Houdini 18.0 Nodes Dynamics nodes

Pyro Solver (Sparse) dynamics node

Performs a sparse pyro simulation on the given object. This solver can be used to create both fire and smoke.

On this page

See Pyro look development for information on using the parameters to achieve different flame and smoke looks.

This node is an extension of the Smoke Solver (Sparse). It considers an extra simulation field (flame, which captures the presence of flames) and adds some extra shaping parameters to allow for more control over the emergent look.

Setting Up

The essential building blocks of a smoke simulation are the object, solver, and sourcing. The Smoke Object (Sparse) node creates a dynamic object containing the required fields, which are then evolved by the solver as the simulation proceeds. The simplest smoke simulation needs the following data:

  • density scalar field that contains where and how much smoke is present;

  • temperature scalar field that’s used for buoyancy calculations;

  • vel vector field that captures the instantaneous motion of the smoke.

This solver takes care of ensuring these fields change in a manner consistent with smoke, but sourcing is responsible for injecting these quantities through the course of the simulation. For example, you may want to continuously add to density at the soot source or temperature to cause hot regions to rise. See pyro sourcing for more information.

Note

Tools under the Sparse Pyro FX shelf can be used to create setups involving the pyro solver.

Sparsity

By default, this solver operates in sparse mode; that is, the needed calculations are performed only in the areas of interest, as governed by the active field. This region is built by looking at the Reference Fields parameter under the Resizing subtab of the Advanced tab: positive areas of the specified fields are flagged as active. This intermediate active region is then dilated to provide a buffer for smoke to expand into. With the Reference Fields set to density, for example, the solver will run its operations near areas which have some soot, thereby concentrating the computational effort to the smoke’s visible region.

Inactive areas in sparse mode are treated as vacuum that smoke is free to move into. As such, if there are two puffs of smoke blowing at each other, they will be completely invisible to one another until they come sufficiently close for their disjoint active regions to merge.

When Enable Sparse Solving is disabled under the aforementioned tab, the solver will work in dense mode, performing a full global solve everywhere within the domain. With the previous example involving two puffs of smoke, they will be immediately aware of each other’s presence. However, dense mode can be substantially slower in some cases.

Tip

You can enable Active Region visualization under the Guides tab of the smoke object to see the active simulation areas.

Flame Field

The flame field stores the remaining lifetime of reactants (such as fuel) that are transported by the flow. This field is replenished through sourcing, and the solver takes care of reducing its values and generating the desired outputs (per settings under the Flames tab). Depending on how close reactants are to depletion, they can

  • emit soot (enable Emit Smoke to affect the density field),

  • increase temperature (enable Add Temperature to affect the temperature field),

  • cause expansion (turn on Add Expansion to affect the divergence field).

Additionally, flame can be used as the Emission Field for visualization (on the Smoke Object (Sparse)) or the Fire Intensity Field for rendering (on the Pyro Shader).

For example, you may want reactants that release a lot of temperature as they are "young", then start emitting soot as they are used up. Assuming flame is being sourced with a value of 1, you can accomplish this by setting the Flame Range under Temperature to 0.5-1, so that reactants generate a temperature output throughout the first half of their life. The Flame Range under Smoke can be set to 0.1-0.4 and remapped using a hill ramp. Then reactants will leave smoke behind during that part of their life; as long as the Flame Ramp evaluates to 0 at both of its endpoints, soot will be generated only within the specified Flame Range.

Inputs

Objects

A smoke object to work on.

Note

When working in sparse mode, Enable Sparse Solving must be enabled on the smoke object.

Advection

Nodes attached to this input will be able to use the smoke’s accurate velocity field. The Gas Advect node can be hooked up, for instance, to advect the points of an attached geometry data along with the smoke.

Note

It is not safe to modify the velocity through this input; use the Sourcing or Forces inputs instead.

Sourcing

This input should be used to modify the simulation fields, by sourcing with a Volume Source, for example. It is important to perform any sourcing that affects the active region in sparse mode through this input.

Note

The active field at this point is not up-to-date; thus, if you want to perform an operation that can be done sparsely, it is best to use the Forces input.

Forces

Microsolvers attached to this input will be run before the final pressure projection. At this point, the active field can be used as a stencil for DOPs that support it.

Note

Before the nodes attached to this input are executed, the active field is updated to account for any operations that were performed in the Sourcing input.

Parameters

Simulation

Time Scale

A scaling factor for time inside this solver. 1 is normal speed, greater than 1 speeds up the simulation, while less than 1 slows it down.

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.

Advection-Reflection

Advection-Reflection

Advection-Reflection attempts to inject energy lost due to pressure projection back into the simulation. Enabling this option may exhibit better vortex retainment in the flow.

Disabled

No reflection is performed; this is the recommended setting for simulations that involve non-zero goal divergence, such as explosions.

Single-Project

Performs a single pressure projection per timestep and adds the removed velocity components back at the next step. This option is marginally slower than Disabled, but requires an extra vector field to be carried between timesteps.

Double-Project

Performs two pressure projections and velocity advection passes per timestep. This option is a lot slower than Single-Project, but may yield better results and stability.

Reflection Amount

Fraction of the projected velocities to re-inject when Advection-Reflection is not set to Disabled. Values near 1 will do a better job of conserving energy, but may result in instabilities.

Temperature

Temperature Diffusion

A blur factor on the temperature field. Higher values diffuse the temperature out further, emulating the spread of heat from hotter to colder areas.

Cooling Rate

How fast the temperature field cools to zero.

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 value of 1 in the temperature field (in Kelvin). The temperature range is used to calculate strength of the buoyancy force.

Note

In general, value of T in the temperature field corresponds to a temperature of Ambient Temp (K) + T * (Reference Temp (K) - Ambient Temp (K)).

Buoyancy Scale

Hot gas expands, causing it to rise due to lowered density. Acceleration due to buoyancy is calculated using values of the ambient and reference temperatures, as well as the Gravity settings. Value of this parameter is used as a multiplier for the buoyancy force.

Gravity

Gravity Acceleration

Acceleration due to gravity. Stronger gravity results in stronger buoyancy forces.

Gravity Direction

The direction in which gravity pulls. Hotter gas will tend to rise in the opposite direction.

Flames

Parameters in this tab of the solver control evolution of the flame field and its effect on the simulation. Three possible outputs can be generated from flame: soot (density field), heat (temperature field), and expansion (divergence field). Each of these sets has an amount, a flame range, and the option to remap the flame field. The flame value is first fitted from the repsective flame range to the 0-1 range; if remapping is turned on, the ramp is then evaluated at the fitted value. This number is then multiplied by the amount parameter to get the output, which is finally merged with the target field.

Flame Lifespan

The number of seconds it takes to use up a value of 1 in the flame field.

Smoke

Emit Smoke

When enabled, density is added to the simulation in the specified Flame Range.

Emission Amount

Amount of density output from the flame field. This parameter acts as a multiplier for the remapped flame value.

Merge Method

Controls how the output of the flame field is mixed with the density field.

Max

Larger of the two values is taken. This merge method ensures that density does not keep accumulating.

Add

Output of the flame field is scaled by the timestep and added to the density field.

Flame Range

The range of values in the flame field that will generate an output. The flame field is first fitted from this range to 0-1; if Remap Flame is enabled, the Flame Ramp is then evaluated at this value. The final output is the product of this remapped flame value and Emission Amount.

Remap Flame

When enabled, Flame Ramp is evaluated at the refitted flame value (from Flame Range to 0-1) to generate the output.

Flame Ramp

Ramp that controls outputs at different flame field values.

Temperature

Add Temperature

When enabled, temperature is added to the simulation in the specified Flame Range.

Temperature Amount

Amount of temperature output from the flame field. This parameter acts as a multiplier for the remapped flame value.

Merge Method

Controls how the output of the flame field is mixed with the temperature field.

Pull

Wherever output from the flame field exceeds the temperature value, temperature is pushed towards the output. This merge method ensures that temperature does not keep accumulating.

Add

Output of the flame field is scaled by the timestep and added to the temperature field.

Strength

How strongly the temperature field values are pushed towards the hotter flame output when Merge Method is set to Pull.

Flame Range

The range of values in the flame field that will generate an output. The flame field is first fitted from this range to 0-1; if Remap Flame is enabled, the Flame Ramp is then evaluated at this value. The final output is the product of this remapped flame value and Temperature Amount.

Remap Flame

When enabled, Flame Ramp is evaluated at the refitted flame value (from Flame Range to 0-1) to generate the output.

Flame Ramp

Ramp that controls outputs at different flame field values.

Expansion

Add Expansion

When enabled, goal divergence is added to the simulation in the specified Flame Range, causing expansion.

Expansion Rate

Amount of divergence from the flame field. Larger values result in a more violent expansion. Negative values cause the gas to be sucked inwards (instead of blown outwards).

Flame Range

The range of values in the flame field that will generate an output. The flame field is first fitted from this range to 0-1; if Remap Flame is enabled, the Flame Ramp is then evaluated at this value. The final output is the product of this remapped flame value and Expansion Rate.

Remap Flame

When enabled, Flame Ramp is evaluated at the refitted flame value (from Flame Range to 0-1) to generate the output.

Flame Ramp

Ramp that controls outputs at different flame field values.

Shape

The shape of the resultant smoke can be greatly changed by tweaking the settings that are located in this section. Depending on values of these parameters, simulation results may fall anywhere between simple laminar smoke flow to small fires to huge explosions.

Dissipation reduces the density of smoke over time, so that it fades and eventually disappears. It is important to set an appropriate value for the Clamp Below parameter when performing a sparse simulation. Otherwise, tiny density values will linger and unnecessarily inflate the active simulation region.

Disturbance and shredding apply random forces to break up the simulation. Former exerts linear accelerations and is useful for breaking up smooth smoke caps. The latter rotates velocities to redirect the flow. Shredding is effective at adding chaotic motion without speeding up or slowing down the flow; it is especially useful for fire simulations, which are dominated by vertical licks when no shredding is used.

Turbulence can be used to add powerful large-scale noise to the simulation velocities.

Each shaping operation has a checkbox to turn it on and a scaling factor to specify how strongly to apply it. There is also a tab containing further parameters for each built-in operator. A common theme here is the control field, which can be used to spatially attenuate strength of the shaping operator. When enabled, value of the Control Field is fitted from the Control Range to 0-1; this is further passed through the Control Ramp if Remap Control Field is enabled. The remapped control value is then applied as a scaling factor on top of the global strength.

Dissipation

Causes smoke to disappear over time. Low values cause smoke to disappear more slowly. A value of 0.1, for example, means that 10% of the smoke will disappear every twenty-fourth of a second, whereas a value of 1 will make all smoke disappear immediately.

See the Dissipation tab below.

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.

See the Disturbance tab below.

Shredding

Randomly redirects the flow without speeding it up or slowing it down. This operator is especially useful for flame simulations, where it can be used to emulate random motion of licks characteristic to fire.

See the Shredding tab below.

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.

See the Turbulence tab below.

Dissipation

Clamp Below

When this option is turned on, density values that fall below the provided threshold are driven all the way down to 0. It is recommended to leave this enabled for sparse simulations, for otherwise tiny density values will keep the active region unnecessarily large.

Control Settings

Control Field

When enabled, the force exerted is scaled by the content of this field.

Control Range

Map from this range of values in the control field.

Remap Control Field

Enables or disables the control field ramp.

Control field ramp

The ramp’s vertical axis is strength of the effect and the horizontal axis is the value in the control field.

Disturbance

Threshold Field

Disturbance is meant to mimic random motion in the air surrounding the smoke. To this end, it is applied only where the value of the Threshold Field falls below Cutoff.

Cutoff

Disturbance is applied only where value of the Threshold Field falls below this Cutoff.

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.

Reference Scale

Variance of the aggregated force over a region of this size will be equal to Disturbance amount 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. The global Disturbance amount can be used to more finely control how much force is applied.

Base 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; only applies when Mode is set to Block-Based.

Note

The noise pattern changes on every frame in Continuous mode.

Lacunarity

The ratio of block sizes between successive noise layers. Value of 2, for example, 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. Value of 0.5, for instance, 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.

Max Octaves

The maximum number of noise levels to compose in Block-Based mode.

Control Settings

Control Field

When enabled, the force exerted is scaled by the content of this field.

Control Range

Map from this range of values in the control field.

Remap Control Field

Enables or disables the control field ramp.

Control field ramp

The ramp’s vertical axis is strength of the effect and the horizontal axis is the value in the control field.

Visualization

Visualize Strength

This option can be enabled to visualize strength of the applied force at different points in space.

Note

The strengths will also be saved into the Visualization Field.

Visualization Field

When Visualize Strength is enabled, the amount of applied force at each voxel is stored in this scalar field.

Mode

Determines how the visualization will appear in the viewport.

Plane

Viewport will show a color-coded cutout of the strength field.

Smoke

Viewport will show a fog volume whose denser areas correspond to regions of higher applied strength.

Plane Orientation

Orientation of the cutting plane for Plane visualization.

Plane Position

Relative position of the cutting plane inside the bounding box.

Color Mapping

Controls how strength values are mapped from the Guide Range to colors.

Guide Range

Range of strength values that gets mapped into the 0-1 range before color conversion. The final visualization colors are controlled by Color Mapping.

Smoke Density

Multiplier on density of the fog volume representing force strength.

Shredding

Shredding Field

Shredding is meant to add chaotic motion inside the fire. To this end, value of the Shredding Field (flame by default) is fitted from the Field Range to 0-1 to act as a multiplier on top of the global Shredding amount.

Field Range

Shredding Field value is fitted from this range to 0-1 to act as a multiplier on top of the global Shredding amount.

Base 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; only applies when Mode is set to Block-Based.

Note

The noise pattern changes on every frame in Continuous mode.

Lacunarity

The ratio of block sizes between successive noise layers. Value of 2, for example, 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. Value of 0.5, for instance, 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.

Max Octaves

The maximum number of noise levels to compose in Block-Based mode.

Control Settings

Control Field

When enabled, the force exerted is scaled by the content of this field.

Control Range

Map from this range of values in the control field.

Remap Control Field

Enables or disables the control field ramp.

Control field ramp

The ramp’s vertical axis is strength of the effect and the horizontal axis is the value in the control field.

Visualization

Visualize Strength

This option can be enabled to visualize strength of the applied force at different points in space.

Note

The strengths will also be saved into the Visualization Field.

Visualization Field

When Visualize Strength is enabled, the amount of applied force at each voxel is stored in this scalar field.

Mode

Determines how the visualization will appear in the viewport.

Plane

Viewport will show a color-coded cutout of the strength field.

Smoke

Viewport will show a fog volume whose denser areas correspond to regions of higher applied strength.

Plane Orientation

Orientation of the cutting plane for Plane visualization.

Plane Position

Relative position of the cutting plane inside the bounding box.

Color Mapping

Controls how strength values are mapped from the Guide Range to colors.

Guide Range

Range of strength values that gets mapped into the 0-1 range before color conversion. The final visualization colors are controlled by Color Mapping.

Smoke Density

Multiplier on density of the fog volume representing force strength.

Turbulence

Swirl Size

Base swirl size in world units. Lower values produce smaller, more localized vortices, while larger values give rise to coherent long-range forces.

Grain

Controls the ratio of amplitudes between successive noise bands. Higher values increase the prevalence of higher-frequency vortices (smaller than the base Swirl Size).

Pulse Length

Governs how fast the noise evolves. Higher values of this parameter result in slower evolution.

Seed

Acts as an offset into the noise field. Change this value to modify the resultant forces.

Levels

Number of turbulence levels to apply. Each successive layer has half the swirl size, and amplitude of the previous layer scaled by Grain.

Influence Field

This field determines which areas are affected by turbulence. In particular, turbulence is applied wherever value of this field exceeds Influence Threshold.

Influence Threshold

Turbulence is applied wherever value of the Influence Field exceeds this threshold.

Control Settings

Control Field

When enabled, the force exerted is scaled by the content of this field.

Control Range

Map from this range of values in the control field.

Remap Control Field

Enables or disables the control field ramp.

Control field ramp

The ramp’s vertical axis is strength of the effect and the horizontal axis is the value in the control field.

Visualization

Visualize Turbulence

This option can be enabled to visualize the applied turbulence force.

Plane Orientation

Orientation of the cutting plane for visualization.

Visualization Type

The method for coloring the force streamers. See Vector Field Visualization help for more information on these types.

Visualization Mode

Determines how values in the Visualization Range are converted to colors.

Visualization Scale

Magnitude of the force is multiplied by this value to calculate the actual speed to use when the Visualization Mode is set to Speed.

Note

The magnitude is scaled by this value before mapping from the Visualization Range.

Plane Position

Relative position of the cutting plane inside the bounding box.

Streamer Length

Distance in world space that each streamer will travel.

Note

Streamer lengths are not indicative of force magnitude.

Streamer Minimum Speed

The cut-off force magnitude at which the streamers will be abandoned.

Visualization Range

When Visualization Mode is set to Speed, the scaled force magnitude is fitted from this range to 0-1 before being mapped to color (per Visualization Mode).

Advanced

Use OpenCL

Use the OpenCL device to accelerate computations.

Note

OpenCL acceleration is currently only supported in dense mode (when Enable Sparse Solving is disabled).

Min Substeps

The solver will take at least this many substeps per frame. If you have unusual forces, you may want to increase this parameter for better stability. Increasing this parameter usually makes the simulation run noticeably slower.

Max Substeps

The solver will take at most this many substeps per frame.

CFL Condition

When Max Substeps is greater than 1, the solver uses this parameter to determine the number of substeps. The condition is that no substep can allow objects to interpenetrate by more than this many voxels. Higher values let the solver take larger substeps, possibly letting smoke pass through colliders.

Quantize to Max Substeps

When enabled, all substeps will divide the frame by Max Substeps. For example, if Max Substeps is set to 4, but the CFL Condition only requires 3 substeps, the solver will take frame steps 0.25, 0.5, and 0.25. This option can be useful for re-using input geometry that has been cached to file at increments of 1/Max Substeps.

Frames Before Solve

Delays the actual simulation this many frames after the object creation. Nodes attached to the Sourcing input will still be executed. This may be needed if some solve nodes can’t be processed before certain initial conditions have been met.

Resizing

Resize in Full Tiles

When enabled, size changes to the fields will be done in increments of 16 voxels. This is marginally more efficient, but the resultant fields will be larger than necessary.

Note

Resizing is always done in full tiles when Enable Sparse Solving is turned on.

Reference Fields

List of fields that determine size of the simulation container. Resizing is done by first computing the bounding box around all voxels of Reference Fields that have a positive value, then expanding this intermediate region by Padding on all sides. This list of fields is also used to build the active region in sparse mode.

Padding

Amount of padding to add to the simulation region around the Reference Fields. Padding should be as small as possible, but large enough to ensure that moving smoke does not leave the container within a timestep.

Note

When Enable Sparse Solving is turned on, Padding also controls size of the buffer built into the active region.

Extra Fields

By default, the smoke solver will resize density, temperature, divergence, active, vel, collisionvel, and flame (for pyro only). Additional fields may be resized by specifying them here.

Sparsity

Enable Sparse Solving

Puts the solver in sparse mode, allowing it to perform its computations only in relevant areas.

Note

Enable Sparse Solving must also be enabled on the smoke object for sparse mode to work correctly.

Reset Rule

Rule that determines where the fields specified in Fields to Reset are modified.

Disabled

Fields are not modified anywhere.

Newly Occupied

Fields are reset in the areas that were previously inactive but are now active.

Newly Deoccupied

Fields are reset in the areas that were previously active but are now inactive.

Newly Occupied or Deoccupied

Fields are reset in the areas that changed their activity status in either direction.

Fields to Reset

List of fields to reset, based on the Reset Rule. In the regions where they are modified, these fields are set to their initial value.

External Forces

Scaled Forces

A list of forces to scale by the value of the density field at each voxel.

Absolute Forces

A list of forces to apply uniformly to all voxels (ignoring their density value).

Advection

Field Advection

Advection Scheme

The algorithm used to perform advection. Semi-Lagrangian is the most basic: it simply traces trajectories through the Velocity Field once to update the Field values. Modified MacCormack carries out an extra tracing step to approximate and compensate for the introduced error; as a result, sharp features of the original field can be better preserved. BFECC performs yet another trace to predict the motion of the estimated error, producing the best results at the highest computational cost.

Clamp Values

The error correction steps of Modified MacCormack and BFECC advection may introduce final voxel values that lie outside the range of the original field: this can create negative densities or large velocities, for example. When such values are detected, the final field value depends on the setting of this parameter.

None

No clamping is performed.

Clamp

Clamps the value to ensure it lies in the range that would have been seen by Semi-Lagrangian advection.

Revert

Falls back to the value predicted by Semi-Lagrangian advection.

Blend

Apply a smooth blend between non-clamped and clamped values as the advected field approaches the clamping limit. Particularly with the Revert option, applying a small amount of Blend (0.05-0.1) can reduce grid artifacts in the advected field.

Trace Method

Controls how trajectories are traced through the velocity field. Options in this menu are listed in the order of increasing accuracy and computational cost.

Note

With an appropriate value for the CFL Condition, Forward Euler should be sufficient. Consider using a higher-order Trace Method if you need to use a larger CFL Condition or if you choose to disable that option altogether.

CFL Condition

When enabled, trajectory tracing will be done in steps to ensure that the calculated path reflects variations in the velocity field. The step size is governed by the value of this parameter. Particularly, the number of field voxels traveled in each step is equal to the CFL Condition.

Max Steps

Provides a safety limit on the number of steps that can be taken to trace trajectories.

Note

Step limiting will also always apply to velocity advection, even when Use Field Advection Settings for Velocity is disabled.

Max Batch Size

To minimize the cost of tracing paths through the Velocity Field, the target fields are organized into batches (based on their voxel sampling settings), and each batch is advected simultaneously. Enabling this option allows you to limit the number of fields that can be processed in each batch. This is useful for reducing peak memory usage of the advection step.

Note

The batch settings will also always apply to velocity advection, even when Use Field Advection Settings for Velocity is disabled.

Extra Fields

By default, the solver will advect density, temperature, vel, and flame (for pyro only). Additional fields may be advected by specifying them here.

Velocity Advection

Use Field Advection Settings for Velocity

When enabled, Field Advection settings will also be used to advect the velocity field. Turning this option off allows you to change advection settings for velocity.

The remaining settings in this section are the same as the ones listed under Field Advection.

Collisions

Build Collision Mask

If this option is enabled, the solver will build the collision and collisionvel fields, allowing automatic interaction between smoke and collision objects.

Bandwidth

Controls how far from the collision objects the relevant fields are to be built. This value is measured in voxels. If disabled, the fields will be initialized everywhere.

Use Point Velocity for Collisions

The local velocity of an affector object is a combination of the angular and linear velocity. However, if the object is deforming and points match frame to frame, the local point velocity can be used as well to estimate the deformation effect.

Use Volume Velocity for Collisions

If an affector object doesn’t have a stable point count, but does have a volume representation, the change in the volume representation can be used as an estimate of deformation velocity.

Note

This does not include any velocity tangential to the volume surface: a conveyor belt will appear to be stationary as the volume remains unchanged frame to frame.

Collide with Non-SDF

Normally, the collision relationship uses the signed distance field for each object. However, if the object is a different type you can use other ways of getting its effective signed distance field. If this option is enabled, the object is examined for a surface scalarfield, which is treated as a signed distance field. If a density field is present, it is treated as a fog volume with a 0.5 cutoff. If a Geometry geometry is attached, and it consists of a single volume, that volume will be treated as a fog volume (with cutoff of 0.5). However, if its boundary condition is set to SDF, it will be treated as an SDF.

Correct Collisions

When enabled, the specified fields will be reset inside the colliders.

Fields to Correct

These fields will be reset inside the colliders when Correct Collisions is turned on.

Feedback Scale

The degree to which the colliders are affected by smoke is controlled by the value of this parameter. Higher values will increase the effect of pressure forces on the colliders. A value of 0 will prevent any feedback.

IOP Iterations

Colliders are integrated into the system using a weak coupling approach. The number of projection iterations is controlled by this parameter. Larger values will slow down the simulation, but yield better interaction with collision objects.

Hourglass Filtering

Filter Hourglass Modes

Enables filtering of spurious divergent modes that may survive pressure projection when Velocity Sampling on the smoke object is set to Center.

Amount

Strength of hourglass filtering. Value of 0 disables the filtering altogether, while 1 performs full filtering.

Scale by Divergence

Instead of performing the filtering everywhere, it can be selectively applied to voxels where divergence is still detected by turning this option on.

Use Relative Divergence

Similar to Scale by Divergence, this setting applies the filtering with different strength in different places. Instead of pure divergence, however, the quantity used to control filtering strength is the ratio of divergence to speed.

Divergence Scale

Controls how sensitive filter strength is to the remaining divergence (or divergence relative to speed if Use Relative Divergence is enabled). That is, the relevant quantity is multiplied by this amount before it is used to determine filter strength.

Visualize Filter Strength

When using an adaptive filter (Scale by Divergence turned on), the strength field can be visualized by enabling this option.

Plane Orientation

Orientation of the cutting plane for visualization.

Plane Position

Relative position of the cutting plane inside the bounding box.

Visualization Mode

Determines how strength values (which fall between 0 and 1) are converted to colors.

See also

Dynamics nodes