A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item The Effects of Coupling Delay and Amplitude / Phase Interaction on Large Coupled Oscillator Networks(2012) Lee, Wai Shing; Ott, Edward; Antonsen, Thomas M.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The interaction of many coupled dynamical units is a theme across many scientific disciplines. A useful framework for beginning to understanding such phenomena is the coupled oscillator network description. In this dissertation, we study a few problems related to this. The first part of the dissertation studies generic effects of heterogeneous interaction delays on the dynamics of large systems of coupled oscillators. Here, we modify the Kuramoto model (phase oscillator model) to incorporate a distribution of interaction delays. Corresponding to the continuum limit, we focus on the reduced dynamics on an invariant manifold of the original system, and derive governing equations for the system, which we use to study stability of the incoherent state and the dynamical transitional behavior from stable incoherent states to stable coherent states. We find that spread in the distribution function of delays can greatly alter the system dynamics. The second part of this dissertation is a sequel to the first part. Here, we consider systems of many spatially distributed phase oscillators that interact with their neighbors, and each oscillator can have a different natural frequency, and a different response time to the signals it receives from other oscillators in its neighborhood. By first reducing the microscopic dynamics to a macroscopic partial-differential-equation description, we then numerically find that finite oscillator response time leads to many interesting spatio-temporal dynamical behaviors, and we study interactions and evolutionary behaviors of these spatio-temporal patterns. The last part of this dissertation addresses the behavior of large systems of heterogeneous, globally coupled oscillators each of which is described by the generic Landau-Stuart equation, which incorporates both phase and amplitude dynamics. Our first goal is to investigate the effect of a spread in the amplitude growth parameter of the oscillators and that of a homogeneous nonlinear frequency shift. Both of these effects are of potential relevance to recently reported experiments. Our second goal is to gain further understanding of the observation that, at large coupling strength, a simple constant-amplitude sinusoidal oscillation is always a solution for the dynamics of the global order parameter when the system has constant nonlinear characteristics.Item Control of Networked Robotic Systems(2012) Liu, Yen-Chen; Chopra, Nikhil; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the infrastructure of ubiquitous networks around the world, the study of robotic systems over communication networks has attracted widespread attention. This area is denominated as networked robotic systems. By exploiting the fruitful technological developments in networking and computing, networked robotic systems are endowed with potential and capabilities for several applications. Robots within a network are capable of connecting with control stations, human operators, sensors, and other robots via digital communication over possibly noisy channels/media. The issues of time delays in communication and data losses have emerged as a pivotal issue that have stymied practical deployment. The aim of this dissertation is to develop control algorithms and architectures for networked robotic systems that guarantee stability with improved overall performance in the presence of time delays in communication. The first topic addressed in this dissertation is controlled synchronization that is utilized for networked robotic systems to achieve collective behaviors. Exploiting passivity property of individual robotic systems, the proposed control schemes and interconnections are shown to ensure stability and convergence of synchronizing errors. The robustness of the control algorithms to constant and time-varying communication delays is also studied. In addition to time delays, the number of communication links, which prevents scalability of networked robotic systems, is another challenging issue. Thus, a synchronizing control with practically feasible constraints of network topology is developed. The problem of networked robotic systems interacting with human operators is then studied subsequently. This research investigates a teleoperation system with heterogeneous robots under asymmetric and unknown communication delays. Sub-task controllers are proposed for redundant slave robot to autonomously achieve additional tasks, such as singularity avoidance, joint angle limits, and collision avoidance. The developed control algorithms can enhance the efficiency of teleoperation systems, thereby ameliorating the performance degradation due to cognitive limitations of human operator and incomplete information about the environment. Compared to traditional robotic systems, control of robotic manipulators over networks has significant advantages; for example, increased flexibility and ease of maintenance. With the utilization of scattering variables, this research demonstrates that transmitting scattering variables over delayed communications can stabilize an otherwise unstable system. An architecture utilizing delayed position feedback in conjunction with scattering variables is developed for the case of time-varying communication delays. The proposed control architecture improves tracking performance and stabilizes robotic manipulators with input-output communication delays. The aforementioned control algorithms and architectures for networked robotic systems are validated via numerical examples and experiments.Item Application of Chaotic Synchronization and Controlling Chaos to Communications(2005-04-19) Dronov, Vasily; Ott, Edward; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis addresses two important issues that are applicable to chaotic communication systems: synchronization of chaos and controlling chaos. Synchronization of chaos is a naturally occurring phenomenon where one chaotic dynamical system mimics dynamical behavior of another chaotic system. The phenomenon of chaotic synchronization is a popular topic of research, in general, and has attracted much attention within the scientific community. Controlling chaos is another potential engineering application. A unique property of controlling chaos is the ability to cause large long-term impact on the dynamics using arbitrarily small perturbations. This thesis is broken up into three chapters. The first chapter contains a brief introduction to the areas of research of the thesis work, as well as the summaries the work itself. The second chapter is dedicated to the study of a particular situation of chaotic synchronization which leads to a novel structure of the basin of attraction. This chapter also develops theoretical scalings applicable to these systems and compares results of our numerical simulations on three different chaotic systems. The third chapter consists or two logically connected parts (both of them study chaotic systems that can be modeled with delayed differential equations). The first and the main part presents a study of a chaotically behaving traveling wave tube, or TWT, with the objective of improving efficiency of satellite communication systems. In this work we go through an almost complete design cycle, where, given an objective, we begin with developing a nonlinear model for a generic TWT; we then study numerically the dynamics of the proposed model; we find conditions where chaotic behavior occurs (we argue that TWT in chaotic mode could be more power efficient); then we use the idea of controlling chaos for information encoding; we support the concept with numerical simulations; and finally analyze the performance of the proposed chaotic communication system. The second part of this chapter describes an experiment with a pair of electronic circuits modeling the well-known Mackey-Glass equation. An experiment where human voice was encoded into chaotic signal had been conducted which showed a possibility of engineering application of chaos to secure communications.