Recent zbMATH articles in MSC 37J30 https://www.zbmath.org/atom/cc/37J30 2022-04-28T18:15:44.554837Z Werkzeug Integrability of point-vortex dynamics via symplectic reduction: a survey https://www.zbmath.org/1482.37056 2022-04-28T18:15:44.554837Z "Modin, Klas" https://www.zbmath.org/authors/?q=ai:modin.klas "Viviani, Milo" https://www.zbmath.org/authors/?q=ai:viviani.milo The authors consider point-vertex dynamics and their integrability. This dynamics is described via idealized non-smooth solutions to the incompressible Euler equations on two-dimensional manifolds. The aim is to provide a unified treatment for proving integrability results for 2-, 3-, or 4-point-vertices. Part of their goal is to show how the symplectic reduction can provide a broader approach for proving integrability results, especially for point-vertex dynamics. Euler equations on an orientable Riemannian manifold that govern an incompressible inviscid fluid have the form $$\dot{\mathbf{v}} + \nabla _\mathbf{v} \mathbf{v} = - \nabla p$$ with div $$\mathbf{v} = 0$$, where $$\mathbf{v}$$ is a vector field on a manifold $$M$$ incorporating the motion of the fluid's particles, $$p$$ is the pressure function and $$\nabla _\mathbf{v}$$ is the covariant derivative along $$\mathbf{v}$$. \textit{H. Helmholtz} [J. Reine Angew. Math. 55, 25--55 (1858; ERAM 055.1448cj)] showed that the two-dimensional Euler equations have special solutions with a finite number of point-vertices. These solutions are not smooth and are characterized by the vorticity \mbox{curl $$\mathbf{v} = \sum_{i=1} ^ {n} \Gamma _i \delta_{\mathbf{r}_i}$$} where non-zero $$\Gamma_i$$ is the strength of the vortex $$i$$, $$\mathbf{r}_i$$ is its position, and $$\delta_{\mathbf{r}_i}$$ is a delta function. The authors describe point-vertex equations and their Hamiltonian structures on the sphere, the plane, the hyperbolic plane, and the flat torus. Each of these cases has a different symmetry group, and the symplectic reduction is treated separately in each case to establish integrability. The authors also briefly review nonintegrability results. They conclude with some observations about how their results pertain to long term predictions for the Euler equations. An appendix offers a kind of visual portrait of point-vortex solutions. Reviewer: William J. Satzer Jr. (St. Paul)