Title: Vanishing viscosity limit for axisymmetric vortex rings
For the incompressible Navier-Stokes equations in R3 with low viscosity ν > 0, we consider the Cauchy problem with initial vorticity ω0 that represents an infinitely thin vortex filament of arbitrary given strength \Gamma supported on a circle. The vorticity field ω(x, t) of the solution is smooth at any positive time and corresponds to a vortex ring of thickness√νt that is translated along its symmetry axis due to self-induction, an effect anticipated by Helmholtz in 1858 and quantified by Kelvin in 1867. For small viscosities, we show that ω(x, t) is well-approximated on a large time interval by ω_lin (x − a(t), t), where ω_lin(·, t) = exp(νt\Delta)ω0 is the solution of the heat equation with initial data ω0, and ˙a(t) is the instantaneous velocity given by Kelvin’s formula. This gives a rigorous justification of the binormal motion for circular vortex filaments in weakly viscous fluids. The proof relies on the construction of a precise approximate solution, using a perturbative expansion in self-similar variables. To verify the stability of this approximation, one needs to rule out potential instabilities coming from very large advection terms in the linearized operator. This is done by adapting V. I. Arnold’s geometric stability methods developed in the inviscid case ν = 0 to the slightly viscous situation. It turns out that although the geometric structures behind Arnold’s approach are no longer preserved by the equation for ν >0, the relevant quadratic forms behave well on larger subspaces than those originally used in Arnold’s theory and interact favorably with the viscous terms. more »« less
Agrawal, Siddhant; Nahmod, Andrea R
(, Nonlinearity)
Abstract We consider the 2D incompressible Euler equation on a corner domain Ω with angle νπ with 1 2 < ν < 1 . We prove that if the initial vorticity ω 0 ∈ L 1 (Ω) ∩ L ∞ (Ω) and if ω 0 is non-negative and supported on one side of the angle bisector of the domain, then the weak solutions are unique. This is the first result which proves uniqueness when the velocity is far from Lipschitz and the initial vorticity is non-constant around the boundary.
Gallay, Thierry; Šverák, Vladimír
(, Analysis & PDE)
We consider variational principles related to V. I. Arnold’s stability criteria for steady-state solutions of the two-dimensional incompressible Euler equation. Our goal is to investigate under which conditions the quadratic forms defined by the second variation of the associated functionals can be used in the stability analysis, both for the Euler evolution and for the Navier–Stokes equation at low viscosity. In particular, we revisit the classical example of Oseen’s vortex, providing a new stability proof with a stronger geometric flavor. Our analysis involves a fairly detailed functional-analytic study of the inviscid case, which may be of independent interest, and a careful investigation of the influence of the viscous term in the particular example of the Gaussian vortex.
Farah, Luiz Gustavo; Holmer, Justin; Roudenko, Svetlana; Yang, Kai
(, American Journal of Mathematics)
Abstract: We consider the quadratic Zakharov-Kuznetsov equation $$\partial_t u + \partial_x \Delta u + \partial_x u^2=0$$ on $$\Bbb{R}^3$$. A solitary wave solution is given by $Q(x-t,y,z)$, where $$Q$$ is the ground state solution to $$-Q+\Delta Q+Q^2=0$$. We prove the asymptotic stability of these solitary wave solutions. Specifically, we show that initial data close to $$Q$$ in the energy space, evolves to a solution that, as $$t\to\infty$$, converges to a rescaling and shift of $Q(x-t,y,z)$ in $L^2$ in a rightward shifting region $$x>\delta t-\tan\theta\sqrt{y^2+z^2}$$ for $$0\leq\theta\leq{\pi\over 3}-\delta$$.
Costin, Ovidiu; Costin, Rodica; Jauslin, Ian; Lebowitz, Joel L
(, Communications in Mathematical Physics)
Springer
(Ed.)
We analyze non-perturbatively the one-dimensional Schrödinger equation describing the emission of electrons from a model metal surface by a classical oscillating electric field. Placing the metal in the half-space x 0, the Schrödinger equation of the system is i∂t ψ = − 2 1 ∂x 2 ψ + (x)(U − E x cos ωt)ψ, t > 0, x ∈ R, where (x) is the Heaviside function and U > 0 is the effective confining potential (we choose units so that m = e = = 1). The amplitude E of the external electric field and the frequency ω are arbitrary. We prove existence and uniqueness of classical solutions of the Schrödinger equation for general initial conditions ψ(x, 0) = f (x), x ∈ R. When 2the initial condition is in L the evolution is unitary and the wave function goes to zero at any fixed x as t → ∞. To show this we prove a RAGE type theorem and show that the discrete spectrum of the quasienergy operator is empty. To obtain positive electron current we consider non-L 2 initial conditions containing an incoming beam from the left. The beam is partially reflected and partially transmitted for all t > 0. For these initial conditions we show that the solution approaches in the large t limit a periodic state that satisfies an infinite set of equations formally derived, under the assumption that the solution is periodic by Faisal et al. (Phys Rev A 72:023412, 2005). Due to a number of pathological features of the Hamiltonian (among which unboundedness in the physical as well as the spatial Fourier domain) the existing methods to prove such results do not apply, and we introduce new, more general ones. The actual solution exhibits a very complex behavior, as seen both analytically and numerically. It shows a steep increase in the current as the frequency passes a threshold value ω = ωc , with ωc depending on the strength of the electric field. For small E, ωc represents the threshold in the classical photoelectric effect, as described by Einstein’s theory.
Abstract We study the singularity formation of a quasi-exact 1D model proposed by Hou and Li (2008Commun. Pure Appl. Math.61661–97). This model is based on an approximation of the axisymmetric Navier–Stokes equations in therdirection. The solution of the 1D model can be used to construct an exact solution of the original 3D Euler and Navier–Stokes equations if the initial angular velocity, angular vorticity, and angular stream function are linear inr. This model shares many intrinsic properties similar to those of the 3D Euler and Navier–Stokes equations. It captures the competition between advection and vortex stretching as in the 1D De Gregorio (De Gregorio 1990J. Stat. Phys.591251–63; De Gregorio 1996Math. Methods Appl. Sci.191233–55) model. We show that the inviscid model with weakened advection and smooth initial data or the original 1D model with Hölder continuous data develops a self-similar blowup. We also show that the viscous model with weakened advection and smooth initial data develops a finite time blowup. To obtain sharp estimates for the nonlocal terms, we perform an exact computation for the low-frequency Fourier modes and extract damping in leading order estimates for the high-frequency modes using singularly weighted norms in the energy estimates. The analysis for the viscous case is more subtle since the viscous terms produce some instability if we just use singular weights. We establish the blowup analysis for the viscous model by carefully designing an energy norm that combines a singularly weighted energy norm and a sum of high-order Sobolev norms.
@article{osti_10552303,
place = {Country unknown/Code not available},
title = {Vanishing viscosity limit for axisymmetric vortex rings},
url = {https://par.nsf.gov/biblio/10552303},
DOI = {10.1007/s00222-024-01261-5},
abstractNote = {For the incompressible Navier-Stokes equations in R3 with low viscosity ν > 0, we consider the Cauchy problem with initial vorticity ω0 that represents an infinitely thin vortex filament of arbitrary given strength \Gamma supported on a circle. The vorticity field ω(x, t) of the solution is smooth at any positive time and corresponds to a vortex ring of thickness√νt that is translated along its symmetry axis due to self-induction, an effect anticipated by Helmholtz in 1858 and quantified by Kelvin in 1867. For small viscosities, we show that ω(x, t) is well-approximated on a large time interval by ω_lin (x − a(t), t), where ω_lin(·, t) = exp(νt\Delta)ω0 is the solution of the heat equation with initial data ω0, and ˙a(t) is the instantaneous velocity given by Kelvin’s formula. This gives a rigorous justification of the binormal motion for circular vortex filaments in weakly viscous fluids. The proof relies on the construction of a precise approximate solution, using a perturbative expansion in self-similar variables. To verify the stability of this approximation, one needs to rule out potential instabilities coming from very large advection terms in the linearized operator. This is done by adapting V. I. Arnold’s geometric stability methods developed in the inviscid case ν = 0 to the slightly viscous situation. It turns out that although the geometric structures behind Arnold’s approach are no longer preserved by the equation for ν >0, the relevant quadratic forms behave well on larger subspaces than those originally used in Arnold’s theory and interact favorably with the viscous terms.},
journal = {Inventiones mathematicae},
volume = {237},
number = {1},
publisher = {Invent. Math., published by Springer},
author = {Gallay, Thierry and Šverák, Vladimír},
}
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