Computation of Time-Periodic Solutions of the Benjamin-Ono Equation

TL;DR

This paper introduces a spectrally accurate numerical method to find and analyze non-trivial time-periodic solutions of the Benjamin-Ono equation, connecting stationary and traveling wave solutions through continuation and analytical derivation.

Contribution

The paper develops a novel numerical approach for computing time-periodic solutions of nonlinear PDEs and derives exact formulas for solutions along solution paths.

Findings

Successfully computed global paths of solutions connecting stationary and traveling waves.

Identified analytical forms of solutions on the solution paths.

Derived exact formulas for soliton solutions using numerical insights.

Abstract

We present a spectrally accurate numerical method for finding non-trivial time-periodic solutions of non-linear partial differential equations. The method is based on minimizing a functional (of the initial condition and the period) that is positive unless the solution is periodic, in which case it is zero. We solve an adjoint PDE to compute the gradient of this functional with respect to the initial condition. We include additional terms in the functional to specify the free parameters, which, in the case of the Benjamin-Ono equation, are the mean, a spatial phase, a temporal phase and the real part of one of the Fourier modes at $t=0$. We use our method to study global paths of non-trivial time-periodic solutions connecting stationary and traveling waves of the Benjamin-Ono equation. As a starting guess for each path, we compute periodic solutions of the linearized problem by solving an infinite dimensional eigenvalue problem in closed form. We then use our numerical method to continue these solutions beyond the realm of linear theory until another traveling wave is reached. By experimentation with data fitting, we identify the analytical form of the solutions on the path connecting the one-hump stationary solution to the two-hump traveling wave. We then derive exact formulas for these solutions by explicitly solving the system of ODE's governing the evolution of solitons using the ansatz suggested by the numerical simulations.