Using Motion Fields

Use motion fields to influence the velocities of liquid and foam.

To add a motion field to a fluid simulation:

From the Create panel > Space Warps, click Motion Field and drag in the viewport.
Alternatively, you can also create a Motion Field object using the menu:
- Default menu: Animation menu > Fluids > Motion Field
- Alt menu: Animation menu > Fluids > Motion Field
Select the Liquid object where you want to add the motion field.
From the Setup rollout, click Simulation View to open the Simulation View window.
Under Liquid Attributes > Motion Fields > Add Motion Fields, click Pick and select the motion field.
The motion field now interacts with the fluid simulation. To adjust the parameters, select the motion field object again in the scene and use the controls on the Modify panel.

Tip: To visualize the effect of a motion field on a fluid simulation, enable Velocity Grid under the Display rollout of the Modify panel.

To apply motion field controls to geometry:

Add a motion field to the scene.
Under Group Controls, enable Geometry.
Pick the object that you want to inherit motion field controls.
Add the object as a collider in your simulation.
Add the motion field to your simulation.
The selected collider now inherits all of the motion field controls, which you can then modify to adjust the result.

Common Techniques

You can enable and adjust the following parameters to create these common fluid effects using motion fields.

Damping

To slow down a simulation, simply enable the Drag option in the Group Controls area of the Motion Field properties.

Wind

Use the Direction controls in combination with the Drag option in the Group Controls area of the Motion Field properties, and enable the Turbulence and Noise option, if desired.

Churning

Enable Turbulence and Noise to view the Turbulence and Noise rollout. There, adjust Noise Magnitutude to add some random motion. In the Velocity rollout, enable Clamp Speed to keep the fluid churning, with Max Speed to set to a higher value and the Min Speed animated with a value increasing from 0.0 .

Whirlpool

Create a cylinder in the scene. In the Group Controls area of the Motion Field properties, enable Geometry to view the Geometry rollout. Click the Pick button and select a cylinder. Enable Falloff. In the Direction rollout, make sure that Direction Magnitude is 0.0, and adjust the Around Axis option. You can also add Drag if the velocities become too high.

Wave

To create a wave that forms spontaneously and then breaks, set up a cylindrical motion field as for a whirlpool above. Rotate the cylinder onto its side so that it intersects a portion of the liquid surface, then animate it moving forward. You can add a bit of Direction to help the fluid move forward and against gravity, and use a negative value for Away From Axis to keep the liquid from flying away.

Break up falling water

To help break up a waterfall or similar flow into droplets, enable Drag and use Normal Drag with a low Max Depth. For spray, add foam to the simulation, and apply a separate field directly to the foam with Drag and Turbulence enabled.