Toggle Main Menu Toggle Search

Open Access padlockePrints

Camassa-Holm, Korteweg-de Vries and related models for water waves

Lookup NU author(s): Professor Robin Johnson


Full text for this publication is not currently held within this repository. Alternative links are provided below where available.


In this paper we first describe the current method for obtaining the Camassa-Holm equation in the context of water waves; this requires a detour via the Green-Naghdi model equations, although the important connection with classical (Korteweg-de Vries) results is included. The assumptions underlying this derivation are described and their roles analysed. (The critical assumptions are, (i) the simplified structure through the depth of the water leading to the Green-Naghdi equations, and, (ii) the choice of submanifold in the Hamiltonian representation of the Green-Naghdi equations. The first of these turns out to be unimportant because the Green-Naghdi equations can be obtained directly from the full equations, if quantities averaged over the depth are considered. However, starting from the Green-Naghdi equations precludes, from the outset, any role for the variation of the flow properties with depth; we shall show that this variation is significant. The second assumption is inconsistent with the governing equations.) Returning to the full equations for the water-wave problem, we retain both parameters (amplitude, ε, and shallowness, δ) and then seek a solution as an asymptotic expansion valid for, ε → O, δ → O, independently. Retaining terms O(ε), O(δ2) and O(εδ2), the resulting equation for the horizontal velocity component, evaluated at a specific depth, is a Camassa-Holm equation. Some properties of this equation, and how these relate to the surface wave, are described; the role of this special depth is discussed. The validity of the equation is also addressed; it is shown that the Camassa-Holm equation may not be uniformly valid: on suitably short length scales (measured by δ) other terms become important (resulting in a higher-order Korteweg-de Vries equation, for example). Finally, we indicate how our derivation can be extended to other scenarios; in particular, as an example, we produce a two-dimensional Camassa-Holm equation for water waves.

Publication metadata

Author(s): Johnson RS

Publication type: Article

Publication status: Published

Journal: Journal of Fluid Mechanics

Year: 2002

Volume: 455

Pages: 63-82

ISSN (print): 0022-1120

ISSN (electronic): 1469-7645

Publisher: Cambridge University Press


DOI: 10.1017/S0022112001007224


Altmetrics provided by Altmetric