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arXiv 1808.01769math-phmath.MPmath.SGnlin.SIphysics.flu-dyn
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平面上$N$点涡的辛约化与Lie-Poisson形状动力学

Symplectic Reduction and the Lie--Poisson Shape Dynamics of $N$ Point Vortices on the Plane

Tomoki Ohsawa

摘要:

我们表明,由特殊的欧几里德群$\mathsf{SE}(2)$的平面上的$N$点涡的动力学的辛约化产生一个Lie-Poisson方程的涡的相对配置。具体来说,我们结合辛减少阶段与对偶对与减少旋转表明,$\mathsf{SE}(2)$约化空间与非零角脉冲是一个coadjoint轨道。这一结果补充了一些现有的工作,通过建立原动力学和约化动力学的辛/哈密顿结构之间的关系。我们还发现了一个家族的Casimirs与Lie-Poisson结构,包括一些显然是新的。我们证明,通过例子,人们可以利用这些卡西米尔表明,一些形状的动力学是周期性的。

英文摘要:

We show that the symplectic reduction of the dynamics of $N$ point vortices on the plane by the special Euclidean group $\mathsf{SE}(2)$ yields a Lie--Poisson equation for relative configurations of the vortices. Specifically, we combine symplectic reduction by stages with a dual pair associated with the reduction by rotations to show that the $\mathsf{SE}(2)$-reduced space with non-zero angular impulse is a coadjoint orbit. This result complements some existing works by establishing a relationship between the symplectic/Hamiltonian structures of the original and reduced dynamics. We also find a family of Casimirs associated with the Lie--Poisson structure including some apparently new ones. We demonstrate through examples that one may exploit these Casimirs to show that some shape dynamics are periodic.

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