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arXiv 2201.09762math.AP
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二维欧拉方程紧支集稳态解的对称性结果

Symmetry results for compactly supported steady solutions of the 2D Euler equations

David Ruiz

AI总结:

本文证明二维欧拉方程紧支集稳态解在环形区域或适当正则性条件下流线为圆形,并通过移动平面方法处理边界法向导数非零情形,克服非线性项非 Lipschitz 的困难。

摘要:

本文证明了二维欧拉方程紧支集稳态解的对称性。假设 $Ω= \{x \in \mathbb{R}^2:\\ u(x) \neq 0\}$ 是一个环形区域,我们证明流动的流线是圆形的。如果对 $u$ 在 $\partial Ω$ 上施加正则性和非退化性假设,我们还能去掉关于 $Ω$ 的拓扑条件。证明利用了相应的流函数求解椭圆半线性问题 $-Δϕ= f(ϕ)$,且在边界上 $\nabla ϕ=0$。我们研究中的一个主要困难是 $f$ 在边界值附近不是 Lipschitz 连续的。然而,$f(ϕ)$ 在边界值处为零,因此我们可以应用 F. Brock 的局部对称性结果来得出结论。在 $\partial Ω$ 上 $\partial_ν u \neq 0$ 的情形下,这一论证不可行。此时,尽管 $f$ 可能缺乏正则性,我们仍能使用移动平面方法来证明对称性。我们认为这一结果本身就很有意义,并将对更高维情形进行陈述和证明。证明需要研究具有奇异系数的椭圆线性算子的极值原理、Hopf 引理和 Serrin 角点引理。

英文摘要:

In this paper we prove symmetry of compactly supported steady solutions of the 2D Euler equations. Assuming that $Ω= \{x \in \mathbb{R}^2:\ u(x) \neq 0\}$ is an annular domain, we prove that the streamlines of the flow are circular. We are also able to remove the topological condition on $Ω$ if we impose regularity and nondegeneracy assumptions on $u$ at $\partial Ω$. The proof uses that the corresponding stream function solves an elliptic semilinear problem $-Δϕ= f(ϕ)$ with $\nabla ϕ=0$ at the boundary. One of the main difficulties in our study is that $f$ is not Lipschitz continuous near the boundary values. However, $f(ϕ)$ vanishes at the boundary values and then we can apply a local symmetry result of F. Brock to conclude. In the case $\partial_ν u \neq 0$ at $\partial Ω$ this argument is not possible. In this case we are able to use the moving plane scheme to show symmetry, despite the possible lack of regularity of $f$. We think that such result is interesting in its own right and will be stated and proved also for higher dimensions. The proof requires the study of maximum principles, Hopf lemma and Serrin corner lemma for elliptic linear operators with singular coefficients.

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