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  • The video is created using Phoenix 3.0, but the text version of the tutorial is updated and uses Phoenix 4.30 Official. In any case of doubt you may refer to the text.
  • Another way to create a Gasoline Explosion is to use the newer and improved version of the Gasoline Explosion Toolbar Quick Setup preset which is included in the Nightly Builds since 16 Sep 2020.

 

System Units Setup

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Scale is crucial for the behavior of any simulation. The real-

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world size of the

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Simulator in units is important for the simulation dynamics. Large-scale simulations appear to move more slowly, while mid-to-small scale simulations have lots of vigorous movement. When you create your Simulator, you must check the 

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Grid rollout where the real-world extents of the Simulator are shown. If the size of the Simulator in the scene cannot be changed, you can cheat the solver into working as if the scale is larger or smaller by changing the Scene Scale option in the 

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Grid rollout.

The Phoenix solver is not affected by how you choose to view the Display Unit Scale - it is just a matter of convenience.

 

Go to Windows → Settings and Preferences → Preferences → Settings and set the Working Units to Meters. 

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Scene Setup

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In the following steps we will show how to create a create a gasoline explosion simulation with the Phoenix Gasoline Explosion Preset.

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We will begin by using a quick Gasoline Explosion preset.

 

Create a Sphere with a Radius of 24.0 meters. This sphere will be the source of the explosion.

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With the sphere selected, click on the Gasoline Explosion Preset button from the Phoenix Shelf.

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Now press the Start Simulation button in the Shelf.

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Let the simulation run for a few seconds and you will have a chance to see the results in the viewport, click the Stop button to end the simulation process.

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Here is a GPU Preview of the simulation.

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To enable the GPU Preview as seen in the picture, select the Phoenix Simulator → Preview rollout → GPU Shade Preview → Enable GPU Preview.

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Manual Explosion Setup

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Let’s take a look at setting up a gasoline explosion simulation manually.

 

If you are continuing from the preset steps above, select the Simulator and press the Clear Simulator Cache button from the Phoenix Shelf and then delete the Simulator and the Source objects from your scene.

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If the sphere has been deleted, create a new Sphere with a Radius of 24.0 meters.

 

Click on the Create Phoenix Fluid Simulator button in the Phoenix Shelf and click and drag in the viewport to create a volume to encompass the sphere, while leaving some room for the explosion to spread. Move the sphere near the bottom of the Simulator's volume space. Make sure the sphere is still inside the volume.

Open the Grid rollout and set the following values:

  • Scene Scale: 1.0.
  • Cell Size: 1.0 m.
  • Size XYZ: [ 229, 123, 219 ].
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Use the Size attributes of the Simulator as opposed to simply scaling the Simulator container with Maya's Scale Tool, as that may adversely affect the simulation.

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Click the Create a Fire/Smoke Source button on the Phoenix Shelf and place the Source in your scene.

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The Source object is a 2D non-renderable icon, so size and placement are only important for being able to select the Source when needed.

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Select the sphere and then shift-select the Source and click Add Selected Objects in the Attribute Editor.

The Object Set of the Source is used to specify the geometry in the scene that will be used to emit fluid into the Simulator.

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The Source node is where we control the Emitter properties, like the Emit Mode ant the Discharge. The sphere is the actual emitter of the fluid inside the Simulator.

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Within the Fire/Smoke Source menu, we will disable Temperature and Smoke, as they will not be needed for this demonstration. Make sure Fuel is enabled.

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Since we are creating an explosion that will use a large amount of fuel very quickly, we will need to increase the Discharge. The higher this number, the more fluid will be generated per second. In order to create the short but powerful burst of fluid, we will animate the Discharge.

Make sure you're at Frame 0, change the Discharge value to 2000, right-click on the Discharge tab and Set Key.

Then, go to Frame 1, change the Discharge value to 0.0, and set a keyframe.

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Select the Simulator. In the Attribute Editor under the Grid rollout are located the parameters to control the resolution of the volume grid, which greatly affects the look and performance of the simulation.

Currently, there are about 6 million Total Cells. To save on simulation time during the iteration process, click Decrease Resolution several times until the Total Cells are around 825,000.


For more information regarding simulation resolution, please refer to the Basic Liquids QuickStart page.

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Click the Start Simulation icon, and notice that the explosion does not happen. Select the Simulator and navigate to the Fuel rollout. Select Enable Burning.

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Once again, if you click Start Simulation, you will see that the explosion is still absent. This is due to the Ignition Temperature being set at 600.0. This temperature is rather high. By default, Phoenix uses 300.0 as a default ambient temperature. Change the Ignition Temperature to a value slightly lower: 290.0.

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Navigate to the Rendering rollout → Smoke Opacity tab and disable the Scale Opacity by Scene Units option.

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Start the simulation and you will see a puffy preview. To see the explosion more clearly, navigate to the Preview rollout and turn on the GPU Preview by clicking Enable in Viewport.

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Currently, the explosion is being cut off at the top and sides by the Simulator's Grid.

Adjust this in the Grid rollout by turning on Adaptive Grid by Temperature. Lower the Threshold temperature to 600.0 to ensure expansion based on the temperature of the fluid inside when it meets the specified threshold.

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If you experience clipping of your smoke, set adaptive to Smoke with a Threshold of 0.02.

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To prevent the explosion from expanding the bottom, go to Container Walls and select Jammed (-) in the Y axis. This will act as a floor. 

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Start the simulation. The resulting explosion looks very uniform.

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To add variation, select the Fire/Smoke Source and increase the Noise value to 10.

Notice the variation that is added to the simulation.

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Start the simulation once more. While it is running, select the Simulator and go to the Rendering rollout → Fire tab.

Under the Fire settings, there are a few Fire Opacity Modes available: Use Smoke Opacity, Fully Visible, and Use Own Opacity.

Select Use Own Opacity, and stop the simulation.

When you use Own Opacity mode, the fire curve will control the opacity of the fire instead of the intensity. The intensity in this mode is controlled by the color gradient and can be boosted or lowered using the Fire Multiplier. 

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The graph here The graph in the Color and Opacity rollout controls only the opacity of the fire. Double-click to add a new point to the curve and drag it down to reduce the opacity of the fire, revealing more of the internal fire content and making it look brighter. Drag the point up to increase the opacity and hide more of the internal structure. Add points in the middle for a gentle curve.

Click the Expand button for a larger graph to work with.

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You can further adjust the opacity with the Opacity Multiplier above the graph. For this example, we will lower this value to 0.5, and notice how the fire increases in brightness.

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The Physically Based setting blends between artistic and physically accurate results. Change Physically Based to 0.75 and observe the more "fiery" look in the simulation. This parameter balances between how much of the fire intensity comes from the color gradient plus the fire multiplier versus how much is calculated using the physically-based black body shader.

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To change the color of the fire, double-click on the carrots above the graph and select a new color. Select Cancel to return to the previous color.

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To adjust the explosion to look less contained, navigate to the Dynamics rollout and under Conservation, adjust the Quality setting. This setting allows the simulation to spread more and gives it a swirling motion. Increase Quality to 80. Note that increasing this value will increase simulation time. Start another simulation.

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The explosion is breaking up a bit more, but it's not quite there yet. Open the Rendering rollout → Fire again. Disable the Fire for now. We can see there is a lot of smoke as a result of the fuel burning so much. Stop the simulation to address this.

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In the Fuel settings of the simulation, reduce the Smoke Amount to 0.4 to allow for more burning and a brighter fire, and also increase the Smoke Threshold to 1.0. The Smoke Threshold will lessen how much of the fuel is created as smoke. Reduce Propagation of the fuel to 2 to reduce how fast it propagates through the simulation.

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In the Fire rollout, remember to set the Fire's Based on parameter back to Temperature before restarting the simulation.

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The fire now looks too hot. Go to the Fuel rollout and reduce the Fuel's Energy to 5 and restart the simulation.

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The explosion is starting to look good, but it stays hot for too long. We need to increase the cooling of the fire by going to Dynamics rollout and increasing Cooling to 0.3.

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Our smoke looks very thin. In the Rendering rollout, expand the Smoke Opacity tab and increase Simple Smoke Opacity to 0.9.

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Simple Smoke Opacity: 0.5

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Simple Smoke Opacity: 0.9

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Expand the Smoke Color rollout and reduce the Constant color slightly to make darker smoke. In this example, we used a Value of 29. Also, lower the External Scatter Multiplier to 0.8 so that the light inside the smoke scatters less.

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The fire looks a little weaker now. Under the Fire rollout, increase the Fire Multiplier to 5.0 so the fire is hotter inside the explosion.

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Rendering

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To prepare your scene for rendering a simulation make sure V-Ray is set as your Renderer in the the Render Setup window window.

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Here is how the render looks so far.

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Notice some areas of the floor are too bright. You are able to control this in Rendering → Fire Lights rollout.

Set the Light Power on Scene value to 0.5 and re-render the frame. By reducing this value, the light is more evenly distributed.

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Here is the new render.

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To get finer detail for a final render, increase the Resolution of the Grid. In the Attribute Editor, go to the Grid rollout and click Increase Resolution a couple of times to have about 6.1 million Total cells and re-run the simulation.

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Here is how the final render looks.

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Example Scene

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Now let's apply what we've learned to a real-world example and make these barrels explode!

The following scene file can be downloaded from the Overview section above.

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Select the blue barrel, pCylinder3, and apply the Gasoline Explosion Preset.

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Select the Simulator and change the Cell Size to 3.0. This will decrease the Total Cells to around 573,000 and will save you time during the iteration process.

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Select the Source and set a keyframe on the Discharge to 3100 at Frame 1.

Keep the keyframe on the Discharge set to 0.0 at Frame 2.

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Start a simulation and you'll see that the blue barrel explodes. Now we will focus on the other barrels.

Stop the simulation.

Select the Fire/Smoke Source and press Ctrl+D to Duplicate it and move it over a little so it's not overlapping the original.

Notice that the Discharge is set to 0.0, because we duplicated the Source, and the keys don’t transfer over with a simple Duplicate in Maya.

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Select the second Source and set a keyframe on the Discharge to 0.0 at Frame 5.

At Frame 6, set Discharge to 3100 and keyframe.

At Frame 7, key the Discharge back to 0.0.

Run the simulation, and you can see that the first explosion sets off the second explosion.

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Now when you start the simulation again you will see two explosions, the second being delayed by five frames.

Stop the simulation.

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For this last barrel we are going to let the explosion cool off some before ignition.

Select the third Source and set a keyframe on the Discharge to 0.0 at Frame 41.

At Frame 42, set Discharge to 6000 and keyframe.

At Frame 43, key the Discharge back to 0.0.

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Start the simulation and let it run. The third explosion starts as the first two are cooling off.

Do a test render to see the results. If the fire is too bright, go into the Fire rollout and decrease the Fire Multiplier value.

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Go to the Rendering → Fire Lights tab and change the Light Power on Scene to 0.1.

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To make the final simulation, go into the Grid rollout and increase the Cell Size to 1.5. This will increase the Total Cells to about 4.5 million.

Set the Adaptive Grid to Smoke and the Threshold to 0.002.

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Run the final simulation and make a final render.

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