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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 l.jpg

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 l.jpg
Motivation

  • Fluid Animation: smoke, clouds, fire, explosion, splashes, sea…

  • Simulation vs Animation

[ Areté Entertainment, inc. 96]

[ LOTR ]


Motivation3 l.jpg
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 l.jpg
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 l.jpg
Background [AN05]

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

‘‘Chart of methods for numerical fluid simulation’’


Background l.jpg

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 l.jpg

vorticity

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

velocity v

Curl


Background8 l.jpg

vorticity

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

velocity v

BIOT-SAVART


Background9 l.jpg
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 l.jpg
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Eulerian

Lagrangian

in grid

at particle


Background11 l.jpg
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

NAVIER-STOKES

( incompressible )


Background12 l.jpg
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian


Background13 l.jpg
Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

VORTICITY EQUATION

( inviscid )


Background14 l.jpg
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 l.jpg

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 l.jpg

w

Background

Velocity

Vorticity

moving

quantity

representation

popular

Eulerian

our

method

Lagrangian

Vorticity:

Our primitive = curves

= tangent


Background17 l.jpg
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 l.jpg
Lagrangian primitives

  • Curves carry the vorticity

  • Each local vortex induces a weighted rotation


Lagrangian primitives19 l.jpg
Lagrangian primitives

  • Curves carry the vorticity

  • Each local vortex induces a weighted rotation


Method of simulation l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
Contributions

  • A new representation of vortex curves

    Compact, stable, controlable motion primitives

  • Controls of the motion primitives

  • Fast ‘‘noise’’ for fake turbulence details


Contributions24 l.jpg
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 l.jpg
Deformation of curves previous approach [AN05]

If not refined:

undersampling

Polygon

If refined:

too complex

Strategy to control complexity


New representation l.jpg

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 l.jpg

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 l.jpg

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 l.jpg

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 l.jpg

ez

ey

o

ex

Meaning of description

  • ez points towards moving direction

  • Frequencies cx cy cz give texture to the flow

  • Thickness



Contributions32 l.jpg
Contributions

  • A new representation of vortex curves

    Compact, stable, controlable motion primitives

  • Controls of the motion primitives

  • Fast ‘‘noise’’ for fake turbulence details


Control l.jpg

+

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 l.jpg

+

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 l.jpg

+

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 l.jpg
How to control

  • One cannot just translate the curves: the smoke does not follow

  • Solution: paddle(servoing )

ez

ey

o

ex



Contributions38 l.jpg
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 l.jpg

[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 l.jpg

[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 l.jpg

[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 l.jpg
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 l.jpg
Octree cache

  • Velocity computed at octree leaves + inbetween interpolation

  • Velocity computed at every smoke particle &every vorticity curve sample


Octree cache45 l.jpg
Octree cache

  • Velocity computed at octree leaves + inbetween interpolation

  • Velocity computed at every smoke particle &every vorticity curve sample


Rendering l.jpg
Rendering

  • Thick smoke: plain particles

  • Thin smoke: adaptive particles[AN05]

    • accumulate stretching


Rendering47 l.jpg

l

n

e

Rendering

  • Thin smoke behaves like a surface

[ William Brennan ]


Results video l.jpg
Results - video

fpsForest fire Genie&lamp Walkthrough Fly

Modeler quality5 12 5 18

Final rendering quality0.54 0.2 1. 0.37


Conclusion l.jpg
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.jpg

l

n

e

Rendering

  • Thin smoke behaves like a surface

Diffuse off

Diffuse on


Rendering54 l.jpg
Rendering

  • Thin smoke behaves like a surface


Lagrangian primitives55 l.jpg
Lagrangian primitives

  • Curves carry the vorticity

  • Each vortex induces a weighted rotation

Effect of one vortex on ashape :


Control currents l.jpg

Without control

With control

Control currents

ez

t

L

L


Checkpoint l.jpg
Checkpoint

  • With control


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