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SCA 2006. Vortex Fluid Structure For Smoke Control. Alexis Angelidis (1) Fabrice Neyret (2) Karan Singh (1) Derek Nowrouzezahrai (1) (1): DGP, U of Toronto (2): Evasion-GRAVIR / IMAG-INRIA. Motivation. Fluid Animation: smoke , clouds, fire, explosion, splashes, sea…

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vortex fluid structure for smoke control

SCA 2006

Vortex Fluid StructureFor Smoke Control

Alexis Angelidis (1)

Fabrice Neyret (2)

Karan Singh (1)

Derek Nowrouzezahrai (1)

(1): DGP, U of Toronto

(2): Evasion-GRAVIR / IMAG-INRIA

motivation
Motivation
  • Fluid Animation: smoke, clouds, fire, explosion, splashes, sea…
  • Simulation vs Animation

[ Areté Entertainment, inc. 96]

[ LOTR ]

motivation3
Motivation
  • Fluid Animation: smoke, clouds, fire, explosion, splashes, sea…
  • Simulation vs Animation
  • Approaches to control:
    • Phenomenological, limited
    • Fake forces
    • Control by keyframing ‘shapes’

[ Areté Entertainment, inc. 96]

[ LotR ]

motivation4
Motivation

[Treuille et al.03],[McNamara et al.04],[Fattal et al.04]

Most related work

  • Density field given at keyframes
  • Solver between frames

What we want

  • No hand-drawn smoke
  • Natural control

key2

key1

[McNamara et al.04]

background an05
Background [AN05]

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

‘‘Chart of methods for numerical fluid simulation’’

background

vorticity

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

3D

field

velocity v

Rotation in rad s-1

translation in m s-1

background7

vorticity

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

velocity v

Curl

background8

vorticity

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

velocity v

BIOT-SAVART

background9
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Dynamics :

Eulerian

The flow modifies quantities

held at static positions

Lagrangian

The flow carries floaters that

hold the quantities

background10
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Eulerian

Lagrangian

in grid

at particle

background11
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

NAVIER-STOKES

( incompressible )

background12
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

background13
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

VORTICITY EQUATION

( inviscid )

background14
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

No diffusion

Implicit incompressibility

compact

Unbounded

Easy boundary conditions

Easy extra differential eqn

background15

VORTICITY EQUATION

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Vorticity:

Vortex particle advected, vector stretched

vorticity moves as material lines

background16

w

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Vorticity:

Our primitive = curves

= tangent

background17
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Density:

Dedicated particles

- passive floaters

- for rendering

- only where smoke is

Density:

a quantity at nodes

lagrangian primitives
Lagrangian primitives
  • Curves carry the vorticity
  • Each local vortex induces a weighted rotation
lagrangian primitives19
Lagrangian primitives
  • Curves carry the vorticity
  • Each local vortex induces a weighted rotation
method of simulation
Method of simulation
  • Vortex particles (for motion) organized as curves. = tangent
  • Smoke particles (for visualisation)
  • Curves carry vortices
  • Vortices induce a velocity field
  • velocity field deforms curves & smoke

At every step:

  • Advect the curves
  • Stretch
  • Advect the smoke
method of simulation21
Method of simulation
  • Vortex particles (for motion) organized as curves. = tangent
  • Smoke particles (for visualisation)
  • Curves carry vortices
  • Vortices induce a velocity field
  • velocity field deforms curves & smoke

At every step:

  • Advect the curves
  • Stretch
  • Advect the smoke
method of simulation22
Method of simulation
  • Vortex particles (for motion) organized as curves. = tangent
  • Smoke particles (for visualisation)
  • Curves carry vortices
  • Vortices induce a velocity field
  • velocity field deforms curves & smoke

At every step:

  • Advect the curves
  • Stretch
  • Advect the smoke
contributions
Contributions
  • A new representation of vortex curves

Compact, stable, controlable motion primitives

  • Controls of the motion primitives
  • Fast ‘‘noise’’ for fake turbulence details
contributions24
Contributions
  • A new representation of vortex curves

Compact, stable, controlable motion primitives

  • Controls of the motion primitives
  • Fast ‘‘noise’’ for fake turbulence details
deformation of curves previous approach an05
Deformation of curves previous approach [AN05]

If not refined:

undersampling

Polygon

If refined:

too complex

Strategy to control complexity

new representation

New representation
  • Solution: harmonic analysis of coordinates

x

= in y

z

a pair of coefficients for each harmonic

  • Reference frame: best ellipsoid

Complexity control

  • Curves described by :
    • Frame o ex ey ez
    • Frequencies <cx cy cz>1..N

Synthesis

Advection

Analysis

new representation27

New representation
  • Solution: harmonic analysis of coordinates

x

= in y

z

a pair of coefficients for each harmonic

ez

ey

  • Reference frame: best ellipsoid

o

ex

Complexity control

  • Curves described by :
    • Frame o ex ey ez
    • Frequencies <cx cy cz>1..N

Synthesis

Advection

Analysis

new representation28

New representation
  • Solution: harmonic analysis of coordinates

x

= in y

z

a pair of coefficients for each harmonic

ez

ey

  • Reference frame: best ellipsoid

o

ex

Complexity control

  • Curves described by :
    • Frame o ex ey ez
    • Frequencies <cx cy cz>1..N

Synthesis

Advection

Analysis

new representation29

New representation
  • Solution: harmonic analysis of coordinates

x

= in y

z

a pair of coefficients for each harmonic

ez

ey

  • Reference frame: best ellipsoid

o

ex

Complexity control

  • Curves described by :
    • Frame o ex ey ez
    • Frequencies <cx cy cz>1..N

Synthesis

Advection

Analysis

meaning of description

ez

ey

o

ex

Meaning of description
  • ez points towards moving direction
  • Frequencies cx cy cz give texture to the flow
  • Thickness
contributions32
Contributions
  • A new representation of vortex curves

Compact, stable, controlable motion primitives

  • Controls of the motion primitives
  • Fast ‘‘noise’’ for fake turbulence details
control

+

without

with

ez

ey

<cx cy cz>1..N

o

ex

Control
  • direction: align ez with tangent
  • Targets:
  • Twisting smoke: spin vortices around ez
  • Edit, delete …
  • Modulate cx cy cz to texturethe flow
control34

+

without

with

ez

ey

<cx cy cz>1..N

o

ex

Control
  • direction: align ez with tangent
  • Targets:
  • Twisting smoke: spin vortices around ez
  • Edit, delete …
  • Modulate cx cy cz to texturethe flow
control35

+

without

with

ez

ey

<cx cy cz>1..N

o

ex

Control
  • direction: align ez with tangent
  • Targets:
  • Twisting smoke: spin vortices around ez
  • Edit, delete …
  • Modulate cx cy cz to texturethe flow
how to control
How to control
  • One cannot just translate the curves: the smoke does not follow
  • Solution: paddle(servoing )

ez

ey

o

ex

contributions38
Contributions
  • A new representation of vortex curves

Compact, stable, controlable motion primitives

  • Controls of the motion primitives
  • Fast ‘‘noise’’ for fake turbulence details
noise fake turbulence details
[AN05]:

noise = extra vortex particles

advected in the flow, no stretch

Costly (needs a lot)

Source, sampling

Tiled vortex noise:

noise layer =

separate simulation, in toroidal space

Tiled in space

Additional evolving velocity field

Noise: fake turbulence details
noise fake turbulence details40
[AN05]:

noise = extra vortex particles

advected in the flow, no stretch

Costly (needs a lot)

Source, sampling

Tiled vortex noise:

noise layer =

separate simulation, in toroidal space

Tiled in space

Additional evolving velocity field

Noise: fake turbulence details
noise fake turbulence details41
[AN05]:

noise = extra vortex particles

advected in the flow, no stretch

Costly (needs a lot)

Source, sampling

Tiled vortex noise:

noise layer =

separate simulation, in toroidal space

Tiled in space

Additional evolving velocity field

Noise: fake turbulence details
contributions43
Contributions
  • A new representation of vortex curves

Compact, stable, controlable motion primitives

  • Controls of the motion primitives
  • Fast ‘‘noise’’ for fake turbulence details
  • Velocity cache, rendering
octree cache
Octree cache
  • Velocity computed at octree leaves + inbetween interpolation
  • Velocity computed at every smoke particle &every vorticity curve sample
octree cache45
Octree cache
  • Velocity computed at octree leaves + inbetween interpolation
  • Velocity computed at every smoke particle &every vorticity curve sample
rendering
Rendering
  • Thick smoke: plain particles
  • Thin smoke: adaptive particles[AN05]
    • accumulate stretching
rendering47

l

n

e

Rendering
  • Thin smoke behaves like a surface

[ William Brennan ]

results video
Results - video

fpsForest fire Genie&lamp Walkthrough Fly

Modeler quality5 12 5 18

Final rendering quality0.54 0.2 1. 0.37

conclusion
Conclusion

Vorticity filaments:

  • Compact, high-res, fast
  • Good handles to manipulate a fluid
  • Can be manipulated interactively or post-

Future work:

  • Split/merge
  • High-quality collisions
  • 2-phase, buoyancy, …

Coupling with grids

rendering53

l

n

e

Rendering
  • Thin smoke behaves like a surface

Diffuse off

Diffuse on

rendering54
Rendering
  • Thin smoke behaves like a surface
lagrangian primitives55
Lagrangian primitives
  • Curves carry the vorticity
  • Each vortex induces a weighted rotation

Effect of one vortex on ashape :

checkpoint
Checkpoint
  • With control