Boussinesq equations and other systems for small-amplitude long waves in nonlinear dispersive media

Part II: the nonlinear theory

Abstract

In Part I of this work, a four-parameter family of Boussinesq systems was derived to describe the propagation of surface water waves. Similar systems are expected to arise in other physical settings where the dominant aspects of propagation are a balance between the nonlinear effects of convection and the linear effects of frequency dispersion. In addition to deriving these systems, we determined in Part I exactly which of them are linearly well posed in various natural function classes. It was argued that linear well-posedness is a natural necessary requirement for the possible physical relevance of the model in question. In the present article, it is shown that the first-order correct models that are linearly well posed are in fact locally nonlinearly well posed. Moreover, in certain specific cases, global well-posedness is established for physically relevant initial data. In Part I, higher-order correct models were also derived. A preliminary analysis of a promising subclass of these models shows them to be well posed.