Next Generation Fluid Simulations with Mantaflow

It's about time that Blender gets an updated fluid simulator. Good that Mantaflow is around the corner!

Mantaflow is a fluid simulation framework from research. It's currently being developed at the Technical University of Munich under the supervision of Nils Thuerey - the creator of Blenders current fluid simulator. And although it's primarily used in research it turns out to be a great addition for Blender too!

In this talk you will first learn how a research-oriented framework like Mantaflow technically fits into Blender. The main part of this talk will then focus on the current state of Mantaflow in Blender: We will explore mesh- and particle-based liquid simulations, see examples of novel research finding practical application, take a look at results from Google Summer of Code fluid projects, and compare the new with the current fluid implementation. In a final outlook, you will find out what to expect for Blender 2.8.

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The links to the papers (slides 4-6) are barely readable on the slides. Here they are again:

Narrow Band FLIP for Liquid Simulations:
https://wwwcg.in.tum.de/research/research/publications/2016/narrow-band-flip-for-liquid-simulations.html

Primal-Dual Optimization for Fluids:
https://ge.in.tum.de/publications/2017-cgf-eckert/

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A video of this talk can be found here:
https://www.youtube.com/watch?v=h9TViIgm8Yc

Transcript

1. N E X T G E N E R AT I O N F L U I D S I M U L AT I O N S W I T H M A N TA F L O W B L E N D E R C O N F E R E N C E 2 0 1 7 - S E B A S T I Á N B A R S C H K I S
2. T E S T S C E N E N O . 1 ( 2 0 1 5 ) H O W I T A L L S TA R T E D …
3. B L E N D E R M A N TA F L O W I N T E G R AT I O N T H E S T O RY S O FA R … • 2014: Kickoff, Smoke, Python API • 2015: Fire, High-res smoke (Wavelets) • 2016: Liquids (NB-FLIP), Unified cache & solver • 2017: Particles (FLIP + secondary), Fluid guiding Google Summer of Code Blender 2.8 / 40 3 https://summerofcode.withgoogle.com/ http://mantaflow.com/ https://www.tum.de/
4. R E S E A R C H AT T U M - T H U E R E Y G R O U P T H E S T O RY S O FA R … Narrow Band FLIP for Liquid Simulations F. Ferstl, R. Ando, C. Wojtan, R. Westermann, N.Thuerey Primal-Dual Optimization for Fluids T. Inglis, M.-L. Eckert, J. Gregson, N. Thuerey / 40 4 https://wwwcg.in.tum.de/research/research/publications/2016/narrow-band-flip-for-liquid-simulations.html https://ge.in.tum.de/publications/2017-cgf-eckert/
5. R E S E A R C H AT T U M - T H U E R E Y G R O U P T H E S T O RY S O FA R … Narrow Band FLIP for Liquid Simulations F. Ferstl, R. Ando, C. Wojtan, R. Westermann, N.Thuerey NB-FLIP ON 64x64x64 grid 104.604 particles NB-FLIP OFF 64x64x64 grid 682.822 particles Particles (FLIP) only at surface! + Save memory + Save computation time / 40 5 https://wwwcg.in.tum.de/research/research/publications/2016/narrow-band-flip-for-liquid-simulations.html
6. R E S E A R C H AT T U M - T H U E R E Y G R O U P T H E S T O RY S O FA R … Primal-Dual Optimization for Fluids T. Inglis, M.-L. Eckert, J. Gregson, N. Thuerey 64x64 grid, blur radius = 2 Target velocity field constrains flow velocity! + Avoids artificial viscosity (force-based methods) + Fictitious but plausible motion / 40 6 https://ge.in.tum.de/publications/2017-cgf-eckert/
7. D E V E L O P E R S P E R S P E C T I V E M A N TA F L O W ( S TA N D A L O N E ) Mantaflow C++ solver core C++ Plugins (e.g. Guiding, Wavelets, Fire) Python scene definition 2D slice view in Mantaflow GUI / 40 7
8. D E V E L O P E R S P E R S P E C T I V E A N AT O M Y O F M A N TA S C R I P T Basic Mantaflow Python Script Solver object setup • Domain size • Timestep • 2D / 3D? Grid / Particle System Init • Density, velocity, pressure, (…) grids • FLIP, Secondary particle systems Main loop (frame step) • Advection • External forces • Pressure solve Scene setup • Domain boundaries • Inflow & obstacle objects / 40 8
9. Python snippets Callable from bpy Export scene as Mantascript Better debugging Future: Node editor D E V E L O P E R S P E R S P E C T I V E B L E N D E R M A N TA F L O W A P I Basic Mantaflow Python Script / 40 9
10. W H AT C H A N G E S ? S E T T I N G S O V E R V I E W W I T H M A N TA F L O W “ S a m e ” S m o k e & F i re H i g h - re s o p t i o n s Wa v e l e t n o i s e N o t p o s s i b l e A d a p t i v e D o m a i n N e w / 40 10
11. W H AT C H A N G E S ? S E T T I N G S O V E R V I E W And: Fluid = Smoke or Liquid! W I T H M A N TA F L O W “ S a m e ” S m o k e & F i re H i g h - re s o p t i o n s Wa v e l e t n o i s e N o t p o s s i b l e A d a p t i v e D o m a i n N e w F L I P L i q u i d s A d a p t i v e t i m e - s t e p p i n g F l u i d p a r t i c l e s F l u i d g u i d i n g
12. ( F L I P ) L I Q U I D S G O O G L E S U M M E R O F C O D E 2 0 1 6 FLIP = Fluid Implicit Particle Particles track surface Generate mesh from particles Cache: Mesh and/or particles High resolution (FLIP) liquid splash (512 divisions) / 40 12
13. ( F L I P ) L I Q U I D S C O M PA R I S O N E L B E E M V S . M A N TA F L O W With Mantaflow Blender 2.79
14. Demo FLIP Liquids + New cache options
15. F L U I D PA R T I C L E S G O O G L E S U M M E R O F C O D E 2 0 1 7 Types: • FLIP (Fluid Implicit Particle) / 40 15 Just (FLIP) particles (FLIP) particles + mesh
16. Types: • FLIP (Fluid Implicit Particle) • Drop • Bubble • Float • Tracer F L U I D PA R T I C L E S G O O G L E S U M M E R O F C O D E 2 0 1 7 Secondary Particles “Recycled” / 40 16 Just (FLIP) particles (FLIP) particles + mesh
17. Types: • FLIP (Fluid Implicit Particle) • Drop • Bubble • Float • Tracer F L U I D PA R T I C L E S G O O G L E S U M M E R O F C O D E 2 0 1 7 Secondary Particles “Recycled” FLIP Drop Bubble Float Tracer Mesh / 40 17
18. F L U I D PA R T I C L E S F L I P & S E C O N D A RY PA R T I C L E S & L I F E C Y C L E FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] / 40 18
19. F L U I D PA R T I C L E S F L I P PA R T I C L E S FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Is in narrow band? / 40 19
20. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Next position with Euler’s method: x i+1 =x i +v i ·∆t Is convex? Is fast enough? FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Generate Gravity / 40 20
21. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Is inside fluid? FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Generate Gravity Buoyancy Convert Buoyancy = Inverse Gravity · “Rise Up” Factor / 40 21
22. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Is on surface? FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Generate Gravity Buoyancy Convert Convert Float / 40 22
23. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Is on surface? FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] “Drop, bubble & float particles recycled (Lifecycle)” Generate Gravity Buoyancy Convert Convert Float / 40 23
24. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Is inside fluid? FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Generate with x% / 40 24
25. F L U I D PA R T I C L E S S E C O N D A RY PA R T I C L E S & L I F E C Y C L E Additional floats! FLIP Drop Bubble Float Tracer [Thresh] [Factor] [Sample %] [Sample %] Generate with x% Generate with x% / 40 25
26. Demo Fluid particles
27. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Blur radius = 1 Blur radius = 5 Blur radius = 9 for each step: 1. Guide vel constrains main vel 2. Ensure divergence-free motion / 40 27
28. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Blur radius = 1 Blur radius = 5 Blur radius = 9 for each step: 1. Guide vel constrains main vel 2. Ensure divergence-free motion Guiding object / 40 28
29. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Blur radius = 1 Blur radius = 5 Blur radius = 9 for each step: 1. Guide vel constrains main vel 2. Ensure divergence-free motion Guiding object Animation Guiding velocity grid / 40 29
30. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Blur radius = 1 Blur radius = 5 Blur radius = 9 for each step: 1. Guide vel constrains main vel 2. Ensure divergence-free motion Guiding object Animation Guiding velocity grid Blur, weight Manta pressure solve / 40 30
31. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Blur radius = 1 Blur radius = 5 Blur radius = 9 for each step: 1. Guide vel constrains main vel 2. Ensure divergence-free motion Guiding object Animation Guiding velocity grid Blur, weight Manta pressure solve / 40 31
32. F L U I D G U I D I N G G O O G L E S U M M E R O F C O D E 2 0 1 7 Guided Smoke Tornado Weight = 2 (Lag) Blur radius = 5 (Size vortices) Frame 10 Frame 20 Frame 30 Frame 40 Frame 50 Frame 60 Frame 70 Frame 80 Frame 90 / 40 32
33. Demo Fluid guiding + Script export + Mantaflow GUI
34. O B S TA C L E S F L U I D I N T E R A C T I O N P R O B L E M R E A S O N S O L U T I O N O b s t a c l e n o t h i t Reality Expectation / 40 34
35. O B S TA C L E S F L U I D I N T E R A C T I O N P R O B L E M R E A S O N S O L U T I O N O b s t a c l e n o t h i t O b s t a c l e t o o t h i n Obstacle Levelset in Mantaflow GUI (2D view from above) Thickening “0.0” Thickening “0.5” / 40 35
36. O B S TA C L E S F L U I D I N T E R A C T I O N P R O B L E M R E A S O N S O L U T I O N O b s t a c l e n o t h i t O b s t a c l e t o o t h i n O b s t a c l e “ t h i c k e n i n g ” Obstacle Levelset in Mantaflow GUI (2D view from above) Thickening “0.0” Thickening “0.5” Thickening “1.5” Thickening “2.5” / 40 36
37. O B S TA C L E S F L U I D I N T E R A C T I O N P R O B L E M R E A S O N S O L U T I O N O b s t a c l e n o t h i t O b s t a c l e t o o t h i n O b s t a c l e “ t h i c k e n i n g ” T i m e - s t e p t o o b i g Some (FLIP) particles “slip” through obstacle wall Frame i Frame i+1 / 40 37
38. O B S TA C L E S F L U I D I N T E R A C T I O N P R O B L E M R E A S O N S O L U T I O N O b s t a c l e n o t h i t O b s t a c l e t o o t h i n O b s t a c l e “ t h i c k e n i n g ” T i m e - s t e p t o o b i g A d a p t i v e t i m e - s t e p p i n g Some (FLIP) particles “slip” through obstacle wall Frame i Frame i+1 / 40 38
39. N E X T S T E P S R O A D T O B L E N D E R 2 . 8 • ToDo’s for 2.8: • Bug fixes — Blenderartists! • Remove (Elbeem) Fluid modifier • Merge in 2.8 branch • After 2.8 merge (Ideas): • Node editor • Fluid particles: Smoke & Fire / 40 39
40. R E S O U R C E S • Blender-Wiki: • https://wiki.blender.org/index.php/User:Sebbas • Research: • https://ge.in.tum.de/ • Code: • Branch “fluid-mantaflow” • Me: • Twitter @sebbas WA N T M O R E ? Thanks! / 40 40