Fluid MPM Affector
Updated: 2 Sep 2025
Simulates fluid dynamics on Particles with an MLS-MPM simulation.
Fluid MPM Affector
Method #
This node applies a fluid simulation using a variant of the MLS-MPM (Moving Least Squares - Material Point Method) fluid solver. This fluid simulation method can generate faster and more stable fluid simulations than other methods, while also highly detailed, better at settling over time, and maintains volume throughout. Best used for water simulations, not designed for high viscosity lquids (e.g, toothpaste).
The MPM simulation is an adaptive voxel based method, meaning the fluid is broken up into a grid cells which run the fluid sim, and the simulation is only calculated for the cells which contain particles. This means the sim is generally efficient, but it can be slower if every cell has a particle in it.
Parameters
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
The objects position along the local x-axis.
Position Y
The objects position along the local y-axis.
Position Z
The objects position along the local z-axis.
Rotation Heading
The objects rotation around the local y-axis.
Rotation Pitch
The objects rotation around the local x-axis.
Rotation Bank
The objects rotation around the local z-axis.
Scale X
The objects scale along the local x-axis.
Scale Y
The objects scale along the local y-axis.
Scale Z
The objects scale along the local z-axis.
Control the inheritance of the transforms from the parent.
Parameter Details Position
Toggle inheritance of the Position from the parent.
Rotation
Toggle inheritance of the Rotation from the parent.
Scale
Toggle inheritance of the 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.
Parameter Details Cell Size
Size of an individual cell within the fluid sim. Larger cells increase performance, but can lower accuracy of fluids which are meant to be more detailed.
Grid Size
The maximum size for the fluid to simulate within. Greater size can impact performance, depending on how far the the particles spread througout the grid.
Gravity
Constant downward force on the particles.
Dampening
Reduces the particle velocities over time. Useful for improving stability, and acting as a resistive force to particle motion in the scene.
Viscosity
Smooths the velocities of all particles in the sim, making them tend to move together in the same direction. It can make the particles appear more viscous, but it’s aimed at softening the shapes in a fluid sim. High viscosity fluids, such as toothpaste or silly putty, aren’t supported.
Surface Tension
Pulls particles together to form a surface that bounds the liquid. Higher values will create larger droplets.
Rest Density
Controls the density and how close the particles will be packed together. Push particles closer together, so more particles may be required to maintain the same volume.
Solid Boundary
Optionally treat the bounds of the sim as solid walls, to prevent particles from leaving the simulation space.
Inputs
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 | The objects position along the local x-axis. |
| Position Y | The objects position along the local y-axis. |
| Position Z | The objects position along the local z-axis. |
| Rotation Heading | The objects rotation around the local y-axis. |
| Rotation Pitch | The objects rotation around the local x-axis. |
| Rotation Bank | The objects rotation around the local z-axis. |
| Scale X | The objects scale along the local x-axis. |
| Scale Y | The objects scale along the local y-axis. |
| Scale Z | The objects scale along the local z-axis. |
Control the inheritance of the transforms from the parent.
| Parameter | Details |
|---|---|
| Position | Toggle inheritance of the Position from the parent. |
| Rotation | Toggle inheritance of the Rotation from the parent. |
| Scale | Toggle inheritance of the 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. |
| Parameter | Details |
|---|---|
| Cell Size | Size of an individual cell within the fluid sim. Larger cells increase performance, but can lower accuracy of fluids which are meant to be more detailed. |
| Grid Size | The maximum size for the fluid to simulate within. Greater size can impact performance, depending on how far the the particles spread througout the grid. |
| Gravity | Constant downward force on the particles. |
| Dampening | Reduces the particle velocities over time. Useful for improving stability, and acting as a resistive force to particle motion in the scene. |
| Viscosity | Smooths the velocities of all particles in the sim, making them tend to move together in the same direction. It can make the particles appear more viscous, but it’s aimed at softening the shapes in a fluid sim. High viscosity fluids, such as toothpaste or silly putty, aren’t supported. |
| Surface Tension | Pulls particles together to form a surface that bounds the liquid. Higher values will create larger droplets. |
| Rest Density | Controls the density and how close the particles will be packed together. Push particles closer together, so more particles may be required to maintain the same volume. |
| Solid Boundary | Optionally treat the bounds of the sim as solid walls, to prevent particles from leaving the simulation space. |
| Name | Description | Typical Input |
|---|---|---|
| Affected Emitters | Control which Emitters are affected by the Affector. By default, all emitters in the field system are affected. | Primitive Emitter |
| Procedural Falloff | Use the distance field from a procedural system to vary how strong the affector is. | Procedural Root |
| Weightmap | TBC | TBC |
| 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 |