Dissertations / Theses on the topic 'Algorithm stability'
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Chan, Chok You. "Stability and robustness of adaptive pole-zero placement algorithm." Thesis, University of Canterbury. Electrical Engineering, 1987. http://hdl.handle.net/10092/6017.
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A computationally efficient pole-zero placement algorithm for explicit adaptive control of discrete-time plants is presented, It is effectively an implicit algorithm in the sense that the controller design stage is trivial. Although the algorithm is restricted to open-loop stable plants, it is applicable to nonminimum phase plants.
Results concerning the adaptive control of linear, time-invariant plants having purely deterministic or stochastic disturbances are given. In the deterministic case, it is shown that the adaptive control algorithm ensures that the purely deterministic disturbances are removed from the system output and that asymptotic perfect tracking is achieved. In the stochastic case, it is shown that the adaptive control algorithm leads to the required stability properties of the closed-loop system.
The robustness properties of the modified adaptive control algorithm in the presence of bounded external disturbances and unmodelled dynamics are also given. It is shown that if the modelling error is sufficiently small relative to the normalizing signals, then the algorithm ensures the boundedness of the input-output signals.
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Hao, Zhaopeng. "High-order numerical methods for integral fractional Laplacian: algorithm and analysis." Digital WPI, 2020. https://digitalcommons.wpi.edu/etd-dissertations/612.
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The fractional Laplacian is a promising mathematical tool due to its ability to capture the anomalous diffusion and model the complex physical phenomenon with long-range interaction, such as fractional quantum mechanics, image processing, jump process, etc. One of the important applications of fractional Laplacian is a turbulence intermittency model of fractional Navier-Stokes equation which is derived from Boltzmann's theory. However, the efficient computation of this model on bounded domains is challenging as highly accurate and efficient numerical methods are not yet available. The bottleneck for efficient computation lies in the low accuracy and high computational cost of discretizing the fractional Laplacian operator. Although many state-of-the-art numerical methods have been proposed and some progress has been made for the existing numerical methods to achieve quasi-optimal complexity, some issues are still fully unresolved: i) Due to nonlocal nature of the fractional Laplacian, the implementation of the algorithm is still complicated and the computational cost for preparation of algorithms is still high, e.g., as pointed out by Acosta et al \cite{AcostaBB17} 'Over 99\% of the CPU time is devoted to assembly routine' for finite element method; ii) Due to the intrinsic singularity of the fractional Laplacian, the convergence orders in the literature are still unsatisfactory for many applications including turbulence intermittency simulations. To reduce the complexity and computational cost, we consider two numerical methods, finite difference and spectral method with quasi-linear complexity, which are summarized as follows. We develop spectral Galerkin methods to accurately solve the fractional advection-diffusion-reaction equations and apply the method to fractional Navier-Stokes equations. In spectral methods on a ball, the evaluation of fractional Laplacian operator can be straightforward thanks to the pseudo-eigen relation. For general smooth computational domains, we propose the use of spectral methods enriched by singular functions which characterize the inherent boundary singularity of the fractional Laplacian. We develop a simple and easy-to-implement fractional centered difference approximation to the fractional Laplacian on a uniform mesh using generating functions. The weights or coefficients of the fractional centered formula can be readily computed using the fast Fourier transform. Together with singularity subtraction, we propose high-order finite difference methods without any graded mesh. With the use of the presented results, it may be possible to solve fractional Navier-Stokes equations, fractional quantum Schrodinger equations, and stochastic fractional equations with high accuracy. All numerical simulations will be accompanied by stability and convergence analysis.
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Gundu, Pavan Kumar. "Trajectory Tracking Control of Unmanned Ground Vehicles using an Intermittent Learning Algorithm." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/93213.
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Traffic congestion and safety has become a major issue in the modern world's commute.
Congestion has been causing people to travel billions of hours more and to purchase billions
of gallons of fuel extra which account to congestion cost of billions of dollars. Autonomous
driving vehicles have been one solution to this problem because of their huge impact on
efficiency, pollution, and human safety. Also, extensive research has been carried out on
control design of vehicular platoons because a further improvement in traffic throughput
while not compromising the safety is possible when the vehicles in the platoon are provided
with better predictive abilities.
Motion control is a key area of autonomous driving research that handles moving parts of
vehicles in a deliberate and controlled manner. A widely worked on problem in motion
control concerned with time parameterized reference tracking is trajectory tracking. Having
an efficient and effective tracking algorithm embedded in the autonomous driving system is
the key for better performance in terms of resources consumed and tracking error. Many
tracking control algorithms in literature rely on an accurate model of the vehicle and often,
it can be an intimidating task to come up with an accurate model taking into consideration
various conditions like friction, heat effects, ageing processes etc. And typically, control
algorithms rely on periodic execution of the tasks that update the control actions, but such
updates might not be required, which result in unnecessary actions that waste resources.
The main focus of this work is to design an intermittent model-free optimal control algorithm
in order to enable autonomous vehicles to track trajectories at high-speeds. To obtain
a solution which is model-free, a Q-learning setup with an actor-network to approximate
the optimal intermittent controller and a critic network to approximate the optimal cost,
resulting in the appropriate tuning laws is considered.Master of Science
A risen research effort in the area of autonomous vehicles has been witnessed in the past few decades because these systems improve safety, comfort, transport time and energy consumption which are some of the main issues humans are facing in the modern world’s highway systems. Systems like emergency braking, automatic parking, blind angle vehicle detection are creating a safer driving environment in populated areas. Advanced driver assistance systems (ADAS) are what such kind of systems are known as. An extension of these partially automated ADAS are vehicles with fully automated driving abilities, which are able to drive by themselves without any human involvement. An extensively proposed approach for making traffic throughput more efficient on existing highways is to assemble autonomous vehicles into platoons. Small intervehicle spacing and many vehicles constituting each platoon formation improve the traffic throughput significantly. Lately, the advancements in computational capabilities, in terms of both algorithms and hardware, communications, and navigation and sensing devices contributed a lot to the development of autonomous systems (both single and multiagent) that operate with high reliability in uncertain/dynamic operating conditions and environments. Motion control is an important area in the autonomous vehicles research. Trajectory-tracking is a widely studied motion control scenario which is about designing control laws that force a system to follow some time-dependent reference path and it is important to have an effective and efficient trajectory-tracking control law in an autonomous vehicle to reduce the resources consumed and tracking error. The goal of this work is to design an intermittent model-free trajectory tracking control algorithm where there is no need of any mathematical model of the vehicle system being controlled and which can reduce the controller updates by allowing the system to evolve in an open loop fashion and close the loop only when an user defined triggering condition is satisfied. The approach is energy efficient in that the control updates are limited to instances when they are needed rather than unnecessary periodic updates. Q-learning which is a model-free reinforcement learning technique is used in the trajectory tracking motion control algorithm to make the vehicles track their respective reference trajectories without any requirement of their motion model, the knowledge of which is generally needed when dealing with a motion control problem. The testing of the designed algorithm in simulations and experiments is presented in this work. The study and development of a vehicle platform in order to perform the experiments is also discussed. Different motion control and sensing techniques are presented and used. The vehicle platform is shown to track a reference trajectory autonomously without any human intervention, both in simulations and experiments, proving the effectiveness of the proposed algorithm.
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Hasanović, Amer. "A simulation and analysis toolbox for power systems and genetic algorithm based damping controller design." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2173.
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Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains viii, 73 p. : ill. Includes abstract. Includes bibliographical references (p. 71-73).
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Fu, Xuezheng. "Structure Pattern Analysis Using Term Rewriting and Clustering Algorithm." Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/cs_diss/17.
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Biological data is accumulated at a fast pace. However, raw data are generally difficult to understand and not useful unless we unlock the information hidden in the data. Knowledge/information can be extracted as the patterns or features buried within the data. Thus data mining, aims at uncovering underlying rules, relationships, and patterns in data, has emerged as one of the most exciting fields in computational science. In this dissertation, we develop efficient approaches to the structure pattern analysis of RNA and protein three dimensional structures. The major techniques used in this work include term rewriting and clustering algorithms. Firstly, a new approach is designed to study the interaction of RNA secondary structures motifs using the concept of term rewriting. Secondly, an improved K-means clustering algorithm is proposed to estimate the number of clusters in data. A new distance descriptor is introduced for the appropriate representation of three dimensional structure segments of RNA and protein three dimensional structures. The experimental results show the improvements in the determination of the number of clusters in data, evaluation of RNA structure similarity, RNA structure database search, and better understanding of the protein sequence-structure correspondence.
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麥禮安 and Lai-on Mak. "Fuzzy logic statcom controller design with genetic algorithm application for stability enhancement of interconnected power systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B42128699.
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Mak, Lai-on. "Fuzzy logic statcom controller design with genetic algorithm application for stability enhancement of interconnected power systems." Click to view the E-thesis via HKUTO, 2000. http://sunzi.lib.hku.hk/hkuto/record/B42128699.
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Er, Aynur. "Stability of Linear Difference Systems in Discrete and Fractional Calculus." TopSCHOLAR®, 2017. http://digitalcommons.wku.edu/theses/1946.
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The main purpose of this thesis is to define the stability of a system of linear difference equations of the form,
∇y(t) = Ay(t),
and to analyze the stability theory for such a system using the eigenvalues of the corresponding matrix A in nabla discrete calculus and nabla fractional discrete calculus. Discrete exponential functions and the Putzer algorithms are studied to examine the stability theorem.
This thesis consists of five chapters and is organized as follows. In the first chapter, the Gamma function and its properties are studied. Additionally, basic definitions, properties and some main theorem of discrete calculus are discussed by using particular example.
In the second chapter, we focus on solving the linear difference equations by using the undetermined coefficient method and the variation of constants formula. Moreover, we establish the matrix exponential function which is the solution of the initial value problems (IVP) by the Putzer algorithm.
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Hopkins, Brad Michael. "Adaptive Rollover Control Algorithm Based on an Off-Road Tire Model." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/36129.
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Due to a recent number of undesired rollovers in the field for the studied vehicle, rollover mitigation strategies have been investigated and developed. This research begins with the study of the tire, as it is the single component on the vehicle responsible for generating all of the non-inertial forces to direct the motion of the vehicle. Tire force and moment behavior has been researched extensively and several accurate tire models exist. However, not much research has been performed on off-road tire models. This research develops an off-road tire model for the studied vehicle by first using data from rolling road testing to develop a Pacejka Magic Formula tire model and then extending it to off-road surfaces through the use of scaling factors. The scaling factors are multipliers in the Magic Formula that describe how different aspects of the force and moment curves scale when the tire is driven on different surfaces. Scaling factors for dirt and gravel driving surfaces were obtained by using an existing portable tire test rig to perform force and moment tests on a passenger tire driven on these surfaces. The off-road tire model was then used as a basis for developing control algorithms to prevent vehicle rollover on off-road terrain. Specifically, a direct yaw control (DYC) algorithm based on Lyapunov direct method and an emergency roll control (ERC) algorithm based on a rollover coefficient were developed. Emergency evasive maneuvers were performed in a simulation environment on the studied vehicle driven on dry asphalt, dirt, and gravel for the controlled and uncontrolled cases. Results show that the proposed control algorithms significantly improve vehicle stability and prevent rollover on a variety of driving surfaces.Master of Science
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NAGA, SOUMYA. "AN EFFICIENT ALGORITHM FOR CLINICAL MASS CENTER LOCATION OF HUMAN BODY." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1131323551.
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Tbaileh, Ahmad Anan. "Robust Non-Matrix Based Power Flow Algorithm for Solving Integrated Transmission and Distribution Systems." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/89362.
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This work presents an alternative approach to power system computations, Graph Trace Analysis (GTA), and applies GTA to the power flow problem. A novel power flow algorithm is presented, where GTA traces are used to implement a modified Gauss-Seidel algorithm coupled with a continuation method. GTA is derived from the Generic Programming Paradigm of computer science. It uses topology iterators to move through components in a model and perform calculations. Two advantages that GTA brings are the separation of system equations from component equations and the ability to distribute calculations across processors. The implementation of KVL and KCL in GTA is described. The GTA based power flow algorithm is shown to solve IEEE standard transmission models, IEEE standard distribution models, and integrated transmission and distribution models (hybrid models) constructed from modifying IEEE standard models. The GTA power flow is shown to solve a set of robustness testing circuits, and solutions are compared with other power flow algorithms. This comparison illustrates convergence characteristics of different power flow algorithms in the presence of voltage stability concerns. It is also demonstrated that the GTA power flow solves integrated transmission and distribution system models. Advantages that GTA power flow bring are the ability to solve realistic, complex circuit models that pose problems to many traditional algorithms; the ability to solve circuits that are operating far from nominal conditions; and the ability to solve transmission and distribution networks together in the same model.PHD
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Ebrinc, Ali Aslan. "High Speed Viscous Plane Couette-poiseuille Flow Stability." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12604769/index.pdf.
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The linear stability of high speed-viscous plane Couette and Couette-Poiseuille flows are investigated numerically. The conservation equations along with Sutherland�
s viscosity law are studied using a second-order finite difference scheme. The basic velocity and temperature distributions are perturbed by a small-amplitude normalmode disturbance. The small-amplitude disturbance equations are solved numerically using a global method using QZ algorithm to find all the eigenvalues at finite Reynolds numbers, and the incompressible limit of these equations is investigated for Couette-Poiseuille flow. It is found that the instabilities occur, although the corresponding growth rates are often small. Two families of wave modes, Mode I (odd modes) and Mode II (even modes), were found to be unstable at finite Reynolds numbers, where Mode II is the dominant instability among the unstable modes for plane Couette flow. The most unstable mode for plane Couette &
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Poiseuille flow is Mode 0, which is not a member of the even modes. Both even and odd modes are acoustic modes created by acoustic reflections between a will and a relative sonic line. The necessary condition for the existence of such acoustic wave modes is that there is a region of locally supersonic mean flow relative to the phase speed of the instability wave. The effects of viscosity and compressibility are also investigated and shown to have a stabilizing role in all cases studied. Couette-Poiseuille flow stability is investigated in case of a choked channel flow, where the maximum velocity in the channel corresponds to sonic velocity. Neutral stability contours were obtained for this flow as a function if the wave number,Reynolds number and the upper wall Mach number. The critical Reynolds number is found as 5718.338 for an upper wall Mach number of 0.0001, corresponding to the fully Poiseuille case.
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Singh, Ravindra. "A Novel Approach for Tuning of Power System Stabilizer Using Genetic Algorithm." Thesis, Indian Institute of Science, 2004. http://hdl.handle.net/2005/65.
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The problem of dynamic stability of power system has challenged power system engineers since over three decades now. In a generator, the electromechanical coupling between the rotor and the rest of the system causes it to behave in a manner similar to a spring mass damper system, which exhibits an oscillatory behaviour around the equilibrium state, following any disturbance, such as sudden change in loads, change in transmission line parameters, fluctuations in the output of turbine and faults etc. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of low frequency oscillations. The oscillations, which are typically in the frequency range of 0.2 to 3.0 Hz, might be excited by the disturbances in the system or, in some cases, might even build up spontaneously. These oscillations limit the power transmission capability of a network and, sometimes, even cause a loss of synchronism and an eventual breakdown of the entire system.
The application of Power System Stabilizer (PSS) can help in damping out these oscillations and improve the system stability. The traditional and till date the most popular solution to this problem is application of conventional power system stabilizer (CPSS). However, continual changes in the operating condition and network parameters result in corresponding change in system dynamics. This constantly changing nature of power system makes the design of CPSS a difficult task.
Adaptive control methods have been applied to overcome this problem with some degree of success. However, the complications involved in implementing such controllers have restricted their practical usage.
In recent years there has been a growing interest in robust stabilization and disturbance attenuation problem. H∞ control theory provides a powerful tool to deal with robust stabilization and disturbance attenuation problem. However the standard H∞ control theory does not guarantee robust performance under the presence of all the uncertainties in the power plants.
This thesis provides a method for designing fixed parameter controller for system to ensure robustness under model uncertainties. Minimum performance required of PSS is decided a priori and achieved over the entire range of operating conditions.
A new method has been proposed for tuning the parameters of a fixed gain power system stabilizer. The stabilizer places the troublesome system modes in an acceptable region in the complex plane and guarantees a robust performance over a wide range of operating conditions. Robust D-stability is taken as primary specification for design. Conventional lead/lag PSS structure is retained but its parameters are re-tuned using genetic algorithm (GA) to obtain enhanced performance. The advantage of GA technique for tuning the PSS parameters is that it is independent of the complexity of the performance index considered. It suffices to specify an appropriate objective function and to place finite bounds on the optimized parameters. The efficacy of the proposed method has been tested on single machine as well as multimachine systems. The proposed method of tuning the PSS is an attractive alternative to conventional fixed gain stabilizer design as it retains the simplicity of the conventional PSS and still guarantees a robust acceptable performance over a wide range of operating and system condition.
The method suggested in this thesis can be used for designing robust power system stabilizers for guaranteeing the required closed loop performance over a prespecified range of operating and system conditions. The simplicity in design and implementation of the proposed stabilizers makes them better suited for practical applications in real plants.
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Altamirano, Chavez Armando. "An efficient algorithm using Householder's formulas for the solution of faulted power systems." Thesis, Kansas State University, 1986. http://hdl.handle.net/2097/9896.
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Marutani, Kyohei. "Essays on the Theory of Indivisible Good Markets." Kyoto University, 2020. http://hdl.handle.net/2433/253062.
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Rust, Ian Charles. "Control of a nonlinear underactuated system with adaptation, numerical stability verification, and the use of the LQR Trees algorithm." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59934.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 54).
Underactuated robotics, though surrounded by an established body of work, has certain limitations when nonlinear adaptive control principles are applied. This thesis applies a nonlinear adaptative controller that avoids many of these limitations using alterations inspired by the control of a similar underactuated system, the cart-pole. Due to the complexity of the system, a sums-of-squares MATLAB toolbox is used to generate a suitable Lyapunov Candidate used for proofs of stability, with claims of local stability made using Barbalat's Lemma. This provides us with a local domain of attraction for the altered classical nonlinear adaptive controller. In addition, the algorithm known as LQR Trees is applied to the system in order to create a controller with a larger region of attraction and lower torque requirements, though without an adaptive component. Both control systems are implemented in simulations using MATLAB.
by Ian Charles Rust.
S.B.
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Miotto, Ednei Luiz. "Aplicação do algoritmo bioinspirado Novel Bat Algorithm na parametrização dos controladores suplementares de amortecimento e dispositivo FACTS GUPFC." Ilha Solteira, 2018. http://hdl.handle.net/11449/157493.
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Orientador: Percival Bueno de AraujoResumo: Este trabalho apresenta o Novel Bat Algorithm com uma nova técnica para realizar o ajuste coordenado dos parâmetros de controladores suplementares de amortecimento (Estabilizadores de Sistemas de Potência e do conjunto Generalized Unified Power Flow Controller – Power Oscillation Damping) em sistemas elétricos de potência multimáquinas. O objetivo principal é inserir amortecimento adicional aos modos oscilatórios de baixa frequência e, consequentemente, garantir a estabilidade do sistema elétrico frente a pequenas perturbações. Para representar o sistema elétrico de potência será utilizado o Modelo de Sensibilidade de Potência. Desse modo, todos os seus dispositivos e componentes foram modelados por injeções de potência. Análises estáticas e dinâmicas foram realizadas em dois sistemas teste, sendo: o Sistema Simétrico de Duas Áreas e o Sistema New England. A eficiência do dispositivo FACTS Generalized Unified Power Flow Controller atuando em conjunto com uma estrutura de controle baseada em controladores Proporcional – Integral foi criteriosamente avaliada para o controle de fluxos de potências ativa e reativa, para a melhoria do perfil de tensão do sistema elétrico e na redução das perdas no sistema de transmissão. O desempenho do Novel Bat Algorithm, no que concerne ao ajuste dos parâmetros dos controladores, foi comparado a outros quatro algoritmos bio-inspirados bastante difundidos na literatura: Particle Swarm Optimization, Bacterial Foragim Optimization, Bat Algorithm e... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work presents the Novel Bat Algorithm as a new technique for the to perform the coordinated tuning of the parameters of the supplementary damping controllers (Power Systems Stabilizers and Generalized Unified Power Flow Controller - Power Oscillation Damping) in multi-machine electric power systems. The main objective is to insert damping to low-frequency oscillations and thus ensure the stability of the electrical system against minor disturbances. The Power Sensitivity Model is used to represent the system. Thus, all devices and their components are modeled by power injection. Static and dynamic analyzes were performed in the two systems: the two-areas symmetric, and the New England. The performance of the proposed methodology (Novel Bat Algorithm), for tuning of the parameters of the controllers was compared to four other algorithms, presented in the literature: The Particle Swarm Optimization method, Bacterial Foraging Optimization method, Bat Algorithm method and a Genetic Algorithm with elitism. The results demonstrated that the Novel Bat Algorithm was more effective than the other techniques presented, generating robust solutions when variations on the scenarios of loads were considered, and therefore accredited it as a tool in the analysis of the study of small-signal stability.
Doutor
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Kangas, M. (Maria). "Stability analysis of new paradigms in wireless networks." Doctoral thesis, Oulun yliopisto, 2017. http://urn.fi/urn:isbn:9789526215464.
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Abstract Fading in wireless channels, the limited battery energy available in wireless handsets, the changing user demands and the increasing demand for high data rate and low delay pose serious design challenges in the future generations of mobile communication systems. It is necessary to develop efficient transmission policies that adapt to changes in network conditions and achieve the target delay and rate with minimum power consumption. In this thesis, a number of new paradigms in wireless networks are presented. Dynamic programming tools are used to provide dynamic network stabilizing resource allocation solutions for virtualized data centers with clouds, cooperative networks and heterogeneous networks. Exact dynamic programming is used to develop optimal resource allocation and topology control policies for these networks with queues and time varying channels. In addition, approximate dynamic programming is also considered to provide new sub-optimal solutions. Unified system models and unified control problems are also provided for both secondary service provider and primary service provider cognitive networks and for conventional wireless networks. The results show that by adapting to the changes in queue lengths and channel states, the dynamic policy mitigates the effects of primary service provider and secondary service provider cognitive networks on each other. We investigate the network stability and provide new unified stability regions for primary service provider and secondary service provider cognitive networks as well as for conventional wireless networks. The K-step Lyapunov drift is used to analyse the performance and stability of the proposed dynamic control policies, and new unified stability analysis and queuing bound are provided for both primary service provider and secondary service provider cognitive networks and for conventional wireless networks. By adapting to the changes in network conditions, the dynamic control policies are shown to stabilize the network and to minimize the bound for the average queue length. In addition, we prove that the previously proposed frame based does not minimize the bound for the average delay, when there are shared resources between the terminals with queuesTiivistelmä Langattomien kanavien häipyminen, langattomien laitteiden akkujen rajallinen koko, käyttäjien käyttötarpeiden muutokset sekä lisääntyvän tiedonsiirron ja lyhyemmän viiveen vaatimukset luovat suuria haasteita tulevaisuuden langattomien verkkojen suunnitteluun. On välttämätöntä kehittää tehokkaita resurssien allokointialgoritmeja, jotka sopeutuvat verkkojen muutoksiin ja saavuttavat sekä tavoiteviiveen että tavoitedatanopeuden mahdollisimman pienellä tehon kulutuksella. Tässä väitöskirjassa esitetään uusia paradigmoja langattomille tietoliikenneverkoille. Dynaamisen ohjelmoinnin välineitä käytetään luomaan dynaamisia verkon stabiloivia resurssien allokointiratkaisuja virtuaalisille pilvipalveludatakeskuksille, käyttäjien yhteistyöverkoille ja heterogeenisille verkoille. Tarkkoja dynaamisen ohjelmoinnin välineitä käytetään kehittämään optimaalisia resurssien allokointi ja topologian kontrollointialgoritmeja näille jonojen ja häipyvien kanavien verkoille. Tämän lisäksi, estimoituja dynaamisen ohjelmoinnin välineitä käytetään luomaan uusia alioptimaalisia ratkaisuja. Yhtenäisiä systeemimalleja ja yhtenäisiä kontrollointiongelmia luodaan sekä toissijaisen ja ensisijaisen palvelun tuottajan kognitiivisille verkoille että tavallisille langattomille verkoille. Tulokset osoittavat että sopeutumalla jonojen pituuksien ja kanavien muutoksiin dynaaminen tekniikka vaimentaa ensisijaisen ja toissijaisen palvelun tuottajien kognitiivisten verkkojen vaikutusta toisiinsa. Tutkimme myös verkon stabiiliutta ja luomme uusia stabiilisuusalueita sekä ensisijaisen ja toissijaisen palveluntuottajan kognitiivisille verkoille että tavallisille langattomille verkoille. K:n askeleen Lyapunovin driftiä käytetään analysoimaan dynaamisen kontrollointitekniikan suorituskykyä ja stabiiliutta. Lisäksi uusi yhtenäinen stabiiliusanalyysi ja jonon yläraja luodaan ensisijaisen ja toissijaisen palveluntuottajan kognitiivisille verkoille ja tavallisille langattomille verkoille. Dynaamisen algoritmin näytetään stabiloivan verkko ja minimoivan keskimääräisen jonon pituuden yläraja sopeutumalla verkon olosuhteiden muutoksiin. Tämän lisäksi todistamme että aiemmin esitetty frame-algoritmi ei minimoi keskimääräisen viiveen ylärajaa, kun käyttäjät jakavat keskenään resursseja
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Westin, Robin. "Three material decomposition in dual energy CT for brachytherapy using the iterative image reconstruction algorithm DIRA : Performance of the method for an anthropomorphic phantom." Thesis, Linköpings universitet, Institutionen för medicinsk teknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-91297.
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Brachytherapy is radiation therapy performed by placing a radiation source near or inside a tumor. Difference between the current water-based brachytherapy dose formalism (TG-43) and new model based dose calculation algorithms (MBSCAs) can differ by more than a factor of 10 in the calculated doses. There is a need for voxel-by-voxel cross-section assignment, ideally, both the tissue composition and mass density of every voxel should be known for individual patients. A method for determining tissue composition via three material decomposition (3MD) from dual energy CT scans was developed at Linköping university. The method (named DIRA) is a model based iterative reconstruction algorithm that utilizes two photon energies for image reconstruction and 3MD for quantitative tissue classification of the reconstructed volumetric dataset. This thesis has investigated the accuracy of the 3MD method applied on prostate tissue in an anthropomorphic phantom when using two different approximations of soft tissues in DIRA. Also the distributions of CT-numbers for soft tissues in a contemporary dual energy CT scanner have been determined. An investigation whether these distributions can be used for tissue classification of soft tissues via thresholding has been conducted. It was found that the relative errors of mass energy absorption coefficient (MEAC) and linear attenuation coefficient (LAC) of the approximated mixture as functions of photon energy were less than 6 \% in the energy region from 1 keV to 1 MeV. This showed that DIRA performed well for the selected anthropomorphic phantom and that it was relatively insensitive to choice of base materials for the approximation of soft tissues. The distributions of CT-numbers of liver, muscle and kidney tissues overlapped. For example a voxel containing muscle could be misclassified as liver in 42 cases of 100. This suggests that pure thresholding is insufficient as a method for tissue classification of soft tissues and that more advanced methods should be used.
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Zhang, Hongbo. "Use of Statistical Mechanics Methods to Assess the Effects of Localized muscle fatigue on Stability during Upright Stance." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/30888.
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Human postural control is a complex process, but that is critical to understand in order to reduce the prevalence of occupational falls. Localized muscle fatigue (LMF), altered sensory input, and inter-individual differences (e.g. age and gender) have been shown to influence postural control, and numerous methods have been developed in order to quantify such effects. Recently, methods based on statistical mechanics have become popular, and when applied to center of pressure (COP) data, appear to provide new information regarding the postural control system. This study addresses in particular the stabilogram diffusion and Hurst exponent methods. An existing dataset was employed, in which sway during quiet stance was measured under different visual and surface compliance conditions, among both genders and different age groups, as well as before and after induction of localized muscle fatigue at the ankle, knee, torso, and shoulder.
The stabilogram diffusion method determines both short-term and long-term diffusion coefficients, which correspond to open- and closed-loop control of posture, respectively. To do so, a â critical pointâ (or critical time interval) needs to be determined to distinguish between the two diffusion regions. Several limitations are inherent in existing methods to determine this critical point. To address this, a new algorithm was developed, based on a wavelet transform of COP data. The new algorithm is able to detect local maxima over specified frequency bands within COP data; therefore it can identify postural control mechanisms correspondent to those frequency bands.
Results showed that older adults had smaller critical time intervals, and indicating that sway control of older adults was essentially different from young adults. Diffusion coefficients show that among young adults, torso LMF significantly compromised sway stability. In contrast, older adults appeared more resistance to LMF. Similar to earlier work, vision was found to play a crucial role in maintaining sway stability, and that stability was worse under eyes-closed (EC) than eyes-opened (EO) conditions. It was also found that the short-term Hurst exponent was not successful at detecting the effects of LMF on sway stability, likely because of a small sample size. The new critical point identification algorithm was verified to have better sensitivity and reliability than the traditional approach. The new algorithm can be used in future work to aid in the assessment of postural control and the mechanisms underlying this control.Master of Science
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Ramarathinam, Venkatesh. "A control layer algorithm for ad hoc networks in support of urban search and rescue (USAR) applications." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000604.
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Tastan, Mesut. "Analysis And Prediction Of Gene Expression Patterns By Dynamical Systems, And By A Combinatorial Algorithm." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606672/index.pdf.
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Modeling and prediction of gene-expression patterns has an important place in computational biology and bioinformatics. The measure of gene expression is determined from the genomic analysis at the mRNA level by means of microarray
technologies. Thus, mRNA analysis informs us not only about genetic viewpoints of an organism but also about the dynamic changes in environment of that organism. Different mathematical methods have been developed for analyzing
experimental data. In this study, we discuss the modeling approaches and the reasons why we concentrate on models derived from differential equations and improve the pioneering works in this field by including affine terms on the right-hand side of the nonlinear differential equations and by using Runge-
Kutta instead of Euler discretization, especially, with Heun&rsquos method. Herewith, for stability analysis we apply modified Brayton and Tong algorithm to time-discrete dynamics in an extended space.
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Peltonen, Joanna. "Development of effective algorithm for coupled thermal-hydraulics : neutron-kinetics analysis of reactivity transient." Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11033.
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Yilmaz, Ali Emre. "Implementation Of Turbulence Models On 2d Hybrid Grids Using An Explicit/implicit Multigrid Algorithm." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613783/index.pdf.
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In this thesis study, implementation, numerical stability and convergence rate issues of turbulence modeling are explored. For this purpose, a one equation turbulence model, Spalart-Allmaras, and a two-equation turbulence model, SST k-w, are adapted to an explicit, cell centered, finite volume method based, structured / hybrid multi grid flow solver, SENSE2D, developed at TUBITAK-SAGE. Governing equations for both the flow and the turbulence are solved in a loosely coupled manner, however, each set of equations are solved using a coupled, semi-implicit solution algorithm. In multigrid solutions, the semi-implicit solution algorithm and the turbulence model equations are employed only in the finest level grid. As a result, stable and convergent numerical solutions are obtained. In order to validate the turbulence models and the semi-implicit solution algorithm implemented, turbulent flow solutions over a flat plate, RAE2822 airfoil and NLR7301 multi element airfoil are performed. The results are compared with the experimental data and the numerical results of the commercial CFD package FLUENT. It is shown that the numerical results obtained by SENSE2D are in good agreement with the experimental data and the FLUENT results. In addition to the turbulence modeling studies, convergence rate studies are also performed by multigrid and semi-implicit solution methods. It is shown that, the convergence
rates of the semi-implicit solutions are increased about 5 times for single grid and 35% for multigrid solutions in comparison to the explicit solutions.
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Manmek, Thip Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Real-time power system disturbance identification and its mitigation using an enhanced least squares algorithm." Awarded by:University of New South Wales. Electrical Engineering and Telecommunications, 2006. http://handle.unsw.edu.au/1959.4/26233.
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This thesis proposes, analyses and implements a fast and accurate real-time power system disturbances identification method based on an enhanced linear least squares algorithm for mitigation and monitoring of various power quality problems such as current harmonics, grid unbalances and voltage dips. The enhanced algorithm imposes less real-time computational burden on processing the system and is thus called ???efficient least squares algorithm???. The proposed efficient least squares algorithm does not require matrix inversion operation and contains only real numbers. The number of required real-time matrix multiplications is also reduced in the proposed method by pre-performing some of the matrix multiplications to form a constant matrix. The proposed efficient least squares algorithm extracts instantaneous sine and cosine terms of the fundamental and harmonic components by simply multiplying a set of sampled input data by the pre-calculated constant matrix. A power signal processing system based on the proposed efficient least squares algorithm is presented in this thesis. This power signal processing system derives various power system quantities that are used for real-time monitoring and disturbance mitigation. These power system quantities include constituent components, symmetrical components and various power measurements. The properties of the proposed power signal processing system was studied using modelling and practical implementation in a digital signal processor. These studies demonstrated that the proposed method is capable of extracting time varying power system quantities quickly and accurately. The dynamic response time of the proposed method was less than half that of a fundamental cycle. Moreover, the proposed method showed less sensitivity to noise pollution and small variations in fundamental frequency. The performance of the proposed power signal processing system was compared to that of the popular DFT/FFT methods using computer simulations. The simulation results confirmed the superior performance of the proposed method under both transient and steady-state conditions. In order to investigate the practicability of the method, the proposed power signal processing system was applied to two real-life disturbance mitigation applications namely, an active power filter (APF) and a distribution synchronous static compensator (D-STATCOM). The validity and performance of the proposed signal processing system in both disturbance mitigations applications were investigated by simulation and experimental studies. The extensive modelling and experimental studies confirmed that the proposed signal processing system can be used for practical real-time applications which require fast disturbance identification such as mitigation control and power quality monitoring of power systems
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Dargahi, Kafshgarkolaei Mahdi. "Stability analysis and implementation of Power-Hardware-in-the-Loop for power system testing." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/81957/1/Mahdi_Dargahi%20Kafshgarkolaei_Thesis.pdf.
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This project develops the required guidelines to assure stable and accurate operation of Power-Hardware-in-the-Loop implementations. The proposals of this research have been theoretically analyzed and practically examined using a Real-Time Digital Simulator. In this research, the interaction between software simulated power network and the physical power system has been studied. The conditions for different operating regimes have been derived and the corresponding analyses have been presented.
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Li, Zhe. "Développement d'une méthode de simulation de couplage fluide-structure à l'aide de la méthode SPH." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0036/document.
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L’Interaction Fluide-Structure (IFS) est un sujet d’intérêt dans beaucoup de problèmes pratiques aussi bien pour les recherches académiques ainsi que pour les applications industrielles. Différents types d’approches de simulation numérique peuvent être utilisés pour étudier les problèmes d’IFS afin d’obtenir de meilleurs conceptions et d’éviter des incidents indésirables. Dans ce travail, le domaine du fluide est simulé par une méthode hybride sans maillage (SPH-ALE), et la structure est discrétisée par la méthode d’ ´ Eléments Finis (EF). Considérant le fluide comme un ensemble de particules, on peut suivre l’interface entre le fluide et la structure d’une manière naturelle. Une stratégie de couplage conservant l’énergie est proposée pour les problèmes d’IFS transitoires où différents intégrateurs temporels sont utilisés pour chaque sous-domaine: 2nd ordre schéma de Runge-Kutta pour le fluide et schéma de Newmark pour le solide. En imposant la continuité de la vitesse normale à l’interface, la méthode proposée peut assurer qu’il n’y a ni injection d’énergie ni dissipation d’énergie à l’interface. L’énergie de l’interface est donc nulle (aux erreurs de troncature près) durant toute la période de simulation numérique. Cette méthode de couplage assure donc que la simulation de couplage est numériquement stable en temps. Les expérimentations numériques montrent que le calcul converge en temps avec l’ordre de convergence minimal des schémas utilisés dans chaque sous-domaine. Cette méthode proposée est d’abord appliquée `a un problème de piston mono-dimensionnel. On vérifie sur ce cas qu’elle ne dégrade pas l’ordre de précision en temps des schémas utilisés. On effectue ensuite les études des phénomènes de propagation d’ondes de choc au travers de l’interface fluide-structure. Un excellent accord avec la solution analytique est observé dans les cas de teste de propagation d’onde en 1-D. Finalement, les exemples multi-dimensionnels sont présentés. Ses résultats sont comparés avec ceux obtenus par d’autres méthodes de couplageThe Fluid-Structure Interaction (FSI) effects are of great importance for many multi-physical problems in academic researches as well as in engineering sciences. Various types of numerical simulation approaches may be used to investigate the FSI problems in order to get more reliable conception and to avoid unexpected disasters. In this work, the fluid sub-domain is simulated by a hybrid mesh-less method (SPH-ALE), and the structure is discretized by the Finite Element (FE) method. As the fluid is considered as a set of particles, one can easily track the fluid structure interface. An energy-conserving coupling strategy is proposed for transient fluid-structure interaction problems where different time integrators are used for each sub-domain: 2nd order Runge-Kutta scheme for the fluid and Newmark time integrator for the solid. By imposing a normal velocity constraint condition at the interface, this proposed coupling method ensures that neither energy injection nor energy dissipation will occur at the interface so that the interface energy is rigorously zero during the whole period of numerical simulation. This coupling method thus ensures that the coupling simulation shall be stable in time, and secondly, the numerical simulation will converge in time with the minimal convergence rate of all the time integrators chosen for each sub-domain. The proposed method is first applied to a mono-dimensional piston problem in which we verify that this method does not degrade the order of accuracy in time of the used time integrators. Then we use this coupling method to investigate the phenomena of propagation of shock waves across the fluidstructure interface. A good agreement is observed between the numerical results and the analytical solutions in the 1-D shock wave propagation test cases. Finally, some multi-dimensional examples are presented. The results are compared with the ones obtained by other coupling approaches
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Brum, Vinicius Campista. "Análise de agrupamento e estabilidade para aquisição e validação de conhecimento em bases de dados de alta dimensionalidade." Universidade Federal de Juiz de Fora (UFJF), 2015. https://repositorio.ufjf.br/jspui/handle/ufjf/4826.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Análise de agrupamento é uma tarefa descritiva e não-supervisionada de mineração de dados que utiliza amostras não-rotuladas com o objetivo de encontrar grupos naturais, isto é, grupos de amostras fortemente relacionadas de forma que as amostras que per-tençam a um mesmo grupo sejam mais similares entre si do que amostras em qualquer outro grupo. Avaliação ou validação é considerada uma tarefa essencial dentro da análise de agrupamento. Essa tarefa apresenta técnicas que podem ser divididas em dois tipos: técnicas não-supervisionadas ou de validação interna e técnicas supervisionadas ou de va-lidação externa. Trabalhos recentes introduziram uma abordagem de validação interna que busca avaliar e melhorar a estabilidade do algoritmo de agrupamento por meio de identificação e remoção de amostras que são consideradas prejudiciais e, portanto, de-veriam ser estudadas isoladamente. Por meio de experimentos foi identificado que essa abordagem apresenta características indesejáveis que podem resultar em remoção de todo um grupo e ainda não garante melhoria de estabilidade. Considerando essas questões, neste trabalho foi desenvolvida uma abordagem mais ampla utilizando algoritmo genético para análise de agrupamento e estabilidade de dados. Essa abordagem busca garantir melhoria de estabilidade, reduzir o número de amostras para remoção e permitir que o usuário controle o processo de análise de estabilidade, o que resulta em maior aplicabi-lidade e confiabilidade para tal processo. A abordagem proposta foi avaliada utilizando diferentes algoritmos de agrupamento e diferentes bases de dados, sendo que uma base de dados genotípicos também foi utilizada com o intuito de aquisição e validação de conhe-cimento. Os resultados mostram que a abordagem proposta é capaz de garantir melhoria de estabilidade e também é capaz de reduzir o número de amostras para remoção. Os resultados também sugerem a utilização da abordagem como uma ferramenta promissora para aquisição e validação de conhecimento em estudos de associação ampla do genoma (GWAS). Este trabalho apresenta uma abordagem que contribui para aquisição e valida-ção de conhecimento por meio de análise de agrupamento e estabilidade de dados.
Clustering analysis is a descriptive and unsupervised data mining task, which uses non-labeled samples in order to find natural groups, i.e. groups of closely related samples such that samples within the same cluster are more similar than samples within the other clusters. Evaluation and validation are considered essential tasks within the clustering analysis. These tasks present techniques that can be divided into two kinds: unsuper-vised or internal validation techniques and supervised or external validation techniques. Recent works introduced an internal clustering validation approach to evaluate and im-prove the clustering algorithm stability through identifying and removing samples that are considered harmful and therefore they should be studied separately. Through experi-mentation, it was identified that this approach has two undesirable characteristics, it can remove an entire cluster from dataset and still decrease clustering stability. Taking into account these issues, in this work a broader approach was developed using genetic algo-rithm for clustering and data stability analysis. This approach aims to increase stability, to reduce the number of samples for removal and to allow the user control the stability analysis process, which gives greater applicability and reliability for such process. This approach was evaluated using different kinds of clustering algorithm and datasets. A genotype dataset was also used in order to knowledge acquisition and validation. The results show the approach proposed in this work is able to increase stability, and it is also able to reduce the number of samples for removal. The results also suggest the use of this approach as a promising tool for knowledge acquisition and validation on genome-wide association studies (GWAS). This work presents an approach that contributes for knowledge acquisition and validation through clustering and data stability analysis.
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Mims, Mark McGrew. "Dynamical stability of quantum algorithms /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004342.
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Tisseur, Françoise. "Méthodes numériques pour le calcul d'éléments spectraux : étude de la précision, la stabilité et la parallélisation." Saint-Etienne, 1997. http://www.theses.fr/1997STET4006.
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Cette thèse est constituée de deux parties. La première traite de la méthode QR pour le calcul de valeurs propres de matrices quelconques, de tailles modérées. Les contributions originales à ce sujet sont a) une preuve rigoureuse de sa stabilité inverse, b) un nouveau critère d'arrêt justifié par une analyse mathématique. La seconde partie traite de la méthode de Yau et Lu pour le calcul de valeurs propres de matrices symétriques réelles de grandes tailles. Les contributions dans ce travail à ce sujet sont a) une compréhension mathématique accrue de la méthode, b) sa validation numérique, c) une proposition de parallélisation
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Castoldi, Marcelo Favoretto. "Algoritmo híbrido para projeto de controladores de amortecimento de sistemas elétricos de potência utilizando algoritmos genéticos e gradiente descendente." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-07042011-151406/.
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Os sistemas elétricos de potência são frequentemente submetidos a perturbações causadas, por exemplo, por um aumento súbito de carga ou por um curto-circuito em uma linha de transmissão. Estas perturbações podem gerar oscilações eletromecânicas no sistema, uma vez que a velocidade dos geradores oscila. Para reduzir tais oscilações, controladores de sistema de potência são utilizados sendo, os mais comuns, controladores do tipo PSS (Power System Stabilizer). Porém, em alguns sistemas, somente o emprego de PSSs não é suficiente para garantir um nível mínimo satisfatório de amortecimento, sendo necessário recorrer a outros tipos de controladores. Desta forma, controladores do tipo FACTS (Flexible Alternating Current Transmission System), principalmente o TCSC (Thyristor Controlled Series Capacitor) se tornaram uma alternativa atraente no auxílio ao amortecimento dos sistemas de potência. O controle do TCSC é feito por um controlador POD (Power Oscilation Damper) que é empregado como controle suplementar do dispositivo. No entanto, apenas o emprego dos controladores não garante um bom amortecimento, fazendo-se necessária uma boa sintonia dos mesmos. A sintonia destes controladores é, na maioria das vezes, feita de forma manual, ou seja, usando o método de tentativa e erro, podendo demandar um tempo relativamente elevado, mesmo que feita por um engenheiro experiente. Para evitar que o projetista dispense tempo procurando uma sintonia adequada para os controladores, métodos automáticos de sintonia vêm sendo estudados. Tais métodos têm como principal vantagem a sintonia dos controladores considerando vários pontos de operação do sistema simultaneamente, fazendo com que o controlador seja robusto para variações em seu ponto de operação nominal. Os métodos automáticos de sintonia utilizam métodos de otimização local ou métodos de otimização global. Os métodos de busca local têm a rapidez como principal vantagem, porém podem não convergir para um valor satisfatório de amortecimento estipulado pelo projetista. Os métodos de busca global, em grande parte das vezes, convergem para um valor de amortecimento solicitado pelo projetista, porém em um tempo elevado. Este trabalho propõe um método de sintonia dos controladores utilizando uma estrutura híbrida, ou seja, algoritmos de busca global juntamente com algoritmos de busca local. Primeiramente uma busca global é feita pelo algoritmo até que um critério de parada, definido pelo projetista, seja alcançado (geralmente um valor de amortecimento mínimo para o sistema). Assim, os parâmetros dos controladores sintonizados pela busca global serão entrada de um método de busca local. O algoritmo de busca local tende a refinar a sintonia dos controladores aumentando, assim, o amortecimento do sistema até um valor especificado pelo projetista. Neste trabalho a busca global é realizada por um algoritmo genético enquanto que a busca local é feita por um algoritmo baseado no gradiente descendente da função objetivo (neste caso o amortecimento). As principais vantagens do algoritmo proposto são a diminuição do tempo de sintonia e o esforço computacional, se comparado a métodos de busca global, verificadas nos resultados do trabalho.Electric Power Systems are constantly subjected to perturbations, which can be caused for several different reasons, e.g., due to a sudden load increase or a short circuit in a transmission line. These perturbations can induce electromechanical oscillations in the power system, since the angular speed of the generators oscillates. To reduce such oscillations, power system controllers are used, and the most common ones are the PSSs (Power System Stabilizers). In some systems, however, the usage of PSSs is not sufficient to guarantee a satisfactory level for the minimum damping, being necessary the usage of other types of controllers. Hence, FACTS (Flexible Alternating Current Transmission System) controllers, specially the TCSC (Thyristor Controlled Series Capacitor), became an attractive alternative to enhance the damping of electric power systems. The TCSC control action is performed by a POD (Power Oscillation Damper) controller, which is a supplementary control function of the device. However, it is not only the usage of such controllers that guarantees a sufficient damping, but also a good tuning of their parameters. The tuning of such controllers is ordinarily performed manually, using a trial-and-error method, which can last for a long time, even for experienced engineers. To facilitate the designers work in the tuning of the controllers parameters, automatic tuning methods are being studied. Such methods have the main advantage of considering several operating points of the system simultaneously, yielding a robust controller regarding variations in its nominal operating point. The aforementioned automatic tuning methods use local optimization methods or global optimization methods. The local optimization methods have the speed as the main advantage, but they can have convergence issues in the search for the minimum satisfactory damping threshold desired by the designer. The global optimization methods, on the other hand, ordinarily converge for the desired minimum damping threshold, but with large convergence times. This work proposes a controller tuning method using a hybrid structure, i.e., global search methods with local search methods. Initially, a global search is performed by the algorithm until a stop criteria is met, as defined by the designer (usually a minimum damping for the system). Thus, the controller parameters tuned by the global search method are the input values of a local search method. The local search algorithm actually refines the controllers tuning, increasing the system damping to the value defined by the designer. In this work the global search is performed by a genectic algorithm while the local search is performed by an algorithm based in the gradient descent of objective function (damping in this case). The greatest advantages of the proposed algorithm are the possible decrease in computational time and effort, when compared to global search methods, verified in the work results.
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Marenych, M. S. "Procedures analysis for evaluating resistance of passwords." Thesis, Київський національний університет технологій та дизайну, 2019. https://er.knutd.edu.ua/handle/123456789/14358.
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Кондіус, І. С. "Алгоритм побудови комплексної агрегованої моделі стійкого розвитку регіону." Thesis, ДИАЙПИ, 2012. http://essuir.sumdu.edu.ua/handle/123456789/63603.
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В досліджені запропонований авторський алгоритм побудови комплексної агрегованої моделі стійкого розвитку регіону.In a study author proposed algorithm for constructing complex aggregate model of sustainable development in the region.
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Ghamrawi, Ahmad. "Optimisation et gestion des flux énergétiques d'un générateur solaire photovoltaïque." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2304.
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Cette thèse s'inscrit sur une thématique de recherche dédiée aux systèmes de production d'énergie solaire photovoltaïque. En effet, les besoins énergétiques mondiaux sont en croissance continue, l’exploitation et la consommation des énergies fossiles épuisent des ressources limitées et impactent notre environnement. L’énergie solaire photovoltaïque représente une source d'énergie renouvelable des plus prometteuse, même si ses inconvénients demeurent le coût élevé d'installation initiale et la variabilité de sa production. Les travaux présentés visent surtout à optimiser le rendement énergétique global d'un système solaire photovoltaïque non connecté au réseau. Ainsi, ce travail de recherche se focalise sur l’architecture de la chaîne de conversion avec l’intégration de convertisseurs élévateurs DC-DC conventionnel et quadratique et sur une optimisation des algorithmes de recherche du point de puissance maximale lors de variations des conditions climatiques. La modélisation et l’analyse de ces convertisseurs élévateurs sont conduites sous forme de systèmes à commutation afin de proposer une commande stabilisante aux points d’équilibre selon la définition de Lyapunov. Des résultats de simulation sous Matlab/SimulinkTM sont exposés, attestant la maximisation de la puissance électrique récupérée et la stabilité pour le point de fonctionnement. Des résultats expérimentaux, issus du banc expérimental du laboratoire LIAS, viennent corréler et confirmer l'intérêt des approches proposéesThis thesis in part of research thematic dedicated to photovoltaic solar energy production's systems. In fact, energy demands in the world are continuously increasing, the fossil fuels exploitation depletes limited sources and impact our environment. Solar photovoltaic energy represents one of the most promoted renewable energy sources, even if its drawbacks remain its installation’s high initial cost and its production’s variability. The main object of the presented work is to optimize the global efficiency of a stand-alone photovoltaic system. In that respect, this research focuses on the architecture of the conversion chain by integrating DC-DC conventional and quadratic boost converters and on the optimization of maximum power point tracking algorithms during fast changing weather conditions. These converters are modelling as switched affine systems to propose a switching rule that stabilize the operating point according to Lyapunav theory. Several simulation results using Matlab/SimulinkTM are given to declare the maximization of the extracted electrical power and the stability of the operating point. Experimental results recuperated on a test bench in the laboratory LIAS backed and confirmed the interest of the proposed approaches
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Lowery, Bradley R. "Topics in communication avoiding algorithms and stability analysis." Thesis, University of Colorado at Denver, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3621837.
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High performance linear algebra kernels are essential for scientific computing. Fast, accurate, and robust algorithms are required to process the large amount of data present in today's applications. In this thesis, we present new performance analysis, new error analysis, new stable algorithms, and new computational results.
An algorithm's performance depends on the computational cost and the communication cost. We begin with a study of the communication cost for dense linear algebra algorithms. We improve the lower bounds for the amount of communications in matrix multiplication. We also review optimal algorithms for dense linear algebra algorithms focusing on recursive algorithms.
We also consider the communication cost of the reduction operation. A reduction is a collective communication that is often used to communicate data in a parallel application. We present two new algorithms each developed under different models. In a unidirectional model, we prove our new algorithm is optimal. In a bidirectional model, we show experimentally our new algorithm has the same time complexity of a reverse optimal broadcast. Our implementations show that the new algorithms are viable options in practice.
In the remaining chapters, we turn our attention to error analysis. We present a complete error analysis study of computing an oblique QR factorization. As part of this study we introduce a new, stable, communication avoiding algorithm. Performance experiments confirm the benefit of the communication avoiding algorithms.
Finally, we consider the error due to the balancing algorithm, a preprocessing step to the nonsymmetric eigenvalue problem. We modify the balancing algorithm by improving its stopping criteria. We present several test cases where the previous balancing algorithm deteriorated the accuracy of the computation. The new algorithm successfully maintains satisfactory backward error for all test cases.
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Medina, Aguayo Felipe Javier. "Stability and examples of some approximate MCMC algorithms." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/88922/.
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Approximate Monte Carlo algorithms are not uncommon these days, their applicability is related to the possibility of controlling the computational cost by introducing some noise or approximation in the method. We focus on the stability properties of a particular approximate MCMC algorithm, which we term noisy Metropolis-Hastings. Such properties have been studied before in tandem with the pseudo-marginal algorithm, but under fairly strong assumptions. Here, we examine the noisy Metropolis-Hastings algorithm in more detail and explore possible corrective actions for reducing the introduced bias. In this respect, a novel approximate method is presented, motivated by the class of exact algorithms with randomised acceptance. We also discuss some applications and theoretical guarantees of this new approach.
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Andréa-Novel, Brigitte d'. "Sur la commande d'une classe de systèmes mécaniques." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0067.
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Elaboration de lois de commande en particulier pour la robotique. Utilisation de l'approche polynomiale pour placer des zeros de transmission a poles fixes. Cas des systemes non lineaires. Etude par topologie algebrique. Utilisation d'une approche par immersion et bouclage linearisant. Problemes de stabilite dans le cas de grands genres
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Zadehkhost, Sajjad. "Efficient algorithms to expedite transient stability analysis of power systems." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52816.
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With rapid increase in complexity of modern power systems, there is a strong need for better computational tools to ensure the reliable operation of electrical grids. These tools need to be accurate, computationally efficient, and capable of using advanced measurement devices. In this context, transient stability assessment (TSA) is an important study that determines system’s dynamic security margins following a major disturbance. The TSA consists of a set of differential-algebraic equations (DAEs), which are typically solved using time-domain simulation (TDS) approach. While being very accurate, the TDS requires significant computational resources when applied to practical power systems. This problem becomes more significant in transient stability monitoring (TSM), wherein the computational performance of the TDS is typically the bottleneck. This research is to investigate available challenges in the TSM applications and develop new algorithms to help realizing a practical monitoring tool for transient stability studies. The thesis focuses on three research thrusts: i) dynamic reduction of power system to reduce problem size; ii) advanced computation approaches to expedite the TDS method; iii) integration of PMU measurements into the TSM. Initially, a new adaptive aggregation algorithm for dynamic reduction is proposed, wherein parameters of generators and structure of transmission network are considered to aggregate coherent generators and create a reduced-order system. Also, a new criterion is defined to monitor validity of the constructed reduced system. It is shown that the proposed technique is more accurate than traditional aggregation methods. To expedite the TDS approach, this thesis presents two new integration techniques, which are called Multi-Decomposition Approach (MDA) and Successive Linearization and Integration Technique (SLIT). In these methods, the nonlinear DAEs are decomposed into a series of linear subsystems, which participate in approximating actual solution. It is demonstrated that sequential and parallel versions of the MDA and SLIT are faster than state-of-the-art integration techniques. Finally, a dynamic state estimator based on Extended Kalman Filter is developed to convert the PMU measurements into a set of state variables suitable for transient stability studies. Computer studies show that the proposed framework provides accurate results in highly disturbed power systems with fairly low PMU sampling rates.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Rabbani, Ronak. "Developing and deploying enhanced algorithms to enable operational stability control systems with embedded high voltage DC links." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/12293.
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The increasing penetration of renewable energy resources within the Great Britain (GB) transmission system has created much greater variability of power flows within the transmission network. Consequently, modern transmission networks are presented with an ever increasing range of operating conditions. As a result, decision making in the Electricity National Control Centre (ENCC) of the GB electrical power transmission system is becoming more complex and control room actions are required for reducing timescales in the future so as to enable optimum operation of the system. To maximise utilisation of the electricity transmission system there is a requirement for fast transient and dynamic stability control. In this regard, GB electrical power transmissions system reinforcement using new technology, such as High Voltage Direct Current (HVDC) links and Thyristor-Controlled Series Compensation (TCSC), is planned to come into operation. The research aim of this PhD thesis is to fully investigate the effects of HVDC lines on power system small-disturbance stability in the presence of operational uncertainties. The main research outcome is the comprehensive probabilistic assessment of the stability improvements that can be achieved through the use of supplementary damping control when applied to HVDC systems. In this thesis, two control schemes for small-signal dynamic stability enhancement of an embedded HVDC link are proposed: Modal Linear Quadratic Gaussian (MLQG) controller and Model Predictive Controller (MPC). Following these studies, probabilistic methodologies are developed in order to test of the robustness of HVDC based damping controllers, which involves using classification techniques to identify possible mitigation options for power system operators. The Monte Carlo (MC) and Point Estimated Method (PEM) are developed in order to identify the statistical distributions of critical modes of a power system in the presence of uncertainties. In addition, eigenvalue sensitivity analysis is devised and demonstrated to ensure accurate results when the PEM is used with test systems. Finally, the concepts and techniques introduced in the thesis are combined to investigate robustness for the widely adopted MLQG controller and the recently introduced MPC, which are designed as the supplementary controls of an embedded HVDC link for damping inter-area oscillations. Power system controllers are designed using a linearised model of the system and tuned for a nominal operating point. The assumption is made that the system will be operating within an acceptable proximity range of its nominal operating condition and that the uncertainty created by changes within each operating point can possibly have an adverse effect on the controller’s performance.
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McDonald, Dale Brian. "Feedback control algorithms through Lyapunov optimizing control and trajectory following optimization." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Spring2006/D%5FMcDonald%5F050206.pdf.
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Wan, H. B. "Voltage stability analysis using algorithmic and artificial intelligent approaches." Thesis, University of Bath, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337820.
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Diederichs, Benedikt [Verfasser], and Armin [Akademischer Betreuer] Iske. "Sparse Frequency Estimation : Stability and Algorithms / Benedikt Diederichs ; Betreuer: Armin Iske." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1175584649/34.
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Diederichs, Benedikt Verfasser], and Armin [Akademischer Betreuer] [Iske. "Sparse Frequency Estimation : Stability and Algorithms / Benedikt Diederichs ; Betreuer: Armin Iske." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://nbn-resolving.de/urn:nbn:de:gbv:18-95079.
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Kalavagunta, Sushma. "Computational algorithms for stability analysis of linear systems with time-delay /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418036.
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Kandil, Nahi. "Algorithmes pour accélérer la simulation en stabilité transitoire." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0003/NQ42824.pdf.
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Dosso, Mouhamadou. "Sur quelques algorithmes d'analyse de stabilité forte de matrices symplectiques." Brest, 2006. http://www.theses.fr/2006BRES2014.
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Le but de cette thèse est de proposer quelques algorithmes permettant d’analyser la stabilité forte d’une matrice symplectique. Le premier chapitre rassemble quelques propriétés spectrales des matrices symplectiques et leur lien avec la stabilité forte. En particulier, ce chapitre insiste sur les propriétés les plus importantes du point de vue de la stabilité numérique qui sont utilisés tout au long de la thèse. Dans le deuxième chapitre, on adapte les méthodes de dichotomie spectrale à des matrices symplectiques. Cette adaptation permet de trouver les projecteurs spectraux sur les sous-espaces invariants associés aux valeurs propres dans, sur et en dehors du cercle unité. Puis, on propose un algorithme basé encore sur la dichotomie spectrale afin d’analyser la stabilité forte. Dans le troisième chapitre, on propose un algorithme itératif de trichotomie spectrale permettant de trouver les projecteurs spectraux mentionnés ci-dessus. L’analyse théorique clarifie la convergence et donne la vitesse de convergence de cet algorithme. Ce chapitre se termine par une comparaison, en terme de précision et de coût de calcul, entre cette approche et celle du chapitre 2The first chapter of this thesis presents some spectral properties of symplectic matrices and their link to the strong stability. In particular, emphasis is placed on the most numerically useful properties which are used throughout the thesis. In the second chapter we propose an adaptation of spectral dichotomy algorithms to symplectic matrices. This adaptation allows us to find, in a stable way, the spectral projections onto the invariant subspaces associated with the eigenvalues inside, on and outside the unit circle. With these information, we propose an algorithm, based again on the spectral dichotomy techniques, to analyse the strong stability. In the third chapter, we propose another approach referred to as spectral trichotomy, for computing the abovementioned spectral projections. We analyse the convergence behavior of this algorithms and compare it with the approach proposed in chapter 2
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Karmakar, Saurav. "Statistical Stability and Biological Validity of Clustering Algorithms for Analyzing Microarray Data." Digital Archive @ GSU, 2005. http://digitalarchive.gsu.edu/math_theses/3.
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Simultaneous measurement of the expression levels of thousands to ten thousand genes in multiple tissue types is a result of advancement in microarray technology. These expression levels provide clues about the gene functions and that have enabled better diagnosis and treatment of serious disease like cancer. To solve the mystery of unknown gene functions, biological to statistical mapping is needed in terms of classifying the genes. Here we introduce a novel approach of combining both statistical consistency and biological relevance of the clusters produced by a clustering method. Here we employ two performance measures in combination for measuring statistical stability and functional similarity of the cluster members using a set of gene expressions with known biological functions. Through this analysis we construct a platform to predict about unknown gene functions using the outperforming clustering algorithm.
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Noun, Nahla. "Convergence et stabilisation de systèmes dynamiques couplés et multi-échelles vers des équilibres sous contraintes : application à l’optimisation hiérarchique." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20011/document.
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Nous étudions la convergence de systèmes dynamiques vers des équilibres. En particulier, nous nous intéressons à deux types d'équilibres. D'une part, les solutions d'inéquations variationnelles sous contraintes qui interviennent aussi dans la résolution de problèmes d'optimisation hiérarchique. D'autre part l'état stable d'un système dynamique, c'est à dire l'état où l'énergie du système est nulle. Cette thèse est divisée en deux parties principales, chacune focalisée sur la recherche d'un de ces équilibres. Dans la première partie nous étudions une classe d'algorithmes explicite-implicites pour résoudre certaines inéquations variationnelles sous contraintes. Nous introduisons un algorithme proximal-gradient pénalisé, "splitting forward-backward penalty scheme". Ensuite, nous prouvons sa convergence ergodique faible vers un équilibre dans le cas général d'un opérateur maximal monotone, et sa convergence forte vers l'unique équilibre si l'opérateur est de plus fortement monotone. Nous appliquons aussi notre algorithme pour résoudre des problèmes d'optimisation sous contrainte ou hiérarchique dont les fonctions objectif et de pénalisation sont formées d'une partie lisse et d'une autre non lisse. En effet, nous démontrons la convergence faible de l'algorithme vers un optimum hiérarchique lorsque l'opérateur est le sous-différentiel d'une fonction convexe semi-continue inférieurement et propre. Nous généralisons ainsi plusieurs algorithmes connus et nous retrouvons leurs résultats de convergence en affaiblissant les hypothèses utilisées dans nombre d'entre eux.Dans la deuxième partie, nous étudions l'action d'un contrôle interne local sur la stabilisation indirecte d'un système dynamique couplé formé de trois équations d'ondes, le système de Bresse. Sous la condition d'égalité des vitesses de propagation des ondes, nous montrons la stabilité exponentielle du système. En revanche, quand les vitesses sont différentes, nous prouvons sa stabilité polynomiale et nous établissons un nouveau taux de décroissance polynomial de l'énergie. Ceci étend des résultats présents dans la littérature au sens où le contrôle est localement distribué (et non pas appliqué à tout le domaine) et nous améliorons le taux de décroissance polynomial de l'énergie pour des conditions au bord de type Dirichlet et Dirichlet-NeumannWe study the convergence of dynamical systems towards equilibria. In particular, we are interested in two types of equilibria. On one hand solutions of constrained variational inequations that are also involved in the resolution of hierarchical optimization problems. On the other hand the stable state of a dynamical system, i.e. the state when the energy of the system is zero. The thesis is divided into two parts, each focused on one of these equilibria. In the first part, we study a class of forward-backward algorithms for solving constrained variational inequalities. We consider a splitting forward-backward penalty scheme. We prove the weak ergodic convergence of the algorithm to an equilibrium for a general maximal monotone operator, and the strong convergence to the unique equilibrium if the operator is an addition strongly monotone. We also apply our algorithm for solving constrained or hierarchical optimization problems whose objective and penalization functions are formed of a smooth and a non-smooth part. In fact, we show the weak convergence to a hierarchical optimum when the operator is the subdifferential of a closed convex proper function. We then generalize several known algorithms and we find their convergence results by weakening assumptions used in a number of them. In the second part, we study the action of a locally internal dissipation law in the stabilization of a linear dynamical system coupling three wave equations, the Bresse system. Under the equal speed wave propagation condition we show that the system is exponentially stable. Otherwise, when the speeds are different, we prove the polynomial stability and establish a new polynomial energy decay rate. This extends results presented in the literature in the sense that the dissipation law is locally distributed (and not applied in the whole domain) and we improve the polynomial energy decay rate with both types of boundary conditions, Dirichlet and Dirichlet-Neumann
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Aronna, Maria-Soledad. "Second order analysis of optimal control problems with singular arcs : optimality conditions and shooting algorithm." Palaiseau, Ecole polytechnique, 2011. http://tel.archives-ouvertes.fr/docs/00/68/22/76/PDF/These_Aronna.pdf.
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Dans cette thèse on s'intéresse aux problèmes de commande optimale pour des systèmes affines dans une partie de la commande. Premièrement, on donne une condition nécessaire du second ordre pour le cas ou le système est affine dans toutes les commandes. On a des bornes sur les contrôles et une solution bang-singulière. Une condition suffisante est donnée pour le cas d'une commande scalaire. On propose après un algorithme de tir et une condition suffisante pour sa convergence quadratique locale. Cette condition garantit la stabilité de la solution optimale et implique que l'algorithme converge quadratiquement localement pour le problème perturbé, dans certains cas. On présente des essais numériques qui valident notre méthode. Ensuite, on étudie un système affine dans une partie des commandes. On obtient des conditions nécessaire et suffisante du second ordre. Ensuite, on propose un algorithme de tir et on montre que la condition suffisante mentionnée garantit que cet algorithme converge quadratiquement localement. Enfi n, on étudie un problème de plani cation d'une centrale hydro-thermique. On analyse au moyen des conditions nécessaires obtenues par Goh, la possible apparition d'arcs singuliersThis thesis deals with optimal control problems for systems that are affine in one part of the control variable. First, we state necessary and sufficient second order conditions when all control variables enter linearly. We have bound control constraints and a bang-singular solution. The sufficient condition is restricted to the scalar control case. We propose a shooting algorithm and provide a sufficient condition for its local quadratic convergence. This condition guarantees the stability of the optimal solution and the local quadratic convergence of the algorithm for the perturbed problem in some cases. We present numerical tests that validate our method. Afterwards, we investigate an optimal control problems with systems that are affine in one part of the control variable. We obtain second order necessary and sufficient conditions for optimality. We propose a shooting algorithm, and we show that the sufficient condition just mentioned is also sufficient for the local quadratic convergence. Finally, we study a model of optimal hydrothermal scheduling. We investigate, by means of necessary conditions due to Goh, the possible occurrence of a singular arc
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Eskenazi, Sébastien. "On the stability of document analysis algorithms : application to hybrid document hashing technologies." Thesis, La Rochelle, 2016. http://www.theses.fr/2016LAROS019/document.
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Un nombre incalculable de documents est imprimé, numérisé, faxé, photographié chaque jour. Ces documents sont hybrides : ils existent sous forme papier et numérique. De plus les documents numériques peuvent être consultés et modifiés simultanément dans de nombreux endroits. Avec la disponibilité des logiciels d’édition d’image, il est devenu très facile de modifier ou de falsifier un document. Cela crée un besoin croissant pour un système d’authentification capable de traiter ces documents hybrides. Les solutions actuelles reposent sur des processus d’authentification séparés pour les documents papiers et numériques. D’autres solutions reposent sur une vérification visuelle et offrent seulement une sécurité partielle. Dans d’autres cas elles nécessitent que les documents sensibles soient stockés à l’extérieur des locaux de l’entreprise et un accès au réseau au moment de la vérification. Afin de surmonter tous ces problèmes, nous proposons de créer un algorithme de hachage sémantique pour les images de documents. Cet algorithme de hachage devrait fournir une signature compacte pour toutes les informations visuellement significatives contenues dans le document. Ce condensé permettra la création de systèmes de sécurité hybrides pour sécuriser tout le document. Ceci peut être réalisé grâce à des algorithmes d’analyse du document. Cependant ceux-ci ont besoin d’être porté à un niveau de performance sans précédent, en particulier leur fiabilité qui dépend de leur stabilité. Après avoir défini le contexte de l’étude et ce qu’est un algorithme stable, nous nous sommes attachés à produire des algorithmes stables pour la description de la mise en page, la segmentation d’un document, la reconnaissance de caractères et la description des zones graphiquesAn innumerable number of documents is being printed, scanned, faxed, photographed every day. These documents are hybrid : they exist as both hard copies and digital copies. Moreover their digital copies can be viewed and modified simultaneously in many places. With the availability of image modification software, it has become very easy to modify or forge a document. This creates a rising need for an authentication scheme capable of handling these hybrid documents. Current solutions rely on separate authentication schemes for paper and digital documents. Other solutions rely on manual visual verification and offer only partial security or require that sensitive documents be stored outside the company’s premises and a network access at the verification time. In order to overcome all these issues we propose to create a semantic hashing algorithm for document images. This hashing algorithm should provide a compact digest for all the visually significant information contained in the document. This digest will allow current hybrid security systems to secure all the document. This can be achieved thanks to document analysis algorithms. However those need to be brought to an unprecedented level of performance, in particular for their reliability which depends on their stability. After defining the context of this study and what is a stable algorithm, we focused on producing stable algorithms for layout description, document segmentation, character recognition and describing the graphical parts of a document