Symmetries and conservation laws of the Euler equations in Lagrangian coordinates

TL;DR

This paper explores symmetries and conservation laws of the Euler equations in Lagrangian coordinates, revealing new invariants and inequalities that deepen understanding of fluid dynamics and restrict possible solutions.

Contribution

It introduces a new scaling symmetry and a corresponding conservation law for Euler equations in Lagrangian coordinates, linking kinetic energy to a novel integral quantity.

Findings

Derived a new conservation law relating kinetic energy and an integral quantity.

Established an inequality constraining radial deformation of the fluid.

Proved the non-existence of nonzero, finite energy time-periodic solutions.

Abstract

We consider the Euler equations of incompressible inviscid fluid dynamics. We discuss a variational formulation of the governing equations in Lagrangian coordinates. We compute variational symmetries of the action functional and generate corresponding conservation laws in Lagrangian coordinates. We clarify and demonstrate relationships between symmetries and the classical balance laws of energy, linear momentum, center of mass, angular momentum, and the statement of vorticity advection. Using a newly obtained scaling symmetry, we obtain a new conservation law for the Euler equations in Lagrangian coordinates in n-dimensional space. The resulting integral balance relates the total kinetic energy to a new integral quantity defined in Lagrangian coordinates. This relationship implies an inequality which describes the radial deformation of the fluid, and shows the non-existence of time-periodic solutions with nonzero, finite energy.