SPH Affector

Simulates fluid dynamics on Particles with an SPH simulation.

Method #

This node simulates fluid dynamics on a particle system using the SPH (Smoothed Particle Hydrodynamics) simulation method. This is typically used to simulate liquid effects. It solves a fluid simulation by locally solving pressure forces between a particle and others nearby. This allows particles to affect each other and to move in a locally coherent manner. SPH works well for liquid effects like water.

The solver takes into account both the position and velocity of particles and their neighbours. The Viscosity attribute is used to make the simulation behave as a thicker liquid. Surface Tension is used to keep particles together like droplets of water. The radius around each particle in which they interact with their neighbours is controlled using the Cell Size attribute. Larger cell sizes may result in a smoother simulation that increases performance demands. The simulation may be switched from 3D to 2D, in which case one axis is dropped from the simulation.

The grid resolution and size used for the pressure solver is key to the detail and performance of the resultant simulation. A higher resolution grid over a smaller area will give a more detailed simulation, but higher resolution grids are slower to process.

Parameters

Transform

These properties control the 3D transforms of the node. Transforms will generally be inherited by child nodes, although they can be ignored through the Inherit Transform Channels attributes.

Parameter	Details
Position X	Move along the local x-axis.
Position Y	Move along the local y-axis.
Position Z	Move along the local z-axis.
Rotation Heading	Rotate around the local y-axis.
Rotation Pitch	Rotate around the local x-axis.
Rotation Bank	Rotate around the local z-axis.
Scale X	Scale along the local x-axis.
Scale Y	Scale along the local y-axis.
Scale Z	Scale along the local z-axis.

Inherit Transform Channels

Toggle which transform channels should be inherited from the parent node. By default, all transforms will be inherited.

Parameter	Details
Position X	Toggle inheritance of the X Position from the parent.
Position Y	Toggle inheritance of the Y Position from the parent.
Position Z	Toggle inheritance of the Z Position from the parent.
Rotation Heading	Toggle inheritance of the Rotation Heading from the parent.
Rotation Pitch	Toggle inheritance of the Rotation Pitch from the parent.
Rotation Bank	Toggle inheritance of the Rotation Bank from the parent.
Scale X	Toggle inheritance of the X Scale from the parent.
Scale Y	Toggle inheritance of the Y Scale from the parent.
Scale Z	Toggle inheritance of the Z Scale from the parent.
World Position Only	Inherit the world position from the parent only, rotation and scale will be ignored. Overrides above properties.
Inherit Time	Toggle inheritance of time from the parent.

Attributes

These properties control the core behaviours of the node.

Parameter	Details
Weight	How strong an effect has on the particles.
Cell Size	The area around each particle that resists other particles from getting within a certain distance.
Viscosity	The viscosity of the fluid, where smaller values make it more gas-like and larger values make it thicker - more like treacle.
Gravity	How strong gravity is on the particles.
Pressure Scale	Scales the amount by which particles push apart from each other.
Rest Density	Controls the base density of the fluid.
Surface Tension	How much the particles want to stay together at their surface.
Max Force	The limit on the force applied to the particles as a result of the simulation.
Dampening	The amount particle forces are damped - so they decay over time, rather than moving constantly.
Area Scale	Scales the area of space the simulation is processing.
Mode	Choose how the fluid simulation is calculated. SPH : Use smoothed-particle hydrodynamics to generate the fluid dynamics. Position Based : Uses position based fluids, faster but less realistic. Inter-Particle Force : Simply pushes particles away from their neighbours.
Dimension	Choose whether the effect is 2d or 3d.
Life Effect Coeffs	How much the particles are affected by the affector at different stages of the particles life cycle. Values 1 and 2 are control points used to control a bezier curve between values 0 and 3.
Grid Resolution	The resolution of the underlying grid used in neighbourhood searches.

Inputs

Name	Description	Typical Input
Grid Transform Nodes	ERROR: Variable not found: {input-node-particles-grid-transform-node-description}	ERROR: Variable not found: {input-node-particles-grid-transform-node-typical-input}
Affected Emitters	Choose which particle emitters can be affected by the affector.	Primitive Emitter
Procedural Falloff	Use the distance field from a procedural system to vary how strong the affector is.	Procedural Root
Transform Modifiers	Apply the transforms of another node to this node.	Null
Target Node	Modifiy the rotations of the node to always direct the z axis towards the input.	Null
Local Transform Override	Apply the transforms of another node to this node, relative to its parent.	Null