This page provides information on the Active Bodies component.
Overview
The Active Bodies Solver node is used to specify the scene geometry which will partake in the Active Bodies simulation. By default, all geometries in the scene are Solid and act as obstacles to the Phoenix fluid simulation. Active Bodies go one step further and can be pushed by the fluid or can float over the liquid surface, unlike Solid obstacles which stay in place and obstruct the movement of the fluid. Additionally, just like the movement Solid bodies can be animated, the movement of the Active Bodies can be animated, so that an Active Body both follows a trajectory, and also gets influenced by the fluid's movement. You can balance between the influence of the animation and the fluid from an Active Body's right click properties' Original Animation Influence option.
Note that mutual interaction between the Active Bodies themselves is not supported yet. Also, interaction between Active Bodies and the Phoenix FD Fire/Smoke Simulator is still not supported.
The Active Bodies Solver node sets up global simulation parameters which affect all Active Body objects in the Interaction list, in contrast to the Phoenix FD Per-Node Properties which are unique for each Active Body. This way you can have several Active Body Solver nodes, each with their own set of Active Bodies with different rigid body behavior for each set.
||Phoenix FD menu|| > Create > Active Body Solver
Active Body Solver
On earth, an object floats above water because of two forces: Gravity pulling it down, and the Buoyancy of the liquid pushing it up. Depending on the densities of the liquid and the floating object, those forces balance out and the object either sinks (if denser than the liquid its submerged in) or floats.
Fluid Dens. Mult. | interaction_mult – Allows you to override the density of the simulated liquid. By default, 1.0 is considered 1000 kilograms per cubic meter (the density of water). Increasing this value will cause the Active Bodies to appear lighter and sink less inside the fluid simulation., and vice versa.
Sim. Air Drag | simulate_air_drag – Applies a simple Drag force to slow down the translation and rotation of the Active Body. This option helps stabilize the motion of objects in the simulation.
Scene Interaction
Interaction Set | interactionSet – Determines which objects will be processed by the simulation. By default, all objects in the set will be treated as Active Bodies. Scene geometry not preset in the Interaction Set will be ignored by the Active Bodies Solver. Enable the Exclude List option to reverse this behavior.
Exclude List | interExcludeList – When enabled, all objects in the scene will be considered Active Bodies unless they are added to the Interaction Set.
The Active Bodies solver will compute the Center of Mass of an object by looking at its volume. To simplify things, an assumption is made that all parts of the object have an equal weight.
In the case of e.g. a ship, this is not true. The masts and sails of a ship make up a large portion of its volume but contribute little to its total mass.
In such cases, enable the Override Center of Mass option on the Phoenix FD Node Properties of the original object and tweak the Center of Mass Gizmo.
Create Center of Mass – Creates a Center of Mass Gizmo for a scene object. Use this option if you accidentally deleted the Center of Mass Gizmo or would like to reset it to its automatically-computed position.
Destroy Center of Mass – Deletes the Center of Mass Gizmo for a scene object. Using this option is the same as selecting and deleting the gizmo from the Scene Explorer window.
Auto-create dummies | autocreate_dummies – When enabled, a Center of Mass Gizmo is automatically generated for an object when added to the Interaction Set. The Center of Mass gizmo is linked to the object in a parent/child hierarchy.
Auto-delete dummies | autodelete_dummies – When enabled, the Center of Mass Gizmo is automatically deleted for an object when removed from the Interaction Set. The Center of Mass gizmo is linked to the object in a parent/child hierarchy.
Ground Plane Object
Use Ground Plane | use_ground_plane – Enables the calculation of a Ground Plane geometry for the Active Bodies simulation. The Ground Plane is infinite in size, and its orientation is based on the rotation of the specified Plane geometry.
Set Selected Object as Ground Plane | ground_plane – Specifies the Ground Plane geometry. The Solver expects a Phoenix FD menu → Create → Active Bodies Ground Plane object. Other object types will not work with this option.
Ground Friction | ground_friction – Controls the amount of friction between the Ground Plane and the Active Bodies. Low amounts of friction will allow objects to slide across the ground plane. High amounts of friction will slow down both the objects' rotation and movement once they come into contact with the ground plane.
Ground Elasticity | ground_elasticity – Controls the bounciness of the Active Bodies when they hit the Ground Plane.