Numerical Bifurcation and Spectral Stability of Wavetrains in Bidirectional Whitham Models

TL;DR

This paper investigates the existence and spectral stability of periodic traveling waves in bidirectional Whitham models, combining full dispersion with shallow water nonlinearity, using numerical bifurcation and spectral analysis.

Contribution

It provides the first comprehensive numerical bifurcation analysis of these models, revealing the global structure of wave branches and stability properties for large amplitude waves.

Findings

Global bifurcation diagrams constructed for each model

Identification of bifurcation branches ending in peaked waves

Numerical stability spectra align with analytical predictions

Abstract

We consider several different bidirectional Whitham equations that have recently appeared in the literature. Each of these models combine the full two-way dispersion relation from the incompressible Euler equations with a canonical shallow water nonlinearity, providing nonlocal model equations that may be expected to exhibit some of the interesting high-frequency phenomena present in the Euler equations that standard "long-wave" theories fail to capture. Of particular interest here is the existence and stability of periodic traveling wave solutions in such models. Using numerical bifurcation techniques we construct global bifurcation diagrams for each system and compare the global structure of branches, together with the possibility of bifurcation branches terminating in a "highest" singular (peaked/cusped) wave. We also numerically approximate the stability spectrum along these bifurcation branches and compare the stability predictions of these models. Our results confirm a number of analytical results concerning the stability of asymptotically small waves in these models and provide new insights into the existence and stability of large amplitude waves.