g. haller division of applied mathematics lefschetz center for dynamical systems
DESCRIPTION
Finite-Time Mixing and Coherent Structures. G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems Brown University. Collaborators: A. Banaszuk (UTRC), C. Coulliet (Caltech), F. Lekien (Caltech), I. Mezic (Harvard), - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/1.jpg)
1
G. Haller Division of Applied Mathematics
Lefschetz Center for Dynamical Systems Brown University
Finite-Time Mixing and Finite-Time Mixing and Coherent StructuresCoherent Structures
Collaborators: A. Banaszuk (UTRC), C. Coulliet (Caltech), F. Lekien (Caltech), I. Mezic (Harvard), A. Poje (CUNY), H. Salman (Brown/UTRC), G. Tadmor (Northeastern), Y. Wang (Brown), G.-C. Yuan (Brown)
![Page 2: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/2.jpg)
2
Fundamental observation: In 2D turbulence coherent structures emerge
What is a coherent structure?• region of concentrated vorticity that retains its structure for longer times (Provenzale [1999])
• energetically dominant recurrent pattern (Holmes, Lumley, and Berkooz [1996])
• set of fluid particles with distinguished statistical properties (Elhmaidi, Provenzale, and Babiano [1993])
• larger eddy of a turbulent flow (Tritton [1987])
• dynamical systems: no conclusive answer for turbulent flows - spatio-temporal complexity - finite-time nature
Absolute dispersion plot for the 2D QG equations
![Page 3: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/3.jpg)
3
A Lagrangian Approach to Coherent Structures
stretching: fluid blob opens up along a material line
repelling material line folding: fluid blob spreads out along a material line
attracting material line swirling/shearing: fluid blob encircled/enclosed by neutral material lines
Approach coherent structures through material stability
Particle mixing in 2D turbulence
![Page 4: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/4.jpg)
4
is repelling over the time interval if vectors normal to it grow in arbitrarily short times within .
uI)(tluI
Attracting material line: repelling in backward time
)( 0tl
)(tl
)()( 00 xx NF h)( 0xN
)(tx:)( 0xhF
deformation field
:)( 0xN unit normal
Stability of material linesStability of material lines
![Page 5: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/5.jpg)
5
A stretch line is a material line that is repelling for locally the longest/shortest time in the flow
Definitions of hyperbolic Lagrangian structures:
maximal locally is :flowopen uT minimallocally is :slip)-(no near wall uT
A fold line is a material line that is attracting for locally the longest/shortest time in the flow
![Page 6: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/6.jpg)
6
How do we find stretch and fold lines lines from data?How do we find stretch and fold lines lines from data?
Miller, Jones, Rogerson & Pratt [Physica D, 110, 1997]: “straddle” near instantaneous
saddle-type stagnation points
of the velocity fieldBowman [preprint, 1999], Winkler [thesis, Brown, 2000]: use relative dispersion plots
Poje, Haller, & Mezic [Phys. Fluids A,11, 1999]: use Lagrangian mean velocity plots
Couillette & Wiggins [Nonlin. Proc. Geophys., 8, 2001]: straddling near boundary points
Joseph & Legras [J. Atm. Sci., submitted, 2000]: finite-size Lyapunov exponent plots
…
Numerical approaches:
![Page 7: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/7.jpg)
7
How do we find stretch and fold lines lines from data?How do we find stretch and fold lines lines from data?
Analytic view:Analytic view: stability of a fluid trajectory x(t) is governed by
Theorem (necessary criterion):Theorem (necessary criterion): Stretch lines at t=0 maximize the scalar fieldStretch lines at t=0 maximize the scalar field
)()()( 0*
0max0 xFxFx ttt
).()),(( 2ξξxuξ Ott
Linear part is solved by:
.)()( 00 ξxFξ tt
Simplest approach:Simplest approach: look for stretch lines as places of maximal stretching:
(DLE algorithm, Haller [Physica D, 149, 2001])
![Page 8: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/8.jpg)
8
Example 1:Example 1: velocity data 2D geophysical turbulencevelocity data 2D geophysical turbulence
,, 44 Fqq
tq
QG equations in 2D.
•pseudo-spectral code of A. Provenzale•particle tracking with VFTOOL of P. Miller by G-C. Yuan,0 u
• is the potential vorticity
• is the scaled inverse of the Rossby deformation radius
• denotes the coefficient of hyperviscosity
•
`22 q
10
74 105
]2,0[]2,0[ x
![Page 9: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/9.jpg)
9
Eulerian view on coherent structures: potential vorticity gradient
Contour plot of q Contour plot of || q
![Page 10: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/10.jpg)
10
Contour plot of q22 s
Hyperbolic regions:Elliptic regions:
22 )( xyyx uu ;)()( 222yxxYyyxx uuuus
Eulerian view on coherent structures: Okubo-Weiss partition
22 s
![Page 11: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/11.jpg)
11
Stretch lines from DLE analysis
Contour plot of q at t=50 Stretch lines at t=50
(= locally strongest finite-time stable manifolds)
![Page 12: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/12.jpg)
12
Fold lines from DLE analysis
Contour plot of q at t=50 Fold lines at t=50
(= locally strongest finite-time unstable manifolds)
![Page 13: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/13.jpg)
13
Example 2:Example 2: HF radar data from Monterey BayHF radar data from Monterey BayImage by Image by Chad CoullietChad Coulliet & & Francois LekienFrancois Lekien (MANGEN, (MANGEN, http://transport.caltech.eduhttp://transport.caltech.edu))
• Lagrangian separation point
• instantaneous stagnation point
Data by Data by Jeff PaduanJeff Paduan,,Naval Postgraduate SchoolNaval Postgraduate School
DLE analysis of surface velocity
)(logmax)(log
0
0x
xt
t
![Page 14: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/14.jpg)
14
Example 3:Example 3: Experiments by Experiments by Greg VothGreg Voth and and Jerry GollubJerry Gollub (Haverford) (Haverford)
Mixing of dye in charged fluid, forced periodically in time by magnets
Dye Dye+fold lines Dye+stretch lines
![Page 15: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/15.jpg)
15
What is missing? The Eulerian physics
Question:
What is the What is the objectiveobjective Eulerian signature of intense Lagrangian Eulerian signature of intense Lagrangian mixing or non-mixing?mixing or non-mixing?
Room for improvement:• Occasional slow convergence • Shear gradients show up as stretch lines (finite time!)• Nonhyperbolic Lagrangian structures? (jets, vortex cores,…) • What do we learn?
Available frame-dependent results: Haller and Poje [Physica D, 119, 1998], Haller and Yuan [Physica D, 147, 2000], Lapeyre, Hua, and Legras [J. Atm. Sci., submitted, 2000], Haller [Physica D, 149, 2001. (3D flows)]
![Page 16: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/16.jpg)
16
Consider
where M is the strain acceleration tensor (Rivlin derivative of S),2 uSSM
Notation:
Z(x,t) : directions of zero strain
: restriction of M to ZZ|M
.| defpositiveZM .| semidefpositiveZM
indefiniteZ|M 0S
True instantaneous flow geometry
Definitions:
Hyperbolic region: ={ pos.def.}Parabolic region: ={ pos. semidef.}Elliptic region: ={ indef. or S=0}
Z|M
Z|MZ|M
)(tH)(tP)(tE
,),(),(),( *21 ttt xuxuxS
![Page 17: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/17.jpg)
17
EPH partition of 2D turbulenceEPH partition of 2D turbulenceover a finite time interval over a finite time interval II
Fully objectivepicture, i.e., invariant under time-dependentrotations and translations
![Page 18: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/18.jpg)
18
Theorem 1 (Sufficient cond. for Lagrangian hyperbolicity) Assume that x(t) remains in over the time interval I. Then x(t) is contained in a hyperbolic material line over I.
)(tH
Theorem 2 (Necessary cond. for Lagrangian hyperbolicity) Assume that x(t) is contained in a hyperbolic material line over I. Then x(t) can • intersect only at discreet time instances
• stay in only for short enough time intervals J satisfying
)(tP)(tE
dtJ S
M,
Theorem 3 (Sufficient cond. for Lagrangian ellipticity) Assume that x(t) remains in over I and
Then x(t) is contained in an elliptic material line over I.
)(tE
2
,,
dtI S
M
S
M
MAIN RESULTS MAIN RESULTS (Haller [(Haller [Phys. Fluids APhys. Fluids A., 2001,to appear])., 2001,to appear])
local eddyturnover time!
![Page 19: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/19.jpg)
19
Example 1: Lagrangian coherent structures in barotropic turbulence simulations
Time spent in )(tE
![Page 20: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/20.jpg)
20
),()(,0),()(|,)),((|
tttttt
EH
xxxS),( 0xtPlot of
t=85Local minimum curves are stretch lines (finite-time stable manifolds)
Fastest converging:
Earlier result from DLE
local flux!
t=60
![Page 21: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/21.jpg)
21
Example 2:Example 2: HF radar data from Monterey BayHF radar data from Monterey BayImage by Image by Chad CoullietChad Coulliet & & Francois LekienFrancois Lekien (MANGEN, (MANGEN, http://transport.caltech.eduhttp://transport.caltech.edu))
Data by Data by Jeff PaduanJeff Paduan,,Naval Postgraduate SchoolNaval Postgraduate School
Filtering by Filtering by Bruce LipphardtBruce Lipphardt& & Denny KirwanDenny Kirwan (U. of Delaware) (U. of Delaware)
),()(,0),()(|,)),((|
tttttt
EH
xxxS),( 0xt
![Page 22: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/22.jpg)
22
How are Lagrangian coherent structures How are Lagrangian coherent structures related to the governing equations?related to the governing equations?
Answer for 2D, incompressible Navier-Stokes flows:Answer for 2D, incompressible Navier-Stokes flows: ( Haller [Phys. Fluids A, 2001, to appear] )
Theorem (Sufficient dynamic condition for Lagrangian hyperbolicity) Consider the time-dependent physical region defined by
.)()''(2
*max2
12maxmax
1
2
ffS
ps
All trajectories in the above region are contained in finite-time hyperbolic material lines .
![Page 23: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/23.jpg)
23
Hyperbolic Lagrangian structures fall into 10 categories
Existing analytic results in 3D:
• DLE algorithm extends directly
• frame-dependent approach has been extended (Haller [Physica D, 149, 2001])
Towards understanding Lagrangian structures in 3D flowsTowards understanding Lagrangian structures in 3D flows
![Page 24: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/24.jpg)
24
An example: Lagrangian coherent structures in the ABC flow
.cossin,cossin,cossin
xByCzzAxByyCzAx
Henon [1966], Dombre et al. [1986]: Poincare map for A=1, B= , C=1200 iterations used
3/2 3/1
3D DLE analysis
![Page 25: G. Haller Division of Applied Mathematics Lefschetz Center for Dynamical Systems](https://reader035.vdocument.in/reader035/viewer/2022062410/56815a8d550346895dc80297/html5/thumbnails/25.jpg)
25
Some open problems (work in progress):
• Survival of Lagrangian structures (obtained from filtered data) in the “true” velocity field
• Lagrangian structures in 3D (objective approach)
• Dynamic mixing criteria for other fluids equations and different constitutive laws
• Relevance for mixing of diffusive/active tracers