On today's show, I am showing Patrick and Martin a Maya tutorial on how to use turbulence to create the effect of blown mist droplets. For those of you unfamiliar with Maya, it's a 3D animation package from Alias|Wavefront that many artists use to create visual effects for film and other media (learn more about the free version of Maya you can use).

Today's tutorial uses particles. Particles are dots in 3D that represent a point in space. These dots can be used to represent a speck of sand, a drop of water, or piece of ash. Particles are generally used to create visual effects such as smoke, mist, clouds, splashes, sand and dust, or rain. Particles are simulated rather than animated, meaning that you don't individually tell each particle where to go by hand, but instead generally guide them using forces and rules.

When the particles are moving in a certain direction with the wind, there are some tricks that will help you get a good simulation.

Blown mist example

After each item below, play the frame range from 0 to frame 500 to see how each step affects the simulation.

1. Create anemitter. In the Dynamics mode menu choose Particles, then Create Emitter.
   
2. Set the emitter's emitterType attribute to Volume.
   
3. Set the emitter's speed attribute to 0.0, and the awayFromCenter to 0.0. The volumeShape should be a "cube." Also set the emitter's rate to 300.
   
4. Set the scale of the emitter's volume cube to <<0.783, 2.662, 4.341>>. See an example.
   
5. Now select the particles and add a turbulence field. This is done by clicking on Fields and selecting Turbulence.
   
6. Set the magnitude on the turbulence to 4.0, the frequency to 0.6, the noiseRatio to 0.707, and the attenuate to 0.0.
   
7. Change the Particle Render type to Streak and make its lineWidth 2.0, and the tailFade to 1.0 so you can judge the speed of the particles.
   Look at the settings.
   
8. Now add the wind by selecting the particles and choose Fields, then Uniform.
   
9. Set the magnitude of the uniform field to 1.0 and attenuate to 0.0. Set the directionX to 1.0 and directionY and directionZ to 0.0.
   Now if you play the simulation, you can see how the particles fly off in all directions and seem to get out of control. Here's where the little tiny unnoticeable attributes and tricks come into play. See an example.
   
10. Select the particles and change the attribute called conserve to 0.96, as shown here.
    
    Notice the difference that change made in the motion. Now the particles are not so out-of-control any more. What conserve does is basically suck out some of added energy each frame. Every time you add forces to particles you will keep adding more and more energy to the system. Conserve is a way for taking some of that energy out. You have to tread lightly though, a difference of 0.01 can make an enormous difference in motion because the value is multiplied by the particle's velocity every frame.
    
    As shown in Figure 1, if particles are moving in a given direction, then the turbulence field needs to move about 20 percent faster than the particles to emulate natural wind gusts.
    
    
    
11. Now for the finishing touch, we will apply the concept in Figure 1 to our simulation. Select the turbulence node in the Outliner window, as shown here. Set a keyframe for translationX. Now go to frame 500 and set translationX to 47.0 and set a keyframe.
    
    Now if you play the simulation, the turbulence should be moving in the same direction as the particle's uniform field but going slightly faster than the particles. Notice how nicely the turbulence peels off the particles and takes them with the wind.
    

If you're interested in learn more about how Maya was used in "The Perfect Storm," visit How Stuff Works.

Habib Zargarpour is an associate visual effects supervisor for Industrial Light + Magic. He is a contributor to "Maya: Secrets of the Pros," which is available at the techtv store.