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
   

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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 …
   

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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/
   

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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/
   

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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
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   5
   https://wwwcg.in.tum.de/research/research/publications/2016/narrow-band-flip-for-liquid-simulations.html
   

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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/
   

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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
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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
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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
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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
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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
    

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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)
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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
    

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14. Demo
    FLIP Liquids + New cache options
    

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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)
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    Just (FLIP) particles
    (FLIP) particles + mesh
    

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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”
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    Just (FLIP) particles
    (FLIP) particles + mesh
    

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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
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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 %]
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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
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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
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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
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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
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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
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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
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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%
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26. Demo
    Fluid particles
    

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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
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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
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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
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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
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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
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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
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33. Demo
    Fluid guiding + Script export + Mantaflow GUI
    

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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
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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
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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
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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
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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
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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
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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!
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