volume based bubble advection inside particle fluid

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While I planned my next post to be a movie of setting up a wave from scratch using my wave tools, I will post this fluid test first. As was to be expected a interesting potential job comes along that requires some quick R&D, so I had to do this first. That said, I’m quite far in my setup for recording the wave tool movie so that’s definitely coming up soon…

In this test I’m filling a box with water using a particle fluid sim. It has 5 emitters at different positions and angles. For this kind of effect I think particle fluids look better than volume fluids as you get nice splashes. However, there is a distinct advantage for using volumes as the velocity fields in a volume sim can be very nicely used to advect additional particles, for example to add bubbles to the water.

Luckily however, it is fairly simple to generate volumes from the particle sim in Houdini. These take a little time to generate but once you have them advecting ‘bubble’ particles using the volumes becomes REALLY fast.

The same effect could be achieved by using the particles from the fluid sim directly as a point cloud from which velocity is sampled, which in order to advect the particles (as the volumes are generated using this point cloud approach as well), but this would mean that each run of the ‘bubble’ sim needs to resample this data. The volume approach solves this issue by basically caching out the samples into a fixed grid that can be efficiently queried.

Time to show the results… the first animation is a flip book of the fluid particle sim:

The second animation is the flip book of the bubbles sim:

In short this looks like a very cool and interesting approach to create ‘sub surface’ water effects to particle fluid sims. I’m fairly confident that this will find its way into my wave toolkit to add additional water detail both to the water surface (breaking wave lip detail, …) and sub surface effects like the bubbles where the crashing wave lip churns up the water below the surface. The bubble particles that reach the surface should be a really good starting point to generate some realistic foam on the surface as well. Anyway, lots of cool stuff to keep working on 🙂