Basic Data Output

4.1. What are Devices?

Devices are very generalized tools in FDS, as defined in Chapter 20: Devices and Control Logic of the FDS User Guide (McGrattan et al. 2021). They can be used for a wide number of applications in your model. Some of these include recording quantities in the simulation and generating an output, modeling real-life sensors to track their activation state, and triggering other events in the model.

This tutorial will cover the first two of these applications, and a later tutorial in the Fundamentals series will cover the third. However, keep in mind that these are just the basic concepts necessary to get you acquainted with PyroSim and FDS.

4.2. Types of Devices

As can be seen from the Devices menu in PyroSim, there are many categories of Devices. PyroSim divides Devices into these categories to make defining Devices easier. For this tutorial, we will cover the following 3 categories of Devices:

4.3. Defining Devices

With background definitions out of the way, let’s get to actually making some Devices to generate outputs in this model. You will create 3 different Devices to answer the following questions:

4.3.1. Defining a Gas-Phase Temperature Device

To figure out the temperature in the doorway, we will need to know the temperature of the air in one of the cells that make up the opening of the doorway. Because this doorway is a Hole, and the cells there are gaseous, we will use a Gas-Phase Device. To create this device:

1. In the 3D View, select the Device tool.
2. Right-click, then select Lock Z to snap location.
3. Press the TAB key.
4. Enter the XYZ location 0.08,2.5,1.75, then press ENTER.

5. Double-click the new Device in the Navigation View to open the Gas-Phase Device dialog.
6. Rename the Device to Doorway Temperature.
7. Leave the Quantity set to the default Temperature.

The Doorway Temperature Device is now fully configured.

4.3.2. Defining a Solid-Phase Wall Temperature Device

To figure out the ceiling temperature above the fire, we need to know the temperature at the bottom surface of one of the cells that make up the Ceiling obstruction. Because we want to know the properties of a solid cell, we will need to use a Solid-Phase Device. To create this device:

1. In the 3D view, select the Device tool.
2. Right-click, then select Tool Properties.
3. In the Device Type dropdown, select Solid-Phase Device.
4. Change the Name to Ceiling Temperature.
5. In the Quantity dropdown, select Wall Temperature.

6. Click OK to close the Tool Properties dialog.
7. Press TAB to begin entering the device location.
8. Enter the location 2.6,2.6,2.75.
9. Press ENTER to create the Device.

This Device you just created has an X and Y position that places it fully inside of a mesh cell on the ceiling above the Fire obstruction, shown in Figure 4. This is done to avoid ambiguity in the final Device location. We are telling FDS exactly which Mesh cell we want the Device in. In Figure 4, you can see that if we positioned this device directly over the center of the Fire obstruction, it would be placed at the corner boundary of 4 different cells. While FDS can handle this in most situations, it will essentially select a cell at random out of those 4 to place the Device in to. Placing the device squarely inside of a cell lets us, as the maker of the model, know and control which cell is chosen.

Like the X and Y coordinates, the Z coordinate is chosen to avoid ambiguity in the Device location. The Z coordinate coincides directly with the bottom face of the Ceiling obstruction, shown in Figure 5.

The Ceiling Temperature Device is now fully configured.

4.3.3. Defining a Smoke Detector

To figure out when a smoke detector would activate in this fire scenario, we will need to add a device to our model to represent a smoke detector. Thankfully PyroSim has a built in Device Type for this. We will create a simple smoke detector in the model, using one of the built in smoke detector models provided in Table 20.1 of the FDS User Guide (McGrattan et al. 2021, 265). To add this smoke detector to the model:

1. In the 3D view, select the Device tool.
2. Right-click, then select Tool Properties.
3. Change the Name to Smoke Detector.
4. In the Device Type dropdown, select Smoke Detector.
5. Leave the Model field set to Cleary Photoelectric P1.
6. Click OK to close the Tool Properties dialog.
7. Press TAB to begin entering the device location.
8. Enter the location 4.37,0.63,2.635.
9. Press ENTER to create the Device.

The smoke detector you just created is located at the center of one of the cells at the corner of the room. Smoke detectors are technically a type of Gas-Phase Device in FDS, so they need to be placed inside of a gaseous cell, just like the Doorway Temperature device created in Section 4.3.1.

The Smoke Detector Device is now fully configured.

5.1. What are 2D Slices?

Think back to the questions we were looking to answer by adding Devices and think of what they all had in common. Whether it’s the temperature at head-height in the doorway, the temperature of the ceiling above the fire, or a smoke detector in the corner of the room, these questions are all looking for data at a single point. What if we want data for a broader area, and not just for a point?

That is where 2D Slices, also known as Planar Slices, come in to play. 2D Slices allow you to record the value of a Gas-Phase Quantity at more than just a single point by recording the value across an entire plane in your model.

Creating 2D Slices in PyroSim is fairly easy. You will create 3 different Slices to answer the following questions:

5.2. Defining 2D Slices

Defining 2D Slices in PyroSim is very easy. To create the Slices:

This dialog shows a table. Each row in the table defines a separate 2D Slice. You define a 2D Slice by filling out a row in the table.

The Slice you just defined will measure the Temperature in the plane of the doorway opening - the same plane that the Doorway Temperature Device is in. Create the other two Slices:

These Slices measure the temperature below the ceiling, and the visibility at head height, respectively.

The 2D Slices are now fully configured.

6.1. Viewing Device Data

PyroSim provides a handy way to view the output data from Devices in your model. By default, FDS writes the Device data out to a _model_name__devc.csv file. PyroSim parses this, and other csv files, to provide Time History plots.

To view the Time History plots for your Devices:

The column on the left-hand side of the window is a list of all the devices in your model. The plot on the right is a plot of the value of the selected device over time. You can save a screenshot of your plot at any time by using the File > Image Capture action, which will save an image of the plot at its current size.

Viewing the Doorway Temperature plot in Figure 8, you can see that the maximum temperature achieved in the doorway is roughly 270°C, and this occurs around 48s.

Figure 9 shows the plot of the Ceiling Temperature Device. As you can see from the plot, the ceiling stayed at a constant temperature of 22°C throughout the entire simulation. This is obviously not what would happen in real life, with an entire raging fire burning under it, so why does it read 22°C?

The ceiling obstruction in this model had the default INERT surface applied to it. If you remember back to the Your First Fire tutorial, we described the INERT surface.

The `INERT` surface is a surface with a fixed temperature equal to the ambient temperature in the model.

Because our model’s ambient temperature is a constant 22°C, the surface and the device recording it are as well. Try changing the ceiling surface to the ADIABATIC surface and running the model again to see the difference in the results.

6.2. Viewing Smoke Detector Activation Time

Select the Smoke Detector in the Time History Plots dialog to view its output over time.

Figure 10 shows the plot of the Smoke Detector’s Obscuration over time. This value is in units of %/m, which is an industry standard.

By default, smoke detectors will activate at a value of 3.24%/m obscuration. Based on the plot, we would expect the smoke detector to activate around the 4s mark.

To view the exact activation time of our smoke detector, or any device with a Setpoint (covered in later tutorials), you will need to open the model_name.out file, created by FDS when you run your simulation, in a text editor. At the bottom of this file, you will find a DEVICE Activation Times section. In this section, you can see that the Smoke Detector activates at 4.303s.

We can also verify this in the PyroSim Results Viewer. Top open the Results Viewer:

With the Results viewer open, look through the doorway of the room to find the smoke detector.

Figure 12 shows the 3D representation of the smoke detector in Results Viewer. The green light on the detector indicates that it has not yet activated. Press the Play button to advance time until 4.2s, and notice that the detector’s light changes color to red. This indicates that the detector is activated, like we expected it to be.

6.3. Viewing 2D Slice Data

6.4. Doorway Temperature Slice

2D Slice data is also viewed in the Results Viewer. To view the slice, we set up for the doorway temperature:

You should now see the 2D Slice plane, with a colorbar on the right side of the screen. However, if you compare the colorbar to the Doorway Temperature device result plot in Figure 8, the range of the colorbar is quite different. This is because the colorbar uses the default Percentile (rounded) setting, found in the Results User Manual. To change this:

The colorbar should now be a similar range to that in Figure 8. You can click on the colorbar to highlight a specific value. To do this:

As you can see in Figure 15, the 200°C value is highlighted black in the playback results.

6.5. Ceiling Temperature Slice

Viewing the other slices is mostly the same as Section 6.4, however the useful information in those slices is hidden by the geometry of our model. To view the results of the Ceiling Temperature Slice:

You should now see both the doorway temperature and the ceiling temperature slices in the 3D window.

Because you selected Yes in the Use Vector? column for the ceiling temperature slice, there is also an additional 2D Slice Vectors object created for the slice. These can be overlaid on top of the existing 2D slices; however, it might be clearer to show them separately. To show these vectors:

You should now see the vector plot for Temperature. Because Temperature is a scalar quantity, the length and direction of the vector show the direction and relative speed of the flow of the fluid in that cell. The color of the vector shows the value of the quantity, shown in the color bar. (McGrattan et al. 2021, 294-295)

6.6. Visibility Slice Results

Showing the visibility slice results is much the same as the ceiling temperature slice in Section 6.5. The only thing to note here is that because you selected Yes in the Cell Centered? column when defining the slice, the results will look blocky. This is because by default, slices are interpolated at cell corners in order to smooth out the results plot. Defining slices as cell-centered disables this interpolation, so the values will change sharply from cell to cell. To show the visibility slice: