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arXiv 1704.00560math.APcs.NAmath-phmath.MPmath.NAphysics.flu-dyn
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Navier-Stokes初值问题在临界空间中非唯一性的数值研究

Numerical investigations of non-uniqueness for the Navier-Stokes initial value problem in borderline spaces

UFR de Mathématiques, Université Paris-Diderot(巴黎第七大学数学系);School of Mathematics, University of Minnesota(明尼苏达大学数学学院)

Julien Guillod, Vladimír Šverák

AI总结:

本文研究了Navier-Stokes方程在临界空间中的初值问题的非唯一性,通过数值方法分析了轴对称初始数据的标度不变解,并探讨了大数据下初始数据反射对称性的破坏及非唯一性例子的建立。

摘要:

我们考虑了不可压缩Navier-Stokes方程在R^3中的初值问题,针对一个参数族的显式标度不变轴对称初始数据进行研究,这些数据在原点处光滑且关于xy平面反射对称。在轴对称场类中,我们通过其轮廓函数计算了初值问题的标度不变解,这些轮廓函数是光滑的。对于小数据,解是唯一的,但对于大数据,我们观察到初始数据的反射对称性通过pitchfork型分支破坏。通过Jia & Šverák (2013)的先前结果变种可知,若此处的数值结果能被证明,则可建立最优的非唯一性例子,即对于同一个无散、在原点处光滑、紧支撑且在原点附近局部(-1)-齐次的初始数据,存在两种不同的解。特别是,假设我们的(有限维)数值结果真实反映了完整(无限维)系统的行为,则Leray-Hopf解的唯一性问题(非光滑初始数据)的答案为负,此外,Kato (1984)和Koch & Tataru (2001)的扰动论证,或Leray、Prodi、Serrin、Ladyzhenskaya等人的弱-强唯一性结果,已经给出了本质上最优的结果。数值中没有奇点,因为我们只使用光滑轮廓函数。虽然我们的计算可能可以升级为计算机辅助证明,但这将需要大量的额外工作和计算,包括对远距离解的渐进行为的更详细分析。

英文摘要:

We consider the Cauchy problem for the incompressible Navier-Stokes equations in $\mathbb{R}^3$ for a one-parameter family of explicit scale-invariant axi-symmetric initial data, which is smooth away from the origin and invariant under the reflection with respect to the $xy$-plane. Working in the class of axi-symmetric fields, we calculate numerically scale-invariant solutions of the Cauchy problem in terms of their profile functions, which are smooth. The solutions are necessarily unique for small data, but for large data we observe a breaking of the reflection symmetry of the initial data through a pitchfork-type bifurcation. By a variation of previous results by Jia & Šverák (2013) it is known rigorously that if the behavior seen here numerically can be proved, optimal non-uniqueness examples for the Cauchy problem can be established, and two different solutions can exists for the same initial datum which is divergence-free, smooth away from the origin, compactly supported, and locally $(-1)$-homogeneous near the origin. In particular, assuming our (finite-dimensional) numerics represents faithfully the behavior of the full (infinite-dimensional) system, the problem of uniqueness of the Leray-Hopf solutions (with non-smooth initial data) has a negative answer and, in addition, the perturbative arguments such those by Kato (1984) and Koch & Tataru (2001), or the weak-strong uniqueness results by Leray, Prodi, Serrin, Ladyzhenskaya and others, already give essentially optimal results. There are no singularities involved in the numerics, as we work only with smooth profile functions. It is conceivable that our calculations could be upgraded to a computer-assisted proof, although this would involve a substantial amount of additional work and calculations, including a much more detailed analysis of the asymptotic expansions of the solutions at large distances.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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