Rigorous derivation of the Kuramoto-Sivashinsky equation in a 2D weakly nonlinear Stefan problem

TL;DR

This paper rigorously derives the Kuramoto-Sivashinsky equation from a 2D weakly nonlinear Stefan problem, establishing a connection between free boundary problems and the K--S equation through analytical methods.

Contribution

It provides a rigorous derivation of the Kuramoto-Sivashinsky equation from a 2D Stefan problem using Lyapunov-Schmidt reduction and solvability conditions.

Findings

The derived parabolic equation accurately approximates the free boundary dynamics.

The solution remains close to the K--S solution uniformly in small epsilon.

The method applies to a simplified solid-liquid interface model.

Abstract

In this paper we are interested in a rigorous derivation of the Kuramoto-Sivashinsky equation (K--S) in a Free Boundary Problem. As a paradigm, we consider a two-dimensional Stefan problem in a strip, a simplified version of a solid-liquid interface model. Near the instability threshold, we introduce a small parameter $\varepsilon$ and define rescaled variables accordingly. At fixed $\varepsilon$, our method is based on: definition of a suitable linear 1D operator, projection with respect to the longitudinal coordinate only, Lyapunov-Schmidt method. As a solvability condition, we derive a self-consistent parabolic equation for the front. We prove that, starting from the same configuration, the latter remains close to the solution of K--S on a fixed time interval, uniformly in $\varepsilon$ sufficiently small.