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On the dynamics of point vortices with positive intensities collapsing with the boundary

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The first part of this article studies the collapses of point-vortices for the Euler equation in the plane and for surface quasi-geostrophic equations in the general setting of α models. In these models the kernel of the Biot–Savart law is a power function of exponent − α . It is proved that, under a standard non-degeneracy hypothesis, the trajectories of the point-vortices have a Hölder regularity up to the time of collapse. The Hölder exponent obtained is 1 / ( α + 1 ) and this exponent is proved to be optimal for all α by exhibiting an example of a three-vortex collapse. The same question is then addressed for the Euler point-vortex system in smooth bounded connected domains. It is proved that if a given point-vortex has an accumulation point in the interior of the domain as t → T , then it converges towards this point and displays the same Hölder continuity property. A partial result for point-vortices that collapse with the boundary is also established: we prove that their distance to the boundary is Hölder regular.
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1 Introduction.- 2 P-Capacity.- 3 Generalized Sobolev Inequality.- 3.1 Local generalized Sobolev inequality.- 3.2 Critical power integrand.- 3.3 Volume integrand.- 3.4 Plasma integrand.- 4 Concentration Compactness Alternatives.- 4.1 CCA for critical power integrand.- 4.2 Generalized CCA.- 4.3 CCA for low energy extremals.- 5 Compactness Criteria.- 5.1 Anisotropic Dirichlet energy.- 5.2 Conformai metrics.- 6 Entire Extremals.- 6.1 Radial symmetry of entire extremals.- 6.2 Euler Lagrange equation (independent variable).- 6.3 Second order decay estimate for entire extremals.- 7 Concentration and Limit Shape of Low Energy Extremals.- 7.1 Concentration of low energy extremals.- 7.2 Limit shape of low energy extremals.- 7.3 Exploiting the Euler Lagrange equation.- 8 Robin Functions.- 8.1 P-Robin function.- 8.2 Robin function for the Laplacian.- 8.3 Conformai radius and Liouville's equation.- 8.4 Computation of Robin function.- 8.4.1 Boundary element method.- 8.4.2 Computation of conformai radius.- 8.4.3 Computation of harmonic centers.- 8.5 Other Robin functions.- 8.5.1 Helmholtz harmonic radius.- 8.5.2 Biharmonic radius.- 9 P-Capacity of Small Sets.- 10 P-Harmonic Transplantation.- 11 Concentration Points, Subconformai Case.- 11.1 Lower bound.- 11.2 Identification of concentration points.- 12 Conformai Low Energy Limits.- 12.1 Concentration limit.- 12.2 Conformai CCA.- 12.3 Trudinger-Moser inequality.- 12.4 Concentration of low energy extremals.- 13 Applications.- 13.1 Optimal location of a small spherical conductor.- 13.2 Restpoints on an elastic membrane.- 13.3 Restpoints on an elastic plate.- 13.4 Location of concentration points.- 14 Bernoulli's Free-boundary Problem.- 14.1 Variational methods.- 14.2 Elliptic and hyperbolic solutions.- 14.3 Implicit Neumann scheme.- 14.4 Optimal shape of a small conductor.- 15 Vortex Motion.- 15.1 Planar hydrodynamics.- 15.2 Hydrodynamic Green's and Robin function.- 15.3 Point vortex model.- 15.4 Core energy method.- 15.5 Motion of isolated point vortices.- 15.6 Motion of vortex clusters.- 15.7 Stability of vortex pairs.- 15.8 Numerical approximation of vortex motion.
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This book deals with fluid dynamics of incompressible non-viscous fluids. The main goal is to present an argument of large interest for physics, and applications in a rigorous logical and mathematical set-up, therefore avoiding cumbersome technicalities. Classical as well as modern mathematical developments are illustrated in this book, which should fill a gap in the present literature. The book does not require a deep mathematical knowledge. The required background is a good understanding of classical arguments of mathematical analysis, including the basic elements of ordinary and partial differential equations, measure theory and analytic functions, and a few notions of potential theory and functional analysis. The contents of the book begin with the Euler equation, construction of solutions, stability of stationary solutions of the Euler equation. It continues with the vortex model, approximation methods, evolution of discontinuities, and concludes with turbulence.
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A system of linear vortices is considered as a model of two-dimensional turbulence. An exact solution is obtained for the problem of the interaction of three vortices - the first elementary act of interaction in the kinetics of isotropic turbulence. The tendency toward energy transfer in the spectrum from small scales to large scales in two-dimensional flow is examined on the basis of this problem. A steady-state solution corresponding to a Poisson distribution of vortices is obtained for the equation for the determining functional of the vortex system.
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The triple collision singularity in the 3-vortex problem is studied in this paper. Under the necessary condition for vorticities to have the triple collision, the main results are summarized as follows: (i) For k1 = k2, the triple collision singularity is topologically regularizable. (ii) For 0 < |k1 − k2| < with a sufficiently small , the triple collision singularity is not topologically regularizable. First of all, in order to prove these statements, all singularities in the 3-vortex problem are classified. Then, we introduce a dynamical system by blowing up the triple collision singularity with an appropriate time scaling. Roughly speaking, it corresponds to pasting an invariant manifold at the triple collision singularity on the original phase space. This technique is well known as McGehee's collision manifold (1974 Inventions Math. 27 191–227) in the N-body problem of celestial mechanics. Finally, by adopting the viewpoint of Easton (1971 J. Diff. Eqns 10 92–9), topological regularizations of the triple collision singularity are studied in detail.
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A qualitative analysis of the motion of three point vortices with arbitrary strengths is given. This simplifies and extends recent work by Novikov (1975) on the motion of three identical vortices. By using a phase-diagram technique, the possible regimes of motion are classified according to the signs of the arithmetic, geometric, and harmonic means of the three vortex strengths. For the special case where the vortex strengths (k1, k2, k3) take the values (+k, +k, -k), the diagram has an interpretation in terms of the scattering of a neutral pair by a single vortex. Quantitative details are presented for this case. If the harmonic mean of the three vortex strengths is zero, the triangle of vortices can collapse to a point in a finite time for ceratin initial conditions.