Add colliders

Colliders are objects that block movement in a simulation.

1. Add a collider node to a the top level of simulation graph, if there isn't one already.

2. Connect the collider node's collider output into the colliders input of the simulate node.

3. Connect one or more mesh or volume objects to the collider node's geometry input.

   • For volume objects, the method on the collider node must be set to Volume.

You can have any number of geometries connected into a collider node. You can also have any number of collider nodes connected into the simulate node, each with different settings.

Choose the collision method

The method parameter on the collider node controls whether the collider geometries are treated as a mesh or as a volume.

• Volume treats all geometries as volumes. Mesh inputs get converted automatically. For more accurate collisions, reduce detail_size.

• Mesh_for_Points treats meshes as meshes. This method avoids a gap between the mesh surface and the collision location.

Note that for volume objects, the method must be Volume. In addition, the volume object must have a level set (voxel_signed_distance).

View collision areas

You can connect the collider_volumes output from the simulate_aero node or out_colliders output from the simulate_mpm node to an output node to display the exact collision areas affecting these simulations. This can help you visualize collider setting changes or collision problems.

Control particles' collision behavior

Particles can bounce or stick when they hit a collider. This is controlled by a combination of factors:

• Bounciness controls the amount of velocity normal to the collision surface that gets reflected on collision. This affects, for example, how high particles bounce after hitting the ground. The final value is a combination of the bounciness set on the particles and the collider. If both values are 1.0, particles rebound completely and if both values are 0.0, particles do not bounce at all.

• The friction parameter set on the collider node controls the motion along the colliders' surface. If this value is 1.0, particles hitting the ground will not roll and if it is 0.0, particles will roll without slowing down.

• The roughness parameter on the collider node varies the angle at which particles bounce off. This emulates hitting a rough surface.

If fast-moving particles fall through a collider, try increasing the substeps on the particle_solver_settings node.