Vellum grains are all inactive initially (i@stopped=3). As the Collider (Ship) gets within a user defined distance, the grains activate.

Aside from slight performance gains, this helps the tub of grains keep its shape and not crumble away especially around the borders.

Red means it's active. This clip is just a visualization. The activation actually happens together in the sim.

A stripped down proxy version of the ship is brought in as a volume collision (Converted into a VDB in SOPs).

A ground plane was also created so the grains don't fall into oblivion.

The simulated grains are then used as a source for the smoke. Only grains above a certain speed and will be used as a source for the smoke sim.

Using the Volume Rasterize Attributes node, attributes from the grains simulation (v, pscale) and additional attributes (density) are used to create volumes. These volumes are then sourced into the smoke sim.

The finalized effects are then rendered separately using mantra to be comped in Nuke.

The reason it was not rendered altogether was because there was no means to import the volumes into Maya (where everything else is lit and rendered) at the time.

The lighting setup from Maya had to be replicated and the necessary environment geometry was imported to create the shadows.

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The Effects were comped in Nuke by the Lighting and Compositing team.

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