101 Matching Results

Search Results

Advanced search parameters have been applied.

A Control Theoretic Approach for Resilient Network Services

Description: Resilient networks have the ability to provide the desired level of service, despite challenges such as malicious attacks and misconfigurations. The primary goal of this dissertation is to be able to provide uninterrupted network services in the face of an attack or any failures. This dissertation attempts to apply control system theory techniques with a focus on system identification and closed-loop feedback control. It explores the benefits of system identification technique in designing and validating the model for the complex and dynamic networks. Further, this dissertation focuses on designing robust feedback control mechanisms that are both scalable and effective in real-time. It focuses on employing dynamic and predictive control approaches to reduce the impact of an attack on network services. The closed-loop feedback control mechanisms tackle this issue by degrading the network services gracefully to an acceptable level and then stabilizing the network in real-time (less than 50 seconds). Employing these feedback mechanisms also provide the ability to automatically configure the settings such that the QoS metrics of the network is consistent with those specified in the service level agreements.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: December 2018
Creator: Vempati, Jagannadh Ambareesh
Partner: UNT Libraries

NSLS-II Control of Dynamic Aperture

Description: We have outlined how, by an intuitive approach, the on- and off-momentum dynamic aperture for a synchrotron light source can be estimated from a nonlinear system of algebraic equations for the sextupole/multipole strengths. The approach has only two free parameters: the relative weight for resonance vs. tune shift terms and the tune footprint for stable trajectories in a modern third generation synchrotron light source. In other words, we have established a control theory approach for the medium term (10{sup 3} turns) stability for a dynamic system described by a nonlinear system of ordinary differential equations. Equipped with a predictive, quantitative model for stability, we have then evaluated how to improve the control of the dynamics by analyzing and modifying the properties of the corresponding algebraic system. In particular, by changing the number- and characteristics of the parameters, i.e., we have not evaluated how the underlying (linear) optics could be improved. We have also validated our conjectures by numerical simulations with a realistic model. Presumably, our conclusions, summarized in Section 1.0, are a direct result of the presented analysis and observations.
Date: October 31, 2008
Creator: Bengtsson,J.
Partner: UNT Libraries Government Documents Department

A two-timescale approach to nonlinear Model Predictive Control

Description: Model Predictive Control (MPC) schemes generate controls by using a model to predict the plant`s response to various control strategies. A problem arises when the underlying model is obtained by fitting a general nonlinear function, such as a neural network, to data: an exorbitant amount of data may be required to obtain accurate enough predictions. We describe a means of avoiding this problem that involves a simplified plant model which bases its predictions on averages of past control inputs. This model operates on a timescale slower than- the rate at which the controls are updated and the plant outputs are sampled. Not only does this technique give better closed-loop performance from the same amount of open-loop data, but it requires far less on-line computation as well. We illustrate the usefulness of this two-timescale approach by applying it to a simulated exothermic continuously stirred tank reactor with jacket dynamics.
Date: October 1, 1994
Creator: Buescher, K.L. & Baum, C.C.
Partner: UNT Libraries Government Documents Department

H{sub {infinity}} control of chatter in a milling machine

Description: In this paper, preliminary results on the use of active chatter control in a new type of milling machine is presented. It is expected that this machine will cut metal at twice the rate of conventional machines without an appreciable increase in cost. Performance enhancements are achieved by the integration of active feedback control into an existing machine structure. To reduce computational burden, decoupled control is proposed. Extensive simulations have shown that significant performance enhancements are achievable.
Date: May 1, 1997
Creator: Kwan, C.M.; Xu, H.; Lin, C.; Haynes, L.; Dohner, J.; Regelbrugge, M. et al.
Partner: UNT Libraries Government Documents Department

Models, controls, and levels of semiotic autonomy

Description: In this paper the authors consider forms of autonomy, forms of semiotic systems, and any necessary relations among them. Levels of autonomy are identified as levels of system identity, from adiabatic closure to disintegration. Forms of autonomy or closure in systems are also recognized, including physical, dynamical, functional, and semiotic. Models and controls are canonical linear and circular (closed) semiotic relations respectively. They conclude that only at higher levels of autonomy do semiotic properties become necessary. In particular, all control systems display at least a minimal degree of semiotic autonomy; and all systems with sufficiently interesting functional autonomy are semiotically related to their environments.
Date: December 1, 1998
Creator: Joslyn, C.
Partner: UNT Libraries Government Documents Department

Traffic flow wide-area surveillance system definition

Description: Traffic Flow Wide-Area Surveillance (TFWAS) is a system for assessing the state of traffic flow over a wide area for enhanced traffic control and improved traffic management and planning. The primary purpose of a TFWAS system is to provide a detailed traffic flow description and context description to sophisticated traffic management and control systems being developed or envisioned for the future. A successful TFWAS system must possess the attributes of safety, reconfigurability, reliability, and expandability. The primary safety premise of TFWAS is to ensure that no action or failure of the TFWAS system or its components can result in risk of injury to humans. A wide variety of communication techniques is available for use with TFWAS systems. These communication techniques can be broken down into two categories, landlines and wireless. Currently used and possible future traffic sensing technologies have been examined. Important criteria for selecting TFWAS sensors include sensor capabilities, costs, operational constraints, sensor compatibility with the infrastructure, and extent. TFWAS is a concept that can take advantage of the strengths of different traffic sensing technologies, can readily adapt to newly developed technologies, and can grow with the development of new traffic control strategies. By developing innovative algorithms that will take information from a variety of sensor types and develop descriptions of traffic flows over a wide area, a more comprehensive understanding of the traffic state can be provided to the control system to perform the most reasonable control actions over the entire wide area. The capability of characterizing the state of traffic over an entire region should revolutionize developments in traffic control strategies.
Date: November 1994
Creator: Allgood, G. O.; Ferrell, R. K.; Kercel, S. W.; Abston, R. A.; Carnal, C. L. & Moynihan, P. I.
Partner: UNT Libraries Government Documents Department

Online high voltage power supply ripple estimation and feedforward in LEDA

Description: The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of Acceleration Production of Tritium (APT) accelerator. This paper addresses the problem of LLRF control system for LEDA. They propose an estimator of the ripple and its time derivative and a control law which is based on PID control and adaptive feedforward of estimated ripple. The control law reduces the effect of the deterministic cathode ripple that is due to high voltage power supply and achieves tracking of desired set points.
Date: June 1, 1999
Creator: Kwon, S.; Regan, A.; Wang, Y.M. & Rohlev, T.
Partner: UNT Libraries Government Documents Department

Feedback linearization application for LLRF control system

Description: The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of Acceleration Production of Tritium (APT) accelerator. This paper addresses the problem of the LLRF control system for LEDA. The authors propose a control law which is based on exact feedback linearization coupled with gain scheduling which reduces the effect of the deterministic klystron cathode voltage ripple that is due to harmonics of the high voltage power supply and achieves tracking of desired set points. Also, they propose an estimator of the ripple and its time derivative and the estimates based feedback linearization controller.
Date: June 1, 1999
Creator: Kwon, S.; Regan, A.; Wang, Y.M. & Rohlev, T.
Partner: UNT Libraries Government Documents Department

Magnetic damping for maglev

Description: Magnetic damping is one of the important parameters to control the response and stability of maglev systems. An experimental study is presented to measure the magnetic damping using a direct method. A plate attached to a permanent magnet levitated on a rotating drum was tested to investigate the effect of various parameters on magnetic damping such as conductivity, gap, excitation frequency, and oscillation amplitude. The experimental technique is capable of measuring all magnetic damping coefficients, some of which can not be measured by an indirect method.
Date: December 31, 1994
Creator: Chen, S.S.; Zhu, S.; Cai, Y. & Rote, D.M.
Partner: UNT Libraries Government Documents Department

Solving inverse problems of identification type by optimal control methods

Description: Inverse problems of identification type for nonlinear equations are considered within the framework of optimal control theory. The rigorous solution of any particular problem depends on the functional setting, type of equation, and unknown quantity (or quantities) to be determined. Here the authors present only the general articulations of the formalism. Compared to classical regularization methods (e.g. Tikhonov coupled with optimization schemes), their approach presents several advantages, namely: (i) a systematic procedure to solve inverse problems of identification type; (ii) an explicit expression for the approximations of the solution; and (iii) a convenient numerical solution of these approximations.
Date: June 1, 1997
Creator: Lenhart, S.; Protopopescu, V. & Jiongmin Yong
Partner: UNT Libraries Government Documents Department

Intelligent decision support technologies for design and manufacturing

Description: For many of today`s complex manufacturing processes, there exists a solid body of knowledge that enables direct simulations of such processes yielding predictions about the final product and process characteristics using finite element or finite difference methods. However, the computational complexities of these simulations are such that they do not lend themselves easily to routine and timely use in optimization and control of manufacturing processes. More recently, neural network-based decision support technologies have been developed which hold the promise of bringing the body of analytical and simulation knowledge closer to the design and optimization processes in manufacturing industries. The paper discusses the application of a holistic approach wherein existing finite element, neural-network, and optical metrology methods are combined to develop a real time tool for optimization and control of the sheet metal stamping process. Significant issues in the development of such a tool and results from its application to a deformation process are discussed.
Date: June 1, 1997
Creator: Zacharia, T.; Allen, J.D.; Ivezic, N. & Ludtka, G.M.
Partner: UNT Libraries Government Documents Department

Collective search by mobile robots using alpha-beta coordination

Description: One important application of mobile robots is searching a geographical region to locate the origin of a specific sensible phenomenon. Mapping mine fields, extraterrestrial and undersea exploration, the location of chemical and biological weapons, and the location of explosive devices are just a few potential applications. Teams of robotic bloodhounds have a simple common goal; to converge on the location of the source phenomenon, confirm its intensity, and to remain aggregated around it until directed to take some other action. In cases where human intervention through teleoperation is not possible, the robot team must be deployed in a territory without supervision, requiring an autonomous decentralized coordination strategy. This paper presents the alpha beta coordination strategy, a family of collective search algorithms that are based on dynamic partitioning of the robotic team into two complementary social roles according to a sensor based status measure. Robots in the alpha role are risk takers, motivated to improve their status by exploring new regions of the search space. Robots in the beta role are motivated to improve but are conservative, and tend to remain aggregated and stationary until the alpha robots have identified better regions of the search space. Roles are determined dynamically by each member of the team based on the status of the individual robot relative to the current state of the collective. Partitioning the robot team into alpha and beta roles results in a balance between exploration and exploitation, and can yield collective energy savings and improved resistance to sensor noise and defectors. Alpha robots waste energy exploring new territory, and are more sensitive to the effects of ambient noise and to defectors reporting inflated status. Beta robots conserve energy by moving in a direct path to regions of confirmed high status.
Date: April 1, 1998
Creator: Goldsmith, S.Y. & Robinett, R. III
Partner: UNT Libraries Government Documents Department

Decentralized fuzzy control of multiple nonholonomic vehicles

Description: This work considers the problem of controlling multiple nonholonomic vehicles so that they converge to a scent source without colliding with each other. Since the control is to be implemented on simple 8-bit microcontrollers, fuzzy control rules are used to simplify a linear quadratic regulator control design. The inputs to the fuzzy controllers for each vehicle are the (noisy) direction to the source, the distance to the closest neighbor vehicle, and the direction to the closest vehicle. These directions are discretized into four values: Forward, Behind, Left, and Right, and the distance into three values: Near, Far, Gone. The values of the control at these discrete values are obtained based on the collision-avoidance repulsive forces and the change of variables that reduces the motion control problem of each nonholonomic vehicle to a nonsingular one with two degrees of freedom, instead of three. A fuzzy inference system is used to obtain control values for inputs between the small number of discrete input values. Simulation results are provided which demonstrate that the fuzzy control law performs well compared to the exact controller. In fact, the fuzzy controller demonstrates improved robustness to noise.
Date: September 1, 1997
Creator: Driessen, B.J.; Feddema, J.T. & Kwok, K.S.
Partner: UNT Libraries Government Documents Department

Coordinated train control and energy management control strategies

Description: The Bay Area Rapid Transit (BART) system, in collaboration with Hughes Aircraft Company and Harmon Industries, as in the process of developing an Advanced Automatic Train Control (AATC) system to replace the current fixed-block automatic system. In the long run, the AATC system is expected to not only allow for safe short headway operation, but also to facilitate coordinated train control and energy management. This new system will employ spread spectrum radios, installed onboard trains, at wayside locations, and at control stations, to determine train locations and reliably transfer control information. Sandia National Laboratories has worked cooperatively with BART to develop a simulator of the train control and the power consumption of the AATC system. The authors are now in the process of developing enhanced train control algorithms to supplement the safety critical controller in order to smooth out train trajectories through coordinated control of multiple trains, and to reduce energy consumption and power infrastructure requirements. The control algorithms so far considered include (1) reducing peak power consumption to avoid voltage sags, especially during an outage or while clearing a backup, (2) rapid and smooth recovery from a backup, (3) avoiding oscillations due to train interference, (4) limiting needle peaks in power demand at substations to some specified level, (5) coasting, and (6) coordinating train movement, e.g., starts/stops and hills.
Date: May 1, 1998
Creator: Gordon, S.P. & Lehrer, D.G.
Partner: UNT Libraries Government Documents Department

Fast Feedback System for CEBAF

Description: A fast feedback system based on concepts of modern control theory has been implemented in the CEBAF Control System to stabilize various machine parameters. The continuous wave operation of CEBAF requires that parameters such as beam energy and position are stabilized against fast fluctuations. The beam energy must be stabilized against fast gradient and phase fluctuations in the RF accelerating system. This fast feedback system currently operates at 60 Hz rate and is integrated with EPICS. The mathematical model of the system for various feedback loops is expressed in state space formalism. The design of control law and simulation of closed-loop system response is performed using MatlabTM and SimulinkTM. This paper describes the process of designing control algorithms, implementation of the fast feedback system and operational experience with this system at CEBAF. The performance of this feedback system, while operating at much higher rates with high closed loop gain, can be enhanced by continually performing on-line identification of the system from the input and output data. System identification is the process of developing or improving an analytically derived mathematical representation of a physical system using experimental data. The current status of this feature is presented.
Date: October 1, 1995
Creator: Chowdhary, M.P.; Krafft, G.A.; Shoaee, H. & III, W.A. Watson
Partner: UNT Libraries Government Documents Department

A review of dynamic stability of repulsive-force maglev suspension systems

Description: Vehicle dynamics and the need to satisfy ride quality requirements have long been recognized as crucial to the commercial success of passenger-carrying transportation systems. Design concepts for maglev systems are no exception. Early maglev investigators and designers were well aware of the importance of ride quality and took care to ensure that their designs would meet acceptable ride quality standards. In contrast, the dynamic stability of electrodynamic suspension (EDS) systems, which has obvious implications for system safety and cost as well as for ride quality, has not received nearly as much attention. Because of the well-known under-damped nature of EDS suspension systems and the observation of instabilities in laboratory-scale model systems, it is prudent to develop a better understanding of vehicle stability characteristics. The work reported in this was undertaken with the intention of summarizing information that has been accumulated worldwide and that is relevant to dynamic stability of repulsive-force maglev suspension systems, assimilating that information, and gaining an understanding of the factors that influence that stability. Included in the paper is a discussion and comparison of results acquired from some representative tests of large-scale vehicles on linear test tracks, together with analytical and laboratory-scale investigations of stability and dynamics of EDS systems. This paper will also summarize the R and D activities at Argonne National Laboratory (ANL) since 1991 to study the nature of the forces that are operative in an EDS system and the dynamic stability of such systems.
Date: July 1, 1998
Creator: Cai, Y. & Rote, D.M.
Partner: UNT Libraries Government Documents Department

An approach to the development and analysis of wind turbine control algorithms

Description: The objective of this project is to develop the capability of symbolically generating an analytical model of a wind turbine for studies of control systems. This report focuses on a theoretical formulation of the symbolic equations of motion (EOMs) modeler for horizontal axis wind turbines. In addition to the power train dynamics, a generic 7-axis rotor assembly is used as the base model from which the EOMs of various turbine configurations can be derived. A systematic approach to generate the EOMs is presented using d`Alembert`s principle and Lagrangian dynamics. A Matlab M file was implemented to generate the EOMs of a two-bladed, free yaw wind turbine. The EOMs will be compared in the future to those of a similar wind turbine modeled with the YawDyn code for verification. This project was sponsored by Sandia National Laboratories as part of the Adaptive Structures and Control Task. This is the final report of Sandia Contract AS-0985.
Date: March 1, 1998
Creator: Wu, K.C.
Partner: UNT Libraries Government Documents Department

An overview of reliability assessment and control for design of civil engineering structures

Description: Random variations, whether they occur in the input signal or the system parameters, are phenomena that occur in nearly all engineering systems of interest. As a result, nondeterministic modeling techniques must somehow account for these variations to ensure validity of the solution. As might be expected, this is a difficult proposition and the focus of many current research efforts. Controlling seismically excited structures is one pertinent application of nondeterministic analysis and is the subject of the work presented herein. This overview paper is organized into two sections. First, techniques to assess system reliability, in a context familiar to civil engineers, are discussed. Second, and as a consequence of the first, active control methods that ensure good performance in this random environment are presented. It is the hope of the authors that these discussions will ignite further interest in the area of reliability assessment and design of controlled civil engineering structures.
Date: June 1, 1998
Creator: Field, R.V. Jr.; Grigoriadis, K.M.; Bergman, L.A. & Skelton, R.E.
Partner: UNT Libraries Government Documents Department

Designing stable finite state machine behaviors using phase plane analysis and variable structure control

Description: This paper discusses how phase plane analysis can be used to describe the overall behavior of single and multiple autonomous robotic vehicles with finite state machine rules. The importance of this result is that one can begin to design provably asymptotically stable group behaviors from a set of simple control laws and appropriate switching points with decentralized variable structure control. The ability to prove asymptotically stable group behavior is especially important for applications such as locating military targets or land mines.
Date: March 10, 1998
Creator: Feddema, J.T.; Robinett, R.D. & Driessen, B.J.
Partner: UNT Libraries Government Documents Department

Control of nonlinear systems using periodic parametric perturbations with application to a reversed field pinch

Description: In this thesis, the possibility of controlling low- and high-dimensional chaotic systems by periodically driving an accessible system parameter is examined. This method has been carried out on several numerical systems and the MST Reversed Field Pinch. The numerical systems investigated include the logistic equation, the Lorenz equations, the Roessler equations, a coupled lattice of logistic equations, a coupled lattice of Lorenz equations, the Yoshida equations, which model tearing mode fluctuations in a plasma, and a neural net model for magnetic fluctuations on MST. This method was tested on the MST by sinusoidally driving a magnetic flux through the toroidal gap of the device. Numerically, periodic drives were found to be most effective at producing limit cycle behavior or significantly reducing the dimension of the system when the perturbation frequency was near natural frequencies of unstable periodic orbits embedded in the attractor of the unperturbed system. Several different unstable periodic orbits have been stabilized in this way for the low-dimensional numerical systems, sometimes with perturbation amplitudes that were less than 5% of the nominal value of the parameter being perturbed. In high-dimensional systems, limit cycle behavior and significant decreases in the system dimension were also achieved using perturbations with frequencies near the natural unstable periodic orbit frequencies. Results for the MST were not this encouraging, most likely because of an insufficient drive amplitude, the extremely high dimension of the plasma behavior, large amounts of noise, and a lack of stationarity in the transient plasma pulses.
Date: June 1, 1998
Creator: Mirus, K.A.
Partner: UNT Libraries Government Documents Department

Service- and energy-related optimization of advanced automatic train control

Description: The Bay Area Rapid Transit (BART) system, in collaboration with Hughes Aircraft Company and Harmon Industries, is in the process of developing an Advanced Automatic Train Control (AATC) system to replace the current fixed-block automatic system. As in the current ATC system, the trains will be controlled by station computers at the wayside; however, spread-spectrum radios rather than track-circuits will be employed to determine train locations and reliably transfer control information, allowing for finer speed and acceleration control, as well as more precise train locating capabilities and moving-block control. The authors have developed a simulator of the train control and power consumption of the AATC system, and are now employing this tool to develop enhanced train control algorithms to supplement the safety-critical controller. These algorithms do not attempt to globally optimize the control system with respect to a cost function, but rather they modify the baseline vital control to smooth the train trajectories, and to reduce energy consumption and power infrastructure requirements, through coordination of multiple trains. Several control algorithms are under development, including (1) delay recovery, which smoothly and efficiently controls trains approaching and stopped behind a delayed train, (2) interference management, which controls closely-following trains to avoid oscillatory brake/acceleration cycles, and (3) low voltage avoidance, which limits power consumption by multiple trains in an area to prevent low voltage events. The authors discuss progress to date on development of these control algorithms, as well as their service- and energy-related benefits.
Date: May 1998
Creator: Gordon, S. P. & Lehrer, D. G.
Partner: UNT Libraries Government Documents Department

Visual operations control in administrative environments

Description: When asked what comes to mind when they think of ``controlling work`` in the office, people may respond with ``overbearing boss,`` ``no autonomy,`` or ``Theory X management.`` The idea of controlling work in white collar or administrative environments can have a negative connotation. However, office life is often chaotic and miserable precisely because the work processes are out of control, and managers must spend their time looking over people`s shoulders and fighting fires. While management styles and structures vary, the need for control of work processes does not. Workers in many environments are being reorganized into self-managed work teams. These teams are expected to manage their own work through increased autonomy and empowerment. However, even empowered work teams must manage their work processes because of process variation. The amount of incoming jobs vary with both expected (seasonal) and unexpected demand. The mixture of job types vary over time, changing the need for certain skills or knowledge. And illness and turnover affect the availability of workers with needed skills and knowledge. Clearly, there is still a need to control work, whether the authority for controlling work is vested in one person or many. Visual control concepts provide simple, inexpensive, and flexible mechanisms for managing processes in work teams and continuous improvement administrative environments.
Date: March 1, 1995
Creator: Carson, M.L. & Levine, L.O.
Partner: UNT Libraries Government Documents Department

Fast methods for static Hamilton-Jacobi Partial Differential Equations

Description: The authors develop a family of fast methods approximating the solution to a wide class of static Hamilton-Jacobi partial differential equations. These partial differential equations are considered in the context of control-theoretic and front-propagation problems. In general, to produce a numerical solution to such a problem, one has to solve a large system of coupled non-linear discretized equations. The techniques use partial information about the characteristic directions to de-couple the system. Previously known fast methods, available for isotropic problems, are discussed in detail. They introduce a family of new Ordered Upwinding Methods (OUM) for general (anisotropic) problems and prove convergence to the viscosity solution of the corresponding Hamilton-Jacobi partial differential equation. The hybrid methods introduced here are based on the analysis of the role played by anisotropy in the context of front propagation and optimal trajectory problems. The performance of the methods is analyzed and compared to that of several other numerical approaches to these problems. Computational experiments are performed using test problems from control theory, computational geometry and seismology.
Date: May 1, 2001
Creator: Vladimirsky, Alexander Boris
Partner: UNT Libraries Government Documents Department

Analytic Perturbation Analysis of Discrete Event Dynamic Systems

Description: This paper considers a new Analytic Perturbation Analysis (APA) approach for Discrete Event Dynamic Systems (DEDS) with discontinuous sample-path functions with respect to control parameters. The performance functions for DEDS usually are formulated as mathematical expectations, which can be calculated only numerically. APA is based on new analytic formulas for the gradients of expectations of indicator functions; therefore, it is called an analytic perturbation analysis. The gradient of performance function may not coincide with the expectation of a gradient of sample-path function (i.e., the interchange formula for the gradient and expectation sign may not be valid). Estimates of gradients can be obtained with one simulation run of the models.
Date: September 1, 1994
Creator: Uryasev, S.
Partner: UNT Libraries Government Documents Department