Motion Blur Issues with Time-remapped Fluid Simulation in VRay

[k_18]

Hi everyone, We have simulated a simple fluid simulation and want to render it at a slower speed than originally simulated. The original simulation was done with 10 subframe steps, and we have output the velocity channel and advection origin.
However, when we either render subframes through VRay's render settings or adjust the simulation speed via the input rollout (e.g., setting it to 0.2), we only get correct motion blur on some frames. On most frames/subframes, the motion blur is either missing or only partially visible.
What setting do we need to enable to fix this issue? We also tried applying grid channel smoothing to the velocity channel, but that didn’t help.
Thanks in advance for your help!

[zdravko_pavlov1]

Hello, I'm going to try and make a setup similar to what you are describing and see if I can reproduce the issue. Just to verify, you have a liquid simulation and want to slow it down. You have exported both grid and particle velocity channels. Is that correct?

[k_18]

Hi Pavlov, yes that is correct. I could also share the scene minus the cache if that helps?

[zdravko_pavlov1]

Hi Pavlov, yes that is correct. I could also share the scene minus the cache if that helps?

It will be really helpful, thank you.

[k_18]

Hi Pavlov, I just sent you a file via private message. Looking forward to hearing what you say.

[zdravko_pavlov1]

Hi Pavlov, I just sent you a file via private message. Looking forward to hearing what you say.

Thank you for the file - I'll look at it immediately.

[slavina.nikolova]

Hey,

Thanks for the scene! We're checking it out and have some suspicions about the problem, but we'll need some more information.

Could you log a report in the Support Portal - https://support.chaos.com/hc/en-us/requests/new, and provide a cache file, where the problem is visible. Also, if you could attach the Phoenix and V-Ray log files - you could find them in C:\ChaosPhoenix and C:\Users\<username>\AppData\Local\Temp

A video or screenshot showing the problem on your side, will be very useful too


Thanks!

[k_18]

Sure, will do. Does one cache file for one frame suffice or do you need the whole monty?

[slavina.nikolova]

If you could share a sequence of frames - where the problem is visible, and where it's not, it will be great.

[k_18]

Sure, np. Attached a crop of frames 42 to 45. I cannot show the whole image due to an NDA, but the problem is well visible. I could also share the cache files for these frame if you want.

[slavina.nikolova]

That should be enough for now, thanks!

We are looking at the problem and will inform you when we know more.