Adding an Isosurface for an Individual Component


As H2S is toxic to humans at very low concentrations, it is important to determine where toxic gas spreads and at what concentrations. For the purposes of this tutorial, we will look at the 100ppm concentration of H2S in our dispersion simulation.


  1. Toggle off the visibility of the contour generated in the last section.

  2. Click the Add Item tab and select Isosurface from the dropdown menu.

  3. Leave the name as the automatically generated one.

  4. Select the HP Release with H2S on Westerly, 5m/s case as the Simulation.

  5. Set the Variable to be HYDROGEN SULFIDE Volume Fraction, ppm from the dropdown menu.

  6. Enter a value of "100" as the Value.

  7. Set the color to be transparent yellow by selecting the color swatch to open the color palette dropdown menu. Select the Advanced button at the bottom of the palette and change the values to appear as Figure 25 below, with the alpha channel (transparency) set to 150.


    Tutorial 7 - Figure 25 - Setting a transparent yellow color from the Advanced color palette


  8. Click the Add Item button to add the 100ppm H2S isosurface to the project.


    Tutorial 7 - Figure 26 - The isosurface representing 100ppm of H2S for the defined gas mixture


We can see in Figure 26 that the 100ppm H2S cloud and encompasses the small vessel and a large part of the walkway. The westerly wind causes re-circulation behind the large tanks and traps the gas, preventing it from being blown away or dispersed.


Look at the 50ppm concentration by editing the properties panel of the H2S isosurface, indicated by the red arrow in Figure 27. At this concentration we can see that the wind starts to carry the gas eastward (toward the bottom of the below figure) and results in the entire walkway being covered. We can conclude that both 100ppm and 50ppm values of H2S are present along the walkway for this case and could be detrimental to any personnel there. It may be worth considering performing a risk-based assessment investigating H2S exceedance levels for various leak locations and wind directions.


Tutorial 7 - Figure 27 - Process and result of changing the H2S isosurface to show concentrations of 50ppm


Remember that a new isosurface does not have to be defined for each concentration or each variable.


This process can be repeated to view %vol or ppm of other components in the gas mixture. Contours, vectors and isosurfaces can all be applied to components of gas mixtures as well as the bulk properties.


Continue to the next section to view monitor data for the gas mixture dispersion case.