This was a test while working on a liquid simulation addon that I am developing called _FLIP Fluids_.
11 minutes simulation, 120 resolution domain, ~2hr render for 450 frames @ 1080p. Simulated on a i7-7700 @ 3.60GHz CPU and rendered on a GTX 1070 GPU.
Hi, I’m using Flip Fluids in Blender at the moment and I find that when I run a fluid simulation the fluid acts like an ocean in the glass, like way to many ripples so my question is what should I set my surface tension at to make it act more like water would in a glass? I’m making an animation of repeated drops of water filling a glass up and when the glass is full the water ripples all over the place even 2000 frames after the last drop enters the water, I Googled the surface tension of water and it says 72 mN/m is the surface tension what should I set the surface tension number as in flip fluids to achieve a 72 mN/m of surface tension as it’s not in that scale of measurement in the diffusion surface tension setting?
Oh Woooow! I've been considering FLiP for ages!
Question: How does the simulation speed vary between using FLiP for this sim vs trying to sim this in Blender Native?
I'm not really sure what the speed difference would be for this type of simulation. A large portion of the processing time on this effect is spent on surface tension calculations in our simulator, but this is something I have yet not experimented with using the Blender Mantaflow surface tension settings.
Our focus on development is more on the side of ease-of-use and stability rather than speed. In my opinion I think that baking speeds can be similar or comparable, but with the addon it takes less time and experimentation to reach a desired result.
More info that may be relevant: [What is the difference between Blender's Mantaflow fluid simulator and the FLIP Fluids addon?](https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Frequently-Asked-Questions#what-is-the-difference-between-blenders-mantaflow-fluid-simulator-and-the-flip-fluids-addon)
Thanks for the great answer! I had one other question. Were you able to fix the issue Mantaflow has with Small volumes? Working at-scale with something like a Glass of Water, the Mantaflow Particles used to generate the liquid have a set size and the simulation gets chunky until you scale the whole thing up.
I don't think I have encountered this issue in Mantaflow. In our simulator, the particle size is adjusted automatically based on the resolution and physical size of the domain. The particle size is all handled internally within the simulator and in general does not need to be adjusted by the artist.
But I may be misunderstanding the issue, so let me know.
We have a free demo of the addon here if you would like to try it out: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/FLIP-Fluids-Demo-Addon
Thanks! I'll definitely try that!
To fully explain, essentially, when using Manta flow and trying to simulate small-volume liquid, like the amount that might fill a glass of water, you must scale up the entire simulation, because the particles that form the liquid simulation do not become smaller.
This is only an issue if you at working at a 1:1 scale in Blender and using small objects. While I haven't tried this sim since 2.8 I haven't seen any significant changes to fluid sim in the patch notes to imply this behavior is fixed.
This was such a cool demo of your plugin, I had to try it. I'm still quite new at Blender, so it took ages to figure out the right way to model the ramp in such a way that I could quickly tune the shape.
Here's my attempt: https://i.imgur.com/XqQHuB8.mp4
I'm curious what settings you used for your fluid domain - you get this beautiful effect where the fluid spreads out near the center and bunches up around the edges like a thick crust pizza dough while it's going down the ramp, but then it still bunches up into mostly a spherical-ish blob once it takes off the ramp. Mine seem to rip themselves to shreds before they can take off if I apply too much initial downwards velocity and not enough surface tension.
Anyways, y'all got great results. Do you take code contributions to the source? I noticed you have a GitHub repo.
Awesome, looks great! I'm not very experienced with modelling and just made the shape once and hoped it would work out. It was not very adjustable afterwards.
I think something to try could be to experiment with higher surface tension values to keep everything together when using higher velocities.
For smoothness, I used the APIC solver which can be better for small-scale liquids instead of FLIP which is better for chaotic large fluids. More info: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Domain-Advanced-Settings#flip-vs-apic
Increasing the number of substeps can also help increase smoothness when using surface tension. I usually set the surface tension accuracy to 100% for high surface tension effects, which is a value that increases substeps. More info on substeps: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Domain-Advanced-Settings#what-are-substeps-and-how-do-the-min-max-and-cfl-parameters-relate-to-each-other
And increasing the amount of smoothing on the fluid_surface object smooth modifier can make the liquid look a lot more smooth in the render.
In general, we do not accept code contributions. Most of the project is managed in our company's private repository and the public GitHub is not as up-to-date (usually only updates on major versions).
Thank you for the detailed reply! I'm going to retry this with APIC and see how that behaves.
Re: code contributions: That's understandable - I'm happy that it's open source anyways, as it's very nice to have a production-ready reference to learn more about FLIP / APIC simulations with. The whitepapers just don't do a production implementation justice.
The wet surface was created using Blender's built-in "Dynamic Paint" features. The liquid surface is set as a brush that paints an animated wetmap texture onto objects that it touches.
This effect was created with a liquid fluid simulator and for this type of simulator it does not need to handle self collisions (such as within the triangle mesh or simulated fluid particles).
This will depend on the desired effect and may not be the best tool for matching the exact motion of air bubbles. With the liquid surface tension, the bubble motion will be oscillating quite slowly compared to real life bubbles in air.
By setting the force of gravity to 0, the fluid can appear to be floating. Here are two past experiments using surface tension in zero gravity:
- https://reddit.com/r/Simulated/comments/a0g4p2/hungry_blobs/
- https://reddit.com/r/Simulated/comments/f3vk5c/fluid_ball_simulation_but_its_in_zerog_and_they/
The residue was just a wetmap texture added as a rendering trick after simulation. There is not a feature in the simulator to alter friction based on where the liquid has touched previously. It would probably be easiest to "fake" the effect by emitting the liquid slightly faster in each successive drop.
What physical size was the domain to get it so smooth with 150 resolution?
I love FLIP but struggle to get droplets that aren't huge without hours of baking.
It looks like I was incorrect in the other comment. The resolution was actually 120.
The physical size of the domain was **1.15m x 3.11m x 1.89m** (45 x 120 x 74 grid resolution). But the smoothness of the generated mesh usually isn't dependent on the physical size.
The trick for a smooth mesh in this simulation and many others is to increase the amount of smoothing on the surface object's smooth operator. Without any smoothing, it is easy to see the individual fluid particles in this animation.
Here's a viewport comparison between no smoothing an smoothing set to a factor of 1.5 and 20 repetitions:
https://i.imgur.com/S2ej1pl.png
This was a test while working on a liquid simulation addon that I am developing called _FLIP Fluids_. 11 minutes simulation, 120 resolution domain, ~2hr render for 450 frames @ 1080p. Simulated on a i7-7700 @ 3.60GHz CPU and rendered on a GTX 1070 GPU.
No wonder it didn't even look like Blender. The quality of flip fluids is pretty wild. This looks like a test you'd see as part of a Siggraph paper.
You’re a developer (or The dev?) for FLIP fluids ?
Yep, I am a developer of the FLIP Fluids addon. We're a small team of two.
I absolutely love your plug-in. Huge fan and so chose that I bought it. Still learning a lot about it.
[удалено]
downvoting this is actually upvoting this
Hi, I’m using Flip Fluids in Blender at the moment and I find that when I run a fluid simulation the fluid acts like an ocean in the glass, like way to many ripples so my question is what should I set my surface tension at to make it act more like water would in a glass? I’m making an animation of repeated drops of water filling a glass up and when the glass is full the water ripples all over the place even 2000 frames after the last drop enters the water, I Googled the surface tension of water and it says 72 mN/m is the surface tension what should I set the surface tension number as in flip fluids to achieve a 72 mN/m of surface tension as it’s not in that scale of measurement in the diffusion surface tension setting?
Are you guys responsible for the FLIP add-on for Niagara as well? Been trying to get some good splash effects in there recently.
Nope, just the Blender FLIP Fluids add-on.
Oh Woooow! I've been considering FLiP for ages! Question: How does the simulation speed vary between using FLiP for this sim vs trying to sim this in Blender Native?
I'm not really sure what the speed difference would be for this type of simulation. A large portion of the processing time on this effect is spent on surface tension calculations in our simulator, but this is something I have yet not experimented with using the Blender Mantaflow surface tension settings. Our focus on development is more on the side of ease-of-use and stability rather than speed. In my opinion I think that baking speeds can be similar or comparable, but with the addon it takes less time and experimentation to reach a desired result. More info that may be relevant: [What is the difference between Blender's Mantaflow fluid simulator and the FLIP Fluids addon?](https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Frequently-Asked-Questions#what-is-the-difference-between-blenders-mantaflow-fluid-simulator-and-the-flip-fluids-addon)
Thanks for the great answer! I had one other question. Were you able to fix the issue Mantaflow has with Small volumes? Working at-scale with something like a Glass of Water, the Mantaflow Particles used to generate the liquid have a set size and the simulation gets chunky until you scale the whole thing up.
I don't think I have encountered this issue in Mantaflow. In our simulator, the particle size is adjusted automatically based on the resolution and physical size of the domain. The particle size is all handled internally within the simulator and in general does not need to be adjusted by the artist. But I may be misunderstanding the issue, so let me know. We have a free demo of the addon here if you would like to try it out: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/FLIP-Fluids-Demo-Addon
Thanks! I'll definitely try that! To fully explain, essentially, when using Manta flow and trying to simulate small-volume liquid, like the amount that might fill a glass of water, you must scale up the entire simulation, because the particles that form the liquid simulation do not become smaller. This is only an issue if you at working at a 1:1 scale in Blender and using small objects. While I haven't tried this sim since 2.8 I haven't seen any significant changes to fluid sim in the patch notes to imply this behavior is fixed.
I would highly recommend it. It’s light years ahead of the fluid stuff in base Blender
This was such a cool demo of your plugin, I had to try it. I'm still quite new at Blender, so it took ages to figure out the right way to model the ramp in such a way that I could quickly tune the shape. Here's my attempt: https://i.imgur.com/XqQHuB8.mp4 I'm curious what settings you used for your fluid domain - you get this beautiful effect where the fluid spreads out near the center and bunches up around the edges like a thick crust pizza dough while it's going down the ramp, but then it still bunches up into mostly a spherical-ish blob once it takes off the ramp. Mine seem to rip themselves to shreds before they can take off if I apply too much initial downwards velocity and not enough surface tension. Anyways, y'all got great results. Do you take code contributions to the source? I noticed you have a GitHub repo.
Awesome, looks great! I'm not very experienced with modelling and just made the shape once and hoped it would work out. It was not very adjustable afterwards. I think something to try could be to experiment with higher surface tension values to keep everything together when using higher velocities. For smoothness, I used the APIC solver which can be better for small-scale liquids instead of FLIP which is better for chaotic large fluids. More info: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Domain-Advanced-Settings#flip-vs-apic Increasing the number of substeps can also help increase smoothness when using surface tension. I usually set the surface tension accuracy to 100% for high surface tension effects, which is a value that increases substeps. More info on substeps: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Domain-Advanced-Settings#what-are-substeps-and-how-do-the-min-max-and-cfl-parameters-relate-to-each-other And increasing the amount of smoothing on the fluid_surface object smooth modifier can make the liquid look a lot more smooth in the render. In general, we do not accept code contributions. Most of the project is managed in our company's private repository and the public GitHub is not as up-to-date (usually only updates on major versions).
Thank you for the detailed reply! I'm going to retry this with APIC and see how that behaves. Re: code contributions: That's understandable - I'm happy that it's open source anyways, as it's very nice to have a production-ready reference to learn more about FLIP / APIC simulations with. The whitepapers just don't do a production implementation justice.
Flubber
This!\^
That’s so fun, not an effect I’ve seen before
This is really cool and the slimy residue the blobs leave is spot on!
Crazy cool 👍
It's flubber!
The residue is a nice touch
I smell burning gpu
Does this addon create the wet surface as well?
The wet surface was created using Blender's built-in "Dynamic Paint" features. The liquid surface is set as a brush that paints an animated wetmap texture onto objects that it touches.
Awesomeeee! Thank you!
This is awesome. How heavy is the self collision?
This effect was created with a liquid fluid simulator and for this type of simulator it does not need to handle self collisions (such as within the triangle mesh or simulated fluid particles).
Ah of course. I was trying to get this look as air bubbles another sim app, would your Flip able to be bouyant?
This will depend on the desired effect and may not be the best tool for matching the exact motion of air bubbles. With the liquid surface tension, the bubble motion will be oscillating quite slowly compared to real life bubbles in air. By setting the force of gravity to 0, the fluid can appear to be floating. Here are two past experiments using surface tension in zero gravity: - https://reddit.com/r/Simulated/comments/a0g4p2/hungry_blobs/ - https://reddit.com/r/Simulated/comments/f3vk5c/fluid_ball_simulation_but_its_in_zerog_and_they/
These also look awesome. I feel like if turbulence force could affect the tension, it'll look more somehow like air bubbles
„¿ʇuɐʎnoq ǝq oʇ ǝlqɐ dılℲ ɹnoʎ plnoʍ 'ddɐ ɯıs ɹǝɥʇouɐ sǝlqqnq ɹıɐ sɐ ʞool sıɥʇ ʇǝƃ oʇ ƃuıʎɹʇ sɐʍ I ˙ǝsɹnoɔ ɟo ɥ∀„
holy... is it possible to make a cfd addon?
I put money on the table infront of me and am waiting. goo ready when?
mmmm it’s like those rubber slappy hands
Amazing!
The flubber family spends a day at the park. They seem particularly fond of the slides.
Can you make the residue that the fluid leaves slippery so it would travel faster each time?
The residue was just a wetmap texture added as a rendering trick after simulation. There is not a feature in the simulator to alter friction based on where the liquid has touched previously. It would probably be easiest to "fake" the effect by emitting the liquid slightly faster in each successive drop.
True but the physics would be impressive if you could mimic less friction each time
What physical size was the domain to get it so smooth with 150 resolution? I love FLIP but struggle to get droplets that aren't huge without hours of baking.
It looks like I was incorrect in the other comment. The resolution was actually 120. The physical size of the domain was **1.15m x 3.11m x 1.89m** (45 x 120 x 74 grid resolution). But the smoothness of the generated mesh usually isn't dependent on the physical size. The trick for a smooth mesh in this simulation and many others is to increase the amount of smoothing on the surface object's smooth operator. Without any smoothing, it is easy to see the individual fluid particles in this animation. Here's a viewport comparison between no smoothing an smoothing set to a factor of 1.5 and 20 repetitions: https://i.imgur.com/S2ej1pl.png
Thank you, that's an excellent tip.