Problem with foam particles

[haarlem]

Hello Phoenix Team,
Please see the attached images.
1. I have a problem with the foam particles that look like if they are instantly killed when they touch the liquid simulator, but weirdly enough it doesn't happen for the ones generated at the AFT of the ship, although even you can notice that all the particles die at the same time, so there is a seam is visible.
2. Do you have any idea of how to improve the foam on the aft of the ship? I've tried a couple of tricks to get a lot of foam on the back but I still get those clean areas where only underwater bubbles are visible. Also, do underwater bubbles get killed when they reach the surface or do they generate foam particles on top of the water surface?
3. When setting the render mode to Ocean mesh, even at 1080 resolution, it takes about 1:30 minutes for the render to start. It hangs at "transforming vertices". Also when stopping the render 3ds max in "not responding" mode for 20 seconds or more. What could be the cause? My system is a Ryzen 3950X with 64 GB of RAM. Simulation files are on a separate Samsung pro ssd.
4. Is there any workflow to add the motion blur of the particles in post production (Fusion or After Effects) by somehow using the velocity channel?

I am using the trial version of Phoenix (Simulated with v4.10.00, Build ID: 20200305 for 3ds Max 2020 from Mar 5 2020) but it is very important to get this right so I can implement it in my workflow.

Thanks!
Marcel

[georgi.zhekov]

Hey,

For the dying particles - make sure that you're exporting the Age channel for the Foam in the Output rollout.

The "Max Outside Age" parameter in the Foam rollout will control how long the particles will live after they leave the grid.

You can find more about the particle life cycle here - https://docs.chaosgroup.com/display/...les+Life+Cycle

In order to eliminate those dead spots you could probably increase the rising speed a bit and the underwater bubbles will rise faster to the surface.

When rendering in Ocean mode - before the start of the render the ocean surface needs to be generated, that's why it needs a bit of time before rendering. After the render is done the memory needs to be unloaded and this takes some additional time as well. Though your times seem a bit high on a first look. Can you send over the scene to support at chaosgroup dot com with a link to this thread so we can take a look?

As for the motion blur in post - First make sure that you have the Velocity channel exported for each particle system in the Output rollout. Then you need to turn on the Geometry mode checkbox in the Particle Shader nodes for the foam and splashes. Then just add the Velocity render element and render. You can find more about the Geometry mode here - https://docs.chaosgroup.com/display/...er+%7C+PHXFoam

Cheers!

[haarlem]

Hi Georgi,

Thank you for the answer,

I did export the Age channel in the Foam output rollout, that is why I am a bit confused why the particles seem to be killed when hitting the boundaries of the simulator.

About the rising speed, that is a good tip. I thought underwater bubbles burst when they go above the water surface.

In the liquid lifecycle it says that High liquid acceleration (which is related to foam threshold parameter) generates foam. But if the foam amount is set to 0, then my foam is being generated only from the splashes hitting the liquid. Do I understand this correctly?

Yes, I have seen how the mesh is generated in ocean mode, from the camera view (clever trick btw), but it takes really long time, if I set the resolution to 2000 px height for example it becomes almost un-renderable.

Thanks for the tip with the geometry mode-motion blur workflow. And I have one more question:

How is this as a workflow? I would like to have the foam and splashes on a separate layer in my compositing application. So I was thinking to render the ship with the water(hide the splash/)foam particles as one sequence(but I will miss the foam reflection in the hull). Then set the Pheonix FD simulator not visible to the camera, apply a basic reflective material on the ship for faster rendering (so I get reflection of the splash and foam in the hull)-> Render this as a second sequence. Thus, I will have control on the foam reflection on the ship and on the foam on water where for example I could feather-mask some of the particles out.

I will send the scene shortly to support@chaosgroup.com.
Thanks Marcel

[georgi.zhekov]

Hey,

I'm really sorry - I have misled you about the foam age. The Max outside age specifies the total age of the particles.This is not the time since the particle exited the grid, but the time since the particle was born. We have updated our docs page so it should be more clear now.
So if you increase the Max Outside age the particles won't die so soon.

Yes, if you set the Foam amount to 0 in the rollout and in the Splash options you have enabled Foam on hit - the foam will be born only from the splashes.

You ocean mesh takes a lot of generation time because of the Off-screen Margin option. The value is a percentage of the image size and the 75% that you use is quite a lot.

My suggestion is to dial this down unless you really need it. This will bring down the ocean generation time and the RAM consumption.

The rendering part sounds good, though what you can do is to add the V-Ray Atmosphere render element - this will contain the foam,splashes and mist (note that if you use Environment fog for example, it will be present in the Atmosphere render element as well). This way you will have all of the reflections and the foam and splashes as a separate pass, without having to render twice. Then in compositing you can subtract the Atmosphere pass and you will get only the ship and the liquid.

Cheers,

[haarlem]

HI Georgi,

Thank you for the reply. I finally understand the "Max outside age" parameter, I'm glad it is correctly explained now in the documents.
Indeed I have used a higher off-screen margin value because I was getting weird shadows from the plane being cutoff, thus I assume I need to find a proper balance for this value.

I'll send you the simulation through Wetransfer. I have tried adding the V-ray Atmosphere element but it renders fully black. Are there any extra steps I need to take?

Also, I am not very happy with the AFT part of the ship particle simulation. I want them to be bigger but I don't want to affect the overall ones using the size parameter from the PhoenixFX shader.
So I was thinking of the following approach:

- Use particle tuner -> Make a box on the AFT part of the ship where the propellers are. (uncheck solid object from phoenix properties so the simulation ignores it).
Set the particle tuner to affect the particles only inside the box AND which have the age less than 0.1 seconds so that the rest of the particles that are born on other areas of the ship and intersect the box are not affected,
but only the ones being generated by the propellers and AFT area of the ship.

Thanks,
Marcel

[georgi.zhekov]

Yes, you will need to find out the right value for the Off screen margin. Start low and increase it gradually

For the Atmosphere element - if your Particle shader is in Geometry mode then the pass will be empty. But if you need to use Geometry mode, you can add a Multimatte render element, then from the Object Properties of the Particle shader assign an ID in the G-buffer section - if you have a few different particle shaders, you can assign different IDs - this way you can get a selection mask of your foam and splashes and use that in the compositng part. You can find more about the Multimatte pass here - https://docs.chaosgroup.com/display/...tiMatteElement

The Particle Tuner is a great idea. Test it and let us know how it goes.