Helicopter crash - RnD

[LarsSonparsson]

Hi

I have to create a scene where a helicopter is crashing to sea.
First test scene looks promising, but there is few weird things happening and I don't know what is causing it.

I have a lot of experience of Phoenix simulations, but I have done mostly fire and smoke, so everything related to liquids are quite new for me.

This is my second attempt. Helicopter animation is done quite quickly and might be too fast for a realistic look. Waves looks nice and the amount of splash and foam seems right.
But... When those waves moves further away, there is some weird looking "spray" of particles going on. What could cause that? Also in front of the wave, there is some wiggling movement that looks quite distracting. Could it be related to the "spray"?

Should I change splash threshold? Would it help if I increase Min Age from Foam on hit rollout?

I'll attach some settings tomorrow with the new version calculating at the moment.

https://www.dropbox.com/s/b35opzxl94...sh_01.mp4?dl=1

[Svetlin.Nikolov]

Hmm, can you enable and disable different particle systems in the preview in order to find which particles are these? Then we'd know what options to look at. Also, beware that if your geometry has open edges, inverse normals etc, the FLIP solver won't take that lightly and there will be all kinds of weird stuff happening.

Cheers!

[Svetlin.Nikolov]

Ah, regarding the movement in front of the waves, I see there are splashes falling and turning into foam further ahead, but right in front of the waves there seems to be some other flickering. This can happen if you use a vraymtl with fog for the ocean and you don't have a bottom to cap off the fog volume, so foam crossing the water surface and sinking will appear to abruptly change its brightness.

[LarsSonparsson]

So it seems that the spray particles are foam particles.
I'll do another simulation with simple geometry, so we can see if it is some bad geometry causing it.

That flickering in front of the wave could be my own mistake. I tried to build extra "foam" shader using grid velocity to add a bit of whiteness to fast moving parts of the liquid. Have to disable that for now

[Svetlin.Nikolov]

Ah, so if these are foam particles, check if the rising speed is not too high - this could make the foam underwater to accelerate so much that in a single frame it appears high above the liquid.

[LarsSonparsson]

Good point, gonna check that.
I have done a new simulation that looks a lot better. No spray effect anymore. Gonna render that over night, so we have a new scene to check tomorrow.

Is there anyway to speedup particle rendering? I'm currently using point shader everywhere, that renders 20 to 40 mins per frame, but it doesn't look as good as bubbles. With bubbles as foam, it takes 60 to 90 minutes per frame. Well... not bad, but could be faster.

[Svetlin.Nikolov]

Wow, these are horrible render times. How many particles do you have? Are GI and moblur on?

[LarsSonparsson]

Grid: 126M cells
Liquid: 34M particles
Foam: 7M particles
Splashes: 76000 particles

Scene is lit with a HDR from dome light.
GI bf/lc
Motion blur and dof is on


This one took about 18 mins.

[Svetlin.Nikolov]

Ah yes - if you have all of that, and 8 million particles as well, this does add up. However, especially in Point mode, you could try increasing the motion blur step of the Particle Shader - you should be able to get some speedup before the motion blurred paths of the points start looking dashed in the rendering.

[LarsSonparsson]

Does it help, if Foam and Splashes are using same particle shader?
I mean, if I use separate shaders for Foam (bubbles) and Splashes (splash), is there going to be overlapping geometry that could make it harder to render? Or if I use one particle shader that will handle both Foam and Splashes, is there going to be better optimisation?

[Svetlin.Nikolov]

Hmm, that's a very good question! If you use the same particle shader, it should theoretically be at least a bit faster...

[LarsSonparsson]

Latest version looks quite promising already, but not good enough yet.

https://www.dropbox.com/s/67nkm0l6n0...5_PHX.mp4?dl=1

Wave front looks very weird. Especially the second wave moving to left in the end of the shot.
Foam looks like a line moving on top of the wave. There is also some strange "echoes" from those foam particles.
Check the frame attached.

Should I just increase the foam threshold? Or if those foam particles are generated from the splash particles, would increasing the Foam on hit Min Age help?

Also, what would be the proper steps per frame value for these kind of simulations? Currently using 6, but is that enough?

[Svetlin.Nikolov]

Hmm, looking strange indeed. Are you certain that these are foam particles when you look at them in the preview? I'd say it looks like splashes rolling on top of the liquid with the Droplet Surfing option enabled...

[LarsSonparsson]

Yes, definitely foam particles. Just checked again all particle previews and there aren't even that many splash particles left.
Foam - 5.5 millions. Splash - 5600

I had Droplet Surfing enabled thou. Currently doing another sim without it.

[Raven]

Looks great Lasse