Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Aug. 14, 2008). PDF text: vi, 118 p. ; 460 K. UMI publication number: AAT 3297658. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaf 136). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Oregon State University, 1991. / Typescript (photocopy). Includes bibliographical references (leaves 62-64). Also available on the World Wide Web.

In chapter 2 we use functional analytic methods and conservation laws to solve the initial-value problem for the Korteweg-de Vries equation, the Benjamin-Bona-Mahony equation, and the nonlinear Schrodinger equation for initial data that satisfy some suitable conditions. In chapter 3 we use the energy estimates to show that the strong convergence of the family of the solutions of the KdV equation obtained in chapter 2 in H³(R) as ε → 0; also, we show that the strong L²(R)-limit of the solutions of the BBM equation as ε → 0 before a critical time. In chapter 4 we use the Whitham modulation theory and averaging method to find the 2π-periodic solutions and the modulation equations of the KdV equation, the BBM equation, the Klein-Gordon equation, the NLS equation, the mKdV equation, and the P-system. We show that the modulation equations of the KdV equation, the K-G equation, the NLS equation, and the mKdV equation are hyperbolic but those of the BBM equation and the P-system are not hyperbolic. Also, we study the relations of the KdV equation and the mKdV equation. Finally, we study the complex mKdV equation to compare with the NLS equation, and then study the complex gKdV equation.

In this paper we construct explicit examples of solutions to certain nonlinear wave equations. These semilinear equations are the simplest equations known to possess localized solitary waves in more that one spatial dimension. We construct explicit localized standing wave solutions, which generate multidimensional localized traveling solitary waves under the action of velocity boosts. We study the case of two spatial dimensions and a piecewise-linear nonlinearity. We obtain a large subset of the infinite family of standing waves, and we exhibit several interesting features of the family. Our solutions include solitary waves that carry nonzero angular momenta in their rest frames. The spatial profiles of these solutions also furnish examples of symmetry breaking for nonlinear elliptic equations.

En zones côtières, une onde se propageant à la surface de l'océan est fortement influencée par le courant sous-jacent. Les profiles de vitesses sont variables en profondeur du fait du vent soufflant à la surface et des frottements au fond. En considérant les équations d'Euler pour un fluide non-visqueux et incompressible, accompagnées des conditions de surface cinématiques et dynamiques appropriées, l'interaction entre une onde de surface bi-dimensionnelle, progressive et périodique et un courant sous-jacent est étudiée. En ne considérant pas uniquement un champs de vitesses dérivant d'un potentiel scalaire, ce travail étend le modèle d'un courant cisaillé linéairement à des profiles de courant définis par une classe de fonctions de vorticité exponentielle.Il est montré que ces profiles de courant bi-dimensionnelles sont linéairement stables en l'absence d'une perturbation à la surface. L'influence du courant sous-jacent sur des ondes d'amplitude et de profondeur arbitraire est ensuite étudiée numériquement, en présence ou non de capillarité. Malgré le fait que la célérité et l'énergie potentielle et cinématique de l'onde sont fortement influencées par le paramètre de non-linéarité que représente la cambrure, il est montré que l'effet de la vorticité est non-négligeable, surtout pour des ondes de gravité pure. Finalement, des résultats sont présentés pour une étude de stabilité linéaire d'ondes d'amplitude finie (2D) perturbées en trois dimensions. Les classes d'instabilité classiques sont détectées en présence de vorticité constante et non-constante. De plus, un mécanisme est proposé pour une instabilité tri-dimensionnelle dominante en présence de vorticité. / In coastal zones, waves propagating at the surface of the ocean are strongly influenced by underlying shear currents. Depth-dependent velocity profiles are generated by wind blowing at the surface and friction at the bed. Considering the Euler equations for an inviscid and incompressible fluid, along with the appropriate free-surface kinematic and dynamic boundary conditions, the interaction between a two-dimensional progressive periodic free-surface wave of permanent form and an underlying current is studied. By not assuming that the velocity field derives from a scalar potential, this work extends the linear, constant vorticity, shear model to velocity profiles defined by a class of exponential vorticity functions. The two-dimensional current profiles are first shown to be linearly stable in the absence of a free-surface perturbation. The influence of the underlying shear on waves of arbitrary amplitude and depth is then studied numerically, both in the absence and presence of capillarity. Although the celerity and potential and kinetic energy of the wave are strongly influenced by the nonlinear wave steepness parameter, the effect of vorticity is shown to be non-negligible, especially for pure gravity waves. Finally, results are presented for a linear stability analysis of these finite amplitude (2D) waves under three-dimensional perturbations. It is found that the classical classes of instability corresponding to four and five wave resonances are recovered in three-dimensions in the presence of constant or depth-dependent vorticities. Finally, a mechanism is proposed for the dominant three-dimensional instability caused by the presence of an underlying shear current.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 135-143). Available also in a digital version from Dissertation Abstracts.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

We study the initial value problem for the defocusing nonlinear wave equation with cubic nonlinearity F(u)=|u|^2u in the energy-supercritical regime, that is dimensions d\geq 5. We prove that solutions to this equation satisfying an a priori bound in the critical homogeneous Sobolev space exist globally in time and scatter in the case of spatial dimensions d\geq 6 with general (possibly non-radial) initial data, and in the case of spatial dimension d=5 with radial initial data. / text

We carry out a preliminary group classification of the following family of non-linear wave equations u_tt =f(u_x)u_xx+g(u_x)+x. We first re-obtain the principal Lie algebra obtained by Ibragimov et al[3) and then construct the equivalence Lie algebra. In order to partially classify this family of wave equations, optimal systems of one-dimensional sub-algebras of the equivalence Lie algebra are constructed and in so doing, two distinct equations are obtained. We furthermore determine some invariant solutions of these equations. / Thesis (MSc. Mathematics) North-West University, Mafikeng Campus, 2003