Non-linear shallow water dynamics with odd viscosity

TL;DR

This paper derives a KdV equation for shallow water surface dynamics incorporating odd viscosity, revealing a transition between weak and strong parity-breaking regimes with distinct soliton behaviors.

Contribution

It introduces a novel KdV model for fluids with odd viscosity, identifying a sharp transition in soliton characteristics based on parity-breaking strength.

Findings

Existence of two regimes with a transition point in odd viscosity effects

Weak regime shows minor differences in soliton properties

Strong regime produces depression solitons in one chiral sector

Abstract

In this letter, we derive the Korteweg-de Vries (KdV) equation corresponding to the surface dynamics of a shallow depth ($h$) two-dimensional fluid with odd viscosity ($\nu_o$) subject to gravity ($g$) in the long wavelength weakly nonlinear limit. In the long wavelength limit, the odd viscosity term plays the role of surface tension albeit with opposite signs for the right and left movers. We show that there exists two regimes with a sharp transition point within the applicability of the KdV dynamics, which we refer to as weak $(|\nu_o|< \sqrt{gh^3}/6)$ and strong $(|\nu_o|> \sqrt{gh^3}/6)$ parity-breaking regimes. While the `weak' parity breaking regime results in minor qualitative differences in the soliton amplitude and velocity between the right and left movers, the `strong' parity breaking regime on the contrary results in solitons of depression (negative amplitude) in one of the chiral sectors.