Creating particles inside the PhoenixFD liquid

[JuhaHo]

I need sometimes to place a particle system inside the PhoenixFD liquid simulation. The PFlow operator creates the particles outside the surface (or onto surface). Particles are then penetrating through the liquid container walls. I also tried the TyFlow Birth Voxels and Birth flow, but could not set an operator for moving the particles with the liquid as desired. Has anyone succeeded?

The goal is to feed liquid with particles into container, where the particles are kept inside the liquid (some of them can be floating). They should also be following the liquid. So far I got best results by using the Multiscatter. However instead of moving, the particles are born frame by frame, which gives nice still renderings but those are flickering in animations.

[georgi.zhekov]

Hey,

Here is a sample scene how you can create tyFlow particles and make them move with the Phoenix liquid particles. It is saved for Max 2019, let me know if you need it downsaved for an older version.
The particles are created via the Birth Fluid operator and then using the Fluid force operator you can make them move with the liquid.

Cheers!

[JuhaHo]

Thanks Georgi,

My first tests with the actual PhoenixFD simulation looks promising. What I didn't have in my earlier tests, is the Delete event. I wonder what is the purpose for that.

[georgi.zhekov]

The Delete operator in this case will delete the tyflow particles that go outside of the grid.

[JuhaHo]

I've been playing a bit. Maybe I have a wrong approach, but the particles are not staying inside the liquid.

[georgi.zhekov]

Without the scene or a video it is difficult to say what is going on. Can you share the scene so that we can check it out?

[JuhaHo]

Thanks Georgi,

I don't know yet, if the scene is shareable. However here's the screenshot of my latest set up. I replaced the Birth Fluid operator with Birth surface operator, where I use the same emitter geometry, that PhoenixFD is using (see the outlined selected objects). I also created a collision operator to keep the particles inside the container. Therefore the delete Event isn't needed anymore.

However the particles are still leaving the fluid. All of those should be inside the fluid - not in free air.

[JuhaHo]

Here's my latest. I split the formation of particles half. Between frames 0 - 500 they are born in the liquid already in the container and from that point on they are generated at the top emitter. The latter particles are deleted after 500 frames since there are particles in the liquid. I'm still looking a way for keeping them inside the liquid - not in free air. And yes, they are clearly affected by the liquid.

[JuhaHo]

Here's another pair of screenshots. It seems that the particles coming from Birth surface emitters are concentrated to face edges of the collision surface. I wonder what is causing this.

[georgi.zhekov]

I'm afraid I don't have an idea what is causing this. Since this is tyFlow territory may be the guys over at the tyFlow facebook group or the tyFlow forums may help.

[JuhaHo]

I think it was additional emitter on top (the brown particles), that caused the unwanted behavior. So I concentrated on creating particles with the Birth fluid operator. It looks much better, but I have way too few particles. However the particle cache on disk is already more than 80 GB. What would be the preferred Export type? At the moment I'm using the default tyCache. Should I try using VRay Proxy as Export type.

[JuhaHo]

Here's the latest development. To solve the issue of keeping the particles inside the fluid, I changed the grid velocity magnitude settings from the default Blend to Replace and Influence from the default 100% to 200%.

The latest cache file is more than 160 GB, but there's still too few particles in some areas and maybe too much in some other areas. On the screenshot, there's only about 15% of the whole system covered. However this is the area, where the particle coverage should be most dense. Are there any tyFlow operators that would concentrate the particles to some areas while reducing the density on other areas?

[georgi.zhekov]

You can use the thresholds in the Birth fluid operator to spawn particles only at certain points. You can find more about them here - https://docs.tyflow.com/tyflow_parti...s/birth_fluid/
Another option would be to use the Surface test and split the particles based on a certain property and delete some of them. You can find more about the Surface test here - https://docs.tyflow.com/tyflow_parti.../surface_test/

[JuhaHo]

Thanks Georgi,

My workaround was animating the input particle value. That reduced the cache from 160 GB to 60 GB and yet there seems to be more particles in the renderings.

[JuhaHo]

This is more like very basic rendering question, but I'll use this topic. Here's a rendering with fluid and particles. I have used vertex colors for defining fluid colors for PhoenixFDTexmap. There's a little blue tint on the fresh chemical and brownish for the dirty chemical. I wonder what would be the way to use the same map for reflection&refraction channels. Anyway it cannot be used as it is. Is there any filter to tell VRay that blueish should be more transparent than brownish. It's not shown here, but there's also red liquid for demonstrating the heat and that should be almost opaque.