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In this tutorial we explore how to create dust-like simulation using Chaos Phoenix FD smoke. We go through setting the right simulation units, appropriate geometry dimensions and scene setup suggestions. Most importantly, we guide you through how to make a realistic sand smoke coming up as the horses step on the ground using VrayDistanceTex, VRayCompTex and Smoke texture maps as a mask for the smoke emitVoxel Tuner. We compare how different values of some crucial parameters change the whole simulation's look.

Using multiple animated geometry meshes, we show how Phoenix FD handles large scale smoke simulations during animation.

This simulation requires Phoenix 4.10 Official Release and V-Ray Next Official Release for 3ds Max 2017 at least. 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. 

A V-Ray Infinite Plane is used for easily setting the ground.

The dust emitting ground is set by a 3ds Max standard plane with dimensions covering the space under the running horses. Dimensions in this scene Create a 3ds Max Standard Plane. The exact dimensions of the plane are 6225 cm by 2793 cm.

Since Phoenix FD works best with closed geometry, add a Shell modifier to the created plane.

Set the Outer Amount as little as to 1.0 cm. The actual value does not have weight in the final render, as the plane will not be visible at all there.

The exact Position of the plane in the scene is [ X:0cm, Y:-4320cm, Z:-20cm ].

With the plane selected, right-click on the Large-scale Smoke icon in the Phoenix FD toolbar.

This generates a simulator, a PHXSource and sets a smoke shader in the scene automatically.

Import the single_horse_01.ABC geometry by going to File → Import → Import...

This tutorial starts off with pre-built geometry to save time setting up the scene. Feel free to use your own personal models.

The exact start Position of the alembic mesh in the scene is [ X:0cm, Y:0cm, Z:0cm ].

You can control the interaction strength between the horse mesh and the ground plane by adjusting the Motion Velocity Effect, located in the Phoenix Per-Node Properties. The higher the value is, the stronger the fluid reaction to the body's movement is. For this tutorial, its value is set to 2.0.

Now that you have the plane as a smoke source, let's explore the right settings for a nice looking simulationCreate a Fire Smoke Simulator.

The Outgoing Velocity is set to 1410 cm. The Smoke parameter has a value of 30.

There is a texture map set as a Mask.

exact Position of the simulator in the scene is [ X:0cm, Y:-1500cm, Z:-20cm ].

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Let's try We are going to use VRayDistanceTex map as a Mask.

The VRayDistanceTex is a V-Ray specific procedural texture that returns a different color based on a point's distance to an object(s) specified in a selection list. It comes in handy here, where V-Ray will calculate the distance between the horse mesh and the plane and will generate a black-and-white mask procedurally. For that goal add your horse mesh(es) (the alembic file you created earlier) in the list of VRayDistanceTex Objects.

Distance is set to 8.0.

a Voxel Tuner to emit Smoke where the horse model touches the ground. We will do it in such a way, that we don't even need a Phoenix Source.

In this case, the Voxel Tuner will go through all the voxels of the Simulator, and check if each voxel is close to the ground plane and simultaneously close to the horse mesh. If it passes this condition, then the Tuner will create Smoke in this voxel.

The Voxel Tuner expression is created as follows:

• If a voxel's Distance to Plane001 is Less Than 1.7 voxels and If the Distance to horse mesh is Less Than 1.7 voxels.

• Then the Smoke will be Set to 15.0.

We picked very low values for both distance conditions - if you lower them even more, less voxels will pass the condition and Smoke will be emitted in fewer places. On the contrary, if you increase the distances, Smoke will start getting created in the air around the contact points between the horse and the ground.

We also create very dense Smoke - usually we don't need smoke above 1.0, but in this case we emit 15 units of smoke, which would make the smoke render very dense with the default render settings. Below we will enable Smoke Dissipation so the smoke will be thick at first, but then will quickly fade outSwap the far and near colors, so that the far color is black and the near color is white.

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Plug in the VRayDistanceTex to the Diffuse channel of a 3ds Max Standard material.

Assign it to the plane.

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Render Run the simulation for a few frames and render out one frame with a the running horse.

Notice how VRayDistanceTex generates a white circle the Voxel Tuner generates smoke around the horse's hoof when touching it touches the ground. 

The mask is still too uniform, so we need to adjust the texture to make it look more organic.

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The three images here compare the differences between Scene Scale values [set from top to bottom to 1, 5 and 10].

The higher the value of the Scene Scale, the slower the movement of the fluid would be. This will keep the smoke close to the ground.

Our The goal here is to make the smoke look like sand, so we don't need it too diffuse there is no need to be too diffused or raising high from the ground. We settle here for a value of At this tutorial the Scene Scale is set to 5, but feel free to experiment with other values as well.

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In the Dynamics rollout menu, switch the Smoke dissipationDissipation to 0.1 2 and the Smoke buoyancyBuoyancy to 0.06.

The Randomize Amount is given a value of 1.0.

The Conservation Method is set to PCG Symmetric, with a Quality of 100. The PCG Symmetric method, in general, produces the most interesting smoke simulations, preserving both detail and symmetry. The high Conservation Quality will allow the dust to produce swirling motion. For in-depth information, please check the Conservation documentation.

The Material Transfer (Advection) Method is set to Multi-Pass.

The Steps per frame are set to 2.

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Compare the difference in the Smoke Buoyancy values displayed in these two simulation three images.

Top: value of 1 (default value);

Bottom: value of 0.

The values are set as follows from top to bottom to [ 0, 0.6 and 1 ].

The Smoke Buoyancy could be even set With a value of 0 we get closer to a sand similar simulation, where the dust particles stay closer to the ground. You can even set this to a negative value so the dust would subside with time.

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The Smoke dissipationDissipation parameter controls how fast the smoke will disappear. The maximum value of 1 will make the smoke disappear immediately after it was emitted.

Top image: default value of 0.0;

Bottom image: value of 0.1The three images here compare the differences between Smoke Dissipation values [set from top to bottom to 0, 0.2 and 0.7].

You might notice that with a value values of 0.1 2 and 0.7 there is a lot less detail in the smoke simulation because as it becomes more transparent, sharp edges and sharp shadows are diminished. However, the simulation here is done with only one horse and we have quite more in the final scene. They will add up to the total picture and in order not to be covered completely in dust, we choose to stick to a value above 0.0.

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The Randomize parameter is responsible for the random fluctuations of the fluid's velocity for each grid voxel. 

Top image: value of 0 (default value);.

Bottom image: value of 1.0.

The We adopt the value of 1.0 is chosen for this parameter in order to break the natural fluid mushroom shapes and puffs and make the result look more chaotic.

Open the Rendering rollout menu to prepare the simulation for rendering.

The Sampler type parameter determines the blending method between adjacent grid cells. We The sampler is set it to Spherical.

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In those two comparison images you see the default Sampler type, that is, Linear (topimages are compared two different Sampler types - Spherical (top) and Linear (bottom).

The With Linear Sampler Type the produced dust looks grainy, so we switch to Spherical sampling (bottom), that for this tutorial the Spherical sampling is used instead. That effectively reduces this issue.

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Open the Volumetric Render Settings found by pressing the Volumetric Options button in the Rendering rollout menu.

Here you can control the smoke color and its opacity.

The Volumetric Render Settings are tweaked as follows:

The Fire's Based on is set to Disabled.

The Smoke Color is Based on Constant colorSet the color to be Constant. We aim at a sand-looking smoke, so we use RGB [ 225, 191, 163 ] for Constant color, but you can tweak it further.

The External Scatter Mult. is set to 0.3.

The Simple Smoke Opacity is adjusted to 0.3 is set to 0.7.

The Minimum Visible Opacity is set to 0.0.

The Scale Opacity by Scene Units is disabled.

For this setup a Standard Physical Camera is used.

The Film / Sensor Preset is set to 35mm (Full Frame).

The Film / Sensor Width is set to 36.0 mm.

The Focal Length is set to 40.0.

The Aperture is set to 5.0.

The Film Speed (ISO) is set to 100.

The Shutter Duration is set to 1000.0.

The exact position of the Camera is [ -1730cm, -3785cm, 907cm ]

and of the Camera Target is [ 179.267cm, -2317.455cm, 36.06cm ].

In this tutorial we focus mainly on the simulation, so the material used for the Infinite Plane (ground) is a V-Ray Material with the following settings:

Diffuse [197, 135, 93].

All other parameters are left to their default values.

Assign the material to the infinite plane.

Lighting in this scene relies on a V-Ray Dome light with assigned HDRI map. You can also use V-Ray Sky and Sun system. Remember to set your camera exposure to be suitable for outdoor lighting.

the final render a Probabilistic Shading  is used. The option is located in Environment → Atmosphere → PhoenixFD Atmosphere Settings. When Use Probabilistic Shading is enabled, the volumetrics will select a only few samples (based on the smoke density) along each camera ray, and evaluate the volume lighting at those points. In some situations this will make the render time shorter.

The Use Probabilistic Shading is enabled.

All parameters are left with their default values.

A V-Ray Denoiser Render Element is added to the final image. The Denoiser takes an existing render and applies a denoising operation to it after the image is completely rendered in order to remove the noise in the image.

For this tutorial the Custom preset is used.

The strength is set to 0.5.

The radius is set to 10.0.

You are ready to run the simulation.

Here are the final render results.  

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