How to add a thin layer of fluid (as paint)


I want to pour paint (as in opaque liquid) over a humanoid model. The humanoid is not important here and will not be visible at render. The main issue is that the layer of liquid is still far too thick at “400 resolution.” That sounds like a lot to me already. Is it normal to just use higher resolutions or is there a trick that can be used?

Fluids are not really my strongsuit, so any suggestion is welcome.

Blender 2.8
using fluid physics
no obstacle proxy - just the actual model you see.

i7 MX type, Quadro K2100 (2GB VRAM), 32GB RAM - if any of you technical types have ideas about forcing my system to use more than 30% cpu for calculating fluid, or any other workflow-related suggestions.

Thanks in advance.

Well, I would say that, yes if you want a thin layer you would need quite high resolution, but that just a “need”, it does not mean that the fluid will become less thick if you increase the resolution, because then there is the Viscosity Param to set for this !

Think about real life : Resolution is molecular (almost “infinite” compared to Blender) but then, Between molten chocolate, paint, water, and oil, each will have a different thickness based on viscosity :stuck_out_tongue:

See you :slight_smile: ++

Did you already look at Dynamic Paint? Not perfect, as you e.g. cannot make fluid drip through space, and flowing against gravity is not handled particularly physically correct, but it is very fast to bake, and maybe it suffices.

Particles can also ‘flow’ and drip nicely. As far as I know, some people also manage to render these looking like fluid, but currently I don’t know how.

I have, briefly. But aside from not knowing how any of that works the whole dripping and drooping thing is kind of a feature I’m going for.

But I might consider this if nothing else works. Do you think dynamic paint could be made to look like it has some depth? For example have it curve at the edges, like you see with surface tension? Making a normal map could do this I guess, but I don’t see a clear cut way for making it believable in this way.

@tricotou - I admit I haven’t looked into viscosity. Will try that now.

Giving depth, yes, sure, as you say with a bump map, or also with true displacement.

But your suspicion that it might look poor might not be wrong. Optimal it is certainly not.

Looking again at your image, and doing a rough calculation, I would assume that the reason for the thick drops is not mesh resolution but lack of adhesion. (The image is from the 400 resolution sim, yes?) Unfortunately current Blender fluid sim doesn’t have adhesion.

The Flip Fluid addon has, though (the free version, too). And I believe Mantaflow, also (which available in a separate branch of Blender). I’ve already seen pretty nice thin sheets with Flip Fluid, being no more than 3-4 sim cells in thickness). If you can run that with 400 resolution, too, you could get a sheet <1mm, which should be good enough, I guess.

Sizing your domain so that it fits tightly around your fluid effect will concentrate grid resolution (smaller grid cells) which can help create thinner sheets. This documentation topic is for the FLIP Fluids addon, but some of the info still applies to other grid-based simulation systems such as the default Elbeem fluid simulator:

For a reference, here is a dripping wax simulation over a face in the FLIP Fluids addon then uses surface tension (adhesion) and viscosity at 350 resolution:

The documentation is actually really helpful, thanks!

Hey, I’ve run into a curious problem.

The fluid simulation stopped running at one point and I’ve no idea why. Making another scene in a different file works normally, but pressing the bake button in the concurrent work file just runs through the frames as if no obstacle or fluid is calculated… nor is there any fluid in the domain later.

The file (minus some unnecessary things).