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The instructions on this page guide you through the process of setting up a gasoline explosion simulation in Phoenix FD for 3ds Max. By the end of the tutorial, you will be able to create your own explosion simulations, understand how the simulation interacts with other objects and will know the basics of editing some of the main settings of the Phoenix FD Fire/Smoke Simulator.

To follow the described steps, you will need the Phoenix FD for 3ds Max plugin installed. If you notice a major difference between the results shown here and the behavior of your setup, please send an email to support@chaosgroup.com.

This tutorial is a companion to go along with the QuickStart video posted on our YouTube channel.

The Download button below provides you with an archive containing the start and end scenes.

Scale is crucial for the behavior of any simulation. The real-world size of the 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 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 Grid rollout.

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

Go to Customize → Units Setup and set Display Unit Scale to Metric Meters.

Also, set the System Units such that 1 Unit equals 1 Meter.

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.

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

Now press the Start Simulation button in the Toolbar.

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.

Here is a GPU Preview of the simulation.

To enable the GPU Preview as seen in the image above, select the Phoenix FD Simulator → Preview rollout → GPU Preview → Enable in Viewport.

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 Delete the Cache Files button from the Phoenix FD Toolbar and then delete the Simulator and the source objects from your scene.

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

Notice the variation that is added to the simulation.

Start the simulation once more. While it is running, select the Simulator and go to the Rendering rollout and click on the Volumetric Options button.

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. 

The graph here 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.

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.

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.

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.

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.

The explosion is breaking up a bit more, but it's not quite there yet. Open the Volumetric Options in the Rendering rollout 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.

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.

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

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

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.

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

 
Simple Smoke Opacity: 0.5

 
Simple Smoke Opacity: 0.9

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.

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

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

Here is how the render looks so far.

We need a ground plane, so create a floor by navigating to the Create menu → VRay → VRay Plane, and place it in the scene. Set it a little lower than the simulation and give it a gray color.

Do another render. 

Notice some areas of the floor are too bright. You are able to control this in Volumetric Render Settings, under the Fire 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.

Here is the new render.

To get finer detail for a final render, increase the Resolution of the Grid. In the Modify Panel of the Simulator, 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.

Here is how the final render looks.

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.

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

Select the Simulator and change the Cell Size to 0.03 meters. This will decrease the Total Cells to around 573,000 and will save you time during the iteration process.

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

Stop the simulation and select the Fire/Smoke Source. Shift-drag to create a copy.

In the Fire/Smoke Source, Add the red barrel, pCylinder2.

Notice that this barrel laying on its side is slightly outside of the Fire/Smoke Simulator. Select the Simulator box and move it over to hold all three barrels.

When you start the simulation now, you will see that both barrels explode at the same time.

Stop the simulation.

To offset the second explosion so that it looks like a chain reaction, select the second Fire/Smoke Source and navigate to its keyframes. Select both keyframes and drag them over so that the explosion is triggered at Frame 5.

To make sure the explosion is not triggered earlier, step back to Frame 4, turn on Auto Key, and change the Outgoing Velocity of the Fire Source to 0. Then turn off Auto Key.

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

Stop the simulation.

For the third barrel, shift-drag the second Fire/Smoke Source to make a third copy and add pCylinder1 to it.

For this last barrel we are going to let the explosion cool off some before ignition, so with the third Fire/Smoke Source selected, move the timeline slider and the source's keyframes up to Frame 40.

Turn on the Auto Key and navigate the slider to 41st frame. Change the Outgoing Velocity to 60.0.

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 Volumetric Options and decrease the Fire Multiplier value.

Go to the Volumetric Options → Fire tab and change the Light Power on Scene to 0.1.

To make the final simulation, go into the Grid rollout and increase the Cell Size to 0.015 meters. This will increase the Total Cells to about 4.5 million.

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

Run the final simulation and make a final render.