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International scientific conference "Days of Classical Mechanics"
January 26, 2015 10:05–10:40, Moscow, Steklov Mathematical Institute of RAS, Gubkina, 8

KAM theory and the 3d Euler equation

S. B. Kuksin
 Video records: Flash Video 245.6 Mb Flash Video 1,471.3 Mb MP4 245.6 Mb

Abstract: Consider the Euler equation on a closed 3d manifold (e.g. on the 3-torus or on the 3-sphere). Let $u(t,x)$ be its solution, and $\omega(t,x)$ – the vorticity of this solution. By the Kelvin theorem the vorticity-vectorfields, calculated for different values of time, are conjugated by means of volume-preserving diffeomorphisms. Therefore the quantity $\kappa(\omega)$, equal to the volume of the set which is the union of all two-dimensional invariant tori of $\omega$ is time-independent. We use KAM and the Arnold theorem on the structure of steady-states of the 3d Euler to prove that $\kappa$ is continuous at $\omega$'s which are non-degenerate steady-states of the equation, and use this integral of motion to study qualitative properties of the dynamical system, defined by the equation in the space of sufficiently smooth vector-fields. Namely, to study its non-ergodicity and study the problem “does the manifold of steady-states of the equation attracts (in a suitable sense) all trajectories which start from its vicinity?”.