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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Efficient Abstractions in Hierarchical Supervisory Control of Discrete-event Systems

Qu, Xinquan 10 December 2013 (has links)
In this thesis we study two problems in hierarchical supervisory control of discrete-event systems. The first problem is controller reduction, which is to find smaller abstractions of hierarchical controllers for easier understanding. The second problem is controller design, which is to find smaller abstractions of systems for high-level controller design. We employ natural projections to generate abstractions, thus incorporate the two problems into one optimization problem in which we try to minimize the size of the observable event set of the abstractions, subject to the constraints that the abstractions still achieve maximally permissive and nonblocking control. An optimal solution is proposed for the controller reduction problem, and a suboptimal solution is proposed for the controller design problem.
2

Efficient Abstractions in Hierarchical Supervisory Control of Discrete-event Systems

Qu, Xinquan 10 December 2013 (has links)
In this thesis we study two problems in hierarchical supervisory control of discrete-event systems. The first problem is controller reduction, which is to find smaller abstractions of hierarchical controllers for easier understanding. The second problem is controller design, which is to find smaller abstractions of systems for high-level controller design. We employ natural projections to generate abstractions, thus incorporate the two problems into one optimization problem in which we try to minimize the size of the observable event set of the abstractions, subject to the constraints that the abstractions still achieve maximally permissive and nonblocking control. An optimal solution is proposed for the controller reduction problem, and a suboptimal solution is proposed for the controller design problem.
3

Set Stabilization Using Transverse Feedback Linearization

Nielsen, Christopher 25 September 2009 (has links)
In this thesis we study the problem of stabilizing smooth embedded submanifolds in the state space of smooth, nonlinear, autonomous, deterministic control-affine systems. Our motivation stems from a realization that important applications, such as path following and synchronization, are best understood in the set stabilization framework. Instead of directly attacking the above set stabilization problem, we seek feedback equivalence of the given control system to a normal form that facilitates control design. The process of putting a control system into the normal form of this thesis is called transverse feedback linearization. When feasible, transverse feedback linearization allows for a decomposition of the nonlinear system into a “transverse” and a “tangential” subsystem relative to the goal submanifold. The dynamics of the transverse subsystem determine whether or not the system’s state approaches the submanifold. To ease controller design, we ask that the transverse subsystem be linear time-invariant and controllable. The dynamics of the tangential subsystem determine the motion on the submanifold. The main problem considered in this work, the local transverse feedback linearization problem (LTFLP), asks: when is such a decomposition possible near a point of the goal submanifold? This problem can equivalently be viewed as that of finding a system output with a well-defined relative degree, whose zero dynamics manifold coincides with the goal submanifold. As such, LTFLP can be thought of as the inverse problem to input-output feedback linearization. We present checkable, necessary and sufficient conditions for the existence of a local coordinate and feedback transformation that puts the given system into the desired normal form. A key ingredient used in the analysis is the new notion of transverse controllability indices of a control system with respect to a set. When the goal submanifold is diffeomorphic to Euclidean space, we present sufficient conditions for feedback equivalence in a tubular neighbourhood of it. These results are used to develop a technique for solving the path following problem. When applied to this problem, transverse feedback linearization decomposes controller design into two separate stages: transversal control design and tangential control design. The transversal control inputs are used to stabilize the path, and effectively generate virtual constraints forcing the system’s output to move along the path. The tangential inputs are used to control the motion along the path. A useful feature of this twostage approach is that the motion on the set can be controlled independently of the set stabilizing control law. The effectiveness of the proposed approach is demonstrated experimentally on a magnetically levitated positioning system. Furthermore, the first satisfactory solution to a problem of longstanding interest, path following for the planar/vertical take-off and landing aircraft model to the unit circle, is presented. This solution, developed in collaboration with Luca Consolini and Mario Tosques at the University of Parma, is made possible by taking a set stabilization point of view.
4

Genome-scale Dynamic Modeling of the Competition Between Rhodoferax and Geobacter in Anoxic Subsurface Environments

Zhuang, Kai 16 September 2011 (has links)
In situ bioremediation by Fe(III) reducers is a strategy for clean-up of ground water through reductive immobilization. The dynamics of the community involved is complex and needs to be understood better for improving the bioremediation. Here, we have created a dynamic genome-scale metabolic model of Geobacter sulfurreducens and Rhodoferax ferrireducens, the two primary iron-reducers in subsurface environments, in order to understand the community competition prior to and during uranium- bioremediation. The simulation results suggest that the community competition is modulated by two factors: the ability of G. sulfurreducens to fix nitrogen under ammonium limitation, and a rate vs. yield trade-off between these two organisms. This model will be an important tool for the analyses of more complex microbial communities and the design of effective uranium-bioremediation strategies.
5

Genome-scale Dynamic Modeling of the Competition Between Rhodoferax and Geobacter in Anoxic Subsurface Environments

Zhuang, Kai 16 September 2011 (has links)
In situ bioremediation by Fe(III) reducers is a strategy for clean-up of ground water through reductive immobilization. The dynamics of the community involved is complex and needs to be understood better for improving the bioremediation. Here, we have created a dynamic genome-scale metabolic model of Geobacter sulfurreducens and Rhodoferax ferrireducens, the two primary iron-reducers in subsurface environments, in order to understand the community competition prior to and during uranium- bioremediation. The simulation results suggest that the community competition is modulated by two factors: the ability of G. sulfurreducens to fix nitrogen under ammonium limitation, and a rate vs. yield trade-off between these two organisms. This model will be an important tool for the analyses of more complex microbial communities and the design of effective uranium-bioremediation strategies.
6

Set Stabilization Using Transverse Feedback Linearization

Nielsen, Christopher 25 September 2009 (has links)
In this thesis we study the problem of stabilizing smooth embedded submanifolds in the state space of smooth, nonlinear, autonomous, deterministic control-affine systems. Our motivation stems from a realization that important applications, such as path following and synchronization, are best understood in the set stabilization framework. Instead of directly attacking the above set stabilization problem, we seek feedback equivalence of the given control system to a normal form that facilitates control design. The process of putting a control system into the normal form of this thesis is called transverse feedback linearization. When feasible, transverse feedback linearization allows for a decomposition of the nonlinear system into a “transverse” and a “tangential” subsystem relative to the goal submanifold. The dynamics of the transverse subsystem determine whether or not the system’s state approaches the submanifold. To ease controller design, we ask that the transverse subsystem be linear time-invariant and controllable. The dynamics of the tangential subsystem determine the motion on the submanifold. The main problem considered in this work, the local transverse feedback linearization problem (LTFLP), asks: when is such a decomposition possible near a point of the goal submanifold? This problem can equivalently be viewed as that of finding a system output with a well-defined relative degree, whose zero dynamics manifold coincides with the goal submanifold. As such, LTFLP can be thought of as the inverse problem to input-output feedback linearization. We present checkable, necessary and sufficient conditions for the existence of a local coordinate and feedback transformation that puts the given system into the desired normal form. A key ingredient used in the analysis is the new notion of transverse controllability indices of a control system with respect to a set. When the goal submanifold is diffeomorphic to Euclidean space, we present sufficient conditions for feedback equivalence in a tubular neighbourhood of it. These results are used to develop a technique for solving the path following problem. When applied to this problem, transverse feedback linearization decomposes controller design into two separate stages: transversal control design and tangential control design. The transversal control inputs are used to stabilize the path, and effectively generate virtual constraints forcing the system’s output to move along the path. The tangential inputs are used to control the motion along the path. A useful feature of this twostage approach is that the motion on the set can be controlled independently of the set stabilizing control law. The effectiveness of the proposed approach is demonstrated experimentally on a magnetically levitated positioning system. Furthermore, the first satisfactory solution to a problem of longstanding interest, path following for the planar/vertical take-off and landing aircraft model to the unit circle, is presented. This solution, developed in collaboration with Luca Consolini and Mario Tosques at the University of Parma, is made possible by taking a set stabilization point of view.
7

Motion Control of Rigid Bodies in SE(3)

Roza, Ashton 26 November 2012 (has links)
This thesis investigates the control of motion for a general class of vehicles that rotate and translate in three-space, and are propelled by a thrust vector which has fixed direction in body frame. The thesis addresses the problems of path following and position control. For path following, a feedback linearization controller is presented that makes the vehicle follow an arbitrary closed curve while simultaneously allowing the designer to specify the velocity profile of the vehicle on the path and its heading. For position control, a two-stage approach is presented that decouples position control from attitude control, allowing for a modular design and yielding almost global asymptotic stability of any desired hovering equilibrium. The effectiveness of the proposed method is verified both in simulation and experimentally by means of a hardware-in-the-loop setup emulating a co-axial helicopter.
8

Passivity Methods for the Stabilization of Closed Sets in Nonlinear Control Systems

El-Hawwary, Mohamed 30 August 2011 (has links)
In this thesis we study the stabilization of closed sets for passive nonlinear control systems, developing necessary and sufficient conditions under which a passivity-based feedback stabilizes a given goal set. The development of this result takes us to a journey through the so-called reduction problem: given two nested invariant sets G1 subset of G2, and assuming that G1 enjoys certain stability properties relative to G2, under what conditions does G1 enjoy the same stability properties with respect to the whole state space? We develop reduction principles for stability, asymptotic stability, and attractivity which are applicable to arbitrary closed sets. When applied to the passivity-based set stabilization problem, the reduction theory suggests a new definition of detectability which is geometrically appealing and captures precisely the property that the control system must possess in order for the stabilization problem to be solvable. The reduction theory and set stabilization results developed in this thesis are used to solve a distributed coordination problem for a group of unicycles, whereby the vehicles are required to converge to a circular formation of desired radius, with a specific ordering and spacing on the circle.
9

Passivity Methods for the Stabilization of Closed Sets in Nonlinear Control Systems

El-Hawwary, Mohamed 30 August 2011 (has links)
In this thesis we study the stabilization of closed sets for passive nonlinear control systems, developing necessary and sufficient conditions under which a passivity-based feedback stabilizes a given goal set. The development of this result takes us to a journey through the so-called reduction problem: given two nested invariant sets G1 subset of G2, and assuming that G1 enjoys certain stability properties relative to G2, under what conditions does G1 enjoy the same stability properties with respect to the whole state space? We develop reduction principles for stability, asymptotic stability, and attractivity which are applicable to arbitrary closed sets. When applied to the passivity-based set stabilization problem, the reduction theory suggests a new definition of detectability which is geometrically appealing and captures precisely the property that the control system must possess in order for the stabilization problem to be solvable. The reduction theory and set stabilization results developed in this thesis are used to solve a distributed coordination problem for a group of unicycles, whereby the vehicles are required to converge to a circular formation of desired radius, with a specific ordering and spacing on the circle.
10

Supply Chain Operation Modelling and Automation Using Untimed and Timed State Tree Structures

Izadian, Sina 28 November 2013 (has links)
We study the supervisory control of supply chain operation modelled by (timed) State Tree Structures (STS). We model each agent involved in a supply chain using holons. Three operational models, make-to-order, make-to-stock, and assemble-to-order are considered. A strong assumption on the original STS theory is weakened to allow events shared among agents to be located at different levels. A supervisor is synthesized for the example of a mattress supply chain with make-to-stock operation under certain specifications. Moreover, a new version of the Timed STS framework is developed to allow events to have an upper time bound i.e. deadline. With Timed STS framework, more specifications requiring time measurement can be modeled and a supervisory control is synthesized for the timed model of a supply chain. For a nonempty supervisory synthesis result, the maximum time for the inventory periodic review rate, and the minimum cycle time for customer order satisfaction are achieved.

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