Creating the Particle System

Open the SIM_e1_Leak scene from the Tutorials project.

You can hide extraneous elements in the scene by choosing Layers > Layer Control. Deselect View for the other_tires_n_stuff layer.

Create the particle cloud

First, you must create the particle object itself (called a particle cloud) to define the basic particle system.

Select the small disc (the leaky valve) above the tires in the C viewport.

From the Simulate toolbar (press 4), choose Create > Particles > From Selection.

In the ParticlesOp property editor that opens, select Interactive as the Execution State if you want to have the particle animation update interactively as the particle parameters are changed. If not, you will have to move the playback cursor to see the effect of a parameter change.

Leave the default values for Start Frame, Duration, and Particle Percentage as is. Lock the property editor to keep it open (click the lock icon in its upper-right corner).

The Particle Percentage controls the number of particles that originate from emitters belonging to a particle cloud.

Define the particle type

Now rename and define the main particle type, which are the particles originating from the tank's valve:

On the Emission page, beside the ParType text box, click Edit, then type From_valve in the Name text box. Close that property editor.

Back on the main Particle_Type > General property page, enter these values for the following parameters:

Maximum Life: 4 (seconds)
Maximum Life Variance: 1.2
Size: 0.1

Switch to Shaded display mode in a viewport to see the size of the particles.

On the Emission page, leave the default values for Generation and Emission Direction as is: Generation sets the point of origin of the emitted particles, and the Emission Direction sets their direction.

The other parameters control the density, speed, and spread angle of the emitted particles. Enter the following values:

Rate: 350 and its Variance: 50
Spread: 15 and its Variance: 7.5
Speed: 1.4 and its Variance: 0.5
Leave the rest of the parameters at their default values (Inherit Vel considers the source's velocity, if it is in motion).

Move the playback cursor to frame 40 to see what the particles look like.

Setting Up a Second Particle Type for the Death Event

When the From_Valve particles hit the ground and die, a second particle type is emitted at the ground. You need to define this second type:

On the Particle Type > Death Event page, click New to create the decay particle.

Select Particle_Type in the box and click Edit.

In the Particle Type property page that opens, enter the name From_Ground for the decay particle.

Set the Particle Size to 0.08, leave the other parameters as they are, and close the property page.

Now you have to define how the From_Ground particles will behave after the From_Valve particles die off.

Complete the Death Event information:

Set Number to 10. This means that for every dead From_Valve particle, 10 From_Ground particles are generated.
Set Inherit Vel to 75 so that every new From_Ground particle inherits 75% of the velocity from the From_Valve particles.
Set Spread to 60.
Leave the default values for the other parameters and close the property editor.

Applying Gravity to the Particles

Apply a natural gravitational force that will affect the particles.

Choose Get > Force > Gravity from the Simulate toolbar and accept the default Amplitude value of 9.8 (earth's gravity).

If the particle cloud is selected when you create a force, it is applied automatically to that cloud-you don't need to apply it with the Apply Force command.

To see the gravity icon in the viewport, click the eye icon in the title bar and choose Control Objects. Remember that you can keyframe any kind of S\R\T transformations on the gravity icon.

To apply the force, select the cloud icon and choose Modify > Environment > Apply Force from the Simulate toolbar. Pick the gravity icon to apply it to the particle cloud.

Setting Up Obstacles

Next, specify the obstacles that the sludge can slide down the tires and the ground.

Select the cloud and choose Modify > Environment > Set Obstacle from the Simulate toolbar. Pick both tires, then the ground, and right-click to finish.

At this point, if you enter values in the Obstacle property editor, they will be applied to all selected obstacles. Instead, to give the obstacles unique properties, select them individually in the viewport while keeping the Obstacle property editor open (click its Lock icon), then modify their values:

Select the ground and change its Obstacle Type parameter to B-Plane.

Enter these other values for the ground:

Friction: 0.5
Elasticity: 0.35

Select Double-face Collision for when the particles hit both sides of an object's face.

On the ParObstExtSparks page, select From Valve in the box and change its Mode to DECAY.

Shift+click to multi-select the tires and use Actual Shape for the Obstacle parameter. This setting creates a more precise simulation by considering the actual geometry of the obstacles.

Enter these other values for the tires:

Friction: 0.75
Elasticity: 0.25

Close the Obstacle property editor.

Play the simulation to see the particles going around the tires and bouncing on the ground.

Applying the Blob Shader

Select the cloud, then choose Get > Shader > Blob to apply a shader that makes particles look somewhat like metaclay objects. To open the blob shader's property editor, select the cloud icon and choose Modify > Shader.

Draw a render region (press q) around the particles and note how they are casting shadows.

Notice that the particles are too big coming out of the valve. You can animate them to grow from a small size to the normal size. To do this:

In the explorer, expand the cloud node so that you see Particle Cloud, and click on its icon to open the ParticleOp property editor.

Click on the From_valve tab and animate the size of the From_Valve particle type:

Move the playback cursor to frame 1, set the Size is 0.07, and click the animation icon beside this parameter to set a keyframe.
At frame 30, set the Size 0.1, and set another keyframe.
Select the Age% mode beside the Size parameter: this means that the variation of the size of the particle is proportional to its age-as it ages, it increases in size.