value.

2. Remove obstruction in FDS

The obstruction removal can be achieved by:

  • assigning a DEVC_ID to the obstruction
  • and assigning a SETPOINT parameter to the device.

When the device measures a higher/lower quantity than the SETPOINT value, the device will “change state” (from .TRUE. to .FALSE. or vice versa), therefore removing or creating the obstruction.

3. Time dependent obstruction removal

The code you need to implement in your FDS input file is the following:

&OBST XB= 5, 5.01, 1.5, 3.5, 2, 3, TRANSPARENCY=0.9 ,RGB=160, 252, 255, DEVC_ID='timer'/
&DEVC ID='timer', QUANTITY='TIME', XYZ = 1,1,1, SETPOINT=35, INITIAL_STATE=.TRUE. /

As you can see, we’ve told FDS that:

  • the obstruction is dependent on the device “timer”
  • the device initial state is “.TRUE.”
  • the device should change state when the TIME quantity reaches the value of 35 (35 seconds since the beginning of the simulation)

4. Temperature dependent obstruction removal

If you need to remove an obstruction when the temperature reaches a certain value, you can use this code:

&OBST XB= 5, 5.01, 1.5, 3.5, 2, 3, TRANSPARENCY=0.9 ,RGB=160, 252, 255, DEVC_ID='control temperature'/
&DEVC ID='control temperature', QUANTITY = 'THERMOCOUPLE', XYZ = 4.8, 3.6, 2.8, SETPOINT=100, INITIAL_STATE=.TRUE. /

The main structure of the code is the same as before, but now:

  • the obstruction is dependent on the device “control temperature”
  • a thermocouple device is placed in XYZ = 4.8, 3.6, 2.8
  • the device will change state when the THERMOCOUPLE quantity reaches the value of 100 (100 °C)
  • the device initial state is still “.TRUE.”
Download the FDS input fileDownload

FDS guides and examples list

Check out the complete FDS guides and examples list