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| Since | 21.0 |
Note
Although COP Pyro is in COPs, you need DOP level permissions to use it. This means that COP Pyro is not available in Houdini Core, but only in Houdini FX, Houdini Apprentice, Houdini Indie, and Houdini Education.
This node marks the end of a Pyro simulation block.
It should be paired with a 
Pyro Block Begin COP.
Note
Compiled COP networks don’t support simulation.
Parameters ¶
Reset Simulation
Clears the entire simulation cache.
Simulation ¶
Start Frame
The frame on the Houdini playbar where the simulation starts.
Live Simulation
When Simulate is on, this turns on live simulation to provide an interactive, non-deterministic simulation mode. It simulates independent of the playbar and isn’t associated with any keyframes or caching.
This parameter (and its associated parameters) is intended as a sandbox mode where you don’t have to rely on the playbar.
Tip
Live Simulation doesn’t save the results like other simulation types in Houdini, so use a 
Stash COP to save results.
Toggle Live Simulation
When Live Simulation is on, this lets you pause and resume the live simulation.
Tip
You can also use the 
Live Simulation button to pause and resume live simulation. See Cooking controls for more information.
Live Tick
When Live Simulation is on, this is the current tick (frame) within the live simulation.
Setup ¶
General ¶
Sparse Simulation
When turned on, calculations are performed only in the areas of interest, where fluid exists. When turned off, you must provide a domain geometry (bounds_geo input) in which the calculations take place.
Voxel Size
The size of a voxel in world coordinates.
Advection Reflection ¶
Advection Reflection
Advection-Reflection attempts to inject energy lost due to pressure projection back into the simulation. Turning on this option may exhibit better vortex retention in the flow.
It performs a single pressure projection per timestep and adds the removed velocity components back at the next step. This requires an extra vector field to be carried between timesteps.
Reflection Amount
Fraction of the projected velocities to re-inject. Values near 1 will do a better job of conserving energy, but may result in instabilities.
Cache ¶
Cache
When Simulate is on, this enables the caching of the simulation. If the simulation is uncached, it will always have to cook from the start frame on any new frame.
Cached Frames
When Simulate is on, this is how many frames behind the current frame to keep cached.
Checkpoint Rate
When Simulate is on, this is the rate at which the node continually caches a single frame.
For example, set this to 24 to cache frames 24, 48, 72,
and such. This allows random-scrubbing to be faster as it only
has to re-cook from the checkpoint frame.
Set to 0 to disable checkpointing.
Bounds ¶
Clip Bounds ¶
Clip by Bounds
When Sparse Simulation is turned on, use this to limit how far the fluid can extend.
Clip by
When Sparse Simulation is turned on, use this to limit how far the fluid can extend. If a bounds_geo input is provided, these settings are ignored.
Bounding Box
Use Center and Size parameters to control the extent of the simulation domain.
Separate Sides
Clip the domain between 6 clipping planes.
Group ¶
Size
Controls the size of the domain box.
Center
Controls the center position of the domain box.
Reference Fields ¶
Reference Fields
The fields that contribute to the voxel activation.
Reference Cutoff
Any leaf whose maximum combined value from the reference fields is below the cutoff will be eligible to be deactivated.
Activate Fields ¶
Activate Fields
The fields that are activated in each frame based on the reference fields and additional padding.
Activate Feedbacks
Additional fields inside the feedback cable to be activated.
Padding ¶
Collision ¶
Collision ¶
Enable Collision
Turns on collision detection for the solver.
Velocity Scale
Scales the strength of the velocity calculated from the motion.
Correct Collisions
Zero out the density and temperature that are inside the collision SDF, avoiding any leaking of smoke.
Sourcing ¶
Density ¶
Source Density
When turned on, the density input of the block is sourced into the density field.
Activation
Turns the effect of this sourcing on and off. This node is only active when this value is 1.
Source Mode
Controls when the source volume is mixed with the target volume.
Continuous
Sourcing remains active throughout the simulation and is applied on every solver step. Use this when you need a constant supply of density, temperature or other quantities.
First Frame Only
Sourcing is applied only on the first simulation frame. This is useful when the fluid is already present when the simulation begins. If the source is animated, those animations are ignored after the first frame.
Copy on First Frame
Sourcing remains active throughout the simulation, as in Continuous mode. On the first simulation frame, the source volume is copied into the target volume. On subsequent frames, the operation is determined by Operation.
Operation
Controls how the source volume is mixed with the target volume.
Add
The result is the sum of the source and target values.
Copy
The result is copied from the source volume.
Maximum
The result is the greater of the source and target values.
Average
The result is the average of the source and target values.
Blend
The result is a blend between the source and target values, using Blend as the weight.
Pull
Pushes source values toward the corresponding target values according to the Acceleration Strength and Deceleration Strength settings.
Scale
Scales the source values before they are mixed with the target volume.
Scale by Timestep
Scales the effect of sourcing by the timestep. This ensures that the amount of sourcing remains consistent when substepping occurs. Turn off this parameter if you need the instantaneous source value.
Blend
Controls the weight used to blend between the source values and the corresponding volume values.
Acceleration
Controls how strongly source values that are smaller than the corresponding target values are pushed toward the target field.
Deceleration
Controls how strongly source values that are larger than the corresponding target volume values are pushed toward the target field.
Temperature ¶
Source Temperature
WWhen turned on, the temperature input of the block is sourced into the temperature field.
Activation
Turns the effect of this sourcing on and off. This is only active when this value is 1.
Source Mode
Controls when the source volume is mixed with the target volume.
Continuous
Sourcing remains active throughout the simulation and is applied on every solver step. Use this when you need a constant supply of density, temperature or other quantities.
First Frame Only
Sourcing is applied only on the first simulation frame. This is useful when the fluid is already present when the simulation begins. If the source is animated, those animations are ignored after the first frame.
Copy on First Frame
Sourcing remains active throughout the simulation, as in Continuous mode. On the first simulation frame, the source volume is copied into the target volume. On subsequent frames, the operation is determined by Operation.
Operation
Controls how the source volume is mixed with the target volume.
Add
The result is the sum of the source and target values.
Copy
The result is copied from the source volume.
Maximum
The result is the greater of the source and target values.
Average
The result is the average of the source and target values.
Blend
The result is a blend between the source and target values, using Blend as the weight.
Pull
Pushes source values toward the corresponding target values according to the Acceleration Strength and Deceleration Strength settings.
Scale
Scales the source values before they are mixed with the target volume.
Scale by Timestep
Scales the effect of sourcing by the timestep. This ensures that the amount of sourcing remains consistent when substepping occurs. Turn off this parameter if you need the instantaneous source value.
Blend
Controls the weight used to blend between the source values and the corresponding volume values.
Acceleration
Controls how strongly source values that are smaller than the corresponding target values are pushed toward the target field.
Deceleration
Controls how strongly source values that are larger than the corresponding target volume values are pushed toward the target field.
Velocity ¶
Source Velocity
Activation
Turns the effect of this sourcing on and off. This is only active when this value is 1.
Source Mode
Controls when the source volume is mixed with the target volume.
Continuous
Sourcing remains active throughout the simulation and is applied on every solver step. Use this when you need a constant supply of density, temperature or other quantities.
First Frame Only
Sourcing is applied only on the first simulation frame. This is useful when the fluid is already present when the simulation begins. If the source is animated, those animations are ignored after the first frame.
Copy on First Frame
Sourcing remains active throughout the simulation, as in Continuous mode. On the first simulation frame, the source volume is copied into the target volume. On subsequent frames, the operation is determined by Operation.
Operation
Controls how the source volume is mixed with the target volume.
Add
The result is the sum of the source and target values.
Copy
The result is copied from the source volume.
Maximum
The result is the greater of the source and target values.
Average
The result is the average of the source and target values.
Blend
The result is a blend between the source and target values, using Blend as the weight.
Pull
Pushes source values toward the corresponding target values according to the Acceleration Strength and Deceleration Strength settings.
Scale
Scales the source values before they are mixed with the target volume.
Scale by Timestep
Scales the effect of sourcing by the timestep. This ensures that the amount of sourcing remains consistent when substepping occurs. Turn off this parameter if you need the instantaneous source value.
Blend
Controls the weight used to blend between the source values and the corresponding volume values.
Acceleration
Controls how strongly source values that are smaller than the corresponding target values are pushed toward the target field.
Deceleration
Controls how strongly source values that are larger than the corresponding target volume values are pushed toward the target field.
Flame ¶
Source Flame
When turned on, the flame input of the block is sourced into the flame field.
Activation
Turns the effect of this sourcing on and off. This is only active when this value is 1.
Source Mode
Controls when the source volume is mixed with the target volume.
Continuous
Sourcing remains active throughout the simulation and is applied on every solver step. Use this when you need a constant supply of density, temperature or other quantities.
First Frame Only
Sourcing is applied only on the first simulation frame. This is useful when the fluid is already present when the simulation begins. If the source is animated, those animations are ignored after the first frame.
Copy on First Frame
Sourcing remains active throughout the simulation, as in Continuous mode. On the first simulation frame, the source volume is copied into the target volume. On subsequent frames, the operation is determined by Operation.
Operation
Controls how the source volume is mixed with the target volume.
Add
The result is the sum of the source and target values.
Copy
The result is copied from the source volume.
Maximum
The result is the greater of the source and target values.
Average
The result is the average of the source and target values.
Blend
The result is a blend between the source and target values, using Blend as the weight.
Pull
Pushes source values toward the corresponding target values according to the Acceleration Strength and Deceleration Strength settings.
Scale
Scales the source values before they are mixed with the target volume.
Scale by Timestep
Scales the effect of sourcing by the timestep. This ensures that the amount of sourcing remains consistent when substepping occurs. Turn off this parameter if you need the instantaneous source value.
Blend
Controls the weight used to blend between the source values and the corresponding volume values.
Acceleration
Controls how strongly source values that are smaller than the corresponding target values are pushed toward the target field.
Deceleration
Controls how strongly source values that are larger than the corresponding target volume values are pushed toward the target field.
Divergence ¶
Source Divergence
When turned on, the divergence input of the block is sourced into the divergence field.
Activation
Turns the effect of this sourcing on and off. This is only active when this value is 1.
Source Mode
Controls when the source volume is mixed with the target volume.
Continuous
Sourcing remains active throughout the simulation and is applied on every solver step. Use this when you need a constant supply of density, temperature or other quantities.
First Frame Only
Sourcing is applied only on the first simulation frame. This is useful when the fluid is already present when the simulation begins. If the source is animated, those animations are ignored after the first frame.
Copy on First Frame
Sourcing remains active throughout the simulation, as in Continuous mode. On the first simulation frame, the source volume is copied into the target volume. On subsequent frames, the operation is determined by Operation.
Operation
Controls how the source volume is mixed with the target volume.
Add
The result is the sum of the source and target values.
Copy
The result is copied from the source volume.
Maximum
The result is the greater of the source and target values.
Average
The result is the average of the source and target values.
Blend
The result is a blend between the source and target values, using Blend as the weight.
Pull
Pushes source values toward the corresponding target values according to the Acceleration Strength and Deceleration Strength settings.
Scale
Scales the source values before they are mixed with the target volume.
Scale by Timestep
Scales the effect of sourcing by the timestep. This ensures that the amount of sourcing remains consistent when substepping occurs. Turn off this parameter if you need the instantaneous source value.
Blend
Controls the weight used to blend between the source values and the corresponding volume values.
Acceleration
Controls how strongly source values that are smaller than the corresponding target values are pushed toward the target field.
Deceleration
Controls how strongly source values that are larger than the corresponding target volume values are pushed toward the target field.
Fields ¶
Density ¶
Dissipation ¶
Density Dissipation
Reduces the density field over time.
Dissipation
How fast the density field reduces to zero over time. This controls the percentage of the current amount to be lost per fixed interval (per second).
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect dissipation.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Axis Mask ¶
Use Axis Control
Mask out the effect along an axis direction. Rather than requiring the construction of VDBs to represent this, this allows direct specification of the world space range over which the effect is to be scaled.
Direction
The reference vector along which the effect will be masked.
Axis Range
The position along the axis mask is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
Remap Axis
Turns on the Axis Control Ramp, to change how the position along the axis should scale the effect between the minimum and maximum values of Axis Range.
Axis Ramp
This ramp controls how the position is mapped between the minimum and maximum values of Axis Range.
Diffusion ¶
Density Diffusion
Blurs the density over time, so that it fades and smooths, removing high frequency details.
Diffusion
The size of the blur effect’s radius. Larger values will make the field smooth out faster.
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect diffusion.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Temperature ¶
Cooling ¶
Temperature Cooling
Cools the temperature field over time. Areas with cooler temperature rise slower, so the faster the temperature field cools, the faster the smoke or flame stops rising with buoyancy force.
Cooling
How fast the temperature field cools to zero. This controls the percentage of the current amount to be lost per fixed interval (per second).
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect cooling.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Axis Mask ¶
Use Axis Control
Mask out the effect along an axis direction. Rather than requiring the construction of VDBs to represent this, this allows direct specification of the world space range over which the effect is to be scaled.
Direction
The reference vector along which the effect will be masked.
Axis Range
The position along the axis mask is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
Remap Axis
Turns on the Axis Control Ramp, to change how the position along the axis should scale the effect between the minimum and maximum values of Axis Range.
Axis Ramp
This ramp controls how the position is mapped between the minimum and maximum values of Axis Range.
Diffusion ¶
Temperature Diffusion
Blurs the temperature over time, so that it fades and smooths, removing high-frequency details.
Diffusion
The size of the blur effect’s radius. Larger values will make the field smooth out faster.
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect diffusion.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Flame ¶
Cooling ¶
Flame Cooling
Cools the flame field over time.
Cooling
How fast the flame field cools to zero. This controls the percentage of the current amount to be lost per fixed interval (per second).
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect cooling.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Emit Density ¶
Emit Density
When turned on, density is added to the simulation using the flame field.
Operation
Controls how the emitted density is mixed with the incoming density field.
Add
The result is the sum of the values in the emitted density and the incoming density field.
Maximum
The result is the larger of the values in the emitted density and the incoming density field.
Average
The result is the average of the values in the emitted density and the incoming density field.
Blend
The result is a blend of the values in the emitted density and the incoming density field, using the Blend parameter as weight.
Pull
Values in the emitted density are pushed toward the corresponding incoming density field values, according to the Acceleration and Deceleration settings.
Emission Scale
Scales the amount of density output from the flame, which is calculated by first remapping the flame field from Flame Range to 0-1 or optionally to the range given by Emission Range.
When Cool Flame is turned on, this is further scaled by the flame cooling ratio before multiplying the density output by this number.
Flame Range
Controls the flame region to emit density from. The flame field is first fitted from this range to 0-1 or optionally to the range given by Emission Range.
Emission Range
When turned on, this maps the flame field from the minimum and maximum values of Flame Range to this range.
Acceleration
Deceleration
Where the emitted density values are larger than the incoming density field values, controls how strongly those values are pushed toward the incoming density field.
Blend
Controls the weight by which to blend between the incoming density field and the emitted density values.
Remap Flame
When turned on, use the Flame Ramp to change how the flame values scale between the minimum and maximum values of Flame Range.
Flame Ramp
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect emission.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Emit Temperature ¶
Emit Temperature
When turned on, temperature is added to the simulation using the flame field.
Operation
Controls how the emitted temperature is mixed with the incoming temperature field.
Add
The result is the sum of the values in the emitted temperature and the incoming temperature field.
Maximum
The result is the larger of the values in the emitted temperature and the incoming temperature field.
Average
The result is the average of the values in the emitted temperature and the incoming temperature field.
Blend
The result is a blend of the values in the emitted temperature and the incoming temperature field, using the Blend parameter as weight.
Pull
Values in the emitted temperature are pushed toward the corresponding incoming temperature field values, according to the Acceleration and Deceleration settings.
Emission Scale
Scales the amount of temperature output from the flame, which is calculated by first remapping the flame field from Flame Range to 0-1 or optionally to the range given by Emission Range.
When Cool Flame is turned on, this is further scaled by the flame cooling ratio before multiplying the temperature output by this number.
Flame Range
Controls the flame region to emit temperature from. The flame field is first fitted from this range to 0-1 or optionally to the range given by Emission Range.
Turn on Use Ramp to change how the flame values scale between the minimum and maximum of this range.
Emission Range
When turned on, this maps the flame field from the minimum and maximum values of Flame Range to this range.
Acceleration
Where the emitted temperature values are smaller than the incoming temperature field values, controls how strongly those values are pushed toward the incoming temperature field.
Deceleration
Where the emitted temperature values are larger than the incoming temperature field values, controls how strongly those values are pushed toward the incoming temperature field.
Blend
Controls the weight by which to blend between the incoming temperature field and the emitted temperature values.
Remap Flame
When turned on, use the Flame Ramp to change how the flame values scale between the minimum and maximum values of Flame Range.
Flame Ramp
Controls how the flame values scale the temperature output between the minimum and maximum values of Flame Range.
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect emission.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Expansion ¶
Expansion
When turned on, divergence is added to the simulation using the flame field, allowing the fluid to expand or contract.
Operation
Controls how the emitted divergence is mixed with the incoming divergence field.
Add
The result is the sum of the values in the emitted divergence and the incoming divergence field.
Maximum
The result is the larger of the values in the emitted divergence and the incoming divergence field.
Average
The result is the average of the values in the emitted divergence and the incoming divergence field.
Blend
he result is a blend of the values in the emitted divergence and the incoming divergence field, using the Blend parameter as weight.
Pull
Values in the emitted divergence are pushed toward the corresponding incoming divergence field values, according to the Acceleration and Deceleration settings.
Expansion Scale
Scales the amount of divergence output from the flame, which is calculated by first remapping the flame field from Flame Range to 0-1 or optionally to the range given by Emission Range.
When Cool Flame is turned on, this is further scaled by the flame cooling ratio before multiplying the divergence output by this number.
Flame Range
Controls the flame region to emit divergence from. The flame field is first fitted from this range to 0-1 or optionally to the range given by Emission Range.
Turn on Use Ramp to change how the flame values scale between the minimum and maximum of this range.
Emission Range
When turned on, this maps the flame field from the minimum and maximum values of Flame Range to this range.
Acceleration
Where the emitted divergence values are smaller than the incoming divergence field values, controls how strongly those values are pushed toward the incoming divergence field.
Deceleration
Where the emitted divergence values are larger than the incoming divergence field values, controls how strongly those values are pushed toward the incoming divergence field.
Blend
Controls the weight by which to blend between the incoming divergence field and the emitted divergence values.
Remap Flame
When turned on, use the Flame Ramp to change how the flame values scale between the minimum and maximum values of Flame Range.
Flame Ramp
Controls how the flame values scale the divergence output between the minimum and maximum values of Flame Range.
=== Control Mask ====
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect divergence.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Use Ramp
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Forces ¶
Buoyancy ¶
Enable Buoyancy
Turns the effect of this node on and off. This node is only active when this value is 1.
Buoyancy Scale
A global scale on the amount of buoyancy to apply. Hot gas expands, causing it to rise due to lowered density. Acceleration due to buoyancy is calculated using the values of the ambient and reference temperatures, as well as the Gravity Acceleration scale.
Ambient Temp (K)
Temperature corresponding to value of 0 in the temperature field (in Kelvin). This represents the ambient temperature of the environment.
Reference Temp (K)
Temperature corresponding to a value of 1 in the temperature field (in Kelvin). The temperature range is used to calculate the strength of the buoyancy force.
Note
In general, a value of T in the temperature field corresponds to a temperature of Ambient Temp (K) + T * (Reference Temp (K) - Ambient Temp (K)).
Equilibrium Temp
Hot gas rises in the buoyancy direction where temperature values are above this ambient temperature, and falls where they are below it. Since newly activated areas have zero temperature, this usually needs to be zero to leave dead-space unaffected. This is useful for simulating cloud formation where gases can rise and fall.
Gravity Acceleration
Acceleration due to gravity. Stronger gravity results in a stronger buoyancy force.
Direction
The direction in which temperatures hotter than the ambient temperature will be forced.
Threshold Mask ¶
Threshold Volume
Mask out the effect using the threshold field. Threshold fields are intended to provide harsh on/off effects, but the range can be used to soften the transition.
Control Field
The name of the field to use to affect the force.
Threshold Range
The value of the threshold field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0.01 to 0 range is designed to concentrate the effect on the edges and empty regions of the threshold field, but not inside it.
When the threshold field is a Vector VDB, this value represents the length of the given vector field.
Remap Threshold
Turns on the Threshold Ramp, to change how the threshold field should scale the effect between the minimum and maximum values of Threshold Range.
Threshold Ramp
This ramp controls how the threshold field values are mapped between the minimum and maximum values of Threshold Range.
Control Mask ¶
Control Volume
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Disturbance ¶
Enable Disturbance
Introduces random forces to the simulation to add higher frequency details without changing the general motion or the overall shape. This operator is useful for breaking up undesirable smooth features in the smoke.
Mode
Controls the nature of the generated random vectors.
Continuous
Every voxel gets an independently-assigned random vector.
Block-Based
The random pattern is formed by composing several layers of blockwise-constant noise.
Disturbance
Controls strength of the applied force.
Note
When Rotate is used, Strength governs how fast the vectors are rotated towards their goal.
Reference Scale
Variance of the aggregated noise field over a region of this size will be equal to Strength when Mode is set to Continuous. Provides a scale for normalizing the force against voxel size. A larger value for this parameter will increase magnitude of the applied force.
Tip
You should set this parameter to a reasonable value for your scene scale and leave it there. Strength can be used to more finely control how much force is applied.
Block Size
Controls size of the biggest blocks in the generated noise pattern when Mode is set to Block-Based.
Pulse Length
Length of time (in seconds) that the noise pattern is held fixed. This only applies when Mode is set to Block-Based.
Note
The noise pattern changes on every frame in Continuous mode.
Max Octaves
The maximum number of noise levels to compose in Block-Based mode.
Lacunarity
The ratio of block sizes between successive noise layers. For example, a value of 2 means that the first layer has blocks that are twice the size of the second layer; the second layer will in turn have blocks that are twice as large as the next layer. This parameter is only applicable in Block-Based mode.
Roughness
The ratio of amplitudes between successive noise layers. For example a value of 0.5 means that the second layer will have half the amplitude of the first one. This parameter is only applicable in Block-Based mode.
Tip
Lower Roughness values will better preserve the block structure in the generated noise, whereas higher ones (nearing or exceeding 1) will yield more chaotic patterns resembling white noise.
Rotational Force
Changes how the disturbance force is combined with the velocity field. When this is on, the values in the incoming velocity are rotated towards the randomly-generated directions without changing their length.
Threshold Mask ¶
Threshold Volume
Mask out the effect using the threshold field. Threshold fields are intended to provide harsh on/off effects, but the range can be used to soften the transition.
Threshold Field
The name of the field to use to affect the force.
Threshold Range
The value of the threshold field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0.01 to 0 range is designed to concentrate the effect on the edges and empty regions of the threshold field, but not inside it.
When the threshold field is a Vector VDB, this value represents the length of the given vector field.
Remap Threshold
Turns on the Threshold Ramp, to change how the threshold field should scale the effect between the minimum and maximum values of Threshold Range.
Threshold Ramp
This ramp controls how the threshold field values are mapped between the minimum and maximum values of Threshold Range.
Control Mask ¶
Control Volume
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Turbulence ¶
Enable Turbulence
Adds “churning” noise to the velocity field. You should generally use this operator to add powerful large-scale noise, and rely on disturbance and shredding for smaller features.
Amplitude
Controls the overall strength of the force.
Amplitude Scale
Applies an anisotropic scale to the force.
Element Size
Controls the size of the noise elements at the base level of the noise.
Element Scale
Applies an anisotropic scale to the base-level noise element size.
Pulse Duration
The time, in seconds, required for the base level of the noise to fully change.
Max Octaves
Controls the number of turbulence levels applied relative to the initial Element Size.
Lacunarity
Controls the scale factor between successive turbulence octaves.
Roughness
Controls how much each octave contributes relative to the previous one. Values below 1 ensure that smaller features do not overwhelm larger features.
Seed
Defines the initial noise offset.
Threshold Mask ¶
Threshold Volume
Mask out the effect using the threshold field. Threshold fields are intended to provide harsh on/off effects, but the range can be used to soften the transition.
Threshold Field
The name of the field to use to affect the force.
Threshold Range
The value of the threshold field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0.01 to 0 range is designed to concentrate the effect on the edges and empty regions of the threshold field, but not inside it.
When the threshold field is a Vector VDB, this value represents the length of the given vector field.
Remap Threshold
Turns on the Threshold Ramp, to change how the threshold field should scale the effect between the minimum and maximum values of Threshold Range.
Threshold Ramp
This ramp controls how the threshold field values are mapped between the minimum and maximum values of Threshold Range.
Control Mask ¶
Control Volume
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Viscosity ¶
Enable Viscosity
Blurs the velocity over time, so that it smooths, removing high-frequency details.
Viscosity
A blur factor on the velocity field. A value of 0 allows adjacent voxels to move in different directions without resistance, creating a more chaotic, turbulent look. Higher values of this parameter result in a more coherent velocity field, creating a more flowing look.
Control Mask ¶
Use Control Field
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Vortex Confinement ¶
Enable Vortex Confinement
When turned on, amplifies existing vortices with the intent of undoing the diffusion that occurs during the diffusion stages of the fluid solver.
Type
Controls the method used to recover detail lost through diffusion. The first-order method uses first derivatives to approximate the local vorticity gradient. This method is fast and stable, but tends to introduce more numerical diffusion, resulting in greater loss of fine-scale detail. The second-order method uses a higher-order approximation that better preserves energy and small-scale features. This method can produce more detailed results, but is slower and may introduce instabilities. These can be mitigated using the Positive Diffusion Scale and Negative Diffusion Scale parameters.
Scale
Controls the strength of the vortex confinement force.
Positive Diffusion Scale
Controls the amount of positive diffusion applied. Positive diffusion improves stability by smoothing high-frequency noise and sharp numerical spikes in the vorticity field.
Negative Diffusion Scale
Controls the amount of negative diffusion applied. Negative diffusion acts as an anti-diffusion process, concentrating energy toward the centers of vortex structures instead of spreading it outward.
Kernel Size
Controls the size of the neighborhood stencil used to compute curvature at each pixel. Larger values generally produce smoother curvature results. This parameter has a similar effect to Frequency Separation, as it removes high-frequency detail that can cause unnatural jittering.
Energy Target
Applies smooth clamping based on the energy of the band. The target energy determines the maximum energy level at which curl can be amplified. This can help reduce unstable or noisy behavior.
Target Energy
Applies smooth clamping based on the energy of the band. The target energy determines the maximum energy level at which curl can be amplified. This can help reduce unstable or noisy behavior.
Adaptive Confinement
Restricts vortex confinement to areas where vorticles are more likely to develop. This can help reduce the unnatural jittering that vortex confinement can introduce throughout the simulation.
Frequency Separation ¶
Frequency Separation
Enables frequency separation, allowing you to control which swirl sizes are affected by this node.
Min Swirl Size
Defines the smallest swirl size to include. Swirls with a width equal to this value define the starting frequency of the band. When turned off, all swirl sizes up to Max Swirl Size are included. Increase this value together with Max Swirl Size, or set it close to Max Swirl Size, to affect only larger swirls.
Min Swirl Size
Defines the smallest swirl size to include. Swirls with a width equal to this value define the starting frequency of the band. When turned off, all swirl sizes up to Max Swirl Size are included. Increase this value together with Max Swirl Size, or set it close to Max Swirl Size, to affect only larger swirls.
Max Swirl Size
Defines the largest swirl size to include. Swirls with a width equal to this value define the ending frequency of the band. Increase this value together with Min Swirl Size to affect only larger swirls.
Threshold Mask ¶
Threshold Volume
Mask out the effect using the threshold field. Threshold fields are intended to provide harsh on/off effects, but the range can be used to soften the transition.
Threshold Field
The name of the field to use to affect the force.
Threshold Range
The value of the threshold field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0.01 to 0 range is designed to concentrate the effect on the edges and empty regions of the threshold field, but not inside it.
When the threshold field is a Vector VDB, this value represents the length of the given vector field.
Remap Threshold
Turns on the Threshold Ramp, to change how the threshold field should scale the effect between the minimum and maximum values of Threshold Range.
Threshold Ramp
This ramp controls how the threshold field values are mapped between the minimum and maximum values of Threshold Range.
Control Mask ¶
Control Volume
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Ambient Velocity ¶
Enable Ambient Velocity
When turned on, adds a constant global velocity that moves the fluid.
Ambient Velocity
A constant global velocity that the VDBs are also moved by, in addition to the values in the velocity VDB. This can be used as a wind effect, since it allows the wind to alter speed without affecting local dynamics.
Velocity Scale ¶
Enable Velocity Scale
When turned on, this scales the values of a field by itself. This is useful for fast-rising smoke plumes, like volcano eruptions, where the initial ejection is very fast, but the smoke rapidly loses speed in the air.
Threshold Field
The name of the field that will be scaled by itself based on the selected threshold range.
Threshold Range
Maps the threshold field from this range to Scale at Min Threshold and Scale at Max Threshold.
If the threshold field is a Vector VDB, its length is used.
Scale at Min Threshold
The scale applied at the minimum value of Threshold Range.
Scale Below Threshold
When turned off, scaling has no effect where the threshold field is less than the minimum value of Threshold Range. This can help prevent motion from speeding up indefinitely or coming to a halt.
Scale at Max Threshold
The scale applied at the maximum value of Threshold Range.
Scale Above Threshold
When turned off, scaling has no effect where the threshold field is greater than the maximum value of Threshold Range. This can help prevent motion from speeding up indefinitely or coming to a halt.
Remap Scale Range
Enables the Scale Ramp, which maps Threshold Range to Scale at Min Threshold and Scale at Max Threshold.
Scale Range Ramp
Controls how values within Threshold Range are mapped between Scale at Min Threshold and Scale at Max Threshold.
Control Mask ¶
Control Volume
Mask out the effect using the control field. Control fields are usually used the same way as masks, and represent a smooth engagement of the effect.
Control Field
The name of the field to use to affect the force.
Control Range
The value of the control field is mapped from this range to 0-1 and applied as a multiplier on top of Scale.
The default 0 to 1 range is designed to concentrate the effect on regions with higher control field values.
When the control field is a Vector VDB, this value represents the length of the given vector field.
Remap Control
Turns on the Control Ramp, to change how the control field should scale the effect between the minimum and maximum values of Control Range.
Control Ramp
This ramp controls how the control field values are mapped between the minimum and maximum values of Control Range.
Advanced ¶
Advection ¶
Advect Fields ¶
Advect Fields
The fields that are advected in each frame.
Advect Feedbacks
Additional fields inside the feedback cable to be advected.
Tracing ¶
Trace Method
Controls the integration scheme used for a single trace step through the velocity field. This setting determines how closely the smoke follows turbulent flows and how well the simulation preserves detail over time.
Options in this menu are listed in order of increasing accuracy and computational cost.
Forward Euler
Predicts the next position based on its current velocity using a straight line. This is a 1st-order accurate method that has the fastest computation time, but it introduces more numerical diffusion, making the smoke look blurrier and can flatten turbulent flows.
Average of Two
Predicts the future position, looks at the velocity there, and averages it with the current velocity. It is a step up from Euler, which helps smoke maintain its volume and shape during simple rotations.
Explicit Midpoint
Samples the fluid velocity at a half-step forward to determine the full-step move. This is better at capturing vorticity (swirling). It prevents particles from spiraling outward away from the center of a vortex.
Runge-Kutta 3
A 3rd-order method that takes three samples of the velocity field to calculate the path. Use this when you need high-fidelity “wispy” smoke details without the full performance hit of RK4.
Runge-Kutta 4
A 4th-order method that samples the velocity field four times to find the most accurate “curve” through the fluid. This is essential for complex, turbulent simulations. It minimizes energy loss, ensuring that small eddies and swirls don’t disappear prematurely.
Path Tracing
A single trace step is often not enough to preserve sharp details, wispy tendrils, and small vortices through turbulent or fast-moving velocity flows. When this is turned on, multiple trace steps (given by Trace Method) are taken to better predict the curved path through the velocity field. The number of steps depends on the Maximum Steps and the CFL Condition.
CFL Condition
Controls how large a step should be used when tracing through the velocity field. This is approximately how many voxels will be stepped during a single trace step. Lower values mean better stability, but lower performance. Higher values force the tracing to take larger steps, allowing it to finish faster.
Maximum Steps
Global clamp on how many path tracing steps can be performed. For extremely fast motion this may need to be increased, but it might be better to raise the CFL condition instead.
Adaptive Step Size
When turned on, this dynamically changes the given step size through each tracing step, based on the number of maximum steps.
Scheme ¶
Scheme
The method used to advect the VDB.
BFECC
Perform backwards-forward error correction. This requires considerable time and memory, but does the best job of preserving the sharpness of features.
Euler + Sharpen
Combines the simplest form of advection with a dynamic sharpen field that combats the diffusion introduced by the trilinear operation.
Euler
The simplest and fastest form of advection, but tends to cause excessive blurring.
Sharpen
How much to sharpen the VDB. This is automatically adjusted per voxel based on how the VDB was sampled. While the sharpening kernel is clamped, a value that is too high will create grid artifacts.
Separate Velocity Advection Scheme
Turn this on to provide a different advection scheme for velocity self-advection.
Velocity Scheme
The method used to advect the VDB.
BFECC
Perform backwards-forward error correction. This requires considerable time and memory, but does the best job of preserving the sharpness of features.
Euler + Sharpen
Combines the simplest form of advection with a dynamic sharpen field that combats the diffusion introduced by the trilinear operation.
Euler
The simplest and fastest form of advection, but tends to cause excessive blurring.
Velocity Sharpen
How much to sharpen the VDB. This is automatically adjusted per voxel based on how the VDB was sampled. While the sharpening kernel is clamped, a value that is too high will create grid artifacts.
Pressure Projection ¶
Iterations
Controls how many times the projection process is repeated. Higher values increase computation time but produce more accurate results and improve the reliability of collision handling.
Hourglass Filter
Applies a smoothing operation to remove velocity modes that can be missed when projecting using corner-sampled divergence. This can reduce jagged artifacts.
Feather Blocks
Reduce the strength of the block correction over the farthest blocks. This helps avoid sharp transitions in the corrected velocity when strong impulses are present, but may require more iterations or computation time to fully remove divergence.
Point Pass
Combines the block dipoles into an even coarser set of points. These points are then applied to every voxel, allowing divergence to have a global effect in a single pass.
Output ¶
Velocity ¶
Correct by Time Scale
The output velocity VDB v will be scaled by timescale, ensuring it will motion blur correctly. However, if this is to be used by another simulation, you may want the raw velocity values.
Correct by Ambient Velocity
The output velocity VDB v will be adjusted by ambient velocity, ensuring it will motion blur correctly. However, if this is to be used by another simulation, you may want the raw velocity values.
Inputs ¶
density
A Float VDB of the current voxel densities, fed back to the input.
temperature
A Float VDB of the current voxel temperatures, fed back to the input.
v
A Vector VDB of the current voxel velocities. This is projected to non-divergent values and fed back to the input.
flame
A Float VDB of the current voxel flames, fed back to the input.
divergence
An optional Float VDB providing a goal divergence for the velocity, allowing the fluid to expand or contract, fed back to the input.
collision
An optional Float VDB providing a signed distance field (SDF) of a collider. Negative voxels will act like colliders.
collisionv
An optional Vector VDB providing a velocity of the collision objects. These are in world space, so will be internally adjusted by Ambient Velocity.
feedback
A Cable of the current feedback data. This is fed back to the input. The structure of this cable must match the initial structure provided on the block begin.
passthrough
A Cable of the current passthrough data. This is fed back to the input. The structure of this cable must match the initial structure provided on the block begin.
Outputs ¶
density
A Float VDB of the current voxel densities.
temperature
A Float VDB of the current voxel temperatures.
v
A Vector VDB of the current voxel velocities. This may have been optionally adjusted by timescale and ambient velocity.
flame
A Float VDB of the current voxel flames.
divergence
An optional Float VDB providing a goal divergence for the velocity, allowing the fluid to expand or contract.
collision
An optional Float VDB providing a signed distance field (SDF) of a collider. Negative voxels will act like colliders.
collisionv
An optional Vector VDB providing a velocity of the collision objects. These are in world space, so will be internally adjusted by Ambient Velocity.
feedback
A Cable of the current feedback data. This is fed back to the input.
passthrough
A Cable of the current passthrough data. This is fed back to the input.
| See also |
Pyro Configure
