Colliders act as obstacles to the flow of a simulation. You can use colliders to form barriers, create basins, or create waves and splashes.
Adding and Deleting Colliders
To add a collider to a simulation:
- From the Create panel, create an object to use as a collider in the scene.
- Select the Liquid object and then click Simulation View in the Setup rollout to open the Simulation View window.
- On the Liquid Attributes panel under Colliders/Kill Planes > Add Colliders, click Pick to select the object in the viewport, or Add to select the object from the Add Colliders dialog.
- After selecting your colliders, click Pick again or right-click anywhere in the viewport to disable your selection.
To delete a collider from a simulation:
- From the Liquid Attributes panel under Colliders/Kill Planes > Add Colliders, select the collider to be deleted from the list.
- Click the Trash can button.
The collider is deleted.
You can also select the object used as a collider and delete it directly from the scene. The collider is automatically removed from the simulation.
Working with Colliders
You can use the Conversion options to control how the collider is voxelized.
The Refine Nearby Fluids attribute on colliders prevents the fluid resolution from being coarsened in regions that are close to the collider when Spatial Adaptivity is enabled on the liquid properties node. Enable this option on colliders where less detail is needed, for example, on the bottom and sides of pools, and disable it on for colliders where you want full detail. This does not affect the free surface (air boundary), which always uses full resolution.
You can control how colliders interact with fluids using the Stickiness area of the Emitter parameters. High values of Stickiness Strength cause the particles to adhere and slow down as they move across the surface of colliders, and Stickiness Bandwidth controls how close the particles need to be to the collider surface to be affected by the stickiness.
If you are using a collider as a basin to hold a pool of liquid from a static emitter in place, it's a good idea to have the emitter and collider overlap a little bit. This prevents small gaps of air that can create sudden velocities as the liquid fills the gap. The overlapping fluid will be clipped by the collider to fit the volume.
You might notice that fluid is somewhat offset from colliders' geometry when Thickness is 1.0 or higher in the collider mesh property's Conversion attributes, or that fluid penetrates the collider geometry by a small amount when Thickness is lower. This should not cause problems and becomes less perceptible at higher resolutions with a lower base voxel size.