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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
561

AC microgrids analysis, optimization and planning for resilience enhancement

Vilaisarn, Youthanalack 29 September 2022 (has links)
Face à des événements météorologiques violents, un système de distribution électrique peut souffrir de la perte ou de la défaillance d'un ou de plusieurs de ses composants. Ce phénomène est connu sous le nom de contingence de système. Néanmoins, en tirant parti des systèmes de protection, de l'électronique de puissance et de la pénétration des ressources énergétiques décentralisées dans le réseau électrique, un système de distribution électrique a la possibilité d'être reconfiguré en micro-réseaux. Cela permet de résister contre de telles éventualités en gardant au minimum la possibilité d'une interruption de l'alimentation. Poussé par des facteurs techniques, économiques et environnementaux, ainsi que par le déploiement rapide d'un grand nombre de ressources de production décentralisées, le micro-réseau est récemment devenu un concept important dans un système de distribution actif et rapidement reconfigurable. Les micro-réseaux ont la capacité de fonctionner à la fois en mode connecté au réseau et en mode isolé. En raison de cet avantage, le micro-réseau est devenu un élément clé du futur réseau intelligent. Bien que le concept de micro-réseau puisse apporter différents avantages aux services de distribution et aux clients, à savoir une amélioration de l'économie, de l'environnement et de la résilience, il offre toujours un défi au niveau de la planification et la gestion opérationnelle. Les défis de la planification des micro-réseaux proviennent de : 1) la nature intermittente et incertaine des ressources décentralisées et des charges des systèmes distribués, ainsi que l'incertitude relative aux contingences auxquelles le réseau de distribution est confronté, 2) la charge de calcul que la prise en compte des incertitudes du micro-réseau implique, et 3) le grand nombre de compromis entre les différents objectifs d'optimisation possibles du micro-réseau qui doivent être pris en compte dans la phase de planification. Motivée par ces défis, cette recherche propose le développement de nouvelles méthodologies d'analyse et de planification qui peuvent assurer l'efficacité du processus de création du micro-réseau en tenant compte des caractéristiques particulières et de la philosophie opérationnelle du micro-réseau. Dans un premier temps, les modèles d'étude d'écoulement de puissance linéaires et non linéaires sont développés en prenant compte des caractéristiques réelles d'un micro-réseau insulaire équilibré et déséquilibré, c'est-à-dire l'absence de bus infini, la présence d'une fréquence du système variable et de certains générateurs fonctionnant en mode de contrôle « statisme ». Tout d'abord, nous présentons un algorithme non linéaire basé sur la méthode des mailles et la matrice Z[indice bus] pour un micro-réseau opéré en mode « droop ». Cet algorithme sans inversion est particulièrement adapté aux grandes dimensions des systèmes de distribution pratiques comprenant des milliers de nœuds électriques, lorsqu'ils fonctionnent comme des micro-réseaux insulaires. Deuxièmement, un modèle linéaire pour étudier l'écoulement de puissance (LPF) basé sur la méthode des nœuds est proposé. Étant basé sur la méthode des nœuds, le modèle proposé est utilisable dans différents problèmes d'optimisation de micro-réseaux. Des études de cas numériques sont développées et utilisées pour démontrer la précision des modèles proposés et garantir leur application réussie pour modéliser avec précision l'écoulement d'énergie dans un micro-réseau. Cela permet son application dans un processus d'optimisation présenté à l'étape suivante de cette recherche. Dans la deuxième étape, cette recherche propose un modèle d'écoulement de puissance optimal (OPF) pour le fonctionnement optimal des micro-réseaux à courant alternatif, équilibrés et déséquilibrés, avec un contrôle hiérarchique (c'est-à-dire, un contrôle primaire et secondaire). Le modèle proposé a d'abord été formulé comme un modèle non linéaire en nombres entiers (MINLP), puis il a été linéarisé et converti en un modèle linéaire en nombres entiers (MILP) en utilisant le modèle LPF développé dans la première étape de cette recherche. La philosophie de fonctionnement du micro-réseau, en mode connecté au réseau et en mode îloté, a été prise en compte. De plus, plusieurs types de générateurs distribués, y compris ceux qui sont disptachables et non disptachables, ainsi que des ressources de stockage d'énergie, ont été pris en compte dans le modèle MILP proposé. Plusieurs études de cas numériques ont été menées pour valider et prouver l'efficacité et la précision du modèle MILP développé. Les résultats de ces études de cas ont démontré la précision et la supériorité de calcul du modèle MILP proposé Enfin, un cadre de planification pour les micro-réseaux dans les réseaux de distribution actifs est proposé. Ce cadre de planification vise à améliorer la résilience des systèmes de distribution d'électricité face à des événements de faible probabilité, à fort impact. Dans le cadre proposé, le problème de planification a été présenté comme un problème d'optimisation stochastique à deux niveaux. Tout d'abord, le niveau externe traite du placement optimal des éléments de planification du système de distribution (c.-à-d. les ressources répartissables ou non répartissables, les unités de stockage d'énergie et les interrupteurs d'isolement). Ce problème a été formulé en utilisant une formulation d'optimisation multi-objectifs et ensuite l'algorithme métaheuristique bien connu NSGA-II est adopté pour la recherche d'une solution optimale. Cette approche permet de déterminer les solutions qui impliquent le meilleur compromis entre plusieurs objectifs éventuellement conflictuels du problème de planification, à savoir le coût, la résilience et l'impact environnemental. Deuxièmement, le niveau interne du cadre de planification traite du problème d'optimisation relatif au fonctionnement optimal des micro-réseaux qui peuvent être créés par les éléments de planification du système de distribution alloués dans le niveau externe. Le problème du fonctionnement optimal du micro-réseau est présenté comme un problème d'étude de l'écoulement de puissance optimal linéaire (LOPF). À cette fin, le modèle MILP développé dans la deuxième étape est adopté. Néanmoins, il est nécessaire de prendre en compte différents scénarios stochastiques dans le niveau interne pour tenir compte des différentes incertitudes du système. Il faut aussi considérer la nature métaheuristique du niveau externe ce qui demande la résolution du modèle LOPF pour chacun des scénarios stochastiques et aussi pour chaque individu de la population. La prise en compte de ces facteurs présente un défi au niveau du calcul. Par conséquent, une nouvelle méthodologie utilisant un modèle de réseau de neurones (DNN) est proposée. Cette méthode permet de dériver rapidement l'information requise des solutions LOPF pour les scénarios stochastiques considérés. Enfin, l'efficacité du cadre proposé est validée par des résultats de simulation numérique. / Facing severe weather events, a distribution system may suffer from the loss or failure of one or more of its components, known as N-K contingencies. Nevertheless, taking advantage of the system's isolate switches and the penetration of the distributed energy resources in the electrical grid, a distribution system has the possibility to be clustered into microgrids in order to with stand such contingencies with minimal power interruption. Driven by technical, economic and environmental factors, as well as by the rapid deployment of a large number of distributed generation resources, the microgrid has recently become an important concept in the active distribution system. Microgrids have the ability to operate in both grid-connected and islanded modes. The benefits that the microgrid concept can bring to the operation of the distribution grids make the microgrid a key component of the future smart grid. While, the microgrid concept can bring different benefits to both distribution utilities and customers i.e., economic, environmental and resilience enhancement; the planning and operational management of microgrids still present several challenges for the decision maker and the distribution network operator. The challenges with the planning of microgrids arise from: 1) the intermittent and uncertain nature of the distributed energy resources and loads as well as the uncertainty pertaining to the contingencies facing the distribution network, 2) the computational burden that considering the microgrid's uncertainties entails, and 3) the large number of trade-offs between the different possible microgrid optimization objectives that need to be considered in the planning stage. Motivated by these challenges, this research proposes the development of new analysis and planning methodologies that can ensure the efficacy of the microgrid creation process considering the microgrids special features and operational philosophy. Initially, nonlinear and linear power flow models are developed to cope with the real characteristics of balanced and unbalanced islanded microgrid i.e. the absence of the slack bus, the system frequency being a variable and some DGs operating in droop-control mode. First, a non-linear branch-based Z[subscript bus] algorithm for the droop-controlled islanded microgrid is introduced. This algorithm is inversion free and is particularly suited for the large dimensions of practical distribution systems comprising up to thousands of electrical node, i.e., when operated as islanded microgrids. Secondly, a node-based linear power flow (LPF) model for droop-controlled islanded microgrids is proposed. The node-based nature of the proposed LPF model, allows this model to be integrated in different microgrid optimization models. Numerical case studies are developed and are used to demonstrate the accuracy of the proposed power flow models and guarantee its successful application to accurately model the microgrid power flow in the optimization application in the next stage of this research. In the second stage, this research proposes an optimal power flow (OPF) model for the optima operation of balanced and unbalanced AC microgrids with hierarchical control (i.e., primary droop and secondary control). The proposed model has been first formulated as a mixed integer nonlinear programing (MINLP) model, then it was linearized and converted into a mixed integer linear programing (MILP) model by adapting the LPF model developed in the first stage of this research. The operating philosophy of the microgrid, in both grid-connected and islanded modes of operation, was considered. Additionally, several types of distributed generators, including dispatchable and non-dispatchable, as well as energy storage resources, were considered in the proposed MILP model. Several numerical case studies were conducted to validate, and prove the effectiveness and the accuracy of the developed MILP model. The results from the developed case studies demonstrated the accuracy and the computational superiority of the proposed MILP model. Finally, a planning framework for microgrids in active distribution networks is proposed. The proposed planning framework is aimed at enhancing the resilience of power distribution systems facing high impact low probability events. In the proposed framework, the planning problem has been casted as a stochastic bi-level optimization problem. First, the outer level deals with the optimal placement of the distribution system planning elements (i.e., dispatchable/non-dispatchable resources, energy storage units and isolating switches). This problem has been formulated using a multi-objective optimization formulation and the well know metaheuristic Non-dominated Sorting Genetic Algorithm (NSGA-II) algorithm is adopted for its solution. This approach allows for determining the solutions that entail the best trade-off between the possibly conflicting multi-objectives of the planning problem, namely, cost, resilience and environmental impact. Second, the inner level of the planning framework handles the optimization problem pertaining to the optimal operation of the microgrids that can be created by the distribution system planning elements allocated in the outer level. The problem of the microgrid's optimal operation is casted as a Linear Optimal Power Flow (LOPF) problem. To this end, the proposed MILP model developed in the second stage is adopted. Despite using a LOPF model, considering different stochastic scenarios in the inner level, to account for the different system uncertainties, along with the metaheuristic nature of the outer level make solving the LOPF model for each of the stochastic scenarios for each individual in the metaheuristic optimization's population, using a numerical optimization solver computationally challenging. Motivated by this challenge, a novel methodology using a deep neural network (DNN) model is proposed for deriving the information required from the LOPF solutions for the stochastic scenarios under consideration. The effectiveness of the proposed framework is finally validated by numerical simulation results.
562

The Angular Distribution of the Deuterium-Deuterium Neutrons with 100 Kev Deuterons

Hackfield, Bobby J. 08 1900 (has links)
It is the purpose of this paper to present the experimental techniques used in obtaining. 3.25 MeV neutrons from the H2(d,n)He3 reaction, as well as an analysis of the experimental data.
563

Safety Analysis of Longtan High Dam Considering the Construction Process

Hy, Henrik, Hällqvist, Viktor January 2016 (has links)
To manage China’s growing demands of electricity, more and larger dams could be a part of the solution. It is important to evaluate and perform safety analysis for existing dams, in order to improve our understanding and knowledge about future dams. In this master thesis, a safety research of Longtan Dam on the Hongshui River in China was analysed. The main objectives in this research were to construct a 3D model and determine the critical points of large stress, strain and yield area in the dam for different cases.The factor of safety for sliding when primary loads were acting on the dam was calculated to be 0.50 for the non-overflow section of the dam and 0.48 for the overflow section. A safety factor against overturning was also calculated for the non-overflow and overflow section to 2.24 and 1.96 respectively. The results showed that the dam was safe from both sliding and overturning. The numerical results for distribution of stress, strain and yield area were simulated in 3D models by using ANSYS, a finite element program. Several cases for non-overflow and overflow sections of Longtan Dam were analysed for different heights and load combinations. For the first three cases where only self-weight was applied on the dam, high impacts of stress and strain were located at the dam heel, toe and at the largest maintenance tunnel of the dam. Appearance of plastic strain was also found around these areas. However, when primary loads were applied to the dam sections, the values of stress and strain became larger, especially in the toe area. In the last case when the dam was subjected to seismic activity, the distribution of stress and strain along the z-direction (along the dam) showed an uneven distribution, hence showing the importance of simulation in 3D.
564

Review of Reliability Techniques

Doherty, Eugene Richard 01 May 1966 (has links)
In the development of any product to perform a specific function the first concern of the engineer is to design for satisfactory operation. Engineers originally approached the reliability problem by using excessive safety factors to be assured the structure or material would withstand the calculated loads and stresses. The engineer also learned from operating or testing the equipment until failures occurred and then redesigning as mistakes became apparent. These methods were time consuming and often resulted in bulky over designed products. These approaches became impractical with the advent of new technological advancements. The accelerated industrial development of aircraft, missiles, and modern electronics coupled with a need for a drastic reduction in weight and size magnified the problem. As products became more complex the problem of building a reliable product was intensified. An appreciation for the increase in complexity can be gained from considering that in a period of fifteen years the requirements for electronic tubes on a U.S. Navy destroyer changed from sixty to thirty-six hundred (14). During World War II new equipment was developed that had to be operational for extended period of time if the military mission was to be accomplished. The addition of a time requirement added to the already difficult problem caused by the increasing complexity of equipment. It soon became obvious that new techniques had to be developed that would assist the manufacturer in designing a reliable product.
565

Mathematical modelling and experimental simulation of chlorate and chlor-alkali cells.

Byrne, Philip January 2001 (has links)
The production of chlorate, chlorine and sodium hydroxiderelies heavily on electrical energy, so that savings in thisarea are always a pertinent issue. This can be brought aboutthrough increased mass transfer of reacting species to therespective electrodes, and through increased catalytic activityand uniformity of current density distribution at theseelectrodes. This thesis will present studies involvingmathematical modelling and experimental investigations of theseprocesses. They will show the effect that hydrodynamicbehaviour has on the total current density and cell voltages,along with the effects on current density distributions andindividual overpotentials atthe respective electrodes. Primary, secondary and psuedo-tertiary current densitydistribution models of a chlor-alkali anode are presented anddiscussed. It is shown that the secondary model presentsresults rather similar to the pseudo-tertiary model, when thecurrent density distribution is investigated, although thepotential distribution differs rather markedly. Furthermore, itis seen that an adequate description of the hydrodynamicsaround the anode is required if the potential distribution, andthereby the prevalence of side-reactions, is to be reasonablepredicted. A rigorous tertiary current density distribution model ofthe chlorate cell is also presented, which takes into accountthe developing hydrodynamic behaviour along the height of thecell. This shows that an increased flowrate gives more uniformcurrent density distributions. This is due to the fact that theincreased vertical flowrate of electrolyte replenishes ioncontent at the electrode surfaces, thus reducing concentrationoverpotentials. Furthermore, results from the model lead to theconclusion that it is the hypochlorite ion that partakes in themajor oxygen producing side-reaction. A real-scale cross-section of a segmented anode-cathode pairfrom a chlorate cell was designed and built in order to studythe current density distribution in industrial conditions.These experiments showed that increased flowrate brought aboutmore even current density distributions, reduced cell voltageand increased the total current density. An investigation ofthe hydrodynamic effects on the respective electrodeoverpotentials shows the anode reactions being more favoured byincreased flowrate. This leads to the conclusion that theuniform current density distribution, caused by increasedflowrate, occurs primarily through decreasing the concentrationoverpotential at the anode rather than by decreasing thebubble-induced ohmic drop at the cathode. Finally, results from experiments investigating thebubble-induced free convection from a small electrochemicalcell are presented. These experiments show that Laser DopplerVelocimetry is the most effective instrument for investigatingthe velocity profiles in bubble-containing electrochemicalsystems. The results also show that the flow can transform fromlaminar to turbulent behaviour on both the vertical andhorizontal planes, in electrochemical systems where bubbles areevolved.
566

Dynamic power distribution management for all electric aircraft

Xia, Xiuxian 01 1900 (has links)
In recent years, with the rapid development of electric and electronic technology, the All-Electric Aircraft (AEA) concept has attracted more and more attention, which only utilizes the electric power instead of conventional hydraulic and pneumatic power to supply all the airframe systems. To meet the power requirements under various flight stages and operating conditions, the AEA approach has resulted in the current aircraft electrical power generation capacity up to 1.6 MW. To satisfy the power quality and stability requirements, the advanced power electronic interfaces and more efficient power distribution systems must be investigated. Moreover, with the purpose of taking the full advantages of available electrical power, novel dynamic power distribution management research and design for an AEA must be carried out. The main objective of this thesis is to investigate and develop a methodology of more efficient power distribution management with the purpose of minimizing the rated power generating capacity and the mass of the electrical power system (EPS) including the power generation system and the power distribution system in an AEA. It is important to analyse and compare the subsistent electrical power distribution management approaches in current aircraft. Therefore the electrical power systems of A320 and B777, especially the power management system, will be discussed in this thesis. Most importantly the baseline aircraft, the Flying Crane is the outcome of the group design project. The whole project began in March 2008, and ended in September 2010, including three stages: conceptual design, preliminary design and detailed design. The dynamic power distribution management research is based on the power distribution system of the Flying Crane. The main task of the investigation is to analyse and manage the power usage among and inside typical airframe systems by using dynamic power distribution management method. The characteristics and operation process of these systems will be investigated in detail and thoroughly. By using the method of dynamic power distribution management, all the electrical consumers and sub-systems powered by electricity are managed effectively. The performance of an aircraft can be improved by reducing the peak load requirement on board. Furthermore, the electrical system architecture, distributed power distribution system and the dynamic power distribution management system for AEA are presented. Finally, the mass of the whole electrical power system is estimated and analysed carefully.
567

Mathematical modelling and experimental simulation of chlorate and chlor-alkali cells.

Byrne, Philip January 2001 (has links)
<p>The production of chlorate, chlorine and sodium hydroxiderelies heavily on electrical energy, so that savings in thisarea are always a pertinent issue. This can be brought aboutthrough increased mass transfer of reacting species to therespective electrodes, and through increased catalytic activityand uniformity of current density distribution at theseelectrodes. This thesis will present studies involvingmathematical modelling and experimental investigations of theseprocesses. They will show the effect that hydrodynamicbehaviour has on the total current density and cell voltages,along with the effects on current density distributions andindividual overpotentials atthe respective electrodes.</p><p>Primary, secondary and psuedo-tertiary current densitydistribution models of a chlor-alkali anode are presented anddiscussed. It is shown that the secondary model presentsresults rather similar to the pseudo-tertiary model, when thecurrent density distribution is investigated, although thepotential distribution differs rather markedly. Furthermore, itis seen that an adequate description of the hydrodynamicsaround the anode is required if the potential distribution, andthereby the prevalence of side-reactions, is to be reasonablepredicted.</p><p>A rigorous tertiary current density distribution model ofthe chlorate cell is also presented, which takes into accountthe developing hydrodynamic behaviour along the height of thecell. This shows that an increased flowrate gives more uniformcurrent density distributions. This is due to the fact that theincreased vertical flowrate of electrolyte replenishes ioncontent at the electrode surfaces, thus reducing concentrationoverpotentials. Furthermore, results from the model lead to theconclusion that it is the hypochlorite ion that partakes in themajor oxygen producing side-reaction.</p><p>A real-scale cross-section of a segmented anode-cathode pairfrom a chlorate cell was designed and built in order to studythe current density distribution in industrial conditions.These experiments showed that increased flowrate brought aboutmore even current density distributions, reduced cell voltageand increased the total current density. An investigation ofthe hydrodynamic effects on the respective electrodeoverpotentials shows the anode reactions being more favoured byincreased flowrate. This leads to the conclusion that theuniform current density distribution, caused by increasedflowrate, occurs primarily through decreasing the concentrationoverpotential at the anode rather than by decreasing thebubble-induced ohmic drop at the cathode.</p><p>Finally, results from experiments investigating thebubble-induced free convection from a small electrochemicalcell are presented. These experiments show that Laser DopplerVelocimetry is the most effective instrument for investigatingthe velocity profiles in bubble-containing electrochemicalsystems. The results also show that the flow can transform fromlaminar to turbulent behaviour on both the vertical andhorizontal planes, in electrochemical systems where bubbles areevolved.</p>
568

Mortality associated with arsenic in drinking water /

Bharti, Virendra Kumar, January 1900 (has links)
Thesis (M. Sc.)--Carleton University, 2008. / Includes bibliographical references (p. 57-62). Also available in electronic format on the Internet.
569

Equivalent impedance functions for HVDC converters with inverse cosine control

Bieler, Werner, January 1969 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
570

Noninformative priors for some models useful in reliability and survival analysis /

Lee, Gunhee, January 1996 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 105-108). Also available on the Internet.

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