Journal of Fluid Mechanics

A general approach to linear and non-linear dispersive waves using a Lagrangian

G. B.  Whitham a1
a1 California Institute of Technology

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The basic property of equations describing dispersive waves is the existence of solutions representing uniform wave trains. In this paper a general theory is given for non-uniform wave trains whose amplitude, wave-number, etc., vary slowly in space and time, the length and time scales of the variation in amplitude, wave-number, etc., being large compared to the wavelength and period. Dispersive equations may be derived from a variational principle with appropriate Lagrangian, and the whole theory is developed in terms of the Lagrangian. Boussinesq's equations for long water waves are used as a typical example in presenting the theory.

(Published Online March 28 2006)
(Received October 20 1964)