In chapter 3 of this thesis, I discuss in some detail the historical development of energy localization, emphasizing the particular physical concepts which are important for the understanding of this phenomenon. Furthermore, I describe the mathematical concepts of a discrete breather and homoclinic orbits, which are intimately connected between them and constitute the main object of study of this dissertation. / -

The convective fluid dynamics and chaos between two parallel plates with temperature discrepancy has been investigated via classic and extended Lorenz system. Both the classic 3-dimensional and extended 5-dimensional Lorenz system are developed by truncating a double Fourier series, which is the solution of the streamline function. Boundary conditions are also considered. The implicit discrete mapping method has been employed to solve the classic and extended Lorenz system, and the motion stability is determined by the eigenvalue analysis. Bifurcation diagram varying with Rayleigh parameter and Prandtl parameter are obtained by solving the stable and unstable period-m motions (m=1,2,4). Symmetric period-1 to asymmetric period-4 motions have been illustrated in the phase space. Therefore, the route from period-1 to period-4 motions to chaos through the period-doubling bifurcation has been demonstrated in the classic and extended Lorenz system. For the extended 5-dimensional Lorenz system, the harmonic frequency-amplitude characteristics are also presented, which provides energy distribution in the parameter space. On bifurcation tree, the non-spiral and spiral homoclinic orbits have been seen and been illustrated in 2-D view and 3-D view. Such homoclinic orbits represent the asymptotic convection steady state that generates the chaos in the convective fluid dynamics. The rich dynamical behaviors of the convective fluid are discovered, and this investigation may help one understand the chaotic dynamics for other thermal convection problems.

In this thesis we employ two recent analytical approaches to investigate the possible classes of traveling wave solutions of some members of recently derived integrable family of generalized Camassa-Holm (GCH) equations. In the first part, a novel application of phase-plane analysis is employed to analyze the singular traveling wave equations of four GCH equations, i.e. the possible non-smooth peakon, cuspon and compacton solutions. Two of the GCH equations do no support singular traveling waves. We generalize an existing theorem to establish the existence of peakon solutions of the third GCH equation. This equation is found to also support four segmented, non-smooth M-wave solutions. While the fourth supports both solitary (peakon) and periodic (cuspon) cusp waves in different parameter regimes. In the second part of the thesis, smooth traveling waves of the four GCH equations are considered. Here, we use a recent technique to derive convergent multi-infinite series solutions for the homoclinic and heteroclinic orbits of their traveling-wave equations, corresponding to pulse and front (kink or shock) solutions respectively of the original PDEs. Unlike the majority of unaccelerated convergent series, high accuracy is attained with relatively few terms. Of course, the convergence rate is not comparable to typical asymptotic series. However, asymptotic solutions for global behavior along a full homoclinic/heteroclinic orbit are currently not available.

Three-dimensional gravity-capillary steady waves on water of finite-depth, which are uniformly translating in a horizontal propagation direction and periodic in a transverse direction, are considered. The exact Euler equations are formulated as a spatial dynamic system in which the variable used for the propagating direction is the time-like variable. The existence of the solutions of the system is determined by two non-dimensional constants: the Bond number b and λ (the inverse of the square of the Froude number). The property of Sobolev spaces and the spectral analysis show that the spectrum of the linear part consists of isolated eigenvalues of finite algebraic multiplicity and the number of purely imaginary eigenvalues are finite. The distribution of eigenvalues is described by b and λ. Assume that C₁ is the curve in (b,λ)-plane on which the first two eigenvalues for three-dimensional waves collide at the imaginary axis, and that the intersection point of the curve C₁ with the line λ=1 is (b₀,1) where b₀>0. Two cases (b₀,1) and (b,λ) â C₁ where 0< b< b₀ are investigated. A center-manifold reduction technique and a normal form analysis are applied to show that for each case the dynamical system can be reduced to a system of ordinary differential equations with finite dimensions. The dominant system for the case (b₀,1) is coupled Schrödinger-KdV equations while it is a Schrödinger equation for another case (b,λ) â C₁. Then, from the existence of the homoclinic orbit connecting to the two-dimensional periodic solution (called generalized solitary wave) for the dominant system, it is obtained that such generalized solitary wave solution persists for the original system by using the perturbation method and adjusting some appropriate constants. / Ph. D.