Controls the separation between nearby whitewater particles. Reducing this parameter increases the number of particles in the simulation (with cubic scaling).

Voxel size for the density volume. The volume is used for emission limiting, foam erosion, as well as repellant seeding when Density Threshold is enabled. Voxel Size should be at least twice as large as Whitewater Scale.

Location of foam with respect to the liquid surface. Note that all depth ranges respect this parameter; that is Foam Location can be changed to raise or lower the foam layer without having to modify other parameters.

This parameter controls the interval around the foam layer in which the forces and aging rates are interpolated. Horizontal axes of Buoyancy by Depth, Advection by Depth, Multiplier by Depth, and Repulsion by Depth span a distance of twice this Depth Range around 0.

Specify existing attributes to not delete. Any attributes that match this, and are not deleted by the delete string, will be kept. All others will be deleted.

When enabled, whitewater particles will acquire bubble, foam, and spray point attributes. Values for these attributes lie in the 0-1 range, signalling how “strongly” each particle is of the respective state.

When turned on, per particle relativedensity will be computed by the solver. This attribute represents the number of particles in each particle’s neighborhood. Values for this attribute lie in the (0,1) range, where 1 represents a very dense neighborhood of particles.

How many substeps the DOP simulation should perform every frame.

Enables the simulation cache. For very large simulations, turning off this option is the best way to guarantee the smallest possible memory footprint for the simulation.

The amount of RAM reserved for caching a simulation to memory.

Seed that controls all of the random aspects of particle emission and death.

Aging rate for bubbles. Can be used to extend or reduce the lifetime of bubble particles.

Aging rate for foam. Can be used to extend or reduce the lifetime of foam particles.

Aging rate for spray. Can be used to extend or reduce the lifetime of spray particles.

Turning on this option adds velocity noise to newly birthed particles. See help for Turbulent Noise for more information on noise control.

Specifies the noise type.

The scale of the noise. Decreasing frequency increases feature size.

Allows the noise field to be effectively moved through space.

The amplitude of the noise.

The amplitude reduction of higher frequency noise contributions.

Raises the noise to the given exponent.

The number of noise generations to use.

The direction and magnitude of the ambient wind field.

A scale for the wind velocity, allowing you to easily adjust the magnitude without affecting the direction.

How much particles are to be influenced by this wind field.

Maximum value of the noise field.

Size of the noise pattern.

Range of particles' speed (relative to the wind) that gets mapped to a (0, 1) range to drive how much each particle is influenced by the wind.

By default, the speed is mapped linearly to a (0, 1) range. This behavior can be changed by specifying a custom mapping curve. The default configuration will make fast-moving particles (relative to the wind) more influenced by the wind.

Range of relative density that gets mapped to a (0, 1) range to drive how much each particle is influenced by the wind.

By default, the relative density is transformed using a negative linear mapping from a (0, 1) range. This behavior can be changed by specifying a custom mapping curve. The default configuration should make the loosely packed particles (like spray and mist) easily drift in the wind, whereas densely packed particles will be mostly ignored by the wind.

Use the collision surface field to shadow/occlude the wind.

Use the water surface to shadow/occlude the wind.

The maximum distance to check for occlusions.

Enables density control for whitewater particles.

Particles in this range will be subjected to density control.

Stiffness of the density constraints, controlling how harshly deviations from target density are penalized.

Enable variable enforcement of the density constraints at different liquid depths.

Controls the stiffness of density constraints at different liquid depths. Note that if an endpoint of this ramp evaluates to a non-zero value, then all particles beyond that end will also be subjected to density control.

Desired number of points in each particle’s neighborhood.

Range of allowed kernel radii as multiples of a global radius.

The number of points in a whitewater particle’s neighborhood is not allowed to exceed this value.

This fraction of all particles that are eligible for density control will actually be used. Reducing Inclusion Chance will decrease running times, but may degrade quality.

Number of times to repeat constraint projection for each particle.

The maximum acceleration that can be applied to a particle by constraints.

Particles apply repulsive forces on their neighbors to prevent clustering. This parameter determines the distance (as a fraction of the particle’s kernel radius) at which this force is equal to Tensile Strength.

Magnitude of the repulsive forces between nearby particles.

Enabling viscosity causes velocity diffusion, resulting in more coherent motion among nearby whitewater particles.

Enabling this feature preserves foam in denser areas and erodes it in sparser regions.

Particles within this distance of the liquid surface will be subjected to erosion.

Strength of erosion in less dense foam areas. Higher values for this parameter will result in more rapid disappearance of foam.

Controls the density range at which whitewater is protected from erosion.

Create and maintain repellant particles that push whitewater away and give rise to a cellular foam structure. These particles are contained in the object’s Repellants geometry.

Amount of frames between each reseeding of the repellants.

Range of repellant sizes (stored in the radius point attribute).

Range of repellant strengths (stored in the magnitude point attribute).

Range of values for the repellants' noise point attribute. This attribute controls the shape of each repellant, with 0 being perfectly circular and 1 being maximally “noisy”.

Range of values for the repellants' pulse point attribute. This attribute controls how fast the shape of a “noisy” repellant evolves.

When enabled, repellants will age and die once their life is up. The lifespan for a repellant is randomly selected from the provided range.

Enabling this option limits seeding of repellants to areas that already contain whitewater. A region is considered eligible for seeding if relative whitewater density is above the specified threshold.

Seed that controls random repellant seeding.

When this option is enabled, distribution of repellant sizes matches the given Radius Distribution; otherwise, size distribution is uniform.

Defines the distribution of repellant radii.

When enabled, repellant strengths are attenuated based on liquid’s speed. With default settings, for example, repellants will be active only in slow regions.

Horizontal axis of Repulsion by Speed corresponds to this range.

A multiplier applied to the repellant strengths based on the underlying liquid’s speed.

When enabled, repellant strengths are attenuated based on liquid’s acceleration. With default settings, for example, repellants will be inactive in regions that are rapidly accelerating.

Horizontal axis of Repulsion by Acceleration corresponds to this range.

A multiplier applied to the repellant strengths based on the underlying liquid’s acceleration.

A multiplier applied to the repulsion force based on whitewater particle’s depth.

Enable a depth control mechanism to keep foam attached to the fluid surface.

When this option is enabled, adhesion is only applied to particles on the liquid’s upper surface, as determined by the direction of gravity. Turning this feature on reduces foam sticking to the bottom or sides of the domain.

Particles within this distance of the liquid surface will be subjected to depth control.

Depth control is disabled for particles if the angle between their velocity vector and surface normal is no larger than this value.

Controls how strictly depth control will be enforced at different depths. Lower stiffness values give rise to thicker foam.

Range of particle’s depth that gets mapped to a (0, 1) range.

Use this parameter to visualize the fluid’s velocity differences. All particles with velocities equal to or greater than the adjusted value will be displayed with the same color.

Color ramp using the remapped particle’s depth to color the particles.

Color ramp using the remapped particle’s speed to color the particles.

The color used to visualize bubble particles.

The color used to visualize foam particles.

The color used to visualize spray particles.

Color ramp using the remapped particle’s relative density to color the particles.

The file sequence to save the checkpoints to. These are .sim files, loadable with the File DOP or File SOP. The variable $SF must be used to specify the frame number - $F cannot be used because this is working in simulation space. $SF4 is also supported.

How much of a history to keep before the checkpoint files are deleted. A value of 0 will never delete cache files. Otherwise, frames older than this value will be erased from disk.

Note that only checkpoint files created by this session of Houdini will be deleted. If you restart Houdini with an existent cache files, they will not be deleted. This is done because you were likely restarting from a crashed location and will want to guarantee you can once again restart there if it crashes again.

The frame interval between checkpoints. Setting this to a value of 1 will save a checkpoint every frame. Setting this to higher values will save a checkpoint after every number of frames specified. For example setting this to 5 will save a checkpoint every 5 frames.

This can be done to save disk space if you are running a large simulation.