Realflow C4D 2.0.1. Animating a glass pouring water

[Luke Doyle]

Hi there,

I'm using Real flow for c4d 2.0.1. I have a simple scene setup, the emitter spawns particles into a beaker, rests and then rotates to pour a water base liquid. I originally set this scene up with the beaker modelled to scale at about 7.5cm high and 4.cm in diameter. I found that the RF fluids didn't appear to flow correctly in this scale, am I right in thinking that RF in C4D is less accurate at this scale? I then increased everything to about 10x the original scale (82cm tall) and the fluid is behaving a lot more natural, albeit a little more like an ocean. Because of this increase in scale do I need to compensate by increasing the gravity for example so that it behaves like water in a normal sized beaker?

These are my settings for the fluid.

Liquid SPH
Resolution - 50
Density - 1000
Internal - 1
External - 1
Surface tension - 0
Viscosity - 3
Gravity - 981
I have a K -speed daemon with a spherical fall off at the start the back of the beaker which is intended to help limit the particles sloshing.

Solver
Use geometry velocity - yes
min sub steps 5
Max sub steps 300
min iterations 1
max iterations 1
Accuracy 0
I have increased the substeps to help combat the problem outlined below but it didn't change

RF Volume Tag
Cell size 0.8
Surface Offset 0.5

The simulation with the above settings play out fine, as the beaker rotates the surface of the water stays pretty flat, the rest of the form is consistent and it pours fairly well, however there are only 740 particles so there isn't enough detail. To improve this I've increased the resolution, however when I do this the simulation starts to break down. The surface begins to slosh violently and the once smooth form around the base and sides is now broken and bumpy. I thought at first the bumpy base was due to thin colliding walls so in the duplicate colliding geometry I've increased the thickness, it helped but the problem still persists.

I was wondering is there a way to maintain the initial form of the low res setup while maintaining the level of detail when the resolution is increased to 600-1000?

Also please note that this is just the initial test, the beaker in the final scene will need to move into the shot, naturally being poured buy a hand. I understand that simulations vary from different setups, but It would be go to get a solid understating of this to be able to apply it to any movement.

Finally any advice and typical practices when creating a scene like this in RF for cinema would be great?

I've attached a couple of images illustrating the problems.

Thank you for your time.

[Thomas Schlick]

Scale does indeed affect a simulation and when you change it, then it's also a good idea to change the forces' scales accordingly as well. Besides that I avoid to comment on scale, because it became an almost "religious" discussion. Some say you should always work at real world scales and dimensions, others say it doesn't matter as long as things look good and plausible.

am I right in thinking that RF in C4D is less accurate at this scale?

When you work at small scales you always have to bump up resolution to get enough particles, and this is exactly what you've seen. But, when particles are super close (resolution also defines a particle's radius) you might see unwanted effects. These effects have to be compensated through internal and external pressure.

The interaction with the object/beaker is another thing. There's an issue with fluid-object interaction in Dyverso and I also see these instabilities and explosions from time to time, I couldn't find a common method to get rid of them and I only have a guess what might be the cause. It seems it has something to do with the solver's boundary conditions. They're physcially difficult to handle and often introduce additional velocity. Since it's a rather common thing I'll try to find out more.

And finally, when you animate the poring effect you will have to increase substeps to make things water tight. Depending on the shape of your glass (hard edges, sharp edges) it even might happen that the creation of the collision geometry is not accurate enough to make things water tight at all. When you animate the glass try to avoid fast accelerations and sudden motions. Keep the animation as smooth as possible: fast particles are the #1 reason for particles going through an object. But you have relatively high tag settings (surface offset = 0.5) and you work with SPH. That's a good premise for a working simulation.