92 research outputs found
Simple wave interaction of an elastic string
The equations for the two-dimensional motion of a completely flexible elastic string can be derived from a Lagrangian. The equations of motion possess four characteristic velocities, to which the following four simple wave solutions correspond: leftward and rightward propagating longitudinal and transverse waves. The latter are exceptional (constant shape). By expanding the solution about a steady solution the interaction of simple waves may be studied. A typical result is the following: As a consequence of their interaction two transverse waves running into opposite directions emit a longitudinal wave and undergo themselves a translation over a finite distance but remain otherwise unchanged. The results are also valuable for a full comprehension of the interaction process of simple waves on inextensible strings
Stable model equations for long water waves
In this paper, a sequel to two others [1, 2], some extensions and improvements of this earlier work are presented. Among these are: A more precise version of the proof of the basic canonical theorem, some considerations on conservation laws and their relation, a more complete treatment of the stability of the models, especially with respect to the wave amplitude, a short treatment of the Lagrangian version of the theory, a stable discrete model which might be useful for numerical experiments and an extension of the method to the case of slowly varying water depth
Non-Hamiltonian symmetries of a Boussinesq equation
For a class of Hamiltonian systems there exist infinite series of non-Hamiltonian symmetries. Some properties of these series are illustrated using a Boussinesq equation. It is shown that the recursion operators generated by these non-Hamiltonian symmetries are powers of the original recursion operator. A class of recursion formulas for the constants of the motion (not for the corresponding symmetries!) is given
Modeling water waves beyond perturbations
In this chapter, we illustrate the advantage of variational principles for
modeling water waves from an elementary practical viewpoint. The method is
based on a `relaxed' variational principle, i.e., on a Lagrangian involving as
many variables as possible, and imposing some suitable subordinate constraints.
This approach allows the construction of approximations without necessarily
relying on a small parameter. This is illustrated via simple examples, namely
the Serre equations in shallow water, a generalization of the Klein-Gordon
equation in deep water and how to unify these equations in arbitrary depth. The
chapter ends with a discussion and caution on how this approach should be used
in practice.Comment: 15 pages, 1 figure, 39 references. This document is a contributed
chapter to an upcoming volume to be published by Springer in Lecture Notes in
Physics Series. Other author's papers can be downloaded at
http://www.denys-dutykh.com
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