Explosion

Simulation

The reference for this effect was a gas explosion. The first step was to find what type of source would yield the best result. A flattened and deformed sphere was used as the input for the fluid source SOP. Inside the fluid source SOP, noise was used to add further detail to the volume that I used as the source for density, fuel, and temperature in the sim. A velocity volume was created by converting a particle sim into a VDB. 

The RBD object used for the larger debris pieces was another flattened and deformed sphere. Another sphere was deformed using the mountain SOP, and the normals were used to create a velocity attribute. The velocity attribute was transferred onto the RBD object. The object was simulated as a packed object with inherited point velocities. The debris SOP was used as the source for the particle sim that was used as the small scale debris.

The trail SOP was appended to the debris SOP to source density and velocity for the ground dust and dust trials for the debris.  

Rendering

The project was rendered using Redshift in Maya. The debris was cached out as an alembic from Houdini. The volumes were cached out as VDBs and brought in as Redshift volumes. 

One of the issues with rendering motion-blurred geometry that interacts with volumes on different layers is that the alpha for the geometry doesn't match  holdout in the volumes. The solution was to render the geometry and the volumes together with diffuse and puzzle matte AOV to alter the geometry in Nuke. A second layer was rendered with RGB lighting with the volume lighting AOV another with no lighting with the volume emission AOV. One last layer was rendered with GI.