Source geometry has a large impact on the shape and behavior of newly-injected smoke. In this step, you should focus on creating sources that will introduce interesting variations to the simulation, without worrying about details of the final result.

• For static smoke and fire simulations, add noise to the sourced values.

  • You can use the Attribute Noise SOP to add noise to the sourced point attributes.

  • With smoke, the noise will prevent constant, uninteresting emission.

  • Source noise for fire is important for capturing the look of the base. To get the cellular look for the fire base, use Worley (cellular) F2-F1 for the Noise Type.

• For spreading fire, you should also ensure that the spreading behavior looks right before proceeding with the pyro simulation.

  • The Pyro Source Spread SOP is specifically designed for simulation of fire spreading.

• For explosions, you can use the Pyro Burst Source SOP to create the sourcing for the core of the explosion and shape how the explosion will look. You can also add trails using the Pyro Trail Path and Pyro Trail Source SOPs. For more information see Creating Explosions.

You should also determine the ranges of sourced values in this step, especially for temperature and flame sources. To this end, you can use the Attribute Promote SOP to calculate the maximum of the relevant point attributes (prior to rasterization). This information will be useful later for setting parameters on the solver.

Once sourcing is finalized, next step is to set the basic properties to ensure that the simulation works correctly. These settings can likely be set once and forgotten, assuming reasonable values are used.

Through buoyancy, the temperature field has a large impact on the bulk motion of the smoke. To properly control this force, you need to specify the physical meaning behind the values in the field, by setting the Ambient Temp (K) and Reference Temp (K) parameters. From there, the buoyancy force can be further tweaked with Buoyancy Scale, without modifying the temperature range.

Parameters on the solver’s Flames tab have a significant impact on simulations that make use of the flame field. You should begin by tuning the Flame Lifespan parameter to ensure that the flame values persist for the desired amount of time. From there, you can enable the outputs that you want to generate from the flame field and tune their activation ranges. See the Flames page for more information about these outputs.

The previous steps are meant to determine the bulk shape and motion of the simulated smoke. Once you are happy with these bulk characteristics, you can use shape operators to add details to the simulation. The pyro solver has 4 built-in shape operators: dissipation, disturbance, shredding, and turbulence.

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, the 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. Control fields allow you to build a mask out of desired regions and only apply a shaping operator there.

The Pyro Solver SOP has the ability to perform a Minimal OpenCL solve, which is useful for very rapid prototyping. This option is located on the General tab in the Simulation Type dropdown menu. It allows for interactive manipulation of parameters during a running simulation, which can give you quick feedback of their effects on the simulation.

When this option is selected, some features of the solver are turned off to to ensure that all simulation data can stay in video memory, avoiding costly copies that are necessary when only Use OpenCL is turned on.

To produce fast simulations, Minimal OpenCL uses the OpenCL device and imposes the following limitations.

• Simulation caching is disabled. This means that you cannot scrub the timeline to view saved results.

• Advection-Reflection is not supported.

• Only a dense simulation can be performed.

• Dynamic resizing of the container is turned off. A static size needs to be set under the Bound tab.

• The solver will not dynamically substep based on the CFL Condition.

• Sourcing and collider support are more restricted. A frame range needs to be specified for both, and the solver will loop these input sources throughout the simulation. Additionally, the collider must be converted into a signed distance field (called collision) and a velocity field (v).

There is more you can do to increase performance:

• The use of a Pyro Bake Volume SOP node should be avoided during look development to maintain performance.

• Make sure that the Pyro Solver SOP node’s field and shape guides are turned off: Fields ▸ Field Guides ▸ Field Guide ▸ No Guide and the appropriate parameter in the Shape tab.

• Use looping sources where possible.

• If you use microsolvers, check if the Use OpenCL option is turned on to avoid bottlenecks.