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“Observe the motion of the surface of the water, which resembles that of hair, which has two motions, of which one is caused by the weight of the hair, the other by the direction of the curls; thus the water has eddying motions, one part of which is due to the principal current, the other to random and reverse motion”
Leonardo da Vinci, 1510
Angry sea at Naruto
Ando Hiroshige, 1830
1.-Navier-Stokes equations and singularities
“The open problems in the area of non-linear partial differential equations are very relevant to applied mathematics and science as a whole, perhaps more so than the open problems in any other area of mathematics, and this field seems poised for rapid development. Little is known about the existence, uniqueness and smoothness of solutions of the general equations of flow for a viscous, compressible, and heat conducting fluid. Also, the relationship between this continuum description of a fluid and the more physically valid statistical mechanical description is not well understood. Probably one should first try to prove existence, smoothness, and unique continuation (in time) of flows, conditional on the non-appearance of certain gross types of singularity, such as infinities of temperature or density. A result of this kind would clarify the turbulence problem.”
John F. Nash, 1958
The Millenium prize problems. Clay Mathematics Institute 2000:1) Birch and Swinnerton-Dyer Conjecture
2) Hodge Conjecture
3) Navier-Stokes Equations
4) P vs NP
5) Poincare Conjecture
6) Riemann Hypothesis
7) Yang-Mills Theory
1.- Navier-Stokes equations and singularities.2.- The quasigeostrophic equation3.- Break-up of fluid jets: drops.4.- Kelvin-Helmholtz instability.
Boundary conditions:
Initial condition:
No slip (when in contact with a solid) :
Force balance (when in contact with another fluid)
Decay at infinity (no boundaries):
Euler equations (inviscid fluid, 1755) :
Vorticity :
Vorticity equation :
Local existence (Kato 1972)
Euler:2-D: Global existence and uniqueness (Kato 1967)3-D: Local existence. Singularity if and only if the sup norm of vorticity is not integrable in time (Beale-Kato-Majda 1984). Nonuniqueness (Scheffer 1993).Problem: Finite time blow-up in 3-D?
Navier-Stokes:2-D: Global existence and uniqueness (Kato 1967)3-D: Local existence (Leray 1934). Singularity if and only if the square of the sup norm of velocity is not integrable in time (Serrin 1962). Global existence of weak solutions (Leray 1934).Problems: 1) Uniqueness of weak solutions? 2) Finite time blow-up in 3-D?
Rayleigh’s inestability of a uniform cylinder (Rayleigh 1879)
Consider an inviscid and irrotational fluid
Bernoulli’s law:
At the boundary.
x 1.210.80.60.40.20
0.2
0.1
0
-0.1
-0.2
G(x)
x
Viscous case, Chandrasekhar 1961.
Savart 1833
Rayleigh’s Instab.
D
L
The one dimensional limit
z
n
tNavier-Stokes (axisymmetric)
Boundary conditions
Kinematic condition
-6 -4 -2 0 2 4 6-2
-1
0
1
2
0
-10 0 10 20 30 40 50
0
5
10
15
20
Numerical solution of the system (profiles)
h(z,t)
-6 -4 -2 0 2 4 6-6
-5
-4
-3
-2
-1
0
1
2
3
4
-4 -3.5 -3 -2.5 -2
-5
-4
-3
-2
-1
0
1
2
3
4
-6 -4 -2 0 2 4 6 8 10
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Numerical solution of the system (velocity)
v(z,t)
-10 0 10 20 30 40 50
0
5
10
15
20
-6 -4 -2 0 2 4 6 8 10
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
as
near
Conjecture: The self-similar break-up mechanism is universal
Conjecture: The system presents finite-time singularities in the curvature. Moore 1979. Numerical and asymptotic evidence.
Conclusions
1.- Many physical phenomena related to fluids are linked to the appearence of singularities (finite time blow up of a derivative at some point). Break-up of jets: singularity in the velocity field. Quasigeostrophic equation: singularity on the slope of the temperature field. Kelvin-Helmholtz: singularity in the curvature. Turbulence: (maybe) singularity in the vorticity.
2.- The nature of the singularities indicates the presence of regularizing effects at small length scales (possibly at molecular level).
3.-The existence of a singularity poses an important fundamental question on the consistency of the theory.