高维中的稳态欧拉流与贝尔特拉米场
Steady Euler flows and Beltrami fields in high dimensions
AI总结:
本文利用开书分解,在任意奇数维流形上为欧拉方程构造非消失稳态解,实现于接触Reeb场的不变子流形,并刻画贝尔特拉米场,与三维情形对比,构造无周期轨道的非消失贝尔特拉米场。
摘要:
利用开书分解,我们证明了在任意奇数维流形的非消失向量场的每个同伦类中,对于某个度量,欧拉方程存在非消失的稳态解。作为推论,任何这样的场都可以在高维球面上的接触Reeb场的不变子流形中实现。构造的解是可测地线(geodesible)的,因此属于贝尔特拉米(Beltrami)型,并且可以被修改以获得混沌流体。我们刻画了奇数维中的贝尔特拉米场,并证明总是存在保体积的贝尔特拉米场,它们对于任何度量既不是可测地线的也不是欧拉流。这与三维情形形成对比,在三维中,每个保体积的贝尔特拉米场都是某个度量的稳态欧拉流。最后,我们在每个大于三的奇数维流形中构造了一个无周期轨道的非消失贝尔特拉米场(不一定是保体积的)。
英文摘要:
Using open books, we prove the existence of a non-vanishing steady solution to the Euler equations for some metric in every homotopy class of non-vanishing vector fields of any odd dimensional manifold. As a corollary, any such field can be realized in an invariant submanifold of a contact Reeb field on a sphere of high dimension. The constructed solutions are geodesible and hence of Beltrami type, and can be modified to obtain chaotic fluids. We characterize Beltrami fields in odd dimensions and show that there always exist volume-preserving Beltrami fields which are neither geodesible nor Euler flows for any metric. This contrasts with the three dimensional case, where every volume-preserving Beltrami field is a steady Euler flow for some metric. Finally, we construct a non-vanishing Beltrami field (which is not necessarily volume-preserving) without periodic orbits in every manifold of odd dimension greater than three.
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