I've been trying out the new H17 WW tools from the shelf and get these weird results post solve.

-The emitter looks fine
-Substeps and resolution didnt affect the “stepping”
-I am suspecting collisions but didnt get conclusive results

Any ideas on what might be causing this?



Thank you!

Hey Charles,

Did you ever figure this out?
I'm running into the same stepping issue with a very default sim (sphere with 1m diameter hitting water) in H17.5.173.
So far I found it does not seem to be the sourcing.

I am using narrow-band for the primary flip sim and I'm thinking it might be coming from the bands of the vdb of the volumes of the primary fluid sim.

Considering that the airborne particles are supposed to be ballistic and not affected by the fluid sim, it does not make sense as to where the stepping is coming from. I am going to dig into the h17.5 whitewatersolver some more.

Thanks,
Peter

So I figured out what is causing this and wanted to share for future reference.

This is caused by the surface field that is generated from the narrow band during the primary sim.

The sdf surface from the primary sim has limited information - because of the narrow band. The information is largely stored near the surface as defined by the banding of the vdb.

My solution to get this working was not very elegant, in the sense that I ended up converting the primary fluid surface to polygons, then compute a ‘vdb from polygons’ with “fill interior” turned on and at least 1 meter in banding. This is because the depth of the whitewater solver by default is set to 0.8 (which should be covered by the 1 meter bands - mostly for the splashes above the surface - as I have complete information for the underwater portion as that is covered by the ‘fill interior’).

This provided me with the necessary depth data that I needed. Luckily this can be done as a post process, so you don't have to resim your primary fluid. After that it largely worked as expected.

Not sure if there is a more elegant way, but yeah, careful with high resolution (voxel based distance half band) narrow band sims as they might not capture the required surface depth detail for the whitewater splashes.

– The strange part to some extent is that the ‘vel’ field is totally fine and captures the right kind of information deep into the inside part of the liquid of the primary sim. Almost feels like a bug. Not sure if it is.