Stokes waves with constant vorticity: I. numerical computation

TL;DR

This paper presents a numerical method for computing periodic Stokes waves with constant vorticity, revealing phenomena like overhanging profiles and extreme waves, and comparing favorably with previous results.

Contribution

It introduces an efficient Newton-GMRES based numerical approach for Stokes waves with vorticity, capturing complex wave profiles and behaviors.

Findings

Overhanging wave profiles occur at high steepness with strong positive vorticity.

Touching waves and extreme waves with sharp crests are identified.

Wave speed versus steepness exhibits a gap, indicating physical and unphysical solution regimes.

Abstract

Periodic traveling waves are numerically computed in a constant vorticity flow subject to the force of gravity. The Stokes wave problem is formulated via a conformal mapping as a nonlinear pseudo-differential equation, involving a periodic Hilbert transform for a strip, and solved by the Newton-GMRES method. It works well with a fast Fourier transform and is more effective than a boundary integral method. The result is in excellent agreement, qualitatively and quantitatively, with earlier ones. For strong positive vorticity, in the finite or infinite depth, overhanging profiles are found as the steepness increases and tend to a touching wave, whose profile self-intersects somewhere along the trough line, trapping an air bubble; the numerical solutions become unphysical as the steepness increases further and make a gap in the wave speed versus steepness plane; a touching wave then takes over and the physical solutions follow in the wave speed versus steepness plane until they ultimately tend to an extreme wave, which exhibits a sharp corner at the crest. Overhanging waves of nearly maximum heights are found to approach rigid body rotation of a fluid disk as the strength of positive vorticity increases.