Review Results for Scenario and Frequency Based Analysis

 

The remainder of the tutorial will use of the Tutorial 11 - Completed Simulations.ifx (430MB) file.

 

With a Risk Data Set defined and simulations complete, risk contours can be created.

 

Risk contours can show results based on one of the following methods:

  • Scenario - will display results in the contour showing how many cases (scenarios) above the defined LFL value exist on the defined plane. Can also be thought of as a 'heat map' showing where the most cases exist having above the chosen value.

  • Frequency - rather than representing individual cases, the frequency information combined with the wind probably is used to show regions which are most likely to have a gas leak above the defined LFL value

  • Probability - only used with risk-based ventilation simulations such as Helideck Turbulence.

  • Risk - discussed in the next section, risk contours apply a consequence to the leak frequency data, the contour will show the risk of having an exceedance above the defined LFL value.

 

 

This section will define a Scenario and a Frequency contour:

  1. Ensure that the Risk Data Set 01 has been updated by right-clicking its name and selecting 'regenerate' if the option is not available then the risk data set is updated.

  2. Select Risk Contour from the Add Items Tab

  3. Leave the Name as its auto-defined one

  4. Select the Risk Data to the one created in the previous section - Risk Data Set 01

  5. Set the Data Type to Scenario. This will set the contour to display results based on the number of scenarios in each region with above the exceedance value.

  6. Enter a value of Exceedance as "10%LFL"

  7. Set the On Plane to XY

  8. Enter the Offset as "16 meters"

  9. Leave the Relative To option as Domain

  10. Open the Coloring section and set the Range to be User Defined. Enter a value from "0" to "20" as the Min and Max values, respectively. As the data type was set to scenario this will show regions having more than 20 cases/scenarios with above 10% LFL in red.

  11. Click the Add Item button

 

 

Picture 34

Tutorial 11 - Figure 18 - Added contour showing exceedance of 10% LFL with a scenario basis

 

In the resulting contour, the highest concentration of scenarios having above 10%LFL exist close to the leak locations. Once defined, the contour can be moved to any height or any plane (XY, YZ or ZX) within the Risk Data Set. Click the contour name in the Project Items Tab and change the Plane Offset to "14 meters" in the properties panel.

 

At a height of 14 meters, just 2 meters lower than before, gives a much different picture as seen in Figure 19. Since the leaks were defined at the top of the module much of the gas clouds simulated stayed at a higher elevation. This will not always be the case as there are many factors which affect where gas dispersions travel to.

 

Picture 35

Tutorial 11 - Figure 19 - Risk Contour moved to a lower elevation showing that not many gas clouds traveled under the top deck

 

Add a second risk contour to the project, this time using Frequency as the type:

  1. Toggle off the visibility of the risk contour defined above.

  2. Select Risk Contour from the Add Items Tab

  3. Leave the Name as its auto-defined one

  4. Select the Risk Data to the one created in the previous section - Risk Data Set 01

  5. Set the Data Type to Frequency. This will set the contour to display the frequency of having about 10% LFL for the cases simulated.

  6. Enter a value of Exceedance as "10%LFL"

  7. Set the On Plane to XY

  8. Enter the Offset as "16 meters"

  9. Leave the Relative To option as Domain

  10. Click the Add Item button

 

This frequency contour shown in Figure 20 is the frequency of gas exceeding the defined 10% LFL for the cases simulated. Red regions will have a high frequency and blue regions have a low frequency.

 

Picture 36

Tutorial 11 - Figure 20 - Updated contour showing exceedance of LFL with a frequency basis

 

The Data Type, exceedance values, plane offsets and defined plane may all be changed after the risk contour has been defined. Be wary of the User Defined Max/Min values when changing a contour in this way.

 

 

Continue to the next section to define a consequence value to each of the dispersion cases.