paper

Global existence and asymptotic behavior of affine motion of 3D ideal fluids surrounded by vacuum

arXiv:1512.03288 · doi:10.1007/s00205-017-1106-3

Abstract

The 3D compressible and incompressible Euler equations with a physical vacuum free boundary condition and affine initial conditions reduce to a globally solvable Hamiltonian system of ordinary differential equations for the deformation gradient in . The evolution of the fluid domain is described by a family ellipsoids whose diameter grows at a rate proportional to time. Upon rescaling to a fixed diameter, the asymptotic limit of the fluid ellipsoid is determined by a positive semi-definite quadratic form of rank , 2, or 3, corresponding to the asymptotic degeneration of the ellipsoid along of its principal axes. In the compressible case, the asymptotic limit has rank , and asymptotic completeness holds, when the adiabatic index satisfies . The number of possible degeneracies, , increases with the value of the adiabatic index . In the incompressible case, affine motion reduces to geodesic flow in with the Euclidean metric. For incompressible affine swirling flow, there is a structural instability. Generically, when the vorticity is nonzero, the domains degenerate along only one axis, but the physical vacuum boundary condition fails over a finite time interval. The rescaled fluid domains of irrotational motion can collapse along two axes.

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