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Requires Phoenix FD 3.14.00 Official Release and V-Ray NEXT Official Release for Maya 2015 or newer. You can download official Phoenix and V-Ray from https://download.chaos.com. If you notice a major difference between the results shown here and the behavior of your setup, please reach us using the Support Form.

The instructions on this page guide you through the process of creating a Burning Aroma Stick simulation using Phoenix and Maya. At its core, this is a particle simulation driven by the Velocity channel of the Phoenix Simulator. You may know this process as Advection.

The Phoenix Source is capable of emitting not only Smoke, Fuel or Temperature but also particles. We emit Drag particles for this effect - drag particles are, as the name implies, dragged by the Velocity of the simulation. The Drag particles are then rendered with the Phoenix Particle Shader in Point mode, with very low Point Alpha - the combination of a large amount of particles and a high transparency produces the illusion of smoke.

Finally, the simulation is slowed down using the controls in the Input rollout of the Phoenix Simulator.

Add a Phoenix Simulator and place it at XYZ: [ 0.7, 20, 1.4 ] such that the tip of the stick is inside the simulator's bounds.

The Simulator → Grid parameters are tweaked as follows:

The Scene Scale is set to 1 ( the Vase and Aroma Stick are provided in real-world scale so the Scene Scale multiplier should be 1).

The Cell Size is set to 0.1 - this may seem inappropriate at first - the total number of voxels is 15 625 which is very low for a fluid simulation. However, as mentioned in the Overview, this simulation relies on the drag particles being carried by the Velocity channel of the simulator. The higher the resolution of the simulation becomes (the more voxels there are), the more detailed the Velocity channel will be - we want to avoid this - cigarette smoke, and the type of smoke produced by aroma candles, is very smooth and moves gently - a detailed Velocity channel will disturb the motion of the particles too much to produce a convincing effect.

The X/Y/Z Size of the Simulator is set to 25/25/25 as a starting point. In the next step, Adaptive Grid is enabled to allow the simulation's bounds to scale on-demand.

Lastly, the Container Wall (Y) is set to Jammed(-). Jammed (closed) walls are treated as solid obstacles by the simulated content. Also, The Adaptive Grid algorithm will not re-size the simulation's bounds in the direction of the jammed wall.

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Again under the Simulator → Grid rollout:

Set Adaptive Grid to Speed. The Adaptive Grid algorithm updates the size of the simulation's bounding box to accommodate the movement of the simulated contents (e.g. Smoke rising up).

Set the Threshold to 20 - the Threshold value specifies the minimum value a Cell near the outer edges of the box must be for the Adaptive Grid algorithm to kick in and resize the Simulator. When the Adaptive Grid is set to Speed, with a Threshold of 20, the Velocity channel of the simulation near the outer edges should be of magnitude of at least 20.

Set the Extra Margin to 1 - by default, the Adaptive Grid algorithm tries to expand the simulator to accommodate the movement of the contents inside. However, if the content is moving very quickly (e.g. an explosion, hot smoke, etc.), the simulator may not expand enough and clipping may occur. The Extra Margin option can be used to force an additional number of voxels around the walls to give the fluid a bit more room if the Adaptive Grid can't keep up with the simulation.

Under Grid→ Manual Adaptation Limits, select Enable Limits and set the maximum size of the simulator to [ 20, 20, 120, 0, 20, 20 ].

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To the right is a Playblast of the simulation in its current state.

To the right is a Playblast of the simulation in its current state.

As you can see, the movement of the Drag particles closely resembles the movement of the Smoke from the previous Playblast. Here is a simple explanation for this - both the Smoke and the Drag particles are carried by the exact same Velocity channel. You could achieve the exact same 'thin smoke' effect with Smoke instead of Drag particles – this would require a much higher grid resolution, and consequently would take much longer to simulate.

The chaotic movement is caused by the default Vorticity settings - those work great for regular smoke simulations but in this cause, the additional randomness is working against the effect we are trying to achieve.

To the right is a Playblast of the simulation in its current state.

Disabling the Vorticity slightly reduced the amount of randomness in the simulation. However, the simulation is still too turbulent for the type of effect we're trying to create.

To the right is a Playblast of the simulation in its current state.

Increasing the Conservation Quality, and setting the Method to PCG further simplified the movement of the particles. At this point, it might be a good idea to try reducing the discharge - recall that the particles are carried by the Velocity field - in our simulation, the only thing affecting the Velocity is the Temperature emitted by the Smoke. Even though we disabled the output of Temperature, the Source is still emitting it on every single frame.

Temperature affects the Velocity directly - hot air rises upwards, therefore the higher the amount of Temperature the Source pumps into the simulation is, the faster and more violent the simulation will be.

To the right is a Playblast of the simulation in its current state.

Reducing the Discharge reduced the Temperature, and as a consequence, the upwards velocity is lower, which in turn means the Drag particles will take more time to rise up.

You could further modify this simulation by reducing the Temperature value itself - in this example, we leave it at its default value of 2000 to keep things less complex.

We now need the particles to clump together to create the effect of thin smoke slowly rising up. To achieve this, we can increase the Steps Per Frame.

To the right is a Playblast of the simulation in its current state.

Increasing the SPF gives the Drag particles a much smoother Velocity field to travel on, and as a consequence - they've started nicely clumping up.

You could experiment by increasing the SPF even higher - for this example, we keep the SPF at 5.

Aroma Sticks (and also cigarettes, in case you're going for a cigarette smoke simulation) do not emit smoke from their entire surface. An easy way to limit the emission of particles to a subset of faces on the emission geometry is to use an Emit material.

Select the second row of faces starting from the top of the aromaStick_01 geometry and use the Right Mouse Button → Assign New Material option to give them a new Lambert material.

Rename the new material to mtl_emit_01 and specify it under the Phoenix Source's Emit Material parameter.

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Select the aromaStick_01 geometry and open the Attribute Editor. Under the aromaStick_Shape1 node → Extra Phoenix FD Attributes, set the Voxel Mode Override to Inscirbed.

This option overrides the Simulator → Scene Interaction → Object Voxels parameter. It controls the way the geometry is represented inside the Phoenix simulation. You can think of this as the thickness of the walls of the aroma stick.

We reduce this value to make sure the particles are emitted as close to the surface of the geometry as possible.

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To the right is a Playblast of the simulation in its current state.

The simulation is now starting to take shape. We add a Phoenix Turbulence node to break things up for a more interesting motion.

Also, the vertical movement of the Drag particles is still too quick which we can remedy by using the Phoenix Simulator's Input rollout Time Scale parameter to slow things down.