refraction gets darker with motion blur

[exel]

Got a Mantra question!  I whipped up a test scene to benchmark render speeds on a few different workstations and found a render issue I'd like to solve -- motion blur is adding a lot of dark shading to my image, and I'm not digging it. 

This is a typical FLIP simulation where I gradually attempt to drown the Stanford bunny;  nothing funky or special going on, just a typical fluid mesh and I'm using SESI's off-the-shelf "basic liquid" shader and mantra ray tracing:

No motion blur, splashy water around the bunny is looking how I'd like:

With motion blur:

Why do those areas in the water surface change get so much darker, especially the stuff that shows up down at the water level?  From looking at the light exports, the indirect refraction and indirect shadowing both change significantly.

...I tried boosting the reflection and refraction limits, no difference at all...  can anyone spot what's happening here?  Maybe it's my lights and the shadows?  One environment light and one grid light.  I could attach the .hip file but you'd have to run the sim AND the meshing again just to see anything (I can't attach the mesh geometry as a file, it's ~90 MB).  Anyway, many thanks for any advice you can offer!

Houdini 16.5.536, Windows 10

SESI's "basic liquid" shader

1 grid light, 1 env light

mantra ray tracing engine

 

-JS-

 

[DaJuice]

Does that shader have the "faux caustics" option? If so try enabling that.

[lukeiamyourfather]

Upload the scene file so we can see exactly what's going on?

[exel]

15 hours ago, lukeiamyourfather said:

Upload the scene file so we can see exactly what's going on?

 

drown_the_bunny.hip

[exel]

15 hours ago, lukeiamyourfather said:

Upload the scene file so we can see exactly what's going on?

interesting, attaching a .hip file resulted in a double-post to the forum

Edited August 15, 2018 by exel