Particles follow fluid

[jonnybefree]

hi there,
merry belated x-max first of all.
I do need to simulate a thin liquid covering different sorts of geometry, with lots of particles following the movement.
Now i wonder how to do that..
when i simulate the liquid with velocity grid channel output, and try to add the particles in PF, i need to place the emitter somewhere near the liquid to be part of the fluid. But with multiple fluid emitters its kind of hard.. with phoenix birth operator nothing happens to me.. also its damn slow even with low partilce count. Could someone share a light whats the best workflow for it maybe?
Even i wonder what about the Particles in the Phoenix source? i've found barely information about it, it sounds like this is maybe the way i need to go though..

would appreciate any hints on it!

thanks and best regards

Jonas

[Svetlin.Nikolov]

Hey,

Try a latest nightly regarding the pflow operator speed - I did some changes to the pflow operators, so now you can speed them up by caching some Phoenix frames - you can find that option in the Preferences dialogue

With the birth operator and liquids you need to output the Grid Liquid channel, set the pflow birth channel to Temperature (it's aliased with the Liquid channel since liquid sims don't have temperature and fire sims don't have liquid), and keep in mind that the range of this channel is 0-1 when adjusting the curve.

The Particles in the source are... just particles born by the source - you can emit drag, foam or splash particles by the source the same way you emit smoke, temperature and liquid.

I think you could use a birth operator + a force operator to make the particles look liquid-like, but if they are born all the time, they also need to be deleted by some conditions. Does the geometry need to be covered by liquid at all times, or it's okay for some parts of the geometry to be uncovered from time to time? Would the liquid be born by external sources, or should it be born from the geometry itself?

Cheers!

[jonnybefree]

hey svetlin,
thanks for your reply.
would it be possible to do this non public due to nda? I allready wrote an email to support yesterday, if this is the way to go. ticket number 079-668-340

[Svetlin.Nikolov]

Affirmative, Support should handle anything under NDA. Because of the holidays it might take some time though since many people are away.

Let me try to set it up for a simple scene. Not sure if fluids would be the best approach to such setup though - maybe a pure particle solution would work better.

[jonnybefree]

thanks a lot svetlin! looking forward to the scene.

[Svetlin.Nikolov]

Hey, so something I've been experimenting with is a solid geometry surface with a liquid source in brush mode on top of it; a Body Force placed underneath the surface attracts the liquid and makes it spread and cover the geometry.

Still, there are some specifics - if the front of the liquid grows, the source won't be able to feed in enough liquid and the liquid will spit into several streams. If you use more surface tension, this effect would be multiplied additionally.

Another thing is that if the liquid should stick to the geometry and form a thin layer, it must not have any viscosity, and also the body force geometry must be way below the liquid surface in the direction of movement and not too far to the side, or the liquid particles would start flying off from the surface. Also, since the sim progresses quite slowly, I used just 1 step per frame and also added some mesh smoothing using the liquid particles.

If anyone else knows a clever way to get such an effect, please do shader Also, not sure if this is the dynamic you are looking for.

[jonnybefree]

hey, happy new year!
thats an interesting approach, will give this a try, thanks for that! I got more headaches about the particles wich have to follow the liquid though.. they have to be quite a lot for having the desired result. thought about using foam for it maybe. but since they have to be present right from the start, and should not die, or emitt by collision neither i'm not sure it will work.. havn't try'd it yet though.

[JuhaHo]

Borrowing this topic,

I have similar project going on. Is there any screenshot on sample set ups on how to use Phoenix operators with PFlow? The desired liquid results were quite easily achieved after, but now I'm struggling with the particle part. The desired effect would be screening the particles out of the dirty liquid. I have created three simulations: one for dirty and two clean liquids and they all look nice. Due to NDA, I cannot attach any screenshots.

As a side path, I also have other minor issue on this. How to visualize moving liquid, once the system is full? When it fills up, the liquid/air boundary is visible, but after the system is filled nothing seems to be moving. In reality, there'a a lot going on in the simulation.

[georgi.zhekov]

Hey,

You can check how to emit Pflow particles using Phoenix in the attached scene.

A few important things to note here - in order to spawn particles based on the liquid you need to use the "Temperature" channel in the PhoenixBirth operator and set it's range to be from 0 to 1 as this is the range for Liquids.
Unfortunately our Pflow operators need a bit of improvement but I hope we will get there at some point.

As for the visualizing the moving liquid - if you mean inspecting the simulation in the viewport - there is a "Draw just a Slice" option in the Preview rollout which lets you visualize only the particles along a single axis. This way it should be easier to find out what is going on inside of the filled simulator.
If you mean the rendering - just assigning a refractive material should do the job.

[JuhaHo]

Thanks,

I'm now investigating the settings on the sample scene and will soon be able to do some tests with my scene.

As moving liquid visualization, I meant rendering. On closed systems with rapidly moving water for instance, I cannot see any movement even if I leave one boundary open to be able to create continuous flow. Once it gets full, noting seems to be moving. It is moving, but there's nothing that shows the movement. It needs to have some impurities, so it would not be homogeneous. The impurities should move along the water to make impression of moving water.

[JuhaHo]

OK,

I managed to generate the particles with the Phoenix birth operator. Their birth is following the my Phoenix sim, but they are sent outwards the liquid mesh normals. I want to keep them inside the liquid - not outside. Any ideas on that. Deflector operators didn't change a thing.

[georgi.zhekov]

Well you have two options then - if you count on using pflow you can reduce the isosurface level of the Phoenix liquid from the render options and this will expand the mesh.
The other option is to use foam particles instead of the pflow ones. Just in the Liquid source turn on the particles checkbox and set the type to Foam. Then from the simulator options enable the Foam and set the Amount to 0 (this way only the source will spawn foam). Then set the rising and falling speed of the foam to 0 and the foam particles will stay inside of the liquid.

[Svetlin.Nikolov]

Also, you can pick the actual liquid particles in a particle shader and lower the count multiplier a lot - 0.05 - 0.01 or even less

[JuhaHo]

Thanks,

Changing the Isosurface level did not change anything on PFlow particles behavior. I would like to use the PFlow option, so I could use same particles with all particle systems on the scene.

Other ways, Phoenix birth works fine, but it should send the particles into the liquid - not outwards.

[JuhaHo]

This is the result I got so far.Most, if not all of the particles are outside of the desired volume.