Lesson setup

To ensure the lesson works as described, do these steps before beginning:

1. Open the scene file named Liquid_Simulation_2.mb.

   This file can be found in the GettingStarted directory that you set as your Maya project:

   Getting Started/nParticles/Liquid_Simulation_2.mb

   This scene includes textured models that have been created for you. The desk, ashtray, and cigarette provided are all polygon meshes.

Adjusting the liquid’s volume

To set Liquid Radius Scale

1. In the Outliner, select nParticle_Water.
2. In the Attribute Editor, click the nParticle_WaterShape tab.
3. In the Liquid Simulation section, ensure that Enable Liquid Simulation is turned on.
4. Set Liquid Radius Scale to 2.0.

   

5. Play back the simulation.

   The nParticles are now stacked on top of each other, creating considerably more volume in the pitcher.

   

6. For this liquid simulation, you want the liquid nParticles to fill one-third of the pitcher’s volume. Adjusting the Nucleus solver Substeps and Max Collision Iterations can also affect the amount of volume that is generated by the Liquid Radius Scale value. To adjust Substeps and Max Collision Iterations, do the following:
   • In the Attribute Editor, click the nucleus1 tab.
   • In the Solver Attribute settings, set Substeps to 7.
   • Set Max Collision Iterations to 10.

   

More about Liquid Radius Scale

When creating liquid simulations, Liquid Radius Scale can be affected by other nParticle attributes, such as Radius and Collide Width Scale. For example, Liquid Radius Scale uses the nParticle object's Radius to determine how nParticles overlap, and any change in the nParticle Radius will affect how your nParticles overlap in the liquid simulation. Adjusting the Nucleus solver Substeps and Max Collision Iterations can also affect the amount of volume that is generated by the Liquid Radius Scale value. You can experiment with these settings by changing Substeps to 10 and Max Collision Iterations to 15 and observe how your liquid simulation is affected.

In the next section of this lesson, you adjust nParticle Collide Scale Width and Incompressibility attributes to add fluidity to your nParticles.

Adding fluidity to the nParticles

To make it easier to see how the nParticles are interacting with the pitcher and glass passive collision objects, turn on the Solver Display to see the nParticle collision volume. Collision volumes are a non-renderable surface offset from each nParticle radius that the nucleus solver uses when calculating the nParticle object's with each passive object collisions.

To Edit Collision Width Scale

1. In the Outliner, select nParticle_Water.
2. In the Attribute Editor, click the nParticle_WaterShape tab.
3. In the Collisions section, select Collision Thickness from the Solver Display list.
4. Set Collide Width Scale to 0.6.

   

   For typical liquid simulations, set Collide Width Scale to a value that is one-third the nParticle object Radius value.

5. Play the simulation, and stop at frame 40.

   The water nParticles occupy the pitcher in two distinct layers, one on top of the other. In the bottom layer, the nParticles are evenly spaced and leveled, while in the upper layer, there are numerous gaps between each particles. Since the top layer of nParticles represent the surface of the liquid, the gaps between each particle creates a surface that is uneven, and therefore unlike the surface of a liquid.

Increasing the nParticles’ Incompressibility decreases their tendency to be squeezed by neighboring particles. This forces the nParticles into a more uniform distribution throughout the volume, which creates a leveled surface for the liquid.

To set Incompressibility

1. In the Outliner, select nParticle_Water.
2. In the Attribute Editor, click the nParticle_WaterShape tab.
3. In the Liquid Simulation section, set Incompressibility to 20.

   

More about Liquid Simulation attributes

For this tutorial, you leave the following Liquid Simulation attributes at their default values:

• Viscosity: 0.1
• Rest Density: 2.0

You can experiment with Rest Density by setting it to 0.5 and then 4.0. Play back your simulation with each new setting to observe how the values affect your nParticles. Set Viscosity to 10,play back the simulation, and observe how long it takes in the animation for the nParticles to move from the pitcher to the glass. Ensure you set Viscosity and Rest Density to their default values before continuing the tutorial.

For more information about these attributes, see Viscosity and Rest Density.

Beyond the lesson

In this lesson you learned how to Adjust Liquid Simulation attributes to set the volume and fluidity characteristics of your liquid nParticles.