Extra High Voltage (EHV) transmission lines are designed to transfer large amount of power from one location to another. The length exposed to the environment is a major reason for occurrence of faults on the lines. A fault on a high voltage transmission line affects the stability of the overall power system, which sometimes leads to permanent damage of the equipment. Relays are developed and installed to protect the lines. The transmission line protection relays, in the industry, are based on the fundamental frequency components of the voltages and currents. These relays need at least one fundamental frequency cycle for performing the protection operation. Voltage and current traveling waves are generated when a fault occurs on the transmission line. The velocity of propagation of traveling waves is finite and the level of the waves decreases with increase in the distance traveled. Information about the fault can be obtained by analyzing the traveling waves. A few traveling wave techniques, which are based on analog signal processing, to protect transmission lines have been proposed in the past. Two digital techniques, which use traveling waves for protecting EHV transmission lines, are proposed in this thesis. The traveling waves are extracted from the modal voltages and currents at the terminals of the transmission line. The techniques identify and locate the fault by using the information contained in the waves. A power system was modeled in the Electromagnetic Transient Direct Current Analysis (EMTDC) and several cases were created by varying different parameters related to the fault, fault type, fault location, fault resistance and fault inception angle. The techniques were implemented in hardware and their performance was tested on data, generated from the EMTDC simulations. Some cases are discussed in the thesis. The performance of the digital techniques for protecting EHV transmission lines using traveling waves was confirmed to be satisfactory. The proposed techniques provide protection at speed and discriminate well between internal and external faults.

Extra High Voltage (EHV) transmission lines are designed to transfer large amount of power from one location to another. The length exposed to the environment is a major reason for occurrence of faults on the lines. A fault on a high voltage transmission line affects the stability of the overall power system, which sometimes leads to permanent damage of the equipment. Relays are developed and installed to protect the lines. The transmission line protection relays, in the industry, are based on the fundamental frequency components of the voltages and currents. These relays need at least one fundamental frequency cycle for performing the protection operation. Voltage and current traveling waves are generated when a fault occurs on the transmission line. The velocity of propagation of traveling waves is finite and the level of the waves decreases with increase in the distance traveled. Information about the fault can be obtained by analyzing the traveling waves. A few traveling wave techniques, which are based on analog signal processing, to protect transmission lines have been proposed in the past. Two digital techniques, which use traveling waves for protecting EHV transmission lines, are proposed in this thesis. The traveling waves are extracted from the modal voltages and currents at the terminals of the transmission line. The techniques identify and locate the fault by using the information contained in the waves. A power system was modeled in the Electromagnetic Transient Direct Current Analysis (EMTDC) and several cases were created by varying different parameters related to the fault, fault type, fault location, fault resistance and fault inception angle. The techniques were implemented in hardware and their performance was tested on data, generated from the EMTDC simulations. Some cases are discussed in the thesis. The performance of the digital techniques for protecting EHV transmission lines using traveling waves was confirmed to be satisfactory. The proposed techniques provide protection at speed and discriminate well between internal and external faults.

We analyze a pair of nonlinear PDEs describing viscoelastic fluid flow in one dimension. We give a summary of the physical derivation and nondimensionlize the PDE system. Based on the boundary conditions and parameters, we are able to classify three different categories of traveling wave solutions, consistent with the results in [?]. We extend this work by analyzing the stability of the traveling waves. We thoroughly describe the numerical schemes and software program, VISCO, that were designed specifically to analyze the model we study in this paper. Our simulations lead us to conjecture that the traveling wave solutions found in [?] are globally stable for all sets of initial conditions with the appropriate asymptotic boundary conditions. We are able give some analytical evidence in support of this hypothesis but are unsuccessful in providing a complete proof.

The theory of quantum chromodynamics (QCD) predicts that at high energies, such as those investigated in deep inelastic scattering experiments, hadrons evolve into dense gluonic states described by the BFKL equation, and at very high densities, the more general BK equation. In certain approximations, the BK equation reduces to a well studied reaction-diffusion type nonlinear partial differential equation, the FKPP equation, for which analytical results are known. In this work, we model the BK equation using a classical branching process rooted in the dipole model of QCD evolution. Because the BK equation is inherently two dimensional, our model allows dipole impact parameters to occupy the full transverse space. A one dimensional limit of this model is studied as well. Results are compared with the predictions of the FKPP equation, and correlations between evolution at different impact parameters are presented. The general features of previously studied one dimensional impact parameter models are verified, but the details are refined in what we believe to be a more accurate model. / text

Este trabalho é dedicado a entender alguns aspectos matemáticos dos seguintes modelos não lineares: a equação de Schrödinger não linear com potência dupla, isto é iu t + u xx + u|u| 2 + u|u| 4 = 0, (1) e uma perturbação de tipo delta deste modelo, à saber, iu t + u xx + Z(x)u + u|u| 2 + u|u| 4 = 0. (2) Para o primeiro modelo em (1), usando a teoria de integrais elpticas de Jacobi e o teorema da função implcita, obtemos uma famlia de ondas estacionárias u(x, t) = e iwt w (x), onde w : R R é uma função positiva e periódica de perodo L > 0, conhecida como o perfil da onda. Para L , mostramos que as ondas esta- cionárias periódicas tendem uniformemente sobre intervalos compactos à onda so- litária. Usando uma extensão da teoria de Angulo&Natali assim como as idéias de- senvolvidas por Weinstein, Bona, Grillakis, Shatah e Strauss, mostramos estabilidade orbital desas ondas por perturbações do mesmo perodo que a onda. Por fim, provamos um resultado de instabilidade orbital por perturbações subharmônicas. Para o segundo modelo em (2), usando a onda solitária w,0 no caso em que Z = 0, obtemos duas famlias de picos solitários. Nós observamos que quando Z 0, temos que w,Z w,0 , onde w,0 denota a onda solitária. Então, usando a teoria de perturbação analtica para operadores lineares não limitados, obtemos um resultado detalhado da estabilidade orbital de picos solitários. Além disto, apresentamos alguns problemas naturais que podem ser resolvidos fu- turamente. Em particular, nós propomos uma nova abordagem para resolver questões de estabilidade linear de soluções de equilbrio para certo tipo de equações parabólicas. / This work is devoted to understand some mathematical aspects of the following nonlinear models: the nonlinear Schrödinger equation with double power in its non-linearity, that is iu t + u xx + u|u| 2 + u|u| 4 = 0, (3) and a perturbation of delta type of this model, namely iu t + u xx + Z(x)u + u|u| 2 + u|u| 4 = 0. (4) For the first model, by using the theory of Jacobi elliptic integrals and the implicit function theorem, we obtain a family of standing waves u(x, t) = e iwt w (x), where w : R R is a positive periodic function of period L > 0, known as the wave profile. When L , we show that the periodic standing waves converge uniformly on compact intervals to the solitary waves. Moreover, using an extension of the Angulo&Natali stability theory, as well as, the stability ideas developed by Weinstein, Bona, Grillakis, Shatah and Strauss, we show the orbital stability of the standing waves for perturbations of the same period of the wave profile. Finally, an orbital instability result by subharmonic perturbations is proved. For the second model, by using the existence of the solitary wave w,0 in the case Z = 0, we obtain two families of solitary peaks. We observe that when Z 0, we have that w,Z w,0 , where w,0 denotes the solitary wave. Then, using the analytic perturbation theory of unbounded linear operators, we obtain an accurate result about orbital stability of solitary peaks. Furthermore, we give some natural problems that can be solved futurely. In par- ticular, we propose a new approach to solve question of linear stability of equilibrium solutions for certain type of parabolic equations.

In this work we present some of the general theory of shock waves and their stability properties. We examine the concepts of nonlinear stability and spectral stability, noting that for certain classes of equations the study of nonlinear stability is reduced to the analysis of the spectra of the linearized eigenvalue problem. A useful tool in the study of spectral stability is the Evans function, an analytic function whose zeros correspond to the eigenvalues of the linearized eigenvalue problem. We discuss techniques for numerical Evans function computation that ensure analyticity, allowing standard winding number arguments and rootfinding methods to be used to locate eigenvalues. The Evans function is then used to study the spectra of the high Lewis number combustion system, tracking eigenvalues in the right-half plane.

No description available.

Diese Arbeit betrachtet einen Mikro-Makro-Übergang für die atomare Kette mit Wechselwirkungen zwischen nächsten Nachbarn, deren Dynamik durch ein nichtlineares aber konvexes Wechselwirkungspotential und durch die Newtonschen Bewegungsgleichungen bestimmt ist. Um einen Mikro-Makro-Übergang zu etablieren, wählen wir eine geeignete Skalierung und lassen die Zahl der Teilchen gegen Unendlich laufen. Dabei steht der Fall mit Temperatur im Vordergrund, so dass auf der makroskopischen Skala mikroskopische Oszillationen beschrieben werden müssen. Nach einer Einführung werden im zweiten Kapitel die Grundlagen der atomaren Kette zusammengefasst, und die wesentlichen Probleme beim Mikro-Makro-Übergang mit Temperatur diskutiert. Dabei wird besonders auf die Skalierung, die mikroskopischen Anfangsdaten und die Beschreibung der mikroskopischen Oszillationen eingegangen. Im dritten Kapitel werden so genannte Traveling-Waves betrachtet: Das sind exakte, hochgradig symmetrische Lösungen der atomaren Kette, die generisch von vier Parametern abhängen, und die als Lösungen von Differenzen-Differentialgleichungen bestimmt werden. Im Einzelnen werden die Existenz von Traveling-Waves, ihre thermodynamischen Eigenschaften und ihre Approximierbarkeit untersucht. Im vierten Kapitel werden modulierte Traveling-Waves betrachtet, mit deren Hilfe dann makroskopische Modulationsgleichungen abgeleitet werden. Diese lassen sich als die Erhaltungssätze für Masse, Impuls, Wellenzahl und Entropie interpretieren. Anschließend wird das Rechtfertigungsproblem diskutiert und für einen Spezialfall auch gelöst. Im fünften Kapitel werden numerische Simulationen von Anfangswertproblemen, unter anderem Riemann--Probleme, ausführlich untersucht, wobei die Strukturuntersuchung der auftretenden mikroskopischen Oszillationen im Vordergrund steht. Es zeigt sich, dass die mikroskopischen Oszillationen in vielen Fällen durch modulierte Traveling-Waves beschrieben werden können. / The subject matter of this thesis is a micro-macro transition for the atomic chain with nearest neighbor interaction. The interaction potential is assumed to be nonlinear but convex, and the dynamics of the chain is governed by Newton''s law of motion. To establish the micro-macro transition we choose an appropriate scaling, and let the number of particles tend to infinity. We mainly concentrate on the case with temperature, and therefore we have to describe microscopic oscillations on the macroscopic scale. We start with an introduction in the first chapter. Afterwards in the second chapter we summarize the basics of the atomic chain, and discuss the most important problems concerning a micro-macro transition with temperature. In particular we emphasize the scaling, the microscopic initial data, and the description of the microscopic oscillations. In the third chapter we consider traveling waves: These are highly symmetric solutions of the atomic chain depending on four parameters, and they result as solutions of difference-differential equations. We study the existence of traveling waves, their thermodynamic properties, and we derive schemes for their approximation. The fourth chapter is devoted to modulated traveling waves, because they allow to derive macroscopic modulation equations. These modulation equations can be interpreted as the macroscopic conservations laws for mass, momentum, wave number and entropy. Afterwards we discuss the justification problem, which is moreover solved for a special example. Within the fifth chapter we investigate several numerical simulations of initial value problems for the atomic chain including some Riemann problems. We mainly focus on the structure of the resulting microscopic oscillations, and we will identify many situations in which the microscopic oscillations can be described in terms of modulated traveling waves.

One-dimensional neural networks comprised of large numbers of Integrate-and-Fire neurons have been widely used to model electrical activity propagation in neural slices. Despite these efforts, the vast majority of these computational models have no analytical solutions. Consequently, my Ph.D. research focuses on a specific class of homogeneous Integrate-and-Fire neural network, for which analytical solutions of network dynamics can be derived. One crucial analytical finding is that the traveling wave acceleration quadratically depends on the instantaneous speed of the activity propagation, which means that two speed solutions exist in the activities of wave propagation: one is fast-stable and the other is slow-unstable. Furthermore, via this property, we analytically compute temporal-spatial spiking dynamics to help gain insights into the stability mechanisms of traveling wave propagation. Indeed, the analytical solutions are in perfect agreement with the numerical solutions. This analytical method also can be applied to determine the effects induced by a non-conductive gap of brain tissue and extended to more general synaptic connectivity functions, by converting the evolution equations for network dynamics into a low-dimensional system of ordinary differential equations. Building upon these results, we investigate how periodic inhomogeneities affect the dynamics of activity propagation. In particular, two types of periodic inhomogeneities are studied: alternating regions of additional fixed excitation and inhibition, and cosine form inhomogeneity. Of special interest are the conditions leading to propagation failure. With similar analytical procedures, explicit expressions for critical speeds of activity propagation are obtained under the influence of additional inhibition and excitation. However, an explicit formula for speed modulations is difficult to determine in the case of cosine form inhomogeneity. Instead of exact solutions from the system of equations, a series of speed approximations are constructed, rendering a higher accuracy with a higher order approximation of speed.

This dissertation focuses on the study of spectral stability in traveling waves, with a special interest in planar detonations in the multidimensional reactive Navier-Stokes equations. The chief tool is the Evans function, combined with STABLAB, a numerical library devoted to calculating the Evans function. Properly constructed, the Evans function is an analytic function in the right half-plane whose zeros correspond in multiplicity and location to the spectrum of the traveling wave. Thus the Evans function can be used to verify stability, or to locate precisely any unstable eigenvalues. We introduce a new method that uses numerical continuation to follow unstable eigenvalues as system parameters vary. We also use the Evans function to track instabilities of viscous detonations in the multidimensional reactive Navier-Stokes equations, building on recent results for detonations in one dimension. Finally, we introduce a Python implementation of STABLAB, which we hope will improve the accessibility of STABLAB and aid the future study of large, multidimensional systems by providing easy-to-use parallel processing tools.